Evolution Towards Antibiotic Resistance Induced by Environmental-Level Pesticides

Antibiotic resistance is one of the most challenging issues in public health. One way of bacteria gaining antibiotic resistance is the selection of de novo mutants under certain selection pressures. Antibiotics at low concentrations and some non-antibiotic chemicals can act as selection pressures in selecting antibiotic resistance. Herein, we investigated whether exposure to pesticides also has an impact on antibiotic resistance development. We designed evolutionary experiments with a susceptible Escherichia coli strain being exposed to pesticides only, and co-exposed to ampicillin and pesticides for 500 generations. Resistant mutants were randomly picked and their minimal inhibitory concentrations (MICs) were tested. Higher MICs were found in resistant mutants when exposed to high-level pesticides and co-exposed to ampicillin and pesticides comparing to control groups. The resistant mechanism of these mutants was identified by whole-genome sequencing. The main conclusions are: (1) pesticides alone could induce streptomycin resistance when present at high concentrations; and (2) pesticides at environmental concentrations and low sub-MIC levels of ampicillin could exert synergistic effect in developing antibiotic resistance.