The effect of three frequently applied antibiotics on the colonization resistance of the digestive tract of mice.

The influence of treatment with increasing oral doses of three absorbable antibiotics on the colonization resistance of the digestive tract was investigated in mice. Mice treated with ampicillin or epicillin in any of the applied doses had a strongly decreased colonization resistance as demonstrated by 'bacterial overgrowth' after contamination with resistant strains of Escherichia coli. After a treatment period 2 weeks, Streptococcus faecalis became resistant in a number of animals. Oral treatment with cephradine on the other hand had no obvious influence on the endogenous flora of the mice, nor was the colonization resistance decreased.