Journal article

Publication year: 2018

Journal: Journal of Clinical Microbiology

Volume number: 56

Issue number: 5

ISSN: 0095-1137

eISSN: 1098-660X

Open access status: Green

DOI Link: https://doi.org/10.1128/JCM.01950-17

Publisher: American Society for Microbiology

Abstract: 
The plasmid-located colistin resistance gene mcr-1 confers low-level resistance to colistin, a last-line antibiotic against multidrug-resistant Gram-negative bacteria. Current CLSI-EUCAST recommendations require the use of a broth microdilution (BMD) method with cation-adjusted Mueller-Hinton (CA-MH) medium for colistin susceptibility testing, but approximately 15% of all MCR-1 producers are classified as sensitive in that broth. Here we report on an improved calcium-enhanced MuellerHinton (CE-MH) medium that permits simple and reliable determination of mcr-1containing Enterobacteriaceae. Colistin susceptibility testing was performed for 50 mcr-1-containing Escherichia coli and Klebsiella pneumoniae isolates, 7 intrinsically polymyxin-resistant species, K. pneumoniae and E. coli isolates with acquired resistance to polymyxins due to mgrB and pmrB mutations, respectively, and 32 mcr-1negative, colistin-susceptible isolates of Acinetobacter baumannii, Citrobacter freundii, Enterobacter cloacae, E. coli, K. pneumoniae, and Salmonella enterica serovar Typhimurium. A comparison of the colistin MICs determined in CA-MH medium and those obtained in CE-MH medium was performed using both the BMD and strip-based susceptibility test formats. We validated the data using an isogenic IncX4 plasmid lacking mcr-1. Use of the CE-MH broth provides clear separation between resistant and susceptible isolates in both BMD and gradient diffusion assays; this is true for both mcr-1-containing Enterobacteriaceae isolates and those exhibiting either intrinsic or acquired colistin resistance. CE-MH medium is simple to prepare and overcomes current problems associated with BMD and strip-based colistin susceptibility testing, and use of the medium is easy to implement in routine diagnostic laboratories, even in resource-poor settings.

Harvard Citation style: Gwozdzinski, K., Azarderakhsh, S., Imirzalioglu, C., Falgenhauer, L. and Chakraborty, T. (2018) An Improved Medium for Colistin Susceptibility Testing, Journal of Clinical Microbiology, 56(5), Article e01950-17. https://doi.org/10.1128/JCM.01950-17

APA Citation style: Gwozdzinski, K., Azarderakhsh, S., Imirzalioglu, C., Falgenhauer, L., & Chakraborty, T. (2018). An Improved Medium for Colistin Susceptibility Testing. Journal of Clinical Microbiology. 56(5), Article e01950-17. https://doi.org/10.1128/JCM.01950-17