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The clinical application of polymyxin B (PMB) is limited by its nephrotoxic effects, making the reduction of PMB‐induced nephrotoxicity has become a pressing concern for clinicians. Tetrahydrocurcumin (THC), known for its beneficial characteristics in biological functions, presents an attractive option for intervention therapy to mitigate PMB‐induced nephrotoxicity. However, the underlying mechanism of how THC mitigates PMB‐induced nephrotoxicity is still poorly understood. Here, we first evaluated the potential of THC intervention therapy to mitigate PMB‐induced nephrotoxicity in an in vitro model of PMB‐induced cell injury. Moreover, we demonstrated that THC effectively protected HK‐2 cells from PMB‐induced apoptosis by using cell counting kit‐8 and flow cytometry assay. THC could also suppress PMB‐induced endoplasmic reticulum (ER) stress via PERK/eIF2α/ATF4/CHOP pathway. In addition, using PERK inhibitor GSK2606414 to inhibit ER stress also alleviated PMB‐induced apoptosis. Taken together, these findings provide novel insights that THC possesses the ability to alleviate PMB‐induced nephrotoxicity by inhibiting the ER stress‐mediated PERK/eIF2α/ATF4/CHOP axis, which sheds light on the benefits of THC as an intervention strategy to reduce PMB‐induced nephrotoxicity, thus providing a potential avenue for improved clinical outcomes in patients receiving PMB treatment. [ABSTRACT FROM AUTHOR]

The problem of antimicrobial resistance (AMR) caused by the abuse of antibiotics is becoming serious. The development of antibacterial materials with synergistic efficiency and treatment of deep tissue/organ infections is imminent. Herein, synergistic antibacterial nanoparticles (MPH NPs) are prepared by loading antibacterial peptide polymyxin B (PMB) on Fe‐based MOF (MIL‐100) with hyaluronic acid (HA) modification. MPH NPs exerts antibacterial effects by chemodynamic therapy (CDT) and the release of PMB. MPH NPs have broad‐spectrum antibacterial properties on Gram‐negative bacteria (E. coli, 100%), Gram‐positive bacteria (S. aureus, 98.5 %), and MRSA (98.4%). Importantly, MPH NPs not only promote the healing of infected wounds but also target lungs to accomplish organ infection therapy. Therefore, this study provides a new strategy for designing a synergetic anti‐AMR bacteria system and the function for deep tissue/organ infection therapy in the future. [ABSTRACT FROM AUTHOR]

Lipopeptides are an important class of biomolecules for drug development. Compared with conventional acylation, a chemoselective lipidation strategy offers a more efficient strategy for late‐stage structural derivatisation of a peptide scaffold. It provides access to chemically diverse compounds possessing intriguing and non‐native moieties. Utilising an allenamide, we report the first semisynthesis of antimicrobial lipopeptides leveraging a highly efficient thia‐Michael addition of chemically diverse lipophilic thiols. Using chemoenzymatically prepared polymyxin B nonapeptide (PMBN) as a model scaffold, an optimised allenamide‐mediated thia‐Michael addition effected rapid and near quantitative lipidation, affording vinyl sulfide‐linked lipopeptide derivatives. Harnessing the utility of this new methodology, 22 lipophilic thiols of unprecedented chemical diversity were introduced to the PMBN framework. These included alkyl thiols, substituted aromatic thiols, heterocyclic thiols and those bearing additional functional groups (e.g. amines), ultimately yielding analogues with potent Gram‐negative antimicrobial activity and substantially attenuated nephrotoxicity. Furthermore, we report facile routes to transform the allenamide into a β‐keto amide on unprotected peptides, offering a powerful "jack‐of‐all‐trades" synthetic intermediate to enable further peptide modification. [ABSTRACT FROM AUTHOR]

Novel antimicrobial strategies are urgently needed to treat extensively drug‐resistant (XDR) bacterial infections due to the high mortality rate and lack of effective therapeutic agents. Herein, nanoengineered human umbilical cord mesenchymal stem cells (hUC‐MSCs), named PMZMU, are designed as a sonosensitizer for synergistic sonodynamic‐nano‐antimicrobial therapy against gram‐negative XDR bacteria. PMZMU is composed of a bacterial targeting peptide (UBI29‐41) modified hUC‐MSCs membrane (MSCm), a sonosensitizer meso‐tetra(4‐car‐boxyphenyl) porphine doped mesoporous organo‐silica nanoparticle and an acidity‐responsive metal–organic framework ZIF‐8. This innovative formulation enables efficient loading of polymyxin B, reduces off‐target drug release, increases circulation and targeting efficacy, and generates reactive oxygen species upon ultrasound irradiation. PMZMU exhibits remarkable in vitro inhibitory activity against four XDR bacteria: Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa (PA), and Escherichia coli. Taking advantage of the bacterial targeting ability of UBI29‐41 and the inflammatory chemotaxis of hUC‐MSC, PMZMU can be precisely delivered to lung infection sites thereby augmenting polymyxin B concentration. PMZMU‐mediated sonodynamic therapy significantly reduces bacterial burden, relieves inflammatory damage by promoting the polarization of macrophages toward M2 phenotype, and improves survival rates without introducing adverse events. Overall, this study offers promising strategies for treating deep‐tissue XDR bacterial infections, and guides the design and optimization of biomimetic nanomedicine. [ABSTRACT FROM AUTHOR]

An 8‐year‐old American Quarter Horse gelding was treated with extracorporeal hemoperfusion (HP) therapy for treatment of Clostridioides difficile (C. difficile) colitis‐induced systemic inflammatory response syndrome (SIRS). The gelding developed C. difficile associated peracute colitis and severe SIRS as evidenced by a positive fecal C. difficile PCR and tachypnea, tachycardia, fever, neutropenia, altered mucous membrane color, and hyperlactatemia. Concurrent acute kidney injury in the horse limited the use of routine anti‐inflammatory and anti‐lipopolysaccharide treatments, including flunixin meglumine and polymyxin B, because of potential for nephrosis. Extracorporeal HP therapy was performed twice within 48 hours of the onset of severe SIRS during which the horse's physical examination variables stabilized. The horse was euthanized after 4 days because of laminitis. These findings support further investigation of extracorporeal HP therapy as an adjunctive treatment for severe SIRS/sepsis in horses. [ABSTRACT FROM AUTHOR]

To facilitate clinical therapeutic drug monitoring (TDM) of polymyxin B (PB) and polymyxin E (PE), we developed and validated a simple LC–MS/MS method for simultaneous determination of PB (including polymyxin B1 (PB1), polymyxin B2 (PB2), polymyxin B3 (PB3) and isoleucine‐polymyxin B1 (ile‐PB1)) and PE (including polymyxin E1 (PE1) and polymyxin E2 (PE2)) in human plasma. PB or PE was extracted from 20.0 μL plasma using a 5% (v/v) formic acid acetonitrile solution and separated on a BEH‐C18 column (2.1 × 100 mm, 1.7 μm) with a mobile phase consisting of 0.8% formic acid aqueous solution and 0.2% formic acid acetonitrile solution. Gradient elution was performed over 5.5 min at a flow rate of 0.250 mL/min. Quantitative analysis was conducted in positive ion scanning mode by electrospray ionization and multiple reaction monitoring. The method validation was conducted based on bioanalytical method validation guidance, including specificity, calibration curve, precision, accuracy, recovery, matrix effect, stability and dilution integrity and all of the results satisfied the requirements. The method was simple, robust and high‐throughput and is currently being used to provide a TDM service to enhancing therapeutic efficacy and safety use of the PB and PE. [ABSTRACT FROM AUTHOR]

Polymyxin B (PMB) is often considered as the last line of defense for treating carbapenem‐resistant Klebsiella pneumoniae (CRKP). However, its efficacy is hindered by limited penetration across the blood‐air barrier in the lung due to its low lipid solubility. To simultaneously increase PMB in epithelial lining fluid while suppressing the excessive inflammatory response in the lung, a novel nano‐biomimetic system "Siv‐PMB@G4@MM" is designed and fabricated by encapsulating PMB‐ and anti‐inflammatory Sivelestat (Siv)‐loaded G4 PAMAM dendrimers with macrophage membranes (MM). The Siv‐PMB@G4@MM displayed a superior acidic pH‐responsive release property and can target inflamed lung tissues, greatly increasing the concentrations of PMB and Siv at the infection site. Compared with free drugs, Siv‐PMB@G4@MM demonstrated superior synergistic antibacterial and anti‐inflammatory activities. Moreover, due to the ability of MM to sequester lipopolysaccharide (LPS) and some pro‐inflammatory cytokines, Siv‐PMB@G4@MM further enhanced the anti‐inflammatory potential of Siv. In mouse models of LPS‐induced acute lung injury, pulmonary bacterial infection, and sepsis‐induced pneumonia, Siv‐PMB@G4@MM significantly reduced inflammatory responses and/or bacterial burdens, mitigated neutrophil infiltration and pulmonary edema, and decreased neutrophil extracellular trap (NET) secretion. The highly improved biocompatibility and efficiency of the multifunctional Siv‐PMB@G4@MM presents a promising strategy for the clinical treatment of antibiotic‐resistant bacterial pneumonia. [ABSTRACT FROM AUTHOR]

Most of the Escherichia coli turned into serious pathogens or developed antibiotic resistance, mainly due to their ability to show different phenotypic traits. In order to overcome the resistance to these antibiotics, the use of essential oils (EOs) is of great significance against highly pathogenic microorganisms. This study has been made to compare the in vitro antibacterial activity and further validated the same through the molecular docking study of 13 antibiotics such as ciprofloxacin, chloramphenicol, erythromycin, ampicillin, cefotaxime, rifampicin, kanamycin, vancomycin, streptomycin, penicillin, nalidixic acid, trimethoprim, and polymyxin, and 10 EOs such as garlic, tulsi, neem, clove, thyme, peppermint, coriander, tea, lavender, and eucalyptus against the target protein (DNA gyrase) of E. coli MTCC443. E. coli Microbial Type Culture Collection 443 was found to be highly sensitive to ciprofloxacin (zone of inhibition [ZOI], 2.5 cm ±0.1) and chloramphenicol (ZOI, 1.8 cm ±0.1), whereas garlic oil (ZOI, 5.5 cm ±0.1) and coriander oil (ZOI, 4.4 cm ±0.1) were found comparatively most effective. Further, the in silico investigation observed the same; ciprofloxacin (binding affinity: −7.2 kcal/mol) and chloramphenicol (binding affinity: −6.6 kcal/mol). Penicillin (binding affinity: −4.2 kcal/mol) and polymyxin (binding affinity: −0.3 kcal/mol) were found to be least effective against the tested microbe, whereas vancomycin (binding affinity: +0.8 kcal/mol) had no effect on it. Garlic (binding affinity: −7.8 kcal/mol), coriander (binding affinity: −6.8 kcal/mol), peppermint (binding affinity: −6.2 kcal/mol), and neem (binding affinity: −6.2 kcal/mol) oil exhibited the potent antibacterial activity against E. coli MTCC443, whereas thyme (binding affinity: −6.1 kcal/mol), tea tree (binding affinity: −4.9 kcal/mol), and tulsi (binding affinity: −3.8 kcal/mol) oil were observed moderately effective. Eucalyptus (binding affinity: −2.9 kcal/mol) and lavender (binding affinity: −2.8 kcal/mol) oil were found to be the least effective among all the oils tested. The pharmacokinetics and networking were performed to the pharmacology of the potential compounds. [ABSTRACT FROM AUTHOR]

Background: Polymyxins have re‐emerged as a last‐resort therapeutic option for infections caused by carbapenem‐resistant gram‐negative bacteria. Nephrotoxicity induced by polymyxins is a significant limitation of its use in the clinic. Polymyxin B and colistin sulfate are two widely used active formulations of polymyxins. However, there is a lack of studies conducting a comparative assessment of nephrotoxicity between the two formulations. This study aimed to compare the nephrotoxicity of polymyxin B and colistin sulfate in critically ill patients. Methods: We conducted a retrospective cohort study among critically ill patients who received intravenous polymyxin B or colistin sulfate for over 48 h from January 2017 to January 2024. The primary outcome was the incidence of acute kidney injury (AKI) associated with polymyxins, and the secondary outcome was 30‐day all‐cause mortality. Additionally, the risk factors of polymyxins‐induced AKI and 30‐day all‐cause mortality were identified by Cox proportional hazard regression analysis. Results: A total of 473 patients were included in this study. The overall incidence of AKI was significantly higher in patients who received polymyxin B compared to those who received colistin sulfate in the unmatched cohort (20.8% vs. 9.0%, p = 0.002) and in the propensity score matching cohort (21.1% vs. 7.0%, p = 0.004), respectively. However, there was no significant difference in 30‐day all‐cause mortality between the two groups. Polymyxin type, septic shock, and concomitant use of vasopressors were identified as independent risk factors for polymyxin‐induced AKI. Conclusions: The prevalence of AKI was higher among patients who received polymyxin B compared to those treated with colistin sulfate. However, there was no significant difference in 30‐day all‐cause mortality between the two groups. Further prospective, multicenter studies with larger sample sizes are needed to validate these findings. [ABSTRACT FROM AUTHOR]

Acinetobacter baumannii is a major pathogen in hospital‐acquired infections notorious for its strong acquired resistance and complex drug resistance mechanisms. Owing to the lack of effective drugs, the mortality rate of extensively drug‐resistant A. baumannii pneumonia can reach as high as 65%. This article analyzes a case where a combination of cefoperazone‐sulbactam, polymyxin B, and minocycline with rifampicin successfully treated XDR‐AB pulmonary infection. Combination therapy is effective and has a particular clinical value. [ABSTRACT FROM AUTHOR]

Pathogenic bacteria form biofilms on epithelial cells, and most bacterial biofilms show increased production of membrane vesicles (MVs), also known as outer membrane vesicles in Gram‐negative bacteria. Numerous studies have investigated the MVs released under planktonic conditions; however, the impact of MVs released from biofilms on immune responses remains unclear. This study aimed to investigate the characteristics and immunomodulatory activity of MVs obtained from both planktonic and biofilm cultures of Pseudomonas aeruginosa PAO1. The innate immune responses of macrophages to planktonic‐derived MVs (p‐MVs) and biofilm‐derived MVs (b‐MVs) were investigated by measuring the mRNA expression of proinflammatory cytokines. Our results showed that b‐MVs induced a higher expression of inflammatory cytokines, including Il1b, Il6, and Il12p40, than p‐MVs. The mRNA expression levels of Toll‐like receptor 4 (Tlr4) differed between the two types of MVs, but not Tlr2. Polymyxin B significantly neutralized b‐MV‐mediated cytokine induction, suggesting that lipopolysaccharide of native b‐MVs is the origin of the immune response. In addition, heat‐treated or homogenized b‐MVs induced the mRNA expression of cytokines, including Tnfa, Il1b, Il6, and Il12p40. Heat treatment of MVs led to increased expression of Tlr2 but not Tlr4, suggesting that TLR2 ligands play a role in detecting the pathogen‐associated molecular patterns in lysed MVs. Taken together, our data indicate that potent immunomodulatory MVs are produced in P. aeruginosa biofilms and that this behavior could be a strategy for the bacteria to infect host cells. Furthermore, our findings would contribute to developing novel vaccines using MVs. [ABSTRACT FROM AUTHOR]

Objectives: Maxitrol (Novartis) is a topical ophthalmic medication that contains polymyxin B, neomycin, and dexamethasone. If it possesses antibiofilm activity, it may be useful for treating diseases of the head and neck in which biofilms are implicated, including chronic rhinosinusitis, chronic suppurative otitis media and osteoradionecrosis. We investigated the in vitro efficacy of Maxitrol against Staphylococcus aureus and Pseudomonas aeruginosa biofilms. Methods: Minimum biofilm eradication concentration (MBEC) assays were performed using biofilms of P. aeruginosa ATCC 27853 and S. aureus ATCC 6538 type strains, grown on 96-pin lids and treated in Maxitrol for 30 min, 1 h, or 6 h. Isolates of both species were collected from the middle meatuses of patients with cystic fibrosis. Biofilms of clinical isolates were grown and treated in vitro for 6 h with Maxitrol, both undiluted at full concentration and at the identified MBEC, then cultured to identify bacterial survival. Results: Neither type strain was eradicated at 30 min nor S. aureus at 1 h at any tested concentration. P. aeruginosa was eradicated by a median of 90% and 5.6% Maxitrol at 1 and 6 h, respectively, and S. aureus with 90% Maxitrol at 6 h. Undiluted Maxitrol reliably eradicated all clinical isolates of P. aeruginosa but only one of five S. aureus isolates. Conclusions: Maxitrol reliably eradicates P. aeruginosa biofilm but not S. aureus biofilm in vitro. It may have a therapeutic role against biofilms in which P. aeruginosa is the dominant pathogen. [ABSTRACT FROM AUTHOR]

Developing optimized regimens for combination antibiotic therapy is challenging and often performed empirically over many clinical studies. Novel implementation of a hybrid machine‐learning pharmacokinetic/pharmacodynamic/toxicodynamic (ML‐PK/PD/TD) approach optimizes combination therapy using human PK/TD data along with in vitro PD data. This study utilized human population PK (PopPK) of aztreonam, ceftazidime/avibactam, and polymyxin B along with in vitro PDs from the Hollow Fiber Infection Model (HFIM) to derive optimal multi‐drug regimens de novo through implementation of a genetic algorithm (GA). The mechanism‐based PD model was constructed based on 7‐day HFIM experiments across 4 clinical, extensively drug resistant Klebsiella pneumoniae isolates. GA‐led optimization was performed using 13 different fitness functions to compare the effects of different efficacy (60%, 70%, 80%, or 90% of simulated subjects achieving bacterial counts of 102 CFU/mL) and toxicity (66% of simulated subjects having a target polymyxin B area under the concentration‐time curve [AUC] of 100 mg·h/L and aztreonam AUC of 1,332 mg·h/L) on the optimized regimen. All regimens, except those most heavily weighted for toxicity prevention, were able to achieve the target efficacy threshold (102 CFU/mL). Overall, GA‐based regimen optimization using preclinical data from animal‐sparing in vitro studies and human PopPK produced clinically relevant dosage regimens similar to those developed empirically over many years for all three antibiotics. Taken together, these data provide significant insight into new therapeutic approaches incorporating ML to regimen design and treatment of resistant bacterial infections. [ABSTRACT FROM AUTHOR]

The development of simple, sensitive, and efficient methods for antibiotic detection is of great significance for human health and environmental protection. Currently, although the competitive immunoassays are popular for detecting antibiotic molecules, they need to label antibiotic or specific antibody with signaling molecule. The development of noncompetitive immunoassay for antibiotic detection has always faced significant challenges. Herein, we have developed a light‐assisted noncompetitive immunoassay for the detection of antibiotics based on their photosensitive characteristic. Firstly, the antibody coated on the microplate specifically captures the target antibiotic. Afterward, under light irradiation, the captured photosensitive antibiotic produces reactive oxygen species (ROS), which oxidizes the added ROS dye to generate a fluorescent signal. Therefore, a noncompetitive immunoassay for antibiotic detection is achieved by utilizing the unique property of photosensitive antibiotics to generate ROS instead of labeling signaling molecules. By using antibiotics demeclocycline hydrochloride (DMCO) and polymyxin B (PMB) as research models, the proposed noncompetitive fluorescence immunoassay can specifically detect as low as 5 ng/mL DMCO and 70 ng/mL PMB, respectively. The light‐assisted noncompetitive immunoassay strategy opens a new avenue for simple, sensitive, label‐free, and high‐throughput detection of photosensitive antibiotics or photosensitive drugs. [ABSTRACT FROM AUTHOR]

Objectives: To elucidate the efficacy and safety of aggressive multi‐combination therapy with mycophenolate mofetil, rituximab, and plasma exchange or polymyxin B immobilized fiber column direct hemoperfusion followed by conventional therapy with corticosteroids, calcineurin inhibitors, and intravenous pulse cyclophosphamide in patients with rapidly progressive interstitial lung disease (RPILD) with anti‐melanoma differentiation‐associated gene 5 (MDA5)‐antibody‐positive dermatomyositis (DM). Methods: A total of 23 patients with anti‐MDA5 antibody‐positive DM‐RPILD were enrolled, with nine patients in Group A (treated conventionally before March 2015) and 14 patients in Group B (received aggressive treatment after April 2015). Results: Pretreatment severity of interstitial lung disease (ILD) did not differ between the two groups. However, Group B exhibited a higher cumulative survival rate at 48 weeks than Group A (64.3% vs. 33.3%). The corticosteroid dose, divided by the initial dose at 3 months and 12 months, was significantly lower in Group B than in Group A (p =.046 and.026, respectively). Among the ILD‐related deaths in Group B, there was a tendency toward a higher proportion of males and more severe ILD. The incidence of infection did not differ between the groups, but leukopenia was more common in Group B. Conclusion: This aggressive multi‐combination therapy may improve the survival outcome of patients with anti‐MDA5 antibody‐positive DM‐RPILD. However, careful management of complications, such as opportunistic infections and leukopenia, is essential. Future refinement through longitudinal investigations tracking the long‐term efficacy, safety, and cost‐effectiveness of this treatment strategy is needed. [ABSTRACT FROM AUTHOR]

Over the last decade, New Delhi metallo‐beta‐lactamase (NDM) carbapenemase has silently spread in Brazil. In this study, we analyzed a large collection of Enterobacterales other than Klebsiella spp. received in our reference laboratory between 2013 and 2022. A total of 32 clinical isolates displaying different pulsed‐field gel electrophoresis profiles, and represented by 11 species in the families Enterobacteriaceae (Citrobacter freundii, Citrobacter portucalensis, Enterobacter hormaechei, and Escherichia coli), Morganellaceae (Morganella morganii, Proteus mirabilis, Proteus vulgaris, Providencia rettgeri, Providencia stuartii, and Raoultella ornithinolytica), and Yersiniaceae (Serratia marcescens) had their whole genomes sequenced and further analyzed. Antimicrobial susceptibility was determined by disk diffusion, except for polymyxin B, assessed by broth microdilution. The blaNDM‐1 allele was predominant (n = 29), but blaNDM‐5 was identified in an E. coli specimen with a novel ST, and the blaNDM‐7 allele was found in E. hormaechei ST45 and E. coli ST1049. Polymyxin was active against all but one Enterobacteriaceae isolate: an mcr‐1–producing E. coli presenting minimal inhibitory concentration (4 mg/L). Isolates producing extended‐spectrum β‐lactamases were common: cefotaximase from Munich (CTX‐M)‐15 (n = 10), CTX‐M‐2 (n = 4), and CTX‐M‐8 (n = 3) were detected, and the mcr‐1–producing E. coli was found to co‐produce both CTX‐M‐8 and CTX‐M‐55 β‐lactamases. The mcr‐9 gene was found in 5/8 E. hormaechei isolates, distributed in four different sequence types, all of them presenting susceptibility to polymyxin. This study showed that NDM‐producing Enterobacterales other than Klebsiella are already spread in Brazil, in diversified species, and cocarrying important resistance genes. Prompt detection and effective implementation of measures to prevent further spread are mandatory for mitigating the dissemination of NDM carbapenemase in hospital settings and preserving the already limited antimicrobial therapy options. [ABSTRACT FROM AUTHOR]

Aims: Polymyxin B (PMB) is widely used to treat infections caused by multidrug‐resistant Gram‐negative pathogens. Currently, the pharmacokinetic data of PMB in patients with liver dysfunction are limited. This study aimed to develop a population pharmacokinetic (PopPK) model of PMB in patients with liver dysfunction and identify the factors affecting PMB pharmacokinetics. Methods: We conducted a retrospective pharmacokinetic study involving 136 adults with different levels of liver function. Nonlinear mixed effects modelling was used to develop a PopPK model of PMB. Monte Carlo simulation was used to design PMB dosage schedules across various liver and renal functions. Results: PMB pharmacokinetic analyses included 401 steady‐state concentrations in 136 adult patients. A one‐compartment pharmacokinetic model with first‐order absorption and elimination was used to describe the data. The typical population value of PMB clearance was 2.43 L/h and the volume of distribution was 23.11 L. This study revealed that creatinine clearance (CrCL) and Child–Pugh class were significantly associated with PMB pharmacokinetic parameters; however, clinically relevant variations of dose‐normalized drug exposure were not significant. For patients with a minimum inhibitory concentration of ≤0.5 mg/L, the appropriate dose was 40–75 mg/12‐h. When the dose exceeded 100 mg/12‐h, the risk of nephrotoxicity increased significantly. Conclusions: This study provided PMB pharmacokinetic information for patients with liver dysfunction. Patients with renal and liver dysfunctions may not require an initial dose adjustment. Rather than PopPK‐guided dose adjustment, therapeutic drug monitoring of PMB plays a more direct role in optimizing dosing regimens based on its therapeutic window. [ABSTRACT FROM AUTHOR]

Background: In canine otitis externa (OE), biofilm‐producing bacteria are frequently present but biofilm may be underdiagnosed clinically. Hypothesis/Objectives: The study aimed to investigate an association between clinical and cytological findings with bacteriological data from dogs with OE, to establish, through Environmental Scanning Electron Microscope (ESEM) examination, whether the presence of biofilm in vivo can be predicted and to evaluate the impact of biofilm on antimicrobial susceptibility tests. Materials and Methods: Fifty‐six dogs showing clinical signs of OE were enrolled. One cotton swab each was collected for ESEM, bacterial culture and susceptibility testing and for cytology. Staphylococcus pseudintermedius (n = 42, 48.8%) and Pseudomonas aeruginosa (n = 26, 30.2%) were tested for their ability to form biofilm. Minimum Inhibitory Concentrations (MIC), Minimal Biofilm Inhibitory Concentrations (MBIC) and Minimal Biofilm Eradication Concentrations (MBEC) towards enrofloxacin, gentamicin, polymyxin B and rifampicin were determined. Results: Pseudomonas aeruginosa was positively associated with the biofilm clinical evaluation (p < 0.01) and neutrophils (p < 0.05), nuclear streaks (p < 0.01) and rods bacteria (p < 0.01) on cytology. S. pseudintermedius was associated with a low presence of neutrophils. There was a statistical correlation between clinical and cytological biofilm presence (p ≤ 0.01), but none with the biofilm production assay nor ESEM biofilm detection. No differences were found comparing the results of MIC and MBIC. MBEC results showed higher values than MIC and MBIC for all antimicrobials tested (p ≤ 0.001). Conclusions and Clinical Relevance: Biofilm presence in OE was often underdiagnosed. Even if there is no specific clinical or cytological pattern related to biofilm, its presence should always be suspected. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the association between polymyxin B (PMB) exposure and acute kidney injury (AKI) and analyze the risk factors for PMB‐induced AKI in critically ill patients. Plasma concentrations of PMB were determined using an ultraperformance liquid chromatography–tandem mass spectrometer in intensive care unit patients who were administered PMB. Univariate and multivariate analyses were conducted to identify risk factors. A receiver operating characteristic curve was constructed to assess the discriminant power of the factors and to identify the cutoff value for AKI. The white blood cell count and estimated area under the concentration–time curve (AUC) of patients administered PMB were independent risk factors for PMB‐induced AKI, where AUC were calculated using a first‐order pharmacokinetic equation based on the mid‐dosing interval concentration (C1/2t) and peak concentration. The area under the receiver operating characteristic curve of the final model was 0.805 (95% confidence interval, 0.690–0.921). The cutoff value for the combined predictor was 0.57. Alternatively, when using C1/2t, which was strongly correlated with AUC, as the only independent risk factor, the analysis showed that the 3.47 μg/ml threshold provides favorable differentiation between the AKI and non‐AKI groups. These results provide insightful information for therapeutic drug monitoring–guiding PMB dosing in clinical practice. [ABSTRACT FROM AUTHOR]

The emergence and prevalence of mobile colistin resistance gene mcr have dramatically compromised the clinical efficacy of colistin, a cyclopeptide antibiotic considered to be the last option for treating different-to-treat infections. The combination strategy provides a productive and cost-effective strategy to expand the lifespan of existing antibiotics. Structural-activity relationship analysis of polymyxins indicates that the fatty acyl chain plays an indispensable role in their antibacterial activity. Herein, it is revealed that three saturated fatty acids (SFAs), especially sodium caprate (SC), substantially potentiate the antibacterial activity of colistin against mcr-positive bacteria. The combination of SFAs and colistin effectively inhibits biofilm formation and eliminates matured biofilms, and is capable of preventing the emergence and spread of mobile colistin resistance. Mechanistically, the addition of SFAs reduces lipopolysaccharide (LPS) modification by simultaneously promoting LPS biosynthesis and inhibiting the activity of MCR enzyme, enhance bacterial membrane damage, and impair the proton motive force-dependent efflux pump, thereby boosting the action of colistin. In three animal models of infection by mcr-positive pathogens, SC combined with colistin exhibit an excellent therapeutic effect. These findings indicate the therapeutic potential of SFAs as novel antibiotic adjuvants for the treatment of infections caused by multidrug-resistant bacteria in combination with colistin. [ABSTRACT FROM AUTHOR]

A population pharmacokinetic (pop PK) model of polymyxin B was developed using nonlinear mixed‐effects (NONMEM) modeling based on free plasma concentrations to determine whether dose adjustment is required in critically ill patients. One thousand pharmacokinetic profiles for virtual patients with a body weight of 70 kg were simulated using Monte Carlo simulation at different dose scenarios, and area under the concentration–time curve of free drug (fAUC) was computed. The probability of target attainment (PTA) at each minimum inhibitory concentration (MIC) was calculated using fAUC/MIC as a pharmacokinetic/pharmacodynamic (PK/PD) index. The final population PK model was a 2‐compartment model. PTA showed that 3.5 mg/kg/day regimens of polymyxin B effectively achieved the fAUC/MIC target of 10 (one log10 kill) against Pseudomonas aeruginosa strains with MIC of 1 mg/L or less (PTA, 90.7% or greater), while the dose regimen were ineffective against strains with an MIC of 2 mg/L or greater (PTA, 56.9% or less). For Klebsiella pneumoniae, the fAUC/MIC target of 17.4 (one log10 kill) was achieved in more than 90.4% of cases for MIC of 0.5 mg/L or less with 3 mg/kg/day regimens. However, the PTA decreased dramatically as MICs increased above 1 mg/L (PTA, 56.1% or less). The polymyxin B dosage regimen of 3.5 mg/kg/day and 3 mg/kg/day are sufficient to treat P. aeruginosa infections with an MIC of 1 mg/L or less and K. pneumoniae infections with an MIC of 0.5 mg/L or less, respectively. The current recommended dose (1.5–3 mg/kg/day) of polymyxin B appears inadequate to attain the PK/PD target for therapeutic efficacy against infections caused by P. aeruginosa and K. pneumoniae isolates when MIC is above the values. [ABSTRACT FROM AUTHOR]

Infections with multidrug‐resistant Gram‐negative bacteria constitute a silent pandemic threat that is increasing globally. A major technical and scientific hurdle hampering the development of efficient antibiotics against Gram‐negative species is the low permeability of their outer membrane that prevents the entry of most small molecules into the cells. This can be overcome by targeting active iron transport systems of the pathogens in a Trojan‐Horse strategy that makes use of drug‐loaded artificial siderophores. While we utilized catechols as iron‐binding motifs in previous work, this study reports the design, synthesis and characterization of siderophores with a DOTAM scaffold that was substituted with three hydroxamate arms allowing for a hexacoordination of iron. Their iron‐chelating capabilities were shown colorimetrically, and the ability of compound 1 to deliver iron into Escherichia coli in a chelation‐specific manner was proven by a growth recovery assay. A covalent siderophore‐ciprofloxacin conjugate exerted antibiotic effects against E. coli, albeit it was less potent than the free drug. The study qualifies artificial DOTAM siderophores with hydroxamate binders as scaffolds for bacterial Trojan Horses. This contribution for honoring my mentor Helmut Schwarz echoes two motifs of my work with him: Hydroxylamin, the topic of my first paper ever, and the fascinating properties of iron ions, studied in the gas phase during my Ph.D. Thesis, became a core subject of our current chemical biology research on antiinfectives. [ABSTRACT FROM AUTHOR]

An increased understanding of how the acceptor site in Gcn5‐related N‐acetyltransferase (GNAT) enzymes recognizes various substrates provides important clues for GNAT functional annotation and their use as chemical tools. In this study, we explored how the PA3944 enzyme from Pseudomonas aeruginosa recognizes three different acceptor substrates, including aspartame, NANMO, and polymyxin B, and identified acceptor residues that are critical for substrate specificity. To achieve this, we performed a series of molecular docking simulations and tested methods to identify acceptor substrate binding modes that are catalytically relevant. We found that traditional selection of best docking poses by lowest S scores did not reveal acceptor substrate binding modes that were generally close enough to the donor for productive acetylation. Instead, sorting poses based on distance between the acceptor amine nitrogen atom and donor carbonyl carbon atom placed these acceptor substrates near residues that contribute to substrate specificity and catalysis. To assess whether these residues are indeed contributors to substrate specificity, we mutated seven amino acid residues to alanine and determined their kinetic parameters. We identified several residues that improved the apparent affinity and catalytic efficiency of PA3944, especially for NANMO and/or polymyxin B. Additionally, one mutant (R106A) exhibited substrate inhibition toward NANMO, and we propose scenarios for the cause of this inhibition based on additional substrate docking studies with R106A. Ultimately, we propose that this residue is a key gatekeeper between the acceptor and donor sites by restricting and orienting the acceptor substrate within the acceptor site. [ABSTRACT FROM AUTHOR]

Polymyxin B (PMB) is a polypeptide antibiotic widely used in treating multidrug‐resistant Gram‐negative bacteria. However, nephrotoxicity is a serious adverse effect that limits its clinical use. Therefore, clarification of the molecular mechanism of PMB‐induced renal injury is essential. Our study aimed to explore possible mechanisms of PMB‐induced nephrotoxicity in vivo and in vitro. Mice were treated with PMB to construct the kidney injury model. The antioxidant capacity was assessed by measuring the superoxide dismutase (SOD) and catalase (CAT) activities and the glutathione (GSH) and malondialdehyde (MDA) contents. The pathway of the nuclear factor erythroid 2‐related factor 2/NADH quinone oxidoreductase 1 (Nrf2/NQO1) was examined after PMB treatment in NRK‐52E cells and mice. Finally, the expressions of genes and proteins (Bax, Bcl‐2, Caspase‐3, Caspase‐9) related to apoptosis were evaluated through quantitative polymerase chain reaction and western blot assay. The study verified PMB‐induced nephrotoxicity in mice and NRK‐52E cells in a dose‐ and time‐dependent manner. PMB treatment significantly decreased the expression of Nrf2 and its downstream target gene NQO1 and increased the apoptosis‐related proteins expression. In summary, our results suggested that PMB‐induced oxidative stress damage by inhibiting the Nrf2/NQO1 pathway and promoting apoptosis in kidney tissues. [ABSTRACT FROM AUTHOR]

Summary: A 13‐year‐old Thoroughbred/Oldenburg gelding presented as a tertiary referral for a 6‐year history of immune‐mediated keratitis (IMMK) after the development of corneal and limbal nodules in the presence of medical therapy. A keratectomy extending to the limbus was performed to remove the affected cornea and limbal nodules. Two corneal‐limbal samples were submitted for histopathology and initially diagnosed as marked lympho‐histiocytic stromal keratitis with epithelial hyperplasia, keratinisation and keratinocyte apoptosis consistent with IMMK. Additional testing with immunohistochemical staining for CD3, CD20, PAX5 and IBA1 revealed large, atypical B‐lymphocytes on a background of histiocytes and mature T‐lymphocytes, with concern for T‐cell‐rich large B‐cell lymphoma. PCR antigen receptor rearrangement clonality testing was also performed and was diagnostic for large B‐cell lymphoma. Polymerase chain reaction (PCR) for equine herpesvirus 5 (EHV‐5) was positive. Following keratectomy, a short course of neomycin/polymyxin B/dexamethasone ophthalmic ointment was prescribed; no other treatment nor adjunct therapy was performed. Eighteen months post‐operation, the case remains visual and comfortable on no medications. [ABSTRACT FROM AUTHOR]

In this study, we report ultrafine‐sized antibiotic dot particles targeting gram‐negative bacteria. The water‐soluble ultrafine‐sized hyaluronate dot (dHA) was conjugated with polymyxin B (PMB, as a target material for lipopolysaccharide on a gram‐negative bacteria) and chlorine e6 (Ce6, as a model photosensitizer), and it was denoted as dHA‐(PMB/Ce6). These dot particles interacted with lipopolysaccharide (LPS) on gram‐negative bacteria, which enabled PMB‐mediated docking to the outer membrane of gram‐negative cells. In the antimicrobial experiments using Escherichia coli cells, the phototoxic singlet oxygen generated from the dHA‐(PMB/Ce6) under light irradiation inhibited E. coli cell growth. This demonstrated that dHA‐(PMB/Ce6) can provide light‐activated selective phototoxicity against gram‐negative bacteria. We expect that the dot particle system can be used as an efficient method for improved antimicrobial treatment. [ABSTRACT FROM AUTHOR]

Background: Chronic otitis externa (OE) in dogs frequently requires anaesthetised ear flushing. Objectives: To evaluate hypochlorous acid as an ear flushing and antimicrobial agent in dogs with chronic OE. Animals: Twenty dogs with chronic OE caused by the same organisms bilaterally. Materials and Methods: One ear was flushed under anaesthesia with hypochlorous acid, the other with saline solution. Subsequently, the ear flushed with hypochlorous acid was cleaned with the same solution twice daily for 2 weeks, the other ear with a commercial ear cleaner. An ear medication containing miconazole, polymyxin B and prednisolone was used once daily in both ears. Clinical scores were determined before the flush. Ear cytological results were obtained, a hearing test was conducted before and after the ear flush, and a culture was taken directly after flushing. Ears were evaluated after 2 weeks of therapy. Results: Yeast was present in the ears of 11, cocci in one and a mixed infection in eight dogs. Five ears were negative on culture after flushing with hypochlorous acid, one after the saline flush. Clinical and cytological scores decreased significantly with both solutions after 2 weeks of treatment. There was no difference between treatments in any of the scores at any time point between treatments and in the results of the hearing test before and after the flushing procedure. Adverse effects were not seen. Conclusions and Clinical Relevance: Hypochlorous acid is a suitable cleaning solution for canine OE. Background – Chronic otitis externa (OE) in dogs frequently requires anaesthetised ear flushing. Objectives – To evaluate hypochlorous acid as an ear flushing and antimicrobial agent in dogs with chronic OE. Conclusions and Clinical Relevance – Hypochlorous acid is a suitable cleaning solution for canine OE. [ABSTRACT FROM AUTHOR]

Background: Outer membrane protein A (OmpA) is the major virulence factor of Acinetobacter baumannii and plays a wide role in the pathogenesis and antimicrobial resistance of A. baumannii. Dendritic cells (DCs) are the most effective antigen‐presenting cells and play a crucial role in regulating the immune response to multiple antigens and immune sentries. We aimed to study the role and molecular mechanisms of OmpA‐induced mouse bone marrow‐derived dendritic cells (BMDCs) autophagy in the immune response of A. baumannii. Methods: First, purified A. baumannii OmpA was assessed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and western blot. OmpA effect on BMDCs viability was evaluated by MTT assay. BMDCs were pretreated with autophagy inhibitor chloroquine or transfected with overexpression plasmids (oe‐NC or oe‐PI3K). Then BMDCs apoptosis, inflammatory cytokines, protein kinase B (PI3K)/mammalian target of rapamycin (mTOR) pathway, and autophagy‐related factors levels were evaluated. Results: SDS‐PAGE and western blot verified the successful purification of OmpA. BMDCs viability repressed gradually with the increase of OmpA concentration. OmpA treatment of BMDCs led to apoptosis and inflammation in BMDCs. OmpA caused incomplete autophagy in BMDCs, and light chain 3 (LC3), Beclin1, P62, and LC3II/I levels were significantly elevated with the increase of the time and concentration of OmpA treatment. Chloroquine reversed OmpA effects on autophagy in BMDCs, that was, LC3, Beclin1, and LC3II/I levels were reduced, while P62 level was elevated. Furthermore, chloroquine reversed OmpA effects on apoptosis and inflammation in BMDCs. PI3K/mTOR pathway‐related factor expression was affected by OmpA treatment of BMDCs. After overexpression of PI3K, these effects were reversed. Conclusions: A. baumannii OmpA induced autophagy in BMDCs involving the PI3K/mTOR pathway. Our study may provide a novel therapeutic target and theoretical basis for treating infections caused by A. baumannii. [ABSTRACT FROM AUTHOR]

Carbapenemase‐resistant Klebsiella pneumoniae (KP) resistant to multiple antibiotic classes necessitates optimized combination therapy. Our objective is to build a workflow leveraging omics and bacterial count data to identify antibiotic mechanisms that can be used to design and optimize combination regimens. For pharmacodynamic (PD) analysis, previously published static time‐kill studies (J Antimicrob Chemother 70, 2015, 2589) were used with polymyxin B (PMB) and chloramphenicol (CHL) mono and combination therapy against three KP clinical isolates over 24 h. A mechanism‐based model (MBM) was developed using time‐kill data in S‐ADAPT describing PMB‐CHL PD activity against each isolate. Previously published results of PMB (1 mg/L continuous infusion) and CHL (Cmax: 8 mg/L; bolus q6h) mono and combination regimens were evaluated using an in vitro one‐compartment dynamic infection model against a KP clinical isolate (108 CFU/ml inoculum) over 24 h to obtain bacterial samples for multi‐omics analyses. The differentially expressed genes and metabolites in these bacterial samples served as input to develop a partial least squares regression (PLSR) in R that links PD responses with the multi‐omics responses via a multi‐omics pathway analysis. PMB efficacy was increased when combined with CHL, and the MBM described the observed PD well for all strains. The PLSR consisted of 29 omics inputs and predicted MBM PD response (R2 = 0.946). Our analysis found that CHL downregulated metabolites and genes pertinent to lipid A, hence limiting the emergence of PMB resistance. Our workflow linked insights from analysis of multi‐omics data with MBM to identify biological mechanisms explaining observed PD activity in combination therapy. [ABSTRACT FROM AUTHOR]

A new, simple‐to‐synthesize and sensitive turn‐on fluorogenic substrate (CFMU‐Glu) for β‐glucosidase activity was developed. This probe was based on a 7‐hydroxycoumarin derivative (CFMU) that could emit green fluorescence and had the low pKa value of 5.61 ± 0.01. CFMU‐Glu could be used for sensitive monitoring of the almond βGLU and Enterococcus faecalis (E. faecalis) at the optimal pHs of 6.50 and 7.00, respectively. Moreover, a new sensitive and selective fluorogenic broth (PBF‐B) for E. faecalis, utilizing CFMU‐Glu and polymyxin B, was also developed. Polymyxin B was discovered to can significantly improve the detection selectivity and signal intensity. The proposed 4‐four method using PBF‐B and a microcentrifuge tube could provide fluorogenic detection limits of 5.01 × 104 and 1.0 × 105 CFU mL−1 by fluorescence microplate reader and naked eye, respectively; it could also provide a turn‐on chromogenic detection limit of 1.0 × 106 CFU mL−1 by naked eye. The proposed method could detect 8 CFU mL−1 of E. faecalis in drinking water, Liangcha (herbal tea) and milk samples within 10 h, without pre‐enrichment. [ABSTRACT FROM AUTHOR]

Streptococcal toxic shock syndrome (STSS) has a high mortality rate, and most patients die within a few days of onset. We report an elderly patient with STSS, necrotizing fasciitis and septic shock caused by group G streptococcus who was successfully treated with multidisciplinary therapy. The elderly patient suffered from streptococcal toxic shock syndrome and went into shock rapidly and progressively. However, prompt surgical treatment, antimicrobial agents, and blood purification therapy such as polymyxin B immobilized fiber column direct hemoperfusion and continuous hemodiafiltration could have saved the patient's life. [ABSTRACT FROM AUTHOR]

Aeromonas salmonicida is a Gram‐negative bacterium that can infect a wide host range of fish populations, including salmonids and non‐salmonids as well as freshwater and marine life. Some strains of A. salmonicida cause the disease furunculosis, which can cause lethargy, intestinal inflammation, ulcers, haemorrhaging and death. The infection is spread through fish‐to‐fish contact, and the presence of infection can have devastating effects on cultivated fish populations. The purpose of this study was to explore the ability of non‐A‐layer and A‐layer A. salmonicida strains to incorporate polyunsaturated fatty acids (PUFAs) into their lipid profile and test the phenotypic effects thereof. Lipids were extracted from PUFA‐exposed cultures and analysed for lipid modification by thin‐layer chromatography and ultraperformance liquid chromatography‐mass spectrometry, showing A. salmonicida, regardless of A‐layer, capable of incorporating all seven of the PUFAs studied. Phenotypic effects were determined through the use of assays that tested for biofilm formation, membrane permeability and cyclic peptide susceptibility. Temperature‐dependent effects on biofilm formation were observed, and PUFA exposure showed significant (p <.001) increases in membrane permeability as tested by the uptake of the hydrophobic compounds crystal violet and ethidium bromide. Additionally, some PUFAs elicited modest protection and vulnerability against the membrane‐targeting cyclic peptides polymyxin B (PMB) and colistin. The diverse, strain‐specific responses to exogenous PUFAs may allude to evolved adaptive strategies that enhance survival, persistence and virulence of non‐pathogenic and pathogenic members of bacteria that oscillate between environmental and fish host niches. [ABSTRACT FROM AUTHOR]

Innate immunity is the first and essential line for resisting pathogens, and the immune intensity and duration need to be strictly regulated to balance excessive or insufficient immune response. MicroRNAs (miRNAs) are crucial regulators of immune response in Drosophila, yet how immune‐related miRNAs are regulated remains poorly understood. Herein, we elucidated that the involvement of miR‐317 in NF‐κB transcription factor Relish mediated Drosophila Imd pathway in response to Gram‐negative (G‐) bacteria stimulation. Remarkably, the dynamic expression profiling for immune response indicated that Relish simultaneously enhances the expression of the effector antimicrobial peptide Dpt as well as miR‐317 post‐infection. Upregulation of miR‐317 could further down‐regulate the expression of PGRP‐LC, thereby forming a feedback in Drosophila Imd pathway to prevent over‐activation and restore immune homeostasis. Taken together, our study not only uncovers a novel Relish/miR‐317/PGRP‐LC regulatory axis to attenuate Drosophila Imd immune response and facilitate immune homeostasis restoration, but also provides vital insights into the complex mechanisms of animal innate immune regulation. [ABSTRACT FROM AUTHOR]

This study presents a set of strategies for producing potent antibacterial fabrics by functionalizing nonwoven fabrics (NWFs) with antimicrobial peptides and polymers (AMPs). The incorporation of AMPs is initially optimized on 2D substrates by evaluating conjugation on a poly(maleic anhydride) copolymer coating versus adsorption on polycationic/anionic films and microgels. The evaluation of the resulting surfaces against S. aureus and E. coli highlights the superior antibacterial activity of poly‐ionic films loaded with daptomycin and polymyxin B as well as microgels featuring controlled release of bacitracin and polymyxin B. These formulations are translated onto spun‐bond polypropylene and poly(ethylene terephthalate) NWFs. The poly‐ionic coatings are either covalently anchored or physically adsorbed onto the surface of the fibers, while the microgels and antibacterial polymers are adsorbed and photo‐crosslinked thereon using a ultraviolet (UV)‐crosslinkable benzophenone‐based polymer. Selected formulations loaded with bacitracin and polymyxin B afford a 105‐fold reduction of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in artificial sweat, respectively, on par with commercial antibacterial NWFs. The proposed antibacterial fabric, however, outperforms its commercial counterparts in terms of biocompatibility, showing virtually no adverse effect on human epidermal keratinocytes. Collectively, these results demonstrate affordable and scalable routes for developing antimicrobial NWFs that efficiently eliminate resilient pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Background: Toxicity is a major concern related to the clinical use of polymyxin B, and available safety data for renal transplant patients are limited. Aims: We investigated the safety of polymyxin B and toxicity risk factors in renal transplant patients. Methods: A prospective study was performed on a group of renal transplant patients who received intravenous polymyxin B between January 2018 and August 2021. Polymyxin B treatment was monitored to evaluate toxicity and risk factors. Results: A total of 235 courses of polymyxin B were administered to 213 patients. Of these, 121 (51.5%) developed skin hyperpigmentation (SH), 149 (63.4%) developed neurotoxicity and 10 (5.5%) developed acute kidney injury of which 80% was reversible. Risk factors for developing SH included a high total dose by weight (odds ration [OR] 1.31, 95% confidence interval [CI] 1.08–1.60, P =.008) and the presence of neurotoxicity (OR 2.86, 95% CI 1.56–5.26, P =.001). Neurotoxicity manifested during the first 2 days of treatment. Neurotoxicity occurred most commonly in women (OR 3.84, 95% CI 1.82–8.10, P <.0001), and the presence of SH (OR 1.98, 95% CI 1.13–3.46, P =.016) was also an independent risk factor. Conclusions: Neurotoxicity and SH are the two major adverse effects of polymyxin B in renal transplant patients, which may limit its clinical use. [ABSTRACT FROM AUTHOR]

In recent years, polymyxin B-associated acute kidney injury (PB-AKI) in critically ill patients has been reported frequently, but polymyxin B (PB) is mainly cleared through non-renal pathways, and the reasons of PB-AKI remain unclear. The aim of this study was to investigate the relationship between the serum concentration of PB and PBAKI. We conducted a prospective cohort study in an intensive care unit between May 2019 and July 2021. Over the study period, 52 patients were included and divided into an AKI group (n = 26) and a non-AKI group (n = 26). The loading dose of PB in the AKI group was significantly higher than that in the non- AKI group. The C1/2, Cmin, and estimated area under the concentration--time curve (AUC)0-24 of PB in the AKI group were dramatically increased compared with those in the non-AKI group, but the Cmax between the two groups showed no differences. Upon obtaining the ROC curve, the areas for the C1/2, Cmin, and estimated AUC0-24 were 0.742, 0.710, and 0.710, respectively. The sensitivity was ascertained to be 61.54%, and the specificity was 76.92% when the cutoff value for the estimated AUC0-24 of 97.72 mg·h/L was used preferentially. The incidence of PB-AKI is high and related to the loading dose of PB. PB- AKI could be predicted when the estimated AUC0-24 of PB was greater than 97.72 mg·h/L. [ABSTRACT FROM AUTHOR]

Purpose: To describe bacterial isolates and associated antibiotic resistance from horses with ulcerative keratitis in Belgium. Methods: Medical records from horses with ulcerative keratitis presented to the ophthalmology service of the Veterinary teaching hospital of Liege, Belgium, between 2014 and 2021 were evaluated. Bacterial isolates were identified and VITEK® 2 (Biomérieux) provided antimicrobial susceptibility testing and resistance detection. Results: Two hundred eyes of 196 horses were sampled. Ninety‐seven eyes had a positive bacterial culture (48.5%) and 139 bacterial isolates were identified. Staphylococcus (63/139: 45.3%) and Streptococcus (33/139: 23.7%) were the most frequent genus isolated. Staphylococcus aureus (21/139: 15.1%) was the most frequent species isolated of which half were methicillin‐resistant (MRS). Streptococcus equi subsp. zooepidemicus (19/139: 13.7%) was the second most identified bacterial isolate. Only two Pseudomonas species were isolated (2/139: 1.4%). The overall resistance of all bacterial isolates against chloramphenicol (12.4%) and fluoroquinolones (14.3%) was low. Resistance against tobramycin, polymyxin B, gentamicin, fusidic acid, tetracycline, and neomycin ranged from 40.8% to 58.6%. When separating the MRS from the other staphylococci, a significant difference was noted in percentage of resistance to gentamicin (p =.00026) and tetracycline (p =.00015). MRS were highly resistant to gentamicin (75%) and tetracycline (100%), whereas the remaining staphylococci were significantly less resistant to gentamicin (17%) and tetracycline (40.4%). Conclusion: Although Pseudomonas species has been rarely cultured, our results are roughly consistent with previous studies. Multiple drug resistance was high and resistance to first‐choice antibiotics in ulcerative keratitis was noted. These results warrant continued monitoring of susceptibility profile. [ABSTRACT FROM AUTHOR]

Summary: The growing problem of antimicrobial resistance affects veterinarians on a daily basis. Antimicrobial stewardship and responsible prescribing are essential for a future with effective antimicrobials, as it is unlikely that new antimicrobials will become available for use in horses in the near future. Extended‐spectrum β‐lactamase (ESBL) producing Enterobacteriaceae, methicillin‐resistant Staphylococcus aureus (MRSA) and Salmonella spp. are pathogens of significant concern but there are also other opportunistic pathogens such as Pseudomonas spp., α‐haemolytic Streptococcus spp., Enterococcus spp. and Acinetobacter spp. which, due to their high intrinsic resistance, have limited treatment options in adult horses. It is essential that highest priority critically important antimicrobials such as ceftiofur, enrofloxacin, rifampicin and polymyxin B are used prudently in horses and ideally based on culture and antimicrobial susceptibility testing (AST). For example, the use of polymyxin B at a low anti‐endotoxic dose rather than at a higher antimicrobial dose in horses for the treatment of systemic inflammatory response syndrome is a potential driver for resistance to colistin (polymyxin E), an antimicrobial used as a last resort in the treatment of multidrug resistant (MDR) Enterobacteriaceae infections in humans. Serum procalcitonin levels are used in humans to distinguish noninfectious inflammatory conditions from inflammation caused by bacteria and other infectious agents and are also used to guide cessation of antimicrobial treatment. Although no such studies have been performed in horses, this or other markers may prove to be helpful in guiding antimicrobial treatment decisions in the future. Optimising sampling techniques and good communication with the microbiology laboratory are essential for generating the accurate culture and AST results that underpin appropriate antimicrobial use. Additionally, there is clearly a need for national and international harmonisation of laboratory methods in order to improve the reliability and consistency of results reported by different laboratories. [ABSTRACT FROM AUTHOR]

Summary: Previously we described the discovery of a Bacillus spp. specific peptidase activity related to d‐stereospecific peptidases (DSPs). The peptidase showed a strong preference for d‐leucine and d‐valine amino acids. These amino acids are present in the structure of the non‐ribosomal peptide (NRP) antibiotics gramicidin A, B and C and polymyxin E. To examine if the Bacillus spp. DSP‐related peptidase can hydrolyze these NRPs, the effect of gramicidin A and C and polymyxin E on peptidase activity in Bacillus anthracis culture supernatant was monitored. It was found that both gramicidins inhibited the DSP‐related activity in a competitive manner. MALDI‐TOF analysis revealed that upon incubation with B. anthracis culture supernatant gramicidin A hydrolyzation products appeared. This study shows that the Bacillus spp. specific DSP‐like peptidase was potentially produced by the bacteria to gain intrinsic resistance against NRP antibiotics. These results are of utmost importance in research towards antimicrobial resistance, whereas transfer of DSP‐related activity to other clinically relevant pathogens can be a serious threat to human health. [ABSTRACT FROM AUTHOR]

Background: Polymyxin B (PolyB) is used to treat endotoxemia in horses; neurologic and nephrogenic adverse effects occur in humans. Objectives: To describe PolyB adverse effects in horses. Animals: Five healthy horses (ataxia 0/5), 1 horse with cervical osteoarthritis (ataxia 1/5). Methods: Prospective blinded randomized cross‐over trial; 3‐weeks wash out. Horses received PolyB (PolyB 6000 IU/kg IV, 7 doses q12h, n = 6) and PolyB/gentamicin (PolyB 6000 IU/kg IV, q12h 7 doses; gentamicin 10 mg/kg IV q24h 4 doses n = 4, or q12‐24 h 5 doses because of an additional erroneous dose, n = 2). Daily neurological examinations were video recorded, and ataxia graded by 3 observers. Urine status, urinary GGT/creatinine ratio, plasma creatinine, and urea were assessed every other day, EMG daily. Mixed model analysis was used to evaluate factors associated with ataxia grade and [PolyB]. Results: Median ataxia score increased from 0/5 (range 0‐2/5) to 2/5 (range 1‐3/5) during administration and declined to 0.5/5 (range 0‐2/5) after cessation. Gentamicin co‐administration (P <.01, effect size:.8), number of PolyB doses (P <.001, effect size:.6), and time since last PolyB dose (P <.001, effect size:.5) had a significant effect on ataxia grades, while horse, day, [Genta], [PolyB], and [PolyB]CSF did not. Gentamicin co‐administration and [Genta] Cpeak had no effect on median [PolyB] Cpeak (4.67 and 4.89 μg/ml for PolyB and PolyB/gentamicin, respectively). Urinary GGT/creatinine ratio was elevated in 3/6 horses receiving PolyB/gentamicin. The EMG remained unchanged. Conclusions and Clinical Importance: PolyB caused transient ataxia, worsening with cumulative PolyB doses and gentamicin co‐administration. Nephrotoxicity of PolyB was only evident when gentamicin was co‐administered. [ABSTRACT FROM AUTHOR]

Polymyxins (PMS), namely Colistin (CS) and polymyxin B (poly B), are antimicrobial drugs that have been recently used to treat multiresistant Gram‐negative bacteria infections and their resurgence, owing to a lack of new antibiotics. A speedy, simple, and ultrasensitive spectrofluorimetric screening of PMS in pharmaceutical formulations and biological fluids was urgently required from this point forwards. A reaction between fluorescamine and the aliphatic amino moiety found in both drugs was performed in a slightly alkaline borate buffer (pH 8.5) resulted in highly fluorescent products measured at λem 460 (after λex 390.5 nm). Linear calibration curves were constructed over the concentration range 70–1800 ng ml−1 and 100 to 1400 ng ml−1, with slope values of 0.273 and 0.286, correlation coefficients of 0.9998 and 0.9997, and determination coefficient of 0.9997 and 0.9994 for poly B and CS, respectively. The ultrasensitivity of the proposed method was demonstrated by the very low limit of quantification values of 67.56 ng ml−1 and 94.89 ng ml−1 for poly B and CS, respectively. The cited drugs were successfully determined in their intravenous market preparations by the prescribed method. Moreover, due to the high sensitivity, the suggested method was used to assay the investigated drugs in biological fluids. [ABSTRACT FROM AUTHOR]

Objectives: We aimed to assess the effectiveness and nephrotoxicity of polymyxin B in critically ill patients with nosocomial pneumonia and to evaluate the utility of its therapeutic drug monitoring (TDM). Methods: We retrospectively analyzed patients who received polymyxin B treatment for ≥48 h since the establishment of polymyxin B TDM in a 26‐bed tertiary referral intensive care unit. Univariate and multivariate analyses were conducted to assess the variables associated with polymyxin B effectiveness and nephrotoxicity. Results: A total of 62 patients were enrolled. Most (56.5%) of the patients performed TDM, 54.3% of them reached the therapeutic target of area under curve across 24 h at steady state (AUCss,24h) of 50–100 mg h L−1, and 10 patients had an AUCss,24h value of <50 mg h L−1. Thirty‐six (58.1) and 31 (50.0%) patients had favorable clinical and microbiological responses, respectively. Reaching the therapeutic target of AUCss,24h (odds ratio [OR] = 13.15, p = 0.015), a favorable microbiological response (OR = 40.80, p = 0.00), and complicated with septic shock (OR = 0.12, p = 0.021) were independently associated with favorable clinical outcomes of polymyxin B treatment. The incidence of acute kidney injury (AKI) was 45.2%. A lower creatinine clearance (OR = 0.96, p = 0.008) and concomitant treatment with loop diuretics (OR = 5.93, p = 0.046) were predictive of nephrotoxicity. Conclusion: Our findings show that TDM of polymyxin B is a valuable intervention, and the achievement of its optimal pharmacodynamic target can improve treatment outcome. Renal insufficiency and concomitant treatment with loop diuretics were found to be associated with the risk of nephrotoxicity. [ABSTRACT FROM AUTHOR]

Acinetobacter baumannii is the causative agent of various hospital‐acquired infections. Biofilm formation is one of the various antimicrobial resistance (AMR) strategies and is associated with high mortality and morbidity. Hence, it is essential to review the potential antibiofilm targets in A. baumannii and come up with different strategies to combat these potential targets. This review covers different pathways involved in the regulation of biofilm formation in A. baumannii like quorum sensing (QS), cyclic‐di‐GMP signaling, two‐component system (TCS), outer‐membrane protein (ompA), and biofilm‐associated protein (BAP). A newly discovered mechanism of electrical signaling‐mediated biofilm formation and contact‐dependent biofilm modulation has also been discussed. As biofilm formation and its maintenance in A. baumannii is facilitated by these potential targets, the detailed study of these targets and pathways can bring light to different therapeutic strategies such as anti‐biofilm peptides, natural and synthetic molecule inhibitors, QS molecule degrading enzymes, and other strategies. These strategies may help in suppressing the lethality of biofilm‐mediated infections. Targeting essential proteins/targets which are crucial for biofilm formation and regulation may render new therapeutic strategies that can aid in combating biofilm, thus reducing the recalcitrant infections and morbidity associated with the biofilm of A. baumannii. [ABSTRACT FROM AUTHOR]

Summary: Antibiotic pollution of non‐clinical environments might have a relevant impact on human health if resistant pathogens are selected. However, this potential risk is often overlooked, since drug concentrations in nature are usually below their minimal inhibitory concentrations (MICs). Albeit, antibiotic resistant bacteria can be selected even at sub‐MIC concentrations, in a range known as the sub‐MIC selective window. Using short‐term evolution experiments, we have determined the sub‐MIC selective windows of the opportunistic pathogen Pseudomonas aeruginosa for seven antibiotics of clinical relevance, finding the ones of quinolones to be the widest, and the ones of polymyxin B and imipenem, the narrowest. Clinically relevant multidrug‐resistant mutants arose within the sub‐MIC selective windows of most antibiotics tested, being some of these phenotypes mediated by efflux pumps' activity. The fact that the concentration of antibiotics reported in aquatic ecosystems – colonizable by P. aeruginosa – are, in occasions, higher than the ones that select multidrug‐resistant mutants in our assays, has implications for understanding the role of different ecosystems and conditions in the emergence of antibiotic resistance from a One‐Health perspective. Further, it reinforces the importance of procuring accurate information on the sub‐MIC selective windows for drugs of clinical value in pathogens with environmental niches. [ABSTRACT FROM AUTHOR]

Summary: Antimicrobials are commonly used in prevention of infections including in aquaculture, agriculture and medicine. Subinhibitory concentrations of antimicrobial peptides can modulate resistance, virulence and persistence effectors in Gram‐negative pathogens. In this study, we investigated the effect of subinhibitory concentrations of polymyxin B (PmB) on the secretome of Vibrio cholerae, a natural inhabitant of aquatic environments and the pathogen responsible for the cholera disease. Our proteomic approach revealed that the abundance of many extracellular proteins is affected by PmB and some of them are detected only either in the presence or in the absence of PmB. The type VI secretion system (T6SS) secreted hemolysin‐coregulated protein (Hcp) displayed an increased abundance in the presence of PmB. Hcp is also more abundant in the bacterial cells in the presence of PmB and hcp expression is upregulated upon PmB supplementation. No effect of the T6SS on antimicrobial resistance was observed. Conversely, PmB increases the T6SS‐dependent cytotoxicity of V. cholerae towards the amoeba Dictyostelium discoideum and its ability to compete with Escherichia coli. [ABSTRACT FROM AUTHOR]

Aims: Data regarding clinical pharmacokinetic/toxicodynamic (PK/TD) of polymyxin B is short of direct quantitative data. This study aims to investigate the risk factors of polymyxin B associated acute kidney injury (AKI) and to assess the relationship between polymyxin B plasma levels and its nephrotoxicity. Methods: A retrospective study was performed in adult patients treated with polymyxin B. Risk factors associated with AKI and plasma trough concentrations of polymyxin B were identified via medical record review. A multivariate logistic regression model was established and the risk of polymyxin B‐associated AKI were predicted by a receiver operating characteristic curve, with maximal Youden index used to identify safety thresholds among the study population. Results: Fifty‐four adult patients were included in the study. AKI was detected in 14 patients during polymyxin B treatment (25.9%, 14 out of 54). Cmin (odds ratio [OR] 2.071; 95% confidence interval [CI] 1.235–3.472) and baseline serum creatinine (OR 1.024; 95% CI 1.005–1.043) were significant independent risk factors for developing AKI. The area under the ROC curve of the combined predictor was larger based on the above factors. When the Youden index was at maximum, the optimal cut‐off point was 6.678 of the ROC curve. When Cmin ≥ 3.13 mg/L, the probability of AKI was more than 50%. Conclusion: In this study, when the calculated combined predictor value was >6.678, there was an increased risk of AKI. Maintaining a polymyxin B Cmin level below 3.13 mg/L may be helpful in reducing the incidence of polymyxin B associated nephrotoxicity. [ABSTRACT FROM AUTHOR]

Using artificial hemes for the reconstruction of natural heme proteins represents a fascinating approach to enhance the bioactivity of the latter. We report the synthesis of various metal 5‐oxaporphyrinium cations as cofactors, and a cobalt 5‐oxaporphyrinium cation was successfully incorporated into the heme‐acquisition protein (HasA) secreted by Pseudomonas aeruginosa. We hypothesize that the oxaporphyrinium cation strongly binds to the HasA‐specific outer membrane receptor (HasR) due to its cationic charge, which prevents the subsequent acquisition of heme. In fact, the reconstructed HasA inhibited the growth of Pseudomonas aeruginosa and even of multidrug‐resistant P. aeruginosa. [ABSTRACT FROM AUTHOR]

Polymyxin B (PMB) has reemerged as a last‐line therapy for infections caused by multidrug‐resistant gram‐negative pathogens, but dosing is challenging because of its narrow therapeutic window and pharmacokinetic (PK) variability. Population PK (POPPK) models based on suitably powered clinical studies with appropriate sampling strategies that take variability into consideration can inform PMB dosing to maximize efficacy and minimize toxicity and resistance. Here we reviewed published PMB POPPK models and evaluated them using an external validation data set (EVD) of patients who are critically ill and enrolled in an ongoing clinical study to assess their utility. Seven published POPPK models were employed using the reported model equations, parameter values, covariate relationships, interpatient variability, parameter covariance, and unexplained residual variability in NONMEM (Version 7.4.3). The predictive ability of the models was assessed using prediction‐based and simulation‐based diagnostics. Patient characteristics and treatment information were comparable across studies and with the EVD (n = 40), but the sampling strategy was a main source of PK variability across studies. All models visually and statistically underpredicted EVD plasma concentrations, but the two‐compartment models more accurately described the external data set. As current POPPK models were inadequately predictive of the EVD, creation of a new POPPK model based on an appropriately powered clinical study with an informed PK sampling strategy would be expected to improve characterization of PMB PK and identify covariates to explain interpatient variability. Such a model would support model‐informed precision dosing frameworks, which are urgently needed to improve PMB treatment efficacy, limit resistance, and reduce toxicity in patients who are critically ill. [ABSTRACT FROM AUTHOR]