[A dynamic study of drug resistance in populations of fecal "Escherichia coli" from axenic mice, fed chlortetracycline continuously and associated with flora from infant, calf and piglet (author's transl)].

In order to prove the effect of low doses of antibiotics on the level of drug resistance of the gastrointestinal flora, gnotoxenic mice, harbouring various microflora from newborn calf, piglet or infant, were given continuously water containing 20 microgram/ml chlortetracycline. Control mice, harbouring the same flora, were maintained as well in isolators. Sensible and resistant fecal Escherichia coli were counted daily. Results showed that even before the introduction of the antibiotic in the water, drug-resistant E. coli were present in the feces at a level of about 10% of the sensible E. coli. In the three experiments, chlortetracycline increased dramatically the level of resistance of fecal flora. The isolators preventing all possible bacterial contaminations, the observed increase was actually the result of the introduction of antibiotic in the water. However the sensible E. coli remained in higher number in the feces, the resistant strains never becoming dominant. These results are discussed.