The virulence characteristics and drug susceptibility of outbreak hemorrhage disease pathogen isolated from grass carp Ctenopharyngodon idllus

Abstract:

A strong pathogenic bacterial strain Jxsks1 was isolated from grass carp, Ctenopharyngodon idllus. The pathogen was identified as Aeromonas hydrophila based on the physiological and biochemical analysis and the sequencing of housekeeping gene 16S rDNA and gyrB. The LD₅₀ of the bacteria infecting the grass carp via intraperitoneal injection was 2.3×10³ CFU/g. The results of genetic typing by ERIC-PCR (enterobacterial repetitive intergenic consensus PCR)-fingerprinting showed that it was a type of A. hydrophila which has not been reported before. The distribution patterns of six virulence genes, including aerolysin (aerA), heat-labile cytotonic enterotoxin (alt), heat-stable cytotoxic enterotoxin (ast), elastase (ahpB), lipase (lip) and flagella (fla), were tested by PCR method and the results showed that its virulence-gene pattern was aerA⁺, alt⁺, ast⁺, ahp⁺, lip⁺, fla^-. The drug susceptibility test of 28 antibiotics by paper extension method showed that the strain was susceptible to quinolones, aminoglycoside, tetracyclines, chloramphenicol, the second and the third generation cephalosporins, intermediately sensitive to nitrofurans, macrolides and polypeptides, but resistant to the first generation cephalosporins, penicillins, sulfamethoxazole compound and lincomycin.