Effects of age and ambient temperature on the responses of infant mice to heat-stable enterotoxin of Escherichia coli: assay modifications.

The response of infant mice to heat-stable enterotoxin from Escherichia coli was affected by the age of the mice (2, 4, 6, and 8 days) and by the ambient temperature (25, 30, and 37 degrees C) after exposure to the enterotoxin. The younger mice and/or mice held at lower temperatures tended to accumulate intestinal fluid (high gut weight/body weight ratios), but older mice and/or mice held at higher temperatures tended to respond with diarrhea and low gut weight/body weight ratios. The standard infant mouse assay forheat-stable E. coli enterotoxin can be simplified, without loss of sensitivity or reliability, by holding the mice at 37 degrees C after exposure and using diarrhea as the index of response. Diarrhea can be detected easily by incorporating dye in the inocula and (at the end of the assay) checking for dye mixed with feces on the rear quarters of the mice or on a sheet of white paper placed under them during incubation.