Study validates disc diffusion to separate Salmonella vaccine strains

Version 1 — Brief

A new paper in Veterinary Sciences reports that a disc diffusion method can reliably distinguish a bivalent live Salmonella vaccine strain from field strains across multiple suppliers, addressing a longstanding practical challenge in poultry diagnostics. The study focuses on live attenuated Salmonella Enteritidis and Salmonella Typhimurium vaccine strains used in poultry, where post-vaccination shedding can complicate surveillance and trigger uncertainty during routine flock testing. That distinction matters because European product information for these vaccines already relies on antibiogram-based differentiation, including erythromycin sensitivity plus characteristic resistance patterns, and live vaccines are expected to have a method that separates vaccine from wild-type isolates. (vmd.defra.gov.uk)

Why it matters: For veterinary professionals working with poultry operations, a validated, low-complexity disc diffusion approach could help labs and field veterinarians avoid misclassifying vaccine-derived isolates as true field infections. That has implications for outbreak response, regulatory reporting, flock management, and the economic consequences of unnecessary interventions. The need is real: prior research has noted that phenotypic antimicrobial resistance testing can sometimes produce ambiguous results, while other groups have moved toward PCR assays to improve confidence when vaccine and field strains are difficult to separate. (sciensano.be)

What to watch: Watch for whether reference labs, integrators, or vaccine manufacturers adopt this method more broadly, or pair it with PCR-based confirmation in contested cases. (sciensano.be)