Detection of Atypical Salmonella Infantis Phenotypes in Broiler Environmental Samples

In numerous countries, strict and targeted measures concerning Salmonella monitoring and control are implemented and high quality of surveillance is ensured by obligatory investigation of samples from the primary production level of animals according to EN/ISO standards. Here, 2 phenotypic characteristics of Salmonella exhibited on compulsory media are crucial, namely, motility demonstrated on modified semisolid Rappaport Vassiliadis agar (MSRV), and production of hydrogen sulfide (H₂S) on xylose lysine deoxycholate agar (XLD). In the present study, we describe the detection of Salmonella Infantis variants found in broiler environmental samples with major alterations in their growth characteristics on MSRV, XLD, and brilliant green-phenol red-agar (BPLS). The variants proved to be non-motile on MSRV and displayed non-confirming colony appearances on the previously mentioned selective agars. The growth spectrum comprised pinhead sized yellow colonies with small black centers, but also pinpoint sized colorless colonies, both colony types of regular shape. Our work contributes to highlight the finding of S. Infantis variants which possess more than one phenotypic deviation from the "typical" growth characteristics and by this limit the detection power of the actual obligatory used media. IMPORTANCE Salmonellosis caused by non-typhoidal Salmonella serovars is the second most frequently reported zoonotic disease in humans in the EU. The transmission of these agents is mainly via contaminated food of animal origin. In this context, poultry products are the main source of infection. Therefore, continuous and standardized surveillance of the prevalence of such Salmonella serovars at the primary production level is essential. Our findings show the phenotypic heterogeneity of the serovar Infantis and provide growth characteristics of atypical variants. Such variants pass unnoticed official screening methods, resulting in incorrect identification and being underrepresented in epidemiological surveillance programs.