Mycobacterium marinum: A Case-Based Narrative Review of Diagnosis and Management

Skin and soft tissue infections caused by non-tuberculous mycobacteria are occurring more frequently in recent years. However, chronic skin and soft tissue lesions present a challenge for clinicians, as the diagnostic work-up and definitive diagnosis require knowledge and available laboratory resources. We present here the case of a 66-year-old male patient who presented with painful abscess-like nodules on his right hand and forearm, which worsened after treatment with an anti-TNF-a agent. The fluid specimen taken from the lesion was positive for mycobacteria according to the acid-fast stain. Mycobacterium marinum was identified, first by next-generation sequencing and finally grown on culture, after eight weeks. Acknowledging the complexity of diagnosing and managing infections by non-tuberculous mycobacteria, and especially Mycobacterium marinum, we provide a review of the current epidemiology, clinical characteristics, diagnosis and management of Mycobacterium marinum infection.

Clinical, Dermatoscopical and Laboratory Essentials of Fish Tank Granuloma

In immunocompetent individuals Mycobacterium marinum (M. marinum) infection usually presents with localized skin lesions, better known as “swimming pool granuloma” or “fish tank granuloma” (FTG). When establishing the diagnosis of FTG, doctors encounter several problems in the clinical practice: granulomas are detected in less than two thirds of biopsies and acid-fast bacilli are identified only in a minority of cases. Majority of disseminated and aggressive FTG forms are unrecognized at the beginning, and occur in immunosuppressed patients, including organ transplant patients. Functional impairment or even amputation of the extremity, visceral involvement and lethal outcome have been reported. Although more than one thousand cases of FTG have been reported worldwide, dermatoscopy of FTG, as a diagnostic aid, has not been reported yet. Presenting the case of FTG of recent onset where, guided by dermatoscopy, microorganisms were isolated and identified from the biopsy material, we summarize the essentials of clinical and laboratory diagnostics of M. marinum infection.

Mycobacterium marinum

Mycobacterium marinum is a well-known pathogenic mycobacterium for skin and soft tissue infections and is associated with fishes and water. Among nontuberculous mycobacteria (NTM), it is the leading cause of extrarespiratory human infections worldwide. In addition, there is a specific scientific interest in M. marinum because of its genetic relatedness to Mycobacterium tuberculosis and because experimental infection of M. marinum in fishes mimics tuberculosis pathogenesis. Microbiological characteristics include the fact that it grows in 7 to 14 days with photochromogenic colonies and is difficult to differentiate from Mycobacterium ulcerans and other mycolactone-producing NTM on a molecular basis. The diagnosis is highly suspected by the mode of infection, which is related to the hobby of fishkeeping, professional handling of marine shells, or swimming in nonchlorinated pools. Clinics distinguished skin and soft tissue lesions (typically sporotrichoid or subacute hand nodules) and lesions disseminated to joint and bone, often related with the local use of corticosteroids. In clinical microbiology, microscopy and culture are often negative because growth requires low temperature (30°C) and several weeks to succeed in primary cultivation. The treatment is not standardized, and no randomized control trials have been done. Therapy is a combination of surgery and antimicrobial agents such as cyclines and rifampin, with successful outcome in most of the skin diseases but less frequently in deep tissue infections. Prevention can be useful with hand protection recommendations for professionals and all persons manipulating fishes or fish tank water and use of alcohol disinfection after contact.

Avian Mycobacteriosis: Still Existing Threat to Humans

The nontuberculous mycobacteria are typically environmental organisms residing in soil and water. These microorganisms can cause a wide range of clinical diseases; pulmonary disease is most frequent, followed by lymphadenitis in children, skin and soft tissue disease, and rare extra pulmonary or disseminated infections. Mycobacterium avium complex is the second most common cause of pulmonary mycobacterioses after M. tuberculosis. This review covers the clinical and laboratory diagnosis of infection caused by the members of this complex and particularities for the treatment of different disease types and patient populations.

Molecular detection of nontuberculous mycobacteria: advantages and limits of a broad-range sequencing approach

The isolation of nontuberculous mycobacteria (NTM) from clinical specimens has become very common in recent years. Such organisms are typically environmental and occasionally pathogenic for humans and animals. Standard diagnosis of mycobacterial infections relies on direct examination and culture. However, molecular tools are now available which allow quicker and more accurate diagnosis. Detection of NTM can be performed directly from clinical samples, although identification is mostly carried out after isolation. Sequencing of genomic targets (such as 16S rRNA, ITS, rpoB or hsp65) allows accurate and rapid identification, but has some technical limitations. A brief summary of the molecular methods available for NTM identification and a discussion of the problems associated with the use of sequencing analysis together with a description of available algorithms for NTM identification are the major objectives of this review.

Mycobacterium marinum infections in humans and tracing of its possible environmental sources

The low frequency of nontuberculous mycobacterial infections, nonspecific symptoms for individual mycobacteria, and the lack of specific identification methods could alter correct diagnosis. This study presents a combined microbiology and molecular-based approach for Mycobacterium marinum detection in four aquarists with cutaneous mycobacterial infection. Simultaneously, ecology screening for M. marinum presence in the aquarists' fish tanks was performed. A total of 38 mycobacterial isolates originated from four human patients (n = 20), aquarium animals (n = 8), and an aquarium environment (n = 10). Isolate identification was carried out using 16S rRNA sequence analysis. A microbiology-based approach, followed by 16S rRNA sequence analysis, was successfully used for detection of M. marinum in all four patients. Animal and environmental samples were simultaneously examined, and a total of seven mycobacterial species were isolated: Mycobacterium chelonae , Mycobacterium fortuitum , Mycobacterium gordonae , Mycobacterium kansasii , Mycobacterium mantenii , Mycobacterium marinum , and Mycobacterium peregrinum . The presence of M. marinum was proven in the aquarium environments of two patients. Although M. marinum is described as being present in water, it was detected only in fish.