Pathogenicity of Aeromonas hydrophila causing mass mortalities of Procambarus clarkia and its induced host immune response

Outbreaks of mass mortalities among cultured Procambarus clarkia occurred in a commercial hatchery during the spring of 2019 in Jiangsu province of China. Here, we exploit the pathogenicity and immune response of Aeromonas hydrophila (GPC1-2), which was isolated from diseased P. clarkia. Crayfish challenged showed similar pathological signs to the naturally diseased P. clarkia, lethal dose 50% (LD50) of the strain GPC1-2 to P. clarkia was 3.8 x 10(6) CFU/mL. Detection of virulence-associated genes by PCR indicated that the strain GPC1-2 carried hlyA, aerA, alt, ast, act, aha, ahp, ahpA, and ahpB. Histopathological analysis of hepatopancreas revealed that the hepatic tubule lumen and the gap between the hepatic tubules became larger, and the brush border disappeared in the P. clarkia infected by GPC1-2. Quantitive real-time PCR (qRT-PCR) was undertaken to measure mRNA expression levels for six immune-related genes in P. clarkia after A. hydrophila infection. The expression level of proPO, NOS, ALFI, TLR2, PX, and AST were detected in hemolymph, hepatopancreas, gill and intestine tissues, and clear transcriptional activation of these genes were observed in the infected individuals. These results revealed pathogenicity of A. hydrophila and its activation of host immune response, which will provide a scientific reference for the breeding and disease prevention in P. clarkia culture.