Selective decontamination and the anaerobic faecal flora.

Selective decontamination with non-absorbable antibiotics of the gastrointestinal tract of patients with impaired host defense is increasingly applied to prevent infections with gram-negative facultatively anaerobic rods. In vivo experiments on the effect of antibiotics on the human intestinal flora were performed with (ex-germ-free) mice. The experiments have shown that the human obligately anaerobic flora did not change during selective decontamination with polymyxin B, but Enterobacteriaceae were eliminated. The magnitude of differences between the sensitivity to antibiotics of the human obligately anaerobic flora and the Enterobacteriaceae in vitro may be used as an index for the usefulness of the antibiotic for selective decontamination. Binding of the antibiotics to intestinal contents has been found to be important for the estimation of the daily dose. The release of the bound antibiotic could contribute to the maintenance of equable concentrations in the intestine.