Environmental impacts on antibiotic resistance in E. coli strains Nissle, MG1655, and W

Question: Antibiotic resistance is a critical public health issue, with extensive resources devoted to discovering new methods to combat it. Recent studies indicate that antibiotic resistance observed in laboratory conditions may differ significantly from clinical scenarios. Additionally, cross-protection against stressors such as acidity may enhance antibiotic resistance and induce cross-sensitivity. Leveraging this phenomenon could optimize antibiotic treatment strategies to reduce resistance; however, differences between experimental and clinical conditions suggest that the clinical implications of cross-sensitivity warrant further investigation. This study aims to compare the antibiotic resistance profiles of E. coli strains Nissle, MG1655, and W under varied environmental conditions that mimic the human gastrointestinal tract, including acidic environments, oxygen and nutrient limitations. Alongside minimal inhibitory concentration (MIC) determination for different antibiotic classes, we investigate the promoter activity of key stress-response pathways in response to antibiotics. This integrated approach seeks to elucidate the relationship between stress pathway activation, at the single-cell level, and antibiotic efficacy across diverse strains.

Methods: MICs for antibiotics - such as ampicillin, chloramphenicol, nalidixic acid, trimethoprim, oxytetracycline, polymyxin B, and norfloxacin - were determined for each strain under various abiotic stress conditions. Additionally, we assessed promoter activity of selected stress-response pathways through fluorescence microscopy to investigate their heterogeneous activation and correlation between stress response and antibiotic resistance.

Results: Significant variability in MIC values was observed among strains and conditions. For instance, MG1655 and Nissle exhibited increased resistance to nalidixic acid under low-nutrient conditions, while pre-exposure to acidic conditions elevated resistance to ampicillin in MG1655 and E. coli strain W.

Conclusion: This study underscores the distinct antibiotic resistance and stress-response profiles of E. coli strains Nissle, MG1655, and W under diverse environmental conditions. The findings provide insights that may refine the clinical and experimental use of E. coli strains, support targeted antimicrobial strategies, and enhance understanding of bacterial stress responses.