Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2009
Publication Date: 2/6/2009
Citation: Bosilevac, J.M., Guerini, M.N., Kalchayanand, N., Koohmaraie, M. 2009. Prevalence and Characterization of Salmonellae in Commercial Ground Beef in the United States. Applied and Environmental Microbiology. 75(7):1892-1900. Interpretive Summary: Salmonella and antibiotic resistant Salmonella are becoming increasingly of concern in food products. There is little information on Salmonella in commercial ground beef in the U.S. Commercially produced ground beef samples (n = 4,136) were collected over a two-year period from seven regions of the United States and analyzed for the presence of Salmonella. Only 4.2% of samples contained Salmonella, and only 0.6% were antibiotic resistant. One-half of the Salmonella isolated were of only four serotypes. DNA fingerprint analysis revealed that identical Salmonella could be found in different regions and during different months. These data indicate that Salmonella contamination of commercial ground beef is very low and suggest that attempts to track Salmonella by combinations of antibiotic susceptibility, serotype and DNA fingerprinting cannot be done in the absence of sound epidemiologic evidence.
Technical Abstract: Commercially produced ground beef samples (n = 4,136) were collected from seven regions of the United States over a 24 month period (July 2005 to June 2007) and analyzed for the presence of Salmonella using methods to examine enumerable levels and total prevalence. All Salmonella isolated were serotyped, their antibiotic susceptibilities determined and analyzed by pulsed-field gel electrophoresis (PFGE). The overall prevalence of Salmonella was found to be 4.2%. Regional monthly prevalence of Salmonella varied from 1.8% to 6.5% but was not statistically different. The most common serotypes identified were Montevideo, Anatum, Muenster and Mbandaka, with these accounting for one-half of the isolates obtained. Enumeration of Salmonella from contaminated samples showed that 94.2% were present at levels less than 2 CFU/g. The prevalence of multi-drug-resistant (MDR) Salmonella was determined to be 0.6%. The most common MDR serotypes were Dublin, Reading and Typhimurium. MDR strains had resistance to between two and ten antibiotics. There were no regional differences in the prevalence of MDR-Salmonella. PFGE analysis revealed that identical XbaI and AvrII patterns could be observed in isolates of the same serotype found in different regions and months of sampling. Comparison of Salmonella XbaI-PFGE patterns identified in this study to the Pulse-Net database found multiple matches. These data show that Salmonella prevalence in commercial ground beef is low and suggest that attempts to track Salmonella by serotype, antibiogram and PFGE cannot be done in the absence of sound epidemiologic evidence.