Streptococcus viridans: Definition from Answers.com

Streptococcus viridans-group

Scientific classification
Kingdom:	Bacteria
Phylum:	Firmicutes
Class:	Cocci
Order:	Lactobacillales
Family:	Streptococcaceae
Genus:	Streptococcus

Viridans Streptococcus is a pseudotaxonomic non-Linnaenan term for a large group of commensal streptococcal bacteria that are either α-hemolytic, producing a green coloration on blood agar plates (hence the name "viridans", from Latin "vĭrĭdis", green), or nonhemolytic. They possess no Lancefield antigens.^[1]

In general, pathogenicity is low.^[2]

Contents

1 Identification
2 Pathology
3 Treatment
4 References

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.^[3]

	Viridans streptococci	Streptococcus pneumoniae
Solubility in bile	Insoluble	Soluble
Fermentation of inulin	Not a fermenter	Fermenter with acid production
Sensitivity to optochin	Not sensitive	Sensitive
Pathogenicity to mice	Nonpathogenic	Pathogenic
Quellung test	Negative	Positive

Pathology

The organisms are most abundant in the mouth, and one member of the group, S. mutans, is the etiologic agent of dental caries. Others may be involved in other mouth or gingival infections.

If they are introduced into the bloodstream, they have the potential of causing endocarditis, particularly in individuals with damaged heart valves. They are the most common causes of subacute bacterial endocarditis.

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 tooth extraction).

Treatment

See List of antibiotics.

References

^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 293–4. ISBN 0838585299.
^ MeSH Viridans+Streptococci
^ Patterson MJ (1996). "Streptococcus". Baron's Medical Microbiology (Baron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1. http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.824.

Firmicutes (low-G+C) Infectious diseases · Bacterial diseases: G+ (primarily A00–A79, 001–041, 080–109)

Bacilli

Lactobacillales
(Cat-)

Streptococcus

α	optochin susceptible: S. pneumoniae (Pneumococcal infection) optochin resistant: S. viridans: S. mitis, S. mutans, S. oralis, S. sanguinis, S. sobrinus, milleri group

β	A, bacitracin susceptible: S. pyogenes (Scarlet fever, Erysipelas, Rheumatic fever, Streptococcal pharyngitis) B, bacitracin resistant, CAMP test+: S. agalactiae ungrouped: Streptococcus iniae (Cutaneous Streptococcus iniae infection)

γ	D, BEA+: Streptococcus bovis

Enterococcus

BEA+: Enterococcus faecalis (Urinary tract infection) · Enterococcus faecium

Bacillales
(Cat+)

Staphylococcus	Cg+ S. aureus (Staphylococcal scalded skin syndrome, Toxic shock syndrome, MRSA) Cg- novobiocin susceptible (S. epidermidis) · novobiocin resistant (S. saprophyticus)

Bacillus	Bacillus anthracis (Anthrax) · Bacillus cereus (Food poisoning)

Listeria	Listeria monocytogenes (Listeriosis)

Clostridia

Clostridium (spore-forming)	motile: Clostridium difficile (Pseudomembranous colitis) · Clostridium botulinum (Botulism) · Clostridium tetani (Tetanus) nonmotile: Clostridium perfringens (Gas gangrene, Clostridial necrotizing enteritis)

Peptostreptococcus (non-spore forming)	Peptostreptococcus magnus

Mollicutes

Mycoplasmataceae	Ureaplasma urealyticum (Ureaplasma infection) · Mycoplasma genitalium · Mycoplasma pneumoniae (Mycoplasma pneumonia)

Anaeroplasmatales	Erysipelothrix rhusiopathiae (Erysipeloid)

M: BAC

bact (clas)

gr+f/gr+a(t)/gr-p(c)/gr-o

drug(J1p, w, n, m, vacc)

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Streptococcus viridans