Induction of colistin resistance and environmental toxicity assessment in Escherichia coli

This study shows that repeated exposure to subinhibitory concentrations of colistin can induce clinically relevant resistance in Escherichia coli. Using a standard laboratory strain, researchers demonstrated a substantial increase in colistin MIC (from 2 to 16 mg/L) after serial low-dose exposure, alongside phenotypic expression of the mcr-1 resistance gene, comparable to a multidrug-resistant clinical isolate. While no full resistance developed to other antibiotics, a modest increase in ceftazidime MIC persisted even after drug withdrawal. Notably, the induced resistant strain also exhibited enhanced growth, suggesting a potential fitness advantage. Overall, the findings highlight that low-level antimicrobial exposure can actively drive the emergence and maintenance of colistin resistance, reinforcing concerns about the role of subtherapeutic antibiotic pressure in the spread of AMR.