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United States Department of Agriculture

Agricultural Research Service

Research Project: Monitoring of Antimicrobial Resistance in Food Animal Production

Location: Bacterial Epidemiology and Antimicrobial Resistance

Title: Occurrence of ß-lactamase genes among non-Typhi Salmonella enterica isolated from humans, food animals, and retail meats in the United States and Canada

Authors
item Sjolund-Karlsson, Maria -
item Howie, Rebecca -
item Blickenstaff, Karen -
item Boerlin, Patrick -
item Ball, Takiyah
item Chalmers, Gabhan -
item Duval, Brea -
item Haro, Jovita -
item Rickert, Regan -
item Zhao, Shaohua -
item Cray, Paula
item Whichard, Jean -

Submitted to: Microbial Drug Resistance
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 26, 2013
Publication Date: June 1, 2013
Citation: Sjolund-Karlsson, M., Howie, R.L., Blickenstaff, K., Boerlin, P., Ball, T.A., Chalmers, G., Duval, B., Haro, J., Rickert, R., Zhao, S., Cray, P.J., Whichard, J.M. 2013. Occurrence of ß-lactamase genes among non-Typhi Salmonella enterica isolated from humans, food animals, and retail meats in the United States and Canada. Microbial Drug Resistance. 19(3):191-197.

Interpretive Summary: Salmonella is a food borne pathogen that can be acquired from ingestion of contaminated foodstuffs. Infection results in mild to severe cases of gastroenteritis in humans which often resolve within five to seven days. However, when indicated, particularly in the young, the elderly or the immunocompromised, treatment with antimicrobials may be warranted. One class of antimicrobials is especially important in treating salmonellosis, the cephalosporins, since they are well tolerated in children as well as adults. However, all bacteria develop ways to evade killing by antimicrobials through use of internal enzymes, some of which are called beta-lactamases. When bacteria evade killing they become resistant to the effect of the antimicrobial and treatment may fail. Three main groups of beta-lactamases have been identified among Salmonella and include the cephamycinases (CMY), the carbapenemases and the extended spectrum beta-lactamases (ESBLs); the most common of these in North America are the CMY beta-lactames. The most difficult bacteria to treat are those that have the ESBL beta-lactamase enzyme. In North America, the antimicrobial susceptibility of Salmonella is monitored by the U.S. National Antimicrobial Resistance Monitoring System (NARMS) and The Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS). In this study, we determined the susceptibility to cephalosporins by broth microdilution among 5,045 non-Typhi Salmonella enterica isolated from food animals, retail meats and humans. In the United States, 109 (4.6%) of isolates collected from humans, 77 (15.6%) from retail meats, and 140 (10.6%) from food animals displayed decreased susceptibility to cephalosporins (DSC). Among the Canadian retail meat and food animal isolates, 52 (13.0%) and 42 (9.4%) displayed DSC. All of these isolates were screened to determine if they carried a gene for any of the beta-lactamase groups. At least one beta-lactamase gene was detected in 74/109 (67.9%) isolates collected from humans and bla(CMY) genes were most prevalent (69/109;63.3%). Similarly, bla(CMY) genes predominated among the beta-lactamase-producing isolates collected from retail meats and food animals. ESBLs were found among three isolates originating from children who had been adopted from outside of North America. The overlap of bla(CMY) genes from the same type of Salmonella in food animals and humans suggests that food animals are reservoirs for the bacteria. Continued surveillance is warranted to monitor the emergence of beta-lactamase resistant bacteria as well as to implement mitigation strategies.

Technical Abstract: Non-Typhi Salmonella cause over 1.7 million cases of gastroenteritis in North America each year, and food-animal products are commonly implicated in human infections. For invasive infections, antimicrobial therapy is implicated. In North America, the antimicrobial susceptibility of Salmonella is monitored by the U.S. National Antimicrobial Resistance Monitoring System (NARMS) and The Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS). In this study, we determined the susceptibility to cephalosporins by broth microdilution among 5,045 non-Typhi Salmonella enterica isolated from food animals, retail meats and humans. In the United States, 109 (4.6%) of isolates collected from humans, 77 (15.6%) from retail meats, and 140 (10.6%) from food animals displayed decreased susceptibility to cephalosporins (DSC). Among the Canadian retail meat and food animal isolates, 52 (13.0%) and 42 (9.4%) displayed DSC. All isolates displaying DSC were screened for ß -lactamase genes (bla(TEM), bla(SHV), bla(CMY), bla(CTX-M), and bla(OXA-1)) by polymerase chain reaction. At least one ß-lactamase gene was detected in 74/109 (67.9%) isolates collected from humans and bla(CMY) genes were most prevalent (69/109;63.3%). Similarly, bla(CMY) genes predominated among the ß-lactamase-producing isolates collected from retail meats and food animals. Three isolates from humans harbored a bla(CTX-M) or a bla(OXA-1) gene. A bla(TEM) gene was found in 5 human, 9 retail meat, and 17 animal isolates. Although serotype distributions varied among human, retail meat, and animal sources, overlap in bla(CMY)-positive serotypes across sample sources supports meat and food-animals sources as reservoirs for human infections.

Last Modified: 7/30/2014