Diversity of Salmonella serotypes in cull (market) dairy cows at slaughter

Objective-To determine the diversity of Salmonella serotypes isolated from a large population of cull (market) dairy cows at slaughter. Design-Cross-sectional study. Sample Population-Salmonella organisms isolated from the cecal-colon conten ts of 5,087 market dairy cows, Procedure-During winter and summer 1996, cecal-colon contents of cull dairy cows at slaughter were obtained from 5 US slaughter establishments. Specim ens were subjected to microbiologic culturing for Salmonella spp at 1 labor atory. Identified isolates were compared with Salmonella isolation lists pu blished by the Centers for Disease Control and Prevention (CDC) and the Nat ional Veterinary Services Laboratory (NVSL) for approximately the same peri od. The Simpson diversity index was used to calculate the likelihood that S almonella isolates selected randomly by establishment were different. Results-Of 58 Salmonella serotypes identified, Salmonella ser. Montevideo w as the most prevalent. Two of the top 10 CDC serotypes identified from huma ns in 1996, Salmonella ser. Typhimurium and S Montevideo, appeared on our t op 10 list; 8 of the top 10 were found on NVSL listings. Thirty-one of 59 S Typhimurium isolates were identified as DT104 and found at a west slaughte r establishment, 30 during the winter and 1 during the summer. The greatest diversity of serotypes was at a southeast establishment during the summer; the least diversity was at a central establishment in the winter. Conclusions and Clinical Relevance-58 Salmonella serotypes were isolated fr om market dairy cows at slaughter and could pose a threat for food-borne il lness. Salmonella Montevideo was the most frequently isolated serotype and may contribute substantially to salmonellosis in dairy cattle.