M. marinum

An overview of Mycobacterium marinum, its characteristics, pathogenesis, and clinical significance.

Mycobacterium marinum

Mycobacterium marinum is a species of Mycobacterium that is known to cause disease in fish and humans. It is a slow-growing, photochromogenic mycobacterium that is closely related to the Mycobacterium tuberculosis complex. M. marinum is primarily found in aquatic environments and is responsible for a condition known as "fish tank granuloma" or "swimming pool granuloma" in humans.

Characteristics

Mycobacterium marinum is a Gram-positive bacterium that is acid-fast, meaning it retains certain dyes after being washed with acidic solutions. It is a rod-shaped bacterium that grows optimally at temperatures between 28°C and 32°C, which is lower than the optimal growth temperature for many other mycobacteria. This temperature preference reflects its adaptation to aquatic environments.

M. marinum is a photochromogen, meaning it produces a yellow pigment when exposed to light. This characteristic is used in laboratory settings to help identify the bacterium.

Pathogenesis

Mycobacterium marinum is an opportunistic pathogen that primarily infects fish, but it can also infect humans, particularly those who have contact with contaminated water or fish. In humans, infection typically occurs through skin abrasions or cuts that come into contact with contaminated water. The bacterium then causes a localized skin infection that can develop into a granulomatous lesion.

The infection is usually limited to the skin and soft tissues, but in rare cases, it can spread to deeper tissues or become systemic, especially in immunocompromised individuals.

Clinical Significance

In humans, M. marinum infection presents as a chronic, non-healing skin lesion that may be nodular or ulcerative. The lesion is often found on the hands, elbows, or knees, reflecting the common sites of exposure. Diagnosis is typically made through clinical history, culture, and histopathological examination of the lesion.

Treatment of M. marinum infection involves the use of antibiotics such as clarithromycin, rifampicin, and ethambutol. The choice of antibiotics and duration of treatment depend on the severity of the infection and the patient's immune status.

Prevention

Preventive measures include wearing protective gloves when handling fish or cleaning aquariums, and ensuring that any cuts or abrasions are covered when in contact with potentially contaminated water.

Also see

• Mycobacterium tuberculosis
• Mycobacterium leprae
• Granuloma
• Acid-fast bacteria