| Abstract: | To identify the aetiology of the disease outbreak in cultured Procambarus clarkii, a dominant bacteria strain from the diseased crayfish hepatopancreas was isolated. It was identified as Aeromonas veronii based on biochemical identification and 16S rDNA sequencing. The symptoms of artificially infected crayfish were similar to those of naturally infected P. clarkii. The A. veronii was sensitive to norfloxacin, ciprofloxacin, ceftazidime, cefuroxime and ceftriaxone antibiotics, while resistant to penicillin, ampicillin, oxacillin and piperacillin. Virulence genes such as the enterotoxin genes (act, alt and ast) and haemolytic toxin genes (hlyA and aerA) were detected. After A. veronii infection, the connections between some liver tubules disappeared, the vacuoles appeared in the brush border and the mitochondria were enlarged. The antagonistic action of previous identified B. subtilis CK3 against A. veronii was also detected. The supernatant of B. subtilis CK3 exhibits a significant bactericidal effect on A. veronii. After B. subtilis CK3 immersion, the antioxidant enzymes and immune-related enzyme activities in hepatopancreas were significantly higher than control. The accumulative mortality caused by infection of A. veronii can be significantly reduced by adding B. subtilis CK3 into the aquatic water. These results demonstrated that B. subtilis CK3 could act as a water additive to improve the immune response of P. clarkii against newly identified A. veronii. The present study will provide a new way for the prevention and control of crayfish bacterial diseases and also provide technical support for the healthy cultivation of P. clarkii. |
