Survival and characterization of Escherichia coli strains in a typical Mexican acid-fermented food.

In this study, the presence and pathogenic characteristics of Escherichia coli strains in pozol, an acid-fermented maize beverage consumed in South-eastern Mexico, were determined. Seventy-three E. coli strains were isolated at early and late times (6 and 48 h) during the pozol fermentation process, when pH values of the doughs were 6.7-4.7 (6 h) and 4.7-3.7 (48 h). Serotypes that belong to diarrheagenic E. coli serogroups O18, O88, O8, O11, O20, O173 were identified. HEp-2 cell adherence in vitro assays showed localized, diffuse and aggregative adherence patterns among some of these strains. A DNA colony hybridization analysis with different probes showed the presence of virulence genes related to diarrheal pathogenesis. Thirty-three percent of the E. coli strains were tetracycline-resistant and 95% had a 20 kb plasmid. The presence and survival of potentially pathogenic E. coli in acid-fermented pozol suggest that such foods may be a potential source of foodborne outbreaks.