PATHOGEN MITIGATION IN LIVESTOCK AND RED MEAT PRODUCTION
Location: Meat Safety & Quality Research
Title: Prevalence, enumeration, serotypes, and antimicrobial resistance phenotypes of Salmonella enterica isolates from carcasses at two large United States pork processing plants
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 2012
Publication Date: March 23, 2012
Citation: Schmidt, J.W., Harhay, D.M., Kalchayanand, N., Bosilevac, J.M., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2012. Prevalence, enumeration, serotypes, and antimicrobial resistance phenotypes of Salmonella enterica isolates from carcasses at two large United States pork processing plants. Applied and Environmental Microbiology. 78(8):2716-2726.
Interpretive Summary: Each year in the United States an estimated 1 million people are sickened by foodborne Salmonella and 5% of these illnesses are attributed to pork products. Infections with multi-drug resistant Salmonella have been increasing and are more difficult to treat than infections caused by non-drug resistant Salmonella. Additionally, over 2500 types of Salmonella have been identified, but they vary in their incidence in swine and their ability to cause disease in humans. Since data on Salmonella in pork processing plants was lacking, this study examined the presence, amount, type, and antibiotic resistance of Salmonella at two U.S. pork processing plants during all four seasons of the year. Salmonella was present on 3.7% of chilled carcasses. While 44.8% of the Salmonella found were multi-drug resistant, only 1.4% of chilled carcasses were contaminated with multi-drug resistant Salmonella. This study demonstrated that antimicrobial interventions used by pork processing plants reduce the Salmonella to low levels on chilled carcasses. However, the presence of multi-drug resistant Salmonella on chilled carcasses demonstrates more research on antimicrobial interventions is needed to further reduce the risk of Salmonella contamination of pork products.
The objective of this study was to characterize Salmonella contamination on carcasses in two large U.S. commercial pork processing plants. Carcasses were sampled before scalding, after dehairing/polishing but before evisceration, and after chilling on two days in each of the four seasons. The prevalence of Salmonella on carcasses at each plant at each of these sampling locations was 97.6%, 32.0%, and 6.4%, and 84.7%, 6.3%, and 0.9%, respectively. Seasonal effects on Salmonella prevalence varied by plant and sample location, but in general prevalences were highest in winter and spring and lowest in summer and fall. The median Salmonella load on pre-scald carcasses varied by plant, ranging from 2.7 × 102 CFU/100 cm2 to 5.3 × 101 CFU/100 cm2. Large seasonal variation in the median Salmonella load on pre-scald carcasses was observed at only the plant that had higher median Salmonella load. Salmonella load was highest in spring and winter, intermediate in fall, and lowest in summer. Derby, Typhimurium, and Anatum were the predominate serotypes on pre-scald carcasses. Typhimurium and London were the most common serotypes on pre-evisceration carcasses and Johannesburg and Typhimurium were most common on final carcasses. Overall, 44.8% of the Salmonella isolates were resistant to more than three antimicrobials and the majority of these isolates were serotype Typhimurium. The results of this study indicate that hogs entering processing plants have a high incidence of Salmonella and multi-drug resistant Salmonella on their skins, with some having high loads. The interventions used by pork processing plants greatly reduced the prevalence of Salmonella on final carcasses, but Salmonella was found at low levels on a low percentage of finished, chilled carcasses.