ABSTRACT
Reports of transmissible colistin resistance show the importance of comprehensive colistin resistance surveillance. Recently, a new allele of the mobile colistin resistance (mcr) gene family designated mcr-9, which shows variation in genetic context and colistin susceptibility, was reported. We tested over 100 Salmonella enterica and Escherichia coli isolates with mcr-9 from the National Antimicrobial Resistance Monitoring System (NARMS) in the United States for their susceptibility to colistin and found that every isolate was susceptible, with an MIC of ≤1 μg/ml. Long-read sequencing of 12 isolates revealed mcr-9 on IncHI plasmids that were either independent or integrated into the chromosome. Overall, these results demonstrate that caution is necessary when determining the clinical relevance of new resistance genes.
FOOTNOTES
- Received 25 March 2020.
- Returned for modification 27 April 2020.
- Accepted 29 May 2020.
- Accepted manuscript posted online 8 June 2020.
Supplemental material is available online only.
- This is a work of the U.S. Government and is not subject to copyright protection in the United States. Foreign copyrights may apply.
