Infections with Salmonella and Shiga-toxin producing E. coli harboring a new mobile colistin resistance gene, mcr-9 – United States, 1999-2019 Open Access
Ryan, Matthew T. (Spring 2020)
Abstract
Background: Colistin is an antibiotic in the polymyxin class that is important for the treatment of patients with certain severe multidrug-resistant (MDR) infections such as carbapenamase resistant Enterobacteriaceae and is referred to as an antibiotic of last resort. In May of 2019, a new mobile (plasmid mediated) colistin resistance gene, mcr-9, was reported in a Salmonella Typhimurium isolate from a U.S. resident of Washington who had no international travel. Nine mcr genes that confer transmissible colistin resistance have been identified since 2015, however most have been associated with international travel. We describe the timeline, geographic distribution, and exposure history of mcr-9 isolates.
Methods: In this ongoing retrospective analysis of surveillance data (n=141), all ~24,000 whole genome assemblies from enteric pathogen isolates in CDC’s surveillance databases were screened for resistance determinants, including mcr-9. Additional mcr-9(+) isolates were identified through the NCBI pathogen detection pipeline and were rescreened for confirmation. State health departments submitted de-identified patient interviews containing pertinent epidemiologic information. Due to variance in questionnaire language by state, variables of interest were standardized before data compilation.
Results: As of December 31st, 2019, 137 patients with mcr-9(+) nontyphoidal Salmonella (NTS) infections and four with mcr-9(+) Shiga toxin-producing E. coli infections in 36 states were identified. Isolates were collected from 1999 to 2019. Twenty-three states had three or more cases of mcr-9(+) enteric infections. The median age of cases was 21 years (IQR=47.5, 25th percentile=5, 75th percentile=52.5); 50% were male. Of those with information on hospitalization and travel, 27% were hospitalized and 13% traveled internationally in the 7 days before their illness. Of those with exposure information, 51% reported poultry consumption, 58% reported consuming unbottled water, and 34% reported dog exposure, which were all the highest in their respective categories (food, water, animal). The most common NTS serotypes were I 4,[5],12:i- (50%), Typhimurium (11%), Heidelberg (10%).
Conclusions: We identified mcr-9 isolates in the U.S. from as early as 1999; however, it is likely that mcr-9 was circulating domestically before that. Most patients acquired these infections domestically, likely via consumption of poultry or contact with untreated water or through animal exposure. A study between these patients and a comparable general population is needed to assess mcr-9 risk factors for the acquisition of mcr-9.
Table of Contents
Introduction………………………………………………………………………………..1
Methods……………………………………………………………………………………..4
Results………………………………………………………………………………….......8
Discussion…………………………………………………………………………….…..12
References………………………………………………………………………………...18
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Infections with Salmonella and Shiga-toxin producing E. coli harboring a new mobile colistin resistance gene, mcr-9 – United States, 1999-2019 () | 2020-04-27 14:57:56 -0400 |
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