Environmental heterogeneity altered the growth fitness of antibiotic-resistant mutants and the resistance prevalence in Escherichia coli populations

Antibiotic resistance is one of the most critical issues in public health. As antibiotic-resistant bacteria emerge under certain selection pressure, their further proliferation can facilitate the prevalence and maintenance of the antibiotic resistance. Here, we investigated which environmental factors could affect the growth fitness of antibiotic-resistant Escherichia coli strains using growth competition assays. We found that when antibiotic resistance selection pressure was removed, lower temperature and nutrient limitations, especially iron (Fe) deficiency, fostered a better fitness to resistant mutants when co-cultivated with the wild type, whereas changes in pH or salinity (Na or K) did not. Moreover, the growth advantage of resistant mutants under the selection pressure was reversed by suboptimal conditions like acidic/basic pH, high K salinity, and Fe limitation. These identified key environmental factors influencing the growth fitness of antibiotic-resistant mutants provide important insights into the prediction and mitigation of antibiotic resistance in heterogeneous environments.