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Pathology of Mycobacterium Marinum Infection

Dr Sampurna Roy MD                  


Dermatopathology Case 150

Diagnosis : Fish Tank Granuloma caused by Mycobacterium Marinum


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Atypical mycobacterial infections are increasingly important in immunosuppressed patients as well as in healthy hosts.

The atypical mycobacterium that most commonly affects the skin is Mycobacterium marinum. 

The infection should be suspected upon the presence of ulcers, nodules or chronic plaques and a history of contact with fresh or salt water.

The disease is typically acquired following contact with infected water and in many instances has been described following the cleaning of fish tanks with minor penetrating trauma being important in the pathogenesis.


The infection usually involves superficial tissues of the distal aspect of the upper or lower limbs.


Deeper soft tissue may also be involved.


In some cases tenosynovitis may occur.


There may be primary synovial involvement or secondary  to skin involvement.


Cutaneous nodules, sometimes with a lymphatic distribution reminiscent of sporotrichosis, are often the presenting sign and some patients have a history of several years of widespread warty lesions clinically resembling sporotrichosis.

Dissemination of Mycobacterium marinum-infection is a  rare condition which occurs mainly in immunocompromised patients and can be life-threatening.

Considerable time may elapse before the diagnosis is made, patients often being treated unsuccessfully for various conditions.

This highlights the importance of a detailed history  including occupational and recreational exposure and recent travel.

Fish tank granuloma: 

Granulomatous lesions of the skin and tendon sheaths after exposure to fish tank or aquarium water are frequently caused by non-tuberculous so-called atypical mycobacteria.

Mycobacterium marinum is the species most often isolated from such lesions.

Fish tank granuloma seems to be a rare sporadic human disease that is often misdiagnosed.

Histopathological examination of involved synovium in patients with disease principally in this site shows hypertrophy and hyperplasia of synovial lining cells together with a fibrinous exudate.

The presence of granulomas is variable.

Granulomas, if present, tend to be well defined and non-caseating, but poorly defined granulomatous foci may be present in some cases, and in others suppurative inflammation may predominate.

Hyperkeratosis and pseudoepitheliomatous hyperplasia of the epidermis may be found in cutaneous infections.

There is a reciprocal relationship between the expression of suppurative inflammation and granulomatous changes.

Such a relationship might be expected, but a combination  of granulomatous inflammation and acute inflammation is a key feature of subcutaneous and deep fungal infections.

The varied histopathological reactions to Mycobacterium marinum infection are difficult to explain but could be related to its growth rate, which is between 5 -14 days, falling intermediate between Mycobacterium tuberculosis  (12 - 28 days) and the rapid growers (Mycobacterium abscessus, Mycobacterium chelonae and Mycobacterium fortuitum) with a rate of 3 - 7 days.

Acid-fast bacilli are rarely identified in tissue sections reinforcing the need to culture tissue for species identification.  

Mycobacterium marinum infections are emerging infections related to fish tank hobby.

Because of the severity of the cases with spread of infection, clinical awareness of Mycobacterium marinum infection and its associated risk factors is important so that the diagnosis can be made and therapy can be initiated promptly.


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Visit: Atypical Mycobacterial Infection ; Mycobacterium Leprae Infection.  ; Mycobacterium Avium Intracellulare ; Mycobacterium ulcerans Infection  ; Mycobacterium tuberculosis  ; Mycobacterium Kansasii Infection.


Further reading:

Mycobacterium marinum infection. Case report and review of the literature.

Preseptal cellulitis due to Mycobacterium marinum.

Disseminated Mycobacterium marinum infection with extensive cutaneous eruption and bacteremia in an immunocompromised patient.

Sporotrichoid presentation of Mycobacterium marinum infection of the upper extremity. A case report.

A case of granulomatous skin lesions caused by Mycobacterium marinum in the Campania region.

Sixty-three cases of Mycobacterium marinum infection: clinical features, treatment, and antibiotic susceptibility of causative isolates.

Mycobacterium marinum infection in a lung transplant recipient.

Retrospective study of Mycobacterium marinum skin infections

Mycobacterium marinum cutaneous infections acquired from occupations and hobbies.




Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)  ;  Dermpath-India  ;   Soft Tissue Tumour Online ; Cardiac Path Online ;

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