The emergence of drug-resistant tuberculosis in New York City

Revolutionizing control strategies against Mycobacterium tuberculosis infection through selected targeting of lipid metabolism

Lipid species play a critical role in the growth and virulence expression of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). During Mtb infection, foamy macrophages accumulate lipids in granulomas, providing metabolic adaptation and survival strategies for Mtb against multiple stresses. Host-derived lipid species, including triacylglycerol and cholesterol, can also contribute to the development of drug-tolerant Mtb, leading to reduced efficacy of antibiotics targeting the bacterial cell wall or transcription. Transcriptional and metabolic analyses indicate that lipid metabolism-associated factors of Mtb are highly regulated by antibiotics and ultimately affect treatment outcomes. Despite the well-known association between major antibiotics and lipid metabolites in TB treatment, a comprehensive understanding of how altered lipid metabolites in both host and Mtb influence treatment outcomes in a drug-specific manner is necessary to overcome drug tolerance. The current review explores the controversies and correlations between lipids and drug efficacy in various Mtb infection models and proposes novel approaches to enhance the efficacy of anti-TB drugs. Moreover, the review provides insights into the efficacious control of Mtb infection by elucidating the impact of lipids on drug efficacy. This review aims to improve the effectiveness of current anti-TB drugs and facilitate the development of innovative therapeutic strategies against Mtb infection by making reverse use of Mtb-favoring lipid species.

Acyldepsipeptide Analogues: A Future Generation Antibiotics for Tuberculosis Treatment

Acyldepsipeptides (ADEPs) are a new class of emerging antimicrobial peptides (AMPs), which are currently explored for treatment of pathogenic infections, including tuberculosis (TB). These cyclic hydrophobic peptides have a unique bacterial target to the conventional anti-TB drugs, and present a therapeutic window to overcome Mycobacterium Tuberculosis (M. tb) drug resistance. ADEPs exerts their antibacterial activity on M. tb strains through activation of the protein homeostatic regulatory protease, the caseinolytic protease (ClpP1P2). ClpP1P2 is normally regulated and activated by the ClpP-ATPases to degrade misfolded and toxic peptides and/or short proteins. ADEPs bind and dysregulate all the homeostatic capabilities of ClpP1P2 while inducing non-selective proteolysis. The uncontrolled proteolysis leads to M. tb cell death within the host. ADEPs analogues that have been tested possess cytotoxicity and poor pharmacokinetic and pharmacodynamic properties. However, these can be improved by drug design techniques. Moreover, the use of nanomaterial in conjunction with ADEPs would yield effective synergistic effect. This new mode of action has potential to combat and eradicate the extensive multi-drug resistance (MDR) problem that is currently faced by the public health pertaining bacterial infections, especially TB.

The host-pathogen-environment triad: Lessons learned through the study of the multidrug-resistant Mycobacterium tuberculosis M strain

Multidrug-resistant tuberculosis is one of the major obstacles that face the tuberculosis eradication efforts. Drug-resistant Mycobacterium tuberculosis clones were initially disregarded as a public health threat, because they were assumed to have paid a high fitness cost in exchange of resistance acquisition. However, some genotypes manage to overcome the impact of drug-resistance conferring mutations, retain transmissibility and cause large outbreaks. In Argentina, the HIV-AIDS epidemics fuelled the expansion of the so-called M strain in the early 1990s, which is responsible for the largest recorded multidrug-resistant tuberculosis cluster of Latin America. The aim of this work is to review the knowledge gathered after nearly three decades of multidisciplinary research on epidemiological, microbiological and immunological aspects of this highly successful strain. Collectively, our results indicate that the successful transmission of the M strain could be ascribed to its unaltered virulence, low Th1/Th17 response, a low fitness cost imposed by the resistance conferring mutations and a high resistance to host-related stress. In the early 2000s, the incident cases due to the M strain steadily declined and stabilized in the latest years. Improvements in the management, diagnosis and treatment of multidrug-resistant tuberculosis along with societal factors such as the low domestic and international mobility of the patients affected by this strain probably contributed to the outbreak containment. This stresses the importance of sustaining the public health interventions to avoid the resurgence of this conspicuous multidrug-resistant strain.

Analysis of the Research Hotspot of Drug Treatment of Tuberculosis: A Bibliometric Based on the Top 50 Cited Literatures

Objective

The objective of the current study was to analyze the research hotspot of drug treatment for tuberculosis via top literatures.

Materials and Methods

A retrospective analysis was performed on June 7th, 2021. Literatures were searched on the Web of Science Core Collection to identify the top 50 cited literatures related to drug treatment of tuberculosis. The characteristics of the literatures were identified. The outcomes included authorship, journal, study type, year of publication, and institution. Cooccurrence network analysis and visualization were conducted using the VOS viewer (Version 1.6.16; Leiden University, Leiden, The Netherlands).

Results

The top 50 cited literatures were cited 308 to 2689 times and were published between 1982 and 2014. The most studied drugs were the first-line drugs such as isoniazid and rifampicin (n = 22), and drug-resistant tuberculosis was most frequently reported (n = 16). They were published in 18 journals, and the New England Journal of Medicine published the most literatures (n = 18), followed by the American Journal of Respiratory and Critical Care Medicine (n = 7), and the Lancet (n = 6). The authors were from 13 countries, and the authors from the USA published most of the literatures (n = 30), while authors from other countries published less than five literatures. The CDC in the USA (n = 4), the World Health Organization (WHO) (n = 3), and the American Philosophical Society (n = 3) were the leading institutions, and only two authors published at least two top-cited literatures as first authors.

Conclusions

This study provides insights into the development and most important literatures on drug therapy for tuberculosis and evidence for future research on tuberculosis treatment.

Development of New Therapeutics to Meet the Current Challenge of Drug Resistant Tuberculosis

Tuberculosis (TB) is a prominent infective disease and a major reason of mortality/ morbidity globally. Mycobacterium tuberculosis causes a long-lasting latent infection in a significant proportion of human population. The increasing burden of tuberculosis is mainly caused due to multi drug-resistance. The failure of conventional treatment has been observed in large number of cases. Drugs that are used to treat extensively drug-resistant tuberculosis are expensive, have limited efficacy, and have more side effects for a longer duration of time and are often associated with poor prognosis. To regulate the emergence of multidrug resistant tuberculosis, extensively drug-resistant tuberculosis and totally drug resistant tuberculosis, efforts are being made to understand the genetic/molecular basis of target drug delivery and mechanisms of drug resistance. Understanding the molecular approaches and pathology of Mycobacterium tuberculosis through whole genome sequencing may further help in the improvement of new therapeutics to meet the current challenge of global health. Understanding cellular mechanisms that trigger resistance to Mycobacterium tuberculosis infection may expose immune associates of protection, which could be an important way for vaccine development, diagnostics, and novel host-directed therapeutic strategies. The recent development of new drugs and combinational therapies for drug-resistant tuberculosis through major collaboration between industry, donors, and academia gives an improved hope to overcome the challenges in tuberculosis treatment. In this review article, an attempt was made to highlight the new developments of drug resistance to the conventional drugs and the recent progress in the development of new therapeutics for the treatment of drugresistant and non-resistant cases.

Structural and Functional Diversity of Resistance-Nodulation-Cell Division Transporters

Multidrug resistant (MDR) bacteria are a global threat with many common infections becoming increasingly difficult to eliminate. While significant effort has gone into the development of potent biocides, the effectiveness of many first-line antibiotics has been diminished due to adaptive resistance mechanisms. Bacterial membrane proteins belonging to the resistance-nodulation-cell division (RND) superfamily play significant roles in mediating bacterial resistance to antimicrobials. They participate in multidrug efflux and cell wall biogenesis to transform bacterial pathogens into "superbugs" that are resistant even to last resort antibiotics. In this review, we summarize the RND superfamily of efflux transporters with a primary focus on the assembly and function of the inner membrane pumps. These pumps are critical for extrusion of antibiotics from the cell as well as the transport of lipid moieties to the outer membrane to establish membrane rigidity and stability. We analyze recently solved structures of bacterial inner membrane efflux pumps as to how they bind and transport their substrates. Our cumulative data indicate that these RND membrane proteins are able to utilize different oligomerization states to achieve particular activities, including forming MDR pumps and cell wall remodeling machineries, to ensure bacterial survival. This mechanistic insight, combined with simulated docking techniques, allows for the design and optimization of new efflux pump inhibitors to more effectively treat infections that today are difficult or impossible to cure.

Trends in burden of multidrug-resistant tuberculosis in countries, regions, and worldwide from 1990 to 2017: results from the Global Burden of Disease study

Background

Antituberculosis-drug resistance is an important public health issue, and its epidemiological patterns has dramatically changed in recent decades. This study aimed to estimate the trends of multidrug-resistant tuberculosis (MDR-TB), which can be used to inform health strategies.

Methods

Data were collected from the Global Burden of Disease study 2017. The estimated annual percentage changes (EAPCs) were calculated to assess the trends of MDR-TB burden at global, regional, and national level from 1990 to 2017 using the linear regression model.

Results

Globally, the age-standardized rate (ASR) of MDR-TB burden including incidence, prevalence, death and disability-adjusted life years (DALYs) had pronounced increasing trends from 1990 to 1999, with the EAPCs were 17.63 [95% confidence interval (CI): 10.77–24.92], 17.57 (95% CI 11.51–23.95), 21.21 (95% CI 15.96–26.69), and 21.90 (95% CI 16.55–27.50), respectively. Particularly, the largest increasing trends were seen in areas and countries with low and low-middle sociodemographic index (SDI). However, the trends in incidence, prevalence, death and DALYs of MDR-TB decreased globally from 2000 to 2017, with the respective EAPCs were − 1.37 (95% CI − 1.62 to − 1.12), − 1.32 (95% CI − 1.38 to − 1.26), − 3.30 (95% CI − 3.56 to − 3.04) and − 3.32 (95% CI − 3.59 to − 3.06). Decreasing trends of MDR-TB were observed in most regions and countries, particularly that of death and DALYs in Slovenia were − 18.96 (95% CI − 20.82 to − 17.06) and -19.35 (95% CI − 21.10 to − 17.55), respectively. Whereas the pronounced increasing trends of MDR-TB occurred in Papua New Guinea, Singapore, and Australia.

Conclusions

The ASR of MDR-TB showed pronounced decreasing trends from 2000 to 2017. However, the MDR-TB burden remains a substantial challenge to the TB control globally, and requires effective control strategies and healthcare systems.

Targeting endogenous gaseous signaling molecules as novel host-directed therapies against tuberculosis infection

Tuberculosis (TB) is a chronic pulmonary disease caused by Mycobacterium tuberculosis which is a major cause of morbidity and mortality worldwide. Due to the complexity of disease and its continuous global spread, there is an urgent need to improvise the strategies for prevention, diagnosis, and treatment. The current anti-TB regimen lasts for months and warrants strict compliance to clear infection and to minimize the risk of development of multi drug-resistant tuberculosis. This underscores the need to have new and improved therapeutics for TB treatment. Several studies have highlighted the unique ability of Mycobacterium tuberculosis to exploit host factors to support its survival inside the intracellular environment. One of the key players to mycobacterial disease susceptibility and infection are endogenous gases such as oxygen, nitric oxide, carbon monoxide and hydrogen sulfide. Nitric oxide and carbon monoxide as the physiological gaseous messengers are considered important to the outcome of Mycobacterium tuberculosis infection. The role of hydrogen sulfide in human tuberculosis is yet not fully elucidated, but this gas has been shown to play a significant role in bacterial respiration, growth and pathogenesis. This review will focus on the host factors majorly endogenous gaseous signaling molecules which contributes to Mycobacterium tuberculosis survival inside the intracellular environment and highlight the potential therapeutic targets.

Surveillance of tuberculosis

Surveillance of tuberculosis is one of the oldest disease surveillance systems in the world. This article briefly reviews its history, describes its methods and main results, with a specific focus on low- and middle-income countries, and underlines its main challenges and future prospects. Surveillance of tuberculosis started more than two centuries ago with the recording of tuberculosis mortality in England and Wales. After Koch's discovery of the tubercle bacillus, repeated tuberculin surveys were implemented to monitor infection, and case notification of active disease was progressively established during the 20th century. Because treatment of tuberculosis disease is the key intervention to stop transmission, monitoring of treatment outcome and more recently of drug resistance became integral parts of tuberculosis surveillance. At global level, the World Health Organization (WHO) is publishing a global TB report annually since 1997. Reports present data notified by each country as well as global estimates. Estimates of tuberculosis incidence are based on case notification adjusted by various correction factors, or on derivation from results of tuberculosis prevalence surveys, e.g. in India. In 2018, 10.1 million cases of tuberculosis are estimated to have occurred, among which about 0.5 million were resistant to rifampicin, and an estimated 1.5 million patients died. While global estimates are useful to raise public awareness and attract public and private funding, their uncertainty make them less useful to guide national policies. The backbone of tuberculosis surveillance at national and subnational level is the case notification. Newly diagnosed cases of active disease, whether new or recurrent, are reported with their key characteristics (age, sex, case category, HIV co-infection, drug resistance), and treatment outcomes are reported after scheduled treatment termination. All countries follow internationally standardized definitions. Incidence rates are compared by time to observe trends, by place to compare geographical areas, and by patient's characteristics to identify high-risk groups. The laboratory plays an essential role, since the surveillance of bacteriologically confirmed cases allows the most reliable comparisons, and because of the importance of the identification of drug resistance. The number of patients examined for tuberculosis diagnosis is also a key indicator to monitor case-finding activities. Tuberculosis surveillance is today among the most performant surveillance systems for infectious diseases. The two major changes currently observed are the move from paper-based registers to individual computerized surveillance databases and the multiplication of indicators for documenting progress towards tuberculosis elimination. There is a risk that implementation of these changes be followed by a loss in data quality. All efforts should be made to accompany these changes with adequate quality control. This will only be possible if health care workers are actively involved in the process of data production and analysis.

The redox-sensing MarR-type repressor HypS controls hypochlorite and antimicrobial resistance in Mycobacterium smegmatis

MarR-family transcription factors often control antioxidant enzymes, multidrug efflux pumps or virulence factors in bacterial pathogens and confer resistance towards oxidative stress and antibiotics. In this study, we have characterized the function and redox-regulatory mechanism of the MarR-type regulator HypS in Mycobacterium smegmatis. RNA-seq transcriptomics and qRT-PCR analyses of the hypS mutant revealed that hypS is autoregulated and represses transcription of the co-transcribed hypO gene which encodes a multidrug efflux pump. DNA binding activity of HypS to the 8-5-8 bp inverted repeat sequence upstream of the hypSO operon was inhibited under NaOCl stress. However, the HypSC58S mutant protein was not impaired in DNA-binding under NaOCl stress in vitro, indicating an important role of Cys58 in redox sensing of NaOCl stress. HypS was shown to be inactivated by Cys58-Cys58' intersubunit disulfide formation under HOCl stress, resulting in derepression of hypO transcription. Phenotype results revealed that the HypS regulon confers resistance towards HOCl, rifampicin and erythromycin stress. In conclusion, HypS was identified as a novel redox-sensitive repressor that contributes to mycobacterial resistance towards HOCl stress and antibiotics.

Drug-Resistant Tuberculosis and HIV Infection: Current Perspectives

Drug-resistant tuberculosis (DR-TB), including multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), is considered a potential obstacle for elimination of TB globally. HIV coinfection with M/XDR-TB further complicates the scenario, and is a potential threat with challenging management. Reports have shown poor outcomes and alarmingly high mortality rates among people living with HIV (PLHIV) coinfected with M/XDR-TB. This coinfection is also responsible for all forms of M/XDR-TB epidemics or outbreaks. Better outcomes with reductions in mortality have been reported with concomitant treatment containing antiretroviral drugs for the HIV component and antitubercular drugs for the DR-TB component. Early and rapid diagnosis with genotypic tests, prompt treatment with appropriate regimens based on drug-susceptibility testing, preference for shorter regimens fortified with newer drugs, a patient-centric approach, and strong infection-control measures are all essential components in the management of M/XDR-TB in people living with HIV.

Epidemiology of Tuberculosis in the United States

Although considerable progress has been made in reducing US tuberculosis incidence, the goal of eliminating the disease from the United States remains elusive. A continued focus on preventing new tuberculosis infections while also identifying and treating persons with existing tuberculosis infection is needed. Continued vigilance to ensure ongoing control of tuberculosis transmission remains key.

Hypoxic Non-replicating Persistent Mycobacterium tuberculosis Develops Thickened Outer Layer That Helps in Restricting Rifampicin Entry

Bacteria undergo adaptive morphological changes to survive under stress conditions. The present work documents the morphological changes in Mycobacterium tuberculosis (Mtb) cells cultured under hypoxic condition using Wayne’s in vitro hypoxia model involving non-replicating persistence stages 1 and 2 (NRP stage 1 and NRP stage 2) and reveals their physiological significance. Transmission electron microscopy of the NRP stage 2 cells showed uneven but thick outer layer (TOL), unlike the evenly thin outer layer of the actively growing mid-log phase (MLP) cells. On the contrary, the saprophytic Mycobacterium smegmatis NRP stage 2 cells lacked TOL. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the Mtb NRP stage 2 cells confirmed the rough uneven surface unlike the smooth surface of the MLP cells. Zeta potential measurements showed high negative charge on the surface of NRP stage 2 cells and polysaccharide specific calcofluor white (CFW) staining of the cells revealed high content of polysaccharide in the TOL. This observation was supported by the real-time PCR data showing high levels of expression of the genes involved in the synthesis of sugars, such as trehalose, mannose and others, which are implicated in polysaccharide synthesis. Experiments to understand the physiological significance of the TOL revealed restricted entry of the biologically low-active 5-carboxyfluorescein-rifampicin (5-FAM-RIF), at concentrations equivalent to microbicidal concentrations of the unconjugated biologically active rifampicin, into the NRP stage 2 cells, unlike in the MLP cells. Further, as expected, mechanical removal of the TOL by mild bead beating or release of the NRP stage 2 cells from hypoxia into normoxia in fresh growth medium also significantly increased 5-FAM-RIF permeability into the NRP stage 2 cells to an extent comparable to that into the MLP cells. Taken together, these observations revealed that Mtb cells under hypoxia develop TOL that helps in restricting rifampicin entry, thereby conferring rifampicin tolerance.

Resisting resistance: gearing up for war

Where do we stand in our fight against antimicrobial resistance (AMR)? Many antimicrobials may lose their clinical efficacy, particularly due to the rise of multidrug-resistant (MDR) and extended drug-resistant (XDR) pathogens, including bacteria, fungi, and parasites. We need weapons against them all. Society must come together against these pathogens, just like we did against HIV, cancer, and heart disease. This opinion piece is, first and foremost, a call to arms for all partners involved in the war against AMR. Even more so, it is an attempt to highlight the positives in a seemingly long line of failures, and to identify the current set of challenges we must work on. So, how do we win the war against AMR? We must learn from the past, so we can act in the present, to save the future.

Effects of drug abuse, smoking and alcohol on donor hearts and lungs

Potential heart and lung donors with a history of illicit drugs and/or smoking and alcohol are frequently offered, though there is no clear guidance on when it is safe to use these organs. A review of the literature on effects of drugs, alcohol and smoking on donor outcomes, and the effects of these on the intact heart and lung was undertaken. There has been a marked increase in deaths from opioid abuse in many developed countries, though recent evidence suggests that outcomes after cardiothoracic transplantation are equivalent to nonopioid donor causes of death. For donor smoking, there is an increased risk with lung transplantation; however, that risk is less when compared to further waiting on the transplant list for a nonsmoking alternative. Heavy alcohol consumption does not adversely affect heart transplantation, and there is no clear evidence of adverse outcomes after lung transplantation. There are no overall effects of cannabis or cocaine on survival after heart or lung transplantation. In all these cases, careful donor assessment can establish if a particular organ can be used. In most cases, use of drugs requires careful assessment, but is not in of itself a contraindication to cardiothoracic transplantation.

Introduction and evaluation of multidrug-resistant tuberculosis supplemental surveillance in the United States

The current tuberculosis (TB) case reporting system for the United States, the Report of Verified Case of TB (RVCT), has minimal capture of multidrug-resistant (MDR) TB treatment and adverse events. Data were abstracted in five states using the form for 13 MDR TB patients during 2012-2015. The Centers for Disease Control and Prevention Guidelines for Evaluating Public Health Surveillance Systems were used to evaluate attributes of the form. Unstructured interviews with pilot sites and stakeholders provided qualitative feedback. The form was acceptable, simple, stable, representative, and provided high-quality data but was not flexible or timely. For the 13 patients on whom data were collected, the median duration of treatment with an injectable medication was 216 days (IQR 203-252). Six (46%) patients reported a side effect requiring a medication change and eight (62%) had a side effect present at treatment completion. A standardized MDR TB supplemental surveillance form was well received by stakeholders whose feedback was critical to making modifications. The finalized form will be implemented nationally in 2020 and will provide MDR TB treatment and morbidity data in the United States to help ensure patients with MDR TB receive the most effective treatment regimens with the least toxic drugs.

Identification of Anti-Mycobacterial Biofilm Agents Based on the 2-Aminoimidazole Scaffold

Tuberculosis (TB) remains a significant global health problem for which new therapeutic options are sorely needed. The ability of the causative agent, Mycobacterium tuberculosis, to reside within host macrophages and form biofilm-like communities contributes to the persistent and drug-tolerant nature of the disease. Compounds that can prevent or reverse the biofilm-like phenotype have the potential to serve alongside TB antibiotics to overcome this tolerance, and decrease treatment duration. Using Mycobacterium smegmatis as a surrogate organism, we report the identification of two new 2-aminoimidazole compounds that inhibit and disperse mycobacterial biofilms, work synergistically with isoniazid and rifampicin to eradicate preformed M. smegmatis biofilms in vitro, are nontoxic toward Galleria mellonella, and exhibit stability in mouse plasma.

Using 2-aminobenzimidazole derivatives to inhibit Mycobacterium smegmatis biofilm formation

Biofilm formation by mycobacteria can lead to enhanced antibiotic tolerance. Herein, we report on the identification of a series of 2-aminobenzimidazole (2-ABI) derivatives that potently inhibit biofilm formation by Mycobacterium smegmatis.

Biosynthetic and Synthetic Strategies for Assembling Capuramycin-Type Antituberculosis Antibiotics

Mycobacterium tuberculosis (Mtb) has recently surpassed HIV/AIDS as the leading cause of death by a single infectious agent. The standard therapeutic regimen against tuberculosis (TB) remains a long, expensive process involving a multidrug regimen, and the prominence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant (TDR) strains continues to impede treatment success. An underexplored class of natural products—the capuramycin-type nucleoside antibiotics—have been shown to have potent anti-TB activity by inhibiting bacterial translocase I, a ubiquitous and essential enzyme that functions in peptidoglycan biosynthesis. The present review discusses current literature concerning the biosynthesis and chemical synthesis of capuramycin and analogs, seeking to highlight the potential of the capuramycin scaffold as a favorable anti-TB therapeutic that warrants further development.

Molecular Targets Related Drug Resistance Mechanisms in MDR-, XDR-, and TDR-Mycobacterium tuberculosis Strains

Tuberculosis (TB) is a formidable infectious disease that remains a major cause of death worldwide today. Escalating application of genomic techniques has expedited the identification of increasing number of mutations associated with drug resistance in Mycobacterium tuberculosis. Unfortunately the prevalence of bacillary resistance becomes alarming in many parts of the world, with the daunting scenarios of multidrug-resistant tuberculosis (MDR-TB), extensively drug-resistant tuberculosis (XDR-TB) and total drug-resistant tuberculosis (TDR-TB), due to number of resistance pathways, alongside some apparently obscure ones. Recent advances in the understanding of the molecular/ genetic basis of drug targets and drug resistance mechanisms have been steadily made. Intriguing findings through whole genome sequencing and other molecular approaches facilitate the further understanding of biology and pathology of M. tuberculosis for the development of new therapeutics to meet the immense challenge of global health.

Evolution of structural fitness and multifunctional aspects of mycobacterial RND family transporters

Drug resistance is a major concern due to the evolution and emergence of pathogenic bacterial strains with novel strategies to resist the antibiotics in use. Mycobacterium tuberculosis (Mtb) is one of such pathogens with reported strains, which are not treatable with any of the available anti-TB drugs. This scenario has led to the need to look for some novel drug targets in Mtb, which may be exploited to design effective treatment strategies against the infection. The goal of this review is to discuss one such class of emerging drug targets in Mtb. MmpL (mycobacterial membrane protein large) proteins from Mtb are reported to be involved in multi-substrate transport including drug efflux and considered as one of the contributing factors for the emergence of multidrug-resistant strains. MmpL proteins belong to resistance nodulation division permeases superfamily of membrane transporters, which are viably and pathogenetically important and their inhibition could be lethal for the bacteria.

Evolution of Mycobacterium tuberculosis: New Insights into Pathogenicity and Drug Resistance

The tuberculosis agent Mycobacterium tuberculosis has undergone a long and selective evolution toward human infection and represents one of the most widely spread pathogens due to its efficient aerosol-mediated human-to-human transmission. With the availability of more and more genome sequences, the evolutionary trajectory of this obligate pathogen becomes visible, which provides us with new insights into the molecular events governing evolution of the bacterium and its ability to accumulate drug-resistance mutations. In this review, we summarize recent developments in mycobacterial research related to this matter that are important for a better understanding of the current situation and future trends and developments in the global epidemiology of tuberculosis, as well as for possible public health intervention possibilities.

Therapy of Multidrug-Resistant and Extensively Drug-Resistant Tuberculosis

The global epidemic of multidrug-resistant tuberculosis (MDR-TB) caused by Mycobacterium tuberculosis strains resistant to at least isoniazid and rifampin was recently reported as larger than previously estimated, with at least 580,000 new cases reported in 2015. Extensively drug-resistant tuberculosis (XDR-TB), MDR-TB with additional resistance to a second-line fluoroquinolone and injectable, continues to account for nearly 10% of MDR cases globally. Cases in India, China, and the Russian Federation account for >45% of the cases of MDR-TB. Molecular testing helps identify MDR more quickly, and treatment options have expanded across the globe. Despite this, only 20% are in treatment, and treatment is challenging due to the toxicity of medications and the long duration. In 2016 the World Health Organization updated guidelines for the treatment of MDR-TB. A new short-course regimen is an option for those who qualify. Five effective drugs, including pyrazinamide (PZA) when possible, are recommended during the initial treatment phase and four drugs thereafter. Revised drug classifications include the use of linezolid and clofazimine as key second-line drugs and the option to use bedaquiline and delamanid to complete a five-drug regimen when needed due to poor medication tolerance or extensive resistance. Despite multiple drugs and long-duration treatment regimens, the outcomes for MDR and especially XDR-TB are much worse than for drug-susceptible disease. Better management of toxicity, prevention of transmission, and identification and appropriate management of infected contacts are important challenges for the future.

Isolation of anti-mycobacterial compounds from Curtisia dentata (Burm.f.) C.A.Sm (Curtisiaceae)

BACKGROUND

Tuberculosis is counted amongst the most infectious and lethal illnesses worldwide and remains one of the major threats to human health. The aim of the current study was to isolate and characterize anti-mycobacterial compounds present in Curtisia dentata (Burm.f.) C.A.Sm , a medicinal plant reportedly used in the treatment of tuberculosis, stomach ailments and sexually transmitted infections.

METHODS

The bioassay guided principle was followed to isolate the anti-mycobacterial compounds. The crude ethanol extracts of the leaves was partitioned with various solvents four compounds such as β-sitosterol, betulinic acid, ursolic acid and lupeol were successfully isolated. The compounds and their derivatives were evaluated for anti-mycobacterial activity using Microplate Alamar Blue Assay (MABA) against Mycobacterium tuberculosis H37RV (ATCC 27294). Furthermore, the derivatives were investigated for their toxicity against HepG2 and HEK293 using the MTT assay.

RESULTS

The methanol fraction had the lowest minimum inhibitory concentration (MIC) of 22.2 μg/ml against the selected Mycobacterium strain when compared to other fractions. Ursolic acid acetate (UAA) was the most active compound with MIC value of 3.4 μg/ml. The derivatives had varying degrees of toxicity, but were generally non-toxic to the selected cell lines. Derivatives also exhibited highest selectivity index and offers a higher safety margin.

CONCLUSIONS

The derivatives had better antimicrobial activity and low cytotoxic effects compared to isolated compounds. These increased their selectivity. It appears that acetylation of both betulinic acid and ursolic acid increased their activity against the selected Mycobacterium species. The results obtained in this study gives a clear indication that Curtisia dentata may serve as major source of new alternative medicines that may be used to treat TB. Furthermore, there is a need to explore the activity of these tested plant against other pathogenic Mycobacterium species.

Complex multifractal nature in Mycobacterium tuberculosis genome

The mutifractal and long range correlation (C(r)) properties of strings, such as nucleotide sequence can be a useful parameter for identification of underlying patterns and variations. In this study C(r) and multifractal singularity function f(α) have been used to study variations in the genomes of a pathogenic bacteria Mycobacterium tuberculosis. Genomic sequences of M. tuberculosis isolates displayed significant variations in C(r) and f(α) reflecting inherent differences in sequences among isolates. M. tuberculosis isolates can be categorised into different subgroups based on sensitivity to drugs, these are DS (drug sensitive isolates), MDR (multi-drug resistant isolates) and XDR (extremely drug resistant isolates). C(r) follows significantly different scaling rules in different subgroups of isolates, but all the isolates follow one parameter scaling law. The richness in complexity of each subgroup can be quantified by the measures of multifractal parameters displaying a pattern in which XDR isolates have highest value and lowest for drug sensitive isolates. Therefore C(r) and multifractal functions can be useful parameters for analysis of genomic sequences.

The Discovery of 2-Aminobenzimidazoles That Sensitize Mycobacterium smegmatis and M. tuberculosis to β-Lactam Antibiotics in a Pattern Distinct from β-Lactamase Inhibitors

A library of 2-aminobenzimidazole derivatives was screened for the ability to suppress β-lactam resistance in Mycobacterium smegmatis. Several non-bactericidal compounds were identified that reversed intrinsic resistance to β-lactam antibiotics in a manner distinct from β-lactamase inhibitors. Activity also translates to M. tuberculosis, with a lead compound from this study potently suppressing carbenicillin resistance in multiple M. tuberculosis strains (including multidrug-resistant strains). Preliminary mechanistic studies revealed that the lead compounds act through a mechanism distinct from that of traditional β-lactamase inhibitors.

Imaging Manifestations of Thoracic Tuberculosis

Despite significant improvements in the diagnosis and treatment of tuberculosis achieved during the last 3 decades, tuberculosis still remains one of the deadliest communicable diseases worldwide. Tuberculosis is still present in all regions of the world, with a more significant impact in developing countries. This article reviews the most common imaging manifestations of primary and postprimary tuberculosis, their complications, and the critical role of imaging in the diagnosis and follow-up of affected patients.

Epidemiology of Drug-Resistant Tuberculosis

As we move into the era of the Sustainable Development Goals (SDGs), the World Health Organization (WHO) has developed the End TB strategy 2016-2035 with a goal to end the global epidemic of tuberculosis (TB) by 2035. Achieving the targets laid out in the Strategy will require strengthening of the whole TB diagnosis and treatment cascade, including improved case detection, the establishment of universal drug susceptibility testing and rapid treatment initiation. An estimated 3.9% of new TB cases and 21% of previously treated cases had rifampicin-resistant (RR) or multidrug-resistant (MDR) TB in 2015. These levels have remained stable over time, although limited data are available from major high burden settings. In addition to the emergence of drug resistance due to inadequate treatment, there is growing evidence that direct transmission is a large contributor to the RR/MDR-TB epidemic. Only 340,000 of the estimated 580,000 incident cases of RR/MDR-TB were notified to WHO in 2015. Among these, only 125,000 were initiated on second-line treatment. RR/MDR-TB epidemics are likely to be driven by direct transmission. The most important risk factor for MDR-TB is a history of previous treatment. Other risk factors vary according to setting but can include hospitalisation, incarceration and HIV infection. Children have the same risk of MDR-TB as adults and represent a diagnostic and treatment challenge. Rapid molecular technologies have revolutionized the diagnosis of drug-resistant TB. Until capacity can be established to test every TB patient for rifampicin resistance, countries should focus on gradually expanding their coverage of testing. DNA sequencing technologies are being increasingly incorporated into patient management and drug resistance surveillance. They offer additional benefits over conventional culture-based phenotypic testing, including a faster turn-around time for results, assessment of resistance patterns to a range of drugs, and investigation of strain clustering and transmission.

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.

Six-Month Toxicity Comparison of the Antituberculosis Drugs Aconiazide and Isoniazid in Fischer 344 Rats

Aconiazide, a hydrazone derivative of isoniazid, has been proposed for the treatment of tuberculosis. The toxicity of aconiazide was assessed by treating male and female Fischer 344 (F344) rats daily by gavage for 6 months at doses up to 400 mg/kg body wt. For comparison, the toxicity of isoniazid was determined following treatment in an identical manner at equimolar doses. Aconiazide resulted in only one death during the 6-month experiment, whereas isoniazid caused a significant increase in morbidity and mortality. Each drug induced significant dose-related decreases in body weight in both sexes, and isoniazid caused a significant decrease in liver weight in male rats. Isoniazid also induced centrilobular hepatic necrosis in male rats, a lesion not observed upon aconiazide treatment. Plasma drug levels were ≥10-fold greater in rats administered isoniazid as compared to aconiazide. The higher levels of free drug observed with isoniazid may contribute to greater toxicity of isoniazid compared to aconiazide.

Substrate Inhibition of VanA by d-Alanine Reduces Vancomycin Resistance in a VanX-Dependent Manner

The increasing resistance of clinical pathogens against the glycopeptide antibiotic vancomycin, a last-resort drug against infections with Gram-positive pathogens, is a major problem in the nosocomial environment. Vancomycin inhibits peptidoglycan synthesis by binding to the d-Ala-d-Ala terminal dipeptide moiety of the cell wall precursor lipid II. Plasmid-transferable resistance is conferred by modification of the terminal dipeptide into the vancomycin-insensitive variant d-Ala-d-Lac, which is produced by VanA. Here we show that exogenous d-Ala competes with d-Lac as a substrate for VanA, increasing the ratio of wild-type to mutant dipeptide, an effect that was augmented by several orders of magnitude in the absence of the d-Ala-d-Ala peptidase VanX. Liquid chromatography-mass spectrometry (LC-MS) analysis showed that high concentrations of d-Ala led to the production of a significant amount of wild-type cell wall precursors, while vanX-null mutants produced primarily wild-type precursors. This enhanced the efficacy of vancomycin in the vancomycin-resistant model organism Streptomyces coelicolor, and the susceptibility of vancomycin-resistant clinical isolates of Enterococcus faecium (VRE) increased by up to 100-fold. The enhanced vancomycin sensitivity of S. coelicolor cells correlated directly to increased binding of the antibiotic to the cell wall. Our work offers new perspectives for the treatment of diseases associated with vancomycin-resistant pathogens and for the development of drugs that target vancomycin resistance.

Evaluation of the effect of Pulicaria gnaphalodes and Perovskia abrotanoides essential oil extracts against Mycobacterium tuberculosis strains

Background:

Mycobacterium tuberculosis (MTB) is the causative agent of tuberculosis (TB), which remains one of the major public health problems in the world. The increasing incidence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) worldwide highlights the urgent need to search for alternative antimycobacterial agents. More and more people in developing countries utilize traditional medicine for their major primary health care needs. It has been determined that the medicinal plants Pulicaria gnaphalodes and Perovskia abrotanoides possess strong antibacterial effect.

Materials and Methods:

In this study, the antimycobacterial effects of P. gnaphalodes and P. abrotanoides essential oil on MTB were examined. Essential oil was prepared from P. gnaphalodes aerial parts and P. abrotanoides flower. The effects of six different concentrations (20 μg/ml, 40 μg/ml, 80 μg/ml, 160 μg/ml, 320 μg/ml, and 640 μg/ml) were examined against sensitive isolates of MTB and MTB H37Rv (ATCC 27294).

Results:

The results showed that P. gnaphalodes and P. abrotanoides essential oil extracts have strong inhibitory effects on MTB. This activity for P. gnaphalodes was observed from very low (4%) to good (70.9%) effect; meanwhile, this activity for P. abrotanoides was observed from very low (4%) to strong (86%) effect.

Conclusion:

The mean of inhibition percentage for P. gnaphalodes and P. abrotanoides in 640 μg/ml was 58.1% and 76.2%, respectively. So, P. abrotanoides plant is more effective against MTB than P. gnaphalodes. Identification of the effective fraction against MTB is a further step to be studied.

Matching AIDS and tuberculosis registry data to identify AIDS/tuberculosis comorbidity cases in California

The purpose of this study was to evaluate the sensitivity and positive predictive value (PPV) of a registry data linkage procedure used in the California AIDS and Tuberculosis (TB) Registry Data Linkage Study to identify AIDS/TB comorbidity cases in California. The California AIDS registry data from 1981 to 2006 were linked to the California TB registry data from 1996 to 2006 using LinkPlus, a probabilistic record linkage program developed by the Centers for Disease Control and Prevention, and matched results were manually reviewed to determine true or false matches. We estimated the sensitivity of this procedure to range from 98.0 per cent (95% confidence interval, CI: 97.3%, 98.7%) to 98.8 per cent (95% CI: 98.1%, 99.2%), and the PPV to be 100 per cent (95% CI: 96.8%, 100.0%). Our study demonstrated the feasibility of using this linkage procedure to match AIDS and TB registry data with a very high degree of accuracy.

Genotypic assessment of drug-resistant tuberculosis in Baghdad and other Iraqi provinces using low-cost and low-density DNA microarrays

We report on a molecular investigation carried out to ascertain the prevalence of drug-resistant tuberculosis (TB) and the specific gene mutations responsible for resistance to rifampicin (RIF) and/or isoniazid (INH) in Iraq. In total, 110 clinical isolates from category II TB cases from Baghdad (58%) and several Iraqi provinces (42%) were analysed using colorimetric, low-cost and low-density (LCD) microarrays (MYCO-Direct and MYCO-Resist LCD array kits) to identify the point mutations responsible for resistance in Mycobacterium tuberculosis isolates. We found 76 patients (69.1%) had resistant strains, of which 40 (36%) were multidrug-resistant (MDR)-TB. Where mono-resistance was identified, it was found to be predominantly to RIF (83%). The most common mutations were rpoB S531L (50%), inhA C15T (25%) and katG S315T (15%). The most common MDR-TB genotypes were rpoB S531L with inhA C15T (60%) and rpoB S531L with katG S315T (20%). Where phenotypic analysis of clinical isolates was also performed, genotypic data were found to show excellent correlation with phenotypic results. Correlation was found between the MYCO-Resist LCD array and GenoType MTBDRplus for detection of resistance to RIF. Our study shows MDR-TB in 36% of category II TB cases in Baghdad and surrounding Iraqi provinces, which reflects the World Health Organization findings based on phenotypic studies. Diagnosis of TB and MDR-TB using culture-based tests is a significant impediment to global TB control. The LCD arrays investigated herein are easy to use, sensitive and specific molecular tools for TB resistance profiling in resource-limited laboratory settings.

Structural Basis for the Regulation of the MmpL Transporters of Mycobacterium tuberculosis

The mycobacterial cell wall is critical to the virulence of these pathogens. Recent work shows that the MmpL (mycobacterial membrane protein large) family of transporters contributes to cell wall biosynthesis by exporting fatty acids and lipidic elements of the cell wall. The expression of the Mycobacterium tuberculosis MmpL proteins is controlled by a complex regulatory network, including the TetR family transcriptional regulators Rv3249c and Rv1816. Here we report the crystal structures of these two regulators, revealing dimeric, two-domain molecules with architecture consistent with the TetR family of regulators. Buried extensively within the C-terminal regulatory domains of Rv3249c and Rv1816, we found fortuitous bound ligands, which were identified as palmitic acid (a fatty acid) and isopropyl laurate (a fatty acid ester), respectively. Our results suggest that fatty acids may be the natural ligands of these regulatory proteins. Using fluorescence polarization and electrophoretic mobility shift assays, we demonstrate the recognition of promoter and intragenic regions of multiple mmpL genes by these proteins. Binding of palmitic acid renders these regulators incapable of interacting with their respective operator DNAs, which will result in derepression of the corresponding mmpL genes. Taken together, these experiments provide new perspectives on the regulation of the MmpL family of transporters.

Molecular Epidemiological Interpretation of the Epidemic of Extensively Drug-Resistant Tuberculosis in South Africa

We show that the interpretation of molecular epidemiological data for extensively drug-resistant tuberculosis (XDR-TB) is dependent on the number of different markers used to define transmission. Using spoligotyping, IS6110 DNA fingerprinting, and DNA sequence data, we show that XDR-TB in South Africa (2006 to 2008) was predominantly driven by the acquisition of second-line drug resistance.

Epidemiologic Correlates of Pyrazinamide-Resistant Mycobacterium tuberculosis in New York City

Pyrazinamide (PZA) has important sterilizing activity in tuberculosis (TB) chemotherapy. We describe trends, risk factors, and molecular epidemiology associated with PZA-resistant (PZA(r)) Mycobacterium tuberculosis in New York City (NYC). From 2001 to 2008, all incident culture-positive TB cases reported by the NYC Department of Health and Mental Hygiene (DOHMH) were genotyped by IS6110-based restriction fragment length polymorphism and spoligotype. Multidrug-resistant (MDR) isolates underwent DNA sequencing of resistance-determining regions of pncA, rpoB, katG, and fabG1. Demographic and clinical information were extracted from the NYC DOHMH TB registry. During this period, PZA(r) doubled (1.6% to 3.6%) overall, accounting for 44% (70/159) of the MDR population and 1.4% (75/5511) of the non-MDR population. Molecular genotyping revealed strong microbial phylogenetic associations with PZA(r). Clustered isolates and those from acid-fast bacillus (AFB) smear-positive cases had 2.7 (95% confidence interval [CI] = 1.71 to 4.36) and 2.0 (95% CI = 1.19 to 3.43) times higher odds of being PZA(r), respectively, indicating a strong likelihood of recent transmission. Among the MDR population, PZA(r) was acquired somewhat more frequently via primary transmission than by independent pathways. Our molecular analysis also revealed that several historic M. tuberculosis strains responsible for MDR TB outbreaks in the early 1990s were continuing to circulate in NYC. We conclude that the increasing incidence of PZA(r), with clear microbial risk factors, underscores the importance of routine PZA drug susceptibility testing and M. tuberculosis genotyping for the identification, control, and prevention of increasingly resistant organisms.

Multidrug-Resistant Tuberculosis and Extensively Drug-Resistant Tuberculosis

The continuing spread of drug-resistant tuberculosis (TB) is one of the most urgent and difficult challenges facing global TB control. Patients who are infected with strains resistant to isoniazid and rifampicin, called multidrug-resistant (MDR) TB, are practically incurable by standard first-line treatment. In 2012, there were approximately 450,000 new cases and 170,000 deaths because of MDR-TB. Extensively drug-resistant (XDR) TB refers to MDR-TB strains that are resistant to fluoroquinolones and second-line injectable drugs. The main causes of the spread of resistant TB are weak medical systems, amplification of resistance patterns through incorrect treatment, and transmission in communities and facilities. Although patients harboring MDR and XDR strains present a formidable challenge for treatment, cure is often possible with early identification of resistance and use of a properly designed regimen. Community-based programs can improve treatment outcomes by allowing patients to be treated in their homes and addressing socioeconomic barriers to adherence.