Bacillus cereus causes fatal disease in soft-shelled turtle (Trionyx sinensis)

Abstract Soft-shelled turtle (Trionyx sinensis) is one of the most important aquacultural species in China. In recent years, an infectious disease frequently occurred in soft-shelled turtle, which exhibited similar symptoms, including craned necks, ulcerated pores on shells, hemorrhagic intestinal mucosa and heart, intumescent liver and spleen. In this study, a Gram-positive rod bacterial strain BC12 with vigorous hemolytic and lipolytic activity isolated from the sick soft-shelled turtles. Strain BC12 was identified as Bacillus cereus via 16S rRNA phylogenetic analysis and species-specific gene amplification. The juvenile soft-shelled turtles challenged with B. cereus BC12 exhibited similar symptoms as those natural infections, and the 50% lethal dose (LD50) is 3.89 × 105 colony-forming unit (CFU). Pure B. cereus re-isolated from the heart and liver of turtles infected with BC12. Noticeable pathological changes, including necrosis in the heart and liver and damage in the germinal center of the spleen, were observed in the B. cereus BC12 infected turtles for the first time. Antibiotics susceptibility assay showed that B. cereus BC12 is sensitive to the aminoglycosides, polypeptides, most of the cephalosporins and quinolones, which might be chosen as candidates to prevent and treat B. cereus infection.