Subinhibitory concentrations of ciprofloxacin induce SOS response and mutations of antibiotic resistance in bacteria

Quantifying Membrane Alterations with Tailored Fluorescent Dyes: A Rapid Antibiotic Resistance Profiling Methodology

Accurate detection of bacterial antibiotic sensitivity is crucial for theranostics and the containment of antibiotic-resistant infections. However, the intricate task of detecting and quantifying the antibiotic-induced changes in the bacterial cytoplasmic membrane, and their correlation with other metabolic pathways leading to antibiotic resistance, poses significant challenges. Using a novel class of 4-aminophthalimide (4AP)-based fluorescent dyes with precisely tailored alkyl chains, namely 4AP-C9 and 4AP-C13, we quantify stress-mediated alterations in E. coli membranes. Leveraging the unique depth-dependent positioning and environment-sensitive fluorescence properties of these dyes, we detect antibiotic-induced membrane damage through single-cell imaging and monitoring the fluorescence peak maxima difference ratio (PMDR) of the dyes within the bacterial membrane, complemented by other methods. The correlation between the ROS-induced cytoplasmic membrane damage and the PMDR of dyes quantifies sensitivity against bactericidal antibiotics, which correlates to antibiotic-induced lipid peroxidation. Significantly, our findings largely extend to clinical isolates of E. coli and other ESKAPE pathogens like K. pneumoniae and Enterobacter subspecies. Our data reveal that 4AP-Cn probes can potentially act as precise scales to detect antibiotic-induced membrane damage ("thinning") occurring at a subnanometer scale through the quantification of dyes' PMDR, making them promising membrane dyes for rapid detection of bacterial antibiotic resistance, distinguishing sensitive and resistant infections with high specificity in a clinical setup.

Effects of antibiotic-induced resistance on the growth, survival ability and virulence of Salmonella enterica

Salmonella enterica is an important foodborne pathogen that constitutes a major health hazard. The emergence and aggravation of antibiotic-resistant Salmonella has drawn attention widely around the world. Conducting a risk assessment of antibiotic-resistant foodborne pathogens throughout the food chain is a pressing requirement for ensuring food safety. The growth, survival capability, and virulence of antibiotic-resistant Salmonella represent crucial biological characteristics that play an important role in microbial risk assessment. In this study, eight antibiotic-sensitive S. enterica strains were induced by Ampicillin (Amp) and Ciprofloxacin (CIP), respectively, and AMP-resistant and CIP-resistant mutants were obtained. The growth characteristics under different temperatures (25, 30, 35 °C), viability after exposure to heat (55, 57.5, 60 °C) and acid (HCl, pH = 3.0), the virulence potential (adhesion and invasion to Caco-2 cells, biofilm formation and motility) and the lethality in a model species (Galleria mellonella) were evaluated and compared for S. enterica strains before and after antibiotic exposure. The induction by AMP and CIP are likely to promote cross-antibiotic resistance to their antibiotic classes, β-lactams and quinolones, as well as some compound antibiotics. It was observed that generally the antibiotic-induction-resistant strains showed decreased growth ability and lower heat resistance, although the differences were not significant at all the conditions tested. The AMP-resistant strains were significantly less acid resistance than the sensitive and the CIP-resistant ones, while exhibiting increased biofilm formation ability. In general, the antibiotic-induced resistance did not significantly affect the motility, adherence, or invasion ability of Caco-2 cells. However, CIP-resistant strains displayed lower lethality in G. mellonella infection, whereas AMP-resistant strains did not, and even two strains improved lethality. The study of the biological characteristics of antibiotic-resistant S. enterica is essential in better understanding the microbial risks to both the food chain and human health, thereby facilitating a more accurate risk assessment.

Reactive oxygen species and uspA overexpession: an alternative bacterial response toward selection and maintenance of multidrug resistance in clinical isolates of uropathogenic E. coli

Emergence of multidrug resistance (MDR) in uropathogenic E. coli (UPEC) demands alternative therapeutic interventions. Bactericidal antibiotics at their sub-inhibitory concentration stimulate production of reactive oxygen species (ROS) that results in oxidative stress, generates mutations, and alters transcription of different genes. Sub-inhibitory concentration of antibiotics facilitates selection of highly resistant population. Universal stress protein A (uspA) overexpression in MDR-UPEC at sub-inhibitory bactericidal antibiotics concentration was investigated to explore alternative survival strategy against them. Fifty clinical UPEC isolates were screened. Minimum inhibitory concentration (MIC) against three different bactericidal antibiotics (ciprofloxacin, CIP; ceftazidime, CAZ; gentamycin, GEN) was determined by broth dilution method; ROS production by DCFDA and overexpression of uspA by real-time PCR were determined at the sub-inhibitory concentration of antibiotics. DNA ladder formation and SEM studies were performed with drug untreated and treated samples. Statistical analysis was done by Student's t test and Pearson's correlation analysis; 25 out of 50 UPEC exhibited high MIC against CIP (> 200 μg/ml), CAZ (> 500 μg/ml), GEN (> 500 μg/ml), with varied ROS production (p ≤ 0.001) in treated than untreated controls. DNA ladder formation confirmed ROS production in drug-treated samples. SEM analysis revealed unaltered cell morphology in both untreated and drug-treated bacteria. uspA was universally overexpressed in all 25 UPEC. A significant correlation (p ≤ 0.001) between ROS production and uspA overexpression was observed in 19 out of 25 MDR isolates at sub-inhibitory doses of the bactericidal antibiotics. Therefore, this study highlights an alternative strategy that the MDR isolates may acquire when exposed to sub-inhibitory drug concentration for their survival.

Antibiotic resistance genes and microcystins in a drinking water treatment plant

Problems with antibiotic resistance genes (ARGs) and secondary pollution from microcystins (MCs), caused by cyanobacterial blooms have become significant global issues. These two pollutants co-occur in drinking water treatment plants (DWTPs), but the exact relationships between them requires further clarification. Here, a high-throughput quantitative real-time PCR and enzyme-linked immunosorbent assay were used to investigate the behavior of ARGs and MCs in a practical DWTP in the first place. After the on-site investigation, the effect of MCs on the horizontal transfer of ARGs was studied under laboratory conditions, and mechanisms explored at both cellular and molecular levels. MCs could promote the spread of ARGs, especially in relatively stationary and stable environments such as biofilms. MC-LR was the most efficient microcystin subtype promoting conjugative transfer, which was 25.13 times higher than for the control group. MCs affected the horizontal transfer of ARGs by regulating a series of gene systems involved in conjugative transfer, stimulating the formation of reactive oxygen species (ROS), and increasing cell membrane permeability. This study can provide a theoretical basis for the control of ARGs and MCs in DWTPs, which is of great significance for the scientific assessment of drinking water safety.

Exposure to sub-inhibitory ciprofloxacin and nitrofurantoin concentrations increases recA gene expression in uropathogenic Escherichia coli: The role of RecA protein as a drug target

Sub-inhibitory concentrations (sub-MIC) of antimicrobial agents can lead to genetic changes in bacteria, modulating the expression of genes related to bacterial stress and leading to drug resistance. Herein we describe the impact of sub-MIC of ciprofloxacin and nitrofurantoin on three uropathogenic Escherichia coli strains. Disk-diffusion assays with different antimicrobial agents were tested to detect phenotype alterations, and quantitative real-time PCR (qRT-PCR) was performed to analyze the expression of ompF and recA genes. Significant reduction on the susceptibility to ciprofloxacin and nitrofurantoin was detected on disk diffusion test. The qRT-PCR results revealed a 1.2-4.7 increase in recA expression in all E. coli studied, while the ompF expression varied. Because RecA was pointed as an important component to the development of drug resistance, molecular docking studies were performed with three experimentally known inhibitors of this enzyme. These studies aimed to understand the inhibitory binding mode of such compounds. The results confirmed the ADP/ATP binding site as a potential site of inhibitor recognition and a binding mode based on π-stacking interactions with Tyr103 and hydrogen bonds with Tyr264. These findings can be useful for guiding the search and design of new antimicrobial agents, mainly concerning the treatment of infections with resistant bacterial strains.

Anaerobic decolorization and detoxification of cationic red X-GRL by Shewanella oneidensis MR-1

The ability of an electrochemically active bacterium, Shewanella oneidensis MR-1, to decolorize azo dye cationic red X-GRL (X-GRL) was investigated. S. oneidensis MR-1 showed a high decolorization capability for X-GRL under anaerobic conditions. The Mtr respiratory pathway was proved to be involved in the extracellular decolorization of X-GRL. The decolorization efficiency of S. oneidensis MR-1 was significantly inhibited when the initial X-GRL concentration was over 200 mg L^-1. Increasing the inoculum volume of S. oneidensis MR-1 could obviously promote the X-GRL decolorization. The 100 mg L^-1 X-GRL and 6% (v/v) inoculum volume were chosen as the optimal parameter. Under such a condition, almost all of X-GRL (100 mg L^-1) could be completely reduced after 12-h incubation at the pH range of 5.5-8.0 and temperature range of 30-40°C. Salinity in the medium also affected X-GRL decolorization. Lactate and citric acid were found to be the suitable electron donors for X-GRL decolorization. Although the genotoxicity increased slightly, the phytotoxicity of X-GRL in the decolorization process was significantly reduced by S. oneidensis MR-1.

A bacterial antibiotic resistance accelerator and applications

The systematic emergence of drug resistance remains a major problem in the treatment of infectious diseases (antibiotics) and cancer (chemotherapy), with possible common fundamental origins linking bacterial antibiotic resistance and emergence of chemotherapy resistance. The common link may be evolution in a complex fitness landscape with connected small population niches. We report a detailed method for observing bacterial adaptive behavior in heterogeneous microfluidic environment designed to mimic the environmental heterogeneity found in natural microbial niches. First, the device is structured with multiple connected micro-chambers that allow the cell population to communicate and organize into smaller populations. Second, bacteria evolve within an antibiotic gradient generated throughout the micro-chambers that creates a wide range of fitness landscapes. High-resolution images of the adaptive response to the antibiotic stress are captured by epifluorescence microscopy at various levels of the bacterial organization for quantitative analysis. Thus, the experimental setup we have developed provides a powerful frame for visualizing evolution at work: bacterial movement, survival and death. It also presents a basis for exploring the rates at which drug resistance arises in bacteria and other biological contexts such as cancer.

Prevalence of antibiotic resistance genes and bacterial pathogens in long-term manured greenhouse soils as revealed by metagenomic survey

Antibiotic resistance genes (ARGs), human pathogenic bacteria (HPB), and HPB carrying ARGs pose a high risk to soil ecology and public health. Here, we used a metagenomic approach to investigate their diversity and abundance in chicken manures and greenhouse soils collected from Guli, Pulangke, and Hushu vegetable bases with different greenhouse planting years in Nanjing, Eastern China. There was a positive correlation between the levels of antibiotics, ARGs, HPB, and HPB carrying ARGs in manures and greenhouse soils. In total, 156.2–5001.4 μg/kg of antibiotic residues, 22 classes of ARGs, 32 HPB species, and 46 species of HPB carrying ARGs were found. The highest relative abundance was tetracycline resistance genes (manures) and multidrug resistance genes (greenhouse soils). The dominant HPB and HPB carrying ARGs in the manures were Bacillus anthracis, Bordetella pertussis, and B. anthracis (sulfonamide resistance gene, sul1), respectively. The corresponding findings in greenhouse soils were Mycobacterium tuberculosis and M. ulcerans, M. tuberculosis (macrolide-lincosamide-streptogramin resistance protein, MLSRP), and B. anthracis (sul1), respectively. Our findings confirmed high levels of antibiotics, ARGs, HPB, and HPB carrying ARGs in the manured greenhouse soils compared with those in the field soils, and their relative abundance increased with the extension of greenhouse planting years.