| Nontyphoid Salmonella (NTS) are a major cause of food borne illness throughout the world. Although most cases are self-limiting, potentially fatal invasive septicemic disease may develop in some individuals---especially children, and the immunocompromised. These bacteria are also a significant problem in veterinary medicine, especially in dairy cattle, and cause a similar spectrum of clinical disease to that seen in humans. The plasmid-encoded cephamycinase blaCMY-2, is the predominant cause of third generation cephalosporin resistance in U.S. NTS isolated from humans and cattle. Third generation cephalosporins have broad clinical applications in both human and veterinary medicine, including the treatment of salmonellosis in children, therefore understanding the basis for the selection and dissemination of blaCMY-2 plasmids could extend the utility of these lifesaving drugs. BlaCMY-2 bearing plasmids, in addition to conferring beta-lactam resistance in NTS, also serve the same function in some commensal Escherichia coli isolated from cattle. Because plasmids are frequently horizontally transferable across microbial genera, commensal bacteria, such as Escherichia coli may serve as reservoirs forblaCMY-2 plasmids for NTS. This work focused on (1) the molecular epidemiology of blaCMY-2 plasmids and their respective Escherichia coli and Salmonella hosts isolated from Pacific Northwestern Cattle, and (2) the role of ceftiofur, a commonly used veterinary cephalosporin antimicrobial drug, on the selection and dissemination of blaCMY-2 mediated resistance in the bovine niche. |
