Screening for the presence of mcr-1/mcr-2 genes in Shiga toxin-producing Escherichia coli recovered from a major produce-production region in California

Authors: Mavrici, Daniela; Yambao, Jaszemyn; Lee, Bertram; Quinones, Beatriz; He, Xiaohua

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2017
Publication Date: 11/8/2017
Citation: Mavrici, D., Yambao, J.C., Lee, B.G., Quinones, B., He, X. 2017. Screening for the presence of mcr-1/mcr-2 genes in Shiga toxin-producing Escherichia coli recovered from a major produce-production region in California. PLoS One. 12(11):e0187827. https://doi.org/10.1371/journal.pone.0187827.
DOI: https://doi.org/10.1371/journal.pone.0187827

Interpretive Summary: The new superbug that confers resistance to the antibiotic colistin has been found in the United States for more than a year. This discovery is of great concern because colistin is used as a last-resort drug to treat patients with multi-drug resistant infections. It is critical to timely evaluate the prevalence of this resistance among human pathogens in order to prevent it further spreading. In this study, the occurrence of the plasmid-borne mcr-1 and mcr-2 genes that determine the colistin resistance were investigated by two different PCR methods using 1000 isolates collected from animal, produce, and the environment in an agricultural production region in California. Our results indicate that all isolates were negative for mcr genes, suggesting zero or very low percent of colistin-resistance strains present in STEC isolated from the major fresh produce fields in California. This could be due to the small sample size or a good control on use of colistin in this region.

Technical Abstract: The rapid spreading of polymyxin E (colistin) resistance among bacterial strains through the horizontally transmissible mcr-1 and mcr-2 plasmids has become a serious concern. The emergence of these genes in Shiga toxin-producing Escherichia coli (STEC), a group of human pathogenic bacteria was even more worrisome, urging us to investigate the prevalence of mcr genes among STEC isolates. A total of 1000 STEC isolates, recovered from livestock, wildlife, produce and other environmental sources in a major production region for leafy vegetables in California during 2006-2014, were screened by PCR for the presence of plasmid-borne mcr-1 and mcr-2. All isolates tested yielded negative results, indicating if any, the occurrence rate of mcr-1/mcr-2 among STEC was very low in this agricultural region. This study provides valuable information such as sample size needed and methodologies for future surveillance programs of antimicrobial resistance.