Colistin resistance and the mcr-1 gene of Pseudomonas aeruginosa: Insights from Indian clinical isolates

Objective: This study aimed to determine the prevalence of colistin resistance mediated by mcr-1 in Pseudomonas ( P .) aeruginosa isolates from clinical samples. Methods: P. aeruginosa isolates were collected from various clinical specimens and tested for colistin resistance using the broth microdilution method. Isolates exhibiting resistance underwent polymerase chain reaction (PCR) screening for mcr-1. Antimicrobial susceptibility testing was performed for multiple antibiotics. Results: Sixty five clinical isolates were obtained; 10 (15.4%) were phenotypically resistant to colistin, with minimum inhibitory concentrations (MIC) values ranging from 4-16 μg/mL. The mcr-1 gene was detected in 4 (40.0%) colistin-resistant isolates, constituting 6.2% of all P. aeruginosa isolates. The highest resistance was observed for ceftazidime (70%), amikacin (60%), and ciprofloxacin (60%). Piperacillin-tazobactam was the most effective antibiotic, with 80% susceptibility. Conclusions: The presence of mcr-1 in P. aeruginosa isolates highlights the growing risk of colistin resistance beyond Enterobacteriaceae. Routine surveillance, antimicrobial stewardship, and molecular detection strategies are essential to curb further resistance spread.