Animal feed contains diverse populations of Salmonella.

Abstract

In food animals, Salmonella can exist as multiserovar populations, and the goal of this study was to determine whether Salmonella-positive animal feed samples also consist of multiserovar populations. In all, 50 Salmonella-positive samples, collected from 10 countries, were cultured using three different media for Salmonella isolation: universal pre-enrichment broth, Rappaport-Vassiliadis (RV) broth and tetrathionate (TT) broth. The samples included 25 samples from feed ingredients, 13 from complete feed and 12 feed mill dust samples. Samples from pelleted overnight cultures were analysed by CRISPR-SeroSeq to examine serovar populations in individual samples. Serovars Anatum and Mbandaka were the most commonly identified and were found in feed, feed ingredients and feed environments. Serovars commonly associated with human illness were also identified, and included serovars Enteritidis, Typhimurium and Infantis. Overall, we detected 12 different serogroups (37 different serovars), with eight serovars belonging to the O:7 serogroup (C1 ). Over half (56%) of the samples contained two or more serovars, with 11 serovars found in one sample. Feed ingredients exhibited higher serovar diversity, with an average of three serovars. Across paired samples of pre-enriched and enriched populations, the Bray-Curtis dissimilarity metric showed that 83% of serovar populations were a strong match. The data presented show that serovars belonging to the O:7 serogroup are commonly found in feed, and that feed can contain multiple serovars. The serovar populations across different Salmonella media were largely concordant. The presence of Salmonella in animal feed is considered a transmission route into meat and poultry products and this study demonstrates that animal feed can contain multiple Salmonella serovars.