Effect of erythromycin on microbial antagonisms: a study in gnotobiotic mice associated with a human fecal flora

The effect of erythromycin base was studied on intestinal resistance to colonization of gnotobiotic mice inoculated with a human fecal flora and challenged with six microbial strains potentially pathogenic for immunocompromised patients. Fecal concentrations of erythromycin were greater than 1,000 micrograms/g in the human donor and in mice. Total intestinal bacterial counts were not significantly different in the human donor and in the recipient mice and were not affected by erythromycin treatment. Strains of various species from the dominant flora (greater than 10(9) colony-forming units/g) and resistant to greater than 1,000 micrograms of erythromycin/ml were present before and persisted during treatment. Strains sensitive to such concentrations - particularly all enterobacteria-were eliminated. Treatment did not reduce colonization resistance against Candida albicans, Clostridium perfringens, and erythromycin-sensitive Escherichia coli. It reduced but did not eliminate some colonization resistance against Pseudomonas aeruginosa, Clostridium difficile, and erythromycin-resistant E coli.