Study validates disc diffusion test for poultry Salmonella vaccine strains

A new paper in Veterinary Sciences reports validation of a simple disc diffusion method to distinguish a bivalent live Salmonella vaccine strain from field isolates across multiple laboratory suppliers, addressing a practical diagnostic problem in poultry health programs. The study focuses on differentiation of vaccine-related isolates from Salmonella Enteritidis and Salmonella Typhimurium field strains, an issue that matters because live poultry vaccines can be shed after administration and may be picked up during routine surveillance. Product information for SALMOVAC 440, one established live poultry Salmonella vaccine, notes that vaccinated chickens can excrete the vaccine strain for up to six weeks, and that the strain’s adenine-histidine auxotrophy supports laboratory differentiation from wild strains. (vmd.defra.gov.uk)

Why it matters: For veterinarians, diagnostic labs, and poultry health teams, faster and more reliable differentiation can reduce the risk of treating a vaccine signal like a field outbreak, or missing a true field strain by assuming it’s vaccine-related. That has direct implications for flock management, egg movement, regulatory response, and public health surveillance, since Salmonella Enteritidis and S. Typhimurium remain major foodborne serovars linked to poultry meat and eggs. Prior work has shown the operational pressure around these calls: in layers, commercialization of eggs can be affected while labs determine whether a detected isolate is vaccine or wild type. (pmc.ncbi.nlm.nih.gov)

What to watch: Watch for whether this disc diffusion approach is adopted into routine poultry lab workflows, referenced by regulators, or paired with PCR-based DIVA tools as a lower-cost first-line screen. (pmc.ncbi.nlm.nih.gov)