AN ORAL FILAMENTOUS MICROORGANISM: CULTURAL CHARACTERISTICS AND MICROBIAL RELATIONSHIPS AFFECTING GROWTH

¹ Department of Bacteriology, College of Medicine, State University of Iowa, Iowa City, Iowa

Ten strains of a Gram-positive filamentous organism which formed unique and characteristic whip-like structures were isolated from plaque material. All strains were morphologically similar to Leptothrix buccalis, described by Bulleid. Biochemically, the organism was catalase positive, Voges-Proskauer positive, hydrolyzed starch, reduced nitrate to nitrite, fermented a number of carbohydrates without gas production, and failed to grow in medium having a pH below 5.8 or above 8.4.

A 1 to 1,000 dilution of unfiltered saliva inhibited growth of the organism on brain-heart infusion agar supplemented with glucose and yeast extract. The inhibition resulted from a bacterial antagonism. Streptococcus salivarius, Streptococcus mitis, and Staphylococcus epidermidis inhibited growth of the filamentous organism. Acid production by the streptococci and staphylococci caused the inhibition.

When the filamentous organism was grown on nutrient agar, or on brain-heart infusion agar supplemented with only yeast extract, stimulatory zones of growth were frequently produced around saliva-soaked disks placed on the surface of the medium. Several strains of Staphylococcus aureus and Staphylococcus epidermis, isolated from saliva of human beings, caused a pronounced stimulation of growth of the filamentous organism on nutrient agar.