Mycobacterium marinum Infection Workup

Updated: Jan 25, 2023
  • Author: Shirin A Mazumder, MD, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

The criterion standard for diagnosis is culture from the tissue biopsy. Cultures have been reported as positive in 70% to 80% of cases. At least a 4-mm skin punch biopsy or multiple biopsy specimens are recommended. M marinum is a nonmotile acid-fast bacillus (AFB) that grows in 2-3 weeks, with optimum growth on Lowenstein-Jensen medium at 30°C. Laboratory personnel should be notified in advance since AFB cultures mostly are carried at higher temperatures. Cultures should be observed for 6-12 weeks. [5]  A negative acid-fast stain does not rule out a non-tuberculous skin and soft tissue infection. Mycobacterial cultures are necessary to confirm or exclude the diagnosis. [6]  

M marinum is a photochromogen (Runyon group 1), producing a yellow pigment when exposed to light.

M marinum produces urease and catalase (weakly) but does not produce niacin or nitrate.

Polymerase chain reaction (PCR) amplification techniques using Mycobacterium genus-specific primers can be used to diagnose M marinum infection directly in the biopsy sample.

Tuberculin skin test using purified protein derivative is positive in 67% to 100% of cases. [7]

Quantiferon-TB Gold and enzyme-linked immunospot assay may be positive in M marinum infections. [7, 8]

Positive blood culture findings have also been reported in disseminated infections. [9]

The presence of granulomas on histopathology can be suggestive of non-tuberculous mycobacteria but the specificty is poor as many disease processes can cause granulmatous inflammation. [6]


Imaging Studies

First, obtain radiography of the affected area to evaluate for underlying osteomyelitis.

Obtain either MRI or CT scanning of the affected area if tenosynovitis or deeper infection is suspected, including osteomyelitis if the screening radiography findings are unrevealing. This would also be indicated in patients with prosthetic material from a previous injury.



Surgical drainage of skin lesions often is unnecessary. Deeper-structure infection may require surgical debridement.


Histologic Findings

Histologic findings often are nonspecific during the first 3 months of infection. An absence of epithelioid and multinuclear cells is not unusual in acute lesions. Younger lesions show epidermal hyperkeratosis, a mixed inflammatory response, or, possibly, frank suppuration. Older lesions may present as organized granuloma. Caseation is uncommon. Granulomatous inflammation is found in 76% of cases. [10]

The organisms are acid-fast and may have a transverse banding pattern. Ziehl-Neelsen staining of the skin tissue specimens is positive in 9% to 13% of localized cases but is more likely to show the organism in disseminated disease. [5]