Prevalence of the colistin resistance gene mcr-1 in colistin-resistant Escherichia coli and Klebsiella pneumoniae isolated from humans in Thailand

Abstract

© 2018 International Society for Chemotherapy of Infection and Cancer Objectives: Historically, colistin has been considered a last-line therapeutic option against multidrug-resistant Gram-negative bacterial infections. However, chromosomally-encoded and plasmid-mediated colistin resistance is increasingly being reported worldwide. Spread of the plasmid-borne colistin resistance gene mcr-1 is of great concern since it can be transferred between bacteria. The aim of this study was to investigate the prevalence of mcr-1 in Escherichia coli and Klebsiella pneumoniae collected from human clinical specimens in Thailand during 2014–2017. Methods: Minimum inhibitory concentrations (MICs) of colistin were determined by the broth microdilution method for 317 non-duplicate Enterobacteriaceae clinical isolates (37 E. coli and 280 K. pneumoniae). All isolates were screened for the mcr-1 gene by PCR. Results: The colistin MIC 50 , MIC 90 and MIC range for the 37 E. coli isolates were 0.5, 8 and 0.5–32 mg/L, respectively. The mcr-1 gene was detected in 11 E. coli isolates (29.7%). Escherichia coli harbouring the mcr-1 gene had a colistin MIC range of 4–32 mg/L. The colistin MIC 50 , MIC 90 , and MIC range for the 280 K. pneumoniae isolates were 32, >128, and 0.25 to >128 mg/L, respectively. The mcr-1 gene was detected in 4 K. pneumoniae isolates (1.4%). Klebsiella pneumoniae harbouring the mcr-1 gene had a colistin MIC range of 4–64 mg/L. Conclusions: This is the first report on the prevalence of the mcr-1 gene in colistin-resistant E. coli and K. pneumoniae isolated from humans in Thailand. These data provide added insight into the mechanism of colistin resistance among Enterobacteriaceae pathogens.