培養條件對Micrococcus roseus及Escherichia coli O157: H7硝酸鹽還原成亞硝酸鹽的影響   全文下載

Effect of Incubation Conditions on the Reduction of Nitrate to Nitrite by Micrococcus roseus and Escherichia coli O157: H7

本試驗目的在比較Escherichia coli O157: H7與Micrococcus roseus、Micrococcus roseus、Staphylococcus carnosus及Vibrio parahaemolyticus四株微生物於含2053 mg／L 硝酸鹽之磷酸緩衝溶液中硝酸鹽還原成亞硝酸鹽的情形，並探討培養條件對M. roseus及E. coli O157: H7硝酸鹽轉換成亞硝酸鹽的影響。M. roseus、E. coli O157: H7及S. carnosus之間的還原能力相似，但較其他菌株強。M. roseus及E. coli O157: H7在pH 7時的硝酸鹽還原能力最大， 但pH值小於5或溫度低於15℃時則被抑制。硝酸鹽之還原隨初菌數的增加顯著增強， 當初菌數為4 log CFU／mL時，還原作用達到最高，然而初菌數愈高則還原率愈強。含503-2006 mg／L 硝酸鹽之pH7緩衝溶液中，M. roseus及E. coli O157: H7均可還原約80%的硝酸鹽，但當硝酸鹽含量大於2006 mg／L 時，還原能力被抑制。E. coli O157: H7於含2098 mg／L 硝酸鹽、37℃、pH 7之緩衝溶液中的硝酸鹽還原量在24小時內可達平衡。本研究顯示雖然E. coli O157: H7具有強硝酸鹽還原特性， 但是所需要的菌量極高，已達到引起食物中毒的危險性， 因此在食物系統中不易發生。

Nitrate reduction of Escherichia coli O157: H7 was compared with that of four microorganisms, namely, Micrococcus roseus, Micrococcus luteus, Staphylococcus carnosus and Vibrio parahaemolyticus in phosphate buffer solution containing 2053 mg/L nitrate, and the factors affecting nitrate reduction of M. roseus and E. coli O157: H7 were also studied. M. roseus, E. coli O157: H7 and S. carnosus showed similar but stronger reduction activities than the other test microorganisms, showing optimum activity in pH 7 buffer solution containing nitrate. Very little nitrite was formed when pH and temperature were below 5 and 15ûC, respectively. Nitrate reduction was significantly increased with cell density and reached optimal level at 4 log CFU/mL. However, the reduction rate was significantly increased with increasing initial cell counts after 24 h incubation. About 80% nitrate was reduced in pH 7 buffer solution containing 503-2006 mg/L nitrate by M. roseus and E. coli O157: H7 at 37ûC after 24h incubation, and the reduction reaction was inhibited at nitrate levels above 2006 mg/L. The reduction of nitrate to nitrite by E. coli O157: H7 in pH 7 buffer solutions containing 2098 mg/L nitrate at 37ûC reached optimal level after 24 h. Results clearly show that E. coli O157: H7 was very active in the reduction of nitrate to nitrite, the number required to reduce nitrate would be extremely hazardous. Thus, nitrate reduction by E. coli O157: H7 would be inconsequential in real systems. 本試驗目的在比較Escherichia coli O157: H7與Micrococcus roseus、Micrococcus roseus、Staphylococcus carnosus及Vibrio parahaemolyticus四株微生物於含2053 mg／L 硝酸鹽之磷酸緩衝溶液中硝酸鹽還原成亞硝酸鹽的情形，並探討培養條件對M. roseus及E. coli O157: H7硝酸鹽轉換成亞硝酸鹽的影響。M. roseus、E. coli O157: H7及S. carnosus之間的還原能力相似，但較其他菌株強。M. roseus及E. coli O157: H7在pH 7時的硝酸鹽還原能力最大， 但pH值小於5或溫度低於15℃時則被抑制。硝酸鹽之還原隨初菌數的增加顯著增強， 當初菌數為4 log CFU／mL時，還原作用達到最高，然而初菌數愈高則還原率愈強。含503-2006 mg／L 硝酸鹽之pH7緩衝溶液中，M. roseus及E. coli O157: H7均可還原約80%的硝酸鹽，但當硝酸鹽含量大於2006 mg／L 時，還原能力被抑制。E. coli O157: H7於含2098 mg／L 硝酸鹽、37℃、pH 7之緩衝溶液中的硝酸鹽還原量在24小時內可達平衡。本研究顯示雖然E. coli O157: H7具有強硝酸鹽還原特性， 但是所需要的菌量極高，已達到引起食物中毒的危險性， 因此在食物系統中不易發生。