Rivas M, Binsztein N, López Moral L, Cinto R
Instituto Nacional de Microbiología Carlos G. Malbrán, Buenos Aires, Argentina.
Rev Argent Microbiol. 1987 Jul-Sep;19(3):91-100.
The production of heat-labile enterotoxin (LT) by E. coli strains was studied. Four strains isolated from acute infant diarrhea cases in Argentina and one reference strain, all of them producers of different levels of LT, were employed. GM1-ELISA was used as titration method. The production was assayed in two culture media; Evans (Ev) and Trypticase Soy Broth (CTS) with or without glucose and with different concentrations of lincomycin (0; 30; 45 y 90/micrograms/ml). The effects of pH and inoculum concentration were also examined. Higher levels of LT were found to be produced in Ev (mean production value X = 233.1 ng/ml) than in CTS (X = 133.8 ng/ml), although the difference was statistically not significant (P = 0.22). Lincomycin addition stimulated toxin synthesis and release in both media, and these effects were found to increase with the concentration of the antibiotic (P less than 0.01). Glucose increased the LT levels of low-producing strains and also the growth rate, cellular yield and LT levels of 40T and CC2e strains. Levels of LT released were found to be independent of inoculum concentration. In CTS without pH control, the LT production was one half the levels attained with regulated pH. This was not an effect on the release of the toxin as the determination included both the extracellular LT and the intracellular toxin accumulated in the periplasmic space, which is released by polymyxin B treatment. A pH-dependent inactivation of the synthetized and release toxin was demonstrated.
对大肠杆菌菌株产生不耐热肠毒素（LT）的情况进行了研究。使用了从阿根廷急性婴儿腹泻病例中分离出的4株菌株和1株参考菌株，它们均能产生不同水平的LT。采用GM1-ELISA作为滴定方法。在两种培养基中测定产量；Evans（Ev）培养基和胰蛋白胨大豆肉汤（CTS）培养基，添加或不添加葡萄糖，并添加不同浓度的林可霉素（0；30；45和90微克/毫升）。还研究了pH值和接种物浓度的影响。发现Ev培养基中产生的LT水平（平均产量值X = 233.1纳克/毫升）高于CTS培养基（X = 133.8纳克/毫升），尽管差异无统计学意义（P = 0.22）。添加林可霉素可刺激两种培养基中的毒素合成和释放，且发现这些作用随抗生素浓度增加而增强（P < 0.01）。葡萄糖可提高低产菌株的LT水平，也可提高40T和CC2e菌株的生长速率、细胞产量和LT水平。发现释放的LT水平与接种物浓度无关。在未控制pH值的CTS培养基中，LT产量是pH值调节时产量的一半。这并非对毒素释放的影响，因为测定包括细胞外LT和周质空间中积累的细胞内毒素，后者可通过多粘菌素B处理释放。证明了合成和释放的毒素存在pH依赖性失活。
