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This study investigates the genetic traits and transmission mechanisms of cephalosporin-resistant Escherichia coli in tropical aquatic environments in Singapore. From 2016 to 2020, monthly samples were collected from wastewater treatment plants, marine niches, community sewage, beaches, reservoirs, aquaculture farms, and hospitals, yielding 557 isolates that were analyzed for antimicrobial resistance genes (ARGs) and mobile genetic elements (MGEs) using genomic methods. Findings reveal significant genotypic similarities between environmental and hospital-derived strains, particularly the pandemic E. coli ST131. Environmental strains exhibited high levels of intrinsic resistance mechanisms, including mutations in porins and efflux pumps, with key ARGs such as CMY-2 and NDM-9 predominantly carried by MGEs, which facilitate horizontal gene transfer. Notably, pathogenic EPEC and EHEC strains were detected in community sewage and aquaculture farms, posing substantial public health risks. This underscores the critical role of these environments as reservoirs for multidrug-resistant pathogens and emphasizes the interconnectedness of human activities and environmental health., Competing Interests: Declaration of Competing Interest We confirmed that there are no competing interests in this study., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Zwitterionic polymers are classical antifouling polymers but they require specialized monomers that have cationic and anionic charges integrated into a single monomer. Herein, we show that pseudo-zwitterionic copolymers synthesized from a mixture of 2 monomers each having a single opposite polarity has excellent antibiofilm efficacy. We have discovered a new mixed-charge copolymer brush (#1-A) synthesized from 2 oppositely charged monomers, the anionic SPM (3-Sulfopropyl methacrylate) and the cationic AMPTMA ((3-Acrylamidopropyl) trimethylammonium chloride), that achieves broad spectrum in vitro antibiofilm effect of greater than 99% reductions against all six Gram-positive and Gram-negative bacteria tested. In the murine subcutaneous wound catheter infection models, the #1-A has good long-term anti-biofilm efficacy against MRSA and Pseudomonas aeruginosa of 3.41 and 3.19 orders respectively, outperforming previous mixed-charge copolymer coatings. We discovered a new method to choose the cationic/anionic pair combination to form the best antibiofilm copolymer brush coating by exploiting the solution polymerization kinetics disparity between the cationic and anionic monomers. We also showed that #1-A is softer and has higher hydration than the classical zwitterionic polymer. This study shows the possibility of achieving potent antibiofilm efficacy by combining readily available opposite singly charged monomers., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Cationic polymers are promising antibacterial agents because bacteria have a low propensity to develop resistance against them, but they usually have low biocompatibility because of their hydrophobic moieties. Herein, we report a new biodegradable and biocompatible chitosan-derived cationic antibacterial polymer, 2,6-diamino chitosan (2,6-DAC). 2,6-DAC shows excellent broad-spectrum antimicrobial activity with minimum inhibitory concentrations (MICs) of 8-32 μg/mL against clinically relevant and multidrug-resistant (MDR) bacteria including Listeria monocytogenes , Staphylococcus aureus , Escherichia coli , Klebsiella pneumoniae , Pseudomonas aeruginosa , and Acinetobacter baumannii . Furthermore, 2,6-DAC shows an excellent synergistic effect with various clinically relevant antibiotics proved by decreasing the MICs of the antibiotics against MDR A. baumannii and methicillin-resistant Staphylococcus aureus to <1 μg/mL. In vivo biocompatibility of 2,6-DAC is proved by a dosage of 100 mg/kg compound via oral administration and 25 mg/kg compound via intraperitoneal injection to mice; 2,6-DAC does not cause any weight loss and any significant change in liver and kidney biomarkers or the important blood electrolytes. The combinations of 2,6-DAC together with novobiocin and rifampicin show >2.4 log 10 reduction of A. baumannii in murine intraperitoneal and lung infection models. The novel chitosan derivative, 2,6-DAC, can be utilized as a biocompatible broad-spectrum cationic antimicrobial agent alone or in synergistic combination with various antibiotics.

For a myriad of different reasons most antimicrobial peptides (AMPs) have failed to reach clinical application. Different AMPs have different shortcomings including but not limited to toxicity issues, potency, limited spectrum of activity, or reduced activity in situ. We synthesized several cationic peptide mimics, main-chain cationic polyimidazoliums (PIMs), and discovered that, although select PIMs show little acute mammalian cell toxicity, they are potent broad-spectrum antibiotics with activity against even pan-antibiotic-resistant gram-positive and gram-negative bacteria, and mycobacteria. We selected PIM1, a particularly potent PIM, for mechanistic studies. Our experiments indicate PIM1 binds bacterial cell membranes by hydrophobic and electrostatic interactions, enters cells, and ultimately kills bacteria. Unlike cationic AMPs, such as colistin (CST), PIM1 does not permeabilize cell membranes. We show that a membrane electric potential is required for PIM1 activity. In laboratory evolution experiments with the gram-positive Staphylococcus aureus we obtained PIM1-resistant isolates most of which had menaquinone mutations, and we found that a site-directed menaquinone mutation also conferred PIM1 resistance. In similar experiments with the gram-negative pathogen Pseudomonas aeruginosa, PIM1-resistant mutants did not emerge. Although PIM1 was efficacious as a topical agent, intraperitoneal administration of PIM1 in mice showed some toxicity. We synthesized a PIM1 derivative, PIM1D, which is less hydrophobic than PIM1. PIM1D did not show evidence of toxicity but retained antibacterial activity and showed efficacy in murine sepsis infections. Our evidence indicates the PIMs have potential as candidates for development of new drugs for treatment of pan-resistant bacterial infections., Competing Interests: Competing interest statement: M.B.C.-P., P.T.H., W.Z., S.H.M., and B.L. are co-inventors in patent filings based on this paper., (Copyright © 2020 the Author(s). Published by PNAS.)

Carbapenem-resistant Gram-negative bacteria (GNB) are heading the list of pathogens for which antibiotics are the most critically needed. Many antibiotics are either unable to penetrate the outer-membrane or are excluded by efflux mechanisms. Here, we report a cationic block β-peptide (PAS8-b-PDM12) that reverses intrinsic antibiotic resistance in GNB by two distinct mechanisms of action. PAS8-b-PDM12 does not only compromise the integrity of the bacterial outer-membrane, it also deactivates efflux pump systems by dissipating the transmembrane electrochemical potential. As a result, PAS8-b-PDM12 sensitizes carbapenem- and colistin-resistant GNB to multiple antibiotics in vitro and in vivo. The β-peptide allows the perfect alternation of cationic versus hydrophobic side chains, representing a significant improvement over previous antimicrobial α-peptides sensitizing agents. Together, our results indicate that it is technically possible for a single adjuvant to reverse innate antibiotic resistance in all pathogenic GNB of the ESKAPE group, including those resistant to last resort antibiotics., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Carbapenem-resistant Enterobacteriaceae (CRE) can be mechanistically classified into carbapenemase-producing Enterobacteriaceae (CPE) and non-carbapenemase-producing carbapenem nonsusceptible Enterobacteriaceae (NCPCRE). We sought to investigate the effect of antecedent carbapenem exposure as a risk factor for NCPCRE versus CPE. Among all patients with CRE colonization and infection, we conducted a case-control study comparing patients with NCPCRE (cases) and patients with CPE (controls). The presence of carbapenemases was investigated with phenotypic tests followed by PCR for predominant carbapenemase genes. We included 843 unique patients with first-episode CRE, including 387 (45.9%) NCPCRE and 456 (54.1%) CPE. The resistance genes detected in CPEs were bla NDM (42.8%), bla KPC (38.4%), and bla OXA-48-like (12.1%). After adjusting for confounders and clustering at the institutional level, the odds of prior 30-day carbapenem exposure was three times higher among NCPCRE than CPE patients (adjusted odds ratio [aOR], 3.48; 95% confidence interval [CI], 2.39 to 5.09; P  < 0.001). The odds of prior carbapenem exposure and NCPCRE detection persisted in stratified analyses by Enterobacteriaceae species ( Klebsiella pneumoniae and Escherichia coli ) and carbapenemase gene ( bla NDM and bla KPC ). CPE was associated with male gender (aOR, 1.45; 95% CI, 1.07 to 1.97; P  = 0.02), intensive care unit stay (aOR, 1.84; 95% CI, 1.24 to 2.74; P  = 0.003), and hospitalization in the preceding 1 year (aOR, 1.42; 95% CI, 1.01 to 2.02; P  = 0.05). In a large nationwide study, antecedent carbapenem exposure was a significant risk factor for NCPCRE versus CPE, suggesting a differential effect of antibiotic selection pressure., (Copyright © 2019 American Society for Microbiology.)

Objectives: MDR Pseudomonas aeruginosa is a serious global threat to healthcare institutions. The mechanism by which drug resistance can be acquired is variable, but acquired carbapenemase production has been reported in P. aeruginosa. An investigation was performed to determine the rate and genomic epidemiology of New Delhi MBL (NDM) in β-lactam-non-susceptible isolates., Methods: P. aeruginosa isolates from a tertiary hospital in Singapore between January 2015 and February 2018 were investigated for the presence of NDM genes., Results: Out of 298 pan-β-lactam-non-susceptible isolates, 31 were found to be NDM positive (10.4%). WGS demonstrated that all 31 NDM-positive isolates were clonal, belonging to ST-308. blaNDM was chromosomally inserted within an integrative and conjugative element (ICE), ICETn43716385. The NDM-P. aeruginosa isolates possessed an extensive repertoire of both cell-associated [flagella, pili, alginate/biofilm, LPS, type III secretion system (T3SS) and type VI secretion system (T6SS)] and secreted virulence factors. Antibiograms revealed higher rates of drug resistance in NDM-positive isolates compared with their non-NDM counterparts. The NDM isolates remained 100% susceptible only to colistin., Conclusions: The combination of chromosomal mutations, acquired resistance genes and virulence factors likely facilitated the persistent and ongoing spread of the ST-308 clade of P. aeruginosa within the hospital. Our study illustrates the particular threat of NDM-positive P. aeruginosa in a tertiary hospital setting in the era of antimicrobial resistance., (© The Author(s) 2019. 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.)

Background: Mycobacterium avium complex prophylaxis is recommended for patients with advanced HIV infection. With the decrease in incidence of disseminated Mycobacterium avium complex infection and the availability of antiretroviral therapy (ART), the benefits of macrolide prophylaxis were investigated. This study examined the impact of macrolide prophylaxis on AIDS-defining conditions and HIV-associated mortality in a cohort of HIV-infected patients on ART., Methods: Patients from TREAT Asia HIV Observational Database (September 2015 data transfer) aged 18 years and older with a CD4 count <50 cells/mm at ART initiation were included. The effect of macrolide prophylaxis on HIV-associated mortality or AIDS-defining conditions (as a combined outcome) and HIV-associated mortality alone were evaluated using competing risk regression. Sensitivity analysis was conducted in patients with a CD4 <100 cells/mm at ART initiation., Results: Of 1345 eligible patients, 10.6% received macrolide prophylaxis. The rate of the combined outcome was 7.35 [95% confidence interval (CI): 6.04 to 8.95] per 100 patient-years, whereas the rate of HIV-associated mortality was 3.14 (95% CI: 2.35 to 4.19) per 100 patient-years. Macrolide use was associated with a significantly decreased risk of HIV-associated mortality (hazard ratio 0.10, 95% CI: 0.01 to 0.80, P = 0.031) but not with the combined outcome (hazard ratio 0.86, 95% CI: 0.32 to 2.229, P = 0.764). Sensitivity analyses showed consistent results among patients with a CD4 <100 cells/mm at ART initiation., Conclusions: Macrolide prophylaxis is associated with improved survival among Asian HIV-infected patients with low CD4 cell counts and on ART. This study suggests the increased usage and coverage of macrolide prophylaxis among people living with HIV in Asia.

Background: In May 2015, we noticed an increase in carbapenem-resistant Acinetobacter baumannii (CRAB) infections in the Medical Intensive Care Unit (MICU). To investigate this, we studied the extent of environmental contamination and subsequent onward clonal transmission of CRAB., Methods: We conducted a one-day point prevalence screening (PPS) of the patients and environment in the MICU. We screened patients using endotracheal tube aspirates and swabs from nares, axillae, groin, rectum, wounds, and exit sites of drains. We collected environmental samples from patients' rooms and environment outside the patients' rooms. CRAB isolates from the PPS and clinical samples over the subsequent one month were studied for genetic relatedness by whole genome sequencing (WGS)., Results: We collected 34 samples from seven patients and 244 samples from the environment. On the day of PPS, we identified 8 CRAB carriers: 3 who screened positive and 5 previously known clinical infections. We detected environmental contamination in nearly two-thirds of the rooms housing patients with CRAB. WGS demonstrated genetic clustering of isolates within rooms but not across rooms. We analysed 4 CRAB isolates from clinical samples following the PPS. One genetically-related CRAB was identified in the respiratory sample of a patient with nosocomial pneumonia, who was admitted to the MICU five days after the PPS., Conclusion: The extensive environmental colonization of CRAB by patients highlights the importance of environmental hygiene. The transmission dynamics of CRAB needs further investigation., Competing Interests: This study was approved by the National Health Group of Singapore Domain Specific Review Board (NHG DSRB: 2014/00046).The authors report no conflict of interest relevant to this article.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.