Immune responses in eight patients infected with Bacteroides fragilis.

Sera from eight patients with either septicemia or pyothorax caused by Bacteroides fragilis were assayed for specific antibody by the agglutination, immunofluorescence, and agar gel diffusion techniques. Antibodies were detected in the sera of all eight patients by all three serological tests employed; titers as high as 1:160 and 1:320 were detected by the agglutination test and the immunofluorescence technique, respectively, and all patients had precipitating antibody. Failure of B. fragilis sub-species thetaiotaomicron to react with any heterologous antisera from the other seven patients infected with B. fragilis subspecies fragilis thetaiotaomicron was not serologically related to any of the other strains studied. Demonstration of an immune response to anaerobic infection supported the pathogenesis of anaerobes in infectious disease processes and indicated the possible diagnostic role that serological tests may serve in the diagnosis of anaerobic infections in humans.