Jordan K N, Oxford L, O'Byrne C P
Microbiology Department, Unilever Research Colworth, Sharnbrook, Bedfordshire MK44 1LQ, England.
Appl Environ Microbiol. 1999 Jul;65(7):3048-55. doi: 10.1128/AEM.65.7.3048-3055.1999.
Survival of a nontoxigenic isolate of Escherichia coli O157:H7 at low pH (pH 3.0) was examined over prolonged time periods for each of three population types: exponential-phase cells, stationary-phase cells, and acid-adapted exponential-phase cells. In each population, approximately 5 x 10(4) CFU ml-1 were detected after a 24-h incubation at pH 3.0. Even after 3 days at pH 3.0, significant numbers of survivors from each of the three populations could be detected. The high level of acid tolerance exhibited by these survivors was found to be quickly lost once they were transferred to conditions which permitted growth to resume, indicating that they were not mutants. Proton flux measurements on the three populations of cells revealed that the initial rates of viability loss at pH 3.0 correlated well with net proton accumulation. Cells showing a high initial rate of viability loss (exponential-phase cells) accumulated protons at the highest rate, whereas resistant populations (adapted or stationary-phase cells) accumulated protons only slowly. Differences in the protein composition of the cell envelope between the three populations were studied by two-dimensional polyacrylamide gel electrophoresis. Complex differences in the pattern of proteins expressed by each population were uncovered. The implications of these findings are discussed in the context of a possible model accounting for acid tolerance in this important food-borne pathogen.
在较长时间段内，针对三种菌群体类型（指数生长期细胞、稳定期细胞和酸适应指数生长期细胞），检测了非产毒型大肠杆菌O157:H7在低pH值（pH 3.0）环境下的存活情况。在每种菌群体中，于pH 3.0下孵育24小时后，均检测到约5×10⁴ CFU/ml。即便在pH 3.0下放置3天后，仍能检测到来自这三种菌群体的大量存活菌。这些存活菌所表现出的高耐酸性，在转移至允许恢复生长的条件后很快丧失，这表明它们并非突变体。对这三种细胞群体进行质子通量测量发现，在pH 3.0下活力丧失的初始速率与净质子积累密切相关。活力丧失初始速率高的细胞（指数生长期细胞）积累质子的速率最高，而抗性群体（适应期或稳定期细胞）积累质子的速度则较慢。通过二维聚丙烯酰胺凝胶电泳研究了这三种细胞群体的细胞膜蛋白质组成差异。发现每种细胞群体所表达蛋白质的模式存在复杂差异。在一个可能解释这种重要食源性病原体耐酸性的模型背景下，讨论了这些发现的意义。
