Impact of different antimicrobial agents on the colonisation resistance in the intestinal tract with special reference to doxycycline.

The administration of antimicrobial agents has a number of effects on the intestinal microflora. One is the reduction of colonisation resistance, i.e., the resistance displayed by the host to implantation of new microorganisms in the intestinal microflora. In the present investigation, the impact of three antimicrobial agents--clindamycin, doxycycline and erythromycin--on the colonisation resistance in the intestinal human microflora was examined. Two of the agents--clindamycin and erythromycin--disturbed the colonisation resistance and caused ecological changes, while the third agent--doxycycline--better preserved the colonisation resistance. Ecological effects are difficult to foresee and clinical studies of antimicrobial agents should include investigations of the impact on the normal human intestinal microflora.