Molecular characterization of emergence of mobile colistin resistance 1 gene-mediated colistin resistance in clinical isolates of <i>Escherichia coli</i> : A concern from North India

Objectives: Colistin is a reserved, last-resort antibiotic used to treat infections caused by multidrug-resistant Gram-negative bacilli. The mobile colistin resistance ( mcr -1) gene has been identified as a key mechanism for colistin resistance. This study aimed to investigate the association between the mcr -1 gene and colistin resistance in Escherichia coli . Methods: A total of 1,149 clinical isolates of E. coli were collected over 1 year from various clinical specimens at a tertiary care center in North India. Initial colistin susceptibility testing was performed using the automated VITEK 2 system, followed by confirmation of resistance by the gold standard broth microdilution (BMD) method. Isolates confirmed as resistant by BMD were further screened for the mcr -1 gene by real-time polymerase chain reaction. The data were analyzed using SYSTAT software version 13.2. Results: Out of the total E. coli isolates, 77.5% was obtained from hospitalized patients. Colistin resistance was initially detected in 11 (0.95%) isolates, of which 9 (0.78%) were confirmed by BMD. The mcr -1 gene was detected in three (33.3%) of these nine phenotypically confirmed resistant isolates. None of the non-resistant isolates tested harbored the mcr -1 gene. Conclusion: The emergence of colistin-resistant E. coli is a clinically important concern because it limits treatment options. Detection of mcr -1-positive isolates supports the need for continued antimicrobial surveillance, stewardship, and infection-control vigilance.