Streptococcus viridans
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|Streptococcus pyogenes Group A
|Streptococcus viridans
|Streptococcus milleri
|Streptococcus agalactiae Group B
|Streptococcus - anaerobes
|Microbiology and Assessment of Streptococcus
ℹ️ About
- Viridans streptococci is a collective term for a group of Gram-positive bacteria within the genus Streptococcus.
- These bacteria belong to different Lancefield groups, or in some cases, do not express Lancefield antigens at all.
Streptococcus viridans Bacteria
- Streptococcus salivarius: Often associated with Lancefield group K or none.
- Streptococcus mutans: Does not belong to any Lancefield group, and is primarily responsible for dental caries.
- Streptococcus sanguis: May belong to group H or none, commonly found in the oral cavity and associated with endocarditis.
- Streptococcus milleri: Belongs to groups A, C, F, or G, and is known for causing abscesses in various organs.
- Streptococcus bovis: Classified within group D, often linked to endocarditis and gastrointestinal malignancies.
- Streptococcus mitior: Does not belong to any Lancefield group, but is part of the oral flora and can cause infections.
Characteristics
- Most viridans streptococci are alpha-haemolytic , meaning they partially lyse red blood cells and produce a greenish discoloration on blood agar.
- These bacteria are resistant to bile and optochin , which distinguishes them from Streptococcus pneumoniae(which is optochin-sensitive).
Source
- These bacteria are part of the normal flora of the oral cavity , gastrointestinal tract , and genitourinary system . They are commensals but can become opportunistic pathogens in certain conditions.
Pathogenicity
- Subacute bacterial endocarditis: Often caused by Streptococcus mutans, Streptococcus mitior, Streptococcus bovis, or Streptococcus salivarius, typically in patients with pre-existing heart conditions or damaged heart valves.
- Dental caries: Streptococcus mutansplays a key role in tooth decay by forming biofilms (plaque) on the teeth and producing acids that erode tooth enamel.
- Abscess formation: Streptococcus milleriis notorious for causing abscesses in the liver, lungs, brain, and abdomen, often in patients with weakened immune systems or following surgery.
- Urinary Tract Infections (UTIs): Though less common, viridans streptococci can cause UTIs, particularly in immunocompromised individuals.
Resistance
- No significant resistance has been observed in viridans streptococci to commonly used antibiotics.
Sensitivity
- Viridans streptococci are generally sensitive to penicillin and erythromycin , which are first-line treatments for infections caused by these bacteria.
