Identification of Salmonella clonal groups and enterobacteria quantification in different risk areas of manufacturing process in four Brazilian feed mills

Abstract

Identification of critical points for contamination of feed and spread of Salmonella may contribute to the development of control plans. A cross-sectional study was conducted to identify Salmonella clonal groups in feed mill facilities. A total of 1,322 samples were collected in four swine feed manufacturing facilities. Samples were taken from ingredients and from dust deposited on the floor and on the inner surface of storage bins, bucket elevators, mills, mixers, scales, pelleting chamber and cooler. Besides, all samples were submitted to enumeration of enterobacteria. Salmonella was isolated from a total of 66 (5.0%) samples; most of positive samples were taken from transportation equipment (bucket elevator and conveyor belt). In two facilities, Salmonella was detected in the end product. Serovars Montevideo, Infantis, Orion, Senftenberg, Agona, Worthington and Tennessee were found in more than one step of the manufacturing process, and they were submitted to molecular typing by pulsed-field gel electrophoresis (PFGE). Results from XbaI and BlnI-digestions revealed from one to nine PFGE-profiles. Pulsotypes analyses indicated that dust deposited on the inner surface of equipments and on the floor is responsible for spreading and persistency of Salmonella in feed mills over time. The highest enterobacteria counts were found in the dosage step in all sampled feed mills, indicating lack of cleanliness in this area. Salmonella was isolated in 8.75% (28/320) of the samples presenting enterobacteria counts >100 cfu.g-1. Dust accumulation on the floor and surface of equipment and a high production flow were identified in all feed mills; these factors may have contributed to the spread of Salmonella clonal groups.