Johnson W M, Lior H, Johnson K G
Infect Immun. 1978 May;20(2):352-9. doi: 10.1128/iai.20.2.352-359.1978.
Six enterotoxigenic strains of Escherichia coli produced variable levels of heat-stable enterotoxin (ST) when grown under pH control at 8.5 in a simple synthetic medium containing neither amino acids nor vitamins. Bacterial growth and ST production were at levels as high as or higher than those observed in complex media. ST elaboration was detectable in the early logarithmic phase of growth and appeared to be related to disappearance of glucose in the growth medium. The results of this study did not suggest pH-dependent release of ST. Imposition of pH control in complex media resulted in increased growth rates, earlier detectable ST synthesis, and elevated levels of ST. In synthetic medium, attainment of the stationary growth phase was followed by a significant decrease in culture density and a concomitant increase in ST. Cellular autolysis experiments revealed that as much as 20% of the total ST activity was present in a cell-associated form.
六株产肠毒素大肠杆菌在不含氨基酸和维生素的简单合成培养基中，于pH值控制为8.5的条件下培养时，产生了不同水平的热稳定肠毒素（ST）。细菌生长和ST产生水平与在复杂培养基中观察到的一样高或更高。在生长的对数早期阶段即可检测到ST的产生，且似乎与生长培养基中葡萄糖的消失有关。本研究结果未表明ST的释放依赖于pH值。在复杂培养基中进行pH值控制可提高生长速率、更早检测到ST合成并提高ST水平。在合成培养基中，达到稳定生长期后，培养物密度显著降低，同时ST增加。细胞自溶实验表明，高达20%的总ST活性以细胞相关形式存在。
