Selective inhibition of enterobacteriaceae in fecal flora of children by oral trimethoprim-sulfamethoxazole.

Fecal flora of nine pediatric inpatients who were receiving trimethoprim-sulfamethoxazole were studied by quantitative aerobic and anaerobic culture methods. During the course of trimethoprim-sulfamethoxazole, the number of Enterobacteriaceae decreased from 10(8-9) to 10(4-5) bacteria per g feces. The isolation rate and the number of Veillonella were also reduced. Other prominent aerobic and anaerobic flora, including Streptococcus, Bacteroidaceae and Bifidobacterium, were not affected. No overgrowth of Pseudomonas, Staphylococcus, Candida or Clostridium was noted. These results support the usefulness of oral trimethoprim-sulfamethoxazole for the prophylaxis of bacterial infection in the compromised host.