Mycobacterium marinum Aronson is generally known as a pathogen of fishes. Since 1962 it has been recognized as causing localized infections on the extremities of humans. Three cases are reported, with cures being effected by use of clarithromycin, ethambutol, minocycline, and rifampin. Cuts or abrasions should not be exposed to aquatic environments or organisms, and wounds received from aquatic organisms should be allowed to bleed for cleansing.

Human Mycobacterium marinum Aronson Infections


Mycobacterium marinum Aronson, the causative organism of fish tuberculosis, is an aquatic acid-fast, Gram-positive, non-motile rod bacterium that causes chronic infections, “wasting,” and death in fishes and is related to bacteria that cause tuberculosis and leprosy in mammals. It can also cause infections in humans known as “fish tank granuloma” and “swimming pool granuloma.” In man this bacterium enters wounds or abrasions and usually causes localized infections in the extremities. Although it was first described in 1962 (Swift and Cohen, 1962), the disease in humans is still not widely recognized. Three cases recently observed in our area are reported.


A 53 year old white male fish farm worker received a puncture to the left middle finger by a fin spine from a hybrid striped bass (Morone saxatilis (Walbaum) X Morone chrysops (Rafinesque)) in late October of 1991. Shortly thereafter the finger became swollen and pink with an accompanying three inch pink streak going toward the palm of the hand, and an open lesion was at the site of initial puncture. The patient was hospitalized for five days and given antibiotics (minocycline and rifampin) by IV, the infection site was incised and a porous tube inserted from finger to palm, and the infected area was irrigated with saline solution. Mycobacterium marinum was diagnosed and Rifadin (rifampin) at 300 mg twice per day, and Minocin (minocycline) at 100 mg twice per day were taken for about six weeks. Liver function was checked during the use of the antibiotics. A black-out reaction to the antibiotics resulted in the patient stopping their use. The patient was considered cured after six weeks. Subsequently, the subject was re-infected twice and quickly treated. One reinfection was initiated when the patient was stuck by a splinter from the handle of a fish net.


A 57 year old white female was preparing to boil blue crabs (Callinectes sapidus Rathbun) on August 27, 1993, when a crab pinched the index fingers of both hands. The left index finger bled freely; the right finger did not bleed and no obvious puncture was observed. About two to three weeks later a lump was observed under the skin on the right finger. The patient saw the first doctor on October 21,1993 and he lanced the area and put the patient on PCE (erythromycin) at 500 mg twice per day for five days. The PCE had no effect and within two weeks more lumps appeared under the skin and the color changed to pinkish-purple on the raised plaque. The second doctor was visited on November 16, 1993 and he prescribed Floxin at 400 mg twice per day for 30 days. Floxin had no noticeable effect and the patient decided to call someone in marine biology; the patient contacted the author on November 22, 1993, and after answering a series of questions the patient was advised to have the infection checked for Mycobacterium marinum. The lesion was lanced again, yielding a granular material, and cultures were sent for identification; the cultures came back positive for Mycobacterium marinum. A diagnostic laboratory did a sensitivity test and found resistance to streptomycin and isoniazid, but sensitivity to ethambutol, rifampin, ethionamide, and kanamycin. The patient was referred to a third doctor and on December 16, 1993 was put on Myambutol (ethambutol) at 400 mg two and a half times per day and Rifadin (rifampin) at 300 mg twice per day. On December 20, 1993 the patient was given Diflucan (fiuconazole) for five days at 100 mg once per day to combat a mouth fungal infection. On January 4, 1994 the patient developed a rash on the abdomen and was given Lotrisone (betamethasone dipropionate and clotrimazole combination) to apply to affected areas twice daily. On or about February 12, 1994 the patient (who also had the flu at this time) developed a reaction (dilated pupils, other eye problems) to ethambutol and stopped its usage. During the whole course of the infection there was no pain associated with the infection except when the finger was hit. As of March 12, 1994 the infection had essentially been eliminated.


A 51 year old white male public aquarium worker received a fish spine puncture from a sheepshead (Archosargus probatocephalus (Walbaum)) to the small finger of right hand in early October of 1993. By late October the finger had become swollen, felt hard, and was dark purple in color. A doctor was seen in late October of 1993 and a culture was taken on November 2, 1993 with a diagnosis of Mycobacterium marinum on November 14, 1993. Treatment was started on November 15, 1993 with Biaxin (clarithromycin) at 500 mg twice a day and treatment was still ongoing as of March 12, 1994, when the infection was almost gone.

The main difference between the three cases was that the fish farm worker and the aquarium worker had both been previously warned about fish tuberculosis by the author during discussions several years ago and sought and received quick treatment. The female patient was not aware of such infections and initially could not find a doctor who could recognize Mycobacterium infections. Thus, in her case, the delay in obtaining a correct diagnosis resulted in a longer treatment time in order to control the infection. This problem was also noted by Gray et al. (1990) for their cases. In addition, since it takes about two to four weeks to diagnose Mycobacterium marinum using culture techniques, and additional time for sensitivity tests, the patient can be further delayed in getting control treatment for the infection. In case 2 the crabs had been obtained from waters where there was a problem with septic tank contamination; it is not known if such contamination would favor increased growth of Mycobacterium marinum. It appears from this case that bleeding might help cleanse the wound and decrease chance of infection because the bleeding wound did not become infected.

We are recently aware of another possible infection by Mycobacterium marinum; a white female opened a refrigerator where blue crabs were stored and one crab fell out and stuck her foot, and an infection resulted. Good sanitation procedures are necessary to prevent infection by Mycobacterium: not exposing cuts or abrasions to aquatic environments or organisms, causing punctures or wounds obtained while working with aquatic organisms to bleed and thus flush out the wound, covering wounds if one has to work in aquatic environments or with aquatic organisms, and sterilizing wounds obtained while working with aquatic environments or organisms.

The author has worked with aquatic organisms for over 40 years without being infected with Mycobacterium and it is presumed that a resistance has developed. Present interest in fish tuberculosis at our facility peaked after construction of two touch tanks for use by the public and our resulting concerns about infecting the public increased. Addition of UV light sterilizers dramatically reduced the bacterial numbers and species in water of the tank systems.

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