GENETIC CHARACTERIZATION OF PLASMID-MEDIATED COLISTIN RESISTANCE GENES IN MULTIDRUG RESISTANT KLEBSIELLA PNEUMONIAE

Abstract

Background: Antimicrobial resistance in Klebsiella pneumoniae is a growing global health concern, with rising multidrug- and carbapenem-resistant strains narrowing treatment options. Colistin remains a last-resort agent, but plasmid-mediated mobile colistin resistance (mcr) genes threaten its efficacy through horizontal transfer. Objective: To detect mcr-1 and mcr-2 genes among multidrug-resistant K. pneumoniae clinical isolates in Karachi, Pakistan. Methods: In this one-year cross-sectional study (April 2025–April 2026) at Fatima Teaching Hospital and Mohammad Ali Jinnah University, 101 clinical samples (urine, blood, sputum) were processed by culture, Gram staining, and biochemical identification. Antimicrobial susceptibility was assessed by Kirby–Bauer disk diffusion (CLSI guidelines). Colistin-resistant isolates underwent plasmid DNA extraction, PCR for mcr-1/mcr-2, gel electrophoresis, and Sanger sequencing. Results: K. pneumoniae was isolated from 50/101 samples (49.5%). All isolates were ampicillin-resistant (100%); resistance was also seen to ceftriaxone (62.0%), ciprofloxacin (62.0%), gentamicin (50.0%), and meropenem (44.0%). Colistin resistance occurred in 15/50 isolates (30.0%). mcr-1 was detected in 7/15 colistin-resistant isolates (46.7%; 14.0% of all isolates); mcr-2 was not detected. Sequencing confirmed 99.8% identity of all 7 mcr-1 amplicons with the reference plasmid sequence (GenBank MH143576.1). Conclusion: mcr-1 is circulating among colistin-resistant K. pneumoniae in Karachi, though most colistin resistant isolates (53.3%) were mcr-negative, suggesting additional chromosomal or non-mcr resistance mechanisms. Continued molecular surveillance, judicious colistin use, and strengthened infection control are needed to preserve its clinical effectiveness.