The AMR Narrative

Carbapenem-resistant Acinetobacter baumannii (CRAB)

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What is carbapenem-resistant Acinetobacter baumannii (CRAB)?

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a type of Acinetobacter baumannii bacteria resistant to carbapenems, a type of last-line antibiotics used to treat serious multidrug-resistant bacterial infections.

Unfortunately, Acinetobacter baumannii has the ability to develop antibiotic resistance through several diverse mechanisms. For example, CRAB can produce substances (called carbapenemases) that break down carbapenems and other so-called beta-lactams antibiotics (such as penicillin), making these medications ineffective. Some CRAB bacteria are even resistant to all available antibiotics, causing infections very difficult to treat.

Moreover, CRAB can share its genetic material with other bacteria, rapidly spreading antibiotic resistance, and potentially causing dramatic hospital outbreaks.

That is why it is considered a serious public health threat, and has been listed among the top priority bacterial pathogens to guide discovery, research and development of new antibiotics by the World Health Organization (WHO).

What is Acinetobacter baumannii?

To understand CRAB, it is important to know what Acinetobacter baumannii is.

Acinetobacter baumannii is a type of bacteria, a gram-negative coccobacillus.

It is an important cause of hospital-associated infections. Acinetobacter baumannii affects particularly patients in intensive care units, and with specific risk factors, causing life-threatening conditions, such as pneumonia and bloodstream infections.

Where can Acinetobacter baumannii be found?

Acinetobacter baumannii is commonly found in the environment, especially in soil and water.

It can also colonize skin, wounds, respiratory secretions (sputum), and gastrointestinal tracts, living in a patient without causing infections or symptoms. Colonization can lead to infection in certain groups of people who are at greater risk than others.

How can Acinetobacter baumannii spread?

Since Acinetobacter baumannii lives in the environment, it can be spread to people when they are exposed to water or soil contaminated with these microorganisms.

In healthcare facilities bacteria can spread from person to person by skin contact (e.g. through healthcare workers’ contaminated hands), or contaminated medical equipment or environmental surfaces.

Moreover, its ability to survive and persist for long periods of time on surfaces (if not properly cleaned) makes it easily transmissible in healthcare settings.

Which infections can Acinetobacter baumannii cause?

Acinetobacter baumannii can cause life-threatening infections in people in healthcare facilities, especially those who are considered at risk.

The most frequent Acinetobacter baumannii infections are:

• Pneumonia. Infections of the lung typically occur in critically ill, hospitalised patients in intensive care units who require mechanical ventilation. That is why this serious condition is called ventilator-associated pneumonia.
• Bloodstream infection. When Acinetobacter baumanni: overcome the defence lines of the body, it can travel inside the bloodstream, causing bacteremia. It can turn into sepsis, an extreme and overactive response of the body to an infection, a life-threatening emergency which requires immediate treatment.


Less frequently Acinetobacter baumannii can cause:


• Skin and soft tissue infections. These conditions are more common in people with burns and wounds due to injuries or surgery.
• Urinary tract infections, typically in people with urinary catheters.
• Endocarditis. In this serious and potentially deadly condition, bacteria stick to one of the valves inside the heart after spreading into the bloodstream.
• Meningitis. This occurs when bacteria infect the meninges (the membranes covering the brain and spinal cord), primarily after neurosurgical procedures.
• Osteomyelitis. Acinetobacter baumannii bacteria target a bone through the bloodstream.
• Ocular infections, including corneal ulcers. This happens when bacteria infect and damage the cornea (the transparent and external part of the eye).

Who is at risk of Acinetobacter baumannii infection?

Acinetobacter baumannii infections typically occur in people in healthcare settings, and certain groups of people are at greater risk than others, including people:

• with chronic illnesses, such as cancer, diabetes, or chronic lung diseases;
• 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 urinary or intravenous catheters;
• with breathing tubes;
• with wounds due to surgical interventions;
• with severe burns;
• who received certain antibiotics for long periods of time;
• who have prolonged hospital stays, particularly in intensive care units.

How are Acinetobacter baumannii infections diagnosed?

To correctly diagnose an infection caused by Acinetobacter baumannii, 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, and distinguish between Acinetobacter baumannii colonisation and infection (that is important to reserve antibiotic treatment for true infections).

Laboratory tests can identify Acinetobacter baumannii using a sample taken from an area of the patient’s body likely to contain the microbe (for example, sputum or blood). 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 carbapenem-resistant Acinetobacter baumannii (CRAB) as this type of resistant Acinetobacter baumannii bacteria may only respond to certain medicines. In some cases, they may respond to none. New rapid genetic tests can provide the mechanism of resistance in a few hours, resulting in your doctor making better antibiotic choices to treat CRAB infections.

Finally, depending on the type of infection, your physician may recommend additional diagnostics, such as imaging tests.

How are Acinetobacter baumannii infections treated?

As Acinetobacter baumannii is a bacterium, therapy is represented by antibiotics. The antibiotic may vary according to the type and severity of the infection, and the results of susceptibility tests. Indeed, some infections, such as those ones caused by carbapenem-resistant Acinetobacter baumannii (CRAB), are resistant to several antibiotics.

Intravenous antibiotics (Medication which is given through a drip or a tube) are used in case of serious infections, which require treatment in a hospital, and need additional therapies, too. In some cases, antibiotics can be inhaled if you have severe pneumonia.

Unfortunately, Acinetobacter baumannii has the ability to develop antibiotic resistance through several diverse mechanisms. Due to increasing resistance to available medications, these type of infections are becoming more and more difficult to treat, and sometimes a combination therapy is needed (which means that two or even three antibiotics are necessary).

How can Acinetobacter baumannii infections be prevented?

Following these precautions can lower your risk of getting an Acinetobacter baumannii infection. Moreover, they help to reduce your chances of spreading this bacteria to others:

• Wash your hands thoroughly and regularly with soap and running water. 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.
• Clean surfaces. Use disinfection products to clean, especially on high-touch surfaces, such as your cell phone, doorknobs, and light switches.


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