Acid and alcohol tolerance of Escherichia coli O157:H7 in pulque, a typical Mexican beverage
2012
Gómez-Aldapa, Carlos A. | Díaz-Cruz, Claudio A. | Villarruel López, Angélica | del Refugio Torres-Vitela, M. | Rangel-Vargas, Esmeralda | Castro-Rosas, Javier
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 O157:H7 in agave nectar and pulque. An initial trial was done of the behavior of E. coli O157:H7 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 O157:H7 strains, storing at 16° and 22°C for 14h, 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 48h (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 O157:H7 strains multiplied in both the single producer nectar and nectar mixture, reaching maximum concentration at 12h. E. coli O157:H7 cell concentration then decreased slowly, although it survived at least 72h in both fermented nectars. E. coli O157:H7 did not multiply in the seed pulque but did survive at least 72h. In the second trial, the numbers of E. coli O157:H7 increased approximately 1.5logCFU/ml at 22°C and 1.2logCFU/ml at 16°C after 14h. After seed pulque was added, E. coli O157:H7 concentration decreased to approximately 2logCFU/ml, and then remained constant until pulque was produced. In the third trial, the E. coli O157:H7 cells multiplied and survived during at least three nectar fermentation cycles. The results suggest that E. coli O157:H7 can develop acid and alcohol tolerance in pulque, and constitutes a public health risk for pulque consumers.
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