Prevalence, Enumeration, Serotypes, and Antimicrobial Resistance Phenotypes of Salmonella enterica Isolates from Carcasses at Two Large United States Pork Processing Plants
ABSTRACTThe objective of this study was to characterizeSalmonella entericacontamination on carcasses in two large U.S. commercial pork processing plants. The carcasses were sampled at three points, before scalding (prescald), after dehairing/polishing but before evisceration (preevisceration), and after chilling (chilled final). The overall prevalences ofSalmonellaon carcasses at these three sampling points, prescald, preevisceration, and after chilling, were 91.2%, 19.1%, and 3.7%, respectively. At one of the two plants, the prevalence ofSalmonellawas significantly higher (P< 0.01) for each of the carcass sampling points. The prevalences of carcasses with enumerableSalmonellaat prescald, preevisceration, and after chilling were 37.7%, 4.8%, and 0.6%, respectively. A total of 294 prescald carcasses hadSalmonellaloads of >1.9 log CFU/100 cm2, but these carcasses were not equally distributed between the two plants, as 234 occurred at the plant with higherSalmonellaprevalences. Forty-one serotypes were identified on prescald carcasses withSalmonella entericaserotypes Derby, Typhimurium, and Anatum predominating.S. entericaserotypes Typhimurium and London were the most common of the 24 serotypes isolated from preevisceration carcasses. TheSalmonellaserotypes Johannesburg and Typhimurium were the most frequently isolated serotypes of the 9 serotypes identified from chilled final carcasses. Antimicrobial susceptibility was determined for selected isolates from each carcass sampling point. Multiple drug resistance (MDR), defined as resistance to three or more classes of antimicrobial agents, was identified for 71.2%, 47.8%, and 77.5% of the tested isolates from prescald, preevisceration, and chilled final carcasses, respectively. The results of this study indicate that the interventions used by pork processing plants greatly reduce the prevalence ofSalmonellaon carcasses, but MDRSalmonellawas isolated from 3.2% of the final carcasses sampled.