Detection of Bacteroides fragilis infection by precipitin antibody

Ultrasonic extracts of three subspecies of B. fragilis were used to detect precipitating antibody against B. fragilis in Ouchterlony plates. Sera of 12 patients with bacteremia due to B. fragilis and of 9 patients in whom B. fragilis was isolated from loculated pus were studied. Sera from 50% of bacteremic patients and from 44% of patients with abscesses formed precipitins with one or more extracts of B. fragilis. Sera from 5 of 8 patients with lung abscesses formed precipitins with extracts of B. fragilis. Sera of 20 normal persons formed no precipitins with these extracts. Sera of 20 hospitalized patients infected with aerobic gram negative organisms formed precipitins with ultrasonic extracts from homologous organisms but did not form precipitins with the extracts of B. fragilis.