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The rapid emergence of multidrug-resistant (MDR) bacteria represents a critical global health threat, underscoring the urgent need for alternative antimicrobial strategies beyond conventional antibiotics. In this study, we report the synthesis of novel biobased antimicrobial polymers bearing quaternary ammonium salts, derived from sustainable feedstocks, maleic anhydride, dimethylaminobenzaldehyde, and furfurylamine. The functional tricyclic oxanorbornene lactam monomer is polymerized via ring opening metathesis polymerization, yielding well-defined polymers with controlled molar masses and low dispersity. Structural characterization is performed using 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, and the polymerization kinetics is monitored by online 1 H NMR spectroscopy. The quaternized biobased polymers demonstrate potent broad-spectrum antimicrobial activity against three clinically isolated MDR bacterial strains. They exhibit minimum inhibitory concentrations (MICs) that are significantly lower than those of several conventional antibiotics while also showing low hemolytic activity toward mammalian cells. This study highlights the potential of bioderived ROMP polymers as promising, sustainable antimicrobial polymers for combating the growing threat of antimicrobial resistance.

Objectives: To define the in vitro pharmacodynamics of taniborbactam against Enterobacterales with CTXM-15, KPC, AmpC, and OXA-48 β-lactamases., Methods: An in vitro pharmacokinetic model was used to simulate serum concentrations associated with cefepime 2G by 1 h infusion 8 h. Taniborbactam was given in exposure ranging and fractionation simulations. Reduction in viable count at 24 h (Δ 24) was the primary end point and four strains were used: Escherichia coli expressing CTXM-15 or AmpC and Klebsiella pneumoniae expressing KPC or OXA-48 enzymes., Results: Taniborbactam was administered as continuous infusions; ≥4 log kill was attained with taniborbactam concentrations of ≥0.01 mg/L against CTXM-15 E. coli, ≥0.5 mg/L against KPC- and OXA-48 K. pneumoniae, and ≥4 mg/L against AmpC E. coli. Analyses were conducted to determine the pharmacokinetic/dynamic driver for each strain. For E. coli (CTXM-15) and E. coli (AmpC), area under the concentration-time curve (AUC) was best related to change in viable count (R 2 0.74 and 0.72, respectively). For K. pneumoniae (KPC) AUC and T > 0.25 mg/L were equally related to bacterial clearance (R 2 0.72 for both), and for K. pneumoniae (OXA-48) T > 0.25 mg/L was the best predictor (R 2 0.94). The taniborbactam AUC range to produce a 1-log 10 reduction in viable count was 4.4-11.2 mg·h/L. Analysis of data from all strains indicated T > MIC divided by 4 was best related to change in viable count; however, curve fit was poor R 2 < 0.49., Conclusions: Taniborbactam was effective in combination with cefepime in producing bacterial clearance for B lactam resistant Enterobacterales. The primary pharmacodynamic driver was AUC or time > threshold, both being closely related to antibacterial effect., Competing Interests: Declaration of competing interests APM holds research grants/activities with Merck, Shionogi, InfectoPharm, GSK, Roche, Bioversys, and Nosopharm. All other authors declare no competing interests., (Copyright © 2024 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.)

The white pollution caused by unsustainable materials is a significant challenge around the globe. Here, a novel and fully biobased polybutyrolactam (PBY) nanofiber membrane was fabricated via the electrospinning method. As-spun PBY nanofiber membranes have good thermal stability, high porosity of up to 71.94%, and excellent wetting behavior. The biodegradability in soil, UV aging irradiation, and seawater was investigated. The PBY nanofiber membrane is almost completely degraded in the soil within 80 days, showing excellent degradability. More interestingly, γ-aminobutyric acid, as a healthcare agent with intrinsic hypotensive, tranquilizing, diuretic, and antidiabetic efficacy, can be detected in the degradation intermediates. In addition, the PBY nanofiber membrane also exhibits antibacterial ability against Escherichia coli . As a fully biomass-derived material, the PBY membrane has excellent biodegradable performance in various environments as well as negligible cytotoxicity and commendable cell proliferation. Our PBY nanofiber membrane shows great potential as biodegradable packaging and in vitro healthcare materials.

Lactam cross-links have been employed to stabilize the helical secondary structure and enhance the activity and physiological stability of antimicrobial peptides; however, stabilization of β-sheets via lactamization has not been observed. In the present study, lactams between the side chains of C- and N-terminal residues have been used to stabilize the β-sheet conformation in a short ten-residue analogue of chicken angiogenin-4. Designed using a combination of molecular dynamics simulations and Markov state models, the lactam cross-linked peptides are shown to adopt stabilized β-sheet conformations consistent with simulated structures. Replacement of the peptide side-chain Cys-Cys disulfide by a lactam cross-link enhanced the broad-spectrum antibacterial activity compared to the parent peptide and exhibited greater propensity to induce proinflammatory activity in macrophages. The combination of molecular simulations and conformational and biological analyses of the synthetic peptides provides a useful paradigm for the rational design of therapeutically active peptides with constrained β-sheet structures.

A new antibiotic named haneummycin (1) was isolated from a culture broth of marine-derived Streptomyces sp. KM77-8 by solvent extraction and HPLC using a C4 column. The structure of 1 was elucidated including relative stereochemistry as a new 22-membered macrolide lactam associated with a cyclopentanone and three sugars by various spectroscopic analyses, such as MS and NMR. Compound 1 displayed significant antibacterial activities against Gram-positive bacteria including vancomycin-resistant Enterococcus faecium (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) with both MIC values of 8.0 µg ml -1 ., (© 2023. The Author(s), under exclusive licence to the Japan Antibiotics Research Association.)

Objectives: Oral β-lactam treatment options for MDR Enterobacterales are lacking. Ledaborbactam (formerly VNRX-5236) is a novel orally bioavailable β-lactamase inhibitor that restores ceftibuten activity against Ambler Class A-, C- and D-producing Enterobacterales. We assessed the ledaborbactam exposure needed to produce bacteriostasis against ceftibuten-resistant Enterobacterales in the presence of humanized ceftibuten exposures in the neutropenic murine thigh infection model., Methods: Twelve ceftibuten-resistant clinical isolates (six Klebsiella pneumoniae, five Escherichia coli and one Enterobacter cloacae) were utilized. Ceftibuten/ledaborbactam MICs ranged from 0.12 to 2 mg/L (ledaborbactam fixed at 4 mg/L). A ceftibuten murine dosing regimen mimicking ceftibuten 600 mg q12h human exposure was developed and administered alone and in combination with escalating exposures of ledaborbactam. The log10 cfu/thigh change at 24 h relative to 0 h controls was plotted against ledaborbactam fAUC0-24/MIC and the Hill equation was used to determine exposures associated with bacteriostasis., Results: The mean ± SD 0 h bacterial burden was 5.96 ± 0.24 log10 cfu/thigh. Robust growth (3.12 ± 0.93 log10 cfu/thigh) was achieved in untreated control mice. Growth of 2.51 ± 1.09 log10 cfu/thigh was observed after administration of humanized ceftibuten monotherapy. Individual isolate exposure-response relationships were strong (mean ± SD R2 = 0.82 ± 0.15). The median ledaborbactam fAUC0-24/MIC associated with stasis was 3.59 among individual isolates and 6.92 in the composite model., Conclusions: Ledaborbactam fAUC0-24/MIC exposures for stasis were quantified with a ceftibuten human-simulated regimen against β-lactamase-producing Enterobacterales. This study supports the continued development of oral ceftibuten/ledaborbactam etzadroxil (formerly ceftibuten/VNRX-7145)., (© The Author(s) 2022. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Serious infections caused by multidrug-resistant (MDR) organisms (Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii) present a critical need for innovative drug development. Herein, we describe the preclinical evaluation of YU253911, 2, a novel γ-lactam siderophore antibiotic with potent antimicrobial activity against MDR Gram-negative pathogens. Penicillin-binding protein (PBP) 3 was shown to be a target of 2 using a binding assay with purified P. aeruginosa PBP3. The specific binding interactions with P. aeruginosa were further characterized with a high-resolution (2.0 Å) X-ray structure of the compound's acylation product in P. aeruginosa PBP3. Compound 2 was shown to have a concentration >1 μg/ml at the 6 h time point when administered intravenously or subcutaneously in mice. Employing a meropenem resistant strain of P. aeruginosa, 2 was shown to have dose-dependent efficacy at 50 and 100 mg/kg q6h dosing in a mouse thigh infection model. Lastly, we showed that a novel γ-lactam and β-lactamase inhibitor (BLI) combination can effectively lower minimum inhibitory concentrations (MICs) against carbapenem resistant Acinetobacter spp. that demonstrated decreased susceptibility to 2 alone., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Masson SAS.)

Condensation (C) domains in non-ribosomal peptide synthetases catalyze peptide elongation steps whereby activated amino acid or peptidyl acyl donors are coupled with specific amino acid acceptors. In the biosynthesis of the β-lactam antibiotic nocardicin A, an unusual C domain converts a seryl tetrapeptide into its pentapeptide product containing an integrated β-lactam ring. While indirect evidence for the intermediacy of a dehydroalanyl species has been reported, here we describe observation of the elusive enzyme-bound dehydroamino acyl intermediate generated from the corresponding allo -threonyl tetrapeptide and partitioned into pentapeptide products containing either a dehydrobutyrine residue or an embedded β-lactam. Contrary to trends in the literature where condensation domains have been deemed flexible as to acyl donor structure, this β-lactam synthesizing domain is highly discriminating. The observation of dehydrobutyrine formation links this C domain to related clades associated with natural products containing dehydroamino acid and d-configured residues, suggesting a common mechanistic link.

Introduction. While colonization by Staphylococcus aureus in haemodialysis patients has been assessed, knowledge about colonization by beta-lactam-resistant Gram-negative bacilli is still limited. Aim. To describe clinical and molecular characteristics in haemodialysis patients colonized by S. aureus (MSSA-MRSA) and beta-lactam-resistant Gram-negative bacilli in an ambulatory renal unit. Methodology. The study included patients with central venous catheters in an outpatient haemodialysis facility in Medellín, Colombia (October 2017-October 2018). Swab specimens were collected from the nostrils and skin around vascular access to assess colonization by S. aureus (MSSA-MRSA). Stool samples were collected from each patient to evaluate beta-lactam-resistant Gram-negative bacilli colonization. Molecular typing included PFGE, multilocus sequence typing (MLST), spa typing and enterobacterial repetitive intergenic consensus-PCR (ERIC). Clinical information was obtained from medical records and personal interview. Results. A total of 210 patients were included in the study. S. aureus colonization was observed in 33.8 % ( n =71) of the patients, 4.8 % ( n =10) of which were colonized by methicillin-resistant S. aureus . Stool samples were collected from 165 patients and of these 41.2 % ( n =68) and 11.5 % ( n =19) were colonized by extended-spectrum-beta-lactamase-producing (ESBL) and carbapenem-resistant bacilli, respectively. Typing methods revealed high genetic diversity among S. aureus and ESBL-producing Gram-negative bacilli (ESBL-GNB). Antibiotic use and hospitalization in the previous 6 months were observed in more than half of the studied population. Conclusion. The high colonization by ESBL-GNB in haemodialysis patients shows evidence for the need for stronger surveillance, not only for S. aureus but also for multidrug-resistant bacilli in order to avoid their spread. Additionally, the high genetic diversity suggests other sources of transmission outside the renal unit instead of horizontal transmission between patients.

Treatment of multidrug-resistant Gram-negative bacterial pathogens represents a critical clinical need. Here, we report a novel γ-lactam pyrazolidinone that targets penicillin-binding proteins (PBPs) and incorporates a siderophore moiety to facilitate uptake into the periplasm. The MIC values of γ-lactam YU253434, 1 , are reported along with the finding that 1 is resistant to hydrolysis by all four classes of β-lactamases. The druglike characteristics and mouse PK data are described along with the X-ray crystal structure of 1 binding to its target PBP3.

Four new phenylspirodrimane-type dimers, namely chartarlactams Q-T, along with stachyin B were isolated from the fermentation broth of a sponge-derived fungus Stachybotrys chartarum WGC-25 C-6. Chartarlactams Q-T were structurally featured by the dimerization of two units of phenylspirodrimane linked by a C-N bond. Their structures were determined on the basis of extensive spectroscopic analysis, while quantum ECD calculation and modified Mosher's method were used for the assignment of absolute configurations. Chartarlactams Q-S and stachyin B showed moderate inhibition against bacterial pathogen Staphylococcus aureus with MIC values ranging from 4 μg/mL to 16 μg/mL, and chartarlactam T exhibited significant inhibition toward ZIKV virus., (© 2020 Wiley-VHCA AG, Zurich, Switzerland.)

Incorporation of the Beckmann rearrangement into the presented research resulted in the formation of nitrogen-containing terpenoid derivatives originating from naturally occurring compounds. Both starting monoterpenes and obtained derivatives were subjected to estimation of their antibacterial potential. In the presented study, Staphylococcus aureus was the most sensitive to examined compounds. The Minimal Inhibitory Concentration (MIC) experiments performed on S. aureus demonstrated that the (-)-menthone oxime (-)-8 and (+)-pulegone oxime (+)-13 had the best antibacterial activity among the tested derivatives and starting compounds. Their MIC 90 value was 100 µg/mL. The obtained derivatives were also evaluated for their inhibitory activity against bacterial urease. Among the tested compounds, three active inhibitors were found - oxime 14 and lactams (-)-15 and 16 limited the activity of Sporosarcina pasteurii urease with K i values of 174.3 µM, 43.0 µM and 4.6 µM, respectively. To our knowledge, derivative 16 is the most active antiureolytic lactam described to date.

Nacubactam is a novel non-β-lactam diazabicyclooctane β-lactamase inhibitor under development for the treatment of serious Gram-negative infections. This study assessed the efficacy of human-simulated epithelial lining fluid (ELF) exposure of nacubactam in combination with meropenem against AmpC-overproducing (n=4) and Klebsiella pneumoniae carbapenemase (KPC)-expressing (n=3) Pseudomonas aeruginosa isolates in the neutropenic murine lung infection model. Meropenem, nacubactam and meropenem-nacubactam (1:1 concentration ratio) minimum inhibitory concentrations (MICs) were determined in triplicate using broth microdilution. Regimens that provided ELF profiles mimicking those observed in humans given nacubactam 2 g q8h (1.5-h infusion) alone and in combination with a subtherapeutic ELF exposure of meropenem were administered 2 h after inoculation. Efficacy was assessed as the change in log 10 colony-forming units (CFU)/lung at 24 h compared with 24-h meropenem monotherapy. Meropenem, nacubactam and meropenem-nacubactam MICs were 8->64, 128->256 and 2-16 mg/L, respectively. Meropenem and nacubactam monotherapy groups demonstrated bacterial growth over 24 h for each isolate. Against AmpC-overproducing and KPC-expressing P. aeruginosa isolates, meropenem-nacubactam resulted in -2.73±0.93 and -4.35±1.90 log 10 CFU/lung reduction, respectively, relative to meropenem monotherapy. Meropenem-nacubactam showed promising in-vivo activity against meropenem-resistant P. aeruginosa, indicative of a potential role for the treatment of infections caused by these challenging pathogens., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Monocyclic β-lactams revive the research field on antibiotics, which are threatened by the emergence of resistant bacteria. A six-step synthetic route was developed, providing easy access to new 3-amino-1-carboxymethyl-4-phenyl-β-lactams, of which the penicillin-binding protein (PBP) inhibitory potency was demonstrated biochemically., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Chemical investigation of the mangrove endophytic fungus Cladosporium sp. SCNU-F0001 resulted in the isolation and identification of a new macrolide compound named thiocladospolide E (1) and a novel macrolide lactam named cladospamide A (2), along with the known cladospolide B (3). The structures were elucidated based on spectroscopic methods, and the absolute configurations were determined by X-ray diffraction and HPLC analysis after chemical derivatization. All compounds were tested for their antibacterial and cytotoxic activity., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Brønsted acids catalyze a multicomponent reaction of benzaldehyde with amines and diethyl acetylenedicarboxylate to afford highly functionalized γ-lactam derivatives. The reaction consists of a Mannich reaction of an enamine to an imine, both generated in situ , promoted by a phosphoric acid catalyst and a subsequent intramolecular cyclization. The hydrolysis of the cyclic enamine substrate can provide enol derivatives and, moreover, a second attack of the amine on the carboxylate can afford amide derivatives. An optimization of the reaction conditions is presented in order to obtain selectively cyclic enamines that can afford the enol species after selective hydrolysis., Competing Interests: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Background: Diazabicyclooctanes (DBOs) are promising β-lactamase inhibitors. Some, including nacubactam (OP0595/RG6080), also bind PBP2 and have an enhancer effect, allowing activity against Enterobacteriaceae with MBLs, which DBOs do not inhibit. We tested the activity of nacubactam/β-lactam combinations against MBL-producing Enterobacteriaceae., Methods: Test panels comprised (i) 210 consecutive Enterobacteriaceae with NDM or VIM MBLs, as referred by UK diagnostic laboratories, and (ii) 99 supplementary MBL-producing Enterobacteriaceae, representing less prevalent phenotypes, species and enzymes. MICs were determined by CLSI agar dilution., Results: MICs of nacubactam alone were bimodal, clustering at 1-8 mg/L or >32 mg/L; >85% of values for Escherichia coli and Enterobacter spp. fell into the low MIC cluster, whereas Proteeae were universally resistant and the Klebsiella spp. were divided between the two groups. Depending on the prospective breakpoint (4 + 4 or 8 + 4 mg/L), and on whether all isolates were considered or solely the Consecutive Collection, meropenem/nacubactam and cefepime/nacubactam inhibited 80.3%-93.3% of MBL producers, with substantial gains over nacubactam alone. Against the most resistant isolates (comprising 57 organisms with MICs of nacubactam >32 mg/L, cefepime ≥128 mg/L and meropenem ≥128 mg/L), cefepime/nacubactam at 8 + 4 mg/L inhibited 63.2% and meropenem/nacubactam at 8 + 4 mg/L inhibited 43.9%. Aztreonam/nacubactam, incorporating an MBL-stable β-lactam partner, was almost universally active against the MBL producers and, unlike aztreonam/avibactam, had an enhancer effect., Conclusions: Nacubactam combinations, including those using MBL-labile β-lactams, e.g. meropenem and cefepime, can overcome most MBL-mediated resistance. This behaviour reflects nacubactam's direct antibacterial and enhancer activity., (© The Author(s) 2018. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The γ-lactam motif is often found in naturally occurring compounds with diverse biological activities. We prepared a 28-member library of N-substituted γ-lactams following a single-pot, three-component Ugi reaction comprising bifunctional building block, l-glutamic acid methyl ester. The reaction tolerates structurally diverse carbonyl and isocyanide components providing a robust access to functionalized γ-lactams. Antimicrobial susceptibility testing, including agar well diffusion assay, serial microdilution broth assay, and antibiofilm activity testing, identified a potent compound with antibiofilm activity against Staphylococcus aureus ATCC 6538.

The in vitro activity of sulopenem was assessed against a collection from 2014 to 2016 of 539 urinary isolates of Escherichia coli from Canadian patients by using CLSI-defined broth microdilution methodology. A concentration of sulopenem 0.03 µg/ml inhibited both 50% (MIC 50 ) and 90% (MIC 90 ) of isolates tested; sulopenem MICs ranged from 0.015 to 0.25 µg/ml. The in vitro activity of sulopenem was unaffected by nonsusceptibility to trimethoprim-sulfamethoxazole and/or ciprofloxacin, multidrug-resistant phenotypes, extended-spectrum β-lactamases, or AmpC β-lactamases., (Copyright © 2018 American Society for Microbiology.)

Antimicrobial resistance is widely recognized as a grave threat to global health in the 21st century, since the past decades have seen a dramatic increase in human-pathogenic bacteria that are resistant to one or multiple antibiotics. New antimicrobial agents are urgently required, particularly in the treatment of chronic infections such as cystic fibrosis, often associated with persistent colonization by drug-resistant pathogens and epithelial damage by pulmonary oxidative stress. In such events, it would be favourable to find agents that could have antioxidant and antibacterial activities combined in one molecule. The discovery of compounds that can show a dual-target activity considerably increased in the last years, reflecting the growing confidence that this new approach could lead to better therapeutic solutions for complex multigenic diseases. The aim of this review is to report those natural and synthetic compounds displaying significant antioxidant and antibacterial activities. In recent years there has been a growing attention on plant-derived antimicrobials as an alternative to antibiotics, for their efficacy and low tendency in developing bacterial resistance. Moreover, it was found that some natural products could enhance the activity of common antibiotics displaying a synergistic effect. We then report some selected synthetic compounds with an in-built capacity to act on two targets or with the combination in a single structure of two pharmacophores with antioxidant and antibacterial activities. Recent literature instances were screened and the most promising examples of dual-active antibacterial-antioxidant molecules were highlighted., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

β-Lactams are the most important class of antibiotics, for which the emergence of resistance threatens their utility. As such, we explored the extent to which the tetramic acid motif, frequently found in naturally occurring antibiotics, can be used to generate novel β-lactam antibiotics with improved antibacterial activity. We synthesized new ampicillin - tetramic acid, cephalosporin - tetramic acid, and cephamycin - tetramic acid analogs and evaluated their activities against problematic Gram-positive and Gram-negative pathogens. Amongst the analogs, a 7-aminocephalosporanic acid analog, 3397, and a 7-amino-3-vinyl cephalosporanic acid, 3436, showed potent activities against S. aureus NRS 70 (MRSA) with MICs of 6.25 μg/mL and 3.13 μg/mL respectively. These new analogs were ≥16-fold more potent than cefaclor and cephalexin. Additionally, a Δ 2 cephamycin - tetramic acid analog 3474 which contained a basic guanidinium substituent at the 5-position of the tetramic acid core displayed potent activity against several clinical strains of K. pneumoniae and E. coli., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A benzofuroquinolinium derivative that exhibits excellent cell division inhibitory effect was discovered through cell-based screening approach. This compound possesses potent antimicrobial activity against both Gram-positive and Gram-negative bacteria including the drug-resistant strains. In addition, this compound is able to restore MRSA susceptibility to beta-lactam antibiotics. The biochemical results suggest that the compound inhibits bacterial cell division through the disruption of GTPase activity and the polymerization of FtsZ, which is probably the mechanism of antibacterial activity., (Copyright © 2018 The Authors. Production and hosting by Elsevier B.V. All rights reserved.)

Bacterial infections, particularly hospital-acquired infections caused by Pseudomonas aeruginosa , have become a global threat with a high mortality rate. Gram-negative bacteria including P. aeruginosa employ N -acyl homoserine lactones (AHLs) as chemical signals to regulate the expression of pathogenic phenotypes through a mechanism called quorum sensing (QS). Recently, strategies targeting bacterial behaviour or QS have received great attention due to their ability to disarm rather than kill pathogenic bacteria, which lowers the evolutionary burden on bacteria and the risk of resistance development. In the present study, we report the design and synthesis of N -alkyl- and N -aryl 3,4 dichloro- and 3,4-dibromopyrrole-2-one derivatives through the reductive amination of mucochloric and mucobromic acid with aliphatic and aromatic amines. The quorum sensing inhibition (QSI) activity of the synthesized compounds was determined against a P. aeruginosa MH602 reporter strain. The phenolic compounds exhibited the best activity with 80% and 75% QSI at 250 µM and were comparable in activity to the positive control compound Fu-30. Computational docking studies performed using the LasR receptor protein of P. aeruginosa suggested the importance of hydrogen bonding and hydrophobic interactions for QSI.

Stapling of side chains to stabilize an α-helical structure has been generally associated with an increased uptake of CPPs. Here, we compare four amphiphilic stapled peptides with their linear counterparts in terms of their membrane binding and conformational features in order to correlate these with uptake efficiency and toxicological effects. The impact of lactam stapling was found to vary strongly with regard to the different aspects of peptide-membrane interactions. Nearly all stapled peptides caused less membrane perturbation (vesicle leakage, hemolysis, bacterial lysis) than their linear counterparts. In one case (MAP-1) where stapling enhanced α-helicity in aqueous and lipid environments, leakage was eliminated while cell uptake in HEK293 and HeLa cells remained high, which improved the overall characteristics. The other systems (DRIM, WWSP, KFGF) did not improve, however. The data suggest that cell uptake of amphipathic CPPs correlates with their adopted α-helix content in membranes rather than their helicity in solution.

An investigation of the formation of fused- and spiro-β-lactone annulate to γ-lactams has shown that the fused systems are formed preferentially, under standard conditions, but that spiro systems are accessible only when the formation of the fused system is blocked and require careful optimisation of reaction conditions. These systems display both weak antibacterial activity and proteasome inhibition.

OP0595 (RG6080) is a novel diazabicyclooctane that inhibits class A and C serine beta-lactamases. Although the combination of OP0595 and cefepime (FEP) showed good in vitro activity against extended-spectrum-beta-lactamase (ESBL)-producing pathogens, the effect of the combination therapy against severe infections, such as pneumonia or bacteremia, remains unknown in vivo In this study, we investigated the efficacy and pharmacokinetics of the combination therapy of OP0595 and FEP in a mouse model of pneumonia caused by Klebsiella pneumoniae harboring SHV- and CTX-M-9-type ESBLs. The infected BALB/c mice were intraperitoneally administered saline (control), 100 mg/kg of body weight of FEP, 20 mg/kg of OP0595, or both FEP and OP0595, twice a day. The MIC of FEP against the bacteria was 8 mg/liter and markedly improved to 0.06 mg/liter with the addition of 0.5 mg/ml of OP0595. In the survival study, the combination of FEP and OP0595 significantly improved the survival rate compared with that reported with either OP0595 or FEP alone ( P < 0.001). The number of bacteria in the lungs and blood significantly decreased in the combination therapy group compared to that reported for the monotherapy groups ( P < 0.001). In addition, the in vivo effect depended on the dose of FEP. However, pharmacokinetic analysis revealed that the percentage of time above MIC remained constant when increasing the dose of FEP in combination with 20 mg/kg of OP0595. The results of our study demonstrated the in vivo effectiveness of the combination of OP0595 and FEP., (Copyright © 2017 American Society for Microbiology.)

A library of 2-aminobenzimidazole derivatives was screened for the ability to suppress β-lactam resistance in Mycobacterium smegmatis. Several non-bactericidal compounds were identified that reversed intrinsic resistance to β-lactam antibiotics in a manner distinct from β-lactamase inhibitors. Activity also translates to M. tuberculosis, with a lead compound from this study potently suppressing carbenicillin resistance in multiple M. tuberculosis strains (including multidrug-resistant strains). Preliminary mechanistic studies revealed that the lead compounds act through a mechanism distinct from that of traditional β-lactamase inhibitors., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pseudomonas aeruginosa is a common cause for healthcare-associated infections, which have been historically treated by antipseudomonal β-lactam agents in the clinical setting. However, P. aeruginosa has evolved to overcome these β-lactam agents via multiple endogenous resistance mechanisms, including derepression of the chromosomal cephalosporinase (AmpC). In this article, we investigated the effective concentration of OP0595 for combination with piperacillin, cefepime or meropenem in in vitro susceptibility tests, and the antibacterial activity of cefepime in combination with OP0595 in both in vitro time-kill studies and in vivo murine thigh infection model study with AmpC-derepressed P. aeruginosa. The sufficient combinational concentration of OP0595 was a 4 μg ml -1 with all these three β-lactam agents. OP0595 increased the antibacterial activity of cefepime in both in vitro and in vivo studies against all strains tested. Taken together, OP0595 is the diazabicyclooctane serine β-lactamase inhibitor with activity against AmpC-derepressed P. aeruginosa and its combinational use with a β-lactam agent will provide a new approach for the treatment of P. aeruginosa infections.

Mono and dihydroxypyrrolidinones are readily available by direct oxygenation of a pyroglutamate-derived bicyclic lactam with high diastereoselectivity, and these may be manipulated further in protected or unprotected form by Grignard addition to a pendant Weinreb amide to give acylhydroxypyrrolidinones, which are analogues of the natural product, pramanicin. Preliminary bioassay against S. aureus and E. coli indicated that some compounds exhibit selective Gram-negative antibacterial activity, and may offer promise for the development of novel systems suitable for antibacterial drug development.

The present work reports a Pd II /Ag I -promoted amidoalkylation reaction involving various γ-hydroxy lactams and C/O/S nucleophiles at room temperature. The dual mode of activation of both the electrophile and nucleophile by in situ generated catalytically active cationic Pd II species facilitates the reaction at room temperature. Among the synthesized isoindoline derivatives, three compounds are found to be active against vancomycin and methicillin-resistant S. aureus strain with appreciable MIC values.

Poly-ether-ether-ketone (PEEK) is currently introduced as an alternative material for orthopedic implants due to its biocompatibility and low elastic modulus compared to titanium. Also, a sulphonation treatment can functionalize PEEK to embed therapeutical substances. The objective of this work was to functionalize a PEEK film to incorporate novel lactam-based antibiofilms compounds. PEEK samples were functionalized by sulphuric acid treatment and then dissolved in dimethylsulfoxide, where lactams were added to be incorporated into the polymer. A dip-coating technique was used to synthesize a thin film on a glass-based substrate. The degree of sulfonation (DS) and the incorporation of lactams into sulphonated PEEK (sPEEK) were analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis (TGA), and scanning electron microscopy. A DS of 65% was obtained and TGA curves confirmed the presence of SO 3 H and lactams in the sPEEK structure. The growth of Streptococcus mutans biofilm decreased on sPEEK surface containing lactams when compared to sPEEK free of lactams. That indicated the antibiofilm activity of those compounds was maintained after incorporation into sPEEK. Planktonic growth analysis showed no long distant effects of sPEEK containing lactams, indicating that no systemic effects should be expected upon clinical uses of medical devices produced with lactam-treated sPEEK. Results revealed that inclusion of lactams into sPEEK represents a good alternative for the production of biomaterials resistant to bacterial accumulation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3015-3020, 2016., (© 2016 Wiley Periodicals, Inc.)

Objectives: The diazabicyclooctane β-lactamase inhibitor OP0595 (RG6080) also acts as an antibiotic, targeting PBP2 in Enterobacteriaceae, but this activity is vulnerable to mutational resistance. We used WGS to investigate the basis of this resistance., Methods: Twenty OP0595-selected mutants, comprising four derived from each of five different Escherichia coli strains, were sequenced on Illumina HiSeq. Reads from each mutant were mapped to the assembled genome of the corresponding parent. A variant-calling file generated with Samtools was parsed to determine genetic alterations., Results: Besides OP0595, the mutants consistently showed decreased susceptibility to mecillinam, which likewise targets PBP2, and grew as stable round forms in the presence of subinhibitory concentrations of OP0595. Among the 20 mutants, 18 had alterations in genes encoding tRNA synthase and modification functions liable to induce expression of the RpoS sigma factor through activation of the stringent response or had mutations suppressing inactivators of RpoS or the stringent response signal-degrading enzyme, SpoT. TolB was inactivated in one mutant: this activates RcsBC regulation and was previously associated with mecillinam resistance. The mechanism of resistance remained unidentified in one mutant. Both the RpoS and RcsBC systems regulate genes of cell division, including ftsAQZ that can compensate for loss or inhibition of PBP2, allowing survival of the challenged bacteria as stable round forms, as seen., Conclusions: WGS identified the global stringent response signal, entailing induction of RpoS, as the main mediator of mutational resistance to OP0595 in E. coli., (© The Author 2016. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Two new compounds, designated paraphaeosphaeride D (1) and berkleasmin F (2) together with a previously known compound, berkleasmin A (3), isolated from a culture broth of the fungus Paraphaeosphaeria sp. TR-022, proved to be new circumventors of arbekacin (ABK) resistance in methicillin-resistant Staphylococcus aureus (MRSA). The structures of 1 and 2 were elucidated by spectroscopic analyses, including various NMR experiments. All compounds showed 10-100 times ABK circumvention activities using the paper disc method and reduced the MIC values of ABK against MRSA from 16 μg ml(-1) to 4 μg ml(-1) (fourfold) using the agar dilution method. These new compounds might be promising lead compounds for developing circumventors of ABK resistance in MRSA.

Heronamides are a class of potent antifungal metabolites produced by marine-derived actinomycetes. The number of hydroxy groups and the stereochemistry of the two hydroxylated methine carbons are important for the activity of heronamide C, whereas the effect of the hydrocarbon chains is not known. In this study, the stereochemistry and the biological activity of BE-14106, another member of the heronamide class of antibiotics, isolated from an actinomycete Actinoalloteichus cyanogriseus IFM 11549 was investigated. Spectroscopic analysis coupled with photo- and O2-induced conversion revealed that BE-14106 and the heronamides had the same stereochemistry. BE-14106 showed potent growth inhibition against fission yeast cells with an MIC value of 0.50 μM (0.21 μg/mL), being 4 times less potent than heronamide C, which revealed the importance of the structure of the hydrocarbon tail for the activity.

Homotypic fusion of early endosomes is important for efficient protein trafficking and sorting. The key controller of this process is Rab5 which regulates several effectors and PtdInsPs levels, but whose mechanisms are largely unknown. Here, we report that vicenistatin, a natural product, enhanced homotypic fusion of early endosomes and induced the formation of large vacuole-like structures in mammalian cells. Unlike YM201636, another early endosome vacuolating compound, vicenistatin did not inhibit PIKfyve activity in vitro but activated Rab5-PAS pathway in cells. Furthermore, vicenistatin increased the membrane surface fluidity of cholesterol-containing liposomes in vitro, and cholesterol deprivation from the plasma membrane stimulated vicenistatin-induced vacuolation in cells. These results suggest that vicenistatin is a novel compound that induces the formation of vacuole-like structures by activating Rab5-PAS pathway and increasing membrane fluidity.

The majority of antifungal compounds reported so far target the cell wall or cell membrane of fungi, suggesting that other types of antibiotics cannot exert their activity because they cannot penetrate into the cells. Therefore, if the permeability of the cell membrane could be enhanced, many antibiotics might be found to have antifungal activity. We here used the polyene antibiotic nystatin, which binds to ergosterol and forms pores at the cell membrane, to enhance the cellular permeability. In the presence of nystatin, many culture extracts from entomopathogenic fungi displayed antifungal activity. Among all the active extracts, two active components were purified and identified as helvolic acid and terramide A. Because the minimum inhibitory concentration of either compound was reduced four-fold in the presence of nystatin, it can be concluded that this screening method is useful for detecting novel antifungal activity., (Copyright © 2015 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Gram-negative bacteria such as Pseudomonas aeruginosa and Escherichia coli use N-acylated l-homoserine lactones (AHLs) as autoinducers (AIs) for quorum sensing (QS), a chief regulatory and cell-to-cell communication system. QS is responsible for social adaptation, virulence factor production, biofilm production and antibiotic resistance in bacteria. Fimbrolides, a class of halogenated furanones isolated from the red marine alga Delisea pulchra, have been shown to exhibit promising QS inhibitory activity against various Gram-negative and Gram-positive bacterial strains. In this work, various lactam analogues of fimbrolides viz., 1,5-dihydropyrrol-2-ones, were designed and synthesized via an efficient lactamization protocol. All the synthesized analogues were tested for QS inhibition against the E. coli AHL-monitor strain JB357 gfp (ASV). Compound 17a emerged as the most potent compound, followed by 9c, with AIC40 values (the ratio of synthetic inhibitor to natural AHL signaling molecule that is required to lower GFP expression to 40%) of 1.95 and 19.00, respectively. Finally, the potential binding interactions between the synthesized molecules and the LasR QS receptor were studied by molecular docking. Our results indicate that 1,5-dihydropyrrol-2-ones have the ability to serve as potential leads for the further development of novel QS inhibitors as antimicrobial therapeutics., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

OP0595 is a novel diazabicyclooctane which, like avibactam, inhibits class A and C β-lactamases. In addition, unlike avibactam, it has antibacterial activity, with MICs of 0.5 to 4 μg/ml for most members of the family Enterobacteriaceae, owing to inhibition of PBP2; moreover, it acts synergistically with PBP3-active β-lactams independently of β-lactamase inhibition, via an "enhancer effect." Enterobacteriaceae mutants stably resistant to 16 μg/ml OP0595 were selected on agar at frequencies of approximately 10(-7). Unsurprisingly, OP0595 continued to potentiate substrate β-lactams against mutants derived from Enterobacteriaceae with OP0595-inhibited class A and C β-lactamases. Weaker potentiation of partners, especially aztreonam, cefepime, and piperacillin--less so meropenem--remained frequent for OP0595-resistant Enterobacteriaceae mutants lacking β-lactamases or with OP0595-resistant metallo-β-lactamases (MBLs), indicating that the enhancer effect is substantially retained even when antibiotic activity is lost., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Background: OP0595 is a diazabicyclooctane that (i) acts as a PBP2-active antibacterial, (ii) inhibits Class A and C β-lactamases and (iii), like mecillinam, gives β-lactamase-independent potentiation of β-lactams targeting other PBPs. We tested its behaviour against β-lactam-resistant Enterobacteriaceae and non-fermenters., Methods: Organisms were UK clinical isolates; MICs were determined by CLSI agar dilution for OP0595 alone or combined at 1-4 mg/L with aztreonam, biapenem, cefepime or piperacillin., Results: MICs of OP0595 for Escherichia coli, Enterobacter, Citrobacter and Klebsiella spp. were mostly 1-4 mg/L but values >4 mg/L were seen for minorities of isolates irrespective of other resistances, and for 50%-60% of those with ertapenem resistance involving porin loss plus ESBL or AmpC activity. OP0595 MICs for Serratia, Proteeae and non-fermenters mostly were >4 mg/L. When its MIC was ≤4 mg/L, OP0595's antibacterial activity dominated combination activity. For 'OP0595-resistant' (MIC >4 mg/L) isolates with Class A or C β-lactamases OP0595 achieved strong potentiation of substrate β-lactams, contingent on β-lactamase inhibition. β-Lactamase-independent potentiation was evident with aztreonam, cefepime and piperacillin-less so for biapenem-for many OP0595-resistant Enterobacteriaceae with Class B carbapenemases, which are not inhibited by OP0595. OP0595 acted solely as a β-lactamase inhibitor for non-fermenters., Conclusions: OP0595 inhibited Enterobacteriaceae, not non-fermenters; its combinations had broad activity versus Enterobacteriaceae, largely contingent on OP0595's antibacterial activity but also on inhibition of Class A and C β-lactamases and on the β-lactam-enhancer effect, which allowed activity against many OP0595-resistant metallo-β-lactamase-producing Enterobacteriaceae. For non-fermenters OP0595 acted only as a β-lactamase inhibitor., (© The Author 2015. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Two new hydroxycitric acid lactone derivatives named cinatrins D (1) and E (2), and a new γ-lactam, virgaricin B (3), along with a known similar compound, virgaricin (4), were isolated from a fermentation broth of the fungus Virgaria boninensis FKI-4958. The absolute stereo structures of the new compounds were established by a combination of spectroscopic methods and chemical modifications. All three newly discovered compounds possessed weak antibacterial activity.

Objectives: The production of a growing diversity of β-lactamases by Gram-negative bacteria challenges antimicrobial chemotherapy. OP0595, discovered separately by each of Meiji Seika Pharma and Fedora Pharmaceuticals, is a new diazabicyclooctane serine β-lactamase inhibitor that also acts as an antibiotic and as a β-lactamase-independent β-lactam 'enhancer'., Methods: Inhibitory activity against serine β-lactamases and affinity for PBPs were determined using nitrocefin and Bocillin FL, respectively. MICs alone and in combination with β-lactam agents were measured according to CLSI recommendations. Morphological changes in Escherichia coli were examined by phase-contrast microscopy., Results: IC50s of OP0595 for class A and C β-lactamases were <1000 nM, with covalent binding demonstrated to the active-site serine of CTX-M-44 and AmpC enzymes. OP0595 also had direct antibiotic activity against many Enterobacteriaceae, associated with inhibition of PBP2 and conversion of the bacteria into spherical forms. Synergy between OP0595 and β-lactam agents was seen against strains producing class A and C β-lactamases vulnerable to inhibition. Lastly, OP0595 lowered the MICs of PBP3-targeted partner β-lactam agents for a non-β-lactamase-producing E. coli mutant that was resistant to OP0595 itself, indicating β-lactamase-independent 'enhancer'-based synergy., Conclusions: OP0595 acts in three ways: (i) as an inhibitor of class A and C β-lactamases, covalently binding at their active sites; (ii) as an antibacterial, by inhibiting PBP2 of several Enterobacteriaceae; and (iii) as an 'enhancer' of β-lactam agents that bind to other PBPs besides PBP2 for several Enterobacteriaceae. OP0595 has considerable potential to overcome resistance when it is combined with various β-lactam agents., (© The Author 2015. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Epoxypyrrolidinones are available by epoxidation of carboxamide-activated bicyclic lactam substrates derived from pyroglutamate using aqueous hydrogen peroxide and tertiary amine catalysis. In the case of an activating Weinreb carboxamide, further chemoselective elaboration leads to the efficient formation of libraries of epoxyketones. Deprotection may be achieved under acidic conditions to give epoxypyroglutaminols, although the ease of this process can be ameliorated by the presence of internal hydrogen bonding. Bioassay against S. aureus and E. coli indicated that some compounds exhibit antibacterial activity. These libraries may be considered to be structural mimics of the natural products pramanicin and epolactaene. More generally, this outcome suggests that interrogation of bioactive natural products is likely to permit the identification of "privileged" structural scaffolds, providing frameworks suitable for optimization in a short series of chemical steps that may accelerate the discovery of new antibiotic chemotypes. Further optimization of such systems may permit the rapid identification of novel systems suitable for antibacterial drug development.

Antimicrobial susceptibility pattern was determined in 100 strains of Vibrio isolated from the Litopenaeus vannamei shrimp and identified phenotypically. A high antibiotic-resistance index (75%) was observed, with the following phenotypic profiles: monoresistance (n = 42), cross-resistance to β-lactams (n = 20) and multiple resistance (n = 13). Plasmid resistance was characterized for penicillin (n = 11), penicillin + ampicillin (n = 1), penicillin + aztreonam (n = 1), and ampicillin (n = 1). Resistance to antimicrobial drugs by the other strains (n = 86) was possibly mediated by chromosomal genes. The findings of this study support the conclusion that the cultured shrimps can be vehicles of vibrios resistant to β-lactam and tetracycline.

A bioassay guided fractionation of the ethyl acetate extract from culture broths of the strain Streptomyces zhaozhouensis CA-185989 led to the isolation of three new polycyclic tetramic acid macrolactams (1-3) and four known compounds. All the new compounds were structurally related to the known Streptomyces metabolite ikarugamycin (4). Their structural elucidation was accomplished using a combination of electrospray-time of flight mass spectrometry (ESI-TOF MS) and 1D and 2D NMR analyses. Compounds 1-3 showed antifungal activity against Aspergillus fumigatus, Candida albicans and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).

Seven β-aryl substituted γ-alkylidene-γ-lactones analogues of rubrolides were synthesized from mucobromic acid and converted through a lactamization with isobutylamine into their corresponding γ-hydroxy-γ-lactams (76-85%). These lactams were converted into (Z)- and (E)-γ-alkylidene-γ-lactams (23-45%). All compounds were fully characterized by IR, NMR ((1)H and (13)C), COSY and HETCOR bidimensional experiments, and NOE difference spectroscopy experiments when necessary. Evaluation of these three different classes of compounds against Enterococcus faecalis biofilm formation showed that all classes are active and the highest biofilm inhibition activity was caused by lactam 13f (IC50 = 0.76 μg/mL). Moreover, in almost all cases at least one of the lactams is more active than its correspondent γ-alkylidene-γ-lactone. The use of rubrolides as a lead structure has proven successful for the identification of new compounds displaying novel antibacterial activities, namely biofilm inhibition, which have the potential for the development of antimicrobial drugs targeted to inhibition of the initial stages of bacterial infections, rather than bacterial viability. Such drugs are less prompt to induce bacterial resistance, being therefore a more cost-effective investment for pharmaceutical research., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)

Since GLT-1 transporters play the key role in terminating synaptic transmission of glutamate, drugs stimulating GLT-1 expression are expected to offer neuroprotection. Of these, beta-lactam antibiotics have been suggested to contribute to various central nervous system disorders, including development of tolerance and dependence to opioids, and tolerance to cannabinoids. Opioids and cannabinoids share many pharmacological properties. All together, it can be hypothesized that beta-lactam antibiotics may reduce the development of dependence to cannabinoids through activating GLT-1., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Biosynthesis of the dithiolopyrrolone antibiotic holomycin in Streptomyces clavuligerus involves the closure of a pair of enethiols to a cyclic disulfide. We have shown that the dithiol oxidase HlmI is responsible for the disulfide formation and this enzyme also plays a role in self-protection. In the present study, we examine how S. clavuligerus deals with the proposed toxic dithiol intermediates when hlmI is deleted. We used differential NMR spectroscopy and mass spectrometry to profile the metabolomes of hlmI deletion mutants along with the wild-type strain and a holomycin-overproducing strain. A number of metabolites unique to ΔhlmI strains were identified. In these metabolites the enethiols have been incapacitated by a combination of mono- and di-S-methylation. We also observed an intriguing dimeric thioether adduct in low quantities in the wild-type strain and at much higher levels in the ΔhlmI strains. The structures of these novel metabolites highlight the reactivity of the dihydrodithiolopyrrolone scaffold. Furthermore, bioassays suggest that modification of the enethiol warhead by S-alkylation provides a host strategy for detoxification, one that is shared amongst multiple species producing such bioactive disulfide natural products., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Armeniaspiroles, a novel class of natural products isolated from Streptomyces armeniacus, are characterized by a novel spiro[4.4]non-8-ene scaffold. Various derivatives of Armeniaspiroles could be obtained by halogenation, alkylation, addition/elimination or reductions. A total synthesis of the 5-chloro analog of Armeniaspirole A has been accomplished in a linear six-step sequence. 5-Chloro-Armeniaspirole A exhibits good activity against a range of multidrug-resistant, Gram-positive bacterial pathogens., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Streptomycetes were isolated out of a soil sample taken from the rhizosphere of a spruce stand and screened by HPLC-diode array analysis for the production of secondary metabolites. This led to the detection of silvalactam, a novel 24-membered macrolactam antibiotic in extracts of Streptomyces strain Tü 6392. The structure was determined by MS and NMR spectroscopy experiments. Silvalactam shows a potent antiproliferative activity against various cancerous and non-cancerous cell lines.

We investigated the short- and long-term effects of ceftriaxone on glutamate transporter subtype 1 (GLT-1) transporter activity and extracellular glutamate in the rat nucleus accumbens. Repeated ceftriaxone administration (50, 100 or 200 mg/kg, i.p.) produced a dose-dependent reduction in glutamate levels that persisted for 20 days following discontinuation of drug exposure. The ceftriaxone effect was prevented by the GLT-1 transporter inhibitor dihydrokainate (1 μM, intra-accumbal). These results suggest that β-lactam antibiotics produce an enduring reduction in glutamatergic transmission in the brain reward center.