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A Case of Opportunity: M. marinum.

Case Presentation

A 46-year-old female was seen in her primary care physician's office for complaints of a sore elbow after having returned from a 3-week long trail ride in rural Arizona. When reporting her recent medical history, the patient could not recall any injuries to her arm or elbow in the past few weeks. She did report that she had been treated with azithromycin for a sinus infection two weeks before she left for the trail ride. However, at the time when she left for Arizona, she had completed the prescription and all of her symptoms had resolved.

She reported that the elbow was not sore or swollen previously. When quizzed about her occupation, she reported that she was a successful horse trainer and an all-around champion of animals in general. She had a thriving dog rescue on her property, which was also home to several exotic birds, five tanks of tropical fish both freshwater and salt water, one iguana, and one pot belly pig.

In reviewing the clinical history, the physician noted that the patient had been a two-pack-a-day smoker for several years prior to this visit, but had been successful in a smoking cessation program within the last year and now did not smoke at all. Over the previous winter, she had experienced some difficulty breathing, and a course of corticosteroids was prescribed by her pulmonologist. The breathing issues were resolved upon completion of the steroids.

Upon physical examination, the patient's vital signs, including blood pressure and respiration, were all within normal adult range, and her temperature was 98.6[degrees]C. The physical exam was unremarkable except for a large swollen area just below the elbow on the right arm. The area on the arm was red, warm, and very sore to the touch. The physician was concerned this was an infectious process with fluid present. An outpatient surgery procedure was scheduled for the next day so the physician could better examine and aspirate the area. The volume of the aspirate was 10 ml. It was thick, opaque, and yellow.

The aspirate was processed for routine bacterial cultures, which included both aerobes and anaerobes, along with orders for fungal cultures and mycobacterial cultures. The patient was released four hours after the procedure and went home to rest.

Laboratory Testing

Prior to the surgery, the physician ordered preoperative testing. The tests included a urinalysis (Table 1), complete blood count (Table 2), and basic metabolic panel (Table 3).

During the surgical procedure, the elbow was aspirated. The Gram stain of the aspirate showed moderate neutrophils and no bacteria. No fungal elements were seen in the Gram stain, and the acid-fast stain using a concentrated Kinyoun stain was negative for acid-fast bacilli. For the routine culture, the aspirate was plated to sheep blood agar, chocolate agar, MacConkey agar, mannitol salt agar and esculin agar, along with a thioglycollate broth. An anaerobic sheep blood agar, along with a kanamycin bile esculin (KBE) agar and a phenyl ethyl alcohol (PEA) agar, was set for the anaerobic culture. Media for the fungal culture included a Sabouraud dextrose agar plate, mycosel agar, and brain heart infusion (BHI) agar. Media for the mycobacterial culture included two Lowenstein-Jensen slants, one incubated at 37[degrees]C and one at 32[degrees]C. All cultures were incubated in their appropriate environment with the following results:

Elbow Aspirate


* Moderate neutrophils

* No bacteria were seen

* No fungal elements


* No acid-fast bacilli seen (modified Kinyoun stain)


* Aerobic culture-negative @ 7 days (final report)

* Anaerobic culture-negative @ 7 days (final report)

* Fungal culture-no fungi isolated @ 7days (preliminary report)


* Lowenstein Jensen media @ 37[degrees]C no growth after seven days

* Lowenstein Jensen media @ 32[degrees]C yellow, smooth colonies-photochromogen (7 days)


* Niacin-negative

* Nitrate-negative

* Pyrazinamidase (Wayne method)-positive

* Arylsulfatase (3 days)-negative

* Arylsulfatase (2 weeks)-positive

* T2H media-growth

* Tween hydrolysis (10 days)-positive

* Urease-positive

PRELIMINARY REPORT: Mycobacterium marinum

MOLECULAR TESTING RESULTS PCR-RFLP testing: Mycobacterium marinum (confirmatory report)


Mycobacterium marinum received its name when it was initially thought to only infect marine fishes. It is now known to be a ubiquitous species and can be the etiologic agent of zoonotic infection. Experiments have shown that M. marinum can infect poikilotherm animals in addition to aquatic animals. Several reptiles, including crocodiles, turtles, lizards and snakes, have been shown to be susceptible to M. marinum. (1)

Disease in fishes caused by M. marinum is common. It is predominantly seen in aquarium fishes. The severity of infections can range from chronic infections to a more acute form. The chronic infections are associated with a low mortality rate where the acute forms can kill an entire population of fish. Fish infections caused by M. marinum are systemic diseases that affect any organ system. Most often, M. marinum affects the spleen, kidney and liver of the fish. (2)

M. marinum is the most common non-tuberculoid mycobacterium present in aquaria containing ornamental fish. (3)

Infections of M. marinum in humans were first reported as a tuberculoid infection and associated with swimming pools in Sweden in 1939. Reports of tuberculoid infections were first reported in the United States in 1951. These early findings of granulomatous skin lesions in patients led to the name of "swimming pool granuloma." (2) Today, M. marinum infections are most often seen in people who have contact with aquariums, fish tanks, and aquatic animals, leading to the name "fish tank granulomas." (1)

M. marinum is an intracellular pathogen that proliferates within macrophages in a nonacid phagosome that does not infuse with the lysosome. (2) Studies have shown M. marinum remains within activated macrophages in granulomas allowing it to replicate and escape from the phagosomes into the cytoplasm leading to direct cell spread. It has been divided into two types based on genetic diversity and virulence. Cluster I contains strains isolated from humans with fish tank granulomas and cause acute disease progression. (2) Cluster II strains were found in poikilothermic species causing chronic disease. (2)

Mycobacterium marinum is considered the most common cause of mycobacterial skin infections in humans. The prevalence of these infections in the United States is 0.27 in every 100,000 people. (4,5,6,7) In humans, most M. marinum infections are seen in people who have close contact with fish tanks, aquariums, fish and other aquatic animals. (1) Infections in humans range from simple cutaneous lesions to debilitating disseminated infections. Deeper infections can involve the joints and tendons. (8) M. marinum infections present as nodular granulomatous skin infections of the extremities with a sporotrichoid pattern. (9) The finger or hand is the most common place to find the granulomatous lesion. Deep infection, such as tenosynovitis, osteomyelitis, arthritis, and bursitis, can occur in 20-40% of the cases. (2) Disseminated skin lesions, severe cutaneous and subcutaneous infections can be seen in immunocompromised patients. Patients who are HIV positive, or have had a solid organ transplant, or are being treated with tumor necrosis factor inhibitors are the main immunosuppressive conditions predisposed to atypical mycobacteriosis. (7,8)

M. marinum is also classified as a nontuberculous mycobacteria (NTM) which can be implicated as an opportunistic pathogen in patients who are immunocompromised due to a variety of clinical conditions. (10)

Mycobacterium marinum is a slow growing, photochromogenic mycobacterium species belonging to Group 1 of the Runyon's classification. (2,7) It is a pathogenic mycobacterium with an optimal growth temperature of 30[degrees]C. Small colonies or no growth is observed at 37[degrees]C. The colonies are smooth or intermediate and white or beige when kept in the dark. When the colonies are exposed to light, they are yellow to orange. The photochromogenic property is due to the active production of beta-carotene mediated by the gene crt[beta] and this can be inhibited by chloramphenico. (12) The organism has positive reactions for two-week arylsulfatase test, pyrazinamidase, growth on T2H, 10-day tween hydrolysis test, and urease. Negative reactions include catalase, iron uptake, niacin, nitrate reduction, and tellurite reduction. It does not grow on MacConkey agar or in 5% NaCl. (10)

Transmission of M. marinum usually occurs through inoculation of the organism through a break in the skin in contaminated water from fish tanks or aquariums. It can also be transmitted from direct contact with infected fish and shellfish. The incubation period can be from 3 weeks up to 9 months long. (2,11) There is often a lag time between the onset of lesions and patients seeking medical care which adds to the delay in diagnosis of M. marinum infections. Diagnosis of these infections can be difficult because the presentation is often nonspecific and very insidious. A M. marinum infection is suspected mainly by clinical history, occupational background, and lifestyle. When key information in the history, such as fish exposure, is missed or not obtained, the diagnosis is often delayed. A definitive diagnosis can be obtained by physical and histological exams and a positive culture. Acid-fast stains give positive results in less than 25% of cases and do not correlate with the severity of the infection. (2,4,7,12)

Due to the absence of better evidence, there is no standard treatment recommended. Mycobacterium marinum is generally sensitive to multiple antibiotics. It is responsive to clarithromycin, minocycline, trimethoprim-sulfamethoxazole, and doxycycline in monotherapy for superficial skin infections. (5,9,12,13) In severe infections including those with a sporotrichosis-like distribution, a multi-drug therapy is recommended. A combination of rifampicin and ethambutol is used. In cases of osteomyelitis and arthritis, clarithromycin, in combination with ethambutol, and the possible addition of rifampicin, is usually used. (7,12) Treatment should be administered for at least six weeks up to 12 months depending on the evolution of the lesion. Resection and debridement of the lesion are generally not recommended. Surgery and debridement are only indicated in cases resistant to treatment with antibiotics or when persistent, deeper infection is present. Distinguishing between invasive and cutaneous infection is important in the management of the disease. Treatment with antibiotics and surgery differs depending on the type of infection. (11,12)

The agar dilution susceptibility method is the recommended method for M. marinum isolates. The SLOMYCO Sensititre[R] panel was commercialized by TREK Diagnostic Systems (Cleveland, OH). This is a broth microdilution panel that can be used to evaluate the susceptibility of slow-growing mycobacteria to 14 antimicrobial agents. A study was performed to determine the accuracy of this susceptibility method. Results of the study show that the SLOMYCO Sensititre[R] panel method could provide an alternative to the reference agar dilution method for all the antibiotics on the panel except doxycycline. (13)

Prevention of infection is the first line of defense for those involved with aquariums whether it be for recreation or working in the marine environment. The following are measures that can be used to prevent infection from M. marinum: bandage any open cut or wound before working with aquariums, clean hands thoroughly after exposure to aquarium water, and use UV germicide lamps to treat aquarium water. M. marinum can be eliminated by UV irradiation. UV disinfection is quick, clean and does not leave any residue. (14) Those who work with fish should be educated to recognize signs of M. marinum disease. A thorough clinical exam and a review of occupational/background exposure to potential pathogens will help expedite the diagnosis of Mycobacterium marinum. (2)

Case Resolution

The physician prescribed a 12-week course of antibiotics, clarithromycin and ethambutol. The patient was seen at eight weeks for an appointment. The elbow area showed no signs of infection. The antibiotics were completed at 12 weeks with a final visit to the physician in week 13. The patient had no complaints of any pain in the area, and the physician was confident the antibiotics had resolved the issue. The physician discussed various routes of exposure with the patient, as well as ways for the patient to be proactive with basic first aid and other protective measures to help prevent similar events from occurring in the future. While there may be more than one possibility for the route of infection in this case, the physician was fairly certain that the fish tanks were the source of the primary infection.


(1) Bouricha M, Castan B, Duchene-Parisi E, Drancourt M. Mycobacterium marinum infection following contact with reptiles: vivarium granuloma. International Journal of Infectious Diseases. 21(2014) 17-18. ijid.2013.11.020

(2) Aubry A, Mougari F, Reibel F, Cambau E. Mycobacterium marinum. Microbiology Spectrum. 2017: 5(2): TNM17-00382016. doi: 10.1128/microbiolspec. TNM17-0038-2016.

(3) Slany M, Jezek P, Bodnarova M. Fish tank granuloma caused by Mycobacterium marinum in two aquarists: Two case reports. BioMed Research International. 2014; 1-4.

(4) Iyengar K, Matar H, Jayeola O, Loh W. Flexor pollicis longus tenosynovitis caused by Mycobacterium marinum infection. BMJ Case Reports. 2014; 1-3. doi: 10.1136/bcr-2014205443.

(5) Huang Y, Xu X, Liu Y, Wu K, Zhang W, Liu P, et al. Successful treatment of refractory cutaneous infection caused by Mycobacterium marinum with a combined regimen containing amikacin. Clinical Interventions in Aging. 2012; (7) 533-538.

(6) Babamahmoodi F, Babamahmoodi A, Nikkhahan B. Review of Mycobacterium marinum infection reported from Iran and report of three new cases with sporotrichoid presentation. Iran Red Crescent Medical Journal. February; 16(2) 1-6. doi:10.5812/ircmj.10120.

(7) Veronese F, Zavattaro E, Farinelli P, Colombo E, Savoia P. An unusual cutaneous infection caused by Mycobacterium marinum. Journal of Medical Microbiology. 2017: 1-3. doi 10.1099/jmmcr.0.005088.

(8) Thomas X, Pedrosa M, Soriano A, Zboromyeska Y, Tudo G, Garcia S, et al. Rare diagnosis of nodular lymphangitis caused by Mycobacterium marinum: MDCT imaging findings. Acta Radiologica Short Reports. 2014; 3(2) 1-3. doi: 10.1177/2047981614523172.

(9) Lata C, Edgar K, Vaughan S. Clinical Implications for the Timely Diagnosis of Mycobacterium marinum in the Age of Biologic Therapy: A case report and review of the literature. Case Reports in Infectious Diseases. 2017: 1-4. http://dx.doi. org/10.1155/2017/5274302.

(10) Mahon C R, Lehman D C, Manuselis G. Textbook of Diagnostic Microbiology. 5th Ed. Maryland Heights, Missouri. Saunders Elsevier. 2015. Chapter 26, pages 563-588.

(11) Johnson MG, Stout JE. Twenty-eight cases of Mycobacterium marinum infection: retrospective case series and literature review. Infection. 2015; 43: 655-662. doi 10.1007/s 15010-0150776-8.

(12) Sett C, Wachholz P, Masuda P, Figueira R, Mattar F, Ura D. Mycobacterium marinum infection: a case report. Journal of Venomous Animals and Toxins including Tropical Diseases. 2015; 21:7. doi 10.1186/s40409-015-0008-9.

(13) Chazel M, Marchandin H, Keck N, Terru D, Carriere C, Ponso da M, et al. Evaluation of The SLOMYCO Sensititre[R] panel for testing the antimicrobial susceptibility of Mycobacterium marinum isolates. Annals of Clinical Microbiology and Antimicrobials. 2016; 15(30): 1-7. doi 10.1186/s12941-016-0145-1.

(14) Edirisinghe E A, Dissanayake, D R, Abayasekera C, Arulkan than A. Efficacy of Calcium

(15) Hypochlorite and Ultraviolet Irradiation against Mycobacterium fortuitum and Mycobacterium marinum. The International Journal of Mycobacteriology. 2017: 1-4.

Deborah A. Johnson, MS, MT(ASCP), SM, Assistant Professor; Beverly J. Barham, PhD, MPH, MT(ASCP), Professor; Kathryn Webster, MS, MT(ASCP), Associate Professor; Medical Laboratory Science Program, Dept. of Health Sciences, Illinois State University, Normal, IL
Table 1. Urinalysis

      Test              Results         Reference

Specific Gravity    1.010             1.003-1.030
Urine pH            7.0               5.0-9.0
WBC Esterase        Negative          Negative
Nitrite             Negative          Negative
Protein, ran-       Negative mg/dL    Negative mg/dL
dom urine
Urine Glucose,      Negative          Negative
Urine Ketones       Negative mg/dL    Negative mg/dL
Urobilinogen        Normal mg/dL      Normal, 1.0mg/
Urine Bilirubin     Negative          Negative
Urine Blood         Negative          Negative
Urinalysis Color    Yellow
Urinalysis          Clear

Table 2. Complete Blood Count (CBC)

      Test        Results        Reference

WBC                 10.0   5.0-10.0 x [10.sup.3]/
RBC                  4.1   4.6-5.9 x [10.sup.6]/
Hemoglobin          11.7          12.2-15.8 g/dL
Hematocrit          35.2              36.0-47.0%
Platelets            275   150-440 x [10.sup.3]/
Neutrophils         58.3              47.0-73.0%
Lymphocytes         26.7              18.0-42.0%
Monocytes            5.0               4.0-12.0%
Eosinophils          0.0                0.0-5.0%
Basophils            0.0                0.0-1.0%
Absolute            5.83        1.60-7.70 10(3)/
neutrophils                                  mcL
Absolute            2.67        1.30-3.20 10(3)/
lymphocytes                                  mcL
Absolute             0.5        0.20-1.00 10(3)/
monocytes                                    mcL
Absolute            0.00        0.00-0.40 10(3)/
eosinophils                                  mcL
Absolute            0.00        0.00-0.10 10(3)/
basophils                                    mcL

Table 3. Basic metabolic panel (BMP)

      Test        Results              Reference
Sodium               136                 136-145
Potassium            4.6                 3.5-5.1
Chloride              98                  98-107
CO2, Venous           26          22-30 (mmol/L)
Anion Gap             12            <18 (mmol/L)
Glucose               80           70-99 (mg/dL)
BUN                   15            7-17 (mg/dL)
Creatinine          0.90          0.60-1.00 (mg/
(Blood)                                      dL)
BUN/Creatinine        16           12-20 (Ratio)
Total protein        6.7            6.3-8.2 g/dL
Albumin              3.9            3.5-5.9 g/dL
A/G ratio            1.4                 1.0-2.2
Calcium              8.4          8.4-10.2 mg/dL
Total bilirubin      1.0           0.2-1.2 mg/dL
SGOT (AST)            30                5-34 U/L
SGPT (ALT)            50                0-55 U/L
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Title Annotation:Article 454 1 Clock Hour; Mycobacterium marinum
Author:Johnson, Deborah A.; Barham, Beverly J.; Webster, Kathryn E.
Publication:Journal of Continuing Education Topics & Issues
Article Type:Clinical report
Date:Aug 1, 2018
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