beta-Lactam resistance in salmonella strains isolated from retail meats in the United States by the National Antimicrobial Resistance Monitoring System between 2002 and 2006.
Ampicillin-resistant (Amp(r)) Salmonella enterica isolates (n = 344) representing 32 serotypes isolated from retail meats from 2002 to 2006 were tested for susceptibility to 21 other antimicrobial agents and screened for the presence of five beta-lactamase gene families (bla(CMY), bla(TEM), bla(SHV), bla(OXA), and bla(CTX-M)) and class 1 integrons. Among the Amp(r) isolates, 66.9% were resistant to five or more antimicrobials and 4.9% were resistant to 10 or more antimicrobials. Coresistance 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, imipenem, and cefquinome. No Salmonella producing extended-spectrum beta-lactamases was found in this study. Approximately 7% of the isolates displayed a typical multidrug-resistant (MDR)-AmpC phenotype, with resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, tetracycline, plus resistance to amoxicillin-clavulanic acid, cefoxitin, and ceftiofur and with decreased susceptibility to ceftriaxone (MIC > or = 4 microg/ml). Pulsed-field gel electrophoresis 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 bla(CMY), 47% carried bla(TEM-1), and 2.6% carried both genes. Only 15% of the isolates harbored class I integrons carrying various combinations of aadA, aadB, and dfrA gene cassettes. The bla(CMY), bla(TEM), and class 1 integrons were transferable through conjugation and/or transformation. Our findings indicate that a varied spectrum of coresistance traits is present in Amp(r) Salmonella strains in the meat supply of the United States, with a continued predominance of bla(CMY) and bla(TEM) genes in beta-lactam-resistant isolates.
Zhao
S
S
Office of Research, U.S. FDA/CVM, 8401 Muirkirk Road, Laurel, MD 20708, USA. shaohua.zhao@fda.hhs.gov
Blickenstaff
K
K
Glenn
A
A
Ayers
S L
SL
Friedman
S L
SL
Abbott
J W
JW
McDermott
P F
PF
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003227:Conjugation, Genetic; D016521:Electrophoresis, Gel, Pulsed-Field; D032023:Integrons / Q000235:genetics; D008460:Meat / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D012475:Salmonella / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D014170:Transformation, Genetic; D014481:United States; D018440:beta-Lactam Resistance; D047090:beta-Lactams / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D047090:beta-Lactams