Atypical Mycobacterium

Atypical mycobacterium infection


Mycobacterium marinum
Swimming pool granuloma
Fish tank granuloma

Mycobacterium marinum, present in fresh and brackish water, is a cause of cutaneous granulomas. The port of entry is usually minor trauma to the skin.

Histologically, granulomas contain acid-fast bacilli. Assuming the specimen is incubated at the proper temperature, a positive culture identification can usually be obtained.

Clinically, the lesion usually appears as a red nodule that breaks down to form a crusted ulcer or abscess. The surface may be verrucous. New nodules can appear in the same area or along the lymphatic drainage channels.

Other atypical mycobacteria that can cause skin infections include M. kansasii, M. avium, and M. fortuitum.


  • There is a tendency towards spontaneous healing.
  • Minocycline 100 mg bid for 8-12 weeks is usually effective.
  • An alternative treatment is rifampin.
Atypical mycobacterium infection

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