Streptococcus or Strep Bacteria: Infection and Disease
The Nature of Steptococcus
Streptococcus is a common bacterium in and on our bodies. Most types of streptococcus are harmless, but some are responsible for diseases such as pneumonia, tooth decay, strep throat, scarlet fever, rheumatic fever, impetigo and necrotizing fasciitis (flesh-eating disease). At least one type is beneficial, however. It's used to create fermented foods like certain yogurts and cheeses.
The singular term "streptococcus" and the plural term "streptococci" are used as general names for all the different forms of bacteria belonging to the genus Streptococcus. Many different species and strains of the genus exist.
Streptococci have round cells, which are often attached to each other to form pairs or chains. They are known as lactic acid bacteria because they feed on carbohydrates and obtain energy by converting the carbohydrates to lactic acid. They don’t need oxygen to survive. Some can use oxygen if it's available but can also live without it; some don't use oxygen but can tolerate its presence; and some are inhibited by oxygen.
Streptococcus pyogenes and Streptococcus mutans are scientific names. The scientific name of an organism consists of two words - the genus and the species. The first word in the name is the genus and the second word is the species.
Streptococci are divided into two major groups.
- Alpha-hemolytic: includes Streptococcus pneumoniae (a major cause of pneumonia) and the viridans streptococci (including Streptococcus mutans, a major cause of tooth decay)
- Beta-hemolytic: includes group A and group B streptococci as well as types classified with other letters
The word "hemolysis" means destruction of red blood cells. When most types of alpha-hemolytic bacteria are grown on blood agar, they change the agar from red to green. Although viridans streptococci are classified in the alpha-hemolytic group, some are non-hemolytic. Beta-hemolytic bacteria turn blood agar into a yellow, transparent material.
In this article I'll discuss some of the health problems caused by group A streptococcus (GAS) and group B streptococcus (GBS). Both types of bacteria can have significant effects on humans.
Group A Streptococcus (GAS)
Streptococci in group A live on our skin and in our throats and usually cause no problems. Occasionally they make us ill, however. The illnesses are generally relatively mild, such as strep throat, impetigo or scarlet fever, but they may be more serious, like rheumatic fever.
Rarely, the bacteria become invasive and penetrate further into the body, as occurs in necrotizing fasciitis. An invasive GAS infection can be very dangerous. In general, the people who develop invasive infections have a chronic illness or are elderly, but this isn't always the case.
The various strains of GAS all belong to one species - Streptococcus pyogenes. Strains are slightly different members of a species.
A Doctor Discusses Strep Throat
Strep throat is also known as streptococcal pharyngitis. The disorder generally occurs in children and young teenagers. It's spread by drops of saliva or nose fluid transferred from an infected person. This transfer is most likely to happen in a crowded environment.
Symptoms of a strep throat include a red, swollen and painful throat and white patches on the tonsils. Lymph nodes may also be swollen. In addition, the sufferer may experience a fever, a headache, nausea, vomiting or stomach pain.
Strep throat is usually treated by antibiotics, even though the infection may go away without treatment, in order to prevent the bacteria from travelling deeper into the body and causing a more serious illness.
Not every sore throat is caused by streptococcus. A sore throat caused by a virus won't respond to antibiotic treatment. A test called a throat swab is often performed to confirm the presence of a streptococcus bacterium.
A Case of Scarlet Fever
An untreated case of strep throat may lead to scarlet fever. Scarlet fever is not the serious disease that it once was, but it's still an unpleasant illness. The streptococcus bacteria responsible for strep throat produce a toxin. In some people, the toxin causes a bright red rash on the skin. The rash generally appears on the face and neck first and then spreads to other parts of the body. Red streaks may form in skin creases.
In addition to a rash and a sore throat, someone with scarlet fever may have swollen neck glands, a fever, body aches, nausea and vomiting. Antibiotics are generally used to treat the disorder.
Complications of Strep Throat
Rheumatic fever is a serious disorder that is a potential complication of a strep throat or scarlet fever infection. The illness involves widespread inflammation that may occur in several parts of the body, including the joints, heart and nervous system. Rheumatic fever generally occurs in children and teenagers, but it sometimes develops in adults. The disorder generally appears two to three weeks after the initial streptococcus infection.
Symptoms of rheumatic fever may include joint pain and swelling, a fever, a rash, nodules under the skin, stomach pain, nosebleeds, chest pain and shortness of breath due to an inflamed heart, and jerky movements. There may be permanent damage to the heart valves. Treatment usually involves antibiotics and anti-inflammatory medications. Adults who develop rheumatic fever may find that they experience recurring episodes of the illness.
As with any of the health problems described in this article, it's important that people with unexplained symptoms consult a doctor for a diagnosis and treatment recommendations.
A Doctor Discusses Impetigo
Impetigo is a common and easily spread skin infection in children. It also occurs in adults. The disorder is caused by group A streptococci as well as some other types of streptococcus. It's characterized by the appearance of blisters on the skin, especially around the nose and mouth. The blisters may also appear on the neck, hands, forearms and diaper area.
Impetigo is spread by body contact with an infected area on someone's skin or by touching items that have rubbed against the blisters, such as toys or towels. Doctors generally treat the disease with a topical antibiotic, which is placed on the blisters, or with an oral antibiotic.
Necrosis is the death of body tissue. A fascia is a sheath of connective tissue that surrounds muscles. In necrotizing fasciitis (pronounced "fasheitis"), fasciae are inflamed and destroyed due to a streptococcus infection. Skin and the fat under the skin may be destroyed as well as the fasciae and muscles.
Necrotizing fasciitis is rare but potentially very serious. It's sometimes known as the flesh-eating bacteria disease. The disease may involve other types of bacteria as well as or instead of streptococcus. The chance of developing necrotizing fasciitis increases if a person has a skin wound when they are exposed to bacteria that can cause the disease. A weakened immune system or a chronic disease such as diabetes, kidney disease, liver disease or cancer may also allow necrotizing fasciitis to develop.
Symptoms of necrotizing fasciitis include a wound that becomes very painful, red, hot and swollen. The tissue will eventually turn purple or black if the infection isn't treated. The patient may also experience a fever, chills, nausea, vomiting and diarrhea. He or she may go into shock and have organ failure.
Flesh-Eating Bacteria and Necrotizing Fasciitis
Treatment for Necrotizing Fasciitis
Necrotizing fasciitis progresses rapidly and requires early and aggressive treatment. Antibiotics are generally given to kill bacteria. Surgery is often needed to remove infected and dead tissue. Sometimes limbs need to be amputated. Extra treatments will be required if a person is in shock or has organ damage. Hyperbaric oxygen therapy is helpful in some cases of necrotizng fasciitis. In this therapy, oxygen is forced into the patient's tissues under high pressure.
Although necrotizing fasciitis can be life threatening, it can be treated successfully. One of my acquaintances (who was in his twenties and healthy at the time) developed the disease after a skin wound on his arm. He required antibiotics and hyperbaric oxygen therapy to treat the infection as well as multiple surgeries to remove infected and dead tissue. Once he recovered from the infection, he received plastic surgery on his arm. Although complete recovery took a long time, he is now able to play the guitar again, which is one of his favourite activities.
Most cases of necrotizing fasciitis are caused by streptococcus. In Aimee Copeland's case, however, the causative agent was a bacterium named Aeromonas hydrophila. Aimee survived the infection, but she required amputations in order to do so. She lost both hands, one leg and one foot. She also experienced multiple organ failure during the infection.
Aimee Copeland's Recovery from Necrotizing Fasciitis
Group B Streptococcus (GBS)
In many people, group B streptococci are a normal component of the bacterial population in the large intestine. The bacteria may also live in the reproductive tract and the urinary tract. They generally produce no symptoms in healthy people. They may cause disease in elderly people or in people who have health problems such as diabetes, cancer, liver disease or kidney disease, however. They may also cause a problem in newborn babies.
As in the case of group A streptococci, the different strains of GBS all belong to one species - in this case, Streptococcus agalactiae. Also like group A bacteria, they may sometimes become invasive.
Group B Strep Infection in Adults
People aged 65 or older or people with certain chronic diseases are most likely to develop symptoms of a GBS infection. Infected people may develop skin problems or a urinary tract infection. More seriously, they may develop pneumonia, a blood infection (sepsis), a bone infection, inflamed heart valves or meningitis. Meningitis is a disorder in which the membranes around the brain become inflamed.
It's important that people with any of the following symptoms visit a doctor for a diagnosis and treatment. A relatively mild infection that is untreated may become more serious. Symptoms of GBS disease may include:
- Inflamed bumps on the skin
- Symptoms of a urinary tract infection, such as a burning sensation when urinating and excessive urination
- Difficulty breathing
- Rapid breathing
- Chest pain
- Stiff joints
Group B Streptococcus and Newborn Babies
If a woman with group B streptococci in her reproductive tract becomes pregnant, her baby may become colonized with the bacteria during birth. Generally this colonization causes no ill effects. However, in some cases (if no treatment is provided), the baby develops a serious disease, such as pneumonia, meningitis or blood infections, all of which may be life-threatening. Premature babies are more susceptible to infection than full-term babies.
Modern prevention and treatment programs have greatly reduced the problem of a GBS infection in newborns. Woman are often tested for the presence of a group B streptococcus before their baby is born. If the bacteria are present, intravenous antibiotics may be given during labour. Doctors generally don't give the mother antibiotics any earlier since the bacteria may regrow before the baby is born. The baby is tested for the presence of the bacteria after birth and treated if necessary.
A GBS infection transmitted to a baby during birth and producing symptoms during the first week of its life is known as early-onset group B strep disease. Some babies develop an infection between one week and three months after birth, however. This infection is known as late-onset disease and is not well understood. Unfortunately, it can't yet be prevented, but it can be treated.
Streptococci are interesting but sometimes troublesome bacteria that may have major effects on our lives. Although the ability of Streptococcus to cause multiple health problems is fascinating biologically, the problems can sometimes be serious or even life threatening. I hope we soon find more effective ways to prevent and treat streptococcus infections.
References and Further Information
© 2011 Linda Crampton