Beta-Lactam Resistance in Salmonella Isolated from Retail Meats in the United States: National Antimicrobial Resistance Monitoring System (NARMS): 2002-2006. Applied and environmental microbiology [Appl Environ Microbiol] Journal article

Ampicillin-resistant (AMP(R)) Salmonella (n=344) representing 32 serotypes isolated from retail meats from 2002-2006 were tested for susceptibility to 21 other antimicrobial agents, and screened for the presence of five beta-lactamase gene families (blaCMY, blaTEM, blaSHV, blaOXA, blaCTX-M) and class 1 integrons. Among the AMP(R) isolates, 66.9% were resistant to >/=5 antimicrobials and 4.9% to >/= 10 antimicrobials. Co-resistance to other beta-lactams was noted for amoxicillin/clavulanic acid (55.5%), ceftiofur (50%), cefoxitin (50%), and ceftazidime (24.7%), whereas less than 5% of isolates were resistant to piperacillin/tazobactam (4.9%), cefotaxime (3.5%), ceftriaxone (2%), and aztreonam (1.2%). All isolates were susceptible to cefepime, imipemen and cefquinome. No Salmonella producing extended-spectrum beta-lactamases (ESBL) was found in this study. Approximately 7% of the isolates displayed a typical MDR-AmpC phenotype, resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, tetracycline (ACSSuT), plus resistance to amoxicillin/clavulanic acid, cefoxitin, and ceftiofur with decreased susceptibility to ceftriaxone (MIC >/=4ug/ml). PFGE results showed that several MDR clones were geographically dispersed in different types of meats throughout the five sampling years. Additionally, 50% of the isolates contained blaCMY, 47% carried blaTEM-1 and 2.6% carried both genes. Only 15% of the isolates contained class I integrons carrying various combinations of aadA, aadB and dfrA gene cassettes. The blaCMY, blaTEM and class 1 integrons were transferable through conjugation and/or transformation. Our findings indicate a varied spectrum of co-resistance traits is present in AMP(R) Salmonella in the U.S. meat supply, with a continued predominance of blaCMYand blaTEM genes in beta-lactam resistant isolates.

Applied and environmental microbiology [Appl Environ Microbiol]