Detection of mcr-1 harbouring multidrug-resistant Escherichia coli from hospitalized patients and aquatic environments

INTRODUCTION: The global dissemination of colistin resistance poses a critical challenge to antimicrobial therapy amid increasing multidrug resistance. The objective of this study was to characterize the epidemiology and transmission of colistin resistance mediated by the mcr-1 gene in multidrug-resistant (MDR) Enterobacteriaceae isolated from hospitalized patients with bloodstream infections and adjacent aquatic environments. METHODOLOGY: A three-year study was conducted to collect MDR Enterobacteriaceae isolates from two distinct sources: blood samples and environmental water samples from five distinct aquatic environments adjacent to the hospital. A systematic analysis was conducted on patient demographic data, bacterial identification, antimicrobial susceptibility profiles, mcr-1 gene screening, and conjugation assays. RESULTS: A total of 159 MDR Enterobacteriaceae were isolated from blood samples, demonstrating an overall colistin resistance rate of 4.4%. Three mcr-1-harbouring Escherichia coli (E. coli) strains were identified: one from an inpatient without colistin exposure, and two from aquatic environmental sources, classified into sequence types (STs) ST10, ST131, and ST155. Conjugation experiments revealed higher transfer frequencies for environmental mcr-1-positive E. coli strains within and across genera. A comparative analysis under varying nutrient conditions identified delayed transfer kinetics in aquatic isolates. Moreover, most transconjugants exhibited levels of colistin resistance that were comparable to or surpassing donor strains, with minimum inhibitory concentrations (MICs) ranging from 4 to 16 mg/L. CONCLUSIONS: This study documents the epidemiological patterns of mcr-1-mediated colistin resistance in clinical and aquatic MDR Enterobacteriaceae. The present findings indicate the dissemination of resistance traits within aquatic environments, where persistence and amplification were observed.