[Subcutaneous abscess formation in the mice inoculated intragastrically with Bacteroides fragilis]

Bacteroides fragilis when inoculated intragastrically induced abscess formation in the mice of which the intestinal microbial flora had been disturbed by the prior intake of streptomycin and erythromycin in their drinking water. The lesion usually developed at the left axillary lymph node one week after inoculation and persisted for at least two months. Without the antibiotic treatment, B. fragilis did not induce such abscess formation. Although B. fragilis was isolated from blood after inoculation, intravenous administration of B. fragilis into mice did not induce the abscess formation. Therefore, B. fragilis inoculated did not appear to spread from the intestine to the distant locus via the bloodstream. The number of B. fragilis in the mesenteric lymph nodes reached 10(5) colony-forming units per lymph node 6 h after oral administration and remained unchanged over a 24-h period of infection. These results suggest that the lymphatic dissemination of B. fragilis accounts for the abscess formation at the left axillary lymph node.