No abstract

Culture-based Salmonella isolation consists of nonselective pre-enrichment, followed by selective enrichment in Rappaport-Vassiliadis (RV) or tetrathionate (TT) broths, and subsequent plating on selective indicator agar. This study aimed to assess the recovery of two strains belonging to serovars Montevideo (strain ATCC-8387) and Typhimurium (strain ATCC-14028) when grown together in different media. The two strains were co-inoculated 1:1, 10:1, 100:1, and the reciprocal, and CRISPR-SeroSeq was used to assess the relative frequency of both strains after each culture step. Individually, there was no growth difference between both strains in universal preenrichment (UP) or RV broths, though both strains had a higher growth in the former.In TT, both strains had reduced growth, especially ser. Montevideo-8387. When the strains were combined, the growth of ser. Typhimurium-14028 strain was higher in UP and TT broths, while the ser. Montevideo strain was higher in RV broth. The ser.Typhimurium strain also grew better on xylose lysine tergitol-4 (XLT-4) agar. Using media that are commonly used for Salmonella isolation, this work reveals strain-tostrain differences in growth and that in three conditions (UP, RV, XLT-4), these differences were only manifested when the strains were in competition with each other. These findings illustrate the importance of dual selective enrichments to be able to capture all Salmonella present in a sample.

Aims 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. Methods and Results 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. Conclusions 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. Significance and Impact of Study 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.