Influence of erythromycin on the normal human flora and colonization of the oral cavity, throat and colon.

Erythromycin stearate was given orally in doses of 500 mg twice daily for 7 days to 10 volunteers. Saliva, throat and faecal specimens were taken up to 16 days for cultivation of aerobic and anaerobic bacteria. In specimens from saliva and throat only minor changes in the numbers of bacteria were detected during the antibiotic administration period, while pronounced changes in the aerobic and anaerobic faecal flora occurred. Thus among aerobes the number of enterobacteria significantly decreased and also the numbers of most anaerobes. During the erythromycin administration period, 8 subjects were colonized by erythromycin-resistant enterobacteria in the oral cavity and throat. All subjects were colonized by erythromycin-resistant enterobacteria, clostridia or yeasts in the colon. Many of the colonizing microorganisms were potential pathogens.