Etiology and genomic characteristics of an Aeromonas hydrophila strain isolated from Ctenopharyngodon idella

In order to determine the pathogen and pathogenic characteristics of Ctenopharyngodon idella haemorrhagic septicemia in a farm of Nanchang, a strain of pathogenic bacteria A1310 was isolated from the liver lesions of the diseased C. idella. The phenotypic characteristics of the isolated strain A1310 included the morphological characteristics, physiological and biochemical characteristics, pathogenicity, susceptibility test. In addition, the whole genome sequencing, phylogeny-based on multilocus sequence typing (MLST) and virulence gene were examined. According to morphological, biochemical characteristics, the pathogen was identified as Aeromonas hydrophilia. Artificial infection experiments showed that it is pathogenic to C. idella after being infected with the 1.0×10⁶ CFU/mL bacteria strains culture. Antibiotic sensitivity test using 20 antimicrobial agents showed that the isolate was resistant to 7 antibiotics including penicillin, but was sensitive to 5 antibiotics including Kanamycin. The A1310 strain genome sequence contains a total of 96 genes related to toxicity and defense, and most of them are multidrug resistance efflux pump genes, about 22%. MLST typing showed that this isolate was genetically related to the American channel catfish isolates (S15-242, S15-458, S15-591, S15-700). Moreover, the comparative genomic analysis showed that A1310 has at least 80% of the core proteins necessary for a complete T6SS, lacking a segment of vgrG and a segment of vca0109. In conclusion, A. hydrophila A1310 from C. idella was genetically related to the American channel catfish isolates genetically and contains multiple reported virulence genes of A. hydrophilia. This study broadened our knowledge to understand the biological traits of A. hydrophlia. This can provide some reference for the effective inspection, prevention, and in-depth study of A. hydrophilia, and it has some significance for the prevention and control of C. idella disease and will be a basis for the disease control during C. idella culture.