[Incidence of Vibrio parahaemolyticus in raw fish, oysters, and shrimp]

The incidence of Vibrio parahaemolyticus in fresh seafood sold in Guadalajara, was studied by two procedures. These two procedures were compared to choose a reliable technique when outbreaks of V. parahaemolyticus illness occur. For one year, 57 samples of fresh oysters, fish and shrimp were analyzed for mesophilic aerobic bacteria (MAB) content, V. parahaemolyticus and pH. Total volatile nitrogen (TVN) was also determined in samples of fish and shrimp. MAB were counted by the pour plate method, and TVN was determined by modified Conway's micro diffusion technique. V. parahaemolyticus was investigated in 20-g samples by enrichment in lauryl dextrose salt broth (LDSB), isolating on plates of thiosulfate citrate bile sucrose agar (TCBS) and bile salts No. 3 agar (BS No. 3), and by direct isolation on TCBS and BS No.3 agar plates. Vibrio was characterized by tests described in standard methods, based upon the halophilism of the organism. Global percent of Vibrio parahaemolyticus positive samples was 45.6%, being 71.4% in fish, 44.0% in oysters, and 27.6% in shrimp. The use of two techniques enhanced the ability to recover the vibrio. There was a greater number of positives during the warm months (p = 0.0038). Means of TVN and pH in both positive and negative samples were not significantly different. Means of MAB counts were similar either in positive or negative samples.