[Infant mouse test for the assay of thermostable (ST) enterotoxin from Escherichia coli. Histological studies and influence of mice age (author's transl)].

Mices with different ages ranging 1 to 60 days old were inoculated with thermostable (ST) enterotoxin of Escherichia coli, either by intragastric injection through the abdominal wall or by intubation. Doses were proportional to body weight and values obtained for intestines/carcass weight ratios (RI/C) of inoculated mice showed that mice remained susceptible to the enterotoxin up to 16 days old, with RI/C values equal or greater than 0.085. Older mice were completely resistant to ST activity as RI/C values demonstrated. Histological observations showed that whole gut's fixation of inoculated mice was absolutely necessary since any handling of intestinal loops evoked artifactual alterations. Even though, alterations were found, probably of mechanical nature, caused by intestinal distension consequent to the increased fluid volume into gut's lumen. These alterations did not differ from those observed for both cholera and LT-E. coli enterotoxins, characterized by lymphatic and blood vascular dilatation within mucosae lamina propria, eventually shrinkage of lamna propria just below the epithelium as well epithelial's vacuolizations.