Salmonella is a pathogen of poultry and humans. Within flocks, it can be transmitted horizontally via the faecal-oral route and vertically to eggs via the reproductive tract. Asymptomatic carriage of Salmonella in poultry is common and compromises food safety. Biosecurity, hygiene, and vaccinations are essential to control Salmonella at source. Live-attenuated S. Typhimurium ∆aroA vaccines (like Poulvac® ST) are used in poultry but are not wholly protective. SiiE is a large adhesin that aids Salmonella pathogenesis in vivo. A recent study in mice demonstrated that deleting the siiE gene from a vaccination strain led to elevated total and Salmonella-specific systemic antibody responses and greater pathogen clearance. Here, S. Typhimurium ∆siiE ∆aroA was generated and its efficacy was compared to S. Typhimurium ∆aroA in a vaccination and homologous challenge experiment in poultry. Both vaccines reduced caecal colonisation by over 2log10 and prevented colonisation at systemic sites, with a slight but insignificant improvement in the ∆siiE ∆aroA-vaccinated group. An increase in total systemic antibody, IgY, was observed in the ∆siiE ∆aroA-vaccinated group but there was no increase in Salmonella-specific IgY, possibly owing to differences in route of vaccination and the time allowed for induction of robust pathogen-specific responses, which warrants further investigation.
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