Mycobacteroides abscessus: Infections, Symptoms & Treatment

Mycobacteroides abscessus is a species of rapidly growing, multidrug-resistant nontuberculous mycobacteria (NTM) distantly related to the organisms that cause tuberculosis and leprosy. Found widely in the environment, M. abscessus is an emerging pathogen, and the incidence of infections it causes has been increasing globally.

Its classification has evolved; it was previously known as Mycobacterium abscessus. The species is divided into three subspecies: M. abscessus subsp. abscessus, M. abscessus subsp. bolletii, and M. abscessus subsp. massiliense. The bacterium’s inherent resistance to many antibiotics makes the infections it causes difficult to manage.

Environmental Presence and Exposure Routes

Mycobacteroides abscessus is ubiquitous, thriving in soil, dust, and numerous water sources, including:

• Municipal tap water
• Well water
• Showerheads
• Ice machines
• Swimming pools
• Hot tubs

A characteristic of M. abscessus is its ability to form biofilms, which are communities of bacteria attached to a surface and encased in a protective matrix. This formation allows it to adhere strongly to surfaces like plumbing pipes, making it difficult to remove with standard disinfectants. This persistence allows the bacterium to become established in hospital water systems and on medical equipment.

Human exposure to M. abscessus occurs through several primary routes. Inhalation of contaminated aerosols is a significant mode of transmission, with showers and humidifiers being common sources. Another major route is direct inoculation, where the bacteria enter the body through breaks in the skin or during invasive surgical procedures. Ingestion of contaminated water is a less frequent cause of infection.

Clinical Manifestations and Affected Populations

Mycobacteroides abscessus infections primarily affect the lungs, skin, and soft tissues. Pulmonary infections are the most common, with symptoms that can include:

• A persistent cough
• Shortness of breath
• Fatigue
• Intermittent fever
• Unintended weight loss

These lung infections are particularly concerning for individuals with pre-existing structural lung diseases.

Skin and soft tissue infections often develop after trauma to the skin or as a complication of surgical procedures. These infections may appear as tender, red nodules, boils, or abscesses that do not heal with standard treatment.

Rarely, M. abscessus causes disseminated infections, spreading through the bloodstream to affect multiple organs. This severe form occurs almost exclusively in individuals with severely weakened immune systems. Person-to-person transmission is not a common route of spread.

Individuals at higher risk include those with chronic lung conditions like cystic fibrosis and COPD. People with compromised immune systems, such as organ transplant recipients, and those with open wounds are also more vulnerable.

Diagnostic Methods

Diagnosing a Mycobacteroides abscessus infection requires isolating and identifying the bacterium from the site of infection. This is achieved through culture-based methods, where a sample like sputum or a tissue biopsy is grown on specialized media. M. abscessus is a “rapidly growing” mycobacterium, often showing visible colonies within three to five days.

Microscopy plays a supporting role. Acid-fast staining can be used on samples to visualize the mycobacteria, though it cannot distinguish M. abscessus from other species.

For precise identification, molecular methods like PCR and DNA sequencing are employed to confirm the species and differentiate between its three subspecies. This is valuable because the subspecies can have different antibiotic susceptibility patterns. In cases of pulmonary infection, imaging tests like chest X-rays or CT scans are used to assess the extent of lung damage.

Complexities in Treatment and Management

The treatment of Mycobacteroides abscessus infections is challenging. The bacterium possesses intrinsic resistance to a wide range of antibiotics, linked to its impermeable cell wall and its ability to pump drugs out of its cell. This natural resistance limits the number of effective antimicrobial agents available.

The bacterium can also develop acquired resistance during therapy, meaning an antibiotic that was initially effective can become ineffective. The formation of biofilms complicates treatment, as this protective layer shields the bacteria from antibiotics and the host’s immune system.

Treatment involves a combination of multiple drugs, including both intravenous and oral antibiotics, that must be taken for many months or even years. To guide the selection of the most effective drug combination, antibiotic susceptibility testing is performed on the patient’s bacterial isolate. In many skin and soft tissue infections, surgical intervention to drain abscesses or remove infected tissue is also necessary. The long duration and multi-drug nature of the treatment often lead to side effects that require frequent monitoring.