Prevalence of Colistin-resistant Gram-negative Isolates Carrying the mcr-1 Gene among Patients Visiting a Tertiary Care Center

INTRODUCTION: Gram-negative isolates harboring mobilized colistin resistance (mcr-1) gene are a great threat to human health. They have been reported worldwide among various bacterial isolates. This work aimed to study the prevalence of colistin resistance among Gram-negative bacteria and the incidence of mcr-1 gene among these isolates. METHODS: A descriptive cross-sectional study was done at a tertiary care center from June 2016 to February 2017. An ethical approval was taken from review board of the Nepal Health Research Council (Reg. no: 274/2016). Convenience sampling was used. The data was collected and analyzed using Microsoft Excel 2010 and Statistical Package for Social Sciences (SPSS) Version 16 . Point estimate at 95% Confidence Interval was calculated along with frequency and proportion for binary data. RESULTS: Among 485 gram-negative isolates, only 13 (2.68%) (1.26-6.62 at 95% Confidence Interval) isolates were colistin-resistant and mcr-1 was present in two isolates. Predominant colistin-resistant isolates were E. coli 6 (4.1%), Enterobacter spp 2 (2.81%), and Acinetobacter spp 2 (2.81%). A high level of colistin-resistance was noted in 4 (30.7%) isolates as indicated by the very high value of colistin MIC (>256 μg/ml). ICU was the major site of isolation of colistin-resistant and mcr-1 positive pathogens. The majority of colistin-resistant isolates were highly drug-resistant and were sensitive only to polymyxin B. Antibiotics like imipenem, amikacin, gentamicin, aztreonam, ciprofloxacin, and piperacillin-tazobactam were effective for few of these isolates. CONCLUSIONS: Though the prevalence of mcr-1 gene was low among colistin-resistant gram-negative isolates, the resistant pattern was quite alarming as these isolates were highly drug-resistant.