The AMR Narrative

Methicillin-resistant Staphylococcus aureus (MRSA)

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What is Methicillin-Resistant Staphylococcus aureus (MRSA)?

Methicillin-resistant Staphylococcus aureus (MRSA) is a type of Staphylococcus aureus bacteria resistant to several common antibiotics, among which the so-called beta-lactams like penicillin and methicillin, for example.

MRSA infections occur mainly in patients who have been in healthcare facilities, such as hospitals, nursing homes, or dialysis centres. In these settings, usually infections are associated with devices or invasive procedures, such as surgical interventions, catheters, or intravenous lines.

MRSA can spread by healthcare workers or visitors touching patients with unclean hands or touching contaminated objects and surfaces (such as bed linens, bed rails, and medical equipment).

MRSA can cause serious, difficult to treat, and life-threatening infections. Antibiotics, such as vancomycin and teicoplanin, are used to treat MRSA infections. However, Staphylococcus aureus can become resistant even to these drugs. Unfortunately, only a few antibiotics can be effective against vancomycin-resistant Staphylococcus aureus (VRSA).

The infection may occur among healthy people in the community, as well. In this case, it is usually spread by close skin contact, and observed among people living in crowded or unsanitary conditions or participating in contact sports. The infection usually involves the skin.

According to the 2024 WHO Bacterial Priority Pathogens list (BPPL), MRSA has been listed among the top priority pathogens to guide discovery, research and development of new antibiotics.

What is Staphylococcus aureus?

To understand MRSA, it is important to know what Staphylococcus aureus is.

Staphylococcus aureus is a bacterium (bacteria).

When observed under a microscope, and from the Greek word, “staphyle” (meaning bunch of grapes) and “kokkos” (meaning berry), Staphylococcus is a type of of gram-positive spherical bacteria that commonly causes surgical and skin infections, respiratory disease, and food poisoning. When these bacteria grow on culture media, they form colonies of a particular shade of yellow (indeed, aureus is a Latin word meaning golden).

Where can Staphylococcus aureus be found?

Staphylococcus aureus is commonly found on the skin or in the nose of many healthy people. About 30% of people carry this bacterium in their noses, and often it lives in the armpits and on the buttocks. Most of the time it is harmless; however, sometimes Staphylococcus aureus can cause infections.

How can Staphylococcus aureus spread?

Staphylococcus aureus can spread from person to person by:

• close skin contact,
• contaminated objects (such as towels, clothing, doorknobs, elevator buttons, telephones, television remote controls, or gym equipment), or
• inhalation of infected droplets (tiny particles of water we breath out and able to carry bacteria in them) dispersed by coughing or sneezing.

Which infections can Staphylococcus aureus cause?

Staphylococcus aureus can cause infections ranging from mild to life-threatening.
Skin infections, such as pimples, boils and abscesses are the most common. They can turn into impetigo (a crusty and highly contagious skin infection, especially observed in newborn babies and schoolchildren), or cellulitis (an infection of the deeper layers of the skin).

Invasive infections happen when bacteria enter the body. They are not as common as the skin infections, but they can be very serious. They include:

• Bacteremia. When Staphylococcus aureus overcomes the defence line of the skin (for example, through a catheter inserted in a vein), it can travel inside the bloodstream, and infect almost any site in the body.
• Endocarditis. In this serious and life-threatening condition, bacteria stick to one of the valves inside the heart after spreading into the bloodstream. It most often affects people having an artificial heart valve, or injecting illicit drugs, or when a catheter inserted in a vein is infected.
• Osteomyelitis. It occurs when bacteria reach and infect a bone through the bloodstream. It is more common in people with deep pressure sores, or foot sores due to diabetes.
• Pneumonia. The infection of the lung is more likely in people who have had influenza, or in patients hospitalised because they need tracheal intubation and mechanical ventilation.
• Septic arthritis. It occurs when Staphylococcus aureus targets a joint (knee, shoulder, hip, or artificial joints, too), and it is more common in people with a weakened immune system.
• Meningitis. When bacteria travel through the bloodstream, they can infect the meninges (the membranes covering the brain and spinal cord).
• Sepsis. It is the extreme and overactive response of the body to an infection. Sepsis is a life-threatening emergency, and requires immediate treatment.
• Toxic shock syndrome. It is a life-threatening condition caused by toxins produced by Staphylococcus aureus.

Who is at risk of a Staphylococcus aureus infection?

Anyone can develop a Staphylococcus aureus infection, but certain groups of people are at greater risk than others, including people:

• with chronic illnesses, such as cancer, diabetes, lung diseases, vascular diseases, kidney diseases requiring dialysis, and eczema;
• with a weakened immune system, such as from HIV, immunosuppressants (medications which slow or stop the response of the immune system), or cancer chemotherapy;
• with implanted medical devices in their bodies (such as pacemaker, artificial joints, or heart valves);
• with urinary or intravenous catheters, breathing tubes, or feeding tubes;
• with burns, especially deep or covering a large area of the body;
• who underwent surgical interventions;
• who are in healthcare facilities, such as hospitals;
• who inject illegal drugs.

How are Staphylococcus aureus infections diagnosed?

To correctly diagnose an infection caused by Staphylococcus aureus, first of all your physician will perform a physical examination and ask you about symptoms and risk factors. Guided by these elements, your doctor will be able to choose the most appropriate diagnostic tests.

Laboratory tests can identify Staphylococcus aureus using a sample taken from an area of the patient’s body likely to contain the microbe (for example, blood or other tissue or fluid). These samples are sent to a laboratory to grow the microorganism over time using a media on a petri dish (culture) and identify it. Then susceptibility tests can be carried out to determine which antibiotics are most effective against it, to start the most appropriate antibiotic therapy.

Understanding which antibiotic will work best is especially key to MRSA and VRSA as these types of resistant Staphylococcus aureus bacteria may only respond to certain medicines. In some cases, they may respond to none. In some cases, MRSA screening may also be done before surgery.
Finally, depending on the type of infection, your physician may recommend additional tests, such as imaging tests.

How are Staphylococcus aureus infections treated?

As Staphylococcus aureus is a bacterium, therapy is represented by antibiotics. The antibiotic may vary depending on the type and severity of the infection, and the results of susceptibility tests. Indeed, some infections, such as those ones caused by Methicillin-resistant Staphylococcus aureus (MRSA), are resistant to several antibiotics.

Most cases of skin infections can be treated with a topical antibiotic (applied to the skin), while oral antibiotics (tablets to swallow) can be used to kill the bacteria inside the body. Serious infections may require intravenous antibiotics (the medication is given through a drip or a tube).

Simple infections can be treated at home, while severe infections need to be treated in hospital, and may require additional therapies in addition to antibiotics.
Carriage of MRSA nasal cream or hibiscrub may also be used under the armpits e.g. before surgery.

How can Staphylococcus aureus infections be prevented?

Following these commonsense precautions can lower your risk of getting a Staphylococcus aureus infection. Moreover, they help to reduce your chances of spreading bacteria to others, as well.

• Wash your hands thoroughly and regularly with soap and running water. Then dry them with a clean towel, or a disposable paper towel. If you are not able to wash your hands, you can use an alcohol-based hand sanitizer. Remember: hand hygiene is your best protection against infections.
• Keep wounds clean and covered with dry and sterile bandages until they heal, to prevent the bacteria from spreading.
• Avoid sharing personal items (such as toothbrushes, towels, sheets, bed linen, razors, clothing, and gym equipment).
• Shower after sport games or practices, using soap and water.
• Wash clothing, towels and bed linens in a washing machine set to the hottest temperature recommended by the item labels. You may use a detergent or bleach to make items clean and safe for use.

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