PHENOTYPE AND MOLECULAR INDENTIFICATION OF VIRULENCE GENES FOR FOUR PATHOGENIC AEROMONAS HYDROPHILA ISOLATED FROM A DYING TRIONYX SINENSIS
四株鳖源致病性嗜水气单胞菌(Aeromonas hydrophila)的表型、分子鉴定及其毒力基因检测

Based on exotoxicology, phenotypic information and molecular biological methods, the identification of pathogenicity, phenotypic characteristics and virulence genes were carried out for four pathogenic bacteria, which were isolated from a dying Trionyx sinensis with typical white abdominal shell disease. We found all of four bacterial strains were pathogenic. The order of killing power of these strains was ZHYYZ-2 > ZHYYZ-4 > ZHYYZ-1 > ZHYYZ-3. After an injection of 2.2×107 CFU/g, the occurrence of clinical infection symptoms or death in experimental turtles was 1 or 19h, respectively. These strains were gram-negative bacteria with short pole-like and hemolytic activity. Both VITEK2 system and ATB expression system showed that the bacteria were Aeromonas hydrophila. ZHYYZ-1, ZHYYZ-2, ZHYYZ-3, and ZHYYZ-4, whose 16S rDNA sequence were of 1460, 1464, 1466, and 1461, respectively, were registered in GenBank, with the accession numbers being GU563992, GU563993, GU563994, and GU563995 respectively. Blast analysis indicated that the similarity of their 16S rDNA sequences and 71 strains of A. hydrophila in the GenBank database was 99%. PCR test showed that all the experimental bacteria contained Aha, AHH, AerA and OMP gene. Based on these phenotype and molecular biology characteristics, the isolated bacteria were identified as A. hydrophila, and they were the strains of pathogenicity.