Streptococcus oralis

eubiotic dental pellicle biofilms, and can be found in high numbers on most oral surfaces.^[4][5] It has been, however, found to be an opportunistic pathogen as well.^[2]

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.^[7][8] S. oralis colonies are white, grey, or colourless; translucent; smooth; entire; raised cluster colonies 0.5-2.0 mm in diameter.^[9]

extracellularly by S. oralis, which directly breaks down MUC5B, an O-glycosylated protein which constitutes the majority of the dental pellicle.^[11] Through this interaction, S. oralis may be able to adhere to dental enamel, acquire nutrients from the broken-down MUC5B molecules, and hence establish the biofilm.^[11] The genome for this protease is highly conserved amongst the S. mitis group, but is notably distant from the genome of S. mutans, indicating that they occupy competing niches;^[11] MdpS is active at pH 6.5-7.5, whilst S. mutans modifies the pH of its environment to 4.5-5.5 by releasing lactic acid.^[11][13] MdpS also showed mild immunomodulatory activity, as the study found that it can cleave IgA to a certain extent.^[11] Since other IgA proteases of S. oralis have been described in prior literature, immunomodulation may be another adaptation advantageous for establishing the eubiotic biofilm.^[14]

septicaemia and meningitis in immunocompromised patients, usually in relation to chronic dental disease and/or prior treatment which could provide a point of entry.^{[2][3][6][7][8][13][15][16][17][18]} The infection most associated with S. oralis is infective endocarditis.^[17]