Acid and alcohol tolerance of Escherichia coli O157:H7 in pulque, a typical Mexican beverage.

ABSTRACT

Pulque is a traditional Mexican fermented alcoholic beverage produced from the nectar of maguey agave plants. No data exist on the behavior of Escherichia coli O157H7 in agave nectar and pulque. An initial trial was done of the behavior of E. coli O157H7 during fermentation of nectar from a single producer, a nectar mixture from different producers and "seed" pulque. A second trial simulating artisanal pulque production was done by contaminating fresh nectar with a cocktail of three E. coli O157H7 strains, storing at 16 ° and 22 °C for 14 h, adding seed pulque and fermenting until pulque was formed. A third trial used pulque from the second trial stored at 22 °C as seed to ferment fresh nectar at 22 °C for 48 h (fermentation cycle). This procedure was repeated for an additional two fermentation cycles. During incubation at 16 ° or 22 °C in the first trial, the E. coli O157H7 strains multiplied in both the single producer nectar and nectar mixture, reaching maximum concentration at 12h. E. coli O157H7 cell concentration then decreased slowly, although it survived at least 72 h in both fermented nectars. E. coli O157H7 did not multiply in the seed pulque but did survive at least 72 h. In the second trial, the numbers of E. coli O157H7 increased approximately 1.5 log CFU/ml at 22 °C and 1.2 log CFU/ml at 16 °C after 14 h. After seed pulque was added, E. coli O157H7 concentration decreased to approximately 2 log CFU/ml, and then remained constant until pulque was produced. In the third trial, the E. coli O157H7 cells multiplied and survived during at least three nectar fermentation cycles. The results suggest that E. coli O157H7 can develop acid and alcohol tolerance in pulque, and constitutes a public health risk for pulque consumers.