| Viridans streptococci | |
|---|---|
 | |
Scientific classification | |
| Domain: | Bacteria |
| Kingdom: | Bacillati |
| Phylum: | Bacillota |
| Class: | Bacilli |
| Order: | Lactobacillales |
| Family: | Streptococcaceae |
| Genus: | Streptococcus |
Theviridans streptococci are a large group ofcommensalstreptococcalGram-positive bacteria species that areα-hemolytic, producing a green coloration onblood 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.[1] 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 termsviridans streptococci,[2]viridans group streptococci (VGS), orviridans streptococcal species.
These species possess noLancefieldantigens.[3] In general,pathogenicity is low.[4]
Viridans streptococci can be differentiated fromStreptococcus pneumoniae using anoptochin test, as viridans streptococci are optochin-resistant; they also lack either thepolysaccharide-basedcapsule typical ofS. pneumoniae or theLancefield antigens of thepyogenic members of the genus.[5]
| Viridans streptococci | Streptococcus pneumoniae | |
|---|---|---|
| Lysed in bile | Insoluble | Soluble |
| Fermentation of inulin | Not a fermenter | Fermenter with acid production |
| Sensitivity tooptochin | Not sensitive | Sensitive |
| Pathogenicity to mice | Nonpathogenic | Pathogenic |
| Quellung test (not actively used[citation needed]) | Negative | Positive |
The organisms are most abundant in the mouth, and one member of the group,S. mutans, is the cause ofdental caries in most cases and populations.S. sanguinis is also another potential cause. Others may be involved in other mouth or gingival infections aspericoronitis. If they are introduced into the bloodstream, they have the potential of causingendocarditis, in particular in individuals with damagedheart valves. They are the most common causes ofsubacute bacterial endocarditis. Viridans streptococci are identified in cases ofneonatal infections.[6]
Viridans streptococci have the unique ability to synthesizedextrans fromglucose, which allows them to adhere tofibrin-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., followingdental extraction).
The "viridans" group is somewhat of awastebasket or "grab bag" in streptococci classification. For a review on its identification and taxonomy, refer to Doern and Burnham (2010).[7]
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.
