Abiotrophia species in early dental plaque

The most characteristic traits that distinguish Abiotrophia strains from ot her streptococci are nutrient requirements, satellitism and pyrrolidonyl ar ylamidase activity. The presence of Abiotrophia strains was studied in earl y dental plaque formed on sucrose-containing and sucrose-free (glucose-cont aining) diets. The isolates were from 0- to 3-day dental plaque formed on t he buccal surface of a lower premolar in six subjects. Identification of Ab iotrophia strains was based on their pyrrolidonyl arylamidase activity. The y were among the predominant cultivable microorganisms isolated from dilute d suspensions of early dental plaque formed on both diets. Using biochemica l tests without testing for pyrrolidonyl arylamidase activity, the Abiotrop hia strains would be biochemically identified as Streptococcus mitis or uni dentified streptococci, and many isolates first classified as unidentified streptococci were Abiotrophia strains. Generally, identifications using par tial 16S rRNA sequences confirmed the identifications obtained biochemicall y. However, Abiotrophia elegans and Gemella strains were biochemically iden tified as Abiotrophia adiacens. Abiotrophia strains produce hydrogen sulfid e, which may influence the metabolism and ecology of dental plaque and act as a virulence factor in periodontal disease. They are not able to grow on tryptic soy agar. In the present study, some S. mitis strains were not able to grow on mitis salivarius agar, and some Abiotrophia strains were able t o grow on this medium. These observations indicate that the use of these me dia for estimation of total viable counts and number of streptococci introd uces systematic error in studies of microorganisms in dental plaque.