Adaptation of Escherichia coli O157:H7 to acid in traditional and commercial goat milk amasi

Abstract

a b s t r a c tAcid resistance of Escherichia coli O157:H7 strains UT 10 and UT 15 were determined in traditional Amasi fermented for 3 days at ambient temperature (ca 30 C) and commercial Amasi fermented at 30 C for 24 h and stored at 7 C for 2 days. Escherichia coli O157:H7 counts in commercial Amasi were detected at 2.7 log 10 cfu/ml after 3 days while those in traditional Amasi could not be detected after the same period. There was no significant difference (p # 0.05) in the survival of acid adapted (AA) and non-adapted (NA) E. coli O157:H7 in traditional Amasi, while in commercial Amasi, the NA strain survived significantly (p # 0.05) better than its AA counterpart. Regardless of prior adaptation to acid, E. coli O157:H7 can survive during fermentation and storage of fermented goat milk Amasi. Also, the fermentation time, pH and storage temperature affects the survival of E. coli O157:H7 in the fermented milk.

Effect of Lactobacillus plantarum on the survival of acid‐tolerant non‐O157 Shiga toxin‐producing E. coli (STEC) strains in fermented goat's milk

“…This can be attributed to the fact that the non‐O157 STEC strains in this study possess a high level of acid tolerance at low pH and this could have possibly enhanced the survival of NAA non‐O157 STEC strains during fermentation due to gradual adaptation to the changing pH. However, the sudden shift of the AA non‐O157 STEC strains to normal optimum growth conditions followed by the subsequent demand to re‐adapt resulted in failure to acquire maximum adaptation as reported by Dlamini and Buys (). According to Ryu and Beuchat (), regardless of prior adaptation to acidic environment, E. coli O157:H7 will again undergo physiological changes during subsequent exposure in response to other organic acids and antimicrobial compounds produced.…”

“…This could be attributed to the high pH and low acidification during exposure which enhanced adaption of non‐O157 STEC strains. According to Dlamini and Buys (), high pH enhanced the survival of E. coli O157:H7 for 3 days in fermented goat's milk amasi. Kingamkono et al .…”

Epidemiology of Shiga toxin-producingEscherichia coliO157:H7 in Africa in review

“…37 Moreover, inanimate objects such as soil, 7 water, 28,46 marine sediments 23 and manure 50 are a source of the pathogen. The risk is potentiated by the ability of the pathogen to survive harsh conditions, such as the low pH of dairy products, 54,55 or in manure for more than four months. 48 Generally, the risk factors for STEC O157:H7 infections include contact with animals and their environment and poor personal hygiene, such as not washing hands after handling animals or prior to eating.…”

Determination of the survival levels of acid-adapted Escherichia coli O157:H7in sucuk (Turkish-type fermented sausage)

“…Dlamini and Buys (13) claimed that a significant difference did not exist between survival levels of acid-adapted and nontreated E. coli O157:H7 cells in amasi, also a traditional fermented dairy product, but that in commercial amasi the nontreated cells had a higher survival rate.…”