A scheme for the identification of clinical isolates of gram-negative anaerobic bacilli by conventional bacteriological tests

* Department of Medical Microbiology, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX Department of Bacteriology, University of Edinburgh Medical School, Teviot Place, Edinburgh EH8 9AG Department of Bacteriology and Immunology, Western Infirmary, Glasgow G11 6NT and Central Microbiological Laboratories, Western General Hospital, Edinburgh EH4 2XU Received June 13, 1979 Accepted August 10, 1979 More than 1000 strains of gram-negative anaerobic bacilli, including reference strains, clinical isolates, and members of the normal flora of the mouth, lower gastro-intestinal tract and vagina of healthy human subjects, were studied by conventional bacteriological methods and by gas-liquid chromato-graphic analysis of metabolic products in a series of investigations. A short combined set of tests with particular discriminant value was selected, and a scheme for the identification of the species and subspecies encountered in the diagnostic bacteriological laboratory was based upon our composite results. The tests are: antibiotic-disk resistance tests with neomycin 1000 µg, kanamy-cin 1000 µg, penicillin 2 units and rifampicin 15µg per disk; tolerance tests with sodium taurocholate, Victoria blue 4R and gentian violet; and tests for pigment production, indole production, aesculin hydrolysis and the fermentation of glucose, lactose, sucrose, rhamnose, trehalose, mannitol and xylose. Gram-negative anaerobic bacilli are divided into four groups: (1) the fragilis group with nine species, which include the five subgroups previously classified as subspecies of B. fragilis; (2) the melaninogenicus-oralis group, which includes the three saccharolytic subspecies (ss.) of B. melaninogenicus -ss. melanino-genicus, ss. intermedius and ss. levii -and four non-pigmented species; (3) the asaccharolytic group, which comprises B. asaccharolyticus (formerly B. melaninogenicus ss. asaccharolyticus), B. corrodens and other non-pigmented non-saccharolytic strains, and (4) the fusobacteria.