Impact of different betalactam antibiotics on the normal human flora, and colonization of the oral cavity, throat and colon.

Phenoxymethylpenicillin was given orally in doses of 800 mg twice daily for seven days to six patients, and bacampicillin was given in doses of 400 mg three times per day for seven days to another six patients. Saliva, throat and faecal specimens were taken for cultivation of aerobic and anaerobic bacteria. Only small changes in the normal saliva and throat flora were observed, and no changes in the faecal flora were noticed during the observation period. Cefoxitin was administered parenterally in doses of 2 g at 6 h intervals for 12 h to six other patients. Pronounced changes in the colon flora occurred. Of the aerobic bacteria, enterobacteria decreased and cefoxitin-resistant enterococci increased in number; of the anaerobic bacteria, gram-negative rods decreased in number. At the end of the administration period, all cefoxitin-resistant strains decreased, and suppressed enterobacteria and bacteroides increased in number.