Characterization of exotoxin produced by a shellfish‐pathogenic Vibrio sp.

Abstract. Broth filtrate of a Vibrio species, isolated from spontaneously occurring epizootics among cultured oyster larvae, Crassostrea virginica (Gmelin), was shown to contain an exotoxin. Bioassays demonstrated that LC50 value was less than 46.6 μg of toxin/l culture of oyster embryos. This quantity was produced by 2.9 × 109 colony‐forming units. Purified toxin showed neither proteolytic nor amylase activity; it did, however, demonstrate bacteriostatic capability. Studies showed that the toxin was heat‐labile and that exposure to heat‐produced toxoid had a beneficial effect on oyster embryonic development. Data revealed that although toxin was inactivated by heating, the bacteriostatic capability of the metabolite was not lost. Molecular weight of the toxin was estimated to be 68000.