Anaerobic, gram-positive, pleomorphic rods in human gingival crevice.

Sixty-two strains of anaerobic, gram-positive, pleomorphic rods were isolated from the gingival crevice of individuals clinically free from peridontal disease, and examined for biochemical characteristics, cellular and colonial morphology, and acid end-products from glucose fermentation. None of them produced indole, hydrogen sulfide, or catalase, but all hydrolysed esculin. Seven, 10 and 45 of 62 strains were identified as Bifidobacterium, Actinomyces naeslundii, and Actinomyces israelii, respectively, on the basis of biochemical characteristics.