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Background Methods Results Conclusion A patient with an extensively drug‐resistant (XDR) New Delhi metallo‐β‐lactamase (NDM) and oxacillinase (OXA‐48) producing Escherichia coli (E. coli) infection was awaiting orthotopic liver transplant. There is no standardized antibiotic prophylaxis regimen; however, in line with the Infectious Diseases Society of America guidance, an antibiotic prophylactic regimen of ceftazidime‐avibactam 2.5 g TDS with aztreonam 2 g three times a day (TDS) IV was proposed.The hollow fiber system (HFS) was applied to inform the individualized pharmacodynamic outcome likelihood prior to prophylaxis.A 4‐log reduction in CFU/mL in the first 10 h of the regimen exposure was observed; however, the killing dynamics were slow and six 8‐hourly infusions were required to reduce bacterial cells to below the limit of quantification. Thus, the HFS supported the use of the regimen for infection clearance; however, it highlighted the need for several infusions. Standard local practice is to administer prophylaxis antibiotics at induction of orthotopic liver transplantation (OLT); however, the HFS provided data to rationalize earlier dosing. Therefore, the patient was dosed at 24 h prior to their OLT induction and subsequently discharged 8 days after surgery.The HFS provides a dynamic culture solution for informing individualized medicine by testing antibiotic combinations and exposures against the bacterial isolates cultured from the patient's infection. . [ABSTRACT FROM AUTHOR]

Pseudomonas aeruginosa (Pa) poses a significant threat to individuals with cystic fibrosis (CF), as this bacterium is highly adaptable and resistant to antibiotics. While early-stage Pa infections can often be eradicated with aggressive antibiotic therapy, chronic infections are nearly impossible to eliminate and require treatments that focus on long-term bacterial suppression. Without such suppression, these persistent infections can severely damage the lungs, leading to serious complications and a reduced life expectancy for CF patients. Evidence for a specific treatment regimen for managing Pa infections in CF patients remains limited. This narrative review provides a detailed analysis of antimicrobial therapies assessed in completed phase IV trials, focusing on their safety and efficacy, especially with prolonged use. Key antibiotics, including tobramycin, colistin, meropenem, aztreonam, ceftolozane/tazobactam, ciprofloxacin, and azithromycin, are discussed, emphasizing their use, side effects, and delivery methods. Inhaled antibiotics are preferred for their targeted action and minimal side effects, while systemic antibiotics offer potency but carry risks like nephrotoxicity. The review also explores emerging treatments, such as phage therapy and antibiofilm agents, which show promise in managing chronic infections. Nonetheless, further research is necessary to enhance the safety and effectiveness of existing therapies while investigating new approaches for better long-term outcomes. [ABSTRACT FROM AUTHOR]

The spread of carbapenemase-producing gram-negative pathogens, especially those producing metallo-β-lactamases (MBLs), has become a major health concern. MBLs are molecularly the most diverse carbapenemases, produced by a wide spectrum of gram-negative organisms, including the Enterobacterales, Pseudomonas spp., Acinetobacter baumannii, and Stenotrophomonas maltophilia, and can hydrolyze most β-lactams using metal ion cofactors in their active sites. Over the years, the prevalence of MBL-carrying isolates has increased globally, particularly in Asia. MBL infections are associated with adverse clinical outcomes including longer length of hospital stay, ICU admission, and increased mortality across the globe. The optimal treatment for MBL infections not only depends on the pathogen but also on the underlying resistance mechanisms. Currently, there are only few drugs or drug combinations that can efficiently offset MBL-mediated resistance, which makes the treatment of MBL infections challenging. The rising concern of MBLs along with the limited treatment options has led to the need and development of drugs that are specifically targeted towards MBLs. This review discusses the prevalence of MBLs, their clinical impact, and the current treatment options for MBL infections and their limitations. Furthermore, this review will discuss agents currently in the pipeline for treatment of MBL infections. [ABSTRACT FROM AUTHOR]

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We report identification of 5 patients with infections caused by NDM-5-producing Escherichia coli harboring PBP3 mutations that showed reduced susceptibility to aztreonam-avibactam and cefiderocol. Durlobactam, a novel diazabicyclooctane β-lactamase inhibitor, demonstrated minimum inhibitory concentrations ranging from 0.5 to 2 µg/mL supporting future investigations into a potential role in clinical management. [ABSTRACT FROM AUTHOR]

Background: The balance between antioxidants and pro-oxidants plays a significant role in the context of oxidative stress, influenced by both physiological and non-physiological factors. Objectives: In this study, 18 prescribed antibiotics (including doxycycline hydrochloride, tigecycline, rifampicin, tebipenem, cefuroxime, cefixime, potassium clavulanate, colistin, ampicillin, amoxicillin, amikacin, nalidixic acid, azithromycin, pipemidic acid trihydrate, pivmecillinam, aztreonam, fosfomycin sodium, and ciprofloxacin) were subjected to simultaneous determination of antioxidant and pro-oxidant potential to assess if pro-oxidant activity is a dominant co-mechanism of antibacterial activity or if any antibiotic exhibits a balanced effect. Methods: This study presents a recently developed approach for the simultaneous assessment of antioxidant and pro-oxidant potential on a single microplate in situ, applied to prescribed antibiotics. Results: Ten antibiotics from eighteen showed lower antioxidant or pro-oxidant potential, while five exhibited only mild potential with DPPH50 values over 0.5 mM. The pro-oxidant antioxidant balance index (PABI) was also calculated to determine whether antioxidant or pro-oxidant activity was dominant for each antibiotic. Surprisingly, three antibiotics—doxycycline hydrochloride, tigecycline, and rifampicin—showed significant measures of both antioxidant and pro-oxidant activities. Especially notable was tebipenem, a broad-spectrum, orally administered carbapenem, showed a positive PABI index ratio, indicating a dominant antioxidant over pro-oxidant effect. Conclusions: These findings could be significant for both therapy, where the antibacterial effect is enhanced by radical scavenging activity, and biotechnology, where substantial pro-oxidant activity might limit microbial viability in cultures and consequently affect yield. [ABSTRACT FROM AUTHOR]

Objectives We aimed to compare the stability of the newly developed β-lactams (cefiderocol) and β-lactam/β-lactamase inhibitor combinations (ceftazidime/avibactam, ceftolozane/tazobactam, aztreonam/avibactam, cefepime/taniborbactam, cefepime/zidebactam, imipenem/relebactam, meropenem/vaborbactam, meropenem/nacubactam and meropenem/xeruborbactam) against the most clinically relevant mechanisms of mutational and transferable β-lactam resistance in Pseudomonas aeruginosa. Methods We screened a collection of 61 P. aeruginosa PAO1 derivatives. Eighteen isolates displayed the most relevant mechanisms of mutational resistance to β-lactams. The other 43 constructs expressed transferable β-lactamases from genes cloned in pUCP-24. MICs were determined by reference broth microdilution. Results Cefiderocol and imipenem/relebactam exhibited excellent in vitro activity against all of the mutational resistance mechanisms studied. Aztreonam/avibactam, cefepime/taniborbactam, cefepime/zidebactam, meropenem/vaborbactam, meropenem/nacubactam and meropenem/xeruborbactam proved to be more vulnerable to mutational events, especially to overexpression of efflux operons. The agents exhibiting the widest spectrum of activity against transferable β-lactamases were aztreonam/avibactam and cefepime/zidebactam, followed by cefepime/taniborbactam, cefiderocol, meropenem/xeruborbactam and meropenem/nacubactam. However, some MBLs, particularly NDM enzymes, may affect their activity. Combined production of certain enzymes (e.g. NDM-1) with increased MexAB-OprM-mediated efflux and OprD deficiency results in resistance to almost all agents tested, including last options such as aztreonam/avibactam and cefiderocol. Conclusions Cefiderocol and new β-lactam/β-lactamase inhibitor combinations show promising and complementary in vitro activity against mutational and transferable P. aeruginosa β-lactam resistance. However, the combined effects of efflux pumps, OprD deficiency and efficient β-lactamases could still result in the loss of all therapeutic options. Resistance surveillance, judicious use of new agents and continued drug development efforts are encouraged. [ABSTRACT FROM AUTHOR]

Carbapenem-resistance in Enterobacter spp due to acquisition of mobile carbapenemases is of concern. An Enterobacter spp grew on ChromID CARBA medium and was positive for the mCIM carbapenemase detection assay. Susceptibility testing showed resistance to aztreonam and reduced susceptibility to imipenem. Conventional PCR using FRI primers detected a blaFRI gene. Whole genome sequencing reveled a new variant; blaFRI−12 was closest in sequence to blaFRI−5 differing by 13 amino acids and was found on a unique 110Kb IncR plasmid. Given the intrinsic nature of Enterobacter spp. to be carbapenem non-susceptible, blaFRI-types may be under reported globally. [ABSTRACT FROM AUTHOR]

A common indicator used to examine the frequency and distribution of antibiotic resistance against other enteric bacteria in humans and animals is the commensal enteric bacterium, Escherichia coli. The transmission of plasmids harboring ESBL enzymes, primarily generated by E. coli, is the cause of this resistance. The purpose of this study was to identify the CTX-M gene in ESBL-producing E. coli from broiler chicken cloacal swabs in traditional Surabaya markets. The samples used were 96 cloacal swabs from broiler chickens in the traditional markets of Dukuh Kupang, Keputran, Pacar Keling, and Pucang. The antibiotic disks used in this study belonged to five different antibiotic classes; they are aztreonam (monobactam), chloramphenicol (phenicol), kanamycin (aminoglycoside), ciprofloxacin (fluoroquinolone), and tetracycline (tetracycline). Presumptive ESBL strains were then molecularly screened for the presence of CTX-M gene. Results revealed that out of the 96 chicken cloacal swab samples collected, 58 (60.42%) were positive for E. coli based on morphological culture, Gram staining, and biochemical tests. Additionally, 15 out of the 58 E. coli isolates recovered from broiler chicken cloacal swabs were multidrug-resistant (MDR) while 7 of E. coli isolates harbored CTX-M gene. Conclusively, this study has shown that broiler chickens sold in traditional Surabaya markets harbor MDR E. coli which possess CTX-M gene. Conditions in traditional markets with low levels of cleanliness and chickens placed close together can spread resistance genes with serious public health consequences. Therefore, it is imperative to observe good hygienic practices in Surabaya traditional markets in order to curtail the spread of MDR bacterial pathogens in the food chain. [ABSTRACT FROM AUTHOR]

Introduction: Intra-abdominal infections are becoming increasingly common and can lead to significant morbidity and mortality. The incidence of these infections due to resistant gram-negative organisms is also increasing. Given this resistance, new antibiotic combinations are being developed, often utilizing older antibiotics and newer β-lactamase inhibitors. Aztreonam/avibactam (ATM-AVI) is one of the combination antibiotics, which combines aztreonam, a monobactam, with avibactam, a broad-spectrum β-lactamase inhibitor for the treatment of complicated intra-abdominal infections in combination with metronidazole. Areas covered: In this drug evaluation manuscript, we provide an overview of intra-abdominal infections and an overview of currently available antimicrobial agents used to treat these infections. ATM-AVI is introduced, including chemistry, pharmacodynamics, pharmacokinetics and clinical studies of this compound. Expert opinion: There are limited treatment options for complicated intra-abdominal infections due to resistant gram-negative organisms, especially those with metallo-β-lactamases. One treatment option for these infections is ATM-AVI, which was recently approved in Europe, in addition to metronidazole. These bacteria are difficult to treat, and this new compound is a safe and effective option for empiric treatment in places with a high incidence of infections due to these bacteria, and also treatment for infections when these resistant bacteria are isolated in culture. [ABSTRACT FROM AUTHOR]

The emission of glyphosate and antibiotic residues from human activities threatens the diversity and functioning of the microbial community. This study examines the impact of a glyphosate-based herbicide (GBH) and common antibiotics on Gram-negative bacteria within the ESKAPEE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp. and Escherichia coli). Ten strains, including type and multidrug-resistant strains for each species were analysed and eight antibiotics (cefotaxime, meropenem, aztreonam, ciprofloxacin, gentamicin, tigecycline, sulfamethoxazole-trimethoprim, and colistin) were combined with the GBH. While most combinations yielded additive or indifferent effects in 70 associations, antagonistic effects were observed with ciprofloxacin and gentamicin in five strains. GBH notably decreased the minimum inhibitory concentration of colistin in eight strains and displayed synergistic activity with meropenem against metallo-β-lactamase (MBL)-producing strains. Investigation into the effect of GBH properties on outer membrane permeability involved exposing strains to a combination of this GBH and vancomycin. Results indicated that GBH rendered strains sensitive to vancomycin, which is typically ineffective against Gram-negative bacteria. Furthermore, we examined the impact of GBH in combination with three carbapenem agents on 14 strains exhibiting varying carbapenem-resistance mechanisms to assess its effect on carbapenemase activity. The GBH efficiently inhibited MBL activity, demonstrating similar effects to EDTA (ethylenediaminetetraacetic acid). Chelating effect of GBH may have multifaceted impacts on bacterial cells, potentially by increasing outer membrane permeability and inactivating metalloenzyme activity. [ABSTRACT FROM AUTHOR]

The significance of Pantoea agglomerans bacteria in diseases linked to healthcare is underappreciated due to a shortage of information on their spread. This is the first study in Saudi Arabia to examine the possible contribution of medical students' cell phones (CPs) to the transmission of P. agglomerans to hospitalized patients and to evaluate their antibiotic susceptibility profiles. In total, 250 CPs were swabbed. P. agglomerans was isolated and identified using standard techniques. The suspected colonies were confirmed by the Vitek 2 compact system. The isolates' antimicrobial susceptibility profiles were assessed using Epsilon assays, and the results were interpreted according to Clinical and Laboratory Standards Institute guidelines. The frequency of P. agglomerans contamination of CPs was found to be relatively high (20.40%; 51 isolates/250 samples). Many isolates showed varying degrees of reduced sensitivity to ampicillin, aztreonam, cefazolin, cefotaxime, cefuroxime, and ertapenem antibiotics. To implement optimal infection prevention and control policies regarding the possibility of antibiotic-resistant P. agglomerans transmission through medical students' contact points with hospitalized patients during their frequent activities in healthcare settings, health policymakers may find value in utilizing this study's results. [ABSTRACT FROM AUTHOR]

Carbapenemase-producing Enterobacterales (CPE) are a serious concern in human clinical settings. Companion animal–origin CPE have been only rarely identified in several countries, but they have not yet been identified in Japan. In this study, we present the first case of a canine infected with CPE in Japan. The patient was hospitalized due to pyometra. The pus discharged from the patient's uterus was subjected to bacteriological analysis. As a result, E. coli was identified in the pus and exhibited resistance to piperacillin, amoxicillin–clavulanic acid, cefazolin, ceftazidime, cefepime, meropenem, amikacin, and sulfamethoxazole–trimethoprim and susceptibility to aztreonam, minocycline, and levofloxacin. Results of the sodium mercaptoacetic acid double-disk synergy test showed that the E. coli isolate was positive for metallo-β-lactamases. Next-generation sequencing identified the bla NDM-5 gene, which was located in the IncFII-type plasmid together with bla TEM-1b , rmtB , aadA2 , ble MBL, sul1 , qacE , and dfrA12. The case was treated successfully with doxycycline and orbifloxacin. Our finding emphasizes that close attention should be paid to the significance of CPE harboring multidrug-resistance plasmid in companion animals, based on the perspective of One Health approach in Japan as well as in other countries. [ABSTRACT FROM AUTHOR]

Our aim was to elucidate the resistance mechanisms and assess the combined synergistic and bactericidal activities of aztreonam in combination with ceftazidime/avibactam (CZA), meropenem/vaborbactam (MEV), and imipenem/relebactam (IMR) against Enterobacterales strains producing dual carbapenemases. Methods: Species identification, antimicrobial susceptibility testing and determination of carbapenemase type were performed for these strains. Plasmid sizes, plasmid conjugation abilities and the localization of carbapenemase genes were investigated. Whole-genome sequencing was performed for all strains and their molecular characteristics were analyzed. In vitro synergistic and bactericidal activities of the combination of aztreonam with CZA, MEV and IMR against these strains were determined using checkerboard assay and time-kill curve assay. Results: A total of 12 Enterobacterales strains producing dual-carbapenemases were collected, including nine K. pneumoniae, two P. rettgeri, and one E. hormaechei. The most common dual-carbapenemase gene pattern observed was bla(KPC-2+NDM-5) (n=4), followed by blaKPC-2+IMP-26 (n=3), bla(KPC-2+NDM-1) (n=2), bla(KPC-2+IMP-4) (n=1), bla(NDM-1+IMP-4) (n=1) and bla(KPC-2+KPC-2) (n=1). In each strain, the carbapenemase genes were found to be located on two distinct plasmids which were capable of conjugating from the original strain to the receipt strain E. coli J53. The results of the checkerboard synergy analysis consistently revealed good synergistic effects of the combination of ATM with CZA, MEV and IMR. Except for one strain, all strains exhibited significant synergistic activity and bactericidal activity between 2 and 8 hours. Conclusion: Dual-carbapenemase-producing Enterobacterales posed a significant threat to clinical anti-infection treatment. However, the combination of ATM with innovative β-lactam/β-lactamase inhibitor compounds had proven to be an effective treatment option. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate literature from a 12-year period (2010–2021) on the antimicrobial resistance profile of Pseudomonas aeruginosa from the Arabian Gulf countries (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates). Methods: An electronic literature search was conducted for articles on antimicrobial resistance in P. aeruginosa and associated phenotypes, covering the period of 1st January 2010 to 1st December 2021. Results: Antimicrobial resistance in the Arabian Gulf was highest to meropenem (10.3–45.7%) and lowest to colistin (0.0–0.8%), among the agents tested. Annual data showed that ceftazidime resistance (Kuwait), piperacillin-tazobactam non-susceptibility (Qatar), and aztreonam, imipenem, and meropenem resistance (Saudi Arabia) increased by 12–17%. Multiple mechanisms of carbapenem resistance were identified and multiple clones were detected, including high-risk clones such as ST235. The most common carbapenemases detected were the VIM-type metallo-β-lactamases. Conclusions: Among P. aeruginosa in the Arabian Gulf countries, resistance to meropenem was higher than to the other agents tested, and meropenem resistance increased in Saudi Arabia during the study period. Resistance to colistin, a classic antibiotic used to treat Pseudomonas spp. infections, remained low. The VIM-type β-lactamase genes were dominant. We recommend local and regional antimicrobial resistance surveillance programs to detect the emergence of resistance genes and to monitor antimicrobial resistance trends in P. aeruginosa. [ABSTRACT FROM AUTHOR]

Abstract The spread of carbapenemase-producing gram-negative pathogens, especially those producing metallo-β-lactamases (MBLs), has become a major health concern. MBLs are molecularly the most diverse carbapenemases, produced by a wide spectrum of gram-negative organisms, including the Enterobacterales, Pseudomonas spp., Acinetobacter baumannii, and Stenotrophomonas maltophilia, and can hydrolyze most β-lactams using metal ion cofactors in their active sites. Over the years, the prevalence of MBL-carrying isolates has increased globally, particularly in Asia. MBL infections are associated with adverse clinical outcomes including longer length of hospital stay, ICU admission, and increased mortality across the globe. The optimal treatment for MBL infections not only depends on the pathogen but also on the underlying resistance mechanisms. Currently, there are only few drugs or drug combinations that can efficiently offset MBL-mediated resistance, which makes the treatment of MBL infections challenging. The rising concern of MBLs along with the limited treatment options has led to the need and development of drugs that are specifically targeted towards MBLs. This review discusses the prevalence of MBLs, their clinical impact, and the current treatment options for MBL infections and their limitations. Furthermore, this review will discuss agents currently in the pipeline for treatment of MBL infections.

Background: Worldwide, the emergence of carbapenem-resistant enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a global concern to public health as they are responsible for several serious infections that lead to elevated treatment expenses, prolonged hospitalization, and a higher mortality rate. Aims and Objectives: To detect Carbapenem resistance in Enterobacterales and Pseudomonas aeruginosa by phenotypic methods such as mCIM and eCIM. To determine synergism between Ceftazidime-Avibactum and Aztreonum in metallobetalactamase producing isolates. Materials and Methods: Total 217 isolates including enterobacterales and Pseudomonas aeruginosa from patient’s samples such as urine, pus, blood, wound swab, sputum, and ET tube were processed as per standard protocol during the study period from July 2023 to January 2024 at Calcutta National Medical College, Kolkata. Results: Resistance to carbapenem was observed in 110/217 (50.69%) isolates. Phenotypically, 99/110 (90%) produced metallo-β-lactamase and 11/110 (10%) produced serine carbapenemase by mCIM with eCIM test. MBLs producing organisms were most commonly isolated from blood culture samples. On an average, 76% of the MBL producing isolates shows positive synergy result to the combination of CZA+AT by disk elution method. Conclusion: eCIM and mCIM test was performed for identification of carbapenemase producing CRE and CRPA, which causes serious infection in patients with no definitive treatment. The combination of CZA-AT is a potential treatment option to manage CRE and CRPA-associated infections.

Background. The minimum inhibitory concentration (MIC) does not predict the risk of antibacterial resistance development due to a small sample of tested bacteria. Minimum inhibitory concentration at an increased inoculum (MICHI) may become a suitable parameter for this purpose as a sample of tested bacteria is larger while the method of determination remains easy.The aim of the study was to evaluate the potential of using MICHI as a parameter for predicting the resistance development in Klebsiella pneumoniae to aztreonam.Methods. Aztreonam MIC and MICHI values were assessed against two strains of K. pneumoniae using the microdilution method (0.2 ml volume; inoculum of 5×105 and 5×107 CFU/ml, respectively) and compared the results with the effect of aztreonam in a dynamic in vitro model, in which aztreonam regimen of 2 grams every 8 hours as a 2-hour infusion for 5 days was simulated.Results. The efficacy of aztreonam against K. pneumoniae observed in the dynamic model was consistent with the MICHIs values assessed based on bacterial viability. During the visual assessment, the MICHIs values were greatly overestimated due to excessive turbidity caused by the formation of filamentous forms of bacteria exposed to aztreonam.Conclusions. The MICHI parameter can be used to predict the development of resistance in K. pneumoniae to aztreonam when assessing the values of this parameter by the number of viable cells, but not by the visual boundary of bacterial growth.

Mateusz Szymański,1,2 Małgorzata M Skiba,2 Małgorzata Piasecka,2 Alina Olender3 1Human Anatomy Department, Medical University, Lublin, Poland; 2Intensive Care Unit, Stefan Cardinal Wyszyński District Specialist Hospital, Lublin, Poland; 3Chair and Department of Medical Microbiology, Medical University, Lublin, PolandCorrespondence: Małgorzata M Skiba, Intensive Care Unit, Stefan Cardinal Wyszyński District Specialist Hospital, Al. Kraśnicka 100, Lublin, 20-718, Poland, Tel +48 81 537 46 60, Email skibamalgorzata@op.plBackground: The difficulties in attaining effective antibiotic therapy arising from the multidrug resistance of Gram-negative bacilli compel the exploration of new possibilities for synergistic interactions among existing antibiotics.Research Design and Methods: An analysis was conducted to assess the efficacy of two antibiotic therapy regimens in the treatment of infections caused by Klebsiella pneumoniae strains producing carbapenemases (MBL). Two patient groups were considered: Group A – individuals in whom the treatment of infection involved the application of ceftazidime-avibactam in combination with aztreonam. Group B comprised patients subjected to an alternative antibiotic therapy regimen.Results: In the group subjected to the treatment regimen involving ceftazidime-avibactam and aztreonam, as compared to alternative antibiotic combinations, a statistically lower mortality rate during the course of treatment and a faster clinical response to the administered therapy were evident.Conclusion: The results obtained may be applicable to routine in vitro assays performed and serve as valuable guidance for the potential utilization of the positive effect of antibiotic therapy through the synergy between ceftazidime-avibactam and aztreonam. The selection of antibiotics employed in the therapy of invasive infections caused by K. pneumoniae influences the ultimate treatment outcome.Keywords: synergism, ceftazidime-avibactam, aztreonam, multidrug-resistant K. pneumoniae, metal-beta-lactamases

AbstractBackgroundMethodsResultsConclusionCombination therapy is an attractive therapeutic option for extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. Existing data support the combination of aztreonam and ceftazidime/avibactam (CZA) against class serine-β-lactamase (SBL)- and metallo-β-lactamase (MBL) - producing Enterobacterales. However, data about that combination against SBL- and MBL-producing P. aeruginosa are scarce. The objective of the study was to assess the in vitro activity of CZA and aztreonam alone and in combination against SBL- and MBL-producing XDR P. aeruginosa isolatesThe combination was analyzed by means of the hollow-fiber infection model in three selected carbapenemase-producing P. aeruginosa isolates that were representative of the three most common XDRP. aeruginosa high-risk clones (ST175, ST111, ST235) responsible for global nosocomial infection outbreaks.The three isolates were nonsusceptible to CZA and nonsusceptible to aztreonam. In the dynamic hollow-fiber infection model, the combination of CZA plus aztreonam exerts a bactericidal effect on the isolates, regardless of their resistance mechanism and demonstrates synergistic interactions against three isolates, achieving a bacterial reduction of 5.07 log10 CFU/ml, 5.2 log10 CFU/ml and 4 log10 CFU/ml, respectively.The combination of CZA and aztreonam significantly enhanced the in vitro efficacy against XDR P. aeruginosa isolates compared to each monotherapy. This improvement suggests that the combination could serve as a feasible treatment alternative for infections caused by carbapenemase-producing XDR P. aeruginosa, especially in scenarios where no other treatment options are available. [ABSTRACT FROM AUTHOR]

Whole-genome sequencing (WGS) is revolutionizing clinical bacteriology. However, bacterial typing remains investigated by reference techniques with inherent limitations. This stresses the need for alternative methods providing robust and accurate sequence type (ST) classification. This study optimized and evaluated a GridION nanopore sequencing protocol, adapted for the PromethION platform. Forty-eight Escherichia coli clinical isolates with diverse STs were sequenced to assess two alternative typing methods and resistance profiling applications. Multi-locus sequence typing (MLST) was used as the reference typing method. Genomic relatedness was assessed using Average Nucleotide Identity (ANI) and digital DNA-DNA Hybridization (DDH), and cut-offs for discriminative strain resolution were evaluated. WGS-based antibiotic resistance prediction was compared to reference Minimum Inhibitory Concentration (MIC) assays. We found ANI and DDH cut-offs of 99.3% and 94.1%, respectively, which correlated well with MLST classifications and demonstrated potentially higher discriminative resolution than MLST. WGS-based antibiotic resistance prediction showed categorical agreements of ≥ 93% with MIC assays for amoxicillin, ceftazidime, amikacin, tobramycin, and trimethoprim-sulfamethoxazole. Performance was suboptimal (68.8–81.3%) for amoxicillin-clavulanic acid, cefepime, aztreonam, and ciprofloxacin. A minimal sequencing coverage of 12× was required to maintain essential genomic features and typing accuracy. Our protocol allows the integration of PromethION technology in clinical laboratories, with ANI and DDH proving to be accurate and robust alternative typing methods, potentially offering superior resolution. WGS-based antibiotic resistance prediction holds promise for specific antibiotic classes. [ABSTRACT FROM AUTHOR]

Background: Worldwide, the emergence of carbapenem-resistant enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a global concern to public health as they are responsible for several serious infections that lead to elevated treatment expenses, prolonged hospitalization, and a higher mortality rate. Aims and Objectives: To detect Carbapenem resistance in Enterobacterales and Pseudomonas aeruginosa by phenotypic methods such as mCIM and eCIM. To determine synergism between Ceftazidime-Avibactum and Aztreonum in metallobetalactamase producing isolates. Materials and Methods: Total 217 isolates including enterobacterales and Pseudomonas aeruginosa from patient's samples such as urine, pus, blood, wound swab, sputum, and ET tube were processed as per standard protocol during the study period from July 2023 to January 2024 at Calcutta National Medical College, Kolkata. Results: Resistance to carbapenem was observed in 110/217 (50.69%) isolates. Phenotypically, 99/110 (90%) produced metallo-β-lactamase and 11/110 (10%) produced serine carbapenemase by mCIM with eCIM test. MBLs producing organisms were most commonly isolated from blood culture samples. On an average, 76% of the MBL producing isolates shows positive synergy result to the combination of CZA+AT by disk elution method. Conclusion: eCIM and mCIM test was performed for identification of carbapenemase producing CRE and CRPA, which causes serious infection in patients with no definitive treatment. The combination of CZA-AT is a potential treatment option to manage CRE and CRPA-associated infections. [ABSTRACT FROM AUTHOR]

Purpose: Amongst all etiologic hospital-acquired infection factors, K. pneumoniae strains producing New Delhi metallo-β-lactamase (KP-NDM) belong to pathogens with the most effective antibiotic resistance mechanisms. Clinical guidelines recommend using ceftazidime/avibactam with aztreonam (CZA + AT) as the preferred option for NDM-producing Enterobacterales. However, the number of observations on such treatment regimen is limited. This retrospective study reports the clinical and microbiological outcomes of 23 patients with KP-NDM hospital-acquired infection treated with CZA + AT at a single center in Poland. Methods: The isolates were derived from the urine, lungs, blood, peritoneal cavity, wounds, and peritonsillar abscess. In microbiological analysis, mass spectrometry for pathogen identification, polymerase chain reaction, or an immunochromatographic assay for detection of carbapenemase, as well as VITEK-2 system, broth microdilution, and microdilution in agar method for antimicrobial susceptibility tests were used, depending of the pathogens' nature. CZA was administered intravenously (IV) at 2.5 g every eight hours in patients with normal kidney function, and aztreonam was administered at 2 g every eight hours IV. Such dosage was modified when renal function was reduced. Results: KP-NDM was eradicated in all cases. Four patients (17.4%) died: three of them had a neoplastic disease, and one - a COVID-19 infection. Conclusion: The combination of CZA + AT is a safe and effective therapy for infections caused by KP-NDM, both at the clinical and microbiological levels. The synergistic action of all compounds resulted in a good agreement between the clinical efficacy of CZA + AT and the results of in vitro susceptibility testing. [ABSTRACT FROM AUTHOR]

Carbapenem-resistant Enterobacteriaceae infections are a considerable challenge for clinicians. In recent years, novel antibiotic options have resulted in a tremendous advance in medical therapy; however, current treatment options are primarily effective for resistance derived from serine-based carbapenemases. The Ambler class B metallo-β-lactamases (MBLs) remain a critical challenge with decidedly fewer effective options. One intriguing option for these MBL pathogens is the combination of ceftazidime-avibactam with aztreonam. While clinical experience with this regimen is limited, in vitro studies are promising, and limited case reports describe success with this regimen; however, significant challenges preclude widespread adoption of this novel treatment regimen. A systemic literature review was performed to offer recommendations based on current evidence for a practical strategy on how to best integrate the use of aztreonam with avibactam combination therapy. [ABSTRACT FROM AUTHOR]

Background and Aim: Recently, the rise in various carbapenemases in Enterobacteriaceae poses a significant challenge to the healthcare systems and limits the treatment options. This study aimed to evaluate different assays such as disc diffusion, VITEK, and Rapidec® Carba NP test for the carbapenemase detection, and investigate the synergistic effects of ceftazidimeavibactam (CAZ/AVI) and aztreonam (AZM) combination therapy using the E-strip method. Materials and Methods: This prospective study was conducted on the samples collected from January 2023 to February 2024 at the Department of Microbiology, Central Laboratory Sree Balaji, Medical College and Hospital Chennai, India. The isolates were cultured and identified using the standard biochemical methods followed by the antibiotic susceptibility testing (AST) both by Kirby Bauer disc diffusion (DD) and the VITEK®2 system. The Rapidec® Carba NP test was performed in detecting carbapenemase. The efficacy and potential synergistic effects of the combination treatment comprising CAZ/AVI and AZM were performed using the E-strip gradient stacking method. Results and Conclusion: According on the AST, the highest resistance rates were detected for ampicillin (78%), then, followed by amoxicillin/clavulanic acid (52%), meropenem (56%), imipenem (56%), cefazolin (56%), and ciprofloxacin (53%). The lowest resistance rates were found for gentamicin (23%), cotrimoxazole (27%), piperacillin/tazobactam (27%), and tobramycin (33%). Rapidec® Carba NP test detected 65 bacterial isolates stored in the laboratory, resulting in a sensitivity of 97% for carbapenemase detection. For carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates, synergy was observed between CAZ/AVI E-strip and AZM E-strip in 66 out of 67 isolates (98.75%). The Rapidec® Carba NP test remains a valuable tool for the initial screening, providing timely information for the clinicians. The high rate of synergy observed in our study suggests that CAZ/AVI and AZM will provide a promising treatment option for the CRKP infections, particularly in the settings with limited therapeutic alternatives. [ABSTRACT FROM AUTHOR]

Purpose: Enterobacteriaceae carrying mcr-9, in particularly those also co-containing metallo-β-lactamase (MBL) and TEM type β-lactamase, present potential transmission risks and lack adequate clinical response methods, thereby posing a major threat to global public health. The aim of this study was to assess the antimicrobial efficacy of a combined ceftazidime/avibactam (CZA) and aztreonam (ATM) regimen against carbapenem-resistant Enterobacter cloacae complex (CRECC) co-producing mcr-9, MBL and TEM. Methods: The in vitro antibacterial activity of CZA plus ATM was evaluated using a time-kill curve assay. Furthermore, the in vivo interaction between CZA plus ATM was confirmed using a Galleria mellonella (G. mellonella) infection model. Results: All eight clinical strains of CRECC, co-carrying mcr-9, MBL and TEM, exhibited high resistance to CZA and ATM. In vitro time-kill curve analysis demonstrated that the combination therapy of CZA + ATM exerted significant bactericidal activity against mcr-9, MBL and TEM-co-producing Enterobacter cloacae complex (ECC) isolates with a 100% synergy rate observed in our study. Furthermore, in vivo survival assay using Galleria mellonella larvae infected with CRECC strains co-harboring mcr-9, MBL and TEM revealed that the CZA + ATM combination significantly improved the survival rate compared to the drug-treatment alone and untreated control groups. Conclusion: To our knowledge, this study represents the first report on the in vitro and in vivo antibacterial activity of CZA plus ATM against CRECC isolates co-harboring mcr-9, MBL and TEM. Our findings suggest that the combination regimen of CZA + ATM provides a valuable reference for clinicians to address the increasingly complex antibiotic resistance situation observed in clinical microorganisms. [ABSTRACT FROM AUTHOR]

Purpose: Aztreonam/avibactam is effective against serious infections caused by Gram-negative bacteria including Enterobacterales harboring metallo-β-lactamases. While the utility of this combination has been established in vitro and in clinical trials, the purpose of this study is to enhance our understanding of the underlying mechanism responsible for their activities through metabolomic profiling of a multidrug-resistant Escherichia coli clinical isolate. Methods: Metabolomic analyses of time-dependent changes in endogenous bacterial metabolites in a clinical isolate of a multidrug-resistant E. coli treated with aztreonam and avibactam were performed. E. coli metabolomes were compared at 15 min, 1 h and 24 h following treatments with either avibactam (4 mg/L), aztreonam (4 mg/L), or aztreonam (4 mg/L) + avibactam (4 mg/L). Results: Drug treatment affected 326 metabolites with magnitude changes of at least 2-fold, most of which are involved primarily in peptidoglycan biosynthesis, nucleotide metabolism, and lipid metabolism. The feedstocks for peptidoglycan synthesis were depleted by aztreonam/avibactam combination; a significant downstream increase in nucleotide metabolites and a release of lipids were observed at the three timepoints. Conclusion: The findings indicate that the aztreonam/avibactam combination accelerates structural damage to the bacterial membrane structure and their actions were immediate and sustained compared to aztreonam or avibactam alone. By inhibiting the production of crucial cell wall precursors, the combination may have inflicted damages on bacterial DNA. [ABSTRACT FROM AUTHOR]

Limited experience exists with ceftazidime-avibactam (CAZ-AVI) in treating bacteremia caused by carbapenem-resistant Enterobacterales (CRE) and Pseudomonas aeruginosa (CRPA) in hematological patients. We performed a single-center, retrospective, observational study including patients who received CAZ-AVI for bacteremia due to CRE or CRPA between 2018 and 2022. The primary outcome was 30-day survival. We conducted a multivariable analysis to identify predictors of survival. 56 patients were included and 57 (41 CRE and 16 CRPA) strains were isolated. 35 strains produced carbapenemase, including 25 metallo-beta-lactamase (MBL) and 10 serine-beta-lactamase. 48 patients (85.7 %) received combination therapy. All patients with MBL-CRE bacteremia (n = 24) received combination therapy with aztreonam (AZT). The susceptibility rates to CAZ-AVI were only 26.8 % (11/41) in CRE and 80.0 % (8/10) in CRPA. The 30-day survival rates were 85.0 % (34/40) in the CRE group and 81.3 % (13/16) in the CRPA group. In patients with MBL-CRE bacteremia, the 30-day survival was as high as 91.7 % (22/24) due to combination with AZT. Ceftazidime did not influence the activity of aztreonam-avibactam against MBL-CRE in-vitro. Multivariable cox analysis revealed neutropenia >14 days (P = 0.002, HR: 34.483, 95%CI: 3.846–333.333) and a higher Pitt bacteremia score (P = 0.005, HR: 2.074, 95%CI: 1.253–3.436) were risk factors for 30-day survival. CAZ-AVI is highly effective in treating bacteremia due to CRPA and serine-beta-lactamase CRE. The combination of avibactam with AZT is highly effective in treating bacteremia due to AZT-resistant MBL producers. [ABSTRACT FROM AUTHOR]

Current antimicrobial susceptibility testing (AST) requires 16–24 hours, delaying initiation of appropriate antibiotics. Hence, there is a need for rapid AST. This study aims to develop and evaluate the feasibility of a rapid flow cytometric AST assay to determine minimum inhibitory concentration (MIC) for carbapenem-resistant Acinetobacter baumannii (CRAB). Antibiotic exposure causes increased intracellular reactive oxygen species (ROS) in bacteria. We hypothesized that ROS can be used as a marker to determine MIC. We assessed three CRAB clinical isolates across fifteen antibiotics at various concentrations in a customized 96-well microtiter plate. The antibiotics assessed include amikacin, beta-lactams (ampicillin/sulbactam, aztreonam, cefepime, ceftolozane/tazobactam, doripenem, imipenem, meropenem, and piperacillin/tazobactam), levofloxacin, polymyxin B, rifampicin, trimethoprim/sulfamethoxazole, and tetracyclines (tigecycline and minocycline). These clinical CRAB isolates were assessed for ROS after antibiotic treatment. Increased ROS levels indicated by increased RedoxSensorTM Green (RSG) fluorescence intensity was assessed using flow cytometry (FCM). MIC was set as the lowest antibiotic concentration that gives a ≥1.5-fold increase in mode RSG fluorescence intensity (MICRSG). Accuracy of MICRSG was determined by comparing against microtiter broth dilution method performed under CLSI guidelines. ROS was deemed accurate in determining the MICs for β-lactams (83.3% accuracy) and trimethoprim/sulfamethoxazole (100% accuracy). In contrast, ROS is less accurate in determining MICs for levofloxacin (33.3% accuracy), rifampicin (0% accuracy), amikacin (33.3% accuracy), and tetracyclines (33.3% accuracy). Collectively, this study described an FCM-AST assay to determine antibiotic susceptibility of CRAB isolates within 5 hours, reducing turnaround time up to 19 hours. [ABSTRACT FROM AUTHOR]

We report a fatal case of New Delhi metallo-β-lactamase (NDM)–producing Escherichia coli in a bacteremic patient with sequential failure of aztreonam plus ceftazidime-avibactam followed by cefiderocol. Acquired resistance was documented phenotypically and mediated through preexisting and acquired mutations. This case highlights the need to rethink optimal treatment for NDM-producing organisms. [ABSTRACT FROM AUTHOR]

The article discusses the growing threat of multidrug-resistant Gram-negative infections. Topics discussed include the rapid evolution of bacterial resistance mechanisms, the pharmaceutical industry's challenges in developing effective antibiotics, and a poignant case study of fatal antibiotic-resistant E. coli in a child.

Background Riemerella anatipestifer encodes an iron acquisition system, but whether it encodes the iron efflux pump and its role in antibiotic resistance are largely unknown. Objectives To screen and identify an iron efflux gene in R. anatipestifer and determine whether and how the iron efflux gene is involved in antibiotic resistance. Methods In this study, gene knockout, streptonigrin susceptibility assay and inductively coupled plasma mass spectrometry were used to screen for the iron efflux gene ietA. The MIC measurements, scanning electron microscopy and reactive oxygen species (ROS) detection were used to verify the role of IetA in aztreonam resistance and its mechanism. Mortality and colonization assay were used to investigate the role of IetA in virulence. Results The deletion mutant Δ ietA showed heightened susceptibility to streptonigrin, and prominent intracellular iron accumulation was observed in Δ fur Δ ietA under excess iron conditions. Additionally, Δ ietA exhibited increased sensitivity to H2O2-produced oxidative stress. Under aerobic conditions with abundant iron, Δ ietA displayed increased susceptibility to the β-lactam antibiotic aztreonam due to heightened ROS production. However, the killing efficacy of aztreonam was diminished in both WT and Δ ietA under anaerobic or iron restriction conditions. Further experiments demonstrated that the efficiency of aztreonam against Δ ietA was dependent on respiratory complexes Ⅰ and Ⅱ. Finally, in a duckling model, Δ ietA had reduced virulence compared with the WT. Conclusion Iron efflux is critical to alleviate oxidative stress damage and β-lactam aztreonam killing in R. anatipestifer , which is linked by cellular respiration. [ABSTRACT FROM AUTHOR]

Objectives To evaluate the performance of an in-house developed disk diffusion method for aztreonam in combination with avibactam against Enterobacteriales. Methods The in vitro antibacterial activity of aztreonam with avibactam against 204 carbapenemase-producing Enterobacteriales was determined by a disk diffusion method, with a broth microdilution method as a reference. Results The optimal S/R breakpoints for disk diffusion tests of 30/20 and 10/4 µg disks, calculated by the dBETs software using the model-based approaches, were ≥22/≤21 and ≥12/≤11 mm, respectively. On the basis of the estimated breakpoints, the CAs for disk diffusion tests of 30/20 and 10/4 µg aztreonam/avibactam disks were both 98.0%, with 0.5% major error and 37.5% very major error. Conclusions The home-made disk diffusion method is an economical and practical method for clinical microbiology laboratories to determine the antibacterial susceptibility of aztreonam with avibactam against Enterobacteriales. [ABSTRACT FROM AUTHOR]

Klebsiella pneumoniae is considered as the most common pathogen of hospital-acquired pneumonia. K. pneumoniae has emerged as the superbug which had shown multidrug resistance (MDR) as well as extensively drug resistance. Carbapenem resistant K. pneumoniae (CRKP) has become a menace for the treatment with monotherapy of the patients mainly admitted in intensive care units. Hence, in the present study we collected total 187 sputum isolates of K. pneumoniae and performed the antimicrobial susceptibility testing by using the automated Vitek-2 system and broth micro-dilution method (67 CRKP). The combination study of solithromycin with meropenem, colistin, cefotaxime, piperacillin and tazobactam, nitrofurantoin, tetracycline, levofloxacin, curcumin and nalidixic acid was performed by using checkerboard assay. We observed the high rate of resistance towards ampicillin, cefotaxime, ceftriaxone, cefuroxime and aztreonam. The colistin and tigecycline were the most sensitive drugs. The CRKP were 36%, maximum were from the patients of ICUs. The best synergistic effect of solithromycin was with meropenem and cefotaxime (100%), colistin and tetracycline (80%). So, these combinations can be a choice of treatment for the infections caused by MDR CRKP and other Gram-negative bacteria where the monotherapy could not work. [ABSTRACT FROM AUTHOR]

With the increasing burden of carbapenem-resistant Klebsiella pneumoniae (CR-Kp), including high rates of healthcare-associated infections, treatment failure, and mortality, a good therapeutic strategy for attacking this multi-resistant pathogen is one of the main goals in current medical practice and necessitates the use of novel antibiotics or new drug combinations. Objectives: We reviewed the clinical and microbiological outcomes of seven patients treated at the "Agrippa Ionescu" Clinical Emergency Hospital between October 2023 and January 2024, aiming to demonstrate the synergistic activity of the ceftazidime–avibactam (C/A) plus aztreonam (ATM) combination against the co-producers of blaNDM + blaOXA-48-like CR-Kp. Material and Methods: Seven CR-Kp with blaNDM and blaOXA-48 as resistance mechanisms were tested. Seven patients treated with C/A + ATM were included. The synergistic activity of C/A + ATM was proven through double-disk diffusion in all seven isolates. Resistance mechanisms like KPC, VIM, OXA-48, NDM, IMP, and CTX-M were assessed through immunochromatography. Results: With a mean of nine days of treatment with the synergistic combination C/A + ATM, all patients achieved clinical recovery, and five achieved microbiological recovery. Conclusions: With the emerging co-occurrence of blaOXA-48 and blaNDM among Kp in Romania, the combination of C/A and ATM could be a promising therapeutic option. [ABSTRACT FROM AUTHOR]

We evaluated the activities of aztreonam/avibactam and recently approved β-lactamase inhibitor combinations (BLICs) to compare the antimicrobial susceptibility patterns of Enterobacterales and Pseudomonas aeruginosa isolated from intensive care unit (ICU) and non-ICU patients. Clinical isolates (1/patient) were consecutively collected from 72 United States medical centres in 2020–2022 and susceptibility tested by broth microdilution. The results for 5421 isolates from ICU patients were analysed and compared to those for 20,649 isolates from non-ICU patients. Isolates from ventilator-associated pneumonia patients were analysed separately. Aztreonam/avibactam inhibited 100.0%/>99.9% Enterobacterales and 100.0%/98.3% of carbapenem-resistant Enterobacterales (CRE) from ICU/non-ICU patients at ≤8 mg/L, respectively. The CRE susceptibility rates were 88.5%/82.9% for ceftazidime/avibactam, 82.1%/81.2% for meropenem/vaborbactam, and 78.2%/72.6% for imipenem/relebactam among ICU/non-ICU isolates. Among the P. aeruginosa isolates from ICU/non-ICU patients, the susceptibility rates were 96.3%/97.6% for ceftazidime/avibactam, 97.2/98.4% for ceftolozane/tazobactam, 97.1%/98.0% for imipenem/relebactam, 77.8%/84.6% for piperacillin/tazobactam, and 76.9%/85.8% for meropenem; aztreonam/avibactam inhibited 78.0%/81.9% of P. aeruginosa at ≤8 mg/L. In summary, lower susceptibility rates were observed among ICU than non-ICU isolates. Aztreonam/avibactam exhibited potent in vitro activity and broad-spectrum activity against Enterobacterales from ICU and non-ICU patients, including CRE and isolates non-susceptible to newer BLICs. Against P. aeruginosa, aztreonam/avibactam showed a spectrum of activity comparable to that of piperacillin/tazobactam, meropenem, and ceftazidime. [ABSTRACT FROM AUTHOR]

Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant non-fermentative Gram-negative bacillus, posing a significant challenge in clinical treatment due to its numerous intrinsic and acquired resistance mechanisms. This study aimed to evaluate the adequacy of antibiotics used for the treatment of S. maltophilia infections in critically ill patients using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The antibiotics studied included cotrimoxazole, levofloxacin, minocycline, tigecycline, cefiderocol, and the new combination aztreonam/avibactam, which is not yet approved. By Monte Carlo simulations, the probability of target attainment (PTA), the PK/PD breakpoints, and the cumulative fraction of response (CFR) were estimated. PK parameters and MIC distributions were sourced from the literature, the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and the SENTRY Antimicrobial Surveillance Program collection. Cefiderocol 2 g q8h, minocycline 200 mg q12h, tigecycline 100 mg q12h, and aztreonam/avibactam 1500/500 mg q6h were the best options to treat empirically infections due to S. maltophilia. Cotrimoxazole provided a higher probability of treatment success for the U.S. isolates than for European isolates. For all antibiotics, discrepancies between the PK/PD breakpoints and the clinical breakpoints defined by EUCAST (or the ECOFF) and CLSI were detected. [ABSTRACT FROM AUTHOR]

ABSTRACT The combination of aztreonam with ceftazidime/avibactam is considered a potential therapeutic approach for the treatment of infections caused by metallo-β-lactamase (MBL)-producing isolates. In this study, in vitro antibacterial activity of aztreonam with avibactam against 204 carbapenemase-producing Enterobacterales was determined by broth disk elution (BDE) method of two detection volumes (5- and 2-mL broth), with broth microdilution (BMD) method as a reference. For the BDE-5mL test, the categorical agreement (CA) of ATM+CZA-lo tube (aztreonam/ceftazidime/avibactam: 6/6/4 mg/L) was 99.5%, with 0.5% major error (ME) and 0% very major error (VME); the CA of 2ATM+CZA-lo tube (12/6/4 mg/L) was 100%, with no ME and VME. For the BDE-2mL test, the CA of ATM+2CZA-hi tube (15/10/4 mg/L) was 98.5%, with 0% ME and 37.5% VME; the CA of 2ATM+2CZA-hi tube (30/10/4 mg/L) was 97.1%, with 0% ME and 75% VME. The BDE-5 mL test is an economical and practical method for clinical microbiology laboratories to determine the antibacterial susceptibility of aztreonam with avibactam against Enterobacterales, especially the 2ATM+CZA-lo tube with a final concentration of 12/6/4 mg/L of aztreonam/ceftazidime/avibactam.IMPORTANCEInfections caused by metallo-β-lactamase (MBL)-producing Enterobacterales are increasingly reported worldwide, and it is a significant challenge for clinical infection treatment. MBLs are adept at hydrolyzing almost all traditional β-lactam antibiotics except aztreonam, and the enzyme activity cannot be inhibited by traditional or novel β-lactamase inhibitors. The good thing is that the combination of aztreonam with ceftazidime/avibactam has been proven to be one of the potential therapeutic approaches for treating infections related with MBL-producing isolates. Broth microdilution (BMD) method is recommended as a reference method for its accuracy, but it is too complex to perform in most routine laboratories. Finding a more convenient, practical, and accurate susceptibility testing method for aztreonam/avibactam in clinical microbiology laboratories is very necessary. Here, we evaluated the performance of broth disk elution (BDE) method for aztreonam in combination with ceftazidime/avibactam against Enterobacterales isolates, with BMD as a reference.

Yiyu Chen,1 Chuxuan Fang,1 Jun Luo,1 Xueling Pan,2 Zongyan Gao,3 Shuangyi Tang,1 Meng Li4– 6 1Department of Pharmacy, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, People’s Republic of China; 2Newborn ICU, Guigang Maternal and Child Health Care Hospital, Guigang City, Guangxi, People’s Republic of China; 3Newborn ICU, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, People’s Republic of China; 4Department of Clinical Laboratory, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, People’s Republic of China; 5Key Laboratory of Clinical Laboratory Medicine, Guangxi Department of Education, Nanning, Guangxi, People’s Republic of China; 6Key Laboratory of Fungi and Mycosis Research and Prevention, Guangxi Health Commission, Nanning, Guangxi, People’s Republic of ChinaCorrespondence: Meng Li, Department of Clinical Laboratory, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, 530021, People’s Republic of China, Tel/Fax +8613367809642, Email gxmulimeng@foxmail.comAbstract: The prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) has been increasing in recent years. Chinese Infectious Disease Surveillance of Pediatrics (ISPED) showed that in 2022, its resistance rate to meropenem was 18.5%. However, there is limited data available on the treatment of CRKP infection in neonates. In this study, we present a case involving a premature infant infected with OXA-48-producing Klebsiella pneumoniae. The combined susceptibility test revealed a significant synergistic effect between ceftazidime–avibactam(CAZ-AVI), and aztreonam(ATM). The infection was successfully treated with a combination of CAZ-AVI, ATM, and fosfomycin. This case represents the first reported instance of sepsis in a premature infant caused by OXA-48-producing Klebsiella pneumoniae in China. The objective of our study is to evaluate the effectiveness and safety of combination therapy in treating CRKP infections in premature infants. We hope that the findings of this study will provide valuable insights for clinicians in their treatment approach.Keywords: OXA-48, Klebsiella pneumoniae, premature infant, ceftazidime–avibactam, aztreonam

Background: Aztreonam-avibactam (ATM-AVI) combination shows promising effectiveness on most carbapenemase-producing Gram-negatives, yet standardized antibiotic susceptibility testing (AST) methods for evaluating the combination in clinical laboratories is lacking. We aimed to evaluate different ATM-AVI AST approaches. Methods: 96 characterized carbapenem-resistant clinical isolates belonging to 9 Enterobacterales (EB; n = 80) and P. aeruginosa (PA; n = 16) species, including 90 carbapenemase producers and 72 strains resistant to both CAZ-AVI and ATM, were tested. Paper disk elution (DE; Bio-Rad) and E-test gradient strips stacking (SS; bioMérieux) were performed for the ATM + CAZ-AVI combination. MIC Test Strip (MTS; Liofilchem) was evaluated for ATM-AVI MIC determination. Results were interpreted applying ATM clinical breakpoints of the EUCAST guidelines and compared to the broth microdilution method (Sensititre, Thermofisher). Results: According to broth microdilution method, 93% of EB and 69% of PA were tested susceptible to ATM-AVI. The synergistic effect of ATM-AVI was of 95% for EB, but of only 17% for PA. The MTS method yielded higher categorical and essential agreement (CA/EA) rates for both EB (89%/91%) and PA (94%/94%) compared to SS, where the rates were 87%/83% for EB and 81%/81% for PA. MTS and SS yielded 2 and 3 major discrepancies, respectively, while 3 very major discrepancies each were observed for both methods. Concerning the DE method, CA reached 91% for EB and 81% for PA, but high number of very major discrepancies were observed for EB (n = 6; 8%) and for PA (n = 3; 19%). Conclusions: The ATM-AVI association displayed excellent in vitro activity against highly resistant clinical Enterobacterales strains. MTS method offers accurate ATM-AVI AST results, while the SS method might serve as better alternative then DE method in assessing the efficacy of ATM + CAZ-AVI combination. However, further investigation is needed to confirm the methods' ability to detect ATM-AVI resistance. [ABSTRACT FROM AUTHOR]

Β-lactamases-producing Escherichia coli are a widely distributed source of antimicrobial resistance (AMR), for animals and humans. Little is known about the sensitivity profile and genetic characteristics of E. coli strains isolated from domestic cats. We report a cross-sectional study that evaluated E. coli strains isolated from domestic cats in Panama. For this study the following antibiotics were analyzed: ampicillin, amoxicillin-clavulanate cefepime, cefotaxime, cefoxitin, ceftazidime, aztreonam, imipenem, gentamicin, kanamycin, streptomycin, tetracycline, ciprofloxacin, nalidixic acid, trimethoprim-sulfamethoxazole, and chloramphenicol. The data obtained were classified as resistant, intermediate, or sensitive. MDR strains were established when the strain presented resistance to at least one antibiotic from three or more antimicrobial classes. Forty-eight E. coli isolates were obtained, of which 80% presented resistance to at least one of the antibiotics analyzed, while only 20% were sensitive to all (p = 0.0001). The most common resistance was to gentamicin (58%). Twenty-nine percent were identified as multidrug-resistant isolates and 4% with extended spectrum beta-lactamase phenotype. The genes blaTEM (39%), blaMOX(16%), blaACC (16%) and blaEBC (8%) were detected. Plasmid-mediated resistance qnrB (25%) and qnrA (13%) are reported. The most frequent sequence types (STs) being ST399 and we reported 5 new STs. Our results suggest that in intestinal strains of E. coli isolated from domestic cats there is a high frequency of AMR. [ABSTRACT FROM AUTHOR]