Incidence of Vibrio cholerae in Fresh Fish and Ceviche in Guadalajara, Mexico.

The incidence of Vibrio cholerae O1 and non-Ol was determined in fresh fish and ceviche, a marinated raw fish dish ready for consumption. Fresh red snapper ( Lutjanus purpureous ) and mackerel ( Scomberomorus sierra ) were obtained from distribution centers, and ceviche from street vendors and small open restaurants in Guadalajara, Mexico. In addition to V. cholerae , the fish samples were tested for aerobic plate count (APC), total volatile nitrogen (TVN), trimethylamine (TMA), and the ceviche for APC, coliforms, and pH. V. cholerae O1 and non-O1 was isolated from 10% and 26% ofthe fish respectively. The mean data for the fish samples were in the region of: APC, 106 CFU/g of fish; more than 25 mg of TVN per 100 g of fish, but less than 5 mg of nitrogen as TMA per 100 g. Eleven percent of the ceviche obtained from street vendors and 6% obtained from restaurants were positive for V. cholerae O1. The mean APC and coliform counts were 6.6 and 4.8 log CFU/g of fish respectively, and the pH of the ceviche ranged from 3.0 to 4.5. All the strains of V. cholerae O1 isolated during this study were identified as biotype El Tor, serotypes Inaba and Ogawa. For both fresh fish and ceviche, the frequency of isolation of V. cholerae was highest during the summer months.