Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2004
Publication Date: 8/20/2004
Citation: Gray, J.T., Hungerford, L.L., Cray, P.J., Headrick, M. 2004. Extended-spectrum cephalosporin resistance in Salmonella enterica isolates of animal origin. Antimicrobial Agents and Chemotherapy. 8:3179-3181. Interpretive Summary: Third generation cephalosporins are an important class of antibiotics used to treat serious infections including infection with Salmonella bacteria. Salmonella are ubiquitous and have been recovered from insects and nearly all vertebrate species, especially humans, livestock and companion animals. We identified a group of Salmonella isolates which were resistant to third generation cephalosporins during routine sampling of animal populations in the United States. Of the 5709 total isolates, 112 (2%) were resistant to 3rd generation cephalosporins. There were 21 Salmonella strains identified among the cephalosporin resistant isolates, the most common was typhimurium-copenhagen (n=28), typhimurium (n=18), and bredeney (n=21). Isolates were recovered from nearly all domestic animals including cattle (n=34), swine (n=10), chickens (n=11), horses (n=16), cats (n=16), dogs (n=4) and turkeys (n=32). The majority of these isolates were resistant to multiple antibiotics. Of the 112 isolates, 91% (n=102) were resistant to 8 or more of 17 antibiotics tested and 70% (n=71) of these isolates were resistant to 10 or more antibiotics tested. All cephalosporin resistant isolates were examined for cephalosporin resistance genes and 100% of isolates were found to be positive for two genes responsible for cephalosporin resistance. This information identifies and characterizes a new group of Salmonella that may be important in public and animal health. These data can be used to identify cephalosporin resistant Salmonella and are useful to scientists and commodity group experts as they develop new prevention and control methods.
Technical Abstract: Resistance to 3rd generation cephalosporins has emerged as a concern in Salmonella isolates from humans and animals. We examined a group of cephalosporin resistant isolates from various animal sources submitted to the National Antimicrobial Resistance Monitoring System. Out of a general Salmonella population of 5709 isolates, one hundred twelve isolates were identified each of which had minimum inhibitory concentrations to Ceftiofur, and Cephalothin of >64 and >32, respectively. There were 21 Salmonella serotypes identified among the cephamycin resistant isolates with the most common being typhimurium-copenhagen (28), typhimurium (18), and bredeney (21). Isolates were recovered from nearly all domestic species including cattle (34), swine (10), chickens (11), horses (16) cats (5) dogs (4) and turkeys (32). The majority of these isolates were resistant to multiple antimicrobials. Of the 112 isolates 91% were found to be resistant to 8 or more of 17 antimicrobials tested and 70% of the isolates were resistant to 10 or more antimicrobials tested as compared to 0.18% of the general population of Salmonella isolates tested (n=5709) having resistance to 10 or more antimicrobials. One hundred percent (112) of the isolates were resistant to amoxicillin-clavulanic acid. The most common non beta-lactam resistances were tetracycline (92%), streptomycin (91%), kanamycin (82%), sulfamethoxazole (90%), ticarcillin (72%), and chloramphenicol (70%). All isolates were examined for cephalosporin resistance mechanisms; 100% of isolates were found to have an AmpC like beta lactamase and tested positive for the blaCMY gene by PCR. Resistance of Salmonella strains to 3rd generation cephalosporins is a concern and these data indicate the predilection of these strains to acquire multiple antimicrobial resistances.