Mixed Salmonella cultures reveal competitive advantages between strains during pre‐enrichment and selective enrichment

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.

Assessing Salmonella prevalence and complexity through processing using different culture methods

“…In some cases, we were able to isolate Salmonella following selective pre-enrichment in novobiocin and bile salts but not with novobiocin and malachite green, and vice versa. This is not unexpected given the differences sometimes seen in isolation between TT and RV broths ( Singer et al, 2009 ; Gorski, 2012 ; Cox et al, 2019 ; Larsen et al, 2021 ), therefore, and similarly to current culture protocols, we suggest performing these selective pre-enrichment steps in parallel to be able to best capture Salmonella .…”

Comparison of Phenotype Nutritional Profiles and Phosphate Metabolism Genes in Four Serovars of Salmonella enterica from Water Sources

“…Culture bias in laboratory media influences the serovars of Salmonella that arise from samples containing multiple subtypes [ 7 , 15 , 16 ]. The Salmonella serovar Kentucky is prevalent in poultry in the U.S. and is frequently isolated in Salmonella enrichments, where it outgrows strains of serovars such as Typhimurium and Enteritidis [ 7 , 17 , 18 ].…”