[Propionate negative saccharolytic bacteroides strains (B. oralis)-occurrence, identification, antimicrobial...

Twenty-three propionate negative non-pigmented Bacteroides strains were isolated from mixed infections (peritonitis, endometritis, abscess of the abdominal wall etc.) as well as vaginal secretions of healthy parturients in the course of 3 years. The cultures were indole negative, produced acetic, isobutyric and isovaleric acids and had a final pH of 5.0-5.5 in glucose broth; they were assigned to B. oralis as described by LOESCHE and coworkers in 1964. tpathogenic significance of this organism may be assumed in those cases of mixed infection where the microbial association consisted solely of gram-positive species with low virulence (lactobacilli, Staphylococcus epidermidis, Peptococcaceae). Antibiotic susceptibility of 12 B. oralis strains was studied by tube dilution tests. Resistance to cephalosporins was detected in 8 strains, about half of them were resistant to ampicillin and penicillin G. Like other Bacteroides species, the B. oralis strains showed resistance to aminoglycosides and sensitivity to clindamycin, chloramphenicol and erythromycin. The serological behaviour of 9 B. oralis strains was studied in cross-agglutinationation and gel-diffusion experiments. Cross-reactivity was particularly pronounced in immunodiffusion tests with autoclaved extracts. According to the results obtained, the strains belonged to a homogeneous group with 1-2 identical antigens. These B. oralis antigens were shared by B. melaninogenicus ss. intermedius 2965. There were, however, no cross-reactions between the aforementioned strains and B. melaninogenicus ss. melaninogenicus 8117/1. The taxonomic implications of a close relationship between B. oralis and B. melaninogenicus ss. intermedius are discussed.