Survival of E. coli O157:H7 Staphylococcus aureus, Shigella flexneri and Salmonella spp. in fermenting `Borde', a traditional Ethiopian beverage

Abstract

The survival and inhibition of food-borne pathogens during the fermentation of different foods and beverages is documented. This prompted the study to evaluate survival of Staphylococcus aureus, Shigella flexneri, Salmonella spp. and Escherichia coli O157:H7 during the fermentation of `Borde', a traditional Ethiopian fermented low-alcohol beverages. The pH of mixtures of `Borde' ingredients at the start of fermentation was between 4.28 and 4.31. At ambient temperatures all test strains grew well in the control and reached counts as high as log 6.6 cfu/ml for E. coli O157:H7 and >log 7 cfu/ml for S. aureus, S. flexneri, and Salmonella spp. When co-inoculated with lactic acid bacteria (LAB), counts of E. coli O157:H7, S. aureus and S. flexneri were >log 2 cfu/ml and >log 1.5 cfu/ml at 12 h and at 16 h, respectively. At 24 h, these counts were <log 1.3 cfu/ml. The count of Salmonella spp., however, was <log 2 at 16 h and they were eliminated at 24 h. LAB-fermented `Borde' had final pH of 3.85 and titratable acidity of 0.41%. At refrigeration temperature, there was no marked growth of test strains in the control. In the presence of LAB, counts of S. aureus were reduced by 2 log units whereas the counts of the other test strains were reduced only by <1 log unit. LAB increased by 1 log unit between 12 and 16 h. The survival of test strains at levels of >2 log cfu/ml between 12 and 16 h indicated health hazard as fermentation of `Borde' is completed within 12 h and consumed within 4 h thereafter.