From Survivors to Superbugs: Evaluating AMR Trajectories in Wastewater Bacteria Under Sequential Chlorination Stress
Description
The potential for chlorine disinfection to cause or increase antimicrobial resistance (AMR) in bacterial isolates obtained from urban sewage treatment plants (STPs) in Gujarat, India, is thoroughly examined in this dataset. From the pre-chlorination stage of municipal wastewater, a total of 19 bacterial strains, 11 Gram-positive and 8 Gram-negative were isolated. These strains are wild-type organisms that can withstand environmental stress before being formally disinfected. Using the Kirby-Bauer disk diffusion technique, these isolates were subjected to antimicrobial susceptibility testing (AST). The Clinical and Laboratory Standards Institute (CLSI) M100-S25 criteria were followed in the interpretation of the zone of inhibition (ZOI) results. In order to evaluate the isolates inherent resistance profiles, baseline ZOI data were first gathered. The same isolates were then subjected to 20 ppm of in vitro chlorination. A panel of 31 antibiotics from important pharmacological classes, such as β-lactams, aminoglycosides, tetracyclines, glycopeptides, macrolides, fluoroquinolones, antifolates, and others, were then tested for post-exposure susceptibility to assess changes in antibiotic response. By comparing ZOI values before and after chlorination, the dataset finds several cases in which isolates showed a noticeable decrease in antibiotic sensitivity. Indicating potential stress induced selection, mutation, or activation of resistance genes, a number of isolates moved from the susceptible (S) to the intermediate (I) or resistant (R) categories. To find patterns and connections between antibiotic classes and the emergence of resistance, visualization methods such bar graphs, density plots, antibiogram heatmaps, and correlation matrices were used. Antibiotics such as ampicillin, ofloxacin, tetracycline, clindamycin, and chloramphenicol showed particularly noteworthy category changes, with Gram-positive isolates exhibiting a more marked reaction in many instances. The findings raise significant concerns regarding the methods used to disinfect wastewater today as they imply that even repeated or sub-lethal exposure to chlorine might alter bacterial resistance phenotypes. Researchers looking at the relationship between ambient AMR dynamics and disinfection procedures may find this well selected dataset to be a useful resource. In order to reduce the unintentional spread of resistance characteristics in environmental microbiomes, it helps upcoming risk evaluations, surveillance initiatives, and the improvement of wastewater treatment procedures.
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Steps to reproduce
Sample Collection: Collect raw municipal wastewater samples from sewage treatment plants (STPs) before chlorination stage. Ensure aseptic handling; transport samples in sterile containers at 4 °C to the laboratory. Isolation of Bacteria: Perform serial dilutions of wastewater. Plate on nutrient agar, MacConkey agar, and selective media to recover diverse Gram positive and Gram negative bacteria. Incubate at 35–37 °C for 24–48 h. Pick morphologically distinct colonies; purify by streaking until single colony isolates are obtained. Maintain cultures on slants and glycerol stocks. Baseline Antimicrobial Susceptibility Testing (AST): Use Kirby–Bauer disk diffusion method on Mueller–Hinton agar. Prepare inoculum adjusted to 0.5 McFarland standard. Place antibiotic discs (panel of 31 drugs across major classes: β lactams, aminoglycosides, tetracyclines, macrolides, glycopeptides, fluoroquinolones, antifolates, etc.). Incubate plates at 35 °C for 18–24 h. Measure Zone of Inhibition (ZOI) in mm. Interpret results using CLSI M100 S25 guidelines (susceptible, intermediate, resistant). Chlorination Stress Exposure: Prepare chlorine solution at 20 ppm (sodium hypochlorite standard). Expose bacterial isolates in vitro for defined contact time (e.g., 30 min). Neutralize residual chlorine with sodium thiosulfate. Recover treated cells by plating on nutrient agar. Post Exposure AST: Repeat Kirby–Bauer AST with the same antibiotic panel. Record ZOI values post chlorination. Compare with baseline values to detect phenotypic shifts (S → I → R). Data Recording & Organization: Tabulate results isolate wise: Antibiotic class, concentration, ZOI (mm), CLSI interpretation. Maintain separate antibiograms for each isolate (19 total: 11 Gram positive, 8 Gram negative). Note significant category changes (e.g., ampicillin, tetracycline, clindamycin, chloramphenicol, ofloxacin). Visualization & Analysis: Generate: Bar graphs: ZOI distributions pre vs post chlorination. Density plots: resistance frequency shifts. Heatmaps: antibiogram profiles across isolates. Correlation matrices: co resistance patterns among antibiotic classes. Highlight isolates showing marked resistance induction. Quality Control: Include reference strains (e.g., E. coli ATCC 25922, S. aureus ATCC 25923). Validate chlorine concentration with DPD colorimetric method. Ensure reproducibility by triplicate testing. Key Reproducibility Notes: Follow CLSI M100 S25 strictly for disc diffusion interpretation. Use consistent chlorine exposure conditions (20 ppm, same contact time). Record both raw ZOI values and categorical interpretations. Maintain sterile technique to avoid contamination. Document metadata: isolate ID, Gram reaction, source STP, date/time. Outcome: By following these steps, you will generate: Baseline vs post chlorination antibiograms for 19 isolates. Evidence of stress induced AMR shifts. Dataset suitable for risk assessment, surveillance, and wastewater treatment optimization.
Institutions
- Institute of Science and Technology for Advanced Studies and Research