Submitted to: Emerging Infectious Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2010
Publication Date: 11/19/2010
Citation: Karlsson, M.S., Howie, R.L., Rickert, R., Krueger, A., Tran, T., Zhao, S., Ball, T.A., Haro, J.H., Pecic, G., Joyce, K., Cray, P.J., Whichard, J., Mcdermott, P. 2010. Plasmid-mediated quinolone resistance among non-typhi Salmonella enterica isolates, USA. Emerging Infectious Diseases. 16(11):1789-1791. Interpretive Summary: Food borne illness is often associated with food of animal origin. In particular, foods contaminated with Salmonella can cause cramping and diarrhea. Most often food borne illness is self-limiting and does not require treatment with antibiotics. However, when antibiotics are needed, bacteria that have developed resistance to the antibiotic may be difficult to treat. Salmonella can acquire resistance to antibiotics through transfer of small pieces of DNA from one bacterium to another on mobile genetic elements called plasmids. Certain plasmids can move between bacteria more readily than others. In this study we looked for a plasmid that carried a specific gene that made the bacteria resistant to a newer antibiotic called quinolones. Bacteria from human, retail meat, and animals were tested for the presence of this plasmid/gene combination. Only bacteria originating from humans were found to harbor this combination. This is important information for physicians, veterinarians and scientists as humans and animals are treated with quinolone antibiotics. It further indicates that we must continue surveillance of this type of resistance and develop ways to ensure that resistance does not increase.
Technical Abstract: We determined the prevalence of plasmid-mediated quinolone resistance mechanisms among non-Typhi Salmonella (NTS) spp. isolates from humans, food animals, and retail meat in the United States in 2007. Fifty-one (2.4%) of human isolates (n=2165), 5 (1.6%) of isolates from animal isolates (n=1915) and 5 (1.6%) of retail meat isolates (n=320) showed decreased susceptibility to ciprofloxacin. Of these, none of the isolates originating from animals or retail meats harbored either an aac(6’)lb-cr or a qnr gene. Of the 51 human isolates, six (11.8%) isolates harbored an aac(6’)lb-cr (n=1) or a qnr (n=5) gene. Five serotypes were identified among the six isolates including one each of Thompson, Corvalis, Enteritidis, and Beaudesert; the two remaining isolates were identified as Typhimurium. The aac(6’)lb-cr gene was harbored by Thompson while Enteritidis and Beaudesert harbored a qnrB2 and qnrB19 gene, respectively. The most prevalent gene was qnrS1 harbored by both Typhimurium isolates as well as the Corvalis isolate. The observation that only human isolates harbored this plasmid-mediated mechanism requires further investigation.