Alpha-hemolytic streptococci

Alpha-hemolytic streptococci are a type of bacteria that, when grown on blood agar, produce a greenish discoloration of the surrounding medium. This is due to the partial (alpha) hemolysis of red blood cells. Alpha-hemolytic streptococci are part of the normal microflora of the mouth and throat in humans.

Classification

Alpha-hemolytic streptococci are classified into two groups: Streptococcus pneumoniae and viridans streptococci. S. pneumoniae is a major cause of pneumonia, meningitis, and otitis media (middle ear infection). Viridans streptococci, on the other hand, are a large group of species that are usually harmless but can cause endocarditis (inflammation of the heart's inner lining) in some cases.

Pathogenesis

Alpha-hemolytic streptococci can cause disease when they enter parts of the body where they are not usually found, such as the bloodstream, lungs, or the central nervous system. S. pneumoniae has a capsule that protects it from the immune system and allows it to cause disease. Viridans streptococci can form biofilms on the heart valves, leading to endocarditis.

Diagnosis and Treatment

Diagnosis of infections caused by alpha-hemolytic streptococci is usually done by culture of the bacteria from a sample of blood or other body fluid. Treatment typically involves antibiotics, with the choice of antibiotic depending on the species of bacteria and the site of infection.

Prevention

Vaccines are available for S. pneumoniae, and are recommended for certain high-risk groups, such as the elderly and people with certain chronic diseases. There is currently no vaccine for viridans streptococci.