Streptococcus viridans

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Light microscopy photo of gram-positive chained cocci, Streptococcus viridans, in blood culture specimen. Image credit: Dr. Mike Miller, CDC.

Classification

Bacteria; Fermicutes; Bacilli; Lactobacillales; Streptococcaceae

Species

NCBI: [1]

Streptococcus viridians

Description and Significance

Streptococcus viridians is a catalase negative and gram positive bacteria characterized as chained cocci. It is found on mucosal membranes such as the oral cavity and the gastrointestinal tract and has a very similar genetic sequence to S. pneumonniae (Doern et al., 2010.)

S. viridians can cause numerous infections including meningitis, arthritis, and septicemia. Those who are infected by this bacteria, may become resistant to various treatments such as antibiotics such as penicillin, drugs for reducing symptoms of cystic fibrosis, and chemotherapy. (Beighton et al., 1991.)

Genome Structure

S. viridians typically contain about 900 genes. The genome is typically circular, containing 2,146,661 base pairs within the sequence (Denapaite et al., 2010).

One interesting feature is that it is closely related to Streptococcus pneunomiae. Amplification using the method polymerase chain reaction (PCR) and gel electrophoresis show that there is very little difference between these species (Suzuki et al., 2005).

Cell Structure, Metabolism and Life Cycle

S. viridans is gram-negative and is shaped as a chain of cocci bacterium (Doern et al., 2010). This bacteria is unique in that it can gain energy anaerobically through glycolysis (Beighton et al., 1991). It can be cultured on various medias and can also grow in various temperatures (Doern et al., 2010).

This species of bacteria produce macromolecules called exopolysaccharides (EPS). EPS play an important roll of the protection of S. viridans within the body and allows them to withstand various environments (Mills et al. 1984).

Ecology and Pathogenesis

This organism causes disease through the invasion of the mucosal membranes in the human body. These regions include the oral cavity, upper respiratory tract, female genital tract, and gastrointestinal tract (Tunkel et al., 2002). S. viridians is unique as it has the ability to resist optochin, a chemical used to kill S. pneumoniae. It is also soluble in bile and lacks a capsule (Khanal, 2022). Virulence factors of S. viridians include dextran which can bind to aggregated heart fibers, and plaque-forming biofilms (Shenep, 2000). These virulence factors enable this organism to cause diseases such as endocarditis, dental infections, brain abscesses, sepsis, and meningitis when paired with S. pneumoniae (Khanal, 2022).