Abstract
Background and Objective: As bacterial resistance to colistin and polymyxin B escalates, prompt detection of resistant strains is necessary, to control the outbreak. This study evaluates possible extremely colistin resistance Enterobacteriaceae clinical isolates from ICU patients and determines their carriage of DNA mcr-1 resistant gene. Also to compare the resistance pattern between colistin and polymyxin B. Materials and Methods: Ninety-one gram-negative bacterial isolates were used, comprising of Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Shigella flexneri, which were clinical isolates that are part of patient care. Vitek compact 2 automated system was used for bacterial ID confirmation. Disc diffusion, Etest and Broth Microdilution (BMD) were used to assess resistance status. Chromosomal mcr-1 gene carriage was investigated. Results: Vitek compact 2 automated system analysis indicated 96% resistance, disc diffusion detecting 89% and Etest with 96% for the isolates. Comparison between disc diffusion and Etest revealed that very major errors (false sensitivity) were encountered with 5 E. coil isolates with zones of inhibition >= 14 mm whereas, Etest MIC ranged between 8-20 mu g mL(-1). None of the K pneumoniae and P. aeruginosa isolates were susceptible to colistin by Etest. Four E. coil isolates tested positive for the mcr-1 gene with 309 bp (2), 500 bp and 1 kb, respectively. Pseudomonas aeruginosa had genes with more than 2 kb amplicons. Conclusion: BMD assay revealed a similar resistance pattern between colistin and polymyxin B. Our findings further confirm the presence of chromosomal mcr-1 genes in the region of study, suggesting timely surveillance to contend the spread of resistance.