Feed-borne Bacillus cereus exacerbates respiratory distress in birds infected with Chlamydia psittaci by inducing hemorrhagic pneumonia.

Chlamydia psittaci is an important zoonotic pathogen and its oral route of infection plays an important role in the transmission and persistence. Bacillus cereus (B. cereus) strains is a common contaminant of animal feed and feedstuffs, can causes severe diarrhea and malnutrition in poultry. In our previous study, a B. cereus strain (Dawu C) isolated from the hemorrhagic lungs of infected chickens was shown to harbor two virulence genes (hblC and cytk) and was able to induce hemorrhagic lesions in the lungs, as well as gizzard erosion and ulceration (GEU) syndrome in broilers. In the present study, we tested the hypothesis that B. cereus-induced GEU would aggravate Chlamydia psittaci infection. Our results showed that SPF chickens exposed to B. cereus developed a severe GEU syndrome. More interestingly, prior infection with B. cereus facilitated Chlamydia psittaci infection, and aggravated GEU and respiratory distress, which were accompanied by characterized as highly chlamydial loads in the lungs and severe lesions in respiratory organs. Moreover, levels of local inflammatory cytokines were elevated and T cell responses were impaired in the infected birds. In conclusion, GEU caused by B. cereus may facilitates chlamydial transmission from the ventriculus to the lungs.