Staphylococcus aureus is a bacterium that commonly grows on the skin. If levels become too high, a staph infection may develop. Methicillin-resistant Staphylococcus aureus (MRSA) causes a type of staph infection that can be hard to treat due to antibiotic resistance.

Both MRSA and non-MRSA staph infections share similar features, including appearance, symptoms, causes, and risk factors. The main difference is what antibiotics will work against MRSA versus other staph infections.

Doctors may refer to non-MRSA staph infections as methicillin-sensitive staph infections (MSSA).

This article discusses the similarities and differences between other staph infections and MRSA.

a doctor is inspecting an MRSA staph infection on a person's armShare on Pinterest
Astrakan Images/Getty Images

About 30% of adults have Staphylococcus aureus in their noses. Comparably, about 5% of patients in United States hospitals carry MRSA in their nose or skin.

For most people, this bacterium can live on their noses without causing any health problems. Those most at risk of developing an infection from Staphylococcus aureus include individuals who have:

  • had recent surgery
  • had wounds to the skin
  • a weakened immune system

MRSA is a type of Staphylococcus aureus that is resistant to antibiotics. Like regular staph infections, it typically causes skin infections that can appear as small red bumps similar to a spider bite.

Both MRSA and staph infections start as skin infections that can spread from the skin to other areas of the body. They can also transmit easily from person to person.

Certain locations and activities can increase an individual’s risk of developing either type of infection. Common areas in which people should take extra precautions include:

  • gyms
  • schools
  • locker rooms
  • prisons
  • hospitals

In these environments, a person should take care to avoid scrapes or cuts. If they do occur, they need to make sure they clean their wound thoroughly with soap and water.

The appearance of MRSA and staph infection can vary between people. Additionally, it will likely be impossible from looks alone whether a skin lesion is due to staph, MRSA, another infection, or something else, such as a spider bite.

Since MRSA simply means the staph infection is resistant to methicillin, there may not be a difference in its appearance compared to another type of staph infection.

Both types of staph infection often start on the skin and may appear as small, red bumps that may look similar to spider bites or pimples. The Centers for Disease Control and Prevention (CDC) state that MRSA infections often appear as flushed, swollen, and pus-filled skin.

In either case, a doctor will often need to run tests to determine if the infection is from Staphylococcus or other bacteria. Tests may include a wound culture, which uses a skin sample, tissue, or fluid to determine the type of bacterium causing the infection.

Staphylococcus is the group of bacteria responsible for staph infections, with Staphylococcus aureus being the most common form. The main difference is that non-MRSA generally responds well to a variety of antibiotics, while MRSA may only respond to a few, making it harder to treat.

Spreading via contact

Staph infections spread primarily from contact with a wound carrying an infection or sharing personal items with someone with the infection, including razors and towels.

Risk factors

People who inject drugs have a rate of contracting a serious staph infection 16 times that of individuals who do not. Other common risk factors of both types of infection include:

  • open sores or wounds
  • close contact with a person with the infection
  • a recent or current stay at an inpatient or hospital setting
  • being immunocompromised
  • other infections present in the body
  • having a catheter or feeding tube in the body
  • receiving kidney dialysis

Staph infections typically start on the skin, but they can spread to other areas of the body without treatment.

When a staph infection affects only the skin, it can cause symptoms according to the impacted skin areas. The following are some symptoms of a staph infection depending on how they affect the skin:

Type of staph infectionEffect on the skin
ImpetigoImpetigo is highly contagious and causes painful sores on the skin.
BoilsBoils are painful bumps on the skin that often appear around the buttocks, face, neck, thighs, and armpits.
CellulitisCellulitis affects a deeper level of the skin and can cause fever and nausea.

The CDC adds that an MRSA infection may have the following symptoms at skin level:

  • fever
  • swelling
  • redness
  • pus-filled skin
  • pain
  • warm

These symptoms also appear with non-MRSA infections. This is because MRSA refers to these infection types that do not respond to certain antibiotics — it does not indicate that the symptoms differ between the two types of staph infection.

If a person does not seek treatment for staph infection or MRSA, or the infection worsens, it can spread to other areas of the body. When the infection becomes invasive, it can cause the following issues and symptoms:

  • Sepsis: This is a medical emergency that occurs when the bacteria enter the bloodstream. It can cause severe symptoms, including:
    • fast heartbeat
    • low blood pressure
    • fever
    • diarrhea
    • possible loss of consciousness
  • Endocarditis: When the infection affects the heart, it can cause symptoms such as:
    • fever
    • fatigue
    • chest pain
    • coughs
    • unexplained weight loss
    • shortness of breath
  • Septic arthritis: When the infection enters the joints, symptoms can include
    • fever
    • pain
    • joint swelling

An individual may not be able to tell whether their skin infection is the result of a staph or MRSA infection.

They should seek medical care as early as possible to prevent complications. A person who notices signs of a possible staph infection should:

  • contact their doctor, especially if they also have a fever
  • avoid picking at or popping the sore
  • cover the area with clean, dry bandages
  • clean the hands well and often

Treatments will vary according to the severity, location, and type of infection. For some topical infections, a person may find that applying warm compresses and keeping the area clean is enough to care for the lesions.

In some cases, a doctor may need to use an incision and drainage to treat the lesion. During the procedure, a healthcare professional will use a sterile scalpel to create a cut and then drain the pus from the lesion.

However, if the infection gets worse, a person should speak with their doctor about additional treatment options. Often, first-line treatment may involve topical ointments with antibiotics or oral antibiotics.

If the infection is severe, a healthcare professional may recommend an antibiotic injection.

In cases of MRSA, a doctor will need to use alternative medications that are effective against antibiotic-resistant infections.

MRSA is a type of staph infection that is resistant to certain antibiotics. The main difference is that an MRSA infection may require different types of antibiotics.

MRSA and staph infections have similar symptoms, causes, risk factors, and treatments. Treatment options can include warm compresses, drainage, topical antibiotics, oral antibiotics, or antibiotic injections.

With treatment, a person should see a full recovery. However, if the treatment is delayed or not effective, staph infections can develop into serious illnesses.