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

A Review of the Industrial Importance, Common Bacterial Diseases, and Zoonotic Risks of Freshwater Aquarium Fish

Background: The ever-increasing popularity of home aquariums, most often involving freshwater varieties, has exploded in recent years partially due to the Coronavirus pandemic and related to stay-at-home public health precautions for social distancing. With this ever-increasing popularity of aquariums as a hobby, and whether this involves freshwater or marine fish species, a number of important economic, ecological, and public health issues arise for both fish and hobbyists alike. Materials and Methods: This review highlights the history and genesis of aquariums as both a hobby and an important economic factor (industrial, commercial) for many countries on a global basis. Types of aquarium fish are described, and culture conditions leading to homeostasis in aquatic environments are detailed. When these conditions are not met and aquatic systems are out of balance, the disease can result due to stressed fish. Results: Major bacterial diseases associated with freshwater aquarium fish are reviewed, as are potential human infections related to the care and maintenance of home aquaria. Conclusion: Besides, scientific information was also combined with the false facts of hobbyists who tried to identify and treat diseases during an outbreak in the aquarium. Finally, unresolved issues and important misconceptions regarding the field are discussed.

Nontuberculous Mycobacteria: Ecology and Impact on Animal and Human Health

Nontuberculous mycobacteria (NTM) represent an important group of environmentally saprophytic and potentially pathogenic bacteria that can cause serious mycobacterioses in humans and animals. The sources of infections often remain undetected except for soil- or water-borne, water-washed, water-based, or water-related infections caused by groups of the Mycobacterium (M.) avium complex; M. fortuitum; and other NTM species, including M. marinum infection, known as fish tank granuloma, and M. ulcerans infection, which is described as a Buruli ulcer. NTM could be considered as water-borne, air-borne, and soil-borne pathogens (sapronoses). A lot of clinically relevant NTM species could be considered due to the enormity of published data on permanent, periodic, transient, and incidental sapronoses. Interest is currently increasing in mycobacterioses diagnosed in humans and husbandry animals (esp. pigs) caused by NTM species present in peat bogs, potting soil, garden peat, bat and bird guano, and other matrices used as garden fertilizers. NTM are present in dust particles and in water aerosols, which represent certain factors during aerogenous infection in immunosuppressed host organisms during hospitalization, speleotherapy, and leisure activities. For this Special Issue, a collection of articles providing a current view of the research on NTM-including the clinical relevance, therapy, prevention of mycobacterioses, epidemiology, and ecology-are addressed.

Clinical Relevance and Environmental Prevalence of Mycobacterium fortuitum Group Members. Comment on Mugetti et al. Gene Sequencing and Phylogenetic Analysis: Powerful Tools for an Improved Diagnosis of Fish Mycobacteriosis Caused by Mycobacterium fortuitum Group Members. Microorganisms 2021, 9, 797

Mycobacterium fortuitum group (MFG) members are able to cause clinical mycobacteriosis in fish and other animals including humans. M. alvei, M. arceuilense, M. brisbanense, M. conceptionense, M. fortuitum, M. peregrinum, M. porcinum, M. senegalense, M. septicum, and M. setense were isolated from fish with mycobacteriosis. In other animals only three MFG species have been isolated: M. arceuilense from camels' milk, M. farcinogenes from cutaneous infections often described as "farcy", and M. fortuitum from different domestic and wild mammals' species. Out of 17, only 3 MFG species (M. arceuilense, M. lutetiense and M. montmartrense) have never been reported in humans. A total of eight MFG members (M. alvei, M. brisbanense, M. conceptionense, M. fortuitum subsp. acetamidolyticum, M. houstonense, M. peregrinum, M. porcinum, and M. septicum) have been isolated from both pulmonary and extrathoracic locations. In extrathoracic tissues five MFG species (M. boenickei, M. farcinogenes, M. neworleansense, M. senegalense, and M. setense) have been diagnosed and only one MFG member (M. fortuitum subsp. acetamidolyticum) has been isolated from pulmonary infection.

Recovery of Mycobacteria from Heavily Contaminated Environmental Matrices

For epidemiology studies, a decontamination method using a solution containing 4.0% NaOH and 0.5% tetradecyltrimethylammonium bromide (TDAB) represents a relatively simple and universal procedure for processing heavily microbially contaminated matrices together with increase of mycobacteria yield and elimination of gross contamination. A contamination rate only averaging 7.3% (2.4% in Cluster S; 6.9% in Cluster R and 12.6% in Cluster E) was found in 787 examined environmental samples. Mycobacteria were cultured from 28.5% of 274 soil and water sediments samples (Cluster S), 60.2% of 251 samples of raw and processed peat and other horticultural substrates (Cluster R), and 29.4% of 262 faecal samples along with other samples of animal origin (Cluster E). A total of 38 species of slow and rapidly growing mycobacteria were isolated. M. avium ssp. hominissuis, M. fortuitum and M. malmoense were the species most often isolated. The parameters for the quantitative detection of mycobacteria by PCR can be significantly refined by treating the sample suspension before DNA isolation with PMA (propidium monoazide) solution. This effectively eliminates DNA residue from both dead mycobacterial cells and potentially interfering DNA segments present from other microbial flora. In terms of human exposure risk assessment, the potential exposure to live non-tuberculous mycobacteria can be more accurately determined.

Investigation of Potential Reservoirs of Non-Tuberculous Mycobacteria in a European Sea Bass (Dicentrarchus labrax) Farm

Fish mycobacteriosis is a widespread global problem caused by species of non-tuberculous mycobacteria (NTM). Mycobacterium marinum is one of the species most often involved in disease episodes of aquarium and farmed fish. Since there is currently no available effective therapy or vaccine, a prompt search for routes of entry is key to limiting the damage induced by the disease. Here we report a case of mycobacteriosis follow up in a European sea bass (Dicentrarchus labrax) farm located in Northern Italy, in which environmental samples and newly added fish batches were analyzed. Samples from fish present on the farm, sediment, and periphyton all resulted positive for M. marinum, whereas the new fish batches and the water samples resulted negative. The environmental resistance of NTM (alcohol-acid resistance, biofilm formation) and the lack of prophylactic and therapeutic strategies make these diseases difficult to manage. Prompt identification of biotic and abiotic reservoirs, combined with good zootechnical hygiene practices, are the most effective measures to control fish mycobacteriosis in intensive farms.

Identification Mycobacterium spp. in the Natural Water of Two Austrian Rivers

Nontuberculous mycobacteria constitute a subgroup among the Mycobacterium genus, a genus of Gram-positive bacteria that includes numerous pathogenic bacteria. In the present study, Mycobacterium spp. were detected in natural water samples from two Austrian rivers (Kamp and Wulka) using three different primers and PCR procedures for the identification of the 16S rRNA and hsp65 genes. Water samples were collected from the Kamp (45 samples) and Wulka (25 samples) in the summer and winter of 2018 and 2019. Molecular evidence showed a high prevalence of Mycobacterium sp. in these rivers with prevalence rates estimated at approximately 94.3% across all rivers. The present study represents the first survey into the prevalence of Mycobacterium sp. in natural water in Austria. Because nontuberculous mycobacteria have known pathogenic potential, including zoonotic, these findings may have implications for health management and public health.

Mycobacterium syngnathidarum sp. nov., a rapidly growing mycobacterium identified in syngnathid fish

Two closely related isolates, 27335^T and 24999, of rapidly growing, non-pigmented mycobacteria, were cultured from two clinically ill fish of the family Syngnathidae. Whole genome sequencing of the two isolates revealed low sequence homology to documented mycobacteria within public databases such as the NCBI. Evaluation of targeted housekeeping genes, including 16S rRNA, ITS, rpoB and hsp65, related the two bacteria distantly to Mycobacterium senegalense CK2 M4421 and Mycobacterium farcinogenes DSM 43637. Phenotypic, biochemical and dDNA-DNA hybridization tests demonstrated that Mycobacterium syngnathidarum is a new species distinct from other recognized rapidly growing mycobacterial species. Phenotypic, chemotaxonomic and phylogenetic data evaluation provided evidence that the two strains represent one novel species. We propose the formal recognition of Mycobacterium syngnathidarum sp. nov., with isolate 27335^T as the type strain (=ATCC TSD-89^T,=DSM 105112^T).

The lifestyle of prokaryotic organisms influences the repertoire of promiscuous enzymes

The metabolism of microbial organisms and its diversity are partly the result of an adaptation process to the characteristics of the environments that they inhabit. In this work, we analyze the influence of lifestyle on the content of promiscuous enzymes in 761 nonredundant bacterial and archaeal genomes. Promiscuous enzymes were defined as those proteins whose catalytic activities are defined by two or more different Enzyme Commission (E.C.) numbers. The genomes analyzed were categorized into four lifestyles for their exhaustive comparisons: free-living, extremophiles, pathogens, and intracellular. From these analyses we found that free-living organisms have larger genomes and an enrichment of promiscuous enzymes. In contrast, intracellular organisms showed smaller genomes and the lesser proportion of promiscuous enzymes. On the basis of our data, we show that the proportion of promiscuous enzymes in an organism is mainly influenced by the lifestyle, where fluctuating environments promote its emergence. Finally, we evidenced that duplication processes occur preferentially in metabolism of free-living and extremophiles species.

Microbiological features and clinical relevance of new species of the genus Mycobacterium

Nontuberculous mycobacteria (NTM) are present in the environment, mainly in water, and are occasionally responsible for opportunistic infections in humans. Despite the fact that NTM are characterized by a moderate pathogenicity, the diseases caused by NTM at various body sites are increasing on a worldwide level. Among over 150 officially recognized NTM species, only two or three dozen are familiar to clinicians, and even to most microbiologists. In this paper, approximately 50 new species described in the last 8 years are reviewed, and their role in human infections is assessed on the basis of reported clinical cases. The small number of reports concerning most of the "new" mycobacterial species is responsible for the widespread conviction that they are very rare. Their role is actually largely underestimated, mainly because they often remain unrecognized and misidentified. Aiming to minimize such bias, emphasis has been placed on more common identification pitfalls. Together with new NTM, new members of the Mycobacterium tuberculosis complex described in the last few years are also an object of the present review.

Disseminated Mycobacterium gordonae and Mycobacterium mantenii infection with elevated anti-IFN-γ neutralizing autoantibodies

A case of disseminated nontuberculous mycobacteria(l) (NTM) infection in a patient with positive neutralizing anti-interferon-γ (IFN-γ) autoantibodies involving bone, bronchus, systemic lymph nodes, and skin is reported. The causative NTMs were two different strains: Mycobacterium gordonae, which rarely causes true disease, and Mycobacterium mantenii, which is extremely rare. Anti-mycobacterial treatment successfully ameliorated all disseminated lesions. Although the concentration of anti-IFN-γ autoantibodies increased during the pre-treatment period, it gradually decreased after anti-mycobacterial treatment was started.

Bacterial zoonoses of fishes: a review and appraisal of evidence for linkages between fish and human infections

Human contact with and consumption of fishes presents hazards from a range of bacterial zoonotic infections. Whereas many bacterial pathogens have been presented as fish-borne zoonoses on the basis of epidemiological and phenotypic evidence, genetic identity between fish and human isolates is not frequently examined or does not provide support for transmission between these hosts. In order to accurately assess the zoonotic risk from exposure to fishes in the context of aquaculture, wild fisheries and ornamental aquaria, it is important to critically examine evidence of linkages between bacteria infecting fishes and humans. This article reviews bacteria typically presented as fish-borne zoonoses, and examines the current strength of evidence for this classification. Of bacteria generally described as fish-borne zoonoses, only Mycobacterium spp., Streptococcus iniae, Clostridium botulinum, and Vibrio vulnificus appear to be well-supported as zoonoses in the strict sense. Erysipelothrix rhusiopathiae, while transmissible from fishes to humans, does not cause disease in fishes and is therefore excluded from the list. Some epidemiological and/or molecular linkages have been made between other bacteria infecting both fishes and humans, but more work is needed to elucidate routes of transmission and the identity of these pathogens in their respective hosts at the genomic level.

Relative prevalence of Mycobacterium marinum in fish collected from aquaria and natural freshwaters in central Europe

A survey was carried out on occurrence of Mycobacterium marinum in fish kept in aquaria and those living in their natural environment. Species-specific qPCR targeting the erp and IS2404 genes together with the conventional culture method were used. The analysis of 72 ornamental fish (n = 216 samples: gills, muscle and intestine) collected from aquaria revealed the presence of M. marinum in 30 individuals (41.7%) of whom 17 (23.6%) were later culture positive. Culture-independent detection revealed the presence of M. marinum in 16 of 83 environmental samples (19.3%) collected in aquaria. The presence of viable M. marinum cells was later confirmed in 5 samples (6.0%). No qPCR or culture positivity was observed when 123 groundwater fish and their corresponding environmental samples (n = 142) were analysed.

A new cultivation-independent tool for fast and reliable detection of Mycobacterium marinum

The Mycobacterium marinum group (MMG) is a class of mycobacteria that includes M. marinum, the cause of chronic systemic infections in fish. This species occasionally causes granulomatous skin lesions in humans. Other members of MMG are mycolactone-producing mycobacteria (MPM; M. ulcerans, M. shottsii and M. pseudoshottsii). The cultivation-independent approach presented in this study brings a fast and reliable alternative to classically used cultivation methods. The developed triplex erp/IS2404 qPCR assay is based on a primary species-specific erp detection, which allows enumeration of MMG in analysed samples, and secondary IS2404 detection is suitable for the differentiation of M. marinum from MPM. The detection of M. marinum in clinical specimens and in artificially contaminated tissue samples has proven its applicability for diagnostic purposes.

Fish tank granuloma caused by Mycobacterium marinum in two aquarists: two case reports

Mycobacterium marinum, the cause of chronic systemic infections in fish, occasionally causes granulomatous skin and soft tissue lesions in humans. Cutaneous mycobacterial infection in two patients owing to unusual circumstances is presented in this report. The first patient was infected through improper hygienic behavior, while infection in the second patient was previously misdiagnosed as rheumatoid arthritis and treated with methylprednisolone for a period of three months, which resulted in a rare systemic spread of M. marinum into the bones of the hand, testis, and epididymis. Simultaneously, screening for possible sources of M. marinum infection in patients' aquaria revealed positive fish harboring VNTR profiles identical to those obtained for clinical isolates from patients.

Mycobacterium marinum: a potential immunotherapy for Mycobacterium tuberculosis infection

Purpose

The aim of the present study was to investigate the immune response induced by Mycobacterium marinum infection in vitro and the potential of M. marinum as an immunotherapy for M. tuberculosis infection.

Methods

The potential human immune response to certain bacillus infections was investigated in an immune cell-bacillus coculture system in vitro. As a potential novel immunotherapy, M. marinum was studied and compared with two other bacilli, Bacillus Calmette-Guérin (BCG) and live attenuated M. tuberculosis. We examined the changes in both the bacilli and immune cells, especially the time course of the viability of mycobacteria in the coculture system and host immune responses including multinuclear giant cell formation by Wright-Giemsa modified staining, macrophage polarization by cell surface antigen expression, and cytokines/chemokine production by both mRNA expression and protein secretion.

Results

The M. marinum stimulated coculture group showed more expression of CD209, CD68, CD80, and CD86 than the BCG and M. tuberculosis (an attenuated strain, H37Ra) groups, although the differences were not statistically significant. Moreover, the M. marinum group expressed more interleukin (IL)-1B and IL-12p40 on day 3 (IL-1B: P = 0.003 and 0.004, respectively; IL-12p40: P = 0.001 and 0.011, respectively), a higher level of CXCL10 on day 1 (P = 0.006 and 0.026, respectively), and higher levels of chemokine (C-X-C motif) ligand (CXCL) 8 and chemokine (C motif) ligand (XCL) 1 on day 3 (CXCL8: P = 0.012 and 0.014, respectively; XCL1: P = 0.000 and 0.000, respectively). The M. marinum stimulated coculture group also secreted more tumor necrosis factor (TNF)-α, IL-1β, and IL-10 on day 1 (TNF-α: P = 0.000 and 0.000, respectively; IL-1β: P = 0.000 and 0.000, respectively; IL-10: P = 0.002 and 0.019, respectively) and day 3 (TNF-α: P = 0.000 and 0.000, respectively; IL-1β: P = 0.000 and 0.001, respectively; IL-10: P = 0.000 and 0.000, respectively). In addition, the colony-forming units (an index of viability) of M. marinum in the M. marinum stimulated coculture group was significantly less than that of BCG and H37Ra in their corresponding bacillus stimulated groups (P = 0.037 and 0.013, respectively).

Conclusion

Our results indicated that M. marinum could be a potentially safe and effective immunotherapy.

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.