Indirect serum haemagglutinating antibody response to black pigmented Bacteroides during experimental pure infections in rats.

The humoral immune response during experimental infection with black pigmented bacteroides was studied by the indirect haemagglutination test. Both Bacteroides melanimogenicus (ATCC 25845) and B. intermedius (ATCC 25611), grown in semi-solid agar culture, produced pure subcutaneous, intra-abdominal and lung infections. In each of these infection models, B. intermedius was found to be more pathogenic than B. melaninogenicus on the basis of gross pathology of the lesion, bacteriological and histopathological findings, and the capacity to produce persistent infection. Cytoplasmic extracts of these strains were used as an antigen for the indirect haemagglutination test. In all the infections, B. intermedius provoked a better and higher antibody response than did B. melaninogenicus, suggesting a potent immunogenic property of the former strain. Peak antibody titres in both groups during all the above infections were seen between the 10th and 15th days post infection (p.i.), which was precisely 3-5 days after peak lesion was achieved. A significant IHA antibody titre persisted up to days 30-37 p.i. These findings suggest that the antibodies to the black pigmented Bacteroides are not protective, but may play a role in the pathogenesis of the diseases.