The effect of acid adaptation conditions on acid tolerance response of Escherichia coli 0157: H7

Bu çalışmada, asit şoku veya aside adaptasyon işleminin E. coli 0157: H7 932 susunun aside tolerans kazanması üzerindeki etkileri incelenmiştir. Duraklama fazı hücreleri pH'sı 6 N HCl ile 4.5, 5.0 ve 5.5' e ayarlanmış tryptic soy broth besiyeri içinde tutulmuştur. Daha sonra asit şokuna maruz bırakılan hücreler 1, 2, 3 ve 4 saat, aside adapte edilen hücreler ise 18 saat 37°C'de inkübe edilmiştir. Asit şoku ve aside adapte edilen hücrelerin aside toleransı, pH 2.5 ve 3.0'te tryptic soy broth besiyeri içinde tespit edilmiştir. Asit şokuna maruz bırakılan kültür, aside adapte edilen kültür ve kontrol kültürü daha sonra 37°C'de inkübe edilmiş ve 0, 2, 4, 6, 7, 24 ve 48 saat sonra canlı sayımları yapılmıştır. Asit şoku E. coli 0157: H7'nin aside olan toleransını pH 3.0'te artırmıştır. Ancak aside adaptasyon E. coli 0157: H7'nin aside olan toleransını pH 2.5'te ve pH 3.0'te artırmamıştır. En yüksek aside tolerans, pH 4.5'te iki saat asit şokuna maruz kalan kültürde tespit edilmiştir (P < 0.05). Elde edilen sonuçlar E. coli 0157: H7'nin asidik ortamlara (pH 4.5- 5.5) kısa bir süre maruz kalması durumunda, aside tolerans kazandığını göstermiştir. Asit şokuna maruz kalmış E. coli 0157: H7 hücreleri özellikle fermente gıdalar, meyve suları ve et endüstrisinde kullanılan asit spreyi işlemlerinde dikkate alınmalıdır.

Aside adaptasyon koşullarının Escherichia coli 0157: H7' nin aside tolerans kazanması üzerindeki etkisi

This study examined the effects of acid shock and acid adaptation on acid tolerance of E. coli 0157: H7 932 strain. E. coli 0157: H7 were exposed to acid at pH 4.5, 5.0 or 5.5 for acid adaptation or acid shock in tryptic soy broth (acidified with 6 N HCl). Acid shocked cells were incubated for 1, 2, 3 or 4 h while acid adapted cells were incubated for 18 h at 37°C and then acid tolerance of acid shocked and acid adapted cells were determined by exposing to acid challenge of pH 2.5 or 3.0 in tryptic soy broth. Acid shocked, acid adapted and control cells were incubated at 37°C and survival of the cells at 0, 2, 4, 6, 7, 24 and 48 h was determined. Acid shock increased acid tolerance of E. coli0157: H7 at pH 3.0. However, acid tolerance was not induced in acid adapted cells at either pH 2.5 or 3.0. Acid shocked cells exposed to acid at pH 4.5 for 2 h had the highest acid tolerance (P < 0.05). The results indicated that exposure to acidic environments (pH 4.5- 5.5) for a short time increased acid tolerance of E. coli0157: H7. Acid shocked cells of E. coli0157: H7 may be considered in fermented foods, fruit juices and for acid spray process in the meat industry.

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