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Streptococcus bacteria is a genus of coccus, or spherelike, Gram-positive, chained bacteria belonging to the lactic acid bacteria (LAB) group. Individual streptococcus cells may be round or ovoid and all lack the enzyme catylase. Because these cells divide along a single plane, streptococci occur in pairs or in chains.
Like many other types of bacteria in the firmicute phylum, streptococcus bacteria stains dark blue or violet when subject to Gram staining due to the composition of its cell wall. This is what is meant by Gram-positive. As a member of the lactic acid bacteria group, this bacteria is resistant to acidic conditions and thrives on no oxygen or levels of oxygen below the concentration of oxygen in air.
Streptococcus bacteria is divided into eighteen alphabetized groups, called Lancefield groups. American bacteriologist Rebecca Craighill Lancefield developed this method of classifying streptococci in 1933 based on the antigens, or antibody producing substances, found in the cell wall of the streptococcus bacteria under examination. Several types of streptococcus do not react to Lancefield grouping, however, and must be classified using hemolysis, which monitors how completely the bacterium breaks down in a blood solution.
The group viridans streptococcus is either non-hemolytic or breaks down only partially, causing the green stain responsible for the name “viridans.” This large and diverse group of streptococcus does not have reliable taxonomy (classification) or nomenclature as of yet. Many types of streptococcus can cause disease and infection in humans, while many others are harmless. Group A streptoccus, Group B streptococcus, Viridans streptococcus and S Pneumoniae are the types most commonly of medical concern.
Group A streptococcus (GAS), or S pyogenes, is one of the most common pathogens in humans. A GAS infection can affect several locations of the body, and are frequently categorized by location. One of the most well known of these is strep throat. Strep throat affects the pharynx and causes several symptoms, among them severe sore throat, swollen tonsils, nausea, headaches and yellow and white patches in the throat.
GAS can be deadly as the cause of puerperal fever, or sepsis in women after childbirth. Sepsis is when a microbe enters the bloodstream, possibly causing a serious systemic reaction. GAS was also responsible for attacks of scarlet fever which, like puerperal fever, are now controlled through better hygiene and antibiotics. In the skin, GAS can cause impetigo, cellulitis and erysipelas. GAS infections may also cause pneumonia, meningitis, tonsillitis, septic arthritis and toxic shock syndrome, amongst other diseases.
Group B streptococcus bacteria (GBS), or S agalactiae, is frequently found in the urogenital tracts and rectums of women of child-bearing age. Complications may arise in women with compromised immune systems, but it is more commonly significant when transmitted to babies during childbirth. A GBS infection of a newborn can cause meningitis or sepsis, which may lead to death or long term hearing loss. Neonatal meningitis presents differently than adult meningitis, with symptoms of vomiting and fever. For this reason, neonatal meningitis often goes undiagnosed and can be fatal.
Streptococcus viridans is often responsible for dental infections and the formation of plaque. This type of bacteria, along with Group C, F, G and particularly D, can cause endocarditis, especially when the valves of the heart are previously damaged. Endocarditis is the inflammation of the inner layer of the heart, known as the endocardium.
Streptococcus pneumoniae, or pneumococcus, is the most common cause of invasive bacterial infection of children and the elderly. It can cause pneumonia, sinusitis and meningitis, amongst other diseases. Streptococcus pneumoniae may cause either lobar pneumonia, which affects an entire lung lobe, usually in younger adults, or bronchial pneumonia, which affects the alveoli, tending towards older adults or children.