Atypical Mycobacterial Infection (ATM)


Last updated: November 2023

Also known as: Non Tuberculous Mycobacteria (NTM)

What is atypical mycobacterial infection?

Infectious organisms known as Atypical Mycobacteria (ATM) cause common skin infections seen in Australia. Mycobacteria have a thick waxy coat surrounding their cell walls to protect them in harsh environments. Individuals can get ATM infections from various environmental sources such as soil, water (e.g., swimming pools, aquariums, spas and ponds), food products and common animals (domestic and wild).

Mycobacteria are highly resistant to medications due to their thick protective cell wall. They are also highly resistant to drying and can survive outside the body without moisture for a long time.

Mycobacterium ulcerans (M.ulcerans), a common type of ATM, can cause Buruli ulcer.

Mycobacterium tuberculosis, causing tuberculosis in the lung, and Mycobacterium leprae, causing leprosy, are also mycobacteria that can result in more serious infections.

Who gets atypical mycobacterial infection?

ATM can affect individuals of any age, but young children, and those with weakened immune systems are more vulnerable. Individuals with medical equipment inside them and those who have recently undergone surgical or non-surgical procedures are also at higher risk.

What causes atypical mycobacterial infection?

A group of infectious organisms causes ATM infections. There are different species, such as Mycobacterium marinum, and Mycobacterium chelonae.

What does atypical mycobacterial infection look like?

The clinical appearance of an ATM infection varies, depending on the infecting ATM.

An initial sign of an ATM infection is skin lesions at the infection’s entry site.  Some individuals may have thickened lumps or plaques causing no symptoms, usually growing slowly. Some of these lumps can become ulcers, such as Buruli ulcers.

How is atypical mycobacterial infection diagnosed?

Along with clinical suspicious, diagnosis usually involves taking a sample of the skin lesions, known as a biopsy. Culturing the tissue from the biopsy helps grow the bacteria. Special tests like polymerase chain reaction identify the presence of the ATM’s genetic material. This will help determine the specific bacteria causing the skin infection.

How is atypical mycobacterial infection treated?

Treatment options will vary depending on the individual and their needs.

The individuals’ immune status, as well as the severity of the ATM infection, the specific bacteria and antibiotic sensitivity are important factors to consider. 

Medical therapy consists of antibiotics, which are used in combination with each other. Antibiotics may include rifampicin, ethambutol, isoniazid, minocycline, ciprofloxacin, clarithromycin, azithromycin, doxycycline and cotrimoxazole (trimethoprim/sulfamethoxazole).

Individuals may require surgical therapy along with medical therapy such as drainage of abscesses and removal of foreign bodies.

The condition may be more challenging to treat if individuals are undernourished, have HIV or are on medications that weaken their immune system.

What is the likely outcome of atypical mycobacterial infection?

Although ATM infections are challenging to treat, it is important to note that these are low-grade infections that are curable with treatment. However, knowing the specific bacteria is essential before starting treatment.

Individuals may undergo prolonged treatment for 6-12 months or even longer. They may often require consultations with infectious disease specialists. An individuals’ response to treatment also influences the outcome.

Dr Monisha Gupta and Helen PeiNovember 2023
Dr Monisha Gupta and Mia Yue YuJuly 2019



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