First tuberculosis cases in Italy resistant to all tested drugs

Anti-tubercular activity evaluation of natural compounds by targeting Mycobacterium tuberculosis resuscitation promoting factor B inhibition: An in silico study

Tuberculosis (TB), an infectious disease caused by the Mycobacterium tuberculosis (Mtb), has been responsible for the deaths of millions of individuals around the globe. A vital protein in viral pathogenesis known as resuscitation promoting factor (RpfB) has been identified as a potential therapeutic target of anti-tuberculosis drugs. This study offered an in silico process to examine possible RpfB inhibitors employing a computational drug design pipeline. In this study, a total of 1228 phytomolecules were virtually tested against the RpfB of Mtb. These phytomolecules were sourced from the NP-lib database of the MTi-OpenScreen server, and five top hits (ZINC000044404209, ZINC000059779788, ZINC000001562130, ZINC000014766825, and ZINC000043552589) were prioritized for compute intensive docking with dock score ≤ - 8.5 kcal/mole. Later, molecular dynamics (MD) simulation and principal component analysis (PCA) were used to validate these top five hits. In the list of these top five hits, the ligands ZINC000044404209, ZINC000059779788, and ZINC000043552589 showed hydrogen bond formation with the functional residue Glu²⁹² of the RpfB protein suggesting biological significance of the binding. The RMSD study showed stable protein-ligand complexes and higher conformational consistency for the ligands ZINC000014766825, and ZINC000043552589 with RMSD 3-4 Å during 100 ns MD simulation. The overall analysis performed in the study suggested promising binding of these compounds with the RpfB protein of the Mtb at its functional site, further experimental investigation is needed to validate the computational finding.

Risk Factors for Poor Outcomes Among Patients with Extensively Drug-Resistant Tuberculosis (XDR-TB): A Scoping Review

In recent years, there has been an upsurge in cases of drug-resistant TB, and strains of TB resistant to all forms of treatment have begun to emerge; the highest level of resistance is classified as extensively drug-resistant tuberculosis (XDR-TB). There is an urgent need to prevent poor outcomes (death/default/failed treatment) of XDR-TB, and knowing the risk factors can inform such efforts. The objective of this scoping review was to therefore identify risk factors for poor outcomes among XDR-TB patients. We searched three scientific databases, PubMed, Scopus, and ProQuest, and identified 25 articles that examined relevant risk factors. Across the included studies, the proportion of patients with poor outcomes ranged from 8.6 to 88.7%. We found that the most commonly reported risk factor for patients with XDR-TB developing poor outcomes was having a history of TB. Other risk factors were human immunodeficiency virus (HIV), a history of incarceration, low body mass, being a smoker, alcohol use, unemployment, being male, and being middle-aged. Knowledge and understanding of the risk factors associated with poor outcomes of XDR-TB can help policy makers and organizations in the process of designing and implementing effective programs.

Resistance to Second-Line Anti-TB Drugs in Cambodia: A Phenotypic and Genetic Study

Background

Due to the emergence of Mycobacterium tuberculosis (M.tb) clinical isolates resistant to most potent first-line drugs (FLD), second-line drugs (SLD) are being prescribed more frequently. We explore the genetic characteristics and molecular mechanisms of M.tb isolates phenotypically resistant to SLD, including pre-extensively drug-resistant (pre-XDR) and extensively drug-resistant (XDR) isolates.

Methods

Drug-resistant (DR) M.tb isolates collected from 2012 to 2017 were tested using sequencing and phenotypic drug susceptibility testing. Genotypes were determined to explore their links with SLD resistance patterns.

Results

Of the 272 DR M.tb isolates, 6 non-multidrug resistant (non-MDR) isolates were fluoroquinolones (FQ)-resistant, 3 were XDR and 16 were pre-XDR (14 resistant to FQ and 2 to second-line injectable drugs). The most frequent mutations in FQ-resistant and second-line injectable drugs resistant isolates were gyrA D94G (15/23) and rrs a1401g (3/5), respectively. Seventy-five percent of pre-XDR isolates and 100% of XDR isolates harbored mutations conferring resistance to pyrazinamide. All XDR isolates belonged to the Beijing genotype, of which one, named XDR+, was resistant to all drugs tested. One cluster including pre-XDR and XDR isolates was observed.

Conclusion

This is the first description of SLD resistance in Cambodia. The data suggest that the proportion of XDR and pre-XDR isolates remains low but is on the rise compared to previous reports. The characterization of the XDR+ isolate in a patient who refused treatment underlines the risk of transmission in the population. In addition, genotypic results show, as expected, that the Beijing family is the main involved in pre-XDR and XDR isolates and that the spread of the Beijing pre-XDR strain is capable of evolving into XDR strain. This study strongly indicates the need for rapid interventions in terms of diagnostic and treatment to prevent the spread of the pre-XDR and XDR strains and the emergence of more resistant ones.

Handling the Hurdles on the Way to Anti-tuberculosis Drug Development

The global epidemic of tuberculosis (TB) imposes a sustained epidemiologic vigilance and investments in research by governments. Mycobacterium tuberculosis, the main causative agent of TB in human beings, is a very successful pathogen, being the main cause of death in the population among infectious agents. In 2018, ~10 million individuals were contaminated with this bacillus and became ill with TB, and about 1.2 million succumbed to the disease. Most of the success of the M. tuberculosis to linger in the population comes from its ability to persist in an asymptomatic latent state into the host and, in fact, the majority of the individuals are unaware of being contaminated. Even though TB is a treatable disease and is curable in most cases, the treatment is lengthy and laborious. In addition, the rise of resistance to first-line anti-TB drugs elicits a response from TB research groups to discover new chemical entities, preferably with novel mechanisms of action. The pathway to find a new TB drug, however, is arduous and has many barriers that are difficult to overcome. Fortunately, several approaches are available today to be pursued by scientists interested in anti-TB drug development, which goes from massively testing chemical compounds against mycobacteria, to discovering new molecular targets by genetic manipulation. This review presents some difficulties found along the TB drug development process and illustrates different approaches that might be used to try to identify new molecules or targets that are able to impair M. tuberculosis survival.

2-Aminooxazole as a Novel Privileged Scaffold in Antitubercular Medicinal Chemistry

To obtain effective eradication of numerous infectious diseases such as tuberculosis, it is important to supply the medicinal chemistry arsenal with novel chemical agents. Isosterism and bioisosterism are widely known concepts in the field of early drug discovery, and in several cases, rational isosteric replacements have contributed to improved efficacy and physicochemical characteristics throughout the hit-to-lead optimization process. However, sometimes the synthesis of isosteres might not be as straightforward as that of the parent compounds, and therefore, novel synthetic strategies must be elaborated. In this regard, we herein report the evaluation of a series of N-substituted 4-phenyl-2-aminooxazoles that, despite being isosteres of a widely used nucleus such as the 2-aminothiazole, have been only seldom explored. After elaboration of a convenient synthetic strategy, a small set of 2-aminothiazoles and their 2-aminooxazole counterparts were compared with regard to antitubercular activity and physicochemical characteristics.

A landscape of genomic alterations at the root of a near-untreatable tuberculosis epidemic

BACKGROUND

Atypical Beijing genotype Mycobacterium tuberculosis strains are widespread in South Africa and have acquired resistance to up to 13 drugs on multiple occasions. It is puzzling that these strains have retained fitness and transmissibility despite the potential fitness cost associated with drug resistance mutations.

METHODS

We conducted Illumina sequencing of 211 Beijing genotype M. tuberculosis isolates to facilitate the detection of genomic features that may promote acquisition of drug resistance and restore fitness in highly resistant atypical Beijing forms. Phylogenetic and comparative genomic analysis was done to determine changes that are unique to the resistant strains that also transmit well. Minimum inhibitory concentration (MIC) determination for streptomycin and bedaquiline was done for a limited number of isolates to demonstrate a difference in MIC between isolates with and without certain variants.

RESULTS

Phylogenetic analysis confirmed that two clades of atypical Beijing strains have independently developed resistance to virtually all the potent drugs included in standard (pre-bedaquiline) drug-resistant TB treatment regimens. We show that undetected drug resistance in a progenitor strain was likely instrumental in this resistance acquisition. In this cohort, ethionamide (ethA A381P) resistance would be missed in first-line drug-susceptible isolates, and streptomycin (gidB L79S) resistance may be missed due to an MIC close to the critical concentration. Subsequent inadequate treatment historically led to amplification of resistance and facilitated spread of the strains. Bedaquiline resistance was found in a small number of isolates, despite lack of exposure to the drug. The highly resistant clades also carry inhA promoter mutations, which arose after ethA and katG mutations. In these isolates, inhA promoter mutations do not alter drug resistance, suggesting a possible alternative role.

CONCLUSION

The presence of the ethA mutation in otherwise susceptible isolates from ethionamide-naïve patients demonstrates that known exposure is not an adequate indicator of drug susceptibility. Similarly, it is demonstrated that bedaquiline resistance can occur without exposure to the drug. Inappropriate treatment regimens, due to missed resistance, leads to amplification of resistance, and transmission. We put these results into the context of current WHO treatment regimens, underscoring the risks of treatment without knowledge of the full drug resistance profile.

ATP-binding cassette (ABC) import systems of Mycobacterium tuberculosis: target for drug and vaccine development

Nutrient procurement specifically from nutrient-limiting environment is essential for pathogenic bacteria to survive and/or persist within the host. Long-term survival or persistent infection is one of the main reasons for the overuse of antibiotics, and contributes to the development and spread of antibiotic resistance. Mycobacterium tuberculosis is known for long-term survival within the host, and develops multidrug resistance. Before and during infection, the pathogen encounters various harsh environmental conditions. To cope up with such nutrient-limiting conditions, it is crucial to uptake essential nutrients such as ions, sugars, amino acids, peptides, and metals, necessary for numerous vital biological activities. Among the various types of transporters, ATP-binding cassette (ABC) importers are essentially unique to bacteria, accessible as drug targets without penetrating the cytoplasmic membrane, and offer an ATP-dependent gateway into the cell by mimicking substrates of the importer and designing inhibitors against substrate-binding proteins, ABC importers endeavour for the development of successful drug candidates and antibiotics. Alternatively, the production of antibodies against substrate-binding proteins could lead to vaccine development. In this review, we will emphasize the role of M. tuberculosis ABC importers for survival and virulence within the host. Furthermore, we will elucidate their unique characteristics to discover emerging therapies to combat tuberculosis.

The Role of Fluoroquinolones in the Treatment of Tuberculosis in 2019

The inability to use powerful antituberculosis drugs in an increasing number of patients seems to be the biggest threat towards global tuberculosis (TB) elimination. Simplified, shorter and preferably less toxic drug regimens are being investigated for pulmonary TB to counteract emergence of drug resistance. Intensified regimens with high-dose anti-TB drugs during the first weeks of treatment are being investigated for TB meningitis to increase the survival rate among these patients. Moxifloxacin, gatifloxacin and levofloxacin are seen as core agents in case of resistance or intolerance against first-line anti-TB drugs. However, based on their pharmacokinetics (PK) and pharmacodynamics (PD), these drugs are also promising for TB meningitis and might perhaps have the potential to shorten pulmonary TB treatment if dosing could be optimized. We prepared a comprehensive summary of clinical trials investigating the outcome of TB regimens based on moxifloxacin, gatifloxacin and levofloxacin in recent years. In the majority of clinical trials, treatment success was not in favour of these drugs compared to standard regimens. By discussing these results, we propose that incorporation of extended PK/PD analysis into the armamentarium of drug-development tools is needed to clarify the role of moxifloxacin, gatifloxacin and levofloxacin for TB, using the right dose. In addition, to prevent failure of treatment or emergence of drug-resistance, PK and PD variability advocates for concentration-guided dosing in patients at risk for too low a drug-exposure.

Differentially Detectable Mycobacterium tuberculosis Cells in Sputum from Treatment-Naive Subjects in Haiti and Their Proportionate Increase after Initiation of Treatment

Measurement of the reduction in CFU in sputum of patients with TB up to 2 weeks after the initiation of treatment is the gateway test for a new TB treatment. Reports have suggested that CFU assays fail to detect the majority of viable M. tuberculosis cells in sputum samples from the majority of patients when the number of M. tuberculosis is estimated by limiting dilution (LD). In an effort to avoid potential methodologic confounders, we applied a modified version of the LD assay in a study of a geographically distinct population. We confirmed that differentially detectable (DD) M. tuberculosis is often found before treatment, albeit at lower proportionate levels than in earlier reports. Strikingly, the prevalence and proportionate representation of DD M. tuberculosis increased during standard treatment. Sublethal exposure to certain antibiotics may help generate DD M. tuberculosis cells or enrich their representation among the surviving bacteria, and this may contribute to the need for prolonged treatment with those agents in order to achieve durable cures.

Recent reports indicate that the sputum of 80% or more of treatment-naive subjects with tuberculosis recruited in England or South Africa contained more viable Mycobacterium tuberculosis cells detected by limiting dilution (LD) in liquid culture than detected as CFU. Efforts to generate such differentially detectable (DD) M. tuberculosis populations in vitro have been difficult to reproduce, and the LD assay is prone to artifact. Here, we applied a stringent version of the LD assay to sputum from 33 treatment-naive, HIV-negative Haitian subjects with drug-sensitive tuberculosis (TB) and to a second sputum sample after two weeks of standard treatment with isoniazid, rifampin, pyrazinamide, and ethambutol (HRZE) for 13 of these subjects. Twenty-one percent had statistically defined levels of DD M. tuberculosis in their pretreatment sputum at an average proportional excess over CFU of 3-fold. Sixty-nine percent of those who received HRZE had statistically defined levels of DD M. tuberculosis in their sputum, and of these, the mean proportionate excess over CFU was 7.9-fold. Thus, DD M. tuberculosis is detectable in pretreatment sputum from a significant proportion of subjects in the Western Hemisphere, and certain drugs or drug regimens, while reducing CFU, may at the same time increase the proportional representation of DD M. tuberculosis among the surviving bacilli. Monitoring DD M. tuberculosis may improve our ability to predict the efficacy of efforts to shorten treatment.

Dynamic model of tuberculosis considering multi-drug resistance and their applications

Infectious diseases have always been a problem that threatens people's health and tuberculosis is one of the major. With the development of medical scientific research, drug-resistant infectious diseases have become a more intractable threat because various drugs and antibiotics are widely used in the process of fighting against infectious diseases. In this paper, an improved dynamic model of infectious diseases considering population dynamics and drug resistance is established. The feasible region, equilibrium points and stability of the model are analyzed. Based on the existing data, this model can predict the development of the epidemic situation through numerical simulation, and put forward some relevant measures and suggestions.

Ultrasound Assisted Synthesis of 4-(Benzyloxy)-N-(3-chloro-2-(substitutedphenyl)-4-oxoazetidin-1-yl) Benzamide as Challenging Anti-Tubercular Scaffold

A series of ten novel derivatives of 4-(benzyloxy)-N-(3-chloro-2-(substituted phenyl)-4-oxoazetidin-1-yl) benzamide 6a⁻j were synthesized in good yield from the key compound 4-(benzyloxy)-N'-(substituted benzylidene) benzo hydrazide, called Schiff 's bases 5a⁻j, by Staudinger reaction ([2 + 2] ketene-imine cycloaddition reaction) with chloro acetyl chloride in the presence of catalyst tri ethylamine and solvent dimethyl formamide (DMF), by using ultra-sonication as one of the green chemistry tools. All the synthesised compounds were evaluated for in vitro anti-tubercular activity against Mycobacterium tuberculosis (MTB) and most of them showed promising activity with an IC₅₀ value of less than 1 µg/mL. To establish the safety, all the synthesized compounds were further tested for cytotoxicity against the human cancer cell line HeLa and all 6a⁻j compounds were found to be non-cytotoxic in nature. The molecular docking study was carried out with essential enzyme InhA (FabI/ENR) of Mycobacterium responsible for cell wall synthesis which suggests that 6a and 6e are the most active derivatives of the series. The theoretical evaluation of cell permeability based on Lipinski's rule of five has helped to rationalize the biological results and hence the synthesized azetidinone derivatives 6a⁻j were also analyzed for physicochemical evaluation that is, absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties and the results showed that all the derivatives could comply with essential features required for a potential lead in the anti-tubercular drug discovery process.

Evaluation of greater wax moth larvae, Galleria mellonella, as a novel in vivo model for non-tuberculosis Mycobacteria infections and antibiotic treatments

PURPOSE

To evaluate the suitability of Galleria mellonella larvae as an in vivo model and drug-screening tool for mycobacteria infections.

METHODOLOGY

Larvae were infected using a range of inoculum sizes from a variety of rapid-growing mycobacteria, including strains of M. fortuitum, M. marinum and M. aurum. Larval survival, internal bacterial burden and the effects of amikacin, ciprofloxacin, ethambutol, isoniazid and rifampicin treatment on larval survival were measured over 144 h. The effects of these anti-mycobacterial drugs on phagocytosis and circulating haemocyte numbers were also examined using microscopy.

RESULTS

Larval survival decreased after infection with M. fortuitum and M. marinum in a dose-dependent manner, but remained unaffected by M. aurum. Heat-killed bacteria did not cause larval death. Where antibiotic monotherapy was efficacious, larval survival post-infection increased in a dose-dependent fashion. However, efficacy varied between different antibiotics and species of infecting mycobacteria and, apart from rifampicin, efficacy in vivo correlated poorly with the in vitro minimum inhibitory concentrations (MICs). Combinations of antibiotics led to higher survival of infected larvae than antibiotic monotherapy. Selected antibiotic treatments that enhanced larval survival reduced the overall internal burden of infecting mycobacteria, but did not eradicate the pathogens. Administration of amikacin or ethambutol to uninfected larvae induced an initial transient increase in the numbers of circulating haemocytes and reduced the phagocytic rate of haemocytes in larvae infected with M. marinum.

CONCLUSIONS

This report demonstrates the potential of employing a wax moth larvae model for studying fast-growing mycobacteria infections, and as a cheap, effective system for initial screening of novel treatments.

Addressing the Challenges of Tuberculosis: A Brief Historical Account

Tuberculosis (TB) is a highly contagious disease that still poses a threat to human health. Mycobacterium tuberculosis (MTB), the pathogen responsible for TB, uses diverse ways in order to survive in a variety of host lesions and to subsequently evade immune surveillance; as a result, fighting TB and its associated multidrug resistance has been an ongoing challenge. The aim of this review article is to summarize the historical sequence of drug development and use in the fight against TB, with a particular emphasis on the decades between World War II and the dawn of the twenty first century (2000).

Delamanid and bedaquiline to treat multidrug-resistant and extensively drug-resistant tuberculosis in children: a systematic review

The new drugs delamanid and bedaquiline are increasingly used to treat multidrug-resistant (MDR-) and extensively drug-resistant tuberculosis (XDR-TB). As evidence is lacking, the World Health Organization recommends their use under specific conditions in adults, delamanid only being recommended in children ≥6 years of age. No systematic review has yet evaluated the efficacy, safety and tolerability of the new drugs in children. A search of peer-reviewed, scientific evidence was performed, to evaluate the efficacy/effectiveness, safety, and tolerability of delamanid or bedaquiline-containing regimens in children with confirmed M/XDR-TB. We used PubMed and Embase to identify any relevant manuscripts in English until 31 December 2016, excluding editorials and reviews. Three out of 96 manuscripts retrieved satisfied the inclusion criteria, while 93 were excluded because dealing exclusively with adults (12: 4 on delamanid and 8 on bedaquiline), being recommendations or guidelines (8 manuscripts), reviews (17 papers) or other studies (56 papers). One of the studies retrieved reported evidence on 19 M/XDR-TB children, 16 of them treated under compassionate use with delamanid (13 achieving consistent bacteriological conversion) and 3 candidates for the drug. Two studies reported details on the first paediatric case treated (and cured) with a delamanid-containing regimen. Eight trials including children were also retrieved (clinicaltrials.gov). Although the methodology used in the study was rigorous, the results are limited by the paucity of the studies available in the literature on the use of new anti-TB drugs in children. In conclusion, more evidence is needed on the use of delamanid and bedaquiline in paediatric patients.

Combined Use of Delamanid and Bedaquiline to Treat Multidrug-Resistant and Extensively Drug-Resistant Tuberculosis: A Systematic Review

The new drugs delamanid and bedaquiline are increasingly being used to treat multidrug-resistant (MDR-) and extensively drug-resistant tuberculosis (XDR-TB). The World Health Organization, based on lack of evidence, recommends their use under specific conditions and not in combination. No systematic review has yet evaluated the efficacy, safety, and tolerability of delamanid and bedaquiline used in combination. A search of peer-reviewed, scientific evidence was carried out, aimed at evaluating the efficacy/effectiveness, safety, and tolerability of delamanid and bedaquiline-containing regimens in individuals with pulmonary/extrapulmonary disease, which were bacteriologically confirmed as M/XDR-TB. We used PubMed to identify any relevant manuscripts in English up to the 23 December 2016, excluding editorials and reviews. Three out of 75 manuscripts retrieved satisfied the inclusion criteria, whilst 72 were excluded for dealing with only one drug (three studies), being recommendations (one study) or identifying need for their use (one study), focusing on drug resistance aspects (six studies) or being generic reviews/other studies (61 papers). The studies retrieved reported two XDR-TB cases observed for six months and achieving consistent sputum smear and culture conversion. Case 2 experienced a short break of bedaquiline, which was re-started after introducing verapamil. After a transient and symptom-free increase of the QT interval from week 5 to 17, it then decreased below the 500 ms threshold.

Insect Vectors of Disease: Untapped Reservoirs for New Antimicrobials?

With the increase in antibiotic resistance among infectious diseases, the need for new strategies for identifying compounds with inhibitory effects is dire. Traditional methods of genome sequencing and systematic characterization of potential antimicrobial gene clusters, although effective, are unfortunately not yielding results at a speed consistent with the rise in antimicrobial resistance. One approach could be to use a more targeted approach to antimicrobial compound discovery. Insect vectors often mediate the transmissions of parasitic infections for example, leishmaniasis, malaria, and trypanosomiasis. Within the insect, among the pathogens, are commensal and/or obligate symbiotic bacteria, which often undergo a population shift upon colonization of the insect host. The remaining bacteria may be either resistant to the effects of the respective parasites, or possibly essential for a successful colonization and continued spread of the parasite due to an obligate symbiosis between bacteria and insect host. Interestingly, these shifts are often toward groups of bacteria known to harbor many polyketide synthase and non-ribosomal peptide synthetase gene clusters involved in bioactive molecule production. This perspective explores the possibility to exploit the natural interactions between parasite, symbiont, and insect host for a more targeted approach toward natural product discovery, in an environment where potential compound producers are naturally interfacing with human pathogens.

Drug-resistant tuberculosis in Central Mozambique: the role of a rapid genotypic susceptibility testing

BACKGROUND

Genotypic molecular testing may be very helpful for tuberculosis (TB) drug-resistance surveillance and for treatment guidance in low resource settings.

METHODS

Descriptive analysis of M. tuberculosis isolates from Beira Central Hospital, Mozambique, during 2014-2015. Genotype MTBDRplus and MTBDRsl were used and patient medical records reviewed. To explore genotypic susceptibility profile of Mycobacterium tuberculosis, to first and second line drugs (SLD) in Beira Mozambique.

RESULTS

Of 155 isolates, 16.1 % (25) were multidrug resistant (MDR), 8.4 % (13) isoniazid-monoresistant and 1.3 % (2) rifampicin-monoresistant. Among MDR-TB, 22.2 % showed primary and 77.8 % represented acquired resistance. The majority of patients with drug resistance had a history of previous TB treatment. Among 125 isolates tested for ethambutol and SLD, 7.2 % (9) were resistant to ethambutol, 4.8 % (6) to fluoroquinolones and 0.8 % (1) to ethambutol and fluoroquinolones. Resistance to injectable SLD was not detected.

CONCLUSIONS

As far as we know this is the first report of a genotypic testing used to provide information about SLD resistance in Mozambique, where phenotypic susceptibility testing is usually unavailable. Extensively drug resistant TB was not detected in this isolates from Beira Mozambique.

First case of extensively drug-resistant tuberculosis treated with both delamanid and bedaquiline

The European Respiratory Journal has recently discussed delamanid and bedaquiline and their use in difficult-to-treat cases affected by multidrug-resistant tuberculosis (MDR-TB) or extensively drug-resistant (XDR-TB) [1–4]. The use of delamanid or bedaquiline is particularly important when four active drugs cannot be identified and included in a regimen, as per World Health Organization (WHO) guidelines [1–6]. Recently a debate has been initiated around the report of a severe, almost untreatable, XDR-TB case who could not access both new drugs simultaneously [7–10] due to concerns about possible additive toxicity (cardiotoxicity), as well as the lack of evidence and specific guidance on their combined use [10–13].

Report of the first case, concerns and challenges of treatment of severe XDR-TB with both delamanid and bedaquilinehttp://ow.ly/WzeB3004Cmo

Epidemiological Trends of Drug-Resistant Tuberculosis in China From 2007 to 2014: A Retrospective Study

The emergence and spread of drug-resistant tuberculosis (DR-TB) has become the major concern in global TB control nowadays due to its limited therapy options and high mortality. A comprehensive evaluation for the epidemiological trends of DR-TB in mainland China, of which TB incidences remain high, is essential but lacking. This study aimed to describe the trends of DR-TB overtime, especially multidrug-resistant TB (MDR-TB); and to identify unique characteristics of MDR-TB cases compared with drug-susceptible TB cases in Mainland China. We retrospectively analyzed surveillance data collected from 36 TB prevention and control institutions in Shandong Province, China over an 8-year period. Unique characteristics of MDR-TB were identified; Chi-square test for trends and linear regression were used to assess the changes in proportions of different resistance patterns overtime. The overall MDR rate was 6.2% in our sample population. There were no statistically significant changes in the percentage of drug-susceptible, isoniazid (INH) resistance, ethambutol (EMB) resistance, streptomycin (SM) resistance, and MDR TB during our study period except that the overall rifampin (RFP) resistance and rifampin monoresistance (RMR) increased at a yearly rate of 0.2% and 0.1%, respectively. Among those with known treatment histories, a higher MDR rate of 8.7% was observed, in which 53.9% were primary MDR-TB patients, and this rate was increasing at a yearly rate of 4.1% over our study period. MDR-TB patients were more likely to be female (odds ratio [OR], 1.23; 95% confidence interval [CI], 1.05-1.34), aged 25 to 44 years (OR, 1.67; 95%CI, 1.45-1.93), retreated (OR, 11.95; 95%CI, 9.68-14.76), having prior TB contact (OR, 1.89; 95%CI, 1.19-2.78) and having cavity (OR, 1.57; 95%CI 1.36-1.81), or bilateral disease (OR, 1.45; 95%CI 1.19-1.76) on chest radiology. Persistent high levels of MDR-TB, increasing rates of primary MDR-TB and RMR characterize DR-TB cases in mainland China; community-acquired drug resistance may be one of the most modifiable factors in future TB control strategies.

The Role of Biotin in Bacterial Physiology and Virulence: a Novel Antibiotic Target for Mycobacterium tuberculosis

Biotin is an essential cofactor for enzymes present in key metabolic pathways such as fatty acid biosynthesis, replenishment of the tricarboxylic acid cycle, and amino acid metabolism. Biotin is synthesized de novo in microorganisms, plants, and fungi, but this metabolic activity is absent in mammals, making biotin biosynthesis an attractive target for antibiotic discovery. In particular, biotin biosynthesis plays important metabolic roles as the sole source of biotin in all stages of the Mycobacterium tuberculosis life cycle due to the lack of a transporter for scavenging exogenous biotin. Biotin is intimately associated with lipid synthesis where the products form key components of the mycobacterial cell membrane that are critical for bacterial survival and pathogenesis. In this review we discuss the central role of biotin in bacterial physiology and highlight studies that demonstrate the importance of its biosynthesis for virulence. The structural biology of the known biotin synthetic enzymes is described alongside studies using structure-guided design, phenotypic screening, and fragment-based approaches to drug discovery as routes to new antituberculosis agents.

Carbapenems to Treat Multidrug and Extensively Drug-Resistant Tuberculosis: A Systematic Review

BACKGROUND

Carbapenems (ertapenem, imipenem, meropenem) are used to treat multidrug-resistant (MDR-) and extensively drug-resistant tuberculosis (XDR-TB), even if the published evidence is limited, particularly when it is otherwise difficult to identify the recommended four active drugs to be included in the regimen. No systematic review to date has ever evaluated the efficacy, safety, and tolerability of carbapenems.

METHODS

A search of peer-reviewed, scientific evidence was carried out, aimed at evaluating the efficacy/effectiveness, safety, and tolerability of carbapenem-containing regimens in individuals with pulmonary/extra-pulmonary disease which was bacteriologically confirmed as M/XDR-TB. We used PubMed to identify relevant full-text, English manuscripts up to the 20 December 2015, excluding editorials and reviews.

RESULTS

Seven out of 160 studies satisfied the inclusion criteria: two on ertapenem, one on imipenem, and four on meropenem, all published between 2005 and 2016. Of seven studies, six were retrospective, four were performed in a single center, two enrolled children, two had a control group, and six reported a proportion of XDR-TB cases higher than 20%. Treatment success was higher than 57% in five studies with culture conversion rates between 60% and 94.8%.

CONCLUSIONS

The safety and tolerability is very good, with the proportion of adverse events attributable to carbapenems below 15%.

Mycobacterium tuberculosis AtsG (Rv0296c), GlmU (Rv1018c) and SahH (Rv3248c) Proteins Function as the Human IL-8-Binding Effectors and Contribute to Pathogen Entry into Human Neutrophils

Mycobacterium tuberculosis is an extremely successful intracellular pathogen that has evolved a broad spectrum of pathogenic mechanisms that enable its manipulation of host defense elements and its survival in the hostile environment inside phagocytes. Cellular influx into the site of mycobacterial entry is mediated by a variety of chemokines, including interleukin-8 (IL-8), and the innate cytokine network is critical for the development of an adaptive immune response and infection control. Using affinity chromatography, liquid chromatography electrospray ionization tandem mass spectrometry and surface plasmon resonance techniques, we identified M. tuberculosis AtsG arylsulphatase, bifunctional glucosamine-1-phosphate acetyltransferase and N-acetylglucosamine-1-phosphate uridyl transferase (GlmU) and S-adenosyl-L-homocysteine hydrolase (SahH) as the pathogen proteins that bind to human IL-8. The interactions of all of the identified proteins (AtsG, GlmU and SahH) with IL-8 were characterized by high binding affinity with K_D values of 6.83x10^-6 M, 5.24x10^-6 M and 7.14x10^-10 M, respectively. Furthermore, the construction of Mtb mutant strains overproducing AtsG, GlmU or SahH allowed determination of the contribution of these proteins to mycobacterial entry into human neutrophils. The significantly increased number of intracellularly located bacilli of the overproducing M. tuberculosis mutant strains compared with those of “wild-type” M. tuberculosis and the binding interaction of AtsG, GlmU and SahH proteins with human IL-8 may indicate that these proteins participate in the modulation of the early events of infection with tubercle bacilli and could affect pathogen attachment to target cells.

Phenotypic and genotypic diversity in a multinational sample of drug-resistant Mycobacterium tuberculosis isolates

OBJECTIVE

To develop and evaluate rapid, molecular-based drug susceptibility testing (DST) for extensively drug-resistant tuberculosis (XDR-TB), we assembled a phenotypically and genotypically diverse collection of Mycobacterium tuberculosis isolates from patients evaluated for drug resistance in four high-burden countries.

METHODS

M. tuberculosis isolates from India (n = 111), Moldova (n = 90), the Philippines (n = 96), and South Africa (n = 103) were selected from existing regional and national repositories to maximize phenotypic diversity for resistance to isoniazid, rifampin (RMP), moxifloxacin, ofloxacin, amikacin, kanamycin, and capreomycin. MGIT™ 960 was performed on viable isolates in one laboratory using standardized procedures and drug concentrations. Genetic diversity within drug resistance phenotypes was assessed.

RESULTS

Nineteen distinct phenotypes were observed among 400 isolates with complete DST results. Diversity was greatest in the Philippines (14 phenotypes), and least in South Africa (9 phenotypes). Nearly all phenotypes included multiple genotypes. All sites provided isolates resistant to injectables but susceptible to fluoroquinolones. Many patients were taking drugs to which their disease was resistant.

DISCUSSION

Diverse phenotypes for XDR-TB-defining drugs, including resistance to fluoroquinolones and/or injectable drugs in RMP-susceptible isolates, indicate that RMP susceptibility does not ensure effectiveness of a standard four-drug regimen. Rapid, low-cost DST assays for first- and second-line drugs are thus needed.

Tackling Threats and Future Problems of Multidrug-Resistant Bacteria

With the advent of the antibiotic era, the overuse and inappropriate consumption and application of antibiotics have driven the rapid emergence of multidrug-resistant pathogens. Antimicrobial resistance increases the morbidity, mortality, length of hospitalization and healthcare costs. Among Gram-positive bacteria, Staphylococcus aureus (MRSA) and multidrug-resistant (MDR) Mycobacterium tuberculosis, and among the Gram-negative bacteria, extended-spectrum beta-lactamase (ESBLs)-producing bacteria have become a major global healthcare problem in the 21st century. The pressure to use antibiotics guarantees that the spread and prevalence of these as well as of future emerging multidrug-resistant pathogens will be a persistent phenomenon. The unfeasibility of reversing antimicrobial resistance back towards susceptibility and the critical need to treat bacterial infection in modern medicine have burdened researchers and pharmaceutical companies to develop new antimicrobials effective against these difficult-to-treat multidrug-resistant pathogens. However, it can be anticipated that antibiotic resistance will continue to develop more rapidly than new agents to treat these infections become available and a better understanding of the molecular, evolutionary and ecological mechanisms governing the spread of antibiotic resistance is needed. The only way to curb the current crisis of antimicrobial resistance will be to develop entirely novel strategies to fight these pathogens such as combining antimicrobial drugs with other agents that counteract and obstruct the antibiotic resistant mechanisms expressed by the pathogen. Furthermore, as many antibiotics are often inappropriately prescribed, a more personalized approach based on precise diagnosis tools will ensure that proper treatments can be promptly applied leading to more targeted and effective therapies. However, in more general terms, also the overall use and release of antibiotics in the environment needs to be better controlled.

Bibliometric analysis of worldwide publications on multi-, extensively, and totally drug - resistant tuberculosis (2006-2015)

BACKGROUND

The year 2015 marked the end of United Nations Millennium Development Goals which was aimed at halting and reversing worldwide tuberculosis (TB). The emergence of drug resistance is a major challenge for worldwide TB control. The aim of this study was to give a bibliometric overview of publications on multi-, extensively, and totally drug-resistant TB.

METHODS

Scopus database was used to retrieve articles on multidrug resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant (TDR) tuberculosis for the study period (2006-2015). The number of publications, top productive countries and institutions, citation analysis, co-authorships, international collaboration, active authors, and active journals were retrieved and analyzed.

RESULTS

A total of 2260 journal articles were retrieved. The mean ± SD citations per article was 7.04 ± 16.0. The h-index of retrieved data was 76. The number of publications showed a three - fold increase over the study period compared with less than two - fold increase in tuberculosis research during the same study period. Stratified by number of publications, the United States of America ranked first while Switzerland ranked first in productivity per 100 million people, and South Africa ranked first in productivity stratified per one trillion Gross Domestic Product. Three of the High Burden Countries (HBC) MDR-TB (India, China, and South Africa) were present in top productive countries. High percentage of international collaboration was seen among most HBC MDR-TB. Except for Plos One journal, most active journals in publishing articles on MDR, XDR, TDR-TB were in infection - related fields and in general medicine. Top 20 cited articles were published in prestigious journal such as Lancet and New England Journal of Medicine. The themes in top 20 cited articles were diverse, ranging from molecular biology, diagnostic tools, co-infection with HIV, and results of new anti-TB drugs.

CONCLUSION

Publications on MDR, XDR and TDR - TB are increasing in the past decade. International collaboration was common. Many low resourced African and Asian countries will benefit from research leading to new diagnostic and screening technology of TB. The exchange of expertise, ideas and technology is of paramount importance in this field.

Metabolic modeling predicts metabolite changes in Mycobacterium tuberculosis

BACKGROUND

Mycobacterium tuberculosis (MTB) is the causal agent of the disease tuberculosis (TB). Metabolic adaptations are thought to be critical to the survival of MTB during pathogenesis. Computational tools that can be used to study MTB metabolism in silico and prioritize resource-intensive experimental work could significantly accelerate research.

RESULTS

We have developed E-Flux-MFC, an enhancement of our original E-Flux method that enables the prediction of changes in the production of external and internal metabolites corresponding to gene expression measurements. We have used this method to simulate the changes in the metabolic state of Mycobacterium tuberculosis (MTB). We have validated the accuracy of E-Flux-MFC for predicting changes in lipids and metabolites during a hypoxia time course using previously published metabolomics and transcriptomics data. We have further validated the accuracy of the method for predicting changes in MTB lipids following the deletion and induction of two well-studied transcription factors (TFs). We have applied the method to predict the metabolic impact of the induction of each of the approximately 180 MTB TFs using a previously generated and publically available expression data set.

CONCLUSIONS

E-flux-MFC can be used to study global changes in MTB metabolites from gene expression data associated with environmental and genetic perturbations. The application of this method to a data set of MTB TF perturbations provides a resource for studying the large number of TFs whose functions remain unknown. Most TFs impact metabolites indirectly through the propagation of gene expression changes through the regulatory network rather than through their direct regulons. E-Flux-MFC is also applicable to any organism for which accurate metabolic models are available.

Elucidation of a protein-protein interaction network involved in Corynebacterium glutamicum cell wall biosynthesis as determined by bacterial two-hybrid analysis

Mycobacterium species have a highly complex and unique cell wall that consists of a large macromolecular structure termed the mycolyl-arabinogalactan-peptidoglycan (mAGP) complex. This complex is essential for growth, survival and virulence of the human pathogen Mycobacterium tuberculosis, and is the target of several anti-tubercular drugs. The closely related species Corynebacterium glutamicum has proven useful in the study of orthologous M. tuberculosis genes and proteins involved in mAGP synthesis. This study examines the construction of a protein-protein interaction network for the major cell wall component arabinogalactan in C. glutamicum based on the use of a bacterial two-hybrid system. We have identified twenty-four putative homotypic and heterotypic protein interactions in vivo. Our results demonstrate an association between glycosyltransferases, GlfT1 and AftB, and interaction between the sub-units of decaprenylphosphoribose epimerase, DprE1 and DprE2. These analyses have also shown that AftB interacts with AftA, which catalyzes the addition of the first three arabinose units onto the galactan chain. Both AftA and AftB associate with other arabinofuranosyltransferases, including Emb and AftC, that elongate and branch the arabinan domain. Moreover, a number of proteins involved in arabinogalactan biosynthesis were shown to form dimers or multimers. These findings provide a useful recourse for understanding the biosynthesis and function of the mycobacterial cell wall, as well as providing new therapeutic targets.

Structural and functional studies of the Mycobacterium tuberculosis VapBC30 toxin-antitoxin system: implications for the design of novel antimicrobial peptides

Toxin-antitoxin (TA) systems play important roles in bacterial physiology, such as multidrug tolerance, biofilm formation, and arrest of cellular growth under stress conditions. To develop novel antimicrobial agents against tuberculosis, we focused on VapBC systems, which encompass more than half of TA systems in Mycobacterium tuberculosis. Here, we report that theMycobacterium tuberculosis VapC30 toxin regulates cellular growth through both magnesium and manganese ion-dependent ribonuclease activity and is inhibited by the cognate VapB30 antitoxin. We also determined the 2.7-Å resolution crystal structure of the M. tuberculosis VapBC30 complex, which revealed a novel process of inactivation of the VapC30 toxin via swapped blocking by the VapB30 antitoxin. Our study on M. tuberculosis VapBC30 leads us to design two kinds of VapB30 and VapC30-based novel peptides which successfully disrupt the toxin-antitoxin complex and thus activate the ribonuclease activity of the VapC30 toxin. Our discovery herein possibly paves the way to treat tuberculosis for next generation.

Transmitted Extended-Spectrum Extensively Drug-Resistant Tuberculosis in Beijing, China, with Discordant Whole-Genome Sequencing Analysis Results

Drug resistance to tuberculosis remains a major public health threat. Here, we report two cases of extended-spectrum extensively drug-resistant (XXDR) tuberculosis showing resistance to most first- and second-line agents. The results of a correlation of whole-genome sequencing (WGS) and phenotypic testing were discordant, suggesting that overreliance on WGS may miss clinically relevant resistance in extensively drug-resistant disease.

Optimization and Evaluation of 5-Styryl-Oxathiazol-2-one Mycobacterium tuberculosis Proteasome Inhibitors as Potential Antitubercular Agents

This is the first report of 5-styryl-oxathiazol-2-ones as inhibitors of the Mycobacterium tuberculosis (Mtb) proteasome. As part of the study, the structure-activity relationship of oxathiazolones as Mtb proteasome inhibitors has been investigated. Furthermore, the prepared compounds displayed a good selectivity profile for Mtb compared to the human proteasome. The 5-styryl-oxathiazol-2-one inhibitors identified showed little activity against replicating Mtb, but were rapidly bactericidal against nonreplicating bacteria. (E)-5-(4-Chlorostyryl)-1,3,4-oxathiazol-2-one) was most effective, reducing the colony-forming units (CFU)/mL below the detection limit in only seven days at all concentrations tested. The results suggest that this new class of Mtb proteasome inhibitors has the potential to be further developed into novel antitubercular agents for synergistic combination therapies with existing drugs.

The role of delamanid in the treatment of drug-resistant tuberculosis

Tuberculosis (TB) remains a significant cause of death worldwide, and emergence of drug-resistant TB requires lengthy treatments with toxic drugs that are less effective than their first-line equivalents. New treatments are urgently needed. Delamanid, previously OPC-67863, is a novel drug of the dihydro-nitroimidazole class with potent anti-TB activity and great promise to be effective in the treatment of drug-resistant TB. This review examines the preclinical and clinical development of delamanid, reviews current guidance on its use and evaluates the opportunities and challenges for its future role in TB management.

Map the gap: missing children with drug-resistant tuberculosis

BACKGROUND

The lack of published information about children with multidrug-resistant tuberculosis (MDR-TB) is an obstacle to efforts to advocate for better diagnostics and treatment.

OBJECTIVE

To describe the lack of recognition in the published literature of MDR-TB and extensively drug-resistant TB (XDR-TB) in children.

DESIGN

We conducted a systematic search of the literature published in countries that reported any MDR- or XDR-TB case by 2012 to identify MDR- or XDR-TB cases in adults and in children.

RESULTS

Of 184 countries and territories that reported any case of MDR-TB during 2005-2012, we identified adult MDR-TB cases in the published literature in 143 (78%) countries and pediatric MDR-TB cases in 78 (42%) countries. Of the 92 countries that reported any case of XDR-TB, we identified adult XDR-TB cases in the published literature in 55 (60%) countries and pediatric XDR-TB cases for 9 (10%) countries.

CONCLUSION

The absence of publications documenting child MDR- and XDR-TB cases in settings where MDR- and XDR-TB in adults have been reported indicates both exclusion of childhood disease from the public discourse on drug-resistant TB and likely underdetection of sick children. Our results highlight a large-scale lack of awareness about children with MDR- and XDR-TB.

Quadruple burden of HIV/AIDS, tuberculosis, chronic intestinal parasitoses, and multiple micronutrient deficiency in ethiopia: a summary of available findings

Human immunodeficiency virus (HIV), tuberculosis (TB), and helminthic infections are among the commonest public health problems in the sub-Saharan African countries like Ethiopia. Multiple micronutrient deficiencies also known as the “hidden hunger” are common in people living in these countries either playing a role in their pathogenesis or as consequences. This results in a vicious cycle of multiple micronutrient deficiencies and infection/disease progression. As infection is profoundly associated with nutritional status resulting from decreased nutrient intake, decreased nutrient absorption, and nutrient losses, micronutrient deficiencies affect immune system and impact infection and diseases progression. As a result, micronutrients, immunity, and infection are interrelated. The goal of this review is therefore to provide a summary of available findings regarding the “quadruple burden trouble” of HIV, TB, intestinal parasitic infections, and multiple micronutrient deficiencies to describe immune-modulating effects related to disorders.

Global epidemiology of tuberculosis

Despite the availability of effective chemotherapy, tuberculosis (TB) killed 1.3 million people in 2012. Alongside HIV, it remains a top cause of death from an infectious disease. Global targets for reductions in the epidemiological burden of TB have been set for 2015 and 2050 within the context of the Millennium Development Goals (MDGs) and by the Stop TB Partnership. Achieving these targets is the focus of national and international efforts in TB control, and showing whether or not they are achieved is of major importance to guide future and sustainable investments. This article provides a short overview of sources of data to estimate TB disease burden; presents estimates of TB incidence, prevalence, and mortality in 2012 and an assessment of progress toward the 2015 targets for reductions in these indicators based on trends since 1990 and projections up to 2015; analyzes trends in TB notifications and in the implementation of the Stop TB Strategy; and considers prospects for elimination of TB after 2015.

Incidence of multidrug-resistant tuberculosis disease in children: systematic review and global estimates

BACKGROUND

Multidrug-resistant tuberculosis threatens to reverse recent reductions in global tuberculosis incidence. Although children younger than 15 years constitute more than 25% of the worldwide population, the global incidence of multidrug-resistant tuberculosis disease in children has never been quantified. We aimed to estimate the regional and global annual incidence of multidrug-resistant tuberculosis in children.

METHODS

We developed two models: one to estimate the setting-specific risk of multidrug-resistant tuberculosis among child cases of tuberculosis, and a second to estimate the setting-specific incidence of tuberculosis disease in children. The model for risk of multidrug-resistant tuberculosis among children with tuberculosis needed a systematic literature review. We multiplied the setting-specific estimates of multidrug-resistant tuberculosis risk and tuberculosis incidence to estimate regional and global incidence of multidrug-resistant tuberculosis disease in children in 2010.

FINDINGS

We identified 3403 papers, of which 97 studies met inclusion criteria for the systematic review of risk of multidrug-resistant tuberculosis. 31 studies reported the risk of multidrug-resistant tuberculosis in both children and treatment-naive adults with tuberculosis and were used for evaluation of the linear association between multidrug-resistant disease risk in these two patient groups. We identified that the setting-specific risk of multidrug-resistant tuberculosis was nearly identical in children and treatment-naive adults with tuberculosis, consistent with the assertion that multidrug-resistant disease in both groups reflects the local risk of transmitted multidrug-resistant tuberculosis. After application of these calculated risks, we estimated that around 999,792 (95% CI 937,877-1,055,414) children developed tuberculosis disease in 2010, of whom 31,948 (25,594-38,663) had multidrug-resistant disease.

INTERPRETATION

Our estimates underscore that many cases of tuberculosis and multidrug-resistant tuberculosis disease are not being detected in children. Future estimates can be refined as more and better tuberculosis data and new diagnostic instruments become available.

FUNDING

US National Institutes of Health, the Helmut Wolfgang Schumann Fellowship in Preventive Medicine at Harvard Medical School, the Norman E Zinberg Fellowship at Harvard Medical School, and the Doris and Howard Hiatt Residency in Global Health Equity and Internal Medicine at the Brigham and Women's Hospital.

A trisubstituted benzimidazole cell division inhibitor with efficacy against Mycobacterium tuberculosis

Trisubstituted benzimidazoles have demonstrated potency against Gram-positive and Gram-negative bacterial pathogens. Previously, a library of novel trisubstituted benzimidazoles was constructed for high throughput screening, and compounds were identified that exhibited potency against M. tuberculosis H37Rv and clinical isolates, and were not toxic to Vero cells. A new series of 2-cyclohexyl-5-acylamino-6-N, N-dimethylaminobenzimidazoles derivatives has been developed based on SAR studies. Screening identified compounds with potency against M. tuberculosis. A lead compound from this series, SB-P17G-A20, was discovered to have an MIC of 0.16 µg/mL and demonstrated efficacy in the TB murine acute model of infection based on the reduction of bacterial load in the lungs and spleen by 1.73±0.24 Log₁₀ CFU and 2.68±Log₁₀ CFU, respectively, when delivered at 50 mg/kg by intraperitoneal injection (IP) twice daily (bid). The activity of SB-P17G-A20 was determined to be concentration dependent and to have excellent stability in mouse and human plasma, and liver microsomes. Together, these studies demonstrate that SB-P17G-A20 has potency against M. tuberculosis clinical strains with varying susceptibility and efficacy in animal models of infection, and that trisubstituted benzimidazoles continue to be a platform for the development of novel inhibitors with efficacy.

In vitro-in vivo activity relationship of substituted benzimidazole cell division inhibitors with activity against Mycobacterium tuberculosis

Structure based drug design was used to develop a compound library of novel 2,5,6- and 2,5,7-trisubstituted benzimidazoles. Three structural analogs, SB-P1G10, SB-P8B2 and SB-P3G2 were selected from this library for advanced study. In vitro studies revealed that SB-P8B2 and SB-P3G2 had sigmoidal kill-curves while in contrast SB-P1G10 showed a narrow zonal susceptibility. The in vitro studies also demonstrated that exposure to SB-P8B2 or SB-P3G2 was bactericidal, while SB-P1G10 treatment never resulted in complete killing. The dose curves for the three compounds against clinical isolates were comparable to their respective dose curves in the laboratory strain of Mycobacterium tuberculosis. SB-P8B2 and SB-P3G2 exhibited antibacterial activity against non-replicating bacilli under low oxygen conditions. SB-P3G2 and SB-P1G10 were assessed in acute short-term animal models of tuberculosis, which showed that SB-P3G2 demonstrated activity against M. tuberculosis. Together, these studies reveal an in vitro-in vivo relationship of the 2,5,6-trisubstituted benzimidazoles that serves as a criterion for advancing this class of cell division inhibitors into more resource intensive in vivo efficacy models such as the long-term murine model of tuberculosis and Pre-IND PK/PD studies. Specifically, these studies are the first demonstration of efficacy and an in vitro-in vivo activity relationship for 2,5,6-trisubstituted benzimidazoles. The in vivo activity presented in this manuscript substantiates this class of cell division inhibitors as having potency and efficacy against M. tuberculosis.

Extensively drug-resistant tuberculosis: epidemiology and management

The advent of antibiotics for the treatment of tuberculosis (TB) represented a major breakthrough in the fight against the disease. However, since its first use, antibiotic therapy has been associated with the emergence of resistance to drugs. The incorrect use of anti-TB drugs, either due to prescription errors, low patient compliance, or poor quality of drugs, led to the widespread emergence of Mycobacterium tuberculosis strains with an expanding spectrum of resistance. The spread of multidrug-resistant (MDR) strains (ie, strains resistant to both isoniazid and rifampicin) has represented a major threat to TB control since the 1990s. In 2006, the first cases of MDR strains with further resistance to fluoroquinolone and injectable drugs were described and named extensively drug-resistant TB (XDR-TB). The emergence of XDR-TB strains is a result of mismanagement of MDR cases, and treatment relies on drugs that are less potent and more toxic than those used to treat drug-susceptible or MDR strains. Furthermore, treatment success is lower and mortality higher than achieved in MDR-TB cases, and the number of drugs necessary in the intensive phase of treatment may be higher than the four drugs recommended for MDR-TB. Linezolid may represent a valuable drug to treat cases of XDR-TB. Delamanid, bedaquiline, and PA-824 are new anti-TB agents in the development pipeline that have the potential to enhance the cure rate of XDR-TB. The best measures to prevent new cases of XDR-TB are the correct management of MDR-TB patients, early detection, and proper treatment of existing patients with XDR-TB.

Global control of tuberculosis: from extensively drug-resistant to untreatable tuberculosis

Extensively drug-resistant tuberculosis is a burgeoning global health crisis mainly affecting economically active young adults, and has high mortality irrespective of HIV status. In some countries such as South Africa, drug-resistant tuberculosis represents less than 3% of all cases but consumes more than a third of the total national budget for tuberculosis, which is unsustainable and threatens to destabilise national tuberculosis programmes. However, concern about drug-resistant tuberculosis has been eclipsed by that of totally and extremely drug-resistant tuberculosis--ie, resistance to all or nearly all conventional first-line and second-line antituberculosis drugs. In this Review, we discuss the epidemiology, pathogenesis, diagnosis, management, implications for health-care workers, and ethical and medicolegal aspects of extensively drug-resistant tuberculosis and other resistant strains. Finally, we discuss the emerging problem of functionally untreatable tuberculosis, and the issues and challenges that it poses to public health and clinical practice. The emergence and growth of highly resistant strains of tuberculosis make the development of new drugs and rapid diagnostics for tuberculosis--and increased funding to strengthen global control efforts, research, and advocacy--even more pressing.

The medical and surgical treatment of drug-resistant tuberculosis

Multi drug-resistant tuberculosis (MDR-TB) and extensively drug-resistant TB (XDR-TB) are burgeoning global problems with high mortality which threaten to destabilise TB control programs in several parts of the world. Of alarming concern is the emergence, in large numbers, of patients with resistance beyond XDR-TB (totally drug-resistant TB; TDR-TB or extremely drug resistant TB; XXDR-TB). Given the burgeoning global phenomenon of MDR-TB, XDR-TB and TDR-TB, and increasing international migration and travel, healthcare workers, researchers, and policy makers in TB endemic and non-endemic countries should familiarise themselves with issues relevant to the management of these patients. Given the lack of novel TB drugs and limited access to existing drugs such as linezolid and bedaquiline in TB endemic countries, significant numbers of therapeutic failures are emerging from the ranks of those with XDR-TB. Given the lack of appropriate facilities in resource-limited settings, such patients are being discharged back into the community where there is likely ongoing disease spread. In the absence of effective drug regimens, in appropriate patients, surgery is a critical part of management. Here we review the diagnosis, medical and surgical management of MDR-TB and XDR-TB.

Emergence in Western African countries of MDR-TB, focus on Côte d'Ivoire

Tuberculosis (TB) is responsible for a high mortality rate (2.5%) worldwide, mainly in developing countries with a high prevalence of human immunodeficiency virus (HIV). The emergence of multiresistant strains of TB poses an extreme risk for TB outbreaks and highlights the need for global TB control strategies. Among Western African countries, Côte d'Ivoire (CI) represents a specific example of a country with great potential to prevent TB. Specifically, CI has a promising healthcare system for monitoring diseases, including vaccination programs. However, military and political conflict in CI favors the spread of infectious diseases, TB being among the most devastating. Compilation of the studies identifying common causes of TB would be extremely beneficial for the development of treatment and prevention strategies. Therefore, the purpose of this comprehensive review is to evaluate the epidemiology of TB in CI, describe the factors involved in pathogenesis, and suggest simple and applicable prevention strategies.

Drug resistance beyond extensively drug-resistant tuberculosis: individual patient data meta-analysis

The broadest pattern of tuberculosis (TB) drug resistance for which a consensus definition exists is extensively drug-resistant (XDR)-TB. It is not known if additional drug resistance portends worsened patient outcomes. This study compares treatment outcomes of XDR-TB patients with and without additional resistance in order to explore the need for a new definition. Individual patient data on XDR-TB outcomes were included in a meta-analysis comparing outcomes between XDR alone and three nonmutually exclusive XDR-TB patient groups: XDR plus resistance to all the second-line injectables (sli) and capreomycin and kanamycin/amikacin (XDR+2sli) XDR plus resistance to second-line injectables and to more than one group 4 drug, i.e. ethionamide/protionamide, cycloserine/terizidone or para-aminosalicylic acid (XDR+sliG4) and XDR+sliG4 plus resistance to ethambutol and/or pyrazinamide (XDR+sliG4EZ). Of 405 XDR-TB cases, 301 were XDR alone, 68 XDR+2sli, 48 XDR+sliG4 and 42 XDR+sliG4EZ. In multivariate analysis, the odds of cure were significantly lower in XDR+2sli (adjusted OR 0.4, 95% CI 0.2-0.8) compared to XDR alone, while odds of failure and death were higher in all XDR patients with additional resistance (adjusted OR 2.6-2.8). Patients with additional resistance beyond XDR-TB showed poorer outcomes. Limitations in availability, accuracy and reproducibility of current drug susceptibility testing methods preclude the adoption of a useful definition beyond the one currently used for XDR-TB.

Mycobacterium tuberculosis mutation rate estimates from different lineages predict substantial differences in the emergence of drug-resistant tuberculosis

A critical question in tuberculosis control is why some strains of Mycobacterium tuberculosis are preferentially associated with multiple drug resistances. We demonstrate that M. tuberculosis strains from Lineage 2 (East Asian lineage and Beijing sublineage) acquire drug resistances in vitro more rapidly than M. tuberculosis strains from Lineage 4 (Euro-American lineage) and that this higher rate can be attributed to a higher mutation rate. Moreover, the in vitro mutation rate correlates well with the bacterial mutation rate in humans as determined by whole genome sequencing of clinical isolates. Finally, using a stochastic mathematical model, we demonstrate that the observed differences in mutation rate predict a substantially higher probability that patients infected with a drug susceptible Lineage 2 strain will harbor multidrug resistant bacteria at the time of diagnosis. These data suggest that interventions to prevent the emergence of drug resistant tuberculosis should target bacterial as well as treatment-related risk factors.

Carbohydrate recognition by RpfB from Mycobacterium tuberculosis unveiled by crystallographic and molecular dynamics analyses

Resuscitation of Mtb is crucial to the etiology of Tuberculosis, because latent tuberculosis is estimated to affect one-third of the world population. The resuscitation-promoting factor RpfB is mainly responsible for Mtb resuscitation from dormancy. Given the impact of latent Tuberculosis, RpfB represents an interesting target for tuberculosis drug discovery. However, no molecular models of substrate binding and catalysis are hitherto available for this enzyme. Here, we identified key interactions involved in substrate binding to RpfB by combining x-ray diffraction studies and computational approaches. The crystal structure of RpfB catalytic domain in complex with N,N',N"-triacetyl-chitotriose, as described here, provides the first, to our knowledge, atomic representation of ligand recognition by RpfB and demonstrates that the strongest interactions are established by the N-acetylglucosamine moiety in the central region of the enzyme binding cleft. Molecular dynamics analyses provided information on the dynamic behavior of protein-substrate interactions and on the role played by the solvent in RpfB function. These data combined with sequence conservation analysis suggest that Glu-292 is the sole residue crucial for catalysis, implying that RpfB acts via the formation of an oxocarbenium ion rather than a covalent intermediate. Present data represent a solid base for the design of effective drug inhibitors of RpfB. Moreover, homology models were generated for the catalytic domains of all members of the Mtb Rpf family (RpfA-E). The analysis of these models unveiled analogies and differences among the different members of the Rpf protein family.

From multidrug- to extensively drug-resistant tuberculosis: upward trends as seen from a 15-year nationwide study

Background

Emergence of extensively drug-resistant tuberculosis (XDR-TB) represents an enormous challenge to Public Health globally.

Methods

Progression towards XDR-TB was investigated in Belgium, a country with a typically low TB incidence, by analyzing the magnitude, characteristics, and treatment success of multidrug-resistant tuberculosis (MDR-TB) through a population-based study from 1994 to 2008.

Results

Among the 174 MDR-TB patients, 81% were foreign-born, 48% of these being asylum seekers. Although the number of MDR-TB patients remained stable through the study period at around 15 new cases annually, frequencies of resistance of the patients’ first MDR-TB isolate to second-line drugs increased, as well as the total number of antibiotics it was resistant to (p<0.001). XDR-TB cases were detected from 2002 onwards. For 24 patients, additional resistance to several second-line drugs was acquired during treatment. Molecular-guided investigations indicated little to no contribution of in-country clonal spread or exogenous re-infection. The increase of pre-XDR and XDR cases could be attributed to rising proportions of patients from Asia and Central and Eastern Europe (p<0.001) and an increase in the isolation of Beijing strains in these groups (p<0.001). Despite augmented resistance, the treatment success rate improved from 63.0% to 75.8% (p = 0.080) after implementation in 2005 of improved surveillance measures and therapeutic access.

Conclusions

Increasing severity in drug resistance patterns leading to more XDR- and “panresistant” TB cases in a country with a low TB incidence like Belgium represents a strong alert on worsening situations in other world regions and requires intense public health measures.

Challenges and controversies in defining totally drug-resistant tuberculosis

In March 2012, in response to reports of tuberculosis (TB) resistant to all anti-TB drugs, the World Health Organization convened an expert consultation that identified issues to be resolved before defining a new category of highly drug-resistant TB. Proposed definitions are ambiguous, and extensive drug resistance is encompassed by the already defined extensively drug-resistant (XDR) TB. There is no evidence that proposed totally resistant TB differs from strains encompassed by XDR TB. Susceptibility tests for several drugs are poorly reproducible. Few laboratories can test all drugs, and there is no consensus list of all anti-TB drugs. Many drugs are used off-label for highly drug resistant TB, and new drugs formulated to combat resistant strains would render the proposed category obsolete. Labeling TB strains as totally drug resistant might lead providers to think infected patients are untreatable. These challenges must be addressed before defining a new category for highly drug-resistant TB.

Dipterinyl calcium pentahydrate inhibits intracellular mycobacterial growth in human monocytes via the C-C chemokine MIP-1β and nitric oxide

Tuberculosis remains one of the top three leading causes of morbidity and mortality worldwide, complicated by the emergence of drug-resistant Mycobacterium tuberculosis strains and high rates of HIV coinfection. It is important to develop new antimycobacterial drugs and immunomodulatory therapeutics and compounds that enhance antituberculous immunity. Dipterinyl calcium pentahydrate (DCP), a calcium-complexed pterin compound, has previously been shown to inhibit human breast cancer cells and hepatitis B virus (HBV). DCP inhibitory effects were attributed to induction of apoptosis and/or increased production of interleukin 12 (IL-12) and granulocyte-macrophage colony-stimulating factor (GM-CSF). In this study, we tested the ability of DCP to mediate inhibition of intracellular mycobacteria within human monocytes. DCP treatment of infected monocytes resulted in a significant reduction in viability of intracellular but not extracellular Mycobacterium bovis BCG. The antimicrobial activity of DCP was comparable to that of pyrazinamide (PZA), one of the first-line antituberculosis drugs currently used. DCP potentiated monocyte antimycobacterial activity by induction of the cysteine-cysteine (C-C) chemokine macrophage inflammatory protein 1β (MIP-1β) and inducible nitric oxide synthase 2. Addition of human anti-MIP-1β neutralizing antibody or a specific inhibitor of the l-arginase-nitric oxide pathway (N(G)-monomethyl l-arginine [l-NMMA] monoacetate) reversed the inhibitory effects of DCP on intracellular mycobacterial growth. These findings indicate that DCP induced mycobacterial killing via MIP-1β- and nitric oxide-dependent effects. Hence, DCP acts as an immunoregulatory compound enhancing the antimycobacterial activity of human monocytes.