Pathogenicity and impact factors of pathogen causing ulcer disease on Mugilogobius chulae

In order to investigate the pathogen and pathogenicity of ulcer disease of Mugilogobius chulae, we isolated the pathogenic bacteria from M.chulae for the artifical infection experiment, physiological and biochemical identification of pathogens and gryB analysis to determine if the environmental factors (temperature, salinity and pH) influence the pathogenicity of isolate strain EtMc1512. The results show that the pathogen was Edwardsiella tarda. The LD₅₀s (lethal dose, 50%) of the isolate strain EtMc1512 to healthy M.chulae and Danio rerio were 57 CFU·ind^–1 and 2.0×10⁴ CFU·ind^–1, respectively. The virulence-related genes (citC, mukF, esrB, katB, fimA, gadB) had been detected in strain EtMc1512, and the homology of their nucleotide between EtMc1512 and other E.tarda which were registered in GenBank was 99%. Cell degeneration, necrosis and inflammatory cell infiltration occurred with severe lesion in kidney and liver. The cumulative mortalities in high-temperature groups of 25 ℃ and 30 ℃ were significantly higher than those in low-temperature group of 20 ℃ and the control group (P<0.05). The cumulative mortality in low-salinity group of 3 was significantly lower than those in high-salinity groups of 15 and 30 (P<0.05). However, there was no significant difference in the cumulative mortality among different pH groups (6.0, 7.5 and 9.0, P>0.05). The results show that E.tarda is a highly pathogenic pathogen of ulcer disease of M.chulae, and the environmental factors of temperature and salinity affect the virulence of E.tarda significantly.