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.

Infection dynamics of Salmonella Infantis strains displaying different genetic backgrounds - with or without pESI-like plasmid - vary considerably.

Food-borne infections with Salmonella are among the most common causes of human diseases worldwide, and infections with the serovar Infantis are becoming increasingly important. So far, diverse phenotypes and genotypes of S. Infantis have been reported. Therefore, the present study aimed to investigate the infection dynamics of two different S. Infantis strains in broilers. For this purpose, 15 birds were infected on day 2 of life with 108 CFU/ml of a pESI+ or a pESI- S. Infantis strain, respectively. Ten uninfected birds served as in-contact birds to monitor transmission. In both groups, an increase of infection was observed from 7 days of age onwards, reaching its peak at 28 days. However, the pESI+ strain proved significantly more virulent being re-isolated from most cloacal swabs and organs by direct plating. In contrast, the pESI- strain could be re-isolated from cloacal swabs and caeca only when enrichment was applied. Although the excretion of this strain was limited, the transmission level to in-contact birds was similar to the pESI+ strain. Differences in infection dynamics were also reflected in the antibody response: whereas the pESI+ strain provoked a significant increase in antibodies, antibody levels following infection with the pESI- strain remained in the range of negative control birds. The actual findings provide for the first time evidence of S. Infantis strain-specific infectivity in broilers and confirm previous observations in the field regarding differences in persistence on farms and resistance against disinfectants.

In-vitro testing of bacteriostatic and bactericidal efficacy of commercial disinfectants against Salmonella Infantis reveals substantial differences between products and bacterial strains.

Salmonella (S.) Infantis is currently the most common serovar in broilers and boiler meat in the European Union. In the field, eradication of S. Infantis in affected poultry flocks is considered extremely difficult. Despite stringent cleaning and disinfection measures between the placement of flocks, recurrent infections are often reported. So far, the efficacy of disinfectants on S. Infantis has rarely been studied. Therefore, in the present in-vitro study the bacteriostatic and bactericidal efficacy of ten commercial disinfectants were tested against seven S. Infantis field isolates. Combinations of aldehyde and quarternary ammonium were the active compounds of five, peroxygen of three, cresol and alkylamines of one disinfectant, respectively. Investigations were performed according to standard protocols and regulations. Different concentrations of disinfectants were used to test the bacteriostatic efficacy. Different temperatures and low and high protein exposures were applied as variables to investigate the bactericidal efficacy. Following neutralization of the disinfectants an additional incubation step was introduced to investigate the revitalisation potential of S. Infantis. The bacteriostatic efficacy could be assessed for seven disinfectants. For three disinfectants a bacteriostatic effect was observed when the recommended concentration was used, whereas with four disinfectants only increased concentrations led to this effect. The bactericidal efficacy was not influenced by temperature, whereas high protein exposure decreased the efficacy of nine disinfectants. Furthermore, reactivation of S. Infantis was revealed after application of disinfectants for the majority of products. Interestingly, the strain of S. Infantis influenced the efficacy of the disinfectants. Overall, products based on aldehydes and quarternary ammonium compounds proved most efficient, followed by peroxgen, cresol and alkylamines.