Mycolactones and Mycobacterium ulcerans disease

Exploring Mycolactone-The Unique Causative Toxin of Buruli Ulcer: Biosynthetic, Synthetic Pathways, Biomarker for Diagnosis, and Therapeutic Potential

Mycolactone is a complex macrolide toxin produced by Mycobacterium ulcerans, the causative agent of Buruli ulcer. The aim of this paper is to review the chemistry, biosynthetic, and synthetic pathways of mycolactone A/B to help develop an understanding of the mode of action of these polyketides as well as their therapeutic potential. The synthetic work has largely been driven by the desire to afford researchers enough (≥100 mg) of the pure toxins for systematic biological studies toward understanding their very high biological activities. The review focuses on pioneering studies of Kishi which elaborate first-, second-, and third-generation approaches to the synthesis of mycolactones A/B. The three generations focused on the construction of the key intermediates required for the mycolactone synthesis. Synthesis of the first generation involves assignment of the relative and absolute stereochemistry of the mycolactones A and B. This was accomplished by employing a linear series of 17 chemical steps (1.3% overall yield) using the mycolactone core. The second generation significantly improved the first generation in three ways: (1) by optimizing the selection of protecting groups; (2) by removing needless protecting group adjustments; and (3) by enhancing the stereoselectivity and overall synthetic efficiency. Though the synthetic route to the mycolactone core was longer than the first generation, the overall yield was significantly higher (8.8%). The third-generation total synthesis was specifically aimed at an efficient, scalable, stereoselective, and shorter synthesis of mycolactone. The synthesis of the mycolactone core was achieved in 14 linear chemical steps with 19% overall yield. Furthermore, a modular synthetic approach where diverse analogues of mycolactone A/B were synthesized via a cascade of catalytic and/or asymmetric reactions as well as several Pd-catalyzed key steps coupled with hydroboration reactions were reviewed. In addition, the review discusses how mycolactone is employed in the diagnosis of Buruli ulcer with emphasis on detection methods of mass spectrometry, immunological assays, RNA aptamer techniques, and fluorescent-thin layer chromatography (f-TLC) methods as diagnostic tools. We examined studies of the structure-activity relationship (SAR) of various analogues of mycolactone. The paper highlights the multiple biological consequences associated with mycolactone such as skin ulceration, host immunomodulation, and analgesia. These effects are attributed to various proposed mechanisms of actions including Wiskott-Aldrich Syndrome protein (WASP)/neural Wiskott-Aldrich Syndrome protein (N-WASP) inhibition, Sec61 translocon inhibition, angiotensin II type 2 receptor (AT2R) inhibition, and inhibition of mTOR. The possible application of novel mycolactone analogues produced based on SAR investigations as therapeutic agents for the treatment of inflammatory disorders and inflammatory pain are discussed. Additionally, their therapeutic potential as anti-viral and anti-cancer agents have also been addressed.

Pharmacokinetics of extended-release clarithromycin in patients with Mycobacterium ulcerans infection

Clarithromycin extended-release (CLA-ER) was used as companion drug to rifampicin (RIF) for Mycobacterium ulcerans infection in the intervention arm of a WHO drug trial. RIF enhances CYP3A4 metabolism, thereby reducing CLA serum concentrations, and RIF concentrations might be increased by CLA co-administration. We studied the pharmacokinetics of CLA-ER at a daily dose of 15 mg/kg combined with RIF at a dose of 10 mg/kg in a subset of trial participants, and compared these to previously obtained pharmacokinetic data. Serial dried blood spot samples were obtained over a period of ten hours, and analyzed by LC-MS/MS in 30 study participants-20 in the RIF-CLA study arm, and 10 in the RIF-streptomycin study arm. Median CLA Cmax was 0.4 mg/L-and median AUC 3.9 mg*h/L, following 15 mg/kg CLA-ER. Compared to standard CLA dosed at 7.5 mg/kg previously, CLA-ER resulted in a non-significant 58% decrease in Cmax and a non-significant 30% increase in AUC. CLA co-administration did not alter RIF Cmax or AUC. Treatment was successful in all study participants. No effect of CLA co-administration on RIF pharmacokinetics was observed. Based on our serum concentration studies, the benefits CLA-ER over CLA immediate release are unclear.

Systematic review: Global host range, case fatality and detection rates of Mycobacterium ulcerans in humans and potential environmental sources

Fundamental aspects of the epidemiology and ecology of Mycobacterium ulcerans (MU) infections including disease burden, host range, reservoir, intermediate hosts, vector and mode of transmission are poorly understood. Understanding the global distribution and burden of MU infections is a paramount to fight against Buruli ulcer (BU). Four databases were queried from inception through December 2023. After critical review of published resources on BU, 155 articles (645 records) published between 1987 and 2023 from 16 countries were selected for this review. Investigating BU in from old endemic and new emerging foci has allowed detection of MU in humans, animals, plants and various environmental samples with prevalence from 0 % up to 100 % depending of the study design. A case fatality rate between 0.0 % and 50 % was described from BU patients and deaths occurred in Central African Republic, Gabon, Democratic Republic of the Congo, Burkina Faso and Australia. The prevalence of MU in humans was higher in Africa. Nucleic Acid Amplification Tests (NAAT) and non-NAAT were performed in > 38 animal species. MU has been recovered in culture from possum faeces, aquatic bugs and koala. More than 7 plant species and several environmental samples have been tested positive for MU. This review provided a comprehensive set of data on the updates of geographic distribution, the burden of MU infections in humans, and the host range of MU in non-human organisms. Although MU have been found in a wide range of environmental samples, only few of these have revealed the viability of the mycobacterium and the replicative non-human reservoirs of MU remain to be explored. These findings should serve as a foundation for further research on the reservoirs, intermediate hosts and transmission routes of MU.

Vaccination efforts for Buruli Ulcer

BACKGROUND

Buruli ulcer is one of the most common mycobacterial diseases usually affecting poorer populations in tropical and subtropical environments. This disease, caused by M. ulcerans infection, has devastating effects for patients, with significant health and economic burden. Antibiotics are often used to treat affected individuals, but in most cases, surgery is necessary.

AREA COVERED

We present progress on Buruli ulcer vaccines and identify knowledge gaps in this neglected tropical disease.

EXPERT OPINION

The lack of appropriate infrastructure in endemic areas, as well as the severity of symptoms and lack of non-invasive treatment options, highlights the need for an effective vaccine to combat this disease. In terms of humoral immunity, it is vital to consider its significance and the magnitude to which it inhibits or slowdowns the progression of the disease. Only by answering these key questions will it be possible to tailor more appropriate vaccination and preventative provisions.

The search for a Buruli Ulcer vaccine and the effectiveness of the Bacillus Calmette-Guérin vaccine

Buruli Ulcer is a neglected tropical disease that is caused by Mycobacterium ulcerans. It is not fatal; however, it manifests a range of devastating symptoms on the hosts' bodies. Various drugs and treatments are available for the disease; however, they are often costly and have adverse effects. There is still much uncertainty regarding the mode of transmission, vectors, and reservoir. At present, there are no official vector control methods, prevention methods, or a vaccine licensed to prevent infection. The Bacillus Calmette-Guérin vaccine developed against tuberculosis has some effectiveness against M. ulcerans. However, it is unable to induce long-lasting protection. Various types of vaccines have been developed based specifically against M. ulcerans; however, to date, none has entered clinical trials or has been released for public use. Additional awareness and funding are needed for research in this field and the development of more treatments, diagnostic tools, and vaccines.

Molecular characterization of Mycobacterium ulcerans DNA gyrase and identification of mutations reduced susceptibility against quinolones in vitro

Buruli ulcer disease is a neglected necrotizing and disabling cutaneous tropical illness caused by Mycobacterium ulcerans. Fluoroquinolone (FQ), used in the treatment of this disease, has been known to act by inhibiting the enzymatic activities of DNA gyrase. However, the detailed molecular basis of these characteristics and the FQ resistance mechanisms in M. ulcerans remains unknown. This study investigated the detailed molecular mechanism of M. ulcerans DNA gyrase and the contribution of FQ resistance in vitro using recombinant proteins from the M. ulcerans subsp. shinshuense and Agy99 strains with reduced sensitivity to FQs. The IC₅₀ of FQs against Ala91Val and Asp95Gly mutants of M. ulcerans shinshuense and Agy99 GyrA subunits were 3.7- to 42.0-fold higher than those against wild-type (WT) enzyme. Similarly, the quinolone concentrations required to induce 25% of the maximum DNA cleavage (CC₂₅) was 10- to 210-fold higher than those for the WT enzyme. Furthermore, the interaction between the amino acid residues of the WT/mutant M. ulcerans DNA gyrase and FQ side chains were assessed by molecular docking studies. This was the first elaborative study demonstrating the contribution of mutations in M. ulcerans DNA GyrA subunit to FQ resistance in vitro.

A need for null models in understanding disease transmission: the example of Mycobacterium ulcerans (Buruli ulcer disease)

Understanding the interactions of ecosystems, humans and pathogens is important for disease risk estimation. This is particularly true for neglected and newly emerging diseases where modes and efficiencies of transmission leading to epidemics are not well understood. Using a model for other emerging diseases, the neglected tropical skin disease Buruli ulcer (BU), we systematically review the literature on transmission of the etiologic agent, Mycobacterium ulcerans (MU), within a One Health/EcoHealth framework and against Hill's nine criteria and Koch's postulates for making strong inference in disease systems. Using this strong inference approach, we advocate a null hypothesis for MU transmission and other understudied disease systems. The null should be tested against alternative vector or host roles in pathogen transmission to better inform disease management. We propose a re-evaluation of what is necessary to identify and confirm hosts, reservoirs and vectors associated with environmental pathogen replication, dispersal and transmission; critically review alternative environmental sources of MU that may be important for transmission, including invertebrate and vertebrate species, plants and biofilms on aquatic substrates; and conclude with placing BU within the context of other neglected and emerging infectious diseases with intricate ecological relationships that lead to disease in humans, wildlife and domestic animals.

Stable and Local Reservoirs of Mycobacterium ulcerans Inferred from the Nonrandom Distribution of Bacterial Genotypes, Benin

Mycobacterium ulcerans is the causative agent of Buruli ulcer, a neglected tropical disease found in rural areas of West and Central Africa. Despite the ongoing efforts to tackle Buruli ulcer epidemics, the environmental reservoir of its pathogen remains elusive, underscoring the need for new approaches to improving disease prevention and management. In our study, we implemented a local-scale spatial clustering model and deciphered the genetic diversity of the bacteria in a small area of Benin where Buruli ulcer is endemic. Using 179 strain samples from West Africa, we conducted a phylogeographic analysis combining whole-genome sequencing with spatial scan statistics. The 8 distinct genotypes we identified were by no means randomly spread over the studied area. Instead, they were divided into 3 different geographic clusters, associated with landscape characteristics. Our results highlight the ability of M. ulcerans to evolve independently and differentially depending on location in a specific ecologic reservoir.

Pharmacologic management of Mycobacterium ulcerans infection

INTRODUCTION

Pharmacological treatment of Buruli ulcer (Mycobacterium ulcerans infection; BU) is highly effective, as shown in two randomized trials in Africa.

AREAS COVERED

We review BU drug treatment - in vitro, in vivo and clinical trials (PubMed: '(Buruli OR (Mycobacterium AND ulcerans)) AND (treatment OR therapy).' We also highlight the pathogenesis of M. ulcerans infection that is dominated by mycolactone, a secreted exotoxin, that causes skin and soft tissue necrosis, and impaired immune response and tissue repair. Healing is slow, due to the delayed wash-out of mycolactone. An array of repurposed tuberculosis and leprosy drugs appears effective in vitro and in animal models. In clinical trials and observational studies, only rifamycins (notably, rifampicin), macrolides (notably, clarithromycin), aminoglycosides (notably, streptomycin) and fluoroquinolones (notably, moxifloxacin, and ciprofloxacin) have been tested.

EXPERT OPINION

A combination of rifampicin and clarithromycin is highly effective but lesions still take a long time to heal. Novel drugs like telacebec have the potential to reduce treatment duration but this drug may remain unaffordable in low-resourced settings. Research should address ulcer treatment in general; essays to measure mycolactone over time hold promise to use as a readout for studies to compare drug treatment schedules for larger lesions of Buruli ulcer.

Drugs for treating Buruli ulcer (Mycobacterium ulcerans disease)

BACKGROUND

Buruli ulcer is a necrotizing cutaneous infection caused by infection with Mycobacterium ulcerans bacteria that occurs mainly in tropical and subtropical regions. The infection progresses from nodules under the skin to deep ulcers, often on the upper and lower limbs or on the face. If left undiagnosed and untreated, it can lead to lifelong disfigurement and disabilities. It is often treated with drugs and surgery.

OBJECTIVES

To summarize the evidence of drug treatments for treating Buruli ulcer.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published in the Cochrane Library; MEDLINE (PubMed); Embase (Ovid); and LILACS (Latin American and Caribbean Health Sciences Literature; BIREME). We also searched the US National Institutes of Health Ongoing Trials Register (clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en/). All searches were run up to 19 December 2017. We also checked the reference lists of articles identified by the literature search, and contacted leading researchers in this topic area to identify any unpublished data.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that compared antibiotic therapy to placebo or alternative therapy such as surgery, or that compared different antibiotic regimens. We also included prospective observational studies that evaluated different antibiotic regimens with or without surgery.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, extracted the data, and assessed methodological quality. We calculated the risk ratio (RR) for dichotomous data with 95% confidence intervals (CI). We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included a total of 18 studies: five RCTs involving a total of 319 participants, ranging from 12 participants to 151 participants, and 13 prospective observational studies, with 1665 participants. Studies evaluated various drugs usually in addition to surgery, and were carried out across eight countries in areas with high Buruli ulcer endemicity in West Africa and Australia. Only one RCT reported adequate methods to minimize bias. Regarding monotherapy, one RCT and one observational study evaluated clofazimine, and one RCT evaluated sulfamethoxazole/trimethoprim. All three studies had small sample sizes, and no treatment effect was demonstrated. The remaining studies examined combination therapy.Rifampicin combined with streptomycinWe found one RCT and six observational studies which evaluated rifampicin combined with streptomycin for different lengths of treatment (2, 4, 8, or 12 weeks) (941 participants). The RCT did not demonstrate a difference between the drugs added to surgery compared with surgery alone for recurrence at 12 months, but was underpowered (RR 0.12, 95% CI 0.01 to 2.51; 21 participants; very low-certainty evidence).An additional five single-arm observational studies with 828 participants using this regimen for eight weeks with surgery (given to either all participants or to a select group) reported healing rates ranging from 84.5% to 100%, assessed between six weeks and one year. Four observational studies reported healing rates for participants who received the regimen alone without surgery, reporting healing rates ranging from 48% to 95% assessed between eight weeks and one year.Rifampicin combined with clarithromycinTwo observational studies administered combined rifampicin and clarithromycin. One study evaluated the regimen alone (no surgery) for eight weeks and reported a healing rate of 50% at 12 months (30 participants). Another study evaluated the regimen administered for various durations (as determined by the clinicians, durations unspecified) with surgery and reported a healing rate of 100% at 12 months (21 participants).Rifampicin with streptomycin initially, changing to rifampicin with clarithromycin in consolidation phaseOne RCT evaluated this regimen (four weeks in each phase) against continuing with rifampicin and streptomycin in the consolidation phase (total eight weeks). All included participants had small lesions, and healing rates were above 90% in both groups without surgery (healing rate at 12 months RR 0.94, 95% CI 0.87 to 1.03; 151 participants; low-certainty evidence). One single-arm observational study evaluating the substitution of streptomycin with clarithromycin in the consolidation phase (6 weeks, total 8 weeks) without surgery given to a select group showed a healing rate of 98% at 12 months (41 participants).Novel combination therapyTwo large prospective studies in Australia evaluated some novel regimens. One study evaluating rifampicin combined with either ciprofloxacin, clarithromycin, or moxifloxacin without surgery reported a healing rate of 76.5% at 12 months (132 participants). Another study evaluating combinations of two to three drugs from rifampicin, ciprofloxacin, clarithromycin, ethambutol, moxifloxacin, or amikacin with surgery reported a healing rate of 100% (90 participants).Adverse effects were reported in only three RCTs (158 participants) and eight prospective observational studies (878 participants), and were consistent with what is already known about the adverse effect profile of these drugs. Paradoxical reactions (clinical deterioration after treatment caused by enhanced immune response to M ulcerans) were evaluated in six prospective observational studies (822 participants), and the incidence of paradoxical reactions ranged from 1.9% to 26%.

AUTHORS' CONCLUSIONS

While the antibiotic combination treatments evaluated appear to be effective, we found insufficient evidence showing that any particular drug is more effective than another. How different sizes, lesions, and stages of the disease may contribute to healing and which kind of lesions are in need of surgery are unclear based on the included studies. Guideline development needs to consider these factors in designing practical treatment regimens. Forthcoming trials using clarithromycin with rifampicin and other trials of new regimens that also address these factors will help to identify the best regimens.

Buruli Ulcer: Review of a Neglected Skin Mycobacterial Disease

Buruli ulcer is caused by Mycobacterium ulcerans This neglected disease occurs in scattered foci around the world, with a higher concentration of cases in West Africa. The mycobacteria produce mycolactones that cause tissue necrosis. The disease presents as a painless skin nodule that ulcerates as necrosis expands. Finding acid-fast bacilli in smears or histopathology, culturing the mycobacteria, and performing M. ulcerans PCR in presumptive cases confirm the diagnosis. Medical treatment with oral rifampin and intramuscular streptomycin or oral treatment with rifampin plus clarithromycin for 8 weeks is supported by the World Health Organization. This review summarizes the epidemiology, pathogenesis, clinical presentation, diagnostic tests, and advances in treatment.

Genetic Susceptibility and Predictors of Paradoxical Reactions in Buruli Ulcer

Introduction

Buruli ulcer (BU) is the third most frequent mycobacterial disease in immunocompetent persons after tuberculosis and leprosy. During the last decade, eight weeks of antimicrobial treatment has become the standard of care. This treatment may be accompanied by transient clinical deterioration, known as paradoxical reaction. We investigate the incidence and the risks factors associated with paradoxical reaction in BU.

Methods

The lesion size of participants was assessed by careful palpation and recorded by serial acetate sheet tracings. For every time point, surface area was compared with the previous assessment. All patients received antimicrobial treatment for 8 weeks. Serum concentration of 25-hydroxyvitamin D, the primary indicator of vitamin D status, was determined in duplex for blood samples at baseline by a radioimmunoassay. We genotyped four polymorphisms in the SLC11A1 gene, previously associated with susceptibility to BU. For testing the association of genetic variants with paradoxical responses, we used a binary logistic regression analysis with the occurrence of a paradoxical response as the dependent variable.

Results

Paradoxical reaction occurred in 22% of the patients; the reaction was significantly associated with trunk localization (p = .039 by Χ²), larger lesions (p = .021 by Χ²) and genetic factors. The polymorphisms 3’UTR TGTG ins/ins (OR 7.19, p < .001) had a higher risk for developing paradoxical reaction compared to ins/del or del/del polymorphisms.

Conclusions

Paradoxical reactions are common in BU. They are associated with trunk localization, larger lesions and polymorphisms in the SLC11A1 gene.

Buruli ulcer is an infectious disease of skin, subcutaneous fat and sometimes bone, mainly affecting children in West Africa. It is considered as one of the Neglected Tropical Diseases but the disease occurs also in moderate climates like South East Australia and Japan where it may also affect adults. Once a patient has started antibiotic treatment, lesions may increase in size even if the antimicrobial treatment is effective; this is highly confusing for doctors and patients as they may think that treatment actually fails. The cause of Buruli ulcer is Mycobacterium ulcerans, related to other mycobacteria that cause disease in man, like leprosy and tuberculosis. Using data from two different studies in West Africa, we show that these paradoxical reactions are associated with trunk localization and that they occur more often in larger lesions. The chance to develop these reactions appeared partly inherited: carrying the homozygous ins/ins genotype of 3’UTR TGTG 285 polymorphism in the SLC11A1 gene increased the risk of paradoxical reactions. Vitamin D is important for the immune defense against infections by mycobacteria. Vitamin D blood concentrations were not associated with paradoxical reactions; patients generally did well, and we did not need corticosteroid immune suppression to overcome these reactions.

Genetic diversity of Staphylococcus aureus in Buruli ulcer

Background

Buruli ulcer (BU) is a necrotizing skin disease caused by Mycobacterium ulcerans. Previous studies have shown that wounds of BU patients are colonized with M. ulcerans and several other microorganisms, including Staphylococcus aureus, which may interfere with wound healing. The present study was therefore aimed at investigating the diversity and topography of S. aureus colonizing BU patients during treatment.

Methodology

We investigated the presence, diversity, and spatio-temporal distribution of S. aureus in 30 confirmed BU patients from Ghana during treatment. S. aureus was isolated from nose and wound swabs, and by replica plating of wound dressings collected bi-weekly from patients. S. aureus isolates were characterized by multiple-locus variable number tandem repeat fingerprinting (MLVF) and spa-typing, and antibiotic susceptibility was tested.

Principal Findings

Nineteen (63%) of the 30 BU patients tested positive for S. aureus at least once during the sampling period, yielding 407 S. aureus isolates. Detailed analysis of 91 isolates grouped these isolates into 13 MLVF clusters and 13 spa-types. Five (26%) S. aureus-positive BU patients carried the same S. aureus genotype in their anterior nares and wounds. S. aureus isolates from the wounds of seven (37%) patients were distributed over two different MLVF clusters. Wounds of three (16%) patients were colonized with isolates belonging to two different genotypes at the same time, and five (26%) patients were colonized with different S. aureus types over time. Five (17%) of the 30 included BU patients tested positive for methicillin-resistant S. aureus (MRSA).

Conclusion/Significance

The present study showed that the wounds of many BU patients were contaminated with S. aureus, and that many BU patients from the different communities carried the same S. aureus genotype during treatment. This calls for improved wound care and hygiene.

Buruli ulcer (BU) is a disease of the skin and soft tissue caused by Mycobacterium ulcerans. The resulting skin lesions provide a niche for survival of other microorganisms such as Staphylococcus aureus, which may cause delayed wound healing. This study investigated the presence, diversity, and spatio-temporal distribution of S. aureus in BU patients from Ghana during treatment by isolating the bacteria from nose and wound swabs or wound dressings. S. aureus isolates were subsequently characterized by two complementary DNA typing approaches. This showed that 19 (63%) of the 30 investigated BU patients carried S. aureus. Five (26%) of these 19 BU patients carried the same S. aureus type in their anterior nares and wounds. Seven (37%) patients carried the same S. aureus type in their wounds, which is indicative of transmission. Three of them (16%) carried at least two different S. aureus types at the same time in their wounds, while five (26%) carried different S. aureus types over time. Notably, five (17%) BU patients tested positive for methicillin-resistant S. aureus (MRSA). These findings imply that the spatio-temporal diversity of S. aureus in BU is most likely related to factors such as antibiotic pressure, and insufficient wound care and hygiene.

Findings in patients from Benin with osteomyelitis and polymerase chain reaction-confirmed Mycobacterium ulcerans infection

BACKGROUND

Mycobacterium ulcerans is known to cause Buruli ulcer (BU), a necrotizing skin disease leading to extensive cutaneous and subcutaneous destruction and functional limitations. However, M. ulcerans infections are not limited to skin, and osteomyelitis, still poorly described in the literature, occurs in numerous young patients in Africa.

METHODS

In a retrospective matched case-control study conducted in a highly endemic area in Benin, we analyzed demographic, clinical, biological, and radiological features in all patients with M. ulcerans infections with bone involvement, identified from a cohort of 1257 patients with polymerase chain reaction-proved M. ulcerans infections.

RESULTS

The 81 patients studied had a median age of 11 years (interquartile range, 7-16 years) and were predominantly male (male-female ratio, 2:1). Osteomyelitis was observed beneath active BU lesions (60.5%) or at a distance from active or apparently healed BU lesions (14.8%) but also in patients without a history of BU skin lesions (24.7%). These lesions had an insidious course, with nonspecific clinical findings leading to delayed diagnosis. A comparison with findings in 243 age- and sex-matched patients with BU without osteomyelitis showed that case patients were less likely to have received BCG immunization than controls (33.3% vs 52.7%; P = .01). They were also at higher risk of longer hospital stay (118 vs 69 days; P = .001), surgery (92.6% vs 63.0%; P = .001), and long-term crippling sequelae (55.6% vs 15.2%; P < .001).

CONCLUSIONS

This study highlighted the difficulties associated with diagnosis of M. ulcerans osteomyelitis, with one-fourth of patients having no apparent history of BU skin lesions, including during the current course of illness. Delays in treatment contributed to the high proportion (55.6%) of patients with crippling sequelae.

Sapronosis: a distinctive type of infectious agent

Sapronotic disease agents have evolutionary and epidemiological properties unlike other infectious organisms. Their essential saprophagic existence prevents coevolution, and no host-parasite virulence trade-off can evolve. However, the host may evolve defenses. Models of pathogens show that sapronoses, lacking a threshold of transmission, cannot regulate host populations, although they can reduce host abundance and even extirpate their hosts. Immunocompromised hosts are relatively susceptible to sapronoses. Some particularly important sapronoses, such as cholera and anthrax, can sustain an epidemic in a host population. However, these microbes ultimately persist as saprophages. One-third of human infectious disease agents are sapronotic, including nearly all fungal diseases. Recognition that an infectious disease is sapronotic illuminates a need for effective environmental control strategies.

Pathogenesis of skin ulcers: lessons from the Mycobacterium ulcerans and Leishmania spp. pathogens

Skin ulcers are most commonly due to circulatory or metabolic disorders and are a major public health concern. In developed countries, chronic wounds affect more than 1 % of the population and their incidence is expected to follow those observed for diabetes and obesity. In tropical and subtropical countries, an additional issue is the occurrence of ulcers of infectious origins with diverse etiologies. While the severity of cutaneous Leishmaniasis correlates with protective immune responses, Buruli ulcers caused by Mycobacterium ulcerans develop in the absence of major inflammation. Based on these two examples, this review aims to demonstrate how studies on microorganism-provoked wounds can provide insight into the molecular mechanisms controlling skin integrity. We highlight the potential interest of a mouse model of non-inflammatory skin ulceration caused by intradermal injection of mycolactone, an original lipid toxin with ulcerative and immunosuppressive properties produced by M. ulcerans.

Associations between Mycobacterium ulcerans and aquatic plant communities of West Africa: implications for Buruli ulcer disease

Numerous studies have associated Buruli ulcer (BU) disease with disturbed aquatic habitats; however, the natural reservoir, distribution, and transmission of the pathogen, Mycobacterium ulcerans, remain unknown. To better understand the role of aquatic plants in the ecology of this disease, a large-scale survey was conducted in waterbodies of variable flow throughout three regions of Ghana, Africa. Our objectives were to characterize plant communities and identify potential relationships with M. ulcerans and other mycolactone-producing mycobacteria (MPM). Waterbodies with M. ulcerans had significantly different aquatic plant communities, with submerged terrestrial plants identified as indicators of M. ulcerans presence. Mycobacterium ulcerans and MPM were detected on 14 plant taxa in emergent zones from both lotic and lentic waterbodies in endemic regions; however, M. ulcerans was not detected in the non-endemic Volta region. These findings support the hypothesis that plants provide substrate for M. ulcerans colonization and could act as potential indicators for disease risk. These findings also suggest that M. ulcerans is a widespread environmental bacteria species, but that it is absent or reduced in regions of low disease incidence. A better understanding is needed regarding the mechanistic associations among aquatic plants and M. ulcerans for identifying the mode of transmission of BU disease.

Clinical efficacy of Rifampicin and Streptomycin in combination against Mycobacterium ulcerans infection: a systematic review

Buruli ulcer (BU) is a cutaneous neglected tropical disease caused by Mycobacterium ulcerans. Synthesizing the evidence on their efficacy of antibiotic in the management of BU can help to better define their roles, identify weaknesses and inform clinicians on relevant measures than can be used to control BU. Our objectives is to assess the clinical efficacy of Rifampicin-Streptomycin given for 8 weeks of treatment of early M. ulcerans infection. We searched the following electronic databases from January 2005 to July 2012: Medline, EMBASE (Excerpta Medica Database), The Cochrane Library, Google Scholar, CINAHL (Cumulative Index to Nursing and Allied Health Literature), WHOLIS (World Health Organization Library Database), LILACS (Latin American and Caribbean Literature on Health Sciences) and contacted experts in the field. There were no restrictions to language or publication status. All study designs that could provide the information we sought for were eligible provided the studies were conducted in the third world. Critical appraisal of all identified citations was done independently by three authors to establish the possible relevance of the articles for inclusion in the review. Of the 115 studies, 09 papers met the inclusion criteria. The duration of treatment ranged from 8 to 48 weeks depending on the severity. Oral chemotherapy alone obtained a curative rate of 50%. The “dual” mode of treatment (surgery + chemotherapy) reduced hospital admission period from 90 to 39.8 days, that's to 44.2%. This treatment for early stages could therefore replace surgery and in severe cases, is an indispensable aid before surgery. These results confirmed that the daily administration of Rifampicin and Streptomycin is an effective treatment for M. ulcerans infection in an early stage. Subsequent systematic reviews should be conducted to determine if antibiotics could heal injuries without resorting to surgery and to compare different treatment durations.

Reactive and infective dermatoses associated with adult-onset immunodeficiency due to anti-interferon-gamma autoantibody: Sweet's syndrome and beyond

Immunodeficiency due to anti-interferon-gamma autoantibody (anti-IFN-γ autoAb) is an emerging adult-onset immunodeficiency syndrome predominantly found in Southeast Asians. It is associated with severe or disseminated infections caused by non-tuberculous mycobacteria (NTM) and other opportunistic pathogens. We describe 3 patients with anti-IFN-γ autoAb who developed reactive and infective dermatoses, and thoroughly review the existing literature on dermatoses associated with the immunodeficiency syndrome. Case 1 developed Sweet's syndrome associated with Mycobacterium chelonae lymphadenitis and penicilliosis. Case 2 suffered from multiple episodes of lobular panniculitis during recurrent infections by NTM, Penicillium marneffei and Burkholderia pseudomallei. Both cases responded to immunomodulating agents including corticosteroid and non-steroidal anti-inflammatory drugs. Case 3 had direct skin invasion by M. chelonae and responded to prolonged anti-mycobacterial therapy. A novel working algorithm is proposed for the diagnosis and treatment of these patients who may be encountered by the dermatologist and histopathologist in clinical practice.

Paradoxical responses after start of antimicrobial treatment in Mycobacterium ulcerans infection

BACKGROUND

 Antimicrobial killing in mycobacterial infections may be accompanied by (transient) clinical deterioration, known as paradoxical reaction. To search for patterns reflecting such reactions in the treatment of Buruli ulcer (Mycobacterium ulcerans infection), the evolution of lesions of patients treated with antimicrobials was prospectively assessed.

METHODS

 The lesion size of participants of the BURULICO antimicrobial trial (with lesions ≤10 cm cross-sectional diameter) was assessed by careful palpation and recorded by serial acetate sheet tracings. Patients were treated with antimicrobials for 8 weeks. For the size analysis, participants whose treatment had failed, had skin grafting, or were coinfected with human immunodeficiency virus were excluded. For every time point, surface area was compared with the previous assessment. A generalized additive mixed model was used to study lesion evolution. Nonulcerative lesions were studied using digital images recording possible subsequent ulceration.

RESULTS

 Of 151 participants, 134 were included in the lesion size analysis. Peak paradoxical response occurred at week 8; >30% of participants showed an increase in lesion size as compared with the previous (week 6) assessment. Seventy-five of 90 (83%) of nonulcerative lesions ulcerated after start of treatment. Nine participants developed new lesions during or after treatment. All lesions subsequently healed.

CONCLUSIONS

 After start of antimicrobial treatment for Buruli ulcer, new or progressive ulceration is common before healing sets in. This paradoxical response, most prominent at the end of the 8-week antimicrobial treatment, should not be misinterpreted as failure to respond to treatment. Clinical Trials Registration. ClinicalTrials.gov, NCT00321178.

A diverted total synthesis of mycolactone analogues: an insight into Buruli ulcer toxins

Mycolactones are complex macrolides responsible for a severe necrotizing skin disease called Buruli ulcer. Deciphering their functional interactions is of fundamental importance for the understanding, and ultimately, the control of this devastating mycobacterial infection. We report herein a diverted total synthesis approach of mycolactones analogues and provide the first insights into their structure-activity relationship based on cytopathic assays on L929 fibroblasts. The lowest concentration inducing a cytopathic effect was determined for selected analogues, allowing a clear picture to emerge by comparison with the natural toxins.

Highly stereoselective total synthesis of fully hydroxy-protected mycolactones A and B and their stereoisomerization upon deprotection

Unprecedentedly efficient and highly (≥98 %) stereoselective syntheses of mycolactones A and B side chains relied heavily on Pd-catalyzed alkenylation (Negishi version) and were completed in 11 longest linear steps from ethyl (S)-3-hydroxybutyrate in 12% and 11% overall yield, respectively, roughly corresponding to an average of 82% yield per step. The synthesis of mycolactone core was realized by using Pd-catalyzed alkenyl-allyl coupling and an epoxide-opening reaction with a trialkylalkenylaluminate as key steps. Fully hydroxy-protected mycolactones A and B of ≥98% isomeric purity were synthesized successfully for the first time. However, unexpected 4:3-5:4 inseparable mixtures of mycolactones A and B were obtained upon deprotection.

Buruli ulcer

Buruli ulcer, an infectious disease caused by Mycobacterium ulcerans, is the third most prevalent mycobacteriosis, after tuberculosis and leprosy. This atypical mycobacteriosis has been reported in over 30 countries, mainly those with tropical and subtropical climates, but its epidemiology remains unclear. The first autochthonous cases of infection in Brazil have recently been described, making this diagnosis important for Brazilian dermatologists. Clinical manifestations vary from nodules, areas of edema, and plaques, but the most typical presentation is a large ulcer, usually in the limbs. Despite considerable knowledge about its clinical manifestations in some endemic countries, in other areas the diagnosis may be overlooked. Therefore, physicians should be educated about Buruli ulcer, since early diagnosis and treatment, including measures to prevent disability, are essential for a good outcome.

Fighting mycobacterial infections by antibiotics, phytochemicals and vaccines

Buruli ulcer is a neglected disease caused by Mycobacterium ulcerans and represents the world's third most common mycobacterial infection. It produces the polyketide toxins, mycolactones A, B, C and D, which induce apoptosis and necrosis. Clinical symptoms are subcutaneous nodules, papules, plaques and ulcerating oedemae, which can enlarge and destroy nerves and blood vessels and even invade bones by lymphatic or haematogenous spread (osteomyelitis). Patients usually do not suffer from pain or systematic inflammation. Surgery is the treatment of choice, although recurrence is common and wide surgical excisions including healthy tissues result in significant morbidity. Antibiotic therapy with rifamycins, aminoglycosides, macrolides and quinolones also improves cure rates. Still less exploited treatment options are phytochemicals from medicinal plants used in affected countries. Vaccination against Buruli ulcer is still in its infancy.

Pharmacokinetics of rifampin and clarithromycin in patients treated for Mycobacterium ulcerans infection

In a randomized controlled trial in Ghana, treatment of Mycobacterium ulcerans infection with streptomycin (SM)-rifampin (RIF) for 8 weeks was compared with treatment with SM-RIF for 4 weeks followed by treatment with RIF-clarithromycin (CLA) for 4 weeks. The extent of the interaction of RIF and CLA combined on the pharmacokinetics of the two compounds is unknown in this population and was therefore studied in a subset of patients. Patients received CLA at a dose of 7.5 mg/kg of body weight once daily, rounded to the nearest 125 mg. RIF was administered at a dose of 10 mg/kg, rounded to the nearest 150 mg. SM was given at a dose of 15 mg/kg once daily as an intramuscular injection. Plasma samples were drawn at steady state and analyzed by liquid chromatography-tandem mass spectroscopy. Pharmacokinetic parameters were calculated with the MW/Pharm (version 3.60) program. Comedication with CLA resulted in a 60% statistically nonsignificant increase in the area under the plasma concentration-time curve (AUC) for RIF of 25.8 mg x h/liter (interquartile ratio [IQR], 21.7 to 31.5 mg x h/liter), whereas the AUC of RIF was 15.2 mg x h/liter (IQR, 15.0 to 17.5 mg x h/liter) in patients comedicated with SM (P = 0.09). The median AUCs of CLA and 14-hydroxyclarithromycin (14OH-CLA) were 2.9 mg x h/liter (IQR, 1.5 to 3.8 mg x h/liter) and 8.0 mg x h/liter (IQR, 6.7 to 8.6 mg x h/liter), respectively. The median concentration of CLA was above the MIC of M. ulcerans, but that of 14OH-CLA was not. In further clinical studies, a dose of CLA of 7.5 mg/kg twice daily should be used (or with an extended-release formulation, 15 mg/kg should be used) to ensure higher levels of exposure to CLA and an increase in the time above the MIC compared to those achieved with the currently used dose of 7.5 mg/kg once daily.

Bacteria-induced phagocyte secondary necrosis as a pathogenicity mechanism

Triggering of phagocyte apoptosis is a major virulence mechanism used by some successful bacterial pathogens. A central issue in the apoptotic death context is that fully developed apoptosis results in necrotic cell autolysis (secondary necrosis) with release of harmful cell components. In multicellular animals, this occurs when apoptosing cells are not removed by scavengers, mainly macrophages. Secondary necrotic lysis of neutrophils and macrophages may occur in infection when extensive phagocyte apoptosis is induced by bacterial cytotoxins and removal of apoptosing phagocytes is defective because the apoptotic process exceeds the available scavenging capacity or targets macrophages directly. Induction of phagocyte secondary necrosis is an important pathogenic mechanism, as it combines the pathogen evasion from phagocyte antimicrobial activities and the release of highly cytotoxic molecules, particularly of neutrophil origin, such as neutrophil elastase. This pathogenicity mechanism therefore promotes the unrestricted multiplication of the pathogen and contributes directly to the pathology of several necrotizing infections, where extensive apoptosis and necrosis of macrophages and neutrophils are present. Here, examples of necrotizing infectious diseases, where phagocyte secondary necrosis is implicated, are reviewed.

Synthesis and structure assignment of the minor metabolite arising from the frog pathogen Mycobacterium liflandii

Total synthesis and structure assignment of the minor metabolite present in lipid extracts of the frog pathogen Mycobacterium liflandii are reported.

Antimicrobial treatment for early, limited Mycobacterium ulcerans infection: a randomised controlled trial

BACKGROUND

Surgical debridement was the standard treatment for Mycobacterium ulcerans infection (Buruli ulcer disease) until WHO issued provisional guidelines in 2004 recommending treatment with antimicrobial drugs (streptomycin and rifampicin) in addition to surgery. These recommendations were based on observational studies and a small pilot study with microbiological endpoints. We investigated the efficacy of two regimens of antimicrobial treatment in early-stage M ulcerans infection.

METHODS

In this parallel, open-label, randomised trial undertaken in two sites in Ghana, patients were eligible for enrolment if they were aged 5 years or older and had early (duration <6 months), limited (cross-sectional diameter <10 cm), M ulcerans infection confirmed by dry-reagent-based PCR. Eligible patients were randomly assigned to receive intramuscular streptomycin (15 mg/kg once daily) and oral rifampicin (10 mg/kg once daily) for 8 weeks (8-week streptomycin group; n=76) or streptomycin and rifampicin for 4 weeks followed by rifampicin and clarithromycin (7.5 mg/kg once daily), both orally, for 4 weeks (4-week streptomycin plus 4-week clarithromycin group; n=75). Randomisation was done by computer-generated minimisation for study site and type of lesion (ulceration or no ulceration). The randomly assigned allocation was sent from a central site by cell-phone text message to the study coordinator. The primary endpoint was lesion healing at 1 year after the start of treatment without lesion recurrence or extensive surgical debridement. Analysis was by intention-to-treat. This trial is registered with ClinicalTrials.gov, number NCT00321178.

FINDINGS

Four patients were lost to follow-up (8-week streptomycin, one; 4-week streptomycin plus 4-week clarithromycin, three). Since these four participants had healed lesions at their last assessment, they were included in the analysis for the primary endpoint. 73 (96%) participants in the 8-week streptomycin group and 68 (91%) in the 4-week streptomycin plus 4-week clarithromycin group had healed lesions at 1 year (odds ratio 2.49, 95% CI 0.66 to infinity; p=0.16, one-sided Fisher's exact test). No participants had lesion recurrence at 1 year. Three participants had vestibulotoxic events (8-week streptomycin, one; 4-week streptomycin plus 4-week clarithromycin, two). One participant developed an injection abscess and two participants developed an abscess close to the initial lesion, which was incised and drained (all three participants were in the 4-week streptomycin plus 4-week clarithromycin group).

INTERPRETATION

Antimycobacterial treatment for M ulcerans infection is effective in early, limited disease. 4 weeks of streptomycin and rifampicin followed by 4 weeks of rifampicin and clarithromycin has similar efficacy to 8 weeks of streptomycin and rifampicin; however, the number of injections of streptomycin can be reduced by switching to oral clarithromycin after 4 weeks.

FUNDING

European Union (EU FP6 2003-INCO-Dev2-015476) and Buruli Ulcer Groningen Foundation.

Highly sensitive, operationally simple, cost/time effective detection of the mycolactones from the human pathogen Mycobacterium ulcerans

A boronate-assisted fluorogenic chemosensor in a solid phase is developed, selectively to detect the mycolactones produced by the human pathogen Mycobacterium ulcerans.

Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer

The necrotising skin infection Buruli ulcer is at present the third most common human mycobacteriosis worldwide, after tuberculosis and leprosy. Buruli ulcer is an emergent disease that is predominantly found in humid tropical regions. There is no vaccine against Buruli ulcer and its treatment is difficult. In addition to the huge social effect, Buruli ulcer is of great scientific interest because of the unique characteristics of its causative organism, Mycobacterium ulcerans. This pathogen is genetically very close to the typical intracellular parasites Mycobacterium marinum and Mycobacterium tuberculosis. We review data supporting the interpretation that M ulcerans has the essential hallmarks of an intracellular parasite, producing infections associated with immunologically relevant inflammatory responses, cell-mediated immunity, and delayed-type hypersensitivity. This interpretation judges that whereas M ulcerans behaves like the other pathogenic mycobacteria, it represents an extreme in the biodiversity of this family of pathogens because of its higher cytotoxicity due to the secretion of the exotoxin mycolactone. The acceptance of the interpretation that Buruli ulcer is caused by an intracellular parasite has relevant prophylactic and therapeutic implications, rather than representing the mere attribution of a label with academic interest, because it prompts the development of vaccines that boost cell-mediated immunity and the use of chemotherapeutic protocols that include intracellularly active antibiotics.

Differences in virulence and immune response induced in a murine model by isolates of Mycobacterium ulcerans from different geographic areas

Buruli ulcer (BU) is the third most common mycobacterial disease in immunocompetent hosts. BU is caused by Mycobacterium ulcerans, which produces skin ulcers and necrosis at the site of infection. The principal virulence factor of M. ulcerans is a polyketide-derived macrolide named mycolactone, which has cytotoxic and immunosuppressive activities. We determined the severity of inflammation, histopathology and bacillary loads in the subcutaneous footpad tissue of BALB/c mice infected with 11 different M. ulcerans isolates from diverse geographical areas. Strains from Africa (Benin, Ghana, Ivory Coast) induced the highest inflammation, necrosis and bacillary loads, whereas the strains collected from Australia, Asia (Japan, Malaysia, New Guinea), Europe (France) and America (Mexico) induced mild inflammation. Subsequently, animals were infected with the strain that exhibited the highest (Benin) or lowest (Mexico) level of virulence in order to analyse the local immune response generated. The Mexican strain, which does not produce mycolactone, induced a predominantly T helper type 1 (Th1) cytokine profile with constant high expression of the anti-microbial peptides beta defensins 3 and 4, in co-existence with low expression of the anti-inflammatory cytokines interleukin (IL)-10, IL-4 and transforming growth factor (TGF)-beta. The highly virulent strain from Benin which produces mycolactone A/B induced the opposite pattern. Thus, different local immune responses were found depending on the infecting M. ulcerans strain.

Comprehensive proteome analysis of Mycobacterium ulcerans and quantitative comparison of mycolactone biosynthesis

Mycobacterium ulcerans is the causative agent of Buruli ulcer, a rapidly emerging human disease in which mycolactone, a cytotoxic and immunosuppressive macrocyclic polyketide, is responsible for massive skin destruction. The genome sequencing of M. ulcerans has recently been accomplished (http://genolist.pasteur.fr/BuruList/) enabling the first proteome study of this important human pathogen. Here, we present a comprehensive proteome analysis of different subcellular fractions and culture supernatant of in vitro grown M. ulcerans. By a combination of gel-based and gel-free techniques for protein and peptide separation with subsequent analysis by MS, we identified 1074 different proteins, corresponding to 25% of the protein-coding DNA sequence. Interestingly, new information was obtained about central metabolism and lipid biosynthesis, and as many as 192 conserved hypothetical proteins were found. Comparative analysis of the wild-type strain and an isogenic mycolactone-deficient mutant, by 2-DE and iTRAQ labeling of the cytoplasmic fraction, revealed differences in the expression profiles of proteins involved in lipid metabolism and information pathways, as well as stress responses.

Ultrasonography for the monitoring of subcutaneous damage in Mycobacterium ulcerans infection (Buruli ulcer)

We used ultrasonography to evaluate the nature and the extent of subcutaneous damage provoked by Mycobacterium ulcerans (M. ulcerans) and to investigate the possible involvement of the tributary lymph nodes during the various stages of progression of Buruli ulcer. Nineteen patients affected by M. ulcerans infection in Benin, West Africa, were studied. Ultrasonography was performed on all subjects, except one, at the site of nonulcerated lesions and/or at perilesional site. The tributary lymph nodes were also studied in six patients. Ultrasound (US) evaluation was carried out using a 10 MHz linear probe and all lesions were compared with the homologous unaffected controlateral site. The ultrasonography showed relevant alterations at the dermo-hypodermic level, in agreement with histological specimens. In the active forms of the disease, these alterations are characterized by significant oedematous imbibition of the adipose tissue and necrosis (adiponecrosis) that leads to varying irregularities in the echogenicity of the hypodermis, which is generally thicker. In agreement with the clinical examination, the lymph nodes in six patients evaluated, despite their possible histological involvement with necrotic phenomena described in literature in M. ulcerans infection, did not display significant alterations visible by ultrasonography. The US scanning we have performed is the first use of this technique for M. ulcerans infection. We have shown that it can reveal the subcutaneous depth and the peripheral extent of the pathological process and it is particularly useful for monitoring the efficacy of or resistance to antibiotic treatment, especially in extensive ulcero-oedomatose forms. Such monitoring offers also a useful guide to the surgeon allowing the reduction or postponement of the removal of the large cutaneous areas that were carried out until recently.

Analysis of the Mycobacterium ulcerans genome sequence reveals new loci for variable number tandem repeats (VNTR) typing

Screening of the genome sequence of the Mycobacterium ulcerans strain Agy99 from Ghana with tandem repeats finder software revealed 34 novel non-degenerate tandem repeats containing loci suitable for variable number tandem repeats (VNTR) typing. All loci revealed polymorphism within M. ulcerans isolates of geographically diverse origins. The results confirm the evolutionary scenario suggested by multi-locus sequence typing in which a progenitor of all M. ulcerans lineages emerged from the environmental species Mycobacterium marinum and subsequently diverged into several geographical lineages. For further attempts to develop a VNTR-based genetic fingerprinting tool for M. ulcerans, it is suggested that the focus should rather be on M. marinum than on the African M. ulcerans Agy99 genome sequence as a starting point.

Development and application of two multiplex real-time PCR assays for the detection of Mycobacterium ulcerans in clinical and environmental samples

Mycobacterium ulcerans is a slow-growing environmental bacterium that causes a severe skin disease known as Buruli ulcer. PCR has become a reliable and rapid method for the diagnosis of M. ulcerans infection in humans and has been used for the detection of M. ulcerans in the environment. This paper describes the development of a TaqMan assay targeting IS2404 multiplexed with an internal positive control to monitor inhibition with a detection limit of less than 1 genome equivalent of DNA. The assay improves the turnaround time for diagnosis and replaces conventional gel-based PCR as the routine method for laboratory confirmation of M. ulcerans infection in Victoria, Australia. Following analysis of 415 clinical specimens, the new test demonstrated 100% sensitivity and specificity compared with culture. Another multiplex TaqMan assay targeting IS2606 and the ketoreductase-B domain of the M. ulcerans mycolactone polyketide synthase genes was designed to augment the specificity of the IS2404 PCR for the analysis of a variety of environmental samples. Assaying for these three targets enabled the detection of M. ulcerans DNA in soil, sediment, and mosquito extracts collected from an area of endemicity for Buruli ulcer in Victoria with a high degree of confidence. Final confirmation was obtained by the detection and sequencing of variable-number tandem repeat (VNTR) locus 9, which matched the VNTR locus 9 sequence obtained from the clinical isolates in this region. This suite of new methods is enabling rapid progress in the understanding of the ecology of this important human pathogen.

Susceptibility to Buruli ulcer is associated with the SLC11A1 (NRAMP1) D543N polymorphism

Similar to other mycobacterial diseases, susceptibility to Buruli ulcer (Mycobacterium ulcerans infection) may be determined by host genetic factors. We investigated the role of SLC11A1 (NRAMP1) in Buruli ulcer because of its associations with both tuberculosis and leprosy. We enrolled 182 Buruli ulcer patients (102 with positive laboratory confirmation) and 191 healthy neighbourhood-matched controls in Ghana, and studied three polymorphisms in the SLC11A1 gene: 3' UTR TGTG ins/del, D543N G/A, and INT4 G/C. Finger prick blood samples from study subjects were dried on filter papers (FTA) and processed. D543N was significantly associated with Buruli ulcer: the odds ratio (adjusted for gender, age, and region of the participant) of the GA genotype versus the GG genotype was 2.89 (95% confidence intervals (CI): 1.41-5.91). We conclude that a genetic polymorphism in the SLC11A1 gene plays a role in susceptibility to develop Buruli ulcer, with an estimated 13% population attributable risk.

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.

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.

In vitro and in vivo activities of rifampin, streptomycin, amikacin, moxifloxacin, R207910, linezolid, and PA-824 against Mycobacterium ulcerans

Seven antimicrobials were tested in vitro against 29 clinical isolates of Mycobacterium ulcerans. R207910 demonstrated the lowest MIC(50) and MIC(90), followed by moxifloxacin (MXF), streptomycin (STR), rifampin (RIF), amikacin (AMK), linezolid (LZD), and PA-824. All but PA-824 demonstrated an MIC(90) significantly less than the clinically achievable peak serum level. Administered as monotherapy to mice, RIF, STR, AMK, MXF, R207910, and LZD demonstrated some degree of bactericidal activity, whereas PA-824 failed to prevent mortality and to reduce the mean number of CFU in the footpads. Because 4 or 8 weeks of treatment by the combinations RIF-MXF, RIF-R207910, and RIF-LZD displayed bactericidal effects similar to those of RIF-STR and RIF-AMK, these three combinations might be considered as orally administered combined regimens for treatment of Buruli ulcer. Taking into account the cost, potential toxicity, and availability, the combination RIF-MXF appears more feasible for application in the field; additional experiments with mice are warranted to define further its activity against M. ulcerans. In addition, a pilot clinical trial is proposed to test the efficacy of RIF-MXF for treatment of Buruli ulcer.

Buruli ulcer: emerging from obscurity

Buruli ulcer is a skin disease caused by infection with Mycobacterium ulcerans, which produces a potent toxin known as mycolactone, thus distinguishing itself from all other mycobacterial diseases. Mycolactone destroys cells in the subcutis, leading to the development of large ulcers with undermined edges. The genome sequence of M ulcerans has now been published and it transpires that two identical copies of a plasmid carry the genetic code for mycolactone. The mode of transmission of infection remains uncertain, although environmental sources of the organisms are now better understood. Considerable progress has been made in understanding the immune response to M ulcerans and there have been major advances in management of the disease with the introduction of rational antibiotic therapy. We summarise the current understanding of M ulcerans and its relations with human beings.