The role and mechanism of quorum sensing on environmental antimicrobial resistance.

As more environmental contaminants emerging, antibiotics and antibiotic resistance genes (ARGs) have caused a substantial increase of antimicrobial resistance (AMR) in environment. Quorum sensing (QS) is a bacterial cell-to-cell communication process that regulates many traits and gene expression, including ARGs and the related genes that contribute to AMR development. Herein, we summarize the role, physiology, and genetic mechanisms of bacterial QS in AMR development in the environment. First, the effect of QS on AMR is introduced. Next, the role of QS in bacterial physiological behaviors that promote AMR development, including membrane permeability, tactic movement, biofilm formation, persister formation, and small colony variants (SCVs), is systematically analyzed. Furthermore, the regulation of QS on the expression of ARGs, generation of reactive oxygen species (ROS), which affects ARGs formation, and horizontal gene transfer (HGT), which accelerates the transmission of ARGs, are discussed to reveal the molecular mechanism for AMR development. This review provides a reference for a better understanding of AMR evolution and novel insights into AMR prevention.

Platinum Nanoparticles Prevent the Resistance of Pseudomonas aeruginosa to Ciprofloxacin and Imipenem: Mechanism Insights.

Metal nanoparticles (MNPs) have recently gained extensive attention due to their broad-spectrum prospect, particularly in biomedical application. Here, we reveal that long-term exposure to platinum nanoparticles (Pt NPs) increases the susceptibility of Pseudomonas aeruginosa PAO1 to imipenem and ciprofloxacin. We exposed PAO1 to Pt NPs (a series of doses, varying from 0.125 to 35 µg/mL) for 60 days and characterized the evolved strains (ES) and compared with wild type (WT) to understand the mechanism of heightened sensitivity. We found that overexpression of oprD and downregulation of mexEF-oprN facilitate the intracellular accumulation of antibiotic, thus increasing susceptibility. Furthermore, loss-of-function mutations were discovered in regulators lasR and mexT. Cloning intact lasR from wild-type (WT) into ES slightly improves imipenem resistance. Strikingly, cloning mexT from WT into ES reverts the imipenem and ciprofloxacin resistance to the original level. Briefly, the increase of membrane permeability controlled by mexT made PAO1 greatly susceptible to imipenem and ciprofloxacin, and the decrease of quorum sensing mediated by lasR made PAO1 slightly susceptible to imipenem. Overall, these results reveal an antibiotic susceptibility mechanism from prolonged exposure to MNPs, which provides a promising approach to prevent antibiotic resistance.

The profile and persistence of clinically critical antibiotic resistance genes and human pathogenic bacteria in manure-amended farmland soils.

Introduction: Microbial contamination in farmlands is usually underestimated and understudied. Different fertilization times and manure origins might introduce and change the microorganism diversity in farmland soils and thus might influence the abundance and persistence of microbial contamination including antibiotic resistance genes (ARGs), human bacterial pathogens (HBPs), and virulence factor genes (VFGs). Methods: A 0.5-/1.5-year fertilization experiment was performed, and metagenomic sequencing was conducted to quantify microbial contamination. The resistomes of soil samples revealed that ARGs against antibiotics which were extensively used in veterinary medicine as well as clinically critical ARGs (CCARGs) persisted in manure-amended soils. Here the extended-spectrum beta-lactamase and carbapenemase bla genes, the high-level mobilized colistin resistance gene mcr, the tigecycline resistance gene tet(X), and the vancomycin resistance gene van, all of which can circumvent the defense line of these "last-resort" antibiotics were selected to investigate CCARG pollution in farm environments. Results: A total of 254 potential HBPs and 2106 VFGs were detected in soil samples. Overall, our results revealed that (1) farmland soils could serve as a reservoir of some important bla, mcr, tet(X), and van gene variants, (2) the diversity and relative abundance of HBPs and VFGs increased significantly with incremental fertilization times and were discrepant among different manureamended soils, and (3) most CCARGs and VFGs coexisted in HBPs. Disscusion: The results of this study suggested a biological risk of manure in spreading antimicrobial resistance and pathogenicity.

Insights into microbial contamination in multi-type manure-amended soils: The profile of human bacterial pathogens, virulence factor genes and antibiotic resistance genes.

Concerns regarding biological risk in environment have garnered increasing attention. Manure has been believed to be a significant source of antibiotic resistance genes (ARGs) in agricultural soil. Nevertheless, the profile of microbial contamination including ARGs, virulence factor genes (VFGs) and human bacterial pathogens (HBPs) in different manure-amended soils remain largely unknown. Here, we conducted the systematic metagenome-based study to explore changes in resistome, VFGs and HBPs in soils treated by frequently-used manures. The results revealed that many manure-borne ARGs, VFGs, and HBPs could be spreaded into soils, and their diversity and abundance were significantly different among chemical fertilizer, pig manure, chicken manure, cow dung and silkworm excrement application. A total of 157 potential HBPs accounting about 1.33% of total bacteria were detected. The main ARGs transferred from manures to soil conferred resistance to vancomycin and macrolide-lincosamide-streptogramin. The series analysis revealed positive co-occurrence patterns of ARGs-HBPs, VFGs-HBPs and ARGs-VFGs. Microbial contamination were more serious in pig manure and silkworm excrement sample than in the other samples, implying the usage of these two manures increased the risk of HBPs and dissemination of ARGs. This study confirmed the prevalence and discrepancy of resistome, VFGs and HBPs in different manure-amended soils.

Resistance elicited by sub-lethal concentrations of ampicillin is partially mediated by quorum sensing in Pseudomonas aeruginosa.

The rapid increase of antibiotic resistance is a serious challenge around the world. Antibiotics are present in various environments at sub-lethal concentrations, but how resistance emerges under sub-lethal conditions is not fully clear. In this study, we evolved Pseudomonas aeruginosa PAO1 under sub-lethal conditions, in the presence of either 15-30 µg/mL or 150-300 µg/mL of ampicillin. We found a ~ 5-6 fold increase in the minimum inhibitory concentration (MIC) among evolved isolates exposed to 15-30 µg/mL of ampicillin, and more than a 19-fold of increase in 150-300 µg/mL of ampicillin exposure. DNA sequencing revealed that mpl and ampD were frequently mutated in these resistant strains. We performed a transcriptome analysis of deletion mutations of mpl or ampD, compared to PAO1. Both showed a two-fold increase in expression of quorum sensing (QS) genes including lasR and rhlI/R; the heightened expression was positively correlated with the expression of the ampicillin resistance gene ampC. We queried if quorum sensing contributes to the increase in the ampicillin MIC. After adding the quorum quencher acylase I, the growth yield both decreased by roughly 50% for Δmpl in 2000 µg/mL of ampicillin and ΔampD in 4000 µg/mL of ampicillin. Addition of the QS signals into synthase mutants restored the higher MIC, but only for the rhlI/R circuit. This study highlights the involvement of QS in antibiotic resistance evolution, and shows the multifactorial contributors to the observed phenotypes.