Emergence of Colistin Resistance in Multidrug-Resistant Escherichia coli and Klebsiella Species From Central India: A Sentinel Study With the Detection of mcr-1 From Blood Isolates

Background and objectives Colistin is increasingly reserved for the treatment of severe infections caused by multidrug-resistant (MDR) Gram-negative bacteria; however, emerging resistance is progressively limiting its clinical effectiveness. Although antimicrobial resistance surveillance has expanded in several regions of India, clinical data from Central India remain limited. This study aimed to estimate the prevalence of colistin resistance among MDR Escherichia coli and Klebsiella spp. in bloodstream isolates from Central India and to determine the presence of the plasmid-mediated mcr-1 gene in colistin-resistant isolates. Methods This prospective study was conducted at a tertiary care hospital over two years. MDR E. coli and Klebsiella spp. isolated from blood cultures were subjected to colistin susceptibility testing using the agar dilution method. Colistin-resistant isolates were further analyzed for the presence of the plasmid-mediated mcr-1 gene using polymerase chain reaction. Results Colistin resistance was seen in 9.67% of E. coli and 0.47% of Klebsiella spp. of MDR isolates. A single Klebsiella pneumoniae isolate harbored the mcr-1 gene, representing the first such clinical detection from Central India. Of the four phenotypically colistin-resistant MDR isolates, three (75.0%, all E. coli) were negative for the mcr-1 gene by reverse transcription polymerase chain reaction (RT-PCR). The single mcr-1-positive isolate, a Klebsiella pneumoniae, was recovered from a surgical intensive care unit patient. No other mcr variants were tested. Interpretation and conclusions The study demonstrates the early emergence of colistin resistance in Central India, predominantly mediated through chromosomal mechanisms, with limited plasmid involvement. These findings emphasize the need for strengthened phenotypic surveillance and targeted infection control measures, particularly in critical care settings.