The contribution of Escherichia coli to microbial colonization resistance.

The contribution of Escherichia coli to the microbial colonization resistance (CR) of the bowel was investigated in six healthy volunteers. Esch. coli was eliminated from faeces by the administration of a low dose (20 mg daily) of pefloxacin. This did not cause an increase in the faecal concentration of aerobic Gram-positive cocci or yeasts, nor did it facilitate colonization of the bowel by a pefloxacin-resistant challenge strain of Klebsiella pneumoniae. Therefore, Esch. coli does not appear to contribute to the microbial CR. After ten days of pefloxacin, clindamycin 300 mg was administered twice daily for 18 days. Clindamycin caused a significant increase in the faecal concentration of enterococci, yeasts and the K. pneumoniae challenge strain, indicating that the study design was suitable to demonstrate disturbance of microbial CR if it occurred.