Little consistency in describing, usually six major groups in modern era.

Heterogeneous group: may be commensals or pathogens.May also be common bloodstream contaminant, but need to clinically correlate and rule out systemic process such as endocarditis.If isolated from CSF or respiratory sections, usually contaminants, but occasionally responsible for disease.Common cause of dental infections, subacute bacterial endocarditis, bacteremia.Usually α-hemolytic or non-(γ)-hemolytic. Viridans Streptococci: oropharynx/GI tract usual niche.Most prevalent in southeast Asia, where it is a common cause of meningitis, hearing loss, cutaneous lesions, and bacteremia.suis: zoonotic pathogen associated with pig farming or exposure to contaminated pork products.

Rarely 'contaminants' when present in blood cultures.

milleri' no longer appropriate): propensity for invasion, meningitis, abscess production (e.g., head & neck infections), bacteremia. constellatus group (microaerophilic strep ' S. bovis biotype I): associated with colonic malignancy and hepatobiliary disease.

Group D streptococci (non-enterococcal, e.g., S.

Groups C, F, G streptococci: bacteremia, endocarditis, septic arthritis, osteomyelitis, pharyngitis, skin and soft tissue infections, meningitis, puerperal infection, neonatal sepsis.

More common in adults >65 and those w/ co-morbidities.

Cause of neonatal sepsis/meningitis, puerperal sepsis, chorioamnionitis, peripartum endometritis, bacteremia (often without clear source), skin and soft-tissue infections, septic arthritis, pneumonia, endocarditis, osteomyelitis.

Facklam classification presented here (see references).

16S rRNA gene sequencing (1990’s) yield true phylogenetic relationships.

Formerly nutritionally-variant Streptococci.

Streptococcal-like, catalase-negative, Gram-positive cocci.

Lactococci: generally not human pathogens.

Other organisms previously classified as Streptococci are now separate genera:.

Usually yield α-hemolysis on blood agar (green surrounding colony - hence name, viridans) may be β-hemolytic or non-hemolytic (latter sometimes termed γ-hemolysis).

See separate module for details on this organism.

Group A streptococci: cause complete hemolysis/lysis of red cells in blood agar media around/under colonies caused by streptolysin (exotoxin), so called β-hemolysis.

Pyogenic (beta-hemolytic) including Groups A, B, C, E, F & G.

Broadly organized into two groups by hemolysis, Lancefield and phenotype testing (1937):.Often described by 5% sheep blood agar hemolysis (1902) or Lancefield carbohydrate group antigens (1933).Nomenclature and taxonomy of streptococci confusing because of many historical efforts at describing the class.

Bet ag sketchy