Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/28/2003
Publication Date: 7/1/2003
Citation: WONDERLING, L.D., PEARCE, R., WALLACE, F.M., CALL, J.E., TAMPLIN, M.L., LUCHANSKY, J.B. USE OF PULSED-FIELD GEL ELECTROPHORESIS TO CHARACTERIZE THE HETEROGENEITY AND CLONALITY OF SALMONELLA ISOLATES OBTAINED FROM THE CARCASS AND FECES OF SWINE AT SLAUGHTER. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. 2003. V. 69. p. 4177-4182. Interpretive Summary: In a previous study, carcass and fecal samples were recovered from swine at a collaborating slaughtering facility over a two month period in the spring of 2000. Salmonella were isolated from samples obtained at the post-kill and post-chiller steps of processing to determine the effectiveness of the processing controls designed to limit carcass contamination, and to investigate the prevalence of Salmonella in swine at slaughter. The Salmonella recovered from this study comprised 581 isolates that could be traced back to an individual animal and date of isolation. In the present study, these Salmonella isolates were analyzed by pulsed-field gel electrophoresis (PFGE), a DNA fingerprinting technique. PFGE analysis revealed that 32 different "pulsotypes" of Salmonella could be clustered into 11 PFGE "groups". Three of the PFGE groups accounted for approximately 85% of the isolates. There was significant heterogeneity in individual samples, since two or more pulsotypes of Salmonella were isolated from 62% of the samples that yielded multiple isolates. Furthermore, for 13 swine, Salmonella was isolated from both the carcass and fecal samples. Analysis of these samples revealed that approximately 54% of these swine carcasses were contaminated with Salmonella pulsotypes that did not originiate from the feces of the same animal, and in 46% of the swine, Salmonella pulsotypes were found in the feces that were not isolated from the carcass of the same animal. The results of this study indicate that recovering multiple isolates from swine samples is necessary to identify all potential carcass contaminants and that each lot of animals introduces new potential contaminants into the plant environment. In addition, the results suggest that fecal spread is common among swine at slaughter and should be minimized to prevent pathogens from entering the food supply.
Technical Abstract: In a previous study, Salmonella were recovered from swine at a collaborating processing plant over a two month period in the spring of 2000. In the present study, molecular subtyping by pulsed-field gel electrophoresis (PFGE) was performed on the 581 confirmed Salmonella isolates from the 84 Salmonella-positive samples obtained from the previous study. A total of 32 different pulsotypes were revewaled by PFGE that could be clustered into 11 PFGE "groups". Groups B, F, and G predominated throughout the sampling period, and were isolated from 39%, 22%, and 13% of the swine, respectively. In addition, multiple isolates were obtained from 67 of the 84 Salmonella-positive samples, and subtyping revealed multiple PFGE pulsotypes in 35 of the 67 (62%) samples. Both carcass and fecal isolates of Salmonella were recovered from 13 swine, resulting in "matched" samples. Molecular typing of the isolates recovered from the matched samples revealed that of the 13 swine with matched isolates, 7 (54%) of the carcasses were contamined with Salmonella pulsotypes that were not isolated from the feces of the same animal. Conversely, from 6 of the 13 (46%) matched animals, Salmonella pulsotypes were isolated from the feces that were not isolated from the carcass of the same animal. These data establish that each lot of swine may introduce new clonal types into the plant and that swine feces from one animal can contaminate many carcasses. In addition, these results indicate that the examination of multiple Salmonella isolates from positive samples is necessary to determine the variety of potential contaminants of swine carcasses during processing.