A live attenuated Salmonella Typhimurium vaccine dose and diluent have minimal effects on the caecal microbiota of layer chickens.

Authors: KHAN, SAMIULLAH - University Of Adelaide; MCWHORTER, ANDREA - University Of Adelaide; ANDREWS, DANIEL - Bioproperties Pty Ltd; UNDERWOOD, GREGORY - Bioproperties Pty Ltd; MOORE, ROBERT - Royal Melbourne Institute Of Technology University; Gast, Richard; CHOUSALKAR, KAPIL - University Of Adelaide

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2024
Publication Date: 4/15/2024
Citation: Khan, S., Mcwhorter, A., Andrews, D.M., Underwood, G.J., Moore, R.J., Gast, R.K., Chousalkar, K.K. 2024. A live attenuated Salmonella Typhimurium vaccine dose and diluent have minimal effects on the caecal microbiota of layer chickens. Frontiers in Veterinary Science. https://doi.org/10.3389/fvets.2024.1364731.
DOI: https://doi.org/10.3389/fvets.2024.1364731

Interpretive Summary: Vaccination is one of the most important and widely used strategies for reducing the presence of Salmonella poultry flocks. Vaccination makes birds less likely to become infected and to shed the pathogen into the environment in their feces. In this study, a commercially available live Salmonella Typhimurium vaccine (altered so that it can stimulate an immune response without persisting in tissues) was prepared in 3 different dilution media and was administered to layer chicks at 3 different doses to assess effects on the total spectrum of bacteria present in the chicks’s intestinal tracts (the gut microbiota). The vaccine diluent and dosage had minimal effects of the diversity of gut microorganims. However, the age of the chickens when tested did have more significant effects on the composition of the gut microbiota. The abundance of several important (and potentially protective) types of bacteria were significantly higher at 14 days of age than at 7 days. Overall, the S. Typhimurium vaccine had only minimal effects on the gut microbiota diversity and structure of layer chicks, although changes in the microbiota were much more pronounced between chicks of different ages. These results indicate that the vaccine can be administered without causing disruption of the intestinal microbiota that are important for gut health in the developing chick.

Technical Abstract: Among the Salmonella reduction strategies in poultry production, one option is to use a Salmonella vaccine. The aim of vaccinating layer flocks is to reduce the shedding of wild-type Salmonella in the poultry environment. In this study, a commercially available live attenuated vaccine was reconstituted in different media and delivered at three different doses (10e7, 10e8 and 10e9 CFU/chick) and were assessed for effects on gut microbiota and Salmonella gut colonisation in layer chickens. The vaccine diluent and dosage minimally affected microbiota alpha diversity and, overall, there was no significant difference between different diluents. Microbiota beta diversity was significantly different based on the vaccine diluent and dose, which indicated that the vaccinated and unvaccinated chickens had different gut microbial communities . Differences were noted in the abundance of several genera, including Blautia, Colidextribacter, Dickeya, Enterococcus, Lactobacillus, Pediococcus and Sellimonas. The abundance of Colidextribacter was significantly lower in the chickens that received vaccine reconstituted in Marek’s and water diluents, while Lactobacillus abundance was significantly lower in the water group. The highest vaccine dose (109 CFU/chick) did not significantly alter the abundance of microbial genera. Chicken age affected the microbiota composition more significantly than vaccine dose and diluent. The abundance of Lactobacillus, Blautia, Caproiciproducens, Pediococcus and Colidextribacter were significantly higher on day 14 compared with day 7 of chicken age. The Salmonella Typhimurium vaccine load in the caeca was not significantly affected by diluent and vaccine dose; however, it was significantly lower on day 14 compared with day 7 of chicken age. Overall, S. Typhimurium vaccine minimally affected the gut microbiota diversity and structure of layer chicks, whereas changes in microbiota were more significant with chicken age.