Production of Escherichia coli Heat‐labile Enterotoxin in Fermenter Dialysis Culture

Production of Escherichia coli heat‐labile enterotoxin was investigated with one porcine and one human strain in three different media under different cultivation conditions. Cultivation in aerated fermenters at pH 7·0 yielded 10–20 times more enterotoxin/ml of culture fluid than cultivation in shake flasks. A trypton‐yeast extract medium was optimal in fermenter cultures. Comparatively good yields of enterotoxin in fermenters were also obtained in a glucose‐salts medium. Continuous feeding of glucose and salts during fermenter cultivation resulted in a lower production of enterotoxin/mg of bacterial cells. Since this decrease in specific yield could be reversed by using dialysis culture, it was concluded that inhibition of toxin formation was due to the accumulation of extracellular low molecular weight metabolites. The highest yield of enterotoxin in dialysis culture was 80 ED 50 ml −1 (rabbit jejunal loop test) which is at least eight times more toxin than in ordinary fermenter culture and 80 times more toxin than in shake flask cultures.