Detection of Bacteroides infection by counter immunoelectrophoresis test.

The counterimmunoelectrophoresis (CIE) test using sonicated antigens of Bacteroides fragilis NCTC 2553 and a B. asaccharolyticus strain, standardised in the laboratory yielded a negative result in the 50 normal sera tested, while it was positive in 24 of 34 (71%) patients with infection due to black pigmented bacteroides and in 10 of 15 (67%) with B. fragilis infection. The microagglutination test (MAT) done in parallel showed a positivity of only 44 and 40 per cent respectively. The CIE test done with B. asaccharolyticus antigen was negative in 87 per cent of patients with infection due to B. fragilis whereas MAT showed cross reactivity to a greater extent.

Rapid identification of clinically important bacteroides by coagglutination method.

A coagglutination technique using indigenous reagents was applied for the rapid identification of Bacteroides fragilis and the black pigmented bacteroides group, using colony suspensions. All the 58 strains of B. fragilis and 42 strains of black pigmented bacteroides tested could be correctly identified by this method. The specificity of the coagglutination reagent was confirmed by the absence of cross reactivity with the related species of bacteroides, viz., B. distasonis, B. ovatus, B. vulgatus and B. thetaiotaomicron as well as other anaerobic and aerobic bacteria. A panel of four antisera against B. fragilis was required for correct identification of the strains tested, indicating the presence of multiple serotypes. On the other hand, all 42 strains of black pigmented bacteroides tested could be identified, using a single reagent as these strains appeared to have no antigenic type variants.