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

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.

Mycobacterium ulcerans challenge strain selection for a Buruli ulcer controlled human infection model

Critical scientific questions remain regarding infection with Mycobacterium ulcerans, the organism responsible for the neglected tropical disease, Buruli ulcer (BU). A controlled human infection model has the potential to accelerate our knowledge of the immunological correlates of disease, to test prophylactic interventions and novel therapeutics. Here we present microbiological evidence supporting M. ulcerans JKD8049 as a suitable human challenge strain. This non-genetically modified Australian isolate is susceptible to clinically relevant antibiotics, can be cultured in animal-free and surfactant-free media, can be enumerated for precise dosing, and has stable viability following cryopreservation. Infectious challenge of humans with JKD8049 is anticipated to imitate natural infection, as M. ulcerans JKD8049 is genetically stable following in vitro passage and produces the key virulence factor, mycolactone. Also reported are considerations for the manufacture, storage, and administration of M. ulcerans JKD8049 for controlled human infection.

Bedaquiline for treatment of non-tuberculous mycobacteria (NTM): a systematic review and meta-analysis

BACKGROUND

Non-tuberculous mycobacteria (NTM) infections are increasing in incidence and associated mortality. NTM are naturally resistant to a variety of antibiotics, complicating treatment. We conducted a literature assessment on the efficacy of bedaquiline in treating NTM species in vitro and in vivo (animal models and humans); meta-analyses were performed where possible.

METHOD

Four databases were searched using specific terms. Publications were included according to predefined criteria. Bedaquiline's impact on NTM in vitro, MICs and epidemiological cut-off (ECOFF) values were evaluated. A meta-analysis of bedaquiline efficacy against NTM infections in animal models was performed. Culture conversion, cure and/or relapse-free cure were used to evaluate the efficacy of bedaquiline in treating NTM infection in humans.

RESULTS

Fifty studies met the inclusion criteria: 33 assessed bedaquiline's impact on NTM in vitro, 9 in animal models and 8 in humans. Three studies assessed bedaquiline's efficacy both in vitro and in vivo. Due to data paucity, an ECOFF value of 0.5 mg/mL was estimated for Mycobacterium abscessus only. Meta-analysis of animal studies showed a 1.86× reduction in bacterial load in bedaquiline-treated versus no treatment within 30 days. In humans, bedaquiline-including regimens were effective in treating NTM extrapulmonary infection but not pulmonary infection.

CONCLUSIONS

Bedaquiline demonstrated strong antibacterial activity against various NTM species and is a promising drug to treat NTM infections. However, data on the genomic mutations associated with bedaquiline resistance were scarce, preventing statistical analyses for most mutations and NTM species. Further studies are urgently needed to better inform treatment strategies.

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.

Drug Efficacy Testing in the Mouse Footpad Model of Buruli Ulcer

Great progress has been made in understanding the pathogenesis and treatment of Buruli ulcer over the last 20 years. The rediscovery of the mouse footpad model of the disease with translation to clinical practice has changed treatment of this infectious disease, caused by Mycobacterium ulcerans, from surgery and skin grafting to the administration of antibiotics for 8 weeks or less with superior cure rates. Here we describe the development and enhancement of the mouse model during the last two decades.

In vitro activity of SPR719 against Mycobacterium ulcerans, Mycobacterium marinum and Mycobacterium chimaera

Nontuberculosis mycobacterial (NTM) infections are increasing in prevalence across the world. In many cases, treatment options for these infections are limited. However, there has been progress in recent years in the development of new antimycobacterial drugs. Here, we investigate the in vitro activity of SPR719, a novel aminobenzimidazole antibiotic and the active form of the clinical-stage compound, SPR720, against several isolates of Mycobacterium ulcerans, Mycobacterium marinum and Mycobacterium chimaera. We show that SPR719 is active against these NTM species with a MIC range of 0.125–4 μg/ml and that this compares favorably with the commonly utilized antimycobacterial antibiotics, rifampicin and clarithromycin. Our findings suggest that SPR720 should be further evaluated for the treatment of NTM infections.

Nontuberculosis mycobacteria represent a large group of diverse bacteria that live across a range of environments. Human contact with the habitats in which these organisms live can result in opportunistic infections. Among the NTM, Mycobacterium ulcerans causes necrotic skin ulcers that can lead to significant long term physical impairment; Mycobacterium marinum causes granulomatous skin lesions; and Mycobacterium chimaera has been linked to contaminated heater-cooler units used during cardiac surgery, resulting in prosthetic heart valve infections that are particularly difficult to treat. We performed laboratory experiments to test the susceptibility of these NTM species (M. ulcerans, M. marinum and M. chimaera) to a recently developed antibiotic, SPR719. We found that SPR719 inhibits the growth of these mycobacteria at concentration ranges similar to or better than commonly used anti-mycobacterial antibiotics. As SPR720, the oral prodrug of SPR719, has recently completed a Phase I safety, tolerability and PK study in healthy human volunteers, the potential exists for this product to be explored for the treatment of NTM infections, where new treatment options are urgently needed.

Therapeutic Drug Monitoring in Non-Tuberculosis Mycobacteria Infections

Nontuberculous mycobacteria can cause minimally symptomatic self-limiting infections to progressive and life-threatening disease of multiple organs. Several factors such as increased testing and prevalence have made this an emerging infectious disease. Multiple guidelines have been published to guide therapy, which remains difficult owing to the complexity of therapy, the potential for acquired resistance, the toxicity of treatment, and a high treatment failure rate. Given the long duration of therapy, complex multi-drug treatment regimens, and the risk of drug toxicity, therapeutic drug monitoring is an excellent method to optimize treatment. However, currently, there is little available guidance on therapeutic drug monitoring for this condition. The aim of this review is to provide information on the pharmacokinetic/pharmacodynamic targets for individual drugs used in the treatment of nontuberculous mycobacteria disease. Lacking data from randomized controlled trials, in vitro, in vivo, and clinical data were aggregated to facilitate recommendations for therapeutic drug monitoring to improve efficacy and reduce toxicity.

Alternative and Experimental Therapies of Mycobacterium abscessus Infections

Mycobacterium abscessus is a non-tuberculous mycobacterium notoriously known for causing severe, chronic infections. Treatment of these infections is challenging due to either intrinsic or acquired resistance of M. abscessus to multiple antibiotics. Despite prolonged poly-antimicrobial therapy, treatment of M. abscessus infections often fails, leading to progressive morbidity and eventual mortality. Great research efforts are invested in finding new therapeutic options for M. abscessus. Clofazimine and rifabutin are known anti-mycobacterial antibiotics, repurposed for use against M. abscessus. Novel antimicrobials active against M. abscessus include delamanid, pretomanid and PIPD1 and the recently approved beta-lactamase inhibitors avibactam, relebactam and vaborbactam. Previously unused antimicrobial combinations, e.g. vancomycin–clarithromycin and dual beta-lactam therapy, have been shown to have synergistic effect against M. abscessus in experimental models, suggesting their possible use in multiple-drug regimens. Finally, engineered phage therapy has been reported to be clinically successful in a severe case of disseminated M. abscessus infection. While many of these experimental therapeutics have shown activity against M. abscessus in vitro, as well as in intracellular and/or animal models, most have little if any evidence of effect in human infections. Clinical studies of M. abscesssus treatments are needed to reliably determine the value of their incorporation in therapeutic regimens.

Telacebec (Q203)-containing intermittent oral regimens sterilized mice infected with Mycobacterium ulcerans after only 16 doses

Buruli ulcer (BU), caused by Mycobacterium ulcerans, is currently treated with a daily combination of rifampin and either injectable streptomycin or oral clarithromycin. An intermittent oral regimen would facilitate treatment supervision. We first evaluated the bactericidal activity of newer antimicrobials against M. ulcerans using a BU animal model. The imidazopyridine amine telacebec (Q203) exhibited high bactericidal activity whereas tedizolid (an oxazolidinone closely related to linezolid), selamectin and ivermectin (two avermectine compounds) and the benzothiazinone PBTZ169 were not active. Consequently, telacebec was evaluated for its bactericidal and sterilizing activities in combined intermittent regimens. Telacebec given twice a week in combination with a long-half-life compound, either rifapentine or bedaquiline, sterilized mouse footpads in 8 weeks, i.e. after a total of only 16 doses, and prevented relapse during a period of 20 weeks after the end of treatment. These results are very promising for future intermittent oral regimens which would greatly simplify BU treatment in the field.

The current treatment for Buruli ulcer (BU), an infection caused by Mycobacterium ulcerans, is based on a daily antibiotic combination of rifampin associated with streptomycin or clarithromycin. A shorter or intermittent treatment without an injectable drug would clearly simplify the management in the field. We evaluated the bactericidal activity of several new antimicrobial drugs in a mouse model of BU and found that telacebec (Q203) exhibited the greatest bactericidal effect. We subsequently identified new antibiotic combinations containing telacebec with high sterilizing activity when administered twice a week for 8 weeks, i.e. at a total of only 16 doses.

Toward a Single-Dose Cure for Buruli Ulcer

A single dose of Q203 (Telacebec), a phase 2 clinical candidate for tuberculosis, eradicates Mycobacterium ulcerans in a mouse model of Buruli ulcer infection without relapse up to 19 weeks posttreatment. Clinical use of Q203 may dramatically simplify the clinical management of Buruli ulcer, a neglected mycobacterial disease.

Risk Factors Associated with Antibiotic Treatment Failure of Buruli Ulcer

Combination antibiotic therapy is highly effective in curing Buruli ulcer (BU) caused by Mycobacterium ulcerans Treatment failures have been uncommonly reported with the recommended 56 days of antibiotics, and little is known about risk factors for treatment failure. We analyzed treatment failures among BU patients treated with ≥56 days of antibiotics from a prospective observational cohort at Barwon Health, Victoria, from 1 January 1998 to 31 December 2018. Treatment failure was defined as culture-positive recurrence within 12 months of commencing antibiotics under the following conditions: (i) following failure to heal the initial lesion or (ii) a new lesion developing at the original or at a new site. A total of 430 patients received ≥56 days of antibiotic therapy, with a median duration of 56 days (interquartile range [IQR], 56 to 80). Seven (1.6%) patients experienced treatment failure. For six adult patients experiencing treatment failure, all were male, weighed >90 kg, did not have surgery, and received combination rifampin-clarithromycin (median rifampin dose, 5.6 mg per kg of body weight per day; median clarithromycin dose, 8.1 mg/kg/day). When compared to those who did not fail treatment on univariate analysis, treatment failure was significantly associated with a weight of >90 kg (P < 0.001), male gender (P = 0.02), immune suppression (P = 0.04), and a first-line regimen of rifampin-clarithromycin compared to a regimen of rifampin-fluoroquinolone (P = 0.05). There is a low rate of treatment failure in Australian BU patients treated with rifampin-based oral combination antibiotic therapy. Our study raises the possibility that treatment failure risk may be increased in males, those with a body weight of >90 kg, those with immune suppression, and those taking rifampin-clarithromycin antibiotic regimens, but future pharmacokinetic and pharmacodynamics studies are required to determine the validity of these hypotheses.

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.

Predicting nitroimidazole antibiotic resistance mutations in Mycobacterium tuberculosis with protein engineering

Our inability to predict which mutations could result in antibiotic resistance has made it difficult to rapidly identify the emergence of resistance, identify pre-existing resistant populations, and manage our use of antibiotics to effectively treat patients and prevent or slow the spread of resistance. Here we investigated the potential for resistance against the new antitubercular nitroimidazole prodrugs pretomanid and delamanid to emerge in Mycobacterium tuberculosis, the causative agent of tuberculosis (TB). Deazaflavin-dependent nitroreductase (Ddn) is the only identified enzyme within M. tuberculosis that activates these prodrugs, via an F420H2-dependent reaction. We show that the native menaquinone-reductase activity of Ddn is essential for emergence from hypoxia, which suggests that for resistance to spread and pose a threat to human health, the native activity of Ddn must be at least partially retained. We tested 75 unique mutations, including all known sequence polymorphisms identified among ~15,000 sequenced M. tuberculosis genomes. Several mutations abolished pretomanid and delamanid activation in vitro, without causing complete loss of the native activity. We confirmed that a transmissible M. tuberculosis isolate from the hypervirulent Beijing family already possesses one such mutation and is resistant to pretomanid, before being exposed to the drug. Notably, delamanid was still effective against this strain, which is consistent with structural analysis that indicates delamanid and pretomanid bind to Ddn differently. We suggest that the mutations identified in this work be monitored for informed use of delamanid and pretomanid treatment and to slow the emergence of resistance.

Empirical ways to identify novel Bedaquiline resistance mutations in AtpE

Clinical resistance against Bedaquiline, the first new anti-tuberculosis compound with a novel mechanism of action in over 40 years, has already been detected in Mycobacterium tuberculosis. As a new drug, however, there is currently insufficient clinical data to facilitate reliable and timely identification of genomic determinants of resistance. Here we investigate the structural basis for M. tuberculosis associated bedaquiline resistance in the drug target, AtpE. Together with the 9 previously identified resistance-associated variants in AtpE, 54 non-resistance-associated mutations were identified through comparisons of bedaquiline susceptibility across 23 different mycobacterial species. Computational analysis of the structural and functional consequences of these variants revealed that resistance associated variants were mainly localized at the drug binding site, disrupting key interactions with bedaquiline leading to reduced binding affinity. This was used to train a supervised predictive algorithm, which accurately identified likely resistance mutations (93.3% accuracy). Application of this model to circulating variants present in the Asia-Pacific region suggests that current circulating variants are likely to be susceptible to bedaquiline. We have made this model freely available through a user-friendly web interface called SUSPECT-BDQ, StrUctural Susceptibility PrEdiCTion for bedaquiline (http://biosig.unimelb.edu.au/suspect_bdq/). This tool could be useful for the rapid characterization of novel clinical variants, to help guide the effective use of bedaquiline, and to minimize the spread of clinical resistance.

Aminoglycoside Revival: Review of a Historically Important Class of Antimicrobials Undergoing Rejuvenation

Aminoglycosides are cidal inhibitors of bacterial protein synthesis that have been utilized for the treatment of serious bacterial infections for almost 80 years. There have been approximately 15 members of this class approved worldwide for the treatment of a variety of infections, many serious and life threatening. While aminoglycoside use declined due to the introduction of other antibiotic classes such as cephalosporins, fluoroquinolones, and carbapenems, there has been a resurgence of interest in the class as multidrug-resistant pathogens have spread globally. Furthermore, aminoglycosides are recommended as part of combination therapy for empiric treatment of certain difficult-to-treat infections. The development of semisynthetic aminoglycosides designed to overcome common aminoglycoside resistance mechanisms, and the shift to once-daily dosing, has spurred renewed interest in the class. Plazomicin is the first new aminoglycoside to be approved by the FDA in nearly 40 years, marking the successful start of a new campaign to rejuvenate the class.

Oxazolidinones Can Replace Clarithromycin in Combination with Rifampin in a Mouse Model of Buruli Ulcer

Rifampin (RIF) plus clarithromycin (CLR) for 8 weeks is now the standard of care for Buruli ulcer (BU) treatment, but CLR may not be an ideal companion for rifamycins due to bidirectional drug-drug interactions. The oxazolidinone linezolid (LZD) was previously shown to be active against Mycobacterium ulcerans infection in mice but has dose- and duration-dependent toxicity in humans. Sutezolid (SZD) and tedizolid (TZD) may be safer than LZD. Here, we evaluated the efficacy of these oxazolidinones in combination with rifampin in a murine BU model. Mice with M. ulcerans-infected footpads received control regimens of RIF plus either streptomycin (STR) or CLR or test regimens of RIF plus either LZD (1 of 2 doses), SZD, or TZD for up to 8 weeks. All combination regimens reduced the swelling and bacterial burden in footpads after two weeks of treatment compared with RIF alone. RIF+SZD was the most active test regimen, while RIF+LZD was also no less active than RIF+CLR. After 4 and 6 weeks of treatment, neither CLR nor the oxazolidinones added significant bactericidal activity to RIF alone. By the end of 8 weeks of treatment, all regimens rendered footpads culture negative. We conclude that SZD and LZD warrant consideration as alternative companion agents to CLR in combination with RIF to treat BU, especially when CLR is contraindicated, intolerable, or unavailable. Further evaluation could prove SZD superior to CLR in this combination.

Triple oral beta-lactam containing therapy for Buruli ulcer treatment shortening

The potential use of clinically approved beta-lactams for Buruli ulcer (BU) treatment was investigated with representative classes analyzed in vitro for activity against Mycobacterium ulcerans. Beta-lactams tested were effective alone and displayed a strong synergistic profile in combination with antibiotics currently used to treat BU, i.e. rifampicin and clarithromycin; this activity was further potentiated in the presence of the beta-lactamase inhibitor clavulanate. In addition, quadruple combinations of rifampicin, clarithromycin, clavulanate and beta-lactams resulted in multiplicative reductions in their minimal inhibitory concentration (MIC) values. The MIC of amoxicillin against a panel of clinical isolates decreased more than 200-fold within this quadruple combination. Amoxicillin/clavulanate formulations are readily available with clinical pedigree, low toxicity, and orally and pediatric available; thus, supporting its potential inclusion as a new anti-BU drug in current combination therapies.

Buruli ulcer (BU) is a chronic debilitating disease of the skin and soft tissue, mainly affecting children and young adults in tropical regions. Before 2004, the only treatment option was surgery; a major breakthrough was the discovery that BU could be cured in most cases with a standard treatment that involved 8 weeks of combination therapy with rifampicin and streptomycin. However, the use of streptomycin is often associated with severe side effects such as ototoxicity, or nephrotoxicity. More recently, a clinical trial demonstrated equipotency of replacing the injectable streptomycin by the clarithromycin, which is orally available and associated with fewer side effects. BU treatment is now moving toward a full orally available treatment of clarithromycin-rifampicin. Although effective and mostly well tolerated, this new treatment is still associated with side effects and only moxifloxacin is additionally recommended by WHO for BU therapy. New drugs are thus needed to increase the number of available treatments, reduce side effects, and improve efficacy with treatments shorter than 8 weeks. In this work, we describe for the first time the potential inclusion of beta-lactams in BU therapy. More specifically, we propose the use of amoxicillin/clavulanate since it is oral, suitable for the treatment of children, and readily available with a long track record of clinical pedigree. Its inclusion in a triple oral therapy complementing current combinatorial rifampicin-clarithromycin treatment has the potential to counteract resistance development and to reduce length of treatment and time to cure.

Targeting the Mycobacterium ulcerans cytochrome bc1:aa3 for the treatment of Buruli ulcer

Mycobacterium ulcerans is the causative agent of Buruli ulcer, a neglected tropical skin disease that is most commonly found in children from West and Central Africa. Despite the severity of the infection, therapeutic options are limited to antibiotics with severe side effects. Here, we show that M. ulcerans is susceptible to the anti-tubercular drug Q203 and related compounds targeting the respiratory cytochrome bc₁:aa₃. While the cytochrome bc₁:aa₃ is the primary terminal oxidase in Mycobacterium tuberculosis, the presence of an alternate bd-type terminal oxidase limits the bactericidal and sterilizing potency of Q203 against this bacterium. M. ulcerans strains found in Buruli ulcer patients from Africa and Australia lost all alternate terminal electron acceptors and rely exclusively on the cytochrome bc₁:aa₃ to respire. As a result, Q203 is bactericidal at low dose against M. ulcerans replicating in vitro and in mice, making the drug a promising candidate for Buruli ulcer treatment.

Mycobacterium ulcerans is the causative agent of Buruli ulcer (BU). Existing anti-tubercular drugs have been used to treat the condition with varying success. Here, the authors show that a clinical-stage drug candidate for tuberculosis, Q203, is effective at killing M. ulcerans and is a promising therapeutic candidate for BU.

Isoniazid Pharmacokinetics in the Presence of Ofloxacin and Norfloxacin Antibiotics

The in vivo effects of norfloxacin (NXC) and ofloxacin (OXC) on isoniazid (INH) pharmacokinetics were investigated in 5 apparently healthy volunteers aged 18-39 years after an informed consent. The study was carried out in 3 phases with an interval drug wash out period of at least 1 week in between the phases. In phase 1 (INH alone), subject received 300 mg (usual adult dose) of INH. In phase 2 (INH + OXC), 300 mg of INH was coadministered with 200 mg of OXC, and in phase 3 (INH + NXC) each received 300 mg of INH together with 400 mg of NXC after 1-week drug wash period. Drugs were taken orally with 350 mL of water after an overnight fast, and the subject fasted 3 hours after drug. Plasma, saliva, and urine concentration of INH were predetermined at zero hour, then hourly until the eighth hour, 12 hours, 24 hours, and finally at 48 hours. The urine samples were further collected at 72 hours after drug(s) administration using validated methods. Various pharmacokinetics parameters were calculated. Various pharmacokinetic parameters of INH significantly differed when administered alone or in combination with OXC or with NXC. The mean saliva to plasma ratio of INH concentration was 0.14. The bioavailability indices of INH in the saliva and plasma were similar in all the groups. NXC and OXC reduced the extent and rate of absorption of INH. The determination of INH levels in saliva may be useful in therapeutic drug monitoring and pharmacokinetic studies.

In Silico Screening of Isocitrate Lyase for Novel Anti-Buruli Ulcer Natural Products Originating from Africa

Buruli ulcer (BU) is caused by Mycobacterium ulcerans and is predominant in both tropical and subtropical regions. The neglected debilitating disease is characterized by chronic necrotizing skin lesions attributed to a mycolactone, which is a macrolide toxin secreted by M. ulcerans. The preferred treatment is surgical excision of the lesions followed by a prolonged combination antibiotic therapy using existing drugs such as rifampicin and streptomycin or clarithromycin. These antibiotics appear not to be adequately potent and efficacious against persistent and late stage ulcers. In addition, emerging drug resistance to treatment poses great challenges. There is a need to identify novel natural product-derived lead compounds, which are potent and efficacious for the treatment of Buruli ulcer. Natural products present a rich diversity of chemical compounds with proven activity against various infectious diseases, and therefore, are considered in this study. This study sought to computationally predict natural product-derived lead compounds with the potential to be developed further into potent drugs with better therapeutic efficacy than the existing anti-buruli ulcer compounds. The three-dimensional (3D) structure of Isocitrate lyase (ICL) of Mycobacterium ulcerans was generated using homology modeling and was further scrutinized with molecular dynamics simulations. A library consisting of 885 compounds retrieved from the AfroDb database was virtually screened against the validated ICL model using AutoDock Vina. AfroDb is a compendium of “drug-like” and structurally diverse 3D structures of natural products originating from different geographical regions in Africa. The molecular docking with the ICL model was validated by computing a Receiver Operating Characteristic (ROC) curve with a reasonably good Area Under the Curve (AUC) value of 0.89375. Twenty hit compounds, which docked firmly within the active site pocket of the ICL receptor, were assessed via in silico bioactivity and pharmacological profiling. The three compounds, which emerged as potential novel leads, comprise ZINC38143792 (Euscaphic acid), ZINC95485880, and ZINC95486305 with reasonable binding energies (high affinity) of −8.6, −8.6, and −8.8 kcal/mol, respectively. Euscaphic acid has been reported to show minimal inhibition against a drug-sensitive strain of M. tuberculosis. The other two leads were both predicted to possess dermatological activity while one was antibacterial. The leads have shown promising results pertaining to efficacy, toxicity, pharmacokinetic, and safety. These leads can be experimentally characterized to assess their anti-mycobacterial activity and their scaffolds may serve as rich skeletons for developing anti-buruli ulcer drugs.

Antibiotic complications during the treatment of Mycobacterium ulcerans disease in Australian patients

BACKGROUND

Antibiotics are the recommended first-line treatment for Mycobacterium ulcerans disease. Antibiotic toxicity is common in Australian patients, yet antibiotic complication rates and their risk factors have not been determined.

AIM

To determine the incidence rate and risk factors for antibiotic toxicity in Australian patients treated for M. ulcerans disease.

METHODS

An analysis of severe antibiotic complications was performed using data from a prospective cohort of M. ulcerans cases managed at Barwon Health from 1 January 1998 to 30 June 2016. A severe antibiotic complication was defined as an antibiotic adverse event that required its cessation. Antibiotic complication rates and their associations were assessed using a Poisson regression model.

RESULTS

A total of 337 patients was included; 184 (54.6%) males and median age 57 years (interquartile range (IQR) 36-73 years). Median antibiotic treatment duration was 56 days (IQR 49-76 days). Seventy-five (22.2%) patients experienced severe antibiotic complications after a median 28 days (IQR 17-45 days) at a rate of 141.53 per 100 person-years (95% confidence interval (CI) 112.86-177.47). Eleven (14.7%) patients required hospitalisation. Compared with rifampicin/clarithromycin combinations, severe complication rates were not increased for rifampicin/ciprofloxacin (rate ratio (RR) 1.49, 95% CI 0.89-2.50, P = 0.13) or rifampicin/moxifloxacin (RR 2.54, 95% CI 0.76-8.50, P = 0.13) combinations, but were significantly increased for 'other' combinations (RR 2.53, 95% CI 1.13-5.68, P = 0.03). In a multivariable analysis, severe complication rates were significantly increased with reduced estimated glomerular filtration rates (EGFR) (adjusted rate ratio (aRR) 2.65, 95% CI 1.24-5.65 for EGFR 60-89 mL/min and aRR 1.31, 95% CI 0.49-3.53 for EGFR 0-59 mL/min compared with EGFR ≥90 mL/min, P < 0.01) and female gender (aRR 2.15, 95% CI 1.38-3.30, P < 0.01).

CONCLUSIONS

Severe antibiotic complications during M. ulcerans treatment are high with increased rates independently associated with reduced renal function and female gender.

Buruli Ulcer, a Prototype for Ecosystem-Related Infection, Caused by Mycobacterium ulcerans

Buruli ulcer is a noncontagious disabling cutaneous and subcutaneous mycobacteriosis reported by 33 countries in Africa, Asia, Oceania, and South America. The causative agent, Mycobacterium ulcerans, derives from Mycobacterium marinum by genomic reduction and acquisition of a plasmid-borne, nonribosomal cytotoxin mycolactone, the major virulence factor. M. ulcerans-specific sequences have been readily detected in aquatic environments in food chains involving small mammals. Skin contamination combined with any type of puncture, including insect bites, is the most plausible route of transmission, and skin temperature of <30°C significantly correlates with the topography of lesions. After 30 years of emergence and increasing prevalence between 1970 and 2010, mainly in Africa, factors related to ongoing decreasing prevalence in the same countries remain unexplained. Rapid diagnosis, including laboratory confirmation at the point of care, is mandatory in order to reduce delays in effective treatment. Parenteral and potentially toxic streptomycin-rifampin is to be replaced by oral clarithromycin or fluoroquinolone combined with rifampin. In the absence of proven effective primary prevention, avoiding skin contamination by means of clothing can be implemented in areas of endemicity. Buruli ulcer is a prototype of ecosystem pathology, illustrating the impact of human activities on the environment as a source for emerging tropical infectious diseases.

Bedaquiline Inhibits the ATP Synthase in Mycobacterium abscessus and Is Effective in Infected Zebrafish

Pulmonary infections caused by Mycobacterium abscessus are emerging as a global threat, especially in cystic fibrosis patients. Further intensifying the concern of M. abscessus infection is the recent evidence of human-to-human transmission of the infection. M. abscessus is a naturally multidrug-resistant fast-growing pathogen for which pharmacological options are limited. Repurposing antitubercular drugs represents an attractive option for the development of chemotherapeutic alternatives against M. abscessus infections. Bedaquiline (BDQ), an ATP synthase inhibitor, has recently been approved for the treatment of multidrug-resistant tuberculosis. Herein, we show that BDQ has a very low MIC against a vast panel of clinical isolates. Despite being bacteriostatic in vitro, BDQ was highly efficacious in a zebrafish model of M. abscessus infection. Remarkably, a very short period of treatment was sufficient to protect the infected larvae from M. abscessus-induced killing. This was corroborated with reduced numbers of abscesses and cords, considered to be major pathophysiological signs in infected zebrafish. Mode-of-action studies revealed that BDQ triggered a rapid depletion of ATP in M. abscessusin vitro, consistent with the drug targeting the F_oF₁ ATP synthase. Importantly, despite a failure to select in vitro for spontaneous mutants that are highly resistant to BDQ, the transfer of single nucleotide polymorphisms leading to D29V or A64P substitutions in atpE conferred high resistance, thus resolving the target of BDQ in M. abscessus Overall, this study indicates that BDQ is active against M. abscessusin vitro and in vivo and should be considered for clinical use against the difficult-to-manage M. abscessus pulmonary infections.

Effectiveness of purified methylene blue in an experimental model of Mycobacterium ulcerans infection

Mycobacterium ulcerans is responsible for Buruli ulcer, characterised by extensive, disabling ulcers. Standard treatment combining rifampicin and streptomycin exposes patients to toxicity and daily painful injections. In this study, the in vitro susceptibilities of 3 M. ulcerans strains, 1 Mycobacterium marinum strain and 18 strains representative of eleven other Mycobacterium species and subspecies to methylene blue were determined. Whilst growth of M. ulcerans was inhibited by 0.0125 g/L methylene blue, growth of all other tested strains was not inhibited by 1 g/L methylene blue. The effectiveness of methylene blue in a murine model of M. ulcerans infection was then tested. Topical treatment by brushing a methylene blue solution on the skin lesion, systemic treatment by intraperitoneal injection of methylene blue, and a combined treatment (topical and systemic) were tested. The three treatment groups exhibited a significantly lower clinical score compared with the non-treated control group (P <0.05). Moreover, subcutaneous nodules were significantly smaller in the systemic treatment group (excluding males) (3 ± 0.7 mm) compared with the other groups (P <0.05). The M. ulcerans insertion sequence IS2404 and the KR-B gene were detected in all challenged mice, but not in negative controls. The density of M. ulcerans (mycobacteria/cell) was significantly lower in the combined treatment group compared with the other groups. These data provide evidence for the effectiveness of purified methylene blue against the initial stage of Buruli ulcer.

Susceptibility Profiles of Mycobacterium ulcerans Isolates to Streptomycin and Rifampicin in Two Districts of the Eastern Region of Ghana

Background. Drug resistance is a major challenge in antibiotic chemotherapy. Assessing resistance profiles of pathogens constitutes an essential surveillance tool in the epidemiology and control of infectious diseases, including Buruli ulcer (BU) disease. With the successful definitive management of BU using rifampicin and streptomycin, little attention had been paid to monitoring emergence of resistant Mycobacterium ulcerans (M. ulcerans) isolates in endemic communities. This study investigated the susceptibility profiles of M. ulcerans isolates from two BU endemic areas in Ghana to streptomycin and rifampicin. Methods. The antibiotic susceptibility of seventy (70) M. ulcerans isolates to rifampicin and streptomycin was determined simultaneously at critical concentrations of 40 µg/mL and 4 µg/mL, respectively, by the Canetti proportion method. Results. Resistance to rifampicin was observed for 12 (17.1%) M. ulcerans isolates tested, whilst 2 (2.9%) showed resistance to streptomycin. None of the isolates tested showed dual resistance to both rifampicin and streptomycin. Conclusion. Outcomes from this study may not be reflective of all BU endemic communities; it, however, provides information on the resistance status of the isolates, which is useful for monitoring of M. ulcerans, as well as BU disease surveillance and control.

Leveraging Advances in Tuberculosis Diagnosis and Treatment to Address Nontuberculous Mycobacterial Disease

Recent advances in TB diagnosis and treatment must be considered in the basic scientific research of other mycobacterial diseases.

The nontuberculous mycobacteria (NTM), defined as any mycobacterial pathogen other than Mycobacterium tuberculosis or Mycobacterium leprae, are a diverse group of pathogens that collectively cause a substantive but often unappreciated worldwide burden of illness. Although NTMs may cause illness similar to M. tuberculosis, these pathogens generally do not respond to classic tuberculosis (TB) drug regimens, resulting in misdiagnosis and poor treatment, particularly in resource-poor settings. Although a few high-quality epidemiologic surveys have been made on the topic, existing evidence suggests that NTM-associated disease is much more common than previously thought: more common than TB in the industrialized world and likely increasing in prevalence globally. Despite this evidence, these organisms remain markedly understudied, and few international grants support basic science and clinical research. Here we suggest that the considerable efforts in developing new treatments and diagnostics for TB can be harnessed in the fight against NTM-associated illnesses.

Sterilizing Activity of Fully Oral Intermittent Regimens against Mycobacterium Ulcerans Infection in Mice

BACKGROUND

The treatment of Buruli ulcer (BU) that is caused by Mycobacterium ulcerans, is currently based on a daily administration of rifampin and streptomycin (RIF-STR). A fully oral intermittent regimen would greatly simplify its treatment on the field.

METHODOLOGY/PRINCIPAL FINDINGS

The objective of this study was to assess the bactericidal and sterilizing activities of intermittent oral regimens in a murine model of established M. ulcerans infection. Regimens combining rifapentine (RFP 20 mg/kg) with either moxifloxacin (MXF 200 mg/kg), clarithromycin (CLR 100 mg/kg) or bedaquiline (BDQ 25 mg/kg) were administrated twice (2/7) or three (only for RFP-CLR 3/7) times weekly during 8 weeks. The bactericidal but also the sterilizing activities of these four intermittent oral regimens were at least as good as those obtained with control weekdays regimens, i.e. RFP-CLR 5/7 or RIF-STR 5/7. A single mouse from the RFP-MFX 2/7 group had culture-positive relapse at the end of the 28 weeks following treatment completion among the 157 mice treated with one of the four intermittent regimens (40 RFP-CLR 2/7, 39 RFP-CLR 3/7, 39 RFP-MXF 2/7, 39 RFP-BDQ 2/7).

CONCLUSIONS/SIGNIFICANCE

These results open the door for a fully intermittent oral drug regimen for BU treatment avoiding intramuscular injections and facilitating supervision by health care workers.

A tanshinone I derivative enhances the activities of antibiotics against Staphylococcus aureus in vitro and in vivo

Infections caused by Staphylococcus aureus are prevalent. The dramatically reduced discovery of new antibiotics, as well as the persistent emergence of resistant bacteria, represents a major health problem in both hospital and community settings. Using antibiotic enhancers to rescue existing classes of antibiotics is an attractive strategy. In this study, 16-aldehyde tanshinone I (ALT) was synthesized and bacteriostatic activity was explored. In addition, synergistic or additive activity between ALT and aminoglycoside antibiotics or β-lactam antibiotics in vitro was identified. Moreover, ALT was documented to augment clearance of streptomycin (STR) and ampicillin (AMP) against S. aureus in a murine infection model. Primary mechanistic insight indicated that ALT could damage the bacterial cell membrane, leading to accumulation of antibiotics inside bacterial cells. This finding might be useful for treating infections caused by S. aureus and expand the scope of application of tanshinones.

Comparative Study of Activities of a Diverse Set of Antimycobacterial Agents against Mycobacterium tuberculosis and Mycobacterium ulcerans

A library of compounds covering a broad chemical space was selected from a tuberculosis drug development program and was screened in a whole-cell assay against Mycobacterium ulcerans, the causative agent of the necrotizing skin disease Buruli ulcer. While a number of potent antitubercular agents were only weakly active or inactive against M. ulcerans, five compounds showed high activity (90% inhibitory concentration [IC90], ≤1 μM), making screening of focused antitubercular libraries a good starting point for lead generation against M. ulcerans.

Mycobacterium ulcerans in the Elderly: More Severe Disease and Suboptimal Outcomes

Background

The clinical presentation of M. ulcerans disease and the safety and effectiveness of treatment may differ in elderly compared with younger populations related to relative immune defficiencies, co-morbidities and drug interactions. However, elderly populations with M. ulcerans disease have not been comprehensively studied.

Methodology/Principal Findings

A retrospective analysis was performed on an observational cohort of all confirmed M. ulcerans cases managed at Barwon Health from 1/1/1998-31/12/2014. The cohort included 327 patients; 131(40.0%) ≥65 years and 196(60.0%) <65 years of age. Patients ≥65 years had a shorter median duration of symptoms prior to diagnosis (p<0.01), a higher proportion with diabetes (p<0.001) and immune suppression (p<0.001), and were more likely to have lesions that were multiple (OR 4.67, 95% CI 1.78–12.31, p<0.001) and WHO category 3 (OR 4.59, 95% CI 1.98–10.59, p<0.001). Antibiotic complications occurred in 69(24.3%) treatment episodes at an increased incidence in those aged ≥65 years (OR 5.29, 95% CI 2.81–9.98, p<0.001). There were 4(1.2%) deaths, with significantly more in the age-group ≥65 years (4 compared with 0 deaths, p = 0.01). The overall treatment success rate was 92.2%. For the age-group ≥65 years there was a reduced rate of treatment success overall (OR 0.34, 95% CI 0.14–0.80, p = <0.01) and when surgery was used alone (OR 0.21, 95% CI 0.06–0.76, p<0.01). Patients ≥65 years were more likely to have a paradoxical reaction (OR 2.06, 95% CI 1.17–3.62, p = 0.01).

Conclusions/Significance

Elderly patients comprise a significant proportion of M. ulcerans disease patients in Australian populations and present with more severe and advanced disease forms. Currently recommended treatments are associated with increased toxicity and reduced effectiveness in elderly populations. Increased efforts are required to diagnose M. ulcerans earlier in elderly populations, and research is urgently required to develop more effective and less toxic treatments for this age-group.

Mycobacterium ulcerans is an infection that can affect all age-groups. It causes necrosis of skin and soft-tissue often resulting in severe outcomes and long-term disability. However, due to the majority of infections worldwide occurring in children and young adults, there is a paucity of information available in elderly patients. It is important that elderly patients are not neglected as the clinical presentation and treatment outcomes may differ significantly from younger patients related to relative immune defficiencies, co-morbidities and increased potential for drug interactions. We specifically examined patients with M. ulcerans disease aged ≥ 65 years and showed that they comprise a significant proportion of patients affected in Australian populations. They present with more severe and advanced disease forms, and suffer from increased toxicity and reduced effectiveness of the currently recommended treatments. Therefore, our study demonstrates that increased efforts are required to diagnose M. ulcerans disease earlier in elderly populations, and that research is urgently required to develop more effective and less toxic treatments for this age-group.

Effect of ofloxacin and norfloxacin on rifampicin pharmacokinetics in man

The in vivo effects of norfloxacin (NXC) and ofloxacin (OXC) on rifampicin (RIF) pharmacokinetics were investigated in 5 apparently healthy volunteers aged 18-39 years after informed consent. The study was carried out in 3 phases with an interval drug washout period of at least 1 week in between the phases. In phase 1 (RIF alone), the subject received 600 mg of RIF. In phase 2 (RIF + OXC), 600 mg of RIF was coadministered with 200 mg of OXC. In phase 3 (RIF + NXC), each subject received 600 mg of RIF together with 400 mg of NXC after 1 week drug washout period. Drugs were taken orally with 350 mL of water after an overnight fast, and the subjects fasted 3 hours after the administration of drug. Plasma, saliva, and urine concentration of RIF were predetermined at 0 hour and then hourly until the 8th, 12th, 24th, and 48th hour. The urine samples were further collected at 72 hours after drug(s) administration using validated methods. Various pharmacokinetics parameters were calculated. NXC reduced the extent and rate of absorption of RIF. Various pharmacokinetic parameters of RIF significantly differ when administered alone or in combination with OXC and NXC. The mean saliva to plasma ratio of RIF concentration was approximately 0.15. The bioavailability indices of RIF in the saliva and plasma were similar in all the groups. Several pharmacokinetic parameters could be calculated using different body fluid concentrations of RIF. The determination of RIF levels in saliva may be useful in therapeutic drug monitoring and pharmacokinetic studies.

Bedaquiline for the treatment of multidrug-resistant tuberculosis: great promise or disappointment?

Acquired drug resistance by Mycobacterium tuberculosis (MTB) may result in treatment failure and death. Bedaquiline was recently approved for the treatment of multidrug-resistant tuberculosis (MDR-TB). This report examines the available data on this novel drug for the treatment of MDR-TB. PubMed searches, last updated 18 February 2015, using the terms bedaquiline, TMC 207 and R207910 identified pertinent English citations. Citation reference lists were reviewed to identify other relevant reports. Pertinent MDR-TB treatment reports on the US Food and Drug Administration, Centers for Disease Control and Prevention (CDC), World Health Organization (WHO) and Cochrane websites were also evaluated. Bedaquiline is an adenosine triphosphate (ATP) synthase inhibitor specific for MTB and some nontuberculous mycobacteria. The early bactericidal activity (EBA) of bedaquiline is delayed until ATP stores are depleted but subsequently it is similar to the EBA of isoniazid and rifampin. Bedaquiline demonstrated excellent minimum inhibitory concentrations (MICs) against both drug-sensitive and MDR-TB. Adding it to the WHO-recommended MDR-TB regimen reduced the time for sputum culture conversion in pulmonary MDR-TB. Rifampin, other cytochrome oxidase 3A4 inducers or inhibitors alter its metabolism. Adverse effects are common with MDR-TB treatment regimens with or without bedaquiline. Nausea is more common with bedaquiline and it increases the QTcF interval. It is not recommended for children, pregnant or lactating women. More patients died in the bedaquiline-treatment arms despite better microbiological outcomes in two recent trials. The WHO and CDC published interim guidelines that recommend restricting its use to patients with MDR-TB or more complex drug resistance who cannot otherwise be treated with a minimum of three effective drugs. It should never be added to a regimen as a single drug nor should it be added to a failing regimen to prevent the emergence of bedaquiline-resistant strains.

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.

TMC207 becomes bedaquiline, a new anti-TB drug

TB still represents a serious public health problem. The latest reports estimate an incidence of 8.7 million cases in 2011 and 1.4 million deaths. Drug resistance contributed an estimated 630,000 cases of multidrug-resistant TB, making control of the disease harder. Recent reports show cases of TB that were almost resistant to all available antibiotics. Therefore, there is an urgent need to develop new anti-TB drugs with the potential of reducing the current length of treatment. Bedaquiline, formerly TMC207, is a new diarylquinoline antibiotic with specific activity against Mycobacterium tuberculosis and several nontuberculous mycobacteria. It acts by inhibiting ATP synthase, interfering with the energy generation needed by the bacterial cell. Based on clinical evaluations for safety, tolerability and efficacy, bedaquiline has recently received accelerated approval for the treatment of pulmonary multidrug-resistant TB in adults. This article will review the main aspects related to the chemistry, microbiology, pharmacology, efficacy and tolerability of bedaquiline.

Pentacyclic nitrofurans with in vivo efficacy and activity against nonreplicating Mycobacterium tuberculosis

The reductively activated nitroaromatic class of antimicrobials, which include nitroimidazole and the more metabolically labile nitrofuran antitubercular agents, have demonstrated some potential for development as therapeutics against dormant TB bacilli. In previous studies, the pharmacokinetic properties of nitrofuranyl isoxazolines were improved by incorporation of the outer ring elements of the antitubercular nitroimidazole OPC-67683. This successfully increased stability of the resulting pentacyclic nitrofuran lead compound Lee1106 (referred to herein as 9a). In the current study, we report the synthesis and antimicrobial properties of 9a and panel of 9a analogs, which were developed to increase oral bioavailability. These hybrid nitrofurans remained potent inhibitors of Mycobacterium tuberculosis with favorable selectivity indices (>150) and a narrow spectrum of activity. In vivo, the pentacyclic nitrofuran compounds showed long half-lives and high volumes of distribution. Based on pharmacokinetic testing and lack of toxicity in vivo,9a remained the series lead. 9a exerted a lengthy post antibiotic effect and was highly active against nonreplicating M. tuberculosis grown under hypoxia. 9a showed a low potential for cross resistance to current antitubercular agents, and a mechanism of activation distinct from pre-clinical tuberculosis candidates PA-824 and OPC-67683. Together these studies show that 9a is a nanomolar inhibitor of actively growing as well as nonreplicating M. tuberculosis.

Rapid, serial, non-invasive assessment of drug efficacy in mice with autoluminescent Mycobacterium ulcerans infection

Background

Buruli ulcer (BU) caused by Mycobacterium ulcerans is the world's third most common mycobacterial infection. There is no vaccine against BU and surgery is needed for patients with large ulcers. Although recent experience indicates combination chemotherapy with streptomycin and rifampin improves cure rates, the utility of this regimen is limited by the 2-month duration of therapy, potential toxicity and required parenteral administration of streptomycin, and drug-drug interactions caused by rifampin. Discovery and development of drugs for BU is greatly hampered by the slow growth rate of M. ulcerans, requiring up to 3 months of incubation on solid media to produce colonies. Surrogate markers for evaluating antimicrobial activity in real-time which can be measured serially and non-invasively in infected footpads of live mice would accelerate pre-clinical evaluation of new drugs to treat BU. Previously, we developed bioluminescent M. ulcerans strains, demonstrating proof of concept for measuring luminescence as a surrogate marker for viable M. ulcerans in vitro and in vivo. However, the requirement of exogenous substrate limited the utility of such strains, especially for in vivo experiments.

Methodology/Principal Finding

For this study, we engineered M. ulcerans strains that express the entire luxCDABE operon and therefore are autoluminescent due to endogenous substrate production. The selected reporter strain displayed a growth rate and virulence similar to the wild-type parent strain and enabled rapid, real-time monitoring of in vitro and in vivo drug activity, including serial, non-invasive assessments in live mice, producing results which correlated closely with colony-forming unit (CFU) counts for a panel of drugs with various mechanisms of action.

Conclusions/Significance

Our results indicate that autoluminescent reporter strains of M. ulcerans are exceptional tools for pre-clinical evaluation of new drugs to treat BU due to their potential to drastically reduce the time, effort, animals, compound, and costs required to evaluate drug activity.

The discovery and development of new drugs to improve the treatment of BU is greatly hampered by the slow growth rate of the organism, which requires up to 3 months to form countable colonies on solid media. Here, we engineered a virulent reporter strain of M. ulcerans with intrinsic bioluminescence to enable serial, real-time, non-invasive in vivo monitoring of viable bacterial counts and demonstrate its utility for high-throughput in vitro and in vivo screening of antibiotic efficacy using a panel of anti-mycobacterial drugs with various mechanisms of action. We show: 1) that a drug's in vitro activity against M. ulcerans is detectable in real time after as little as 2 days of exposure, and 2) that a drug's in vivo activity against M. ulcerans is detectable in as little as 1 week through rapid, serial, non-invasive assessment in live mice performed with a benchtop luminometer. This method promises dramatic reductions in time and effort as well as requirements for animals, compounds and other supplies. We believe such a strain is capable of transforming drug discovery and development efforts for BU.

The urgent need for clinical, diagnostic, and operational research for management of Buruli ulcer in Africa

Despite great advances in the diagnosis and treatment of Buruli ulcer, it is one of the least studied major neglected tropical diseases. In Africa, major constraints in the management of Buruli ulcer relate to diagnosis and treatment, and accessibility, feasibility, and delivery of services. In this Personal View, we outline key areas for clinical, diagnostic, and operational research on this disease in Africa and propose a research agenda that aims to advance the management of Buruli ulcer in Africa. A model of care is needed to increase early case detection, to diagnose the disease accurately, to simplify and improve treatment, to reduce side-effects of treatment, to deal with populations with HIV and tuberculosis appropriately, to decentralise care, and to scale up coverage in populations at risk. This approach will require commitment and support to strategically implement research by national Buruli ulcer programmes and international technical and donor organisations, combined with adaptations in programme design and advocacy. A critical next step is to build consensus for a research agenda with WHO and relevant groups experienced in Buruli ulcer care or related diseases, and we call on on them to help to turn this agenda into reality.

Incidence, clinical spectrum, diagnostic features, treatment and predictors of paradoxical reactions during antibiotic treatment of Mycobacterium ulcerans infections

Background

Paradoxical reactions from antibiotic treatment of Mycobacterium ulcerans have recently been recognized. Data is lacking regarding their incidence, clinical and diagnostic features, treatment, outcomes and risk factors in an Australian population.

Methods

Data was collected prospectively on all confirmed cases of M. ulcerans infection managed at Barwon Health Services, Australia, from 1/1/1998-31/12/2011. Paradoxical reactions were defined on clinical and histological criteria and cases were determined by retrospectively reviewing the clinical history and histology of excised lesions. A Poisson regression model was used to examine associations with paradoxical reactions.

Results

Thirty-two of 156 (21%) patients developed paradoxical reactions a median 39 days (IQR 20-73 days) from antibiotic initiation. Forty-two paradoxical episodes occurred with 26 (81%) patients experiencing one and 6 (19%) multiple episodes. Thirty-two (76%) episodes occurred during antibiotic treatment and 10 (24%) episodes occurred a median 37 days after antibiotic treatment. The reaction site involved the original lesion (wound) in 23 (55%), was separate to but within 3 cm of the original lesion (local) in 11 (26%) and was more than 3 cm from the original lesion (distant) in 8 (19%) episodes. Mycobacterial cultures were negative in 33/33 (100%) paradoxical episodes. Post-February 2009 treatment involved more cases with no antibiotic modifications (12/15 compared with 11/27, OR 5.82, 95% CI 1.12-34.07, p = 0.02) and no further surgery (9/15 compared with 2/27, OR 18.75, 95% CI 2.62-172.73, p < 0.001). Six severe cases received prednisone with marked clinical improvement. On multivariable analysis, age ≥ 60 years (RR 2.84, 95% CI 1.12-7.17, p = 0.03), an oedematous lesion (RR 3.44, 95% CI 1.11-10.70, p=0.03) and use of amikacin in the initial antibiotic regimen (RR 6.33, 95% CI 2.09-19.18, p < 0.01) were associated with an increased incidence of paradoxical reactions.

Conclusions

Paradoxical reactions occur frequently during or after antibiotic treatment of M. ulcerans infections in an Australian population and may be increased in older adults, oedematous disease forms, and in those treated with amikacin. Recognition of paradoxical reactions led to changes in management with less surgery, fewer antibiotic modifications and use of prednisolone for severe reactions.

A Review of the Evidence for Using Bedaquiline (TMC207) to Treat Multi-Drug Resistant Tuberculosis

Existing therapies for multi-drug resistant tuberculosis (MDR-TB) have substantial limitations, in terms of their effectiveness, side-effect profile, and complexity of administration. Bedaquiline is a novel diarylquinoline antibiotic that has recently been investigated as an adjunct to existing therapies for MDR-TB. Currently, limited clinical data are available to evaluate the drug’s safety and effectiveness. In two small randomized-controlled clinical studies, bedaquiline given for 8 or 24 weeks has been shown to improve surrogate microbiological markers of treatment response, but trials have not yet evaluated its impact on clinical failure and relapse. Safety concerns include an increased mortality in the bedaquiline arm of one study, an increased incidence of QT segment prolongation on electrocardiogram, and hepatotoxicity. Until further research data are available, the use of bedaquiline should be confined to settings where carefully selected patients can be closely monitored.

Amikacin-induced Fin Reduction is Mediated by Autophagy

Despite its medical use, little is known about the mechanisms underlying amikacin-induced embryotoxicity, including fin reduction, in zebrafish. In this study, we examined the expression of well-known autophagy markers mTOR (target of rapamycin), atg10 (autophagy-related gene), atg12 and LC3 (mammalian homolog of Atg8) in amikacin-treated zebrafish embryos. Our results indicated that the mRNA expression level of atg12 in the amikacin-treated group was significantly increased by 1.5-fold (p<0.05) compared with the corresponding mock control group, while the expression levels of atg10 and mTOR were significantly decreased by 0.74-fold (p<0.05) and 0.58-fold (p<0.05), respectively. Western blot analysis revealed that LC3 protein expression was induced by amikacin. Taken together, these data suggest that amikacin-induced fin reduction is mediated by fin cell autophagy.

Fin reduction is a novel and unexpected teratogenic effect of amikacin-treated zebrafish embryos

We used zebrafish as a model to assess amikacin-induced embryotoxicity. We exposed zebrafish embryos to amikacin, using different amikacin doses (0-10 ppm), durations (12-48 h), and onsets (0, 24, 48 hpf). Amikacin-induced embryonic toxicity and reduced survival rate were found dependent on the exposure dose, duration and onset. Based on immunostaining with neuron-specific antibodies, amikacin reduced the number and size of zebrafish neuromasts. In addition, Amikacin caused pelvic, dorsal and anal fin defects in dose-dependent and duration-dependent manners. Proliferating cell nuclear antigen immunostaining revealed that amikacin-induced fin defects were not due to reduction of proliferating mesenchymal cells. TUNEL assay demonstrated that amikacin-induced fin defects might not associate with apoptosis. Therefore, further investigations are required to elucidate if other cell death pathways are involved in amikacin-induced fin defects.

Treating Mycobacterium ulcerans disease (Buruli ulcer): from surgery to antibiotics, is the pill mightier than the knife?

Until 2004, the skin disease known as Buruli ulcer, caused by Mycobacterium ulcerans, could only be treated by surgery and skin grafting. Although this worked reasonably well on early lesions typically found in patients in Australia, the strategy was usually impractical on large lesions resulting from diagnostic delay in patients in rural West Africa. Based on promising preclinical studies, treatment trials in West Africa have shown that a combination of rifampin and streptomycin administered daily for 8 weeks can kill M. ulcerans bacilli, arrest the disease, and promote healing without relapse or reduce the extent of surgical excision. Improved treatment options are the focus of research that has increased tremendously since the WHO began its Global Buruli Ulcer Initiative in 1998.