Clinical and microbiological predictors of healing in Buruli ulcer disease.

Introduction: Wound measurements are relevant in monitoring the rate of healing (RoH) and may predict time to healing. Predicting the time to healing can help improve the management of Buruli ulcer. We examine three methods for the determination of RoH and their use as predictors of time to healing. Methods: Lesion measurements of Buruli ulcer patients treated from 2007 to 2022 were obtained with acetate sheet tracings (2D) or Aranz software (3D) fortnightly. RoH was determined using the absolute area, percentage area reduction and linear methods at 4 weeks post onset of antibiotic treatment. Predicted time to healing was compared to the actual healing time. Baseline characteristics were assessed for associations with healing. Results: All three methods for calculating the RoH significantly distinguished between fast and slow healers (p < 0.0001). The predicted healing time using the linear method was comparable to the actual healing time for fast healers (p = 0.34). The RoH was influenced by the form of lesion, with plaques [OR 2.19 5 %CI (1.2-3.6), p = 0.009], and oedemas [OR 8.5; 95 %CI (1.9--36.9), p = 0.004] being associated with delayed healing. The proportion of patients with paradoxical reactions 16 % vs 3 %, p < 0.0001), higher baseline bacterial load (75/104;72 % vs 21/47;45 %, p = 0.001) and delayed clearance of viable organisms (71/104;68 % vs 9/47;19 %, p < 0.0001) was higher in the slow healers than the fast healers. Conclusion: Predicted healing rates were comparatively lower for slow healers than fast healers. Baseline characteristics associated with healing can be explored for an improved disease management plan to reduce patient and caregiver anxiety.

Co-infection of HIV in patients with Buruli ulcer disease in Central Ghana.

BACKGROUND: Previous studies have reported that presence and severity of Buruli ulcer (BU) may reflect the underlying immunosuppression in HIV infected individuals by causing increased incidence of multiple, larger and ulcerated lesions. We report cases of BU-HIV coinfection and the accompanying programmatic challenges encountered in central Ghana. METHODS: Patients with PCR confirmed BU in central Ghana who were HIV positive were identified and their BU01 forms were retrieved and reviewed in further detail. A combined 16S rRNA reverse transcriptase / IS2404 qPCR assay was used to assess the Mycobacterium ulcerans load. The characteristics of coinfected patients (BU+HIV+) were compared with a group of matched controls. RESULTS: The prevalence of HIV in this BU cohort was 2.4% (compared to national HIV prevalence of 1.7%). Eight of 9 BU+HIV+ patients had a single lesion and ulcers were the most common lesion type. The lesions presented were predominantly category II (5/9) followed by category I lesions. The median (IQR) time to healing was 14 (8-28) weeks in the BU+HIV+ compared to 28 (12-33) weeks in the control BU+HIV- group (p = 0.360). Only one BU+HIV+ developed a paradoxical reaction at week 16 but the lesion healed completely at week 20. The median bacterial load (16SrRNA) of BU+HIV+ patients was 750 copies /ml (95% CI 0-398,000) versus 500 copies/ml (95% CI 0-126,855,500) in BU+HIV- group. Similarly, the median count using the IS2404 assay was 500 copies/ml (95% CI 0-500) for BU+HIV+ patients versus 500 copies/ml (95% CI 500-31,000) for BU+HIV- patients. BU+HIV- patients mounted a significantly higher interferon-γ response compared to the BU+HIV+ co-infected patients with respective median (range) responses of [1687(81.11-4399) pg/ml] versus [137.5(4.436-1406) pg/ml, p = 0.03]. There were challenges with the integration of HIV and BU care in this cohort. CONCLUSION: The prevalence of HIV in the BU+ infected population was not significantly increased when compared to the prevalence of HIV in the general population. There was no clear relationship between BU lesion severity and HIV viral load or CD4 counts. Efforts should be made to encourage the integration of care of patients with BU-HIV coinfection.

Rifampicin and clarithromycin (extended release) versus rifampicin and streptomycin for limited Buruli ulcer lesions: a randomised, open-label, non-inferiority phase 3 trial.

BACKGROUND: Buruli ulcer is a neglected tropical disease caused by Mycobacterium ulcerans infection that damages the skin and subcutis. It is most prevalent in western and central Africa and Australia. Standard antimicrobial treatment with oral rifampicin 10 mg/kg plus intramuscular streptomycin 15 mg/kg once daily for 8 weeks (RS8) is highly effective, but streptomycin injections are painful and potentially harmful. We aimed to compare the efficacy and tolerability of fully oral rifampicin 10 mg/kg plus clarithromycin 15 mg/kg extended release once daily for 8 weeks (RC8) with that of RS8 for treatment of early Buruli ulcer lesions. METHODS: We did an open-label, non-inferiority, randomised (1:1 with blocks of six), multicentre, phase 3 clinical trial comparing fully oral RC8 with RS8 in patients with early, limited Buruli ulcer lesions. There were four trial sites in hospitals in Ghana (Agogo, Tepa, Nkawie, Dunkwa) and one in Benin (Pobè). Participants were included if they were aged 5 years or older and had typical Buruli ulcer with no more than one lesion (caterories I and II) no larger than 10 cm in diameter. The trial was open label, and neither the investigators who took measurements of the lesions nor the attending doctors were masked to treatment assignment. The primary clinical endpoint was lesion healing (ie, full epithelialisation or stable scar) without recurrence at 52 weeks after start of antimicrobial therapy. The primary endpoint and safety were assessed in the intention-to-treat population. A sample size of 332 participants was calculated to detect inferiority of RC8 by a margin of 12%. This study was registered with ClinicalTrials.gov, NCT01659437. FINDINGS: Between Jan 1, 2013, and Dec 31, 2017, participants were recruited to the trial. We stopped recruitment after 310 participants. Median age of participants was 14 years (IQR 10-29) and 153 (52%) were female. 297 patients had PCR-confirmed Buruli ulcer; 151 (51%) were assigned to RS8 treatment, and 146 (49%) received oral RC8 treatment. In the RS8 group, lesions healed in 144 (95%, 95% CI 91 to 98) of 151 patients, whereas lesions healed in 140 (96%, 91 to 99) of 146 patients in the RC8 group. The difference in proportion, -0·5% (-5·2 to 4·2), was not significantly greater than zero (p=0·59), showing that RC8 treatment is non-inferior to RS8 treatment for lesion healing at 52 weeks. Treatment-related adverse events were recorded in 20 (13%) patients receiving RS8 and in nine (7%) patients receiving RC8. Most adverse events were grade 1-2, but one (1%) patient receiving RS8 developed serious ototoxicity and ended treatment after 6 weeks. No patients needed surgical resection. Four patients (two in each study group) had skin grafts. INTERPRETATION: Fully oral RC8 regimen was non-inferior to RS8 for treatment of early, limited Buruli ulcer and was associated with fewer adverse events. Therefore, we propose that fully oral RC8 should be the preferred therapy for early, limited lesions of Buruli ulcer. FUNDING: WHO with additional support from MAP International, American Leprosy Missions, Fondation Raoul Follereau France, Buruli ulcer Groningen Foundation, Sanofi-Pasteur, and BuruliVac.

Paradoxical reactions in Buruli ulcer after initiation of antibiotic therapy: Relationship to bacterial load.

BACKGROUND: We investigated the relationship between bacterial load in Buruli ulcer (BU) lesions and the development of paradoxical reaction following initiation of antibiotic treatment. METHODS: This was a longitudinal study involving BU patients from June 2013 to June 2017. Fine needle aspirates (FNA) and swab samples were obtained to establish the diagnosis of BU by PCR. Additional samples were obtained at baseline, during and after treatment (if the lesion had not healed) for microscopy, culture and combined 16S rRNA reverse transcriptase/ IS2404 qPCR assay. Patients were followed up at regular intervals until complete healing. RESULTS: Forty-seven of 354 patients (13%) with PCR confirmed BU had a PR, occurring between 2 and 42 (median 6) weeks after treatment initiation. The bacterial load, the proportion of patients with positive M. ulcerans culture (15/34 (44%) vs 29/119 (24%), p = 0.025) and the proportion with positive microscopy results (19/31 (61%) vs 28/90 (31%), p = 0.003) before initiation of treatment were significantly higher in the PR compared to the no PR group. Plaques (OR 5.12; 95% CI 2.26-11.61; p<0.001), oedematous (OR 4.23; 95% CI 1.43-12.5; p = 0.009) and category II lesions (OR 2.26; 95% CI 1.14-4.48; p = 0.02) were strongly associated with the occurrence of PR. The median time to complete healing (28 vs 13 weeks, p <0.001) was significantly longer in the PR group. CONCLUSIONS: Buruli ulcer patients who develop PR are characterized by high bacterial load in lesion samples taken at baseline and a higher rate of positive M. ulcerans culture. Occurrence of a PR was associated with delayed healing. TRIAL REGISTRATION: ClinicalTrials.gov NCT02153034.

Rapid detection of Mycobacterium ulcerans with isothermal recombinase polymerase amplification assay.

BACKGROUND: Access to an accurate diagnostic test for Buruli ulcer (BU) is a research priority according to the World Health Organization. Nucleic acid amplification of insertion sequence IS2404 by polymerase chain reaction (PCR) is the most sensitive and specific method to detect Mycobacterium ulcerans (M. ulcerans), the causative agent of BU. However, PCR is not always available in endemic communities in Africa due to its cost and technological sophistication. Isothermal DNA amplification systems such as the recombinase polymerase amplification (RPA) have emerged as a molecular diagnostic tool with similar accuracy to PCR but having the advantage of amplifying a template DNA at a constant lower temperature in a shorter time. The aim of this study was to develop RPA for the detection of M. ulcerans and evaluate its use in Buruli ulcer disease. METHODOLOGY AND PRINCIPAL FINDINGS: A specific fragment of IS2404 of M. ulcerans was amplified within 15 minutes at a constant 42°C using RPA method. The detection limit was 45 copies of IS2404 molecular DNA standard per reaction. The assay was highly specific as all 7 strains of M. ulcerans tested were detected, and no cross reactivity was observed to other mycobacteria or clinically relevant bacteria species. The clinical performance of the M. ulcerans (Mu-RPA) assay was evaluated using DNA extracted from fine needle aspirates or swabs taken from 67 patients in whom BU was suspected and 12 patients with clinically confirmed non-BU lesions. All results were compared to a highly sensitive real-time PCR. The clinical specificity of the Mu-RPA assay was 100% (95% CI, 84-100), whiles the sensitivity was 88% (95% CI, 77-95). CONCLUSION: The Mu-RPA assay represents an alternative to PCR, especially in areas with limited infrastructure.

IFN-γ and IL-5 whole blood response directed against mycolactone polyketide synthase domains in patients with Mycobacterium ulcerans infection.

BACKGROUND: Buruli ulcer is a disease of the skin and soft tissues caused by infection with a slow growing pathogen, Mycobacterium ulcerans. A vaccine for this disease is not available but M. ulcerans possesses a giant plasmid pMUM001 that harbours the polyketide synthase (PKS) genes encoding a multi-enzyme complex needed for the production of its unique lipid toxin called mycolactone, which is central to the pathogenesis of Buruli ulcer. We have studied the immunogenicity of enzymatic domains in humans with M. ulcerans disease, their contacts, as well as non-endemic areas controls. METHODS: Between March 2013 and August 2015, heparinized whole blood was obtained from patients confirmed with Buruli ulcer. The blood samples were diluted 1 in 10 in Roswell Park Memorial Institute (RPMI) medium and incubated for 5 days with recombinant mycolactone PKS domains and mycolyltransferase antigen 85A (Ag85A). Blood samples were obtained before and at completion of antibiotic treatment for 8 weeks and again 8 weeks after completion of treatment. Supernatants were assayed for interferon-γ (IFN-γ) and interleukin-5 (IL-5) by enzyme-linked immunosorbent assay. Responses were compared with those of contacts and non-endemic controls. RESULTS: More than 80% of patients and contacts from endemic areas produced IFN-γ in response to all the antigens except acyl carrier protein type 3 (ACP3) to which only 47% of active Buruli ulcer cases and 71% of contacts responded. The highest proportion of responders in cases and contacts was to load module ketosynthase domain (Ksalt) (100%) and enoylreductase (100%). Lower IL-5 responses were induced in a smaller proportion of patients ranging from 54% after ketoreductase type B stimulation to only 21% with ketosynthase type C (KS C). Among endemic area contacts, the, highest proportion was 73% responding to KS C and the lowest was 40% responding to acyltransferase with acetate specificity type 2. Contacts of Buruli ulcer patients produced significantly higher IFN-γ and IL-5 responses compared with those of patients to PKS domain antigens and to mycolyltransferase Ag85A of M. ulcerans. There was low or no response to all the antigens in non-endemic areas controls. IFN-γ and IL-5 responses of patients improved after treatment when compared to baseline results. DISCUSSION: The major response to PKS antigen stimulation was IFN-γ and the strongest responses were observed in healthy contacts of patients living in areas endemic for Buruli ulcer. Patients elicited lower responses than healthy contacts, possibly due to the immunosuppressive effect of mycolactone, but the responses were enhanced after antibiotic treatment. A vaccine made up of the most immunogenic PKS domains combined with the mycolyltransferase Ag85A warrants further investigation.

Clearance of viable Mycobacterium ulcerans from Buruli ulcer lesions during antibiotic treatment as determined by combined 16S rRNA reverse transcriptase /IS 2404 qPCR assay.

INTRODUCTION: Buruli ulcer (BU) caused by Mycobacterium ulcerans is effectively treated with rifampicin and streptomycin for 8 weeks but some lesions take several months to heal. We have shown previously that some slowly healing lesions contain mycolactone suggesting continuing infection after antibiotic therapy. Now we have determined how rapidly combined M. ulcerans 16S rRNA reverse transcriptase / IS2404 qPCR assay (16S rRNA) became negative during antibiotic treatment and investigated its influence on healing. METHODS: Fine needle aspirates and swab samples were obtained for culture, acid fast bacilli (AFB) and detection of M. ulcerans 16S rRNA and IS2404 by qPCR (16S rRNA) from patients with IS2404 PCR confirmed BU at baseline, during antibiotic and after treatment. Patients were followed up at 2 weekly intervals to determine the rate of healing. The Kaplan-Meier survival analysis was used to analyse the time to clearance of M. ulcerans 16S rRNA and the influence of persistent M ulcerans 16S rRNA on time to healing. The Mann Whitney test was used to compare the bacillary load at baseline in patients with or without viable organisms at week 4, and to analyse rate of healing at week 4 in relation to detection of viable organisms. RESULTS: Out of 129 patients, 16S rRNA was detected in 65% of lesions at baseline. The M. ulcerans 16S rRNA remained positive in 78% of patients with unhealed lesions at 4 weeks, 52% at 8 weeks, 23% at 12 weeks and 10% at week 16. The median time to clearance of M. ulcerans 16S rRNA was 12 weeks. BU lesions with positive 16S rRNA after antibiotic treatment had significantly higher bacterial load at baseline, longer healing time and lower healing rate at week 4 compared with those in which 16S rRNA was not detected at baseline or had become undetectable by week 4. CONCLUSIONS: Current antibiotic therapy for BU is highly successful in most patients but it may be possible to abbreviate treatment to 4 weeks in patients with a low initial bacterial load. On the other hand persistent infection contributes to slow healing in patients with a high bacterial load at baseline, some of whom may need antibiotic treatment extended beyond 8 weeks. Bacterial load was estimated from a single sample taken at baseline. A better estimate could be made by taking multiple samples or biopsies but this was not ethically acceptable.

High prevalence of multidrug-resistant tuberculosis among patients with rifampicin resistance using GeneXpert Mycobacterium tuberculosis/rifampicin in Ghana.

OBJECTIVE/BACKGROUND: Drug-resistant strains of tuberculosis (TB) represent a major threat to global TB control. In low- and middle-income countries, resource constraints make it difficult to identify and monitor cases of resistance using drug susceptibility testing and culture. Molecular assays such as the GeneXpert Mycobacterium tuberculosis/rifampicin may prove to be a cost-effective solution to this problem in these settings. The objective of this study is to evaluate the use of GeneXpert in the diagnosis of pulmonary TB since it was introduced into two tertiary hospitals in Ghana in 2013. METHODS: A 2-year retrospective audit of clinical cases involving patients who presented with clinically suspected TB or documented TB not improving on standard therapy and had samples sent for GeneXpert testing. RESULTS: GeneXpert identified 169 cases of TB, including 17 cases of rifampicin-resistant TB. Of the seven cases with final culture and drug susceptibility testing results, six demonstrated further drug resistance and five of these were multidrug-resistant TB. CONCLUSION: These findings call for a scale-up of TB control in Ghana and provide evidence that the expansion of GeneXpert may be an optimal means to improve case finding and guide treatment of drug-resistant TB in this setting.

Recent advances: role of mycolactone in the pathogenesis and monitoring of Mycobacterium ulcerans infection/Buruli ulcer disease.

Infection of subcutaneous tissue with Mycobacterium ulcerans can lead to chronic skin ulceration known as Buruli ulcer. The pathogenesis of this neglected tropical disease is dependent on a lipid-like toxin, mycolactone, which diffuses through tissue away from the infecting organisms. Since its identification in 1999, this molecule has been intensely studied to elucidate its cytotoxic and immunosuppressive properties. Two recent major advances identifying the underlying molecular targets for mycolactone have been described. First, it can target scaffolding proteins (such as Wiskott Aldrich Syndrome Protein), which control actin dynamics in adherent cells and therefore lead to detachment and cell death by anoikis. Second, it prevents the co-translational translocation (and therefore production) of many proteins that pass through the endoplasmic reticulum for secretion or placement in cell membranes. These pleiotropic effects underpin the range of cell-specific functional defects in immune and other cells that contact mycolactone during infection. The dose and duration of mycolactone exposure for these different cells explains tissue necrosis and the paucity of immune cells in the ulcers. This review discusses recent advances in the field, revisits older findings in this context and highlights current developments in structure-function studies as well as methodology that make mycolactone a promising diagnostic biomarker.

Metabolomic profiles delineate mycolactone signature in Buruli ulcer disease.

Infection of human skin with Mycobacterium ulcerans, the causative agent of Buruli ulcer, is associated with the systemic diffusion of a bacterial macrolide named mycolactone. Patients with progressive disease show alterations in their serum proteome, likely reflecting the inhibition of secreted protein production by mycolactone at the cellular level. Here, we used semi-quantitative metabolomics to characterize metabolic perturbations in serum samples of infected individuals, and human cells exposed to mycolactone. Among the 430 metabolites profiled across 20 patients and 20 healthy endemic controls, there were significant differences in the serum levels of hexoses, steroid hormones, acylcarnitines, purine, heme, bile acids, riboflavin and lysolipids. In parallel, analysis of 292 metabolites in human T cells treated or not with mycolactone showed alterations in hexoses, lysolipids and purine catabolites. Together, these data demonstrate that M. ulcerans infection causes systemic perturbations in the serum metabolome that can be ascribed to mycolactone. Of particular importance to Buruli ulcer pathogenesis is that changes in blood sugar homeostasis in infected patients are mirrored by alterations in hexose metabolism in mycolactone-exposed cells.

Simple, Rapid Mycobacterium ulcerans Disease Diagnosis from Clinical Samples by Fluorescence of Mycolactone on Thin Layer Chromatography.

INTRODUCTION: Mycobacterium ulcerans infection, known as Buruli ulcer, is a disease of the skin and subcutaneous tissues which is an important but neglected tropical disease with its major impact in rural parts of West and Central Africa where facilities for diagnosis and management are poorly developed. We evaluated fluorescent thin layer chromatography (f-TLC) for detection of mycolactone in the laboratory using samples from patients with Buruli ulcer and patients with similar lesions that gave a negative result on PCR for the IS2404 repeat sequence of M. ulcerans. METHODOLOGY/PRINCIPAL FINDINGS: Mycolactone and DNA extracts from fine needle aspiration (FNA), swabs and biopsy specimen were used to determine the sensitivity and specificity of f-TLC when compared with PCR for the IS2404. For 71 IS2404 PCR positive and 28 PCR negative samples the sensitivity was 73.2% and specificity of 85.7% for f-TLC. The sensitivity was similar for swabs (73%), FNAs (75%) and biopsies (70%). CONCLUSIONS: We have shown that mycolactone can be detected from M. ulcerans infected skin tissue by f-TLC technique. The technique is simple, easy to perform and read with minimal costs. In this study it was undertaken by a member of the group from each endemic country. It is a potentially implementable tool at the district level after evaluation in larger field studies.

Infection with Mansonella perstans Nematodes in Buruli Ulcer Patients, Ghana.

During August 2010-December 2012, we conducted a study of patients in Ghana who had Buruli ulcer, caused by Mycobacterium ulcerans, and found that 23% were co-infected with Mansonella perstans nematodes; 13% of controls also had M. perstans infection. M. perstans co-infection should be considered in the diagnosis and treatment of Buruli ulcer.

Kinetics of mycolactone in human subcutaneous tissue during antibiotic therapy for Mycobacterium ulcerans disease.

BACKGROUND: Mycobacterium ulcerans (M. ulcerans) causes a devastating necrotising infection of skin tissue leading to progressive ulceration. M. ulcerans is the only human pathogen that secretes mycolactone, a polyketide molecule with potent cytotoxic and immunomodulatory properties. These unique features make mycolactone an attractive biomarker for M. ulcerans disease. We sought to measure the concentration of mycolactone within lesions of patients with Buruli ulcer before, during and after antibiotic treatment to evaluate its association with the clinical and bacteriological response to therapy. METHODS: Biopsies of M. ulcerans infected skin lesions were obtained from patients before, during and after antibiotic therapy. Lipids were extracted from the biopsies and concentration of mycolactone was assayed by mass spectrometry and a cytotoxicity assay and correlated with clinical and bacteriological response to therapy. RESULTS: Baseline concentration of mycolactone measured by mass spectrometry predicted time to complete healing of small nodules and ulcers. Even though intra-lesional concentrations of mycolactone declined with antibiotic treatment, the toxin was still present after antibiotic treatment for 6 weeks and also 4 weeks after the end of treatment for 8 weeks in a subgroup of patients with slowly healing lesions. Additionally viable bacilli were detected in a proportion of these slowly healing lesions during and after treatment. CONCLUSIONS: Our findings indicate that baseline intra-lesional mycolactone concentration and its kinetics with antibiotic therapy are important prognostic determinants of clinical and bacteriological response to antibiotic treatment for Mycobacterium ulcerans disease. Mycolactone may be a useful biomarker with potential utility in optimising antibiotic therapy.

Combined inflammatory and metabolic defects reflected by reduced serum protein levels in patients with Buruli ulcer disease.

Buruli ulcer is a skin disease caused by Mycobacterium ulcerans that is spreading in tropical countries, with major public health and economic implications in West Africa. Multi-analyte profiling of serum proteins in patients and endemic controls revealed that Buruli ulcer disease down-regulates the circulating levels of a large array of inflammatory mediators, without impacting on the leukocyte composition of peripheral blood. Notably, several proteins contributing to acute phase reaction, lipid metabolism, coagulation and tissue remodelling were also impacted. Their down-regulation was selective and persisted after the elimination of bacteria with antibiotic therapy. It involved proteins with various functions and origins, suggesting that M. ulcerans infection causes global and chronic defects in the host's protein metabolism. Accordingly, patients had reduced levels of total serum proteins and blood urea, in the absence of signs of malnutrition, or functional failure of liver or kidney. Interestingly, slow healers had deeper metabolic and coagulation defects at the start of antibiotic therapy. In addition to providing novel insight into Buruli ulcer pathogenesis, our study therefore identifies a unique proteomic signature for this disease.

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.

Clinical and bacteriological efficacy of rifampin-streptomycin combination for two weeks followed by rifampin and clarithromycin for six weeks for treatment of Mycobacterium ulcerans disease.

Buruli ulcer, an ulcerating skin disease caused by Mycobacterium ulcerans infection, is common in tropical areas of western Africa. We determined the clinical and microbiological responses to administration of rifampin and streptomycin for 2 weeks followed by administration of rifampin and clarithromycin for 6 weeks in 43 patients with small laboratory-confirmed Buruli lesions and monitored for recurrence-free healing. Bacterial load in tissue samples before and after treatment for 6 and 12 weeks was monitored by semiquantitative culture. The success rate was 93%, and there was no recurrence after a 12-month follow-up. Eight percent had a positive culture 4 weeks after antibiotic treatment, but their lesions went on to heal. The findings indicate that rifampin and clarithromycin can replace rifampin and streptomycin for the continuation phase after rifampin and streptomycin administration for 2 weeks without any apparent loss of efficacy.

Microbiological, histological, immunological, and toxin response to antibiotic treatment in the mouse model of Mycobacterium ulcerans disease.

Mycobacterium ulcerans infection causes a neglected tropical disease known as Buruli ulcer that is now found in poor rural areas of West Africa in numbers that sometimes exceed those reported for another significant mycobacterial disease, leprosy, caused by M. leprae. Unique among mycobacterial diseases, M. ulcerans produces a plasmid-encoded toxin called mycolactone (ML), which is the principal virulence factor and destroys fat cells in subcutaneous tissue. Disease is typically first manifested by the appearance of a nodule that eventually ulcerates and the lesions may continue to spread over limbs or occasionally the trunk. The current standard treatment is 8 weeks of daily rifampin and injections of streptomycin (RS). The treatment kills bacilli and wounds gradually heal. Whether RS treatment actually stops mycolactone production before killing bacilli has been suggested by histopathological analyses of patient lesions. Using a mouse footpad model of M. ulcerans infection where the time of infection and development of lesions can be followed in a controlled manner before and after antibiotic treatment, we have evaluated the progress of infection by assessing bacterial numbers, mycolactone production, the immune response, and lesion histopathology at regular intervals after infection and after antibiotic therapy. We found that RS treatment rapidly reduced gross lesions, bacterial numbers, and ML production as assessed by cytotoxicity assays and mass spectrometric analysis. Histopathological analysis revealed that RS treatment maintained the association of the bacilli with (or within) host cells where they were destroyed whereas lack of treatment resulted in extracellular infection, destruction of host cells, and ultimately lesion ulceration. We propose that RS treatment promotes healing in the host by blocking mycolactone production, which favors the survival of host cells, and by killing M. ulcerans bacilli.