Characterization of opsonins for Bacteroides fragilis in immune sera collected from experimentally infected mice

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.

The pathogenic properties of Fusobacterium and Bacteroides species from wallabies and other sources

Intracerebral inoculation was more effective than intraperitoneal, intravenous or subcutaneous inoculation as a means of producing lethal infections with Fusobacterium necrophorum in mice. Strains varied in virulence but, of five examined, two had LD50 values as low as ca. 8000 and 14000 viable organisms. Profuse bacterial multiplication in the brain was demonstrated. Intravenous vaccination with a single large dose of heat-killed whole culture or washed bacterial cells failed to protect against intracerebral challenge. Intracerebral injection of other fusobacteria (F. nucleatum, F. varium and F. necrogenes) and of 22 strains belonging to 10 Bacteroides spp. was without apparent effect on mice, except for a slight transient illness in some animals given B. fragilis. This organism (five strains) differed from the other Bacteroides spp. tested, which included eight strains belonging to the fragilis group, in being eliminated more slowly from the mouse brain--a point that may be relevant to the special pathogenicity of B. fragilis in endogenous infections in man. There was no evidence that B. fragilis multiplied in the brain or that intravenous vaccination with a large dose of heat-killed homologous culture affected the rate at which it was eliminated.

Experimental otitis media in guinea pigs. Serum antibody response to Bacteroides fragilis, Propionibacterium acnes and Peptostreptococcus anaerobius upon challenge

The production of antibodies in serum was studied after inoculation of Bacteroides fragilis, Propionibacterium acnes or Peptostreptococcus anaerobius into the middle ear of guinea pigs. Inoculation of B. fragilis resulted in IgG and IgM serum antibodies at an early stage of the infection, while IgA antibodies were seldom detected and at a later stage. In contrast, inoculation of P. acnes or P. anaerobius induced no serum antibody response. Of these three species B. fragilis induced the most intense otitis, whereas P. anaerobius failed to induce otitis.

Antibiotic-induced modification of Bacteroides fragilis and its susceptibility to phagocytosis by human polymorphonuclear leukocytes

Bacteroides fragilis grown in the presence of sub-inhibitory concentrations of clindamycin was shown to be altered its degree of encapsulation and susceptibility to phagocytosis by human polymorphonuclear leukocytes. Little polysaccharide capsule could be demonstrated either by light or transmission electron microscopy when the bacteria were grown anaerobically for four hours in the presence of 1/2 MIC of clindamycin. Such clindamycin-grown cells could be opsonized by normal human serum, and although less complement was consumed in the process, were more effectively taken up by the leukocytes than bacteria grown in the absence of the drug (45% versus 24%). It was also shown that drug treatment caused significant cellular leakage in the presence of serum, the 3H-label appearing extracellularly. In addition there was greater loss of viability of the bacterial cells grown in the presence of the drug and subsequently exposed to the leukocytes for 60 min.