Streptococcus oralis

Streptococcus oralis is a Gram positive viridans streptococcus of the Streptococcus mitis group. S. oralis is one of the pioneer species associated with eubiotic dental pellicle biofilms, and can be found in high numbers on most oral surfaces. It has been, however, found to be an opportunistic pathogen as well.

Individual cells of S. oralis are arranged into characteristic long chains when viewing subcultures under a microscope. It is a non-motile, non-sporulating facultative anaerobe. The optimal culturing temperature range for S. oralis is 35 - 37°C, with growth observed between 10 - 45°C. Blood agars selective for streptococci, such as brain heart infusion blood agar, are optimal for culturing S. oralis as these plates highlight its α-haemolysis, but nutrient agars such as trypticase soy agar or Wilkins-Chalgren anaerobe agar can support its growth also. S. oralis colonies are white, grey, or colourless; translucent; smooth; entire; raised cluster colonies 0.5-2.0 mm in diameter.

S. oralis is catalase negative and oxidase negative. Strains of S. oralis produce neuraminidase and cannot bind α-amylase. S. oralis is also acid-sensitive, producing alkaline metabolites to ameliorate its niche.