Complete genome characterization of mcr-1-mediated colistin-resistant Escherichia coli from outpatients in Bulgaria.

INTRODUCTION

This study reports the emergence of mcr-1-mediated colistin resistance in human Escherichia coli isolates from Bulgaria.

METHODS

Three colistin-resistant E. coli isolates were obtained from outpatient urine specimens. They were subjected to PCR for detection of mcr genes and conjugation experiments. Whole-genome sequencing was employed to analyze the genomic characteristics of the isolates.

RESULTS

PCR identified mcr-1 in all isolates. In E. coli of sequence type (ST) 2067, mcr-1.1 was found on a self-transmissible IncI2 plasmid, while mcr-1.32 was chromosomal in the remaining two ST131 E. coli isolates. E. coli ST2067 co-harbored quinolones resistance mutations (gyrAD87N, gyrAS83L, parCS80I), β-lactam (blaTEM-30) and aminoglycoside (aadA1, aac(3)-IId) resistance genes.

CONCLUSION

This report further confirms the role of IncI2 conjugative plasmids in the dissemination of mcr genes. Our findings involving chromosomal mcr-1 in high-risk ST131 E. coli strains from outpatients underscores the need for enhanced surveillance and systematic screening to combat colistin resistance.