Isolation, enumeration, and characterization of Vibrio parahaemolyticus

Abstract

Isolation and enumeration of Vibrio parahaemolyticus was made by direct-plating on a modified Twedt (MT) medium and by enrichment in Trypticase Soy Broth (7% NaCl) followed by plating on MT medium. Incubation of broth and plates was at 42 C. Recovery of V. parahaemolyticus by this procedure from inoculated seafoods was satisfactory. The method was comparable or more effective than that currently used by the Food and Drug Administration for the isolation of V. parahaemolyticus from fresh seafoods. Suspect (amylase-positive) colonies from MT medium were considered V. parahaemolyticus by the following criteria: gram-negative pleomorphic rod, oxidase-positive, fermentative carbohydrate utilization in Hugh-Leifson medium, sensitive to pteridine 0/129, failure to grow in media without NaCl, and a fluorescent antibody reaction greater than 2+. Fluorescent antibody technique employed fluorescein-isothiocyanate labeled anti-PPA (partially purified A-substance) rabbit globulin by the direct staining technique. Vibrio parahaemolyticus was not isolated from other salted food products. Although there were substantial decreases in population level, V. parahaemolyticus survived in whole and homogenized shrimp stored for 8 days at 3,7,19, and -18 C. Survival was also noted when V. parahaemolyticus was inoculated into the contents of porcine stomach, small intestine, and large intestine. The organism was very sensitive to pH values below 6.0 when inoculated into shrimp homogenate were destroyed by heating at 60,80, and 100 C for 1 min. Larger populations could withstand 60 and 80 C for 15 min, but were destroyed at 100 C after 1 min. Death in mice seemed to be to a septicemia and production of an exotoxin.