Mycobacterium marinum infection

Rapid Diagnosis of Mycobacterium marinum Infection by Next-Generation Sequencing: A Case Report

We present the first report of histology- and culture-proven Mycobacterium marinum infection diagnosed by next-generation sequencing (NGS). It took <2 days to make a microbiological diagnosis using the Oxford Nanopore Technologies' MinION device, compared to 20 days for the mycobacterium to be isolated from the tissue biopsy. NGS is particularly useful for culture-negative and slow-growing microorganism infections, such as mycobacterial, fungal and partially treated pyogenic bacterial infections. Due to its low equipment cost, short turn-around-time and portable size, the Oxford Nanopore Technologies' MinION device is a useful platform for NGS in routine clinical microbiology laboratories.

Nontuberculous mycobacterial disease in childhood - update on diagnostic approaches and treatment

Recent studies suggest that the incidence of nontuberculous mycobacterial infections in children may be increasing. Nontuberculous mycobacterial lymphadenitis, skin and soft tissue infection, and pulmonary disease each present unique challenges in relation to diagnosis and treatment. In this update, we critically review the recent literature on the epidemiology, clinical features, diagnostic approaches and treatment of nontuberculous mycobacterial disease in children. In addition, we outline key areas warranting further research.

Understanding cutaneous tuberculosis: two clinical cases

Tuberculosis (TB) is an ancient human disease and remains today one of the most important public health problems and the second most frequent cause of death from an infectious disease worldwide. While pulmonary TB is the most common form, extra-pulmonary TB is on the rise due to the increase in immunosuppressed subjects. Cutaneous TB manifestations are rare forms of extra-pulmonary TB due to systemic dissemination of bacilli or direct inoculation, involving skin or skin-associated tissue, more common in immunocompromised subjects. Some risk factors and the features of the lesion may prompt the suspicion of cutaneous TB, but only microbiological assays can confirm the diagnosis. Our work summarizes cutaneous TB manifestations and differences from other skin mycobacterial infections, also describes two characteristic clinical cases.

Mycobacteria

The immunocompromised host is at increased risk of Mycobacterium tuberculosis complex and nontuberculous mycobacteria infection. Although Mycobacterium tuberculosis complex is a significant mycobacterial pathogen, nontuberculous mycobacteria causes substantial disease in those with suppressed immune responses. Mycobacterial infections can cause significant morbidity and mortality in this patient population, and rapid identification and susceptibility testing of the mycobacterial species is paramount to patient management and outcomes. Mycobacterial diagnostics has undergone some significant advances in the last two decades with immunodiagnostics (interferon gamma release assay), microscopy (light-emitting diode), culture (automated broth-based systems), identification (direct PCR, sequencing and matrix-assisted laser-desorption ionization–time of flight mass spectrometry) and susceptibility testing (molecular detection of drug resistance from direct specimens or positive cultures). Employing the most rapid and sensitive methods in the mycobacterial laboratory will have a tremendous impact on patient care and, in the case of Mycobacterium tuberculosis complex, in the control of tuberculosis.

Nontuberculous Mycobacterial Disease in Children - Epidemiology, Diagnosis & Management at a Tertiary Center

Background

There are limited data on the epidemiology, diagnosis and optimal management of nontuberculous mycobacterial (NTM) disease in children.

Methods

Retrospective cohort study of NTM cases over a 10-year-period at a tertiary referral hospital in Australia.

Results

A total of 140 children with NTM disease, including 107 with lymphadenitis and 25 with skin and soft tissue infections (SSTIs), were identified. The estimated incidence of NTM disease was 0.6–1.6 cases / 100,000 children / year; no increasing trend was observed over the study period. Temporal analyses revealed a seasonal incidence cycle around 12 months, with peaks in late winter/spring and troughs in autumn. Mycobacterium-avium-complex accounted for most cases (77.8%), followed by Mycobacterium ulcerans (14.4%) and Mycobacterium marinum (3.3%). Polymerase chain reaction testing had higher sensitivity than culture and microscopy for acid-fast bacilli (92.0%, 67.2% and 35.7%, respectively). The majority of lymphadenitis cases underwent surgical excision (97.2%); multiple recurrences in this group were less common in cases treated with clarithromycin and rifampicin compared with clarithromycin alone or no anti-mycobacterial drugs (0% versus 7.1%; OR:0.73). SSTI recurrences were also less common in cases treated with two anti-mycobacterial drugs compared with one or none (10.5% versus 33.3%; OR:0.23).

Conclusions

There was seasonal variation in the incidence of NTM disease, analogous to recently published observations in tuberculosis, which have been linked to seasonal variation in vitamin D. Our finding that anti-mycobacterial combination therapy was associated with a reduced risk of recurrences in patients with NTM lymphadenitis or SSTI requires further confirmation in prospective trials.

Necrotizing Soft Tissue Infection Occurring after Exposure to Mycobacterium marinum

Cutaneous infections caused by Mycobacterium marinum have been attributed to aquarium or fish exposure after a break in the skin barrier. In most instances, the upper limbs and fingers account for a majority of the infection sites. While previous cases of necrotizing soft tissue infections related to M. marinum have been documented, the importance of our presenting case is to illustrate the aggressive nature of M. marinum resulting in a persistent necrotizing soft tissue infection of a finger that required multiple aggressive wound debridements, followed by an amputation of the affected extremity, in order to hasten recovery.

Mycobacterium ulcerans persistence at a village water source of Buruli ulcer patients

Buruli ulcer (BU), a neglected tropical disease of the skin and subcutaneous tissue, is caused by Mycobacterium ulcerans and is the third most common mycobacterial disease after tuberculosis and leprosy. While there is a strong association of the occurrence of the disease with stagnant or slow flowing water bodies, the exact mode of transmission of BU is not clear. M. ulcerans has emerged from the environmental fish pathogen M. marinum by acquisition of a virulence plasmid encoding the enzymes required for the production of the cytotoxic macrolide toxin mycolactone, which is a key factor in the pathogenesis of BU. Comparative genomic studies have further shown extensive pseudogene formation and downsizing of the M. ulcerans genome, indicative for an adaptation to a more stable ecological niche. This has raised the question whether this pathogen is still present in water-associated environmental reservoirs. Here we show persistence of M. ulcerans specific DNA sequences over a period of more than two years at a water contact location of BU patients in an endemic village of Cameroon. At defined positions in a shallow water hole used by the villagers for washing and bathing, detritus remained consistently positive for M. ulcerans DNA. The observed mean real-time PCR Ct difference of 1.45 between the insertion sequences IS2606 and IS2404 indicated that lineage 3 M. ulcerans, which cause human disease, persisted in this environment after successful treatment of all local patients. Underwater decaying organic matter may therefore represent a reservoir of M. ulcerans for direct infection of skin lesions or vector-associated transmission.

Buruli ulcer (BU) is a neglected tropical disease caused by Mycobacterium ulcerans which affects mainly children in West Africa. Although it is commonly believed that the infection originates from an environmental source, both the reservoir of M. ulcerans and the mode of transmission to human patients remain to be elucidated. Previous investigations indicated that transmission likely takes place away from the homes of patients. We therefore screened the farms as well as village and farm water locations of 46 laboratory confirmed BU patients of the Mapé Basin of Cameroon for the presence of M. ulcerans DNA by real-time PCR. In this analysis three positive village water locations were identified. By studying one of these locations in great detail we found that M. ulcerans DNA persists in underwater detritus in one section of the village water location even after all local cases had been treated. The detritus may represent a reservoir of M. ulcerans from where infection could take place through either direct contamination of skin lesions or through contamination or colonization of insect vectors.