Isolation and identification of gram-positive rods in human dental plaque

Abstract

The Gram-positive “diphtheroidal” rods in 48 samples of human dental plaque flora from 12 subjects were placed in genus and species by means of recently introduced diagnostic tables for these organisms. The reactions used included morphological, physiological and biochemical tests. The last involved gas-chromatographic analysis of end-products of glucose fermentation. Immunofluorescence was used in parallel for the identification of isolated cultures and for the detection of actinomycetes and propionibacteria in direct smears of plaque samples. A total of 446 strains of Gram-positive rods were categorized into aerobic facultative and anaerobic facultative groups. Fifteen of the 446 isolates were lost during the identification procedures. Of 283 (66 per cent) isolates of aerobic facultative Gram-positive rods, 268 (95 per cent) could be identified as Rothia dentocariosa, Bacterionema matruchotii, Actinomyces viscosus and Actinomyces naeslundii. Eight isolates were typed as Lactobacillus spp. and Corynebacterium spp. Of 148 anaerobic facultative isolates, 140 (94 per cent) were identified as Actinomyces israelii, Actinomyces odontolyticus, Arachnia propionica, Propionibacterium acnes and a Bifidobacterium species, resembling B. dentium. Thus 93 per cent of the isolates of Grampositive rods from dental plaques could be identified as actinomycetes, propionibacteria, lactobacilli and corynebacteria. No single culture procedure employed was capable of isolating all the recognized species.