Study validates disc diffusion method for Salmonella vaccine checks

Vaccination against Salmonella Enteritidis and Salmonella Typhimurium is a core control tool in laying and breeding hens, but it creates a practical diagnostic problem: when labs recover Salmonella from a flock, they need to know whether they're seeing a live vaccine strain or a true field isolate. A new Veterinary Sciences paper reports multi-supplier validation of a simple disc diffusion method designed to make that distinction reliably for a bivalent live vaccine, using antimicrobial susceptibility patterns rather than more complex molecular workflows. That matters because EU rules require manufacturers of live Salmonella vaccines to provide a bacteriological method that distinguishes vaccine from wild-type strains before those products can be used in national control programs. (eur-lex.europa.eu)

Why it matters: For veterinary professionals working with poultry integrators, hatcheries, and diagnostic labs, the value is operational. A validated, relatively accessible culture-based method could help labs avoid misclassifying vaccine reisolates as field infections, which can trigger unnecessary control measures, commercial disruption, and regulatory concern. The broader backdrop is still significant public health pressure around poultry-associated Salmonella: salmonellosis remained the second most commonly reported gastrointestinal infection in the EU/EEA in 2023, with eggs and egg products still a major outbreak vehicle, while Enteritidis and Typhimurium remain central serovars in poultry control programs. (ecdc.europa.eu)

What to watch: Whether reference labs, vaccine suppliers, and poultry producers adopt this disc diffusion approach alongside, or instead of, PCR- and WGS-based differentiation methods already in use. (pubmed.ncbi.nlm.nih.gov)