Mycobacterium marinum

  • Medical Author:

    Dr. Alai is an actively practicing medical and surgical dermatologist in south Orange County, California. She has been a professor of dermatology and family medicine at the University of California, Irvine since 2000. She is U.S. board-certified in dermatology, a 10-year-certified fellow of the American Academy of Dermatology, and Fellow of the American Society of Mohs Surgery.

  • Medical Editor: Frederick Hecht, MD, FAAP, FACMG
    Frederick Hecht, MD, FAAP, FACMG

    Frederick Hecht, MD, FAAP, FACMG

    Frederick Hecht, MD, lives in Scottsdale, Arizona. Dr. Hecht is a Pediatrician and Medical Geneticist and is certified by both the American Boards of Pediatrics and Medical Genetics. Dr. Hecht was born and raised in Baltimore and attended Dartmouth College in Hanover, N.H. and the Sorbonne at the University of Paris receiving his BA degree cum laude with distinction from Dartmouth.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What tests are available to diagnose the infection?

Lab tests include cultures where a swab or sample is taken and grown in the laboratory. Cultures of M. marinum are fairly difficult to grow and usually may take several weeks in the lab. The culture may be negative, even if there is an active infection. Treatment may still be considered even if the test results are negative, especially if the patient's history supports past fish or fish-tank exposure.

In the absence of positive culture results, a skin or tissue biopsy may be a helpful test for diagnosis. This may help find the microscopic bacteria.

A special test called polymerase chain reaction (PCR) of tissue may be used in difficult cases to assist in naming the exact type of bacteria or Mycobacterium species involved.

How is Mycobacterium marinum infection treated?

Most infections are treated medically with a fairly long course of oral antibiotics. Medications may be required anywhere from three to six months or more depending on the severity of the disease and spread of the infection. Typically, physicians may recommend continuing the medications for an additional four to six weeks even after all of the symptoms have fully cleared.

The gold standard for treatment of infection by M. marinum is oral antibiotics. Clarithromycin is currently the preferred antibiotic selection. Other antibiotic options include rifampin plus ethambutol, tetracyclines, trimethoprim-sulfamethoxazole, and fluoroquinolones.

Some milder infections (mainly in healthy people) have cleared on their own without any treatment. Rarely, surgical treatment and drainage of deeper tissue or skin infections may become necessary in more complicated cases. However, medical treatment remains the primary and preferred treatment for nearly all cases.

Medically Reviewed by a Doctor on 4/15/2015
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