Reliable Differentiation of a Bivalent Live Salmonella Vaccine and Field Strains: Multi-Supplier Validation of a Disc...

Zoonotic Salmonella is one of the most important foodborne zoonoses worldwide, with Salmonella Enteritidis (SE) and Salmonella Typhimurium (ST) being the most important serovars, which may be transmitted via poultry meat and eggs. Vaccination of breeding- and laying-hen flocks using live vaccines administered via drinking water has long been a well-recognized tool and contributed significantly to decreasing cases of salmonellosis in humans and its prevalence in the chicken sector. However, if a vaccine strain is detected in feces from recently vaccinated birds, it is imperative to have methods for reliably distinguishing between field and vaccine strains. In this study, we validated a disc diffusion method based on the antimicrobial resistance patterns of the vaccine strains contained in a live bivalent vaccine conferring protection against SE and ST. Discs from eight suppliers were sourced and tested for their suitability for reliably distinguishing between field and vaccine strains, a requirement fulfilled by discs from four suppliers. This method serves as an alternative approach for laboratories equipped to perform disc diffusion assays, and it is also a more cost-effective solution than real-time PCR assays.