Prevalence and Antimicrobial Susceptibility of Salmonella Serovars Isolated from U.S. Retail Ground Pork

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Abstract
One objective of this study was to determine overall prevalence of Salmonella in ground pork from U.S. retail stores over three seasons including both case-ready and store-ground packages. Package types collected included: overwrap, chub, modified atmosphere packaging, and other (plastic or wax paper wrapped). Because package type represents different production systems and are subject to varied microbiological government regulation and testing methodologies, both USDA-FSIS and FDA Salmonella isolation protocols were performed. Another objective of the study was to determine serotypes and antimicrobial susceptibility profiles of the isolates obtained from the ground pork samples. Ground pork aliquots were subjected to real-time PCR. Recovered isolates were serotyped and minimum inhibitory concentration analysis to 15 antimicrobials was determined using microbroth dilution. Overall prevalence of Salmonella in ground pork from the 865 samples collected was 1.39%. Prevalence was not affected by package type (p = 0.29) nor grind location (case-ready vs. store-ground; p = 0.17). Season affected Salmonella prevalence (p = 0.05) with most isolates found during fall, and there was a tendency for geographic region to affect prevalence (p = 0.07). The USDA Salmonella isolation method was more effective at recovering isolates (p = 0.01) compared with the FDA methodology and yielded a kappa statistic of 0.26 as a measure of agreement. The serotypes isolated included: Infantis, 4,5,12:i:-, Brandenburg, Typhimurium var 5-, Seftenberg, and Johannesburg with only two packages containing multiple serotypes. No isolates were resistant to antibiotics commonly used to treat human Salmonella infections including extended spectrum cephalosporins or fluoroquinolones. Although the recovery of Salmonella from retail ground pork samples was rare, Salmonella Typhimurium (and its monophasic variant 4,5,12:i:-), which are among the most common serovars recovered from human infections, were recovered. Therefore, more effective strategies to further reduce or eliminate these pathogens from retail pork products are warranted.

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