Distribution of Salmonella clonal groups in four Brazilian feed mills

- Salmonella was found in 4.96% (95%CI: 3.77-6.15%) samples taken in feed mills.
- Conveyors and settled dust presented the highest frequencies of positive samples.
- Salmonella was significantly more found in coliforms-positive samples.
- Serovars Montevideo, Anatum and Senftenberg were the most prevalent.
- Salmonella clonal groups were disseminated and endemic in the feed mills.

Feed is one of the major vehicles for Salmonella transmission to pigs, and its spread during the milling process may play an important role in feed contamination. Therefore, a cross-sectional study was carried out in four feed mills in order to evaluate the frequency of Salmonella isolation at various stages of feed production and to track the spread of genotypically related isolates grouped by pulsed-field gel electrophoresis (PFGE). From a total of 1269 analyzed samples, 63 (4.96%) showed the presence of Salmonella. Evaluated feed mills (A, B, C and D) presented 3.5% (n = 11/317), 1.7% (n = 5/289), 7.5% (n = 23/308) and 7.0% (n = 25/355) positive samples, respectively. Twenty-three serovars were identified, with the most frequently detected being Montevideo (n = 14, 22.2%), Anatum (n = 8, 12.7%) and Senftenberg (n = 8, 12.7%). The isolation of Salmonella was significantly higher (p = 0.002) in samples with the presence of total coliforms (36/489; 7.36%) than in the coliform-negative samples (27/780; 3.46%). Conveyors (OR = 4.43, 95% CI: 2.43-8.09) were the most likely sites of Salmonella isolation, followed by dust settled on the feed mill's floor (OR = 2.88, 95% CI: 1.41-5.33). Isolates indistinguishable on PFGE or belonging to pulsotypes with a high similarity (>95%) were identified in serovars Agona, Infantis, Montevideo, Orion, Senftenberg and Worthington. In particular, clonal groups of serovars Montevideo and Senftenberg were found to be disseminated among different sample types (ingredients, dust collected from the premise's floor and complete feed) or to be endemic in the feed mills. The dissemination of Salmonella clonal groups demonstrates the importance of control measures to avoid dust and debris accumulation on equipment surfaces.