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ABSTRACT-The adherence of Edwardsiella tarda strains to HEp-2 cells was studied by the viable cell count and direct microscopic count methods. Three selected E. tarda strains having different hemagglutination activities against guinea pig erythrocytes were cultured in a peptone-yeast extract broth supplemented with 3% NaCl (3%-NaCl culture) or without NaCl (0%-NaCl culture). Strain FK1051 showed significantly higher adherence in the 3%-NaCl culture than in the 0%-NaCl culture. A similar adherence pattern was observed in strain KG8401, though the adherence of the 0%-NaCl culture was higher than that of FK1051. In contrast, both cultures of strain SU166 were low in the adherence. These adherence patterns to the HEp-2 cells correlated well with the previously reported hemagglutinating activities of the strains. N-acetylneuraminic acid markedly inhibited the adherence as well as the hemagglutination. This NaCl-enhanced adherence may be involved in pathogenesis of E. tarda infection particularly in marine fish.

We examined bacterial concentration and granuloma formation at the early and late phases of infection in red sea bream Pagrus major artiˆcially infected with an atypical Edwardiella tarda. Fish at the early and late phases were deˆned asˆsh at 1 day and 30 days after infection, respectively. Concentrations of E. tarda in blood were higher at the early phase than at the late phase, while those in kidney were higher at the late phase than at the early phase. The concentrations in blood and kidney at the late phase were less than 10 1.0 CFU/mL and 10 7.1 7.8 CFU/ g, respectively. Granuloma formation in kidney was found only at the late phase. The IFAT positive areas were scattered in the kidney tissue at the early phase, but only in granulomas at the late phase. These results suggest that E. tarda can survive in granulomas, however, detection rates of E. tarda from kidney by a platinum loop were 29 35 at the late phase but 100 at the early phase. The former low rate is seemingly due to the di‹culty of destroying the granulomas by the platinum loop.

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