Individual cells of S. oralis are arranged into characteristic long chains when viewing
subcultures under
a microscope.[6] It is a
non-motile,
non-sporulatingfacultative anaerobe.[7] The optimal
culturing temperature range for S. oralis is 35 - 37°C, with growth observed between 10 - 45°C.[7][8][9]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. oraliscolonies are white, grey, or colourless; translucent; smooth; entire; raised cluster colonies 0.5-2.0 mm in diameter.[9]
S. oralis is one of a few pioneer species important in early colonisation of the dental pellicle, where it establishes an eubiotic biofilm believed to be protective for
teeth.[5][10][11] It discourages
competition by other mouth
commensals and
pathobionts such as
S. mutans and Candida albicans implicated in
dysbiotic biofilm formation by
sequestering nutrients and releasing metabolites such as
H2O2.[5][12] A recent
study by Leo et al. has investigated the potential
mechanism employed by S. oralis to achieve biofilm establishment.[11] The study described a novel
protease therein named MdpS released
extracellularly by S. oralis, which directly breaks down
MUC5B, an
O-glycosylatedprotein 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] However, further research is required to establish these mechanisms further.
Like other streptococci and oral commensals, S. oralis also shows high genetic diversity.[15] As such, it is competent for
natural genetic transformation.[19]S. oralis cells are able to take up exogenous DNA and incorporate exogenous sequence information into their genomes by
homologous recombination.[20] These bacteria can employ a predatory fratricidal mechanism for active acquisition of homologous DNA.[20]
^
abPatterson, Maria Jevitz (1996), Baron, Samuel (ed.),
"Streptococcus", Medical Microbiology (4th ed.), Galveston (TX): University of Texas Medical Branch at Galveston,
ISBN978-0-9631172-1-2,
PMID21413248, retrieved 2024-02-26
^
abHardie, Jeremy M.; Whiley, Robert A. (2006), Dworkin, Martin; Falkow, Stanley; Rosenberg, Eugene; Schleifer, Karl-Heinz (eds.),
"The Genus Streptococcus—Oral", The Prokaryotes: Volume 4: Bacteria: Firmicutes, Cyanobacteria, New York, NY: Springer US, pp. 76–107,
doi:
10.1007/0-387-30744-3_2,
ISBN978-0-387-30744-2, retrieved 2024-02-26