Colonization pattern of the digestive tract by potentially pathogenic microorganisms: colonization-controlling mechanisms and consequences for antibiotic treatment.

An outline is given of the various host-related and flora-related parts of the colonization resistance of the digestive tract. The host-related part of the colonization resistance has been found to be somewhat decreased by sublethal irradiation and leukemia (or chemotherapy), while treatment with antibiotics active against gram-positive flora may severely decrease the colonization resistance (depending on the antibiotic concentration established within the digestive tract during antibiotic therapy). The flora-related part of the colonization resistance, which controls colonization by potentially pathogenic microorganisms, differs greatly from one individual to the next. This observation appears to be important for the host-related part of the colonization resistance. Finally, it is concluded that in the clinical situation preference should be given to antibiotics which do not affect the part of the flora constituting colonization resistance for two reasons: 1) to limit the spread of (multi-) resistant potentially pathogenic microorganisms and 2) for infection prophylaxis in immunocompromised patients. In the latter situation, the potentially pathogenic microorganisms in the flora are selectively eliminated from the digestive tract, provided the antimicrobial drugs used for selective decontamination are active against the endogenous potentially pathogenic microorganisms and given in sufficient (oral) doses.