Classified into groups based on the presence of serologically defined carbohydrate capsules.
Group A streptoccus infections produce skin and pharyngeal infections.
Group A organisms associated with immunologically related disorders of glomerulonephritis and acute rheumatic fever.
Viridans group streptococci are common commensal components of the human oral pharyngeal flora.
Streptococci mutants is identified as a major contributor to tooth decay and dental caries.
Streptococcal species are the most common cause of native-valve endocarditis in adults, accounting for 45-65% of cases.
A genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group.
Grow in chains or pairs.
Most streptococci are oxidase- and catalase-negative, and many are facultative anaerobes.
Species of streptococcus classified based on their hemolytic properties.
Alpha hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, resulting in the appearance of a greenish color on blood agar.
Beta hemolytic species cause complete rupture of red blood cells, and on blood agar appears as wide areas clear of blood cells surrounding bacterial colonies.
Gamma-hemolytic species cause no hemolysis.
Streptococcal infections may be responsible for streptococcal pharyngitis, pink eye, meningitis, bacterial pneumonia, endocarditis, erysipelas and necrotizing fasciitis.
Infected endocarditis incidence due to Viridans group Streptococci has not increased despite reduction in indications for antibiotic prophylaxis for invasive dental procedures (DeSimone DC et al).
Many species are nonpathogenic, and form part of the normal human flora of the mouth, skin, intestine, and upper respiratory tract.
Beta-hemolytic streptococci are characterized via Lancefield serotyping, which describes specific carbohydrates present on the bacterial cell wall.
There are 20 described serotypes, named Lancefield groups A to V.
Clinically the most important groups are the alpha-hemolytic streptococci, S. pneumoniae and Streptococcus Viridans-group, and the beta-hemolytic streptococci of Lancefield groups A and B, known as Group A strep and Group B strep.
S. pneumoniae (Pneumococcus), is a leading cause of bacterial pneumonia and occasional etiology of otitis media, sinusitis, meningitis and peritonitis.
The Viridans group: has alpha-hemolytic and Beta-hemolytic grous.
Group A S. pyogenes, also known as Group A Streptococcus (GAS), is the causative agent in a wide range of Group A streptococcal infections.
Group A streptococcal infections may be non-invasive or invasive.
The non-invasive infections tend to be more common and less severe, and include streptococcal pharyngitis and impetigo.
Scarlet fever is also a non-invasive infection, but has not been as common in recent years.
Invasive infections cause by Group A β-hemolytic streptococcus tend to be more severe but less common.
Invasive infections cause by Group A β-hemolytic streptococcus are manifested as streptococcal toxic shock syndrome (STSS), necrotizing fasciitis (NF), pneumonia, and bacteremia.
Group A β-hemolytic streptococcus infection complications include acute rheumatic fever and acute glomerulonephritis.
Rheumatic fever, a disease that affects the joints, kidneys, and heart valves, is a consequence of untreated strep A infection and is not caused by the bacterium, rather it is caused by the antibodies created to fight off the infection but cross-reacting with other proteins.
GAS estimated to cause more than 500,000 deaths every year worldwide, making it one of the world’s leading pathogens.
Group A Streptococcus infectionsvare generally diagnosed with a Rapid Strep Test or by culture.
Group B, S. agalactiae, or GBS, causes pneumonia and meningitis in neonates, and in the elderly, with occasional systemic bacteremia.
Group B streptococci can also colonize the intestines and the female reproductive tract, increasing the risk for premature rupture of membranes during pregnancy, and transmission of the organism to the infant.
It is recommend that all pregnant women between 35 and 37 weeks gestation should be tested for GBS, and women with positive tests should be given prophylactic antibiotics during labor, to prevent transmission to the infant.
Group C Streptococcus dysgalactiae is also a β-haemolytic streptococci that can cause pharyngitis and other pyogenic infections similar to Group A streptococci.
Many Group D enterococci have been reclassified and placed in the genus Enterococcus including Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, and Enterococcus avium.
The remaining nonenterococcal Group D strains include Streptococcus bovis and Streptococcus equinus.
Nonhemolytic streptococci rarely cause illness.