Cultural methods for the production of heat-stable enterotoxin by porcine strains of Escherichia coli and its detection by the infant mouse test

Development of a Defined Minimal Medium for the Growth of Edwardsiella ictaluri

In this report, a complete defined medium and a minimally defined medium are described for Edwardsiella ictaluri. The complete defined medium consists of 46 individual components, including a basal salt solution, glucose, magnesium sulfate, iron sulfate, six trace metals, four nucleotides, 10 vitamins, and 19 amino acids. This medium supports growth in broth and on solid media. Optimal growth at 30(deg)C was obtained at pH 7.0, and at an osmolality of 390 mosmol/kg of H(inf2)O, with a glucose concentration of 4 g/liter. The defined minimal medium reduces the 46 components of the complete medium to eight essential components, including the basal salt solution, glucose, magnesium sulfate, pantothenic acid, and niacinamide. In addition, specific amino acids that depend on the specific requirements of the individual strains of E. ictaluri are added.

Comparison between enterotoxic activity and methanol solubility in heat-stable enterotoxins (STa and STb) from Escherichia coli of human, porcine and bovine origins

We have investigated the enterotoxic activity of culture filtrates and their methanol extracted fractions from 10 ST (STa or STb) producing Escherichia coli strains from human, porcine and bovine origin, in the infant mouse test (IMT) as well as in the rabbit intestinal loop test (RILT). Unconcentrated culture filtrates and methanol-soluble fractions from the eight STa-producing strains were positive in the IMT while methanol-insoluble fractions obtained from these STa-positive strains, like methanol-soluble and -insoluble fractions from the two strains producing only STb, lacked activity in the IMT. Unconcentrated culture filtrates from all ST-producing strains were unable to cause fluid accumulation in the rabbit ligated intestinal loops after 6 h incubation. When this material, concentrated 5-fold, was tested again, the culture filtrates and methanol-soluble fractions from all STa-producing strains yielded strongly positive fluid accumulation in the RILT, whereas culture filtrates and their methanol extracted fractions from the strains producing only STb, like methanol-insoluble fractions from four STa-producing strains, caused slight fluid secretion in the rabbit intestinal loops.