Streptococci and Streptococcal Infections (World of Microbiology and Immunology)
Streptococci are spherical, Gram positive bacteria. Commonly they are referred to as strep bacteria. Streptococci are normal residents on the skin and mucous surfaces on or inside humans. However, when strep bacteria normally found on the skin or in the intestines, mouth, nose, reproductive tract, or urinary tract invade other parts of the bodyia a cut or abrasionnd contaminate blood or tissue, infection can be the result.
Numerous strains of strep bacteria have been identified. Those streptococci from groups A, B, C, D, and G are most likely to cause disease. While some of these infections do not produce symptoms, and the infected person can become a carrier of the disease-causing bacteria, other strep infections can be fatal.
Primary strep infections invade healthy tissue, and most often affect the throat. Secondary strep infections invade tissue already weakened by injury or illness. They frequently affect the bones, ears, eyes, joints, or intestines. Both primary and secondary strep infections can travel from affected tissues to lymph glands, enter the bloodstream, and spread throughout the body.
Group A streptococci contains those strep bacteria that are most apt to be associated with serious illness. Between 10,000 and 15,000 infections attributable to group A streptococci occur in the United States every year. Most are mild inflammations of the throat or skin, the environments where the bacteria are normally found. However, other infections can be deadly.
One example of a serious infection is known as necrotizing fasciitis (which is also referred in the popular press as flesh-eating disease). The disease results from the invasion of host tissue cells by the bacteria. There, shielded from the immune responses of the host, toxic bacterial products cause the destruction of muscle tissue and fat. The infection is able to quickly spread outward from the point of origin. Unless intervention is undertaken quickly, which includes antibiotic therapy and, in severe cases where a limb is involved, amputation of the affected limb, the infection can be fatal.
A second example of a serious group A streptococcal infection manifests toxic shock syndrome.
Another division of streptococci is known as group B. Infections caused by group B streptococci most often affects pregnant women, infants, the elderly, and chronically ill adults. Group B was designated in the 1970s. The intervening years have revealed group B streptococci to be the primary cause of life-threatening illness and death in newborns. The bacteria reside in the reproductive tract of a quarter of all pregnant women. Only a small percentage of these women develop invasive infection. However, about half of those who are infected will transmit the bacteria to their babies during delivery.
In the United States, about 12,000 newborns will be infected each year. Of these, about 8,000 develop early-onset infection within hours or days of birth. Complications include inflammation of the membranes covering the brain and spinal cord (meningitis), pneumonia, and blood infection (sepsis). In other infants, meningitis will develop in the first three months of life.
The streptococci in group D are a common cause of wound infections in hospital patients. As well, group D streptococci are associated with abnormal growth of tissue in the gastrointestinal tract, urinary tract infection, and infections of the womb in women who have just given birth.
Another group of the streptococci that is of concern to human health is group G. Normally present on the skin, in the mouth and throat, and in the intestines and genital tract, group G streptococci can cause opportunistic infections in people whose immune systems are compromised by disease, therapy, or neglect. Candidates for infection include severe alcoholics, those with cancer, diabetes mellitus, and rheumatoid arthritis. The bacteria of this group can cause a variety of infections, including infection of the bloodstream (bacteremia), inflammation of the connective tissue structure surrounding a joint (bursitis), infection of various regions of the heart and heart valves (endocarditis), meningitis, inflammation of bone and bone marrow (osteomyelitis), and the inflammation of the lining of the abdomen (peritonitis).
The conventional treatment for streptococcal infections is the administration of antibiotics. Many strains of strep are still susceptible to penicillin. However, strains of Streptococcus pneumonia that are resistant to multiple antibiotics are a problem in hospitals world-wide.
Prevention of infection involves keeping wounds clean and good hygienic practices, such as frequent hand washing, especially before eating and after using the bathroom.
See also Bacteria and bacterial infection