Non-O1/O139 Vibrio cholerae causes severe intestinal disease in bullfrogs (Rana catesbeiana)

Abstract

Bullfrogs (Rana catesbeiana) are amphibians with high economic value, but in recent years, bullfrog farming has encountered serious threats of bacterial diseases, and the “bullfrog economy” is facing a continuous decline. In this study, the dominant strain was isolated from diseased bullfrogs in a bullfrog farm in Nanning, Guangxi, and based on its morphological, physiological, and biochemical characteristics and analysis of 16S rRNA gene sequences, the strain was identified as a non-O1/O139 group Vibrio cholerae and named TC1. Three virulence factors were identified in this strain, including hemolysin, outer membrane protein, and toxin-coregulated pili. Drug susceptibility testing showed that the strain resisted gentamicin, florfenicol, nitrofural, oxytetracycline, neomycin, penicillin, amoxicillin, doxycycline, and sulfamonomethoxine. The results of artificial infection experiments showed that TC1 caused serious pathologies such as abdominal swelling and anal prolapse in bullfrogs, especially severe intestinal bleeding. Histopathological observations revealed that the bullfrog intestine exhibited obvious pathological lesions. These results provide an essential epidemiological basis for controlling V. cholerae infections in aquatic animals and demonstrate the promise of bullfrogs as an amphibian model for studying the pathogenesis of V. cholerae.