ISOLATION, IDENTIFICATION AND VIRULENCE GENE ANALYSIS OF PATHOGENIC AEROMONAS VERONII IN MACROBRACHIUM ROSENBERGII AND ITS HISTOPATHOLOGICAL OBSERVATION

To identify the causative agent causing the death of adult Macrobrachium rosenbergii occurred in a cultured farm of Gaoyou city, Jiangsu Province, a dominant strain named WSQ-1 was isolated from the hepatopantras of dying M. rosenbergii and identified as Aeromonas veronii based on morphological observation, physiology characteristics, biochemical identification and sequencing of 16S rRNA and gyrB gene. The symptoms of M. rosenbergii artificially infected with the strain WSQ-1 were similar with those of natural infected M. rosenbergii, showing weakened vitality, decreased appetite and white muscle. The LD₅₀ to M. rosenbergii was 2.51×10⁶ CFU/mL at 72h post infection. Histopathological observation showed that the pathological damage of hepatopancreas tissue was gradually aggravated with the increase of concentration or the duration of infection: the connective tissue space was enlarged and a small amount of inflammatory cells were accumulated in the early stage or low concentration, and then the lumen of hepatic tubule was deformed, hepatocytes were vacuolized, and some tissues were necrotic. In the late stage or high concentration, large area necrosis of hepatic tubule and connective tissue led to irreversible damage. The amplification result of virulence gene showed that the WSQ-1 carried 7 virulence genes including Acsv, AexT, Act, Aer, GcaT, Acg and OmpAI, which further indicated that the WSQ-1 had high virulence. Drug susceptibility test showed that 18 kinds of drugs such as cefoperazone had the most inhibitive effects on the strain. At the same time, it showed resistance to 11 kinds of drugs such as clarithromycin, completely resistant to 4 kinds of drugs such as penicillin G, only moderately sensitive to kanamycin. The results of this study can provide some reference for the identification of the pathogen of the bacterial disease of M. rosenbergii and the prevention and control of the disease caused by A. veronii.