Ryu J H, Deng Y, Beuchat L R
Center for Food Safety and Quality Enhancement, Department of Food Science and Technology, University of Georgia, Griffin 30223-1797, USA.
J Food Prot. 1999 May;62(5):451-5. doi: 10.4315/0362-028x-62.5.451.
A study was done to determine if various organic acids differ in their inhibitory or lethal activity against acid-adapted and unadapted Escherichia coli O157:H7 cells. E. coli O157:H7 strain EO139, isolated from venison jerky, was grown in tryptic soy broth (TSB) and in TSB supplemented with 1% glucose (TSBG) for 18 h at 37 degrees C, then plated on tryptic soy agar (TSA) acidified with malic, citric, lactic, or acetic acid at pH 5.4, 5.1, 4.8, 4.5, 4.2, and 3.9. Regardless of whether cells were grown in TSB or TSBG, visible colonies were not formed when plated on TSA acidified with acetic, lactic, malic, or citric acids at pH values of < or =5.4, < or =4.5, < or =4.2, or < or =4.2, respectively. Cells not adapted to reduced pH did not form colonies on TSA acidified with lactic acid (pH 3.9) or acetic acid (pH 3.9 and 4.2); however, a portion of acid-adapted cells remained viable on TSA containing lactic acid (pH 3.9) or acetic acid (pH 4.2) and could be recovered in TSB. Inactivation of acid-adapted cells was less than that of unadapted cells in TSB acidified at pH 3.9 with citric, lactic, or acetic acid and at pH 3.4 with malic acid. Significantly (P< or =0.05) higher numbers of acid-adapted cells, compared with unadapted cells, were detected 12 h after inoculation of TSB acidified with acetic acid at pH 3.9; in TSB containing lactic acid (pH 3.9), the number of acid-adapted cells was higher than the number of unadapted cells after 5 h. In TSB acidified at pH 3.9 with citric acid or pH 3.4 with malic acid, significantly higher numbers of acid-adapted cells survived. This study shows that organic acids differ in their inhibitory or lethal activity against acid-adapted and unadapted E. coli O157:H7 cells, and acid-adapted cells are more tolerant than unadapted cells when subsequently exposed to reduced pH caused by these acids.
开展了一项研究，以确定各种有机酸对酸适应型和未适应型大肠杆菌O157:H7细胞的抑制或致死活性是否存在差异。从鹿肉干中分离出的大肠杆菌O157:H7菌株EO139，在胰蛋白胨大豆肉汤（TSB）和添加1%葡萄糖的TSB（TSBG）中于37℃培养18小时，然后接种到用苹果酸、柠檬酸、乳酸或乙酸酸化至pH 5.4、5.1、4.8、4.5、4.2和3.9的胰蛋白胨大豆琼脂（TSA）上。无论细胞是在TSB还是TSBG中培养，当接种到分别用乙酸、乳酸、苹果酸或柠檬酸酸化至pH≤5.4、≤4.5、≤4.2或≤4.2的TSA上时，均未形成可见菌落。未适应低pH值的细胞在用乳酸（pH 3.9）或乙酸（pH 3.9和4.2）酸化的TSA上不形成菌落；然而，一部分酸适应型细胞在含有乳酸（pH 3.9）或乙酸（pH 4.2）的TSA上仍能存活，并可在TSB中复苏。在用柠檬酸、乳酸或乙酸酸化至pH 3.9以及用苹果酸酸化至pH 3.4的TSB中，酸适应型细胞的失活程度低于未适应型细胞。在接种到用乙酸酸化至pH 3.9的TSB中12小时后，与未适应型细胞相比，酸适应型细胞的数量显著（P≤0.05）更多；在含有乳酸（pH 3.9）的TSB中，5小时后酸适应型细胞的数量高于未适应型细胞。在用柠檬酸酸化至pH 3.9或用苹果酸酸化至pH 3.4的TSB中，酸适应型细胞存活的数量显著更多。这项研究表明，有机酸对酸适应型和未适应型大肠杆菌O157:H7细胞的抑制或致死活性存在差异，并且酸适应型细胞在随后暴露于这些酸引起的低pH值环境时比未适应型细胞更具耐受性。
