Genetic traits and transmission of antimicrobial resistance characteristics of cephalosporin resistant Escherichia coli in tropical aquatic environments.

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.

Low concentration quaternary ammonium compounds promoted antibiotic resistance gene transfer via plasmid conjugation.

During the pandemic of COVID-19, the amounts of quaternary ammonium compounds (QACs) used to inactivate the virus in public facilities, hospitals and households increased, which raised concerns about the evolution and transmission of antimicrobial resistance (AMR). Although QACs may play an important role in the propagation of antibiotic resistance gene (ARGs), the potential contribution and mechanism remains unclear. Here, the results showed that benzyl dodecyl dimethyl ammonium chloride (DDBAC) and didecyl dimethyl ammonium chloride (DDAC) significantly promoted plasmid RP4-mediated ARGs transfer within and across genera at environmental relevant concentrations (0.0004-0.4 mg/L). Low concentrations of QACs did not contribute to the permeability of the cell plasma membrane, but significantly increased the permeability of the cell outer membrane due to the decrease in content of lipopolysaccharides. QACs altered the composition and content of extracellular polymeric substances (EPS) and were positively correlated with the conjugation frequency. Furthermore, transcriptional expression levels of genes encode for mating pairing formation (trbB), DNA replication and translocation (trfA), and global regulators (korA, korB, trbA) are regulated by QACs. And we demonstrate for the first time that QACs decreased the concentration of extracellular AI-2 signals, which was verified to be involved in regulating conjugative transfer genes (trbB, trfA). Collectively, our findings underscore the risk of increased disinfectant concentrations of QACs on the ARGs transfer and provide new mechanisms of plasmid conjugation.

[Antibiotics Induce Horizontal Gene Transfer of Resistance at Sublethal Concentrations].

In order to explore the conjugation of genes encoding extended-spectrum ß-lactamase (ESBL), ESBL-expressing P. aeruginosa and E.coli strains isolated from the wastewater of major hospitals in Singapore were used as donors. gfp-tagged E.coli SCC1 strains resistant to chloramphenicol (CHL) were chosen as recipients. Using response surface analysis, we detected and analyzed the induction of conjugal transfer under single-exposure and co-exposure of tetracycline (TC), sulfamethoxazole (SMZ), and ceftazidime (CAZ) at sublethal concentrations. It was found that the ESBL plasmid could be conjugal transferred from P. aeruginosa and E.coli strains to the recipient E.coli SCC1 strains at an average frequency of 0.0015 and 0.0042, respectively, without stress from inducing antibiotics, thus showing a low fitness cost and higher conjugal frequency between E.coli strains under the exposure of sub-MIC antibiotics. A significant conjugation between E.coli strains occurred under the single-exposure or co-exposure of a TC concentration of <0.03 mg·L-1 and a CAZ concentration of <0.002 mg·L-1, as inhibited by a sub-MIC level of TC. The conjugation between P. aeruginosa and E.coli strains was stimulated under the exposure of TC and CAZ with concentrations 5-times larger than the MIC, while no significant induction was detected from the sub-MIC antibiotics.

Occurrence and fate of antibiotic residues and antibiotic resistance genes in a reservoir with ecological purification facilities for drinking water sources.

Antibiotics and antibiotic resistance genes (ARGs) are emerging contaminants in surface waters, especially drinking water sources, where they can pose a risk to human health and aquatic ecology. The ecological purification facilities constructed in the drinking water reservoirs are intended to safeguard water quality. However, their ability to remove antibiotics and ARGs from the water and the presence of ARGs in such river-reservoir systems have not been comprehensively characterized yet. The occurrence, distribution and spatiotemporal variations in antibiotics, ARGs, and mobile genetic elements (MGEs) were investigated in a representative river-reservoir system in Shanghai, China. A total of 283 ARGs and 12 MGEs were detected in the water using high- throughput quantitative PCR analysis. Antibiotic residues and the absolute abundance of total ARGs and MGEs in reservoir inflow were significantly reduced when water from the river passed through the ecological purification processes in the reservoir. Antibiotics in this river-reservoir system posed only limited risks to the aquatic ecosystem and human health. No significant correlation was observed between the distribution pattern of ARGs and spatiotemporal factors. The dominant ARGs were strongly and significantly correlated with integrons. Through redundancy analysis and variation partitioning analysis, we determined that MGEs were the major driver shifting the distribution of ARGs, and the effects of environmental factors and antibiotic residues were reflected in the joint effects with MGEs. The small ecological reservoir was verified as an effective engineering to mitigate ecological risk in the drinking water source.

[Effects of recombinant human NAMPT on physiological/biochemical indexes and brain structure in mice].

OBJECTIVE: To observe the effect of recombinant human nicotinamide phosphoribosyl-transferase (NAMPT) on physiological/biochemical indexes and brain structure in mice. METHODS: Wild type human recombinant NAMPT (10, 30 and 100 µg/kg) or H247A mutant NAMPT (with very weak enzymatic activity) were administrated by intravenous injection in mice once every 3 d for 32 d. The changes of body weight, blood pressure, heart rate, serum glucose, serum total cholesterol and triglyceride were determined, and the morphology of neuron, astrocyte and microglia in hippocampus were observed. RESULTS: The injection of wild and mutated type NAMPT had no significant effect on body weight, blood pressure,heart rate, blood glucose, total cholesterol and triglyceride, and did not affect the morphology of neuron, astrocyte and microglia in hippocampus of mice. CONCLUSION: Elevation of plasma NAMPT may not induce metabolic and neuronal dysfunction in normal individual.