Gut microbiota dysbiosis by antibiotics increases FAdV-4 susceptibility and alters antiviral immunity in chickens.

Immune regulation is significantly affected by gut microbial community. For example, short chain fatty acids (SCFAs), produced by gut symbionts, function as beneficial immune regulators. Antibiotics are widely used in the poultry industry to improve feed efficiency and prevent diseases; however, this treatment strategy disrupts the normal flora but how they might impact on resistance to enteric pathogen is not known. Fowl adenovirus is a major infectious agent that causes acute and severe inflammation in young chickens. This study investigates the impact of antibiotic administration on microbial composition and immune responses during serotype 4 fowl adenovirus (FAdV-4) infection. Oral administration of an antibiotic cocktail increased susceptibility to FAdV-4 challenge. In oral antibiotics administered and FAdV-4 affected chickens, there was a reduction in activated myeloid cells and an increase in pro-inflammatory immune molecules. Additionally, the microbiota evenness and the Firmicutes-to -Bacteroidetes ratio were altered, leading to the suppression of SCFA-producing microbes. These findings provide valuable immunological insights into developing preventive strategies against contagious diseases in the antibiotics-dependent poultry industry.