Mycobacterium marinum infections in fish and humans in Israel

Combined exposure to microplastics and amitriptyline caused intestinal damage, oxidative stress and gut microbiota dysbiosis in zebrafish (Danio rerio)

The potential toxicity of microplastics (MPs) and hydrophilic pharmaceuticals to aquatic organisms has recently raised great public concern, yet their combined effects on aquatic organisms remain largely unknown. Herein, the combined effects of MPs and the commonly prescribed amitriptyline hydrochloride (AMI) on the intestinal tissue and gut microbiota of zebrafish (Danio rerio) were investigated. Adult zebrafish were exposed to microplastics (polystyrene, PS, 440 µg/L), AMI (2.5 µg/L), PS+AMI (440 µg/L PS + 2.5 µg/L AMI), and dechlorinated tap water (control) for 21 days, respectively. Our results showed that zebrafish rapidly ingested PS beads and accumulated them in the gut. Exposure to PS+AMI significantly enhanced the SOD and CAT activities compared to the control group, suggesting that combined exposure might increase ROS production in the zebrafish gut. Exposure to PS+AMI led to severe gut injuries, including cilia defects, partial absence and cracking of intestinal villi. Exposure to PS+AMI caused shifts in the gut bacterial communities, increasing the abundance of Proteobacteria and Actinobacteriota, and decreasing the abundance of Firmicutes, Bacteroidota and beneficial bacteria Cetobacterium, which caused dysbiosis in the gut microbiota, and subsequently may induce intestinal inflammation. Furthermore, exposure to PS+AMI disordered the predicted metabolic functions of gut microbiota, but functional changes in the PS+AMI group at KEGG level 1 and level 2 were not significantly different from those in the PS group. The results of this study extend our knowledge of the combined effects of MPs and AMI on the health of aquatic organisms, and will be helpful in assessing the combined effects of MPs and tricyclic antidepressants on aquatic organisms.

Toxicological responses of Carassius auratus induced by benzophenone-3 exposure and the association with alteration of gut microbiota

Gut microbiota plays a fundamental role in host's physiology. However, the effect of organic UV filters, an emerging contaminant on gut microbiota is poorly understood. Here, fish (Carassius auratus) were exposed to 2, 20 and 200 μg/L of benzophenone-3 (BP3) for 28 days to explore the toxicological effects and its association with the changes in the gut microbiota. The BP3 accumulation is time and dose dependent in the liver and intestine. Under BP3 subchronic exposure, fish's body and intestinal weights, reactive oxygen species (ROS), immunoglobulin M (IgM) and vitellogenin (VTG) levels, as well as 7-benzyloxy-4-trifluoromethylcoumarin-O-debenzyloxylase (BFCOD) activities, were decreased. BP3 exposure has increased the abundance of Bacteroidetes phylum and Mycobacterium genus. Bioinformatic analysis revealed that the levels of ROS, IgM, estrogen receptor and VTG, activities of lysozyme, BFCOD and 7-ethoxyresorufin-O-deethylase were significantly correlated with the relative abundance of intestinal microbial genus (p < 0.05). These results highlight for the first time the association between the effects of organic UV filters on the antioxidant, immune, endocrine, and metabolic systems of the fish and changes in the gut microbiota, which extend knowledge of the role of gut microbiota in ecotoxicology.

Mycobacteriosis and Infections with Non-tuberculous Mycobacteria in Aquatic Organisms: A Review

The Mycobacteriaceae constitute a family of varied Gram-positive organisms that include a large number of pathogenic bacteria. Among these, non-tuberculous mycobacteria are endemic worldwide and have been associated with infections in a large number of organisms, including humans and other mammals and reptiles, as well as fish. In this review, we summarize the most recent findings regarding this group of pathogens in fish. There, four species are most commonly associated with disease outbreaks: Mycobacterium marinum, the most common of these fish mycobacterial pathogens, Mycobacterium fortuitum, Mycobacterium gordonae, and Mycobacterium chelonae. These bacteria have a broad host range: they are zoonotic, and infections have been reported in a large number of fish species. The main route of entry of the bacterium into the fish is through the gastrointestinal route, and the disease is associated with ulcerative dermatitis as well as organomegaly and the development of granulomatous lesions in the internal organs. Mycobacteriaceae are slow-growing and fastidious and isolation is difficult and time consuming and diagnostic is mostly performed using serological and molecular tools. Control of the disease is also difficult: there is currently no effective vaccine and infections react poorly to antibiotherapy. For this reason, more research is needed on the subject of these vexing pathogens.

Molecular Identification and Characterization of Vibrio Species and Mycobacterium Species in Wild and Cultured Marine Fish from the Eastern Mediterranean Sea

In contrast to numerous documented pathogens and infectious diseases of aquaculture, there is a lack of baseline data and information regarding pathogenic agents' prevalence in wild marine fish populations. This study focused on two common fish pathogenic microorganisms, namely Mycobacterium species and Vibrio species, both of which are known to be major causes of fish loss, occasionally to the extent of being a limiting factor in fish production. Both microorganisms are known as zoonotic agents. In total, 210 wild marine indigenous and Lessepsian fish from four different species from the eastern Mediterranean Sea were sampled and tested for Vibrio species and Mycobacterium species during a two-year period (2016-2017). Using PCR with 16S rRNA primers, we detected different strain variations of Mycobacterium species and Vibrio species and, based on the sequencing results, the overall prevalence for Vibrio species in wild fish in 2016 was significantly higher compared to 2017. No significant difference was detected for Mycobacterium species prevalence in wild fish between 2016 and 2017. In addition, 72 gilthead seabream (Sparus aurata) from an Israeli offshore marine farm were also examined during the two-year period (2017-2018). The results suggest that Mycobacterium species prevalence was significantly higher in 2018, while in 2017 there was no positive results for Mycobacterium species. In addition, there was no significant difference between both years in regard to the prevalence of Vibrio species for maricultured fish. These results highlight the necessity of continuous molecular monitoring in order to evaluate the prevalence of pathogenic microorganisms in both wild and cultured fish populations.

Mycobacterium marinum infection in fish and man: epidemiology, pathophysiology and management; a review

Mycobacterium marinum is an opportunistic pathogen inducing infection in fresh and marine water fish. This pathogen causes necrotizing granuloma like tuberculosis, morbidity and mortality in fish. The cell wall-associated lipid phthiocerol dimycocerosates, phenolic glycolipids and ESAT-6 secretion system 1 (ESX-1) are the conserved virulence determinant of the organism. Human infections with Mycobacterium marinum hypothetically are classified into four clinical categories (type I-type IV) and have been associated with the exposure of damaged skin to polluted water from fish pools or contacting objects contaminated with infected fish. Fish mycobacteriosis is clinically manifested and characterized in man by purple painless nodules, liable to develop into superficial crusting ulceration with scar formation. Early laboratory diagnosis of M. marinum including histopathology, culture and PCR is essential and critical as the clinical response to antibiotics requires months to be attained. The pathogenicity and virulence determinants of M. marinum need to be thoroughly and comprehensively investigated and understood. In spite of accumulating information on this pathogen, the different relevant data should be compared, connected and globally compiled. This article is reviewing the epidemiology, virulence factors, diagnosis and disease management in fish while casting light on the potential associated public health hazards.

Humoral and Cellular Immune Response of European Seabass Dicentrarchus labrax Vaccinated with Heat-Killed Mycobacterium marinum (iipA::kan Mutant)

No vaccine is yet commercially available against Mycobacterium marinum, the etiological agent of fish mycobacteriosis (also known as "fish tuberculosis"). The mycobacterial gene responsible for invasion and intracellular persistence, iipA, is known to moderate M. marinum pathology in Zebrafish Danio rerio. Two doses of heat-killed, wild-type, virulent M. marinum and two doses of a heat-killed, avirulent M. marinum iipA::kan mutant strain were used in parallel to vaccinate European Seabass Dicentrarchus labrax. The fish were then challenged with live, virulent M. marinum, and the pathogenesis of the infection was monitored. High specific immunoglobulin M (IgM) response and an increase in cytokine tumor necrosis factor alpha (TNF-α) messenger RNA expression levels were observed in all vaccinated fish. At 1 month postchallenge, TNF-α expression levels increased in spleen tissues of fish vaccinated with the virulent type and in those of unvaccinated fish, whereas in the head kidney, expression was up-regulated only in unvaccinated fish. The expression then decreased, and at 2 months postchallenge, expression appeared similar in all vaccination types. The highest survival rate (75%) was recorded in the group of fish that were vaccinated with a high dose of avirulent iipA::kan mutant. The iipA::kan mutant induced a strong immune response accompanied by only modest tissue disruption. Coupled with an effective program of booster treatments, the iipA::kan mutant vaccine may be developed into a powerful preventive measure against fish mycobacteriosis.

Extensive genomic diversity among Mycobacterium marinum strains revealed by whole genome sequencing

Mycobacterium marinum is the causative agent for the tuberculosis-like disease mycobacteriosis in fish and skin lesions in humans. Ubiquitous in its geographical distribution, M. marinum is known to occupy diverse fish as hosts. However, information about its genomic diversity is limited. Here, we provide the genome sequences for 15 M. marinum strains isolated from infected humans and fish. Comparative genomic analysis of these and four available genomes of the M. marinum strains M, E11, MB2 and Europe reveal high genomic diversity among the strains, leading to the conclusion that M. marinum should be divided into two different clusters, the "M"- and the "Aronson"-type. We suggest that these two clusters should be considered to represent two M. marinum subspecies. Our data also show that the M. marinum pan-genome for both groups is open and expanding and we provide data showing high number of mutational hotspots in M. marinum relative to other mycobacteria such as Mycobacterium tuberculosis. This high genomic diversity might be related to the ability of M. marinum to occupy different ecological niches.

Comparative genomics of Mycobacterium reveals evolutionary trends of M. avium complex

Mycobacterium is gram positive, slow growing, disease causing Actinobacteria. Beside potential pathogenic species, Mycobacterium also contains opportunistic pathogens as well as free living non-pathogenic species. Disease related various analyses on Mycobacterium tuberculosis are very widespread. However, genomic study of overall Mycobacterium species for understanding the selection pressure on genes as well as evolution of the organism is still illusive. MLSA and 16s rDNA based analysis has been generated for 241 Mycobacterium strains and a detailed analysis of codon and amino acid usage bias of mycobacterial genes, their functional analysis have been done. Further the evolutionary features of M. avium complex also have been revealed. Mycobacterial genes are moderately GC rich showed higher expression level in PPs and significant negative correlation with biosynthetic cost of proteins. Translational selection pressure was observed in mycobacterial genes. MAC showed close relationship with NPs and higher evolutionary rate in MAC revealed their constant evolving nature.

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.

Zebrafish: an animal model for research in veterinary medicine

The zebrafish (Danio rerio) has become known as an excellent model organism for studies of vertebrate biology, vertebrate genetics, embryonal development, diseases and drug screening. Nevertheless, there is still lack of detailed reports about usage of the zebrafish as a model in veterinary medicine. Comparing to other vertebrates, they can lay hundreds of eggs at weekly intervals, externally fertilized zebrafish embryos are accessible to observation and manipulation at all stages of their development, which makes possible to simplify the research techniques such as fate mapping, fluorescent tracer time-lapse lineage analysis and single cell transplantation. Although zebrafish are only 2.5 cm long, they are easy to maintain. Intraperitoneal and intracerebroventricular injections, blood sampling and measurement of food intake are possible to be carry out in adult zebrafish. Danio rerio is a useful animal model for neurobiology, developmental biology, drug research, virology, microbiology and genetics. A lot of diseases, for which the zebrafish is a perfect model organism, affect aquatic animals. For a part of them, like those caused by Mycobacterium marinum or Pseudoloma neutrophila, Danio rerio is a natural host, but the zebrafish is also susceptible to the most of fish diseases including Itch, Spring viraemia of carp and Infectious spleen and kidney necrosis. The zebrafish is commonly used in research of bacterial virulence. The zebrafish embryo allows for rapid, non-invasive and real time analysis of bacterial infections in a vertebrate host. Plenty of common pathogens can be examined using zebrafish model: Streptococcus iniae, Vibrio anguillarum or Listeria monocytogenes. The steps are taken to use the zebrafish also in fungal research, especially that dealing with Candida albicans and Cryptococcus neoformans. Although, the zebrafish is used commonly as an animal model to study diseases caused by external agents, it is also useful in studies of metabolic disorders including fatty liver disease and diabetes. The zebrafish is also a valuable tool as a model in behavioral studies connected with feeding, predator evasion, habituation and memory or lateralized control of behavior. The aim of the present article is to familiarize the reader with the possibilities of Danio rerio as an experimental model for veterinary medicine.

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.

Genetic diversity of PCR-positive, culture-negative and culture-positive Mycobacterium ulcerans isolated from Buruli ulcer patients in Ghana

Culture of Mycobacterium ulcerans from Buruli ulcer patients has very low sensitivity. Thus confirmation of M. ulcerans infection is primarily based on PCR directed against IS2404. In this study we compare the genotypes obtained by variable number of tandem repeat analysis of DNA from IS2404-PCR positive cultures with that obtained from IS2404 positive, culture-negative tissue. A significantly greater genetic heterogeneity was found among culture-negative samples compared with that found in cultured strains but a single genotype is over-represented in both sample sets. This study provides evidence that both the focal location of bacteria in a lesion as well as differences in the ability to culture a particular genotype may underlie the low sensitivity of culture. Though preliminary, data from this work also suggests that mycobacteria previously associated with fish disease (M. pseudoshottsii) may be pathogenic for humans.

History, biology and chemistry of Mycobacterium ulcerans infections (Buruli ulcer disease)

Mycobacterium ulcerans infections (Buruli ulcer disease) have a long history that can be traced back 150 years. The successive discoveries of the mycobacteria in 1948 and of mycolactone A/B in 1999, the toxin responsible for this dramatic necrotic skin disease, resulted in a paradigm shift concerning the disease itself and in a broader sense, delineated an entirely new role for bioactive polyketides as virulence factors. The fascinating history, biology and chemistry of M. ulcerans infections are discussed in this review.

Comparative genome analysis of fish and human isolates of Mycobacterium marinum

Mycobacterium marinum is a major causative agent of mycobacteriosis in fish that has a broad range of hosts, including in human isolates. So far, genomic analyses have focused on the human isolate. Here, we compared the draft genome sequences of two strains of M. marinum isolated from fish (MB2 and Europe) with the M. marinum M isolated from humans. M. marinum MB2 and Europe have single, circular chromosomes of 6,134,389 and 6,029,340 bp, and average G + C contents of 65.7 and 65.5 %, respectively. A total of 5,464 coding DNA sequences were annotated in both M. marinum MB2 and Europe genome. Dot plot analyses showed that M. marinum MB2 and Europe were closer to M. marinum M when compared to three other Mycobacterium species. The insertion/deletion gene analysis showed that M. marinum MB2 and Europe contained 342 and 487 genes that were not found in M. marinum M, and lacked 625 and 776 genes found in M. marinum M, respectively. Most of the inserted and deleted genes were classified in the fatty acid, lipid, and isoprenoid subsystem and the virulence, disease, and defense subsystem. Therefore, these results provide insights into the genomic diversity associated with variable hosts and pathogens.

Environmental distribution and seasonal prevalence of Mycobacterium ulcerans in Southern Louisiana

Mycobacterium ulcerans is an emerging environmental pathogen that causes debilitating, ulcerative disease in humans and other vertebrates. The majority of human cases occur in tropical and temperate regions of Africa and Australia, and outbreaks of piscine mycobacteriosis caused by M. ulcerans have been reported in disparate geographic locations spanning the globe. While exposure to a natural body of water is the most common risk factor for human infection, the environmental distribution of M. ulcerans in aquatic habitats has not been extensively studied. Although no human cases have been reported in the United States, a strain of M. ulcerans has been identified as the cause of a piscine mycobacteriosis in Striped bass (Morone saxatilis) within the Chesapeake Bay. Infected fish exhibit bright red ventral and lateral dermal lesions. We observed a possible outbreak causing similar lesions on red drum (Sciaenops ocellatus) in wetlands of southern Louisiana and detected M. ulcerans-specific genetic markers in lesion samples from these fish. Based on these findings, we studied the geographic and seasonal prevalence of these markers across southern Louisiana. M. ulcerans was detected in each of the nine areas sampled across the state. M. ulcerans prevalence was significantly lower in the fall samples, and the low prevalence coincided with decreased nutrient levels and an increase in water temperature. To our knowledge, this is the first study of M. ulcerans biomarkers in the southern United States.

Genetic diversity and population structure of Mycobacterium marinum: new insights into host and environmental specificities

Mycobacterium marinum causes a systemic tuberculosis-like disease in fish and skin infections in humans that can spread to deeper structures, resulting in tenosynovitis, arthritis, and osteomyelitis. However, little information is available concerning (i) the intraspecific genetic diversity of M. marinum isolated from humans and animals; (ii) M. marinum genotype circulation in the different ecosystems, and (iii) the link between M. marinum genetic diversity and hosts (humans and fish). Here, we conducted a genetic study on 89 M. marinum isolates from humans (n = 68) and fish (n = 21) by using mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR) typing. The results show that the M. marinum population is genetically structured not only according to the host but also according to the ecosystem as well as to tissue tropism in humans. This suggests the existence of different genetic pools in the function of the biological and ecological compartments. Moreover, the presence of only certain M. marinum genotypes in humans suggests a different zoonotic potential of the M. marinum genotypes. Considering that the infection is linked to aquarium activity, a significant genetic difference was also detected when the human tissue tropism of M. marinum was taken into consideration, with a higher genetic polymorphism in strains isolated from patients with cutaneous forms than from individuals with deeper-structure infection. It appears that only few genotypes can produce deeper infections in humans, suggesting that the immune system might play a filtering role.

Mycobacterium ulcerans causes minimal pathogenesis and colonization in medaka (Oryzias latipes): an experimental fish model of disease transmission

Mycobacterium ulcerans causes Buruli ulcer in humans, a progressive ulcerative epidermal lesion due to the mycolactone toxin produced by the bacterium. Molecular analysis of M. ulcerans reveals it is closely related to Mycobacterium marinum, a pathogen of both fish and man. Molecular evidence from diagnostic PCR assays for the insertion sequence IS2404 suggests an association of M. ulcerans with fish. However, fish infections by M. ulcerans have not been well documented and IS2404 has been found in other mycobacteria. We have thus, employed two experimental approaches to test for M. ulcerans in fish. We show here for the first time that M. ulcerans with or without the toxin does not mount acute or chronic infections in Japanese Medaka "Oryzias latipes" even at high doses. Moreover, M. ulcerans-infected medaka do not exhibit any visible signs of infection nor disease and the bacteria do not appear to replicate over time. In contrast, similar high doses of the wild-type M. marinum or a mycolactone-producing M. marinum "DL" strain are able to mount an acute disease with mortality in medaka. Although these results would suggest that M. ulcerans does not mount infections in fish we have evidence that CLC macrophages from goldfish are susceptible to mycolactones.

A low prevalence of mycobacteria in freshwater fish from water reservoirs, ponds and farms

A survey of the occurrence of mycobacteria was conducted from 717 freshwater fish (25 species) in two water reservoirs, five ponds and two farms in the Czech Republic. A total of 2182 tissue samples from these fish were examined using the conventional culture method. Thirteen mycobacterial isolates were obtained from 12 (1.7%) fish belonging to nine species. Isolates were identified using sequence analysis of the 16SrRNA gene as: Mycobacterium algericum, M. fortuitum, M. gordonae, M. insubricum, M. kumamotonense, M. nonchromogenicum, two isolates of M. peregrinum, M. terrae and M. triplex. Mycobacteria were isolated more frequently from fish skin and gills than from internal organs or muscles.

Comparative pathogenomics of bacteria causing infectious diseases in fish

Fish living in the wild as well as reared in the aquaculture facilities are susceptible to infectious diseases caused by a phylogenetically diverse collection of bacterial pathogens. Control and treatment options using vaccines and drugs are either inadequate, inefficient, or impracticable. The classical approach in studying fish bacterial pathogens has been looking at individual or few virulence factors. Recently, genome sequencing of a number of bacterial fish pathogens has tremendously increased our understanding of the biology, host adaptation, and virulence factors of these important pathogens. This paper attempts to compile the scattered literature on genome sequence information of fish pathogenic bacteria published and available to date. The genome sequencing has uncovered several complex adaptive evolutionary strategies mediated by horizontal gene transfer, insertion sequence elements, mutations and prophage sequences operating in fish pathogens, and how their genomes evolved from generalist environmental strains to highly virulent obligatory pathogens. In addition, the comparative genomics has allowed the identification of unique pathogen-specific gene clusters. The paper focuses on the comparative analysis of the virulogenomes of important fish bacterial pathogens, and the genes involved in their evolutionary adaptation to different ecological niches. The paper also proposes some new directions on finding novel vaccine and chemotherapeutic targets in the genomes of bacterial pathogens of fish.

Expression of common fluorescent reporters may modulate virulence for Mycobacterium marinum: dramatic attenuation results from Gfp over-expression

Mycobacterium marinum is an established surrogate pathogen for Mycobacterium tuberculosis because of its strong conservation of thousands of orthologous genes, lower risk to researchers and similar pathology in fish. This pathogen causes TB-like chronic disease in a wide variety of fish species. As in human TB, the microbe grows within the host macrophages, can mount life-long chronic infections and produces granulomatous lesions in target organs. One of the fish species known to manifest chronic "fish TB" is the small laboratory fish, Japanese ricefish (medaka; Oryzias latipes). Our laboratory is currently characterizing the disease progression in medaka using fluorescent reporter systems that are introduced into engineered strains of M. marinum. While conducting these studies we observed differences in growth, plasmid stability, and virulence depending on which fluorescent reporter construct was present. Here, we describe large negative effects on virulence and organ colonization that occurred with a commonly used plasmid pG13, that expresses green fluorescent protein (Gfp). The studies presented here, indicate that Gfp over-expression was the basis for the reduced virulence in this reporter construct. We also show that these negative effects could be reversed by significantly reducing Gfp expression levels or by using low-expression constructs of Rfp.

Aquaculture effects on environmental and public welfare - the case of Mediterranean mariculture

Aquatic farming has been considered, during the last decades, as the fastest growing food production industry powered by governmental and technological impulsion. Compensation for fisheries decline, creation of new jobs and source of financial windfall are the most important benefits. However, similar to most of the human food-production activities, aquaculture raised several issues related to the environmental welfare and consumer safety. An effort to record the aquaculture-environment and -human safety interactions with regard to the Mediterranean mariculture, is attempted herein. We focused on this geographical area due to its individualities in both the hydrological and physicochemical characteristics and the forms of aquaculture activities. The cage farming of euryhaline marine fish species and more recently of bluefin tuna and mollusk farming are the dominating aquaculture activities. The impacts of these activities to the environment, through wastes offloads, introduction of alien species, genetic interactions, disease transfer, release of chemicals, use of wild recourses, alterations of coastal habitats and disturbance of wildlife, are analytically considered. Also the consumer safety issues related to the farming are assessed, including generation of antibiotic-resistant microorganisms, contaminants transferred to humans though food chain and other hazards from consumption of aquacultured items. Within these, the major literature findings are critically examined and suggestions for scientific areas that need further development are made. The major tasks for future aquaculture development in this region are: (i) to ensure sustainability and (ii) to balance the risks to public or environmental health with the substantial economical benefits. In regard with monitoring, tools must be created or adapted to predict the environmental costs and estimate consumer impact. At a canonistic and legal basis, the establishment of appropriate legal guidelines and common policies from all countries involved should be mandatory.

[Infections due to Mycobacterium marinum: a review]

Mycobacterium marinum belongs to the non-tuberculous or "atypical" mycobacteria. The reservoirs for these ubiquitous and slowly growing bacteria are both fresh water and salt water. In particular, aquaria should be considered as important source of hobby-related infections especially of fingers, hands and forearms. Affected are both immunosuppressed patients and persons with an intact immune system. Distinctive are erythematous plaques and nodules with tendency for hyperkeratosis, crusting, and superficial ulcerations, sometimes as sporotrichoid lymphocutaneous infection. The histology shows non-caseation granulomas containing epithelioid cells and Langhans giant cells. Using the Ziehl Neelsen staining, typical acid-fast rods are not always detectable. The molecular biological detection of mycobacterial DNA using polymerase chain reaction represents the standard method of diagnosis. Cryotherapy is frequently used as first treatment. For the often long-term tuberculostatic therapy, rifampicin, ethambutol, and clarithromycin are the most used agents.

Serological evaluation of Mycobacterium ulcerans antigens identified by comparative genomics

A specific and sensitive serodiagnostic test for Mycobacterium ulcerans infection would greatly assist the diagnosis of Buruli ulcer and would also facilitate seroepidemiological surveys. By comparative genomics, we identified 45 potential M. ulcerans specific proteins, of which we were able to express and purify 33 in E. coli. Sera from 30 confirmed Buruli ulcer patients, 24 healthy controls from the same endemic region and 30 healthy controls from a non-endemic region in Benin were screened for antibody responses to these specific proteins by ELISA. Serum IgG responses of Buruli ulcer patients were highly variable, however, seven proteins (MUP045, MUP057, MUL_0513, Hsp65, and the polyketide synthase domains ER, AT propionate, and KR A) showed a significant difference between patient and non-endemic control antibody responses. However, when sera from the healthy control subjects living in the same Buruli ulcer endemic area as the patients were examined, none of the proteins were able to discriminate between these two groups. Nevertheless, six of the seven proteins showed an ability to distinguish people living in an endemic area from those in a non-endemic area with an average sensitivity of 69% and specificity of 88%, suggesting exposure to M. ulcerans. Further validation of these six proteins is now underway to assess their suitability for use in Buruli ulcer seroepidemiological studies. Such studies are urgently needed to assist efforts to uncover environmental reservoirs and understand transmission pathways of the M. ulcerans.

Buruli ulcer is a slowly progressive but potentially devastating disease of skin and subcutaneous tissue caused by the bacterium Mycobacterium ulcerans. The disease is widespread throughout West and Central Africa, and some countries in the region have established Buruli ulcer control programs. Buruli ulcer is difficult to distinguish from other chronic skin conditions that require different treatments, and there is an urgent need for an accurate point-of-care diagnostic test. In this study, we have used genomic techniques to identify 45 potential M. ulcerans–specific antigens, 33 of which we have been able to produce and purify. We tested these proteins against sera from patients, healthy people living in the same region as the patients and from individuals living in a region with no cases of Buruli ulcer. We found that seven proteins were able to elicit antibody responses that were significantly different between patients and the control subjects from the non-endemic region but not from the healthy individuals in the same Buruli ulcer endemic region. Further analysis showed that six of these M. ulcerans proteins might be useful as markers of exposure to M. ulcerans and could be developed into tools to uncover environmental reservoirs and understand transmission pathways of the bacterium.

A sensitive FRET probe assay for the selective detection of Mycobacterium marinum in fish

Mycobacterium marinum is the causative agent of mycobacteriosis in wild and cultured fish and of atypical infection in humans. For the diagnosis of M. marinum, cultural and traditional polymerase chain reaction (PCR) methods are currently used. However, these protocols, although able to discriminate within Mycobacterium spp., have proved to be time-consuming or difficult to carry out. For this reason, the aim of this study was to obtain a rapid and specific diagnostic tool to quantify fish Mycobacterium spp. or to discriminate M. marinum from other mycobacteria. A primary PCR amplification with SYBR Green had a detection limit (dl) of 10(2)Mycobacterium DNA copies with a log-linear quantification range up to 10(4) (R(2) = 0.99). The second PCR using FRET probes, flanking a region containing species specific nucleotide variations, was designed and validated with synthetic erp gene fragments corresponding to different mycobacterial species, different whole mycobacteria suspensions, experimentally infected fish tissues, tissues from experimentally infected fish, and samples of cultured fish. The results show that the FRET probes demonstrate a high specificity as the melting curve analysis allowed efficient discrimination of M. marinum from Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium pseudoshottsii, Mycobacterium shottsii and Mycobacterium ulcerans. The kidney is the organ with the strongest detection signal and using fish tissues the method has a mean sensitivity of 50 DNA copies/PCR.

A review of mycobacteriosis in marine fish

Mycobacteriosis is a serious and often lethal disease of fish, affecting a wide range of species globally both in culture and wild settings. Caused by several species of the genus Mycobacterium, the disease has received considerable attention in recent years because of the discovery of new species in piscine hosts, epizootics in wild fisheries, and the ability of a few species to infect humans. The impact of this disease in aquaculture and the aquaria trade has been well reported and there is currently no widely accepted cure other than depopulation and facility disinfection. However, the impact on wild fisheries is poorly understood and may relate to species-specific interactions (host-pathogen) and possibly environmental stressors. In this review, much of what is known about mycobacteriosis in marine fish is summarized with particular attention to an epizootic in striped bass, Morone saxatilis, (Walbaum), in Chesapeake Bay, USA.

Deciphering the genetic basis for polyketide variation among mycobacteria producing mycolactones

Background

Mycolactones are immunosuppressive and cytotoxic polyketides, comprising five naturally occurring structural variants (named A/B, C, D, E and F), produced by different species of very closely related mycobacteria including the human pathogen, Mycobacterium ulcerans. In M. ulcerans strain Agy99, mycolactone A/B is produced by three highly homologous type I polyketide megasynthases (PKS), whose genes (mlsA1: 51 kb, mlsA2: 7.2 kb and mlsB: 42 kb) are found on a 174 kb plasmid, known as pMUM001.

Results

We report here comparative genomic analysis of pMUM001, the complete DNA sequence of a 190 kb megaplasmid (pMUM002) from Mycobacterium liflandii 128FXT and partial sequence of two additional pMUM replicons, combined with liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis. These data reveal how PKS module and domain differences affecting MlsB correlate with the production of mycolactones E and F. For mycolactone E these differences from MlsB in M. ulcerans Agy99 include replacement of the AT domain of the loading module (acetate to propionate) and the absence of an entire extension module. For mycolactone F there is also a reduction of one extension module but also a swap of ketoreductase domains that explains the characteristic stereochemistry of the two terminal side-chain hydroxyls, an arrangement unique to mycolactone F

Conclusion

The mycolactone PKS locus on pMUM002 revealed the same large, three-gene structure and extraordinary pattern of near-identical PKS domain sequence repetition as observed in pMUM001 with greater than 98.5% nucleotide identity among domains of the same function. Intra- and inter-strain comparisons suggest that the extreme sequence homogeneity seen among the mls PKS genes is caused by frequent recombination-mediated domain replacement. This work has shed light on the evolution of mycolactone biosynthesis among an unusual group of mycobacteria and highlights the potential of the mls locus to become a toolbox for combinatorial PKS biochemistry.

Mycobacteriosis in fishes: a review

Mycobacterium species have long been recognised as a significant source of morbidity and mortality in finfish aquaculture, as well as in wild finfishes. Mycobacteria infecting fishes also include zoonotic pathogens that can cause protracted illness, especially in immunocompromised individuals. Several basic aspects of mycobacterial pathobiology in aquatic animals remain poorly understood, although a number of important recent developments have been made, especially with respect to identification of novel Mycobacterium spp. infecting fishes and a new group of mycobacteria closely related to the human pathogen Mycobacterium ulcerans. This review will encompass important aspects of mycobacterial disease in fishes, discuss recent research including studies of mycobacteriosis in striped bass (Morone saxatilis) of Chesapeake Bay, USA, and suggest directions for future work.

Occurrence of Mycobacterium spp. in ornamental fish in Italy

The occurrence of Mycobacterium spp. in freshwater and marine ornamental fish was studied in Italy from June 2002 to May 2005. Two surveys were carried out, one of aquarium fish sent to the Laboratory for diagnosis, and the other of prevalence of infection by mycobacteria in ornamental fish imported into Italy. Bacterial isolation was carried out from the spleen, kidney and liver, and the isolates were subsequently identified by biochemical tests. In the first survey, 387 fish were examined and Mycobacterium spp. were isolated from 181 (46.8%) fish. In the second survey 127 batches of ornamental fish from different countries were examined. Mycobacterium spp. were isolated from 38 (29.9%) batches. The following species were found: M. fortuitum, M. peregrinum, M. chelonae, M. abscessus, M. marinum, M. gordonae, M. nonchromogenicum and M. interjectum. There was a high prevalence of infection independent of the presence of macroscopic lesions. Mycobacterium fortuitum and M. chelonae were more prevalent than M. marinum in the samples examined.

Mycolactones: immunosuppressive and cytotoxic polyketides produced by aquatic mycobacteria

Mycolactones are a family of highly related macrocyclic polyketides that exhibit immunosuppressive and cytotoxic properties. First discovered in 1999, they are the primary virulence factors produced by the environmental human pathogen Mycobacterium ulcerans, the causative agent of Buruli ulcer, and by some closely-related aquatic mycobacteria that cause disease in fish and frogs. Mycolactones are characterized by a common 12-membered lactone core to which is appended an unsaturated fatty acyl side-chain of variable length and oxidation state. This Highlight summarizes recent progress in understanding the structural diversity of the mycolactones, their biological activity and mode of action in mammalian cells, and the genetics, evolution, and enzymology of their biosynthesis.

Distribution of Mycobacterium ulcerans in buruli ulcer endemic and non-endemic aquatic sites in Ghana

Mycobacterium ulcerans, the causative agent of Buruli ulcer, is an emerging environmental bacterium in Australia and West Africa. The primary risk factor associated with Buruli ulcer is proximity to slow moving water. Environmental constraints for disease are shown by the absence of infection in arid regions of infected countries. A particularly mysterious aspect of Buruli ulcer is the fact that endemic and non-endemic villages may be only a few kilometers apart within the same watershed. Recent studies suggest that aquatic invertebrate species may serve as reservoirs for M. ulcerans, although transmission pathways remain unknown. Systematic studies of the distribution of M. ulcerans in the environment using standard ecological methods have not been reported. Here we present results from the first study based on random sampling of endemic and non-endemic sites. In this study PCR-based methods, along with biofilm collections, have been used to map the presence of M. ulcerans within 26 aquatic sites in Ghana. Results suggest that M. ulcerans is present in both endemic and non-endemic sites and that variable number tandem repeat (VNTR) profiling can be used to follow chains of transmission from the environment to humans. Our results suggesting that the distribution of M. ulcerans is far broader than the distribution of human disease is characteristic of environmental pathogens. These findings imply that focal demography, along with patterns of human water contact, may play a major role in transmission of Buruli ulcer.

Skin and soft tissue infections and envenomations acquired at the beach

Millions of people spend vacation and leisure time on the shores of the lakes and oceans of North America. Many others are employed in water-related industries. In doing so, they potentially expose themselves to infections and envenomations that other people do not even consider when making their plans for leisure time activities or in going to work each day. This article reviews some common and uncommon beach-related infections and envenomations that can affect the skin and soft tissues of people frequenting the shores and beaches of North America. Physicians are thereby provided with a guide to such skin and soft tissue injuries and infections and will be better able to recognize and treat these maladies associated with recreational and occupational activities.

Mycobacterium marinum: ubiquitous agent of waterborne granulomatous skin infections

Mycobacterium marinum is a waterborne mycobacterium that commonly infects fish and amphibians worldwide. Infection in humans occurs occasionally, in most cases as a granulomatous infection localized in the skin, typically following minor trauma on the hands. For this reason, infection is especially common among aquarium keepers. Such local infection may-though infrequently-spread to tendon sheaths or joints. Disseminated disease, which is rare, can occur in immunosuppressed patients. In order to obtain a definitive diagnosis, culture and histopathological examination of biopsies from skin or other tissues are recommended. Infections sometimes heal spontaneously, but drug treatment is usually necessary for several months in order to cure the infection. Doxycycline or clarithromycin is used most commonly, although in severe cases, a combination of rifampicin and ethambutol is recommended.

Evolution of Mycobacterium ulcerans and other mycolactone-producing mycobacteria from a common Mycobacterium marinum progenitor

It had been assumed that production of the cytotoxic polyketide mycolactone was strictly associated with Mycobacterium ulcerans, the causative agent of Buruli ulcer. However, a recent study has uncovered a broader distribution of mycolactone-producing mycobacteria (MPM) that includes mycobacteria cultured from diseased fish and frogs in the United States and from diseased fish in the Red and Mediterranean Seas. All of these mycobacteria contain versions of the M. ulcerans pMUM plasmid, produce mycolactones, and show a high degree of genetic relatedness to both M. ulcerans and Mycobacterium marinum. Here, we show by multiple genetic methods, including multilocus sequence analysis and DNA-DNA hybridization, that all MPM have evolved from a common M. marinum progenitor to form a genetically cohesive group among a more diverse assemblage of M. marinum strains. Like M. ulcerans, the fish and frog MPM show multiple copies of the insertion sequence IS2404. Comparisons of pMUM and chromosomal gene sequences demonstrate that plasmid acquisition and the subsequent ability to produce mycolactone were probably the key drivers of speciation. Ongoing evolution among MPM has since produced at least two genetically distinct ecotypes that can be broadly divided into those typically causing disease in ectotherms (but also having a high zoonotic potential) and those causing disease in endotherms, such as humans.

The evolving story of Mycobacterium tuberculosis clade members detected in fish

Advances in molecular analyses have permitted documentation of an increasing spectrum of mycobacteria infecting fish. Although some of these mycobacteria are not closely related, several species belong to the Mycobacterium tuberculosis clade. One member of the clade, M. marinum, is well known as an agent of piscine mycobacteriosis. Three other clade species, M. shottsii, M. pseudoshottsii and M. 'chesapeaki', have recently been identified as predominant disease agents in a widespread, continuing epizootic in wild striped bass of the Chesapeake Bay. A fifth clade member, M. ulcerans, has recently been indirectly detected in wild, African cichlid fish. As M. ulcerans is the third most common human mycobacterial infection worldwide, even such indirect evidence of M. ulcerans in fish must be more thoroughly investigated. Complicating the differentiation of these clade members is the growing recognition of intraspecies and interspecies variation in phenotypes, genes and virulence. Thus, researchers must be aware of the variety of piscine isolates within the M. tuberculosis clade. This review summarizes the methods of detection and differentiation for this important group of mycobacteria.

Globally distributed mycobacterial fish pathogens produce a novel plasmid-encoded toxic macrolide, mycolactone F

Mycobacterium ulcerans and Mycobacterium marinum are closely related pathogens which share an aquatic environment. The pathogenesis of these organisms in humans is limited by their inability to grow above 35 degrees C. M. marinum causes systemic disease in fish but produces localized skin infections in humans. M. ulcerans causes Buruli ulcer, a severe human skin lesion. At the molecular level, M. ulcerans is distinguished from M. marinum by the presence of a virulence plasmid which encodes a macrolide toxin, mycolactone, as well as by hundreds of insertion sequences, particularly IS2404. There has been a global increase in reports of fish mycobacteriosis. An unusual clade of M. marinum has been reported from fish in the Red and Mediterranean Seas and a new mycobacterial species, Mycobacterium pseudoshottsii, has been cultured from fish in the Chesapeake Bay, United States. We have discovered that both groups of fish pathogens produce a unique mycolactone toxin, mycolactone F. Mycolactone F is the smallest mycolactone (molecular weight, 700) yet identified. The core lactone structure of mycolactone F is identical to that of M. ulcerans mycolactones, but a unique side chain structure is present. Mycolactone F produces apoptosis and necrosis on cultured cells but is less potent than M. ulcerans mycolactones. Both groups of fish pathogens contain IS2404. In contrast to M. ulcerans and conventional M. marinum, mycolactone F-producing mycobacteria are incapable of growth at above 30 degrees C. This fact is likely to limit their virulence for humans. However, such isolates may provide a reservoir for horizontal transfer of the mycolactone plasmid in aquatic environments.