What is Streptococcus Pyogenes? - Causes, Symptoms & Treatment

Lesson Transcript
Thomas Higginbotham

Tom has taught math / science at secondary & post-secondary, and a K-12 school administrator. He has a B.S. in Biology and a PhD in Curriculum & Instruction.

Expert Contributor
Amanda Robb

Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

Streptococcus pyogenes is a gram-positive bacterium found on the skin and in the mucous membranes of its host. Discover the symptoms and illnesses caused by this bacterium, including secondary infections, and how to treat them. Updated: 11/01/2021

Pathogen for Many Illnesses

Bacteria: they live in our intestines, on our skin, in the soil, and in our food. In fact, without bacteria, we would not be able to live. There are a huge number of bacteria with whom we have formed a cooperative relationship, even the ones that make us sick in larger quantities. So why is it that bacteria seem to have such a bad reputation? Look no further than the bacterium Streptococcus pyogenes. This little bug is responsible for hundreds of millions of illnesses in the world each year. These include some of the most familiar illnesses and some of the most sensationalized illnesses we see in the media. Its effects can range from mildly annoying to lethal.

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  • 0:00 Pathogen for Many Illnesses
  • 0:47 Streptococcus Pyogenes…
  • 2:44 Illnesses Caused by S.…
  • 4:52 Secondary S. Pyogenes…
  • 6:48 Treatment for S.…
  • 7:26 Lesson Summary
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Streptococcus Pyogenes Characteristics

Before getting into some of the specific illnesses this bug can cause, it is helpful to learn more about the bacterium itself. Streptococcus pyogenes (S. pyogenes) is a gram-positive bacterium, known as a Group A Streptococcus, or GAS. It can be found primarily on the skin and in the mucous membranes of its host. It is estimated between 15 and 20 percent of people in the United States are carrying and shedding the bacterium at any given time, even though most of these carriers are asymptomatic.

The bacterium is spread easily through the types of interactions that occur when people are living and working closely with one another. Because the bacterium exists on people's skin and in their mucus, it can be spread through hand-to-hand contact; surfaces, like tabletops and drinking fountains; or through the tried-and-true sneezing and coughing. One of the best ways to avoid the spread of this nasty bug is basic hand washing and hygiene techniques.

The bug itself is not particularly hardy, as are some other pathogenic bacteria. It can be killed easily. However, it is a veritable poison factory, and once it settles on a host and finds the right conditions, one of about a dozen or more toxins can wreak havoc in just about any part of the body. These toxins do not only influence many parts of the body, they can also do so in many different ways, ranging from mildly irritating to deadly. The bacterium produces a coating that helps it avoid the body's natural defense of phagocytosis, or the body's defense cells surrounding and eating the bacterium.

Before the widespread use of antibiotics, S. pyogenes infections were often lethal. However, the best news about 'Strep' is that it has and continues to remain highly susceptible to penicillin and has demonstrated a rather limited capacity to develop resistance to antibiotics, especially in comparison to some other so-called 'super bugs.' Now strep infections are not often fatal in developed countries where antibiotics are readily available.

Illnesses Caused by S. Pyogenes

Now for the fun stuff. The diseases caught by this bacterium are varied in both severity and presentation of symptoms. For ease, we'll start with the more benign types of the illness and move progressively towards the more serious illnesses caused by S. pyogenes.

Colonization by S. pyogenes on the skin can cause mild infections that don't even always need to be treated by antibiotics. S. pyogenes can also cause impetigo, characterized by a spate of lesions, often on the neck, face, and upper body, that are purulent and eventually crust over in a brown/yellow scab-like manner. Impetigo generally requires antibiotic topical treatment or systemic antibiotics.

Most people have heard of strep throat, and many have also had it. When S. pyogenes colonizes the throat, it typically induces fever, very sore throat (pharyngitis), swollen lymph nodes, and inflamed tonsils.

Otitis media is a painful ear infection resulting from the colonization by S. pyogenes in the Eustachian tubes. The route of infection can either be directly through the sinuses or following a throat infection.

When S. pyogenes colonizes the subcutaneous level of the skin (the layers below the skin surface, but right above the muscle, bone, or cartilage), necrotizing fasciitis can occur. This is reported in the media as 'flesh-eating' bacteria, and it can spread rapidly, eating through skin sub-surface layers quickly. Often, surgical removal of the infected area is necessary. These infections are also more likely than strep throat or minor skin irritations to develop into even more serious infections. Necrotizing fasciitis is often fatal if untreated, or if diagnosed too late. While S. pyogenes is not the only 'flesh-eating' bacterium, it is one of the most common ones.

Bacterial sepsis occurs when an infection of S. pyogenes gets into and overwhelms the blood supply. This incredibly serious condition can escalate rapidly. Even when diagnosed relatively early, this type of infection is often fatal.

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Additional Activities

Medical Vignettes

In this activity, students will be writing three short stories, called a vignette, about different patients with Streptococcus pyogenes infections. This bacteria causes a wide range of infections that can show up in different ways in humans, and thus students should have a wide variety of material to choose from for their vignettes. For example, students could write about a young boy with strep throat or a patient in the hospital that develops an infection of S. pyogenes in their skin after being exposed to contaminated surfaces.


In this activity, you will be writing three short stories called vignettes about different patients that have a Streptococcus pyogenes infection. In each story, you should explain what the symptoms of the infection are, how the patient seeks treatment, and what the doctor recommends. You should use three different types of infections caused by the bacteria as described in the lesson. To make sure your stories are the correct length, and have the required information, review the criteria for success below.

Criteria for Success

  • Each vignette is at least 500 words
  • Three vignettes are written
  • Each vignette is about a person that has a different Streptococcus pyogenes infection
  • Each vignette covers the symptoms, treatment, and prognosis for each patient

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