Effect of an Enterococcus faecium probiotic on specific IgA following live Salmonella Enteritidis vaccination of layer chickens.

Probiotics and immunization are being widely adopted by the poultry industry with the goal of controlling Salmonella enterica. However, the interaction between these two management protocols has been sparsely studied. The present study aimed to understand the role of an Enterococcus faecium probiotic in the production of salmonella-specific IgA in layers immunized with a live vaccine. Four groups were used: Control (no vaccine or probiotic); Probiotic (which received an E. faecium product); Vaccine (immunized with two doses of a live attenuated S. Enteritidis vaccine); and Vaccine+probiotic. Faecal salmonella-specific IgA was analysed 7 and 20 days post-vaccination (dpv) boost. At 7 dpv, the Vaccine and Vaccine+probiotic groups had similar IgA levels. However, at 20 dpv, IgA levels were two times higher in the Vaccine+probiotic group compared to the Vaccine group. To understand the role of the intestinal microbiota in this finding, bacterial diversity in faeces was analysed by 16S rRNA gene sequencing. The improvement in IgA production in probiotic-treated birds was accompanied by marked changes in the faecal microbiome. Some of the main differences between the Vaccine and Vaccine+probiotic groups included reduction of Escherichia-Shigella and increases in Blautia, Anaerotruncus and Lactobacillus in the latter group. Although no direct causal link can be established from this study design, it is possible that the E. faecium probiotic induces improved antibody production following vaccination via modulation of the intestinal microbiota.