Mycobacterium marinum – Culture; Molecular diagnosis (PCR)


Mycobacterium marinum is a gram-positive and acid-alcohol-resistant bacterium of the genus Mycobacterium, family Mycobacteriaceae. The infection by this microorganism has been identified in different species of fish, both from cold, warm, fresh and salty waters, although it can also affect people, in which it causes a disease called "pool granuloma" or "aquarium granuloma".

Mycobacterium marinum survives in macrophages and has the ability to sporulate. Unlike other Mycobacterium species, most strains of Mycobacterium marinum cannot grow at the usual incubation temperature of 37°C, but grow between 30 and 33°C. Their colonies are cream-colored and turn yellow when exposed to light.

This microorganism is found in the soil and in the fresh and salty water lakes, pools and aquariums. Due to their presence in these media, infection by Mycobacterium marinum can be an occupational hazard in some professions, such as animal shop workers, although most infections occur in domestic fish keepers who keep an aquarium at home. The transmission of Mycobacterium marinum occurs through the external inoculation of wounds in contact with contaminated water from swimming pools and aquariums. Although the infection can be caused by a direct injury of fish fins or bites, most are acquired during the handling of aquariums. In addition, indirect infections can occur when using utensils that have previously contacted fish tanks.

In fish, Mycobacterium marinum infection causes a chronic progressive disease manifested through weight loss, open ulcers that do not heal, distended abdomen, loss of appetite, fin erosion, unusual coloration, bulging eyes, deformities in the spine and changes in behavior.

Este microorganismo se encuentra en el suelo y en el agua dulce y salada de lagos, piscinas y acuarios. Debido a su presencia en estos medios, la infección por Mycobacterium marinum puede ser un riesgo laboral en algunas profesiones, como los trabajadores de tiendas de animales, aunque la mayoría de las infecciones ocurren en criadores domésticos de peces que mantienen un acuario en casa. La transmisión de Mycobacterium marinum se produce a través de la inoculación externa de heridas en contacto con agua contaminada de piscinas y acuarios. Aunque la infección puede ser causada por una lesión directa de las aletas de peces o mordeduras, la mayoría se adquieren durante la manipulación de los acuarios. Además, pueden darse infecciones indirectas al usar utensilios que previamente han contactado con peceras.

In people, Mycobacterium marinum has an incubation period of 2 to 8 weeks after inoculation. The two most common manifestations of this infection are a single large granuloma, or an ascending lymphangitic granuloma (a series of small nodules usually beginning in the hand and progressing in an ascending line to the arm). Although granulomas are usually unique, they often evolve to multiple, describing superficial papules on the skin and erythematous plaques that may present suppuration and ulceration. The lesions can be painful, without pain or with intermittent pain. The injuries usually occur on the elbows, knees and feet of those infected in swimming pools, and on the hands and fingers of the owners of the aquarium. The inhibition of the growth of Mycobacterium marinum at 37°C is related to its ability to infect the colder parts of the body, especially the extremities. Less frequently, cases of involvement of the underlying tissues have been described with arthritis, tenosynovitis, osteomyelitis or bursitis. Rarely, a type of disease has been described where the infection is spread, observed in immunosuppressed patients that can be fatal.

Recommended tests for diagnosis:

The diagnosis is based on the microscopic identification, culture methods or molecular diagnostic methods (PCR).

Tests carried out in IVAMI:

  • Detection by isolation by cultivation in selective media.
  • Molecular diagnosis (PCR), to detect Mycobacterium marinum DNA.

Recommended sample:

  • Skin lesion biopsy.

Conservation and shipment of the sample:

  • Refrigerated (preferred) for less than 2 days.
  • Frozen: more than 2 days.

Delivery of results:

  • Culture and identification: 15 to 30 days.
  • Molecular diagnosis (PCR): 24 to 48 hours.

Cost of the test: