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Streptococcus Bacteria in Groups A and B: Facts and Diseases

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Streptococcus pyogenes cells (stained red) often join to form chains.

Streptococcus pyogenes cells (stained red) often join to form chains.

Streptococcus Bacteria

Streptococcus is a common genus of bacteria in and on our bodies. Some members of the genus are harmless, but others are responsible for problems such as tooth decay, pneumonia, strep throat, 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.

Genus names are normally capitalized. Streptococcus is such a common genus that the uncapitalized terms "streptococcus" (singular) and "streptococci" (plural) are often used to refer to the members of the genus. The genus is divided into a number of groups. Two groups that are important with respect to human health are Group A and Group B. I discuss the following topics related to these groups in this article.

  1. The Lancefield classification system for bacteria
  2. Features of streptococcus cells
  3. Group A streptococcus (or GAS) facts
  4. Five diseases caused by GAS
  5. Group B streptococcus (or GBS) facts
  6. Adult and infant problems caused by GBS
Streptococcus mutans, an important cause of tooth decay

Streptococcus mutans, an important cause of tooth decay

Scientific Names

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. Like S. pyogenes, S. mutans cells often join to form chains.

The Lancefield Classification System

Bacteria are amazing organisms with many different features. Scientists have tried to bring order to their classification. The Lancefield system for classifying a particular category of bacteria was created by a microbiologist named Rebecca Lancefield (1891 to 1985). The bacteria that she studied belonged to the family Streptococcaceae and were Gram-positive and catalase-negative.

The results of the Gram staining test depend on the structure of the outer covering of a bacterial cell. Gram-positive cells and Gram-negative ones display a different color when they are tested with the stain. The term "Gram" is derived from the name of Hans Christian Gram, who created the staining procedure. Catalase is an enzyme that converts hydrogen peroxide to water and oxygen. It's found in many organisms that use oxygen. Streptococci lack the enzyme, however.

Lancefield divided the bacteria into alphabetical groups going from Group A to Group S. Her system is not often used in its original form today, but the Group A and B categories are still used. As in the case of the name of the bacterium’s genus, the word "group" in the terms “Group A” and “Group B” is sometimes capitalized but often isn't.

Groups and Features of Streptococcus Cells

The various strains of group A streptococcus (GAS) all belong to one species—Streptococcus pyogenes. Strains are slightly different members of a species. As in the case of group A streptococci, the different strains of group B streptococcus (GBS) all belong to one species—in this case, Streptococcus agalactiae.

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 into 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.

An Important Note

The disease information in this article is given for general interest. Someone who experiences any of the symptoms that are mentioned below should visit a doctor for a diagnosis and treatment. People who are at risk for a streptococcus infection or who have questions about any of the disorders that the genus can cause should also consult their doctor.

Group A Streptococcus (GAS) Facts

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.

A normal and an infected throat; one cause of white spots on tonsils is group A streptococcus

A normal and an infected throat; one cause of white spots on tonsils is group A streptococcus

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 may 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 often treated by antibiotics 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.

Scarlet Fever Disease

An untreated case of strep throat may lead to scarlet fever. Scarlet fever is generally 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 often used to treat the disorder.

A Disease Comeback

In recent years, researchers have noticed that scarlet fever appears to be making a comeback. At the moment, this observation hasn't been explained, but at least one theory has appeared. Researchers at the University of Queensland in Australia have been studying the situation in cooperation with scientists from other countries. They believe that the increased occurrence of scarlet fever has been caused by a viral infection of the bacteria. They are afraid that the bacteria are becoming “stronger” as well as more common.

Viruses contain genetic material, but they don't consist of cells and can't reproduce on their own. They must enter a cell in order to use its equipment for generating new virus particles. The researchers believe that a virus has left genes behind in scarlet fever bacteria that enable the bacteria to make novel toxins. As the microbes with the new genes reproduce and pass copies of their genes to their offspring, the disease that they cause becomes more serious.

Though the researchers’ idea is still a theory, the fact that scientists from multiple institutions are contributing to the research suggests that it should be taken seriously. At the moment, though the disease is becoming more common, the researchers haven’t noticed fatalities due to the infection. Antibiotics are still helping. The potential development of antibiotic resistance in the bacteria is a concern, however, as it is in all bacterial infections.

Rheumatic Fever

Rheumatic fever is a potentially serious disorder that may be a 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, shortness of breath due to an inflamed heart, and jerky movements. There may be permanent damage to the heart valves. Treatment often involves antibiotics and anti-inflammatory medications. Adults who develop rheumatic fever may find that they experience recurring episodes of the illness.


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 or red patches 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 often treat the disease with a topical antibiotic, which is placed on the blisters, or with an oral antibiotic.

In this example of necrotizing fasciitis, the tissue in the middle has undergone necrosis (tissue death). This is why the cells are no longer visible.

In this example of necrotizing fasciitis, the tissue in the middle has undergone necrosis (tissue death). This is why the cells are no longer visible.

Necrotizing Fasciitis

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 eventually turns 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.

Possible Treatment for Necrotizing Fasciitis

Necrotizing fasciitis progresses rapidly and requires early and aggressive treatment. Antibiotics are generally given to kill bacteria. Surgery is sometimes 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 necrotizing 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.

Aeromonas hydrophila

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. Her story is told below.

Group B Streptococcus (GBS) Facts

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. Unfortunately, they may cause disease in elderly people or in ones who have health problems such as diabetes, cancer, liver disease, or kidney disease. They may also cause a problem in newborn babies. Like group A bacteria, group B ones sometimes become invasive.

Streptococcus agalactiae growing on blood agar

Streptococcus agalactiae growing on blood agar

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
  • fever
  • chills
  • difficulty breathing
  • rapid breathing
  • cough
  • 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. This colonization may cause no ill effects. In some cases, however (if no treatment is provided), the baby may develop 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.

Interesting and Troublesome Bacteria

Streptococci are interesting but sometimes troublesome bacteria that may have major effects on our lives. Although the ability of groups A and B streptococci to cause multiple health problems is fascinating biologically, the problems can sometimes be serious or even life threatening. Hopefully, we will soon find more effective ways to prevent and treat streptococcus infections of any type.


  • Group A Streptococcal Infections” from HealthLinkBC (a government of British Columbia organization)
  • Strep throat information from the Mayo Clinic
  • Facts about scarlet fever from the CDC (Centers for Disease Control and Infection)
  • Scarlet fever is making a comeback from ABC (Australian Broadcasting Corporation) news
  • Information about rheumatic fever from the Mayo Clinic
  • Impetigo facts from the NHS (National Health Service)
  • Information about necrotizing fasciitis from WebMD
  • Group B Strep“ description from the CDC
  • Group B Strep infections in babies from WebMD

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2011 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on September 20, 2011:

Thanks for a very interesting comment, Seeker7, and for the vote as well! Antibiotics are an interesting topic to explore.

Helen Murphy Howell from Fife, Scotland on September 20, 2011:

A fascinating hub about the Streps! I know they can be dangerous but they are so interesting as well. It was also interesting to hear about scarlet fever and rheumatic fever. I remember my Mum, many years ago, telling me about people - especially children - that she had looked after. In those days when 'the fevers' were very dangerous nurses could train to be a Fever Nurse and then go on to do general training, which is what Mum did. Some of her stories were scary but fascinating as well.

I liked how you mention about anti-biotics!! I don't know how many times I've had to tell people not to throw their anti-biotics out but to finish the course. This is not even patients, but my own family! As soon as folks feel better they think it's okay just to dump the rest of their medication down the loo! Then they complain either because they think that the anti-biotics haven't worked or because they need to make another trip to the doctor??!!

I really enjoyed this hub - very interesting indeed! Voted up.

Linda Crampton (author) from British Columbia, Canada on September 11, 2011:

Thank you very much, Prasetio! I appreciate the comment and the vote.

prasetio30 from malang-indonesia on September 11, 2011:

Nice hub and I thought we should know about this information. I really enjoy your explanation about Streptococcus bacterial and all the videos above. You have done a great job. Vote up!


Linda Crampton (author) from British Columbia, Canada on September 07, 2011:

Thanks a lot for the comment and the votes, Tina. Yes, bacteria can be our friends or our enemies!

Christina Lornemark from Sweden on September 07, 2011:

A very interesting hub and you have done a great job writing this in a way that is easy to read. Great videos to. Bacteria are important but can also cause trouble! Voted up, interesting

Linda Crampton (author) from British Columbia, Canada on August 31, 2011:

Oh my goodness, Susan! That must have been a horrible experience for you. I’m so glad that you recovered. A former student of mine developed necrotizing fasciitis in his hand last year from a Staphylococcus infection. At one point the doctors though that they would have to perform an amputation, which is traumatic for anyone, but was also very depressing for my student because he loves to play the guitar. Luckily he recovered and is still able to play the guitar.

Susan Zutautas from Ontario, Canada on August 31, 2011:

Very informative hub. I have a hub which is a short story written on Necrotizing Fasciitis as I had this in my arm.

Linda Crampton (author) from British Columbia, Canada on August 30, 2011:

Thanks a lot for the comment, Danette. Streptococcus is certainly a versatile bacterium! Yes, impetigo is usually caused by the same bacterium that causes a strep throat, but sometimes it's caused by a different bacterium called Staphylococcus. Either way, it’s not a very nice condition!

Danette Watt from Illinois on August 30, 2011:

Hey Alicia, I always enjoy your science-y hubs - lots of good info and interesting topics. I didn't realize impetigo was from the same strep bacteria as strep throat. I remember my younger son having that as an infant. Voted up and interesting