Escherichia coli O157:H7 Raw sequence reads

Antibiotic resistance is a major threat to public health globally. To combat antibiotic resistance, it is essential to identify selective pressures in the environments which could promote the evolution of antibiotic resistant bacteria. We previously identified pesticides as co-stressors to promote the emergence of more resistant mutants in an Escherichia coli K-12 strain. Nevertheless, it is not clear whether this type of synergistic effects could be exerted to other bacterial genera. Here, we conducted long-term evolutionary experiments by exposing bacterial strains of different genera, including E. coli O157:H7, P. putida, and S. epidermidis, to pesticides at environmentally relevant concentrations and low-level streptomycin. The results suggest that the synergistic effect of the coexposure to pesticides and streptomycin on the development of stronger resistance was specific to E. coli populations. Significant increase (> 40-fold) in streptomycin resistance was observed for coexposed E. coli O157:H7 populations, similar to that observed for another two E. coli strains, whereas the coexposure did not promote stronger streptomycin resistance for the other two bacterial populations. We have identified distinct genetic mutations developed in the coexposed E. coli O157:H7 populations compared to those developed under the antibiotic-only exposure. The pesticide and streptomycin coexposure induced streptomycin target modifications, such as rpsL mutations, which can lead to high-level phenotypic resistance. It seems a common mechanism of the evolved phenotypic resistance among different E. coli strains by the exposure to pesticide co-stressors. Other de novo mutations that likely conferred stronger resistance occurred in genes related to stress response, motility, and phage proteins. These findings imply a higher risk of strong and inheritable antibiotic resistance of pathogenic E. coli in certain environments where pesticides and antibiotics coexist.