Lack of effect of trimethoprim and nitrofurantoin on colonization resistance in the vagina of monkeys.

The effects of trimethoprim and nitrofurantoin, two antibiotics often used for treatment and long-term prophylaxis of urinary tract infections, on colonization resistance in the vagina of monkeys were investigated. Female monkeys were flushed intravaginally with one of the antibiotics or buffered saline or amoxicillin (controls) for six days. During or after this antibiotic administration a pyelonephritogenic Escherichia coli, strain DS17, was flushed into the vagina. A persistent colonization was obtained in two of eight trimethoprim experiments and a transient colonization in one trimethoprim and two of seven nitrofurantoin experiments. These results did not differ significantly from those of the buffer control experiments. Neither the number of anaerobic bacteria nor the composition of the anaerobic microflora was much affected by these antibiotic agents, while amoxicillin both reduced the number of anaerobic bacteria and promoted E. coli colonization. We conclude that trimethoprim and nitrofurantoin exert a limited effect on the microecology and the colonization resistance in the vagina. From an ecological aspect both drugs seem to be good choices for treatment and prophylaxis of urinary tract infections.