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Viridans streptococci
Scientific classification
Domain:	Bacteria
Phylum:	Bacillota
Class:	Bacilli
Order:	Lactobacillales
Family:	Streptococcaceae
Genus:	Streptococcus

The viridans streptococci are a large group of commensal streptococcal Gram-positive bacteria species that are α-hemolytic, producing a green coloration on blood agar plates (hence the name "viridans", from Latin "vĭrĭdis", green), although some species in this group are actually γ-hemolytic, meaning they produce no change on blood agar. The pseudo-taxonomic term "Streptococcus viridans" is often used to refer to this group of species, but writers who do not like to use the pseudotaxonomic term (which treats a group of species as if they were one species) prefer the terms viridans streptococci, viridans group streptococci (VGS), or viridans streptococcal species.

These species possess no Lancefield antigens. In general, pathogenicity is low.

Identification

Viridans streptococci can be differentiated from Streptococcus pneumoniae using an optochin test, as viridans streptococci are optochin-resistant; they also lack either the polysaccharide-based capsule typical of S. pneumoniae or the Lancefield antigens of the pyogenic members of the genus.

Pathology

The organisms are most abundant in the mouth, and one member of the group, S. mutans, is the cause of dental caries in most cases and populations. S. sanguinis is also another potential cause. Others may be involved in other mouth or gingival infections as pericoronitis. If they are introduced into the bloodstream, they have the potential of causing endocarditis, in particular in individuals with damaged heart valves. They are the most common causes of subacute bacterial endocarditis. Viridans streptococci are identified in cases of neonatal infections.

Viridans streptococci have the unique ability to synthesize dextrans from glucose, which allows them to adhere to fibrin-platelet aggregates at damaged heart valves. This mechanism underlies their ability to cause subacute valvular heart disease following their introduction into the bloodstream (e.g., following dental extraction).

Identification

The "viridans" group is somewhat of a wastebasket or "grab bag" in streptococci classification. For a review on its identification and taxonomy, refer to Doern and Burnham (2010).

References

1. Sinner, Scott W.; Tunkel, Allan R. (2015-01-01), Bennett, John E.; Dolin, Raphael; Blaser, Martin J. (eds.), "204 - Viridans Streptococci, Nutritionally Variant Streptococci, Groups C and G Streptococci, and Other Related Organisms", Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases (Eighth Edition), Philadelphia: W.B. Saunders, pp. 2349–2361.e2, doi:10.1016/b978-1-4557-4801-3.00204-6, ISBN 978-1-4557-4801-3, retrieved 2022-04-01
2. Dorland's Illustrated Medical Dictionary, headword "streptococcus", subentry "viridans streptococci".
3. Ryan KJ, Ray CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 293–4. ISBN 978-0-8385-8529-0.
4. Viridans+Streptococci at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
5. Patterson MJ (1996). "Streptococcus". In Baron S; et al. (eds.). Baron's Medical Microbiology (4th ed.). Univ of Texas Medical Branch. ISBN 978-0-9631172-1-2.
6. Baucells, B.J.; Mercadal Hally, M.; Álvarez Sánchez, A.T.; Figueras Aloy, J. (2015). "Asociaciones de probióticos para la prevención de la enterocolitis necrosante y la reducción de la sepsis tardía y la mortalidad neonatal en recién nacidos pretérmino de menos de 1.500g: una revisión sistemática". Anales de Pediatría. 85 (5): 247–255. doi:10.1016/j.anpedi.2015.07.038. ISSN 1695-4033. PMID 26611880.
7. Doern, Christopher D.; Burnham, Carey-Ann D. (November 2010). "It's Not Easy Being Green: the Viridans Group Streptococci, with a Focus on Pediatric Clinical Manifestations". Journal of Clinical Microbiology. 48 (11): 3829–3835. doi:10.1128/JCM.01563-10. ISSN 0095-1137. PMC 3020876. PMID 20810781.

Further reading

Naveen Kumar, Venkatesan; van der Linden, Mark; Menon, Thangam; Patric Nitsche-Schmitz, D. (May 2014). "Viridans and bovis group streptococci that cause infective endocarditis in two regions with contrasting epidemiology". International Journal of Medical Microbiology. 304 (3–4): 262–268. doi:10.1016/j.ijmm.2013.10.004. PMID 24220665.

• Biology

• Streptococcaceae
• Gram-positive bacteria