Virulence factors of the Mycobacterium tuberculosis complex

The Role of Dendritic Cells in TB and HIV Infection

Dendritic cells are the principal antigen-presenting cells (APCs) in the host defense mechanism. An altered dendritic cell response increases the risk of susceptibility of infections, such as Mycobacterium tuberculosis (M. tb), and the survival of the human immunodeficiency virus (HIV). The altered response of dendritic cells leads to decreased activity of T-helper-1 (Th1), Th2, Regulatory T cells (Tregs), and Th17 cells in tuberculosis (TB) infections due to a diminishment of cytokine release from these APCs, while HIV infection leads to DC maturation, allowing DCs to migrate to lymph nodes and the sub-mucosa where they then transfer HIV to CD4 T cells, although there is controversy around this topic. Increases in the levels of the antioxidant glutathione (GSH) plays a critical role in maintaining dendritic cell redox homeostasis, leading to an adequate immune response with sufficient cytokine release and a subsequent robust immune response. Thus, an understanding of the intricate pathways involved in the dendritic cell response are needed to prevent co-infections and co-morbidities in individuals with TB and HIV.

Orphan response regulator Rv3143 increases antibiotic sensitivity by regulating cell wall permeability in Mycobacterium smegmatis

About one quarter of people worldwide are infected with tuberculosis, and multi-drug resistant tuberculosis (MDR-TB) remains a health threat. It is known that two-Component Signal Transduction Systems (TCSs) of Mycobacterium tuberculosis are closely related to tuberculosis resistance, but the mechanism by which orphan response protein Rv3143 regulates strain sensitivity to drug is still unclear. This study found that Rv3143 overexpression resulted in approximately two-fold increase in Mycobacterium smegmatis antibiotic sensitivity. Transcriptome sequencing indicated that 198 potential genes were regulated by Rv3143, affecting the sensitivity of the strain to rifampicin (RIF). MSMEG_4740 promoter binding with Rv3143, was screened out by surface plasmon resonance (SPR). Rv1524, the homologous gene of MSMEG_4740, belonging to the glycosyltransferase (Gtf) family, was related to cell wall modification. By measuring ethidium bromide (EB) accumulation, we found when Rv3143 or MSMEG_4740, or Rv1524 was overexpressed, the cell wall permeability of Mycobacterium smegmatis was increased. In addition, a combination of Rv3143 and RIF was observed. Our findings provide a new strategy for treating drug-resistant tuberculosis by increasing the expression of Rv3143 to enhance the strain sensitivity to antibiotics.

DNA vaccination with the Mycobacterium marinum MMAR_4110 antigen inhibits reactivation of a latent mycobacterial infection in the adult Zebrafish

BACKGROUND

Tuberculosis is a major challenge for health care, as options for its treatment and prevention are limited. Therefore, novel approaches, such as DNA vaccination, to both prevent primary infections and the reactivation of latent infections need to be developed. A Mycobacterium marinum infection in adult zebrafish (Danio rerio) recapitulates features of the human Mycobacterium tuberculosis infection, providing a convenient preclinical animal model for studying tuberculosis.

METHODS

Hypoxic M. marinum cultures were produced with the Wayne model, and further reaerated to replicate the in vivo reactivation in vitro. Expression levels of M. marinum genes were studied with mRNA sequencing from exponentially growing bacteria, anaerobic cultures and at 2 and 12 h after reaeration. Seven reactivation-associated genes were selected for further studies, where their antigen potentiality as DNA-vaccines to prevent reactivation of a latent mycobacterial infection was investigated in the adult zebrafish model. The Mann-Whitney test was used to evaluate differences in bacterial counts between the groups.

RESULTS

The mRNA sequencing data showed that, seven M. marinum genes, MMAR_0444, MMAR_0514, MMAR_0552, MMAR_0641, MMAR_1093, MMAR_4110 and MMAR_4524, were upregulated during reactivation when compared to both dormant and logarithmic growing bacteria. Four different MMAR_4110 antigens prevented the reactivation of a latent mycobacterial infection in the adult zebrafish.

CONCLUSION

This study provides novel information about reactivation-related M. marinum genes. One of the antigens, MMAR_4110, inhibited the reactivation of a latent M. marinum infection in zebrafish, implicating that the characterized genes could be potential targets for further vaccine and drug development against mycobacterial diseases.

New insights into the evasion of host innate immunity by Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is an extremely successful intracellular pathogen that causes tuberculosis (TB), which remains the leading infectious cause of human death. The early interactions between Mtb and the host innate immune system largely determine the establishment of TB infection and disease development. Upon infection, host cells detect Mtb through a set of innate immune receptors and launch a range of cellular innate immune events. However, these innate defense mechanisms are extensively modulated by Mtb to avoid host immune clearance. In this review, we describe the emerging role of cytosolic nucleic acid-sensing pathways at the host-Mtb interface and summarize recently revealed mechanisms by which Mtb circumvents host cellular innate immune strategies such as membrane trafficking and integrity, cell death and autophagy. In addition, we discuss the newly elucidated strategies by which Mtb manipulates the host molecular regulatory machinery of innate immunity, including the intranuclear regulatory machinery, the ubiquitin system, and cellular intrinsic immune components. A better understanding of innate immune evasion mechanisms adopted by Mtb will provide new insights into TB pathogenesis and contribute to the development of more effective TB vaccines and therapies.

Host-Pathogen Interaction as a Novel Target for Host-Directed Therapies in Tuberculosis

Tuberculosis (TB) has been a transmittable human disease for many thousands of years, and M. tuberculosis is again the number one cause of death worldwide due to a single infectious agent. The intense 6- to 10-month process of multi-drug treatment, combined with the adverse side effects that can run the spectrum from gastrointestinal disturbances to liver toxicity or peripheral neuropathy are major obstacles to patient compliance and therapy completion. The consequent increase in multidrug resistant TB (MDR-TB) and extensively drug resistant TB (XDR-TB) cases requires that we increase our arsenal of effective drugs, particularly novel therapeutic approaches. Over the millennia, host and pathogen have evolved mechanisms and relationships that greatly influence the outcome of infection. Understanding these evolutionary interactions and their impact on bacterial clearance or host pathology will lead the way toward rational development of new therapeutics that favor enhancing a host protective response. These host-directed therapies have recently demonstrated promising results against M. tuberculosis, adding to the effectiveness of currently available anti-mycobacterial drugs that directly kill the organism or slow mycobacterial replication. Here we review the host-pathogen interactions during M. tuberculosis infection, describe how M. tuberculosis bacilli modulate and evade the host immune system, and discuss the currently available host-directed therapies that target these bacterial factors. Rather than provide an exhaustive description of M. tuberculosis virulence factors, which falls outside the scope of this review, we will instead focus on the host-pathogen interactions that lead to increased bacterial growth or host immune evasion, and that can be modulated by existing host-directed therapies.

Cell wall peptidoglycan in Mycobacterium tuberculosis: An Achilles' heel for the TB-causing pathogen

Tuberculosis (TB), caused by the intracellular pathogen Mycobacterium tuberculosis, remains one of the leading causes of mortality across the world. There is an urgent requirement to build a robust arsenal of effective antimicrobials, targeting novel molecular mechanisms to overcome the challenges posed by the increase of antibiotic resistance in TB. Mycobacterium tuberculosis has a unique cell envelope structure and composition, containing a peptidoglycan layer that is essential for maintaining cellular integrity and for virulence. The enzymes involved in the biosynthesis, degradation, remodelling and recycling of peptidoglycan have resurfaced as attractive targets for anti-infective drug discovery. Here, we review the importance of peptidoglycan, including the structure, function and regulation of key enzymes involved in its metabolism. We also discuss known inhibitors of ATP-dependent Mur ligases, and discuss the potential for the development of pan-enzyme inhibitors targeting multiple Mur ligases.

[Pseudotumoral ocular tuberculosis: about 2 cases]

Les manifestations oculaires de la tuberculose sont non spécifiques et polymorphes pouvant toucher toutes les tuniques de l’œil et entrainer une perte visuelle sévère en l’absence d’un traitement précoce et adapté. Nous rapportons 2 cas de forme pseudo tumorale de tuberculose oculaire ayant bien évolué sous traitement anti bacillaire; le premier présentant un éclatement spontané récent du globe avec issue d’une masse bourgeonnante charnue et suppurée de 10cm/6cm, le second patient présente un granulome du corps ciliaire mimant un mélanome; puis nous discutons les particularités cliniques et thérapeutiques de cette affection.

Does Mycobacterium bovis persist in cattle in a non-replicative latent state as Mycobacterium tuberculosis in human beings?

Members of the Mycobacterium tuberculosis complex (MTBC) are responsible for tuberculosis in several mammals. In this complex, Mycobacterium tuberculosis and Mycobacterium bovis, which are closely related, show host preference for humans and cattle, respectively. Although human and bovine tuberculosis are clinically similar, M. tuberculosis mostly causes latent infection in humans, whereas M. bovis frequently leads to an acute infection in cattle. This review attempts to connect the pathology in experimental animal models as well as the cellular responses to M. bovis and M. tuberculosis regarding the differences in protein expression and regulatory mechanisms of both pathogens that could explain their apparent divergent latency behaviour. The occurrence of latent bovine tuberculosis (bTB) would represent a serious complication for the eradication of the disease in cattle, with the risk of onward transmission to humans. Thus, understanding the physiological events that may lead to the state of latency in bTB could assist in the development of appropriate prevention and control tools.

Interest of bacterial pangenome analyses in clinical microbiology

Thanks to the progress and decreasing costs in genome sequencing technologies, more than 250,000 bacterial genomes are currently available in public databases, covering most, if not all, of the major human-associated phylogenetic groups of these microorganisms, pathogenic or not. In addition, for many of them, sequences from several strains of a given species are available, thus enabling to evaluate their genetic diversity and study their evolution. In addition, the significant cost reduction of bacterial whole genome sequencing as well as the rapid increase in the number of available bacterial genomes have prompted the development of pangenomic software tools. The study of bacterial pangenome has many applications in clinical microbiology. It can unveil the pathogenic potential and ability of bacteria to resist antimicrobials as well identify specific sequences and predict antigenic epitopes that allow molecular or serologic assays and vaccines to be designed. Bacterial pangenome constitutes a powerful method for understanding the history of human bacteria and relating these findings to diagnosis in clinical microbiology laboratories in order to optimize patient management.

Poor stimulation of bovine dendritic cells by Mycobacterium bovis culture supernatant and surface extract is associated with decreased activation of ERK and NF-B and higher expression of SOCS1 and 3

The cell envelope of pathogenic mycobacteria interfaces with the host. As such, the interaction of bacterial products localized at or released from the cell surface with the host’s immune system can determine the fate of the bacterium in its host. In this study, the effects of three different types of Mycobacterium bovis cell envelope fractions—purified protein derivative, total cell wall lipids and culture supernatant and surface extract—on bovine dendritic cells were assessed. We found that the culture supernatant and surface extract fraction induced little to no production of the pro-inflammatory cytokines TNF-α and IL-12 in bovine dendritic cells. Moreover, this muted response was associated with poor activation of ERK and NF-κB, both of which are critical for the pro-inflammatory response. Furthermore, culture supernatant and surface extract treatment increased the expression of suppressor of cytokine signaling 1 and 3, both of which are negative regulators of pro-inflammatory signaling, in bovine dendritic cells. These observations taken together suggest the M. bovis culture supernatant and surface extract fraction contain immunomodulatory molecules that may aid in M. bovis pathogenesis.

Alveolar lipids in pulmonary disease. A review

Lung lipid metabolism participates both in infant and adult pulmonary disease. The lung is composed by multiple cell types with specialized functions and coordinately acting to meet specific physiologic requirements. The alveoli are the niche of the most active lipid metabolic cell in the lung, the type 2 cell (T2C). T2C synthesize surfactant lipids that are an absolute requirement for respiration, including dipalmitoylphosphatidylcholine. After its synthesis and secretion into the alveoli, surfactant is recycled by the T2C or degraded by the alveolar macrophages (AM). Surfactant biosynthesis and recycling is tightly regulated, and dysregulation of this pathway occurs in many pulmonary disease processes. Alveolar lipids can participate in the development of pulmonary disease from their extracellular location in the lumen of the alveoli, and from their intracellular location in T2C or AM. External insults like smoke and pollution can disturb surfactant homeostasis and result in either surfactant insufficiency or accumulation. But disruption of surfactant homeostasis is also observed in many chronic adult diseases, including chronic obstructive pulmonary disease (COPD), and others. Sustained damage to the T2C is one of the postulated causes of idiopathic pulmonary fibrosis (IPF), and surfactant homeostasis is disrupted during fibrotic conditions. Similarly, surfactant homeostasis is impacted during acute respiratory distress syndrome (ARDS) and infections. Bioactive lipids like eicosanoids and sphingolipids also participate in chronic lung disease and in respiratory infections. We review the most recent knowledge on alveolar lipids and their essential metabolic and signaling functions during homeostasis and during some of the most commonly observed pulmonary diseases.

Potential Diagnostic Value of the Peripheral Blood Mononuclear Cell Transcriptome From Cattle With Bovine Tuberculosis

Bovine tuberculosis (bTB) is a chronic disease of cattle caused by Mycobacterium bovis. During early-stage infection, M. bovis-infected cattle shed mycobacteria through nasal secretions, which can be detected via nested-polymerase chain reaction (PCR) experiments. Little research has focused on immune responses in nested PCR-positive (bTB PCR-P) or nested PCR-negative (bTB PCR-N) M. bovis-infected cattle. Here, we investigated the transcriptomes of peripheral blood mononuclear cells (PBMCs), with or without stimulation by purified protein derivative of bovine tuberculin (PPD-B), among bTB PCR-P, bTB PCR-N, and healthy cattle using RNA-Seq. We also explored the potential value of PBMC transcripts as novel biomarkers for diagnosing bTB. Numerous differentially expressed genes were identified following pair-wise comparison of different groups, with or without PPD-B stimulation (adjusted p < 0.05). Compared with healthy cattle, bTB PCR-P, and bTB PCR-N cattle shared 5 significantly dysregulated biological pathways, including Cytokine-cytokine receptor interaction, NF-kappa B signaling pathway, Hematopoietic cell lineage, Osteoclast differentiation and HTLV-I infection. Notably, dysregulated biological pathways of bTB PCR-P and bTB PCR-N cattle were associated with cell death and phagocytosis, respectively. Lymphotoxin alpha and interleukin-8 could potentially differentiate M. bovis-infected and healthy cattle upon stimulation with PPD-B, with area-under-the-curve (AUC) values of 0.9991 and 0.9343, respectively. B cell lymphoma 2 and chitinase 3-like 1 might enable differentiation between bTB PCR-P and bTB PCR-N upon stimulation with PPD-B, with AUC values of 0.9100 and 0.8893, respectively. Thus, the PBMC transcriptome revealed the immune responses in M. bovis-infected cattle (bTB PCR-P and bTB PCR-N) and may provide a novel sight in bTB diagnosis.

Whole Genome and Transcriptome Sequencing of Two Multi-Drug Resistant Mycobacterium tuberculosis Strains to Facilitate Illustrating Their Virulence in vivo

Mycobacterium tuberculosis clinical strains usually possess traits different from the laboratory strains like H37Rv, especially those clinical drug resistant strains. With whole genome and transcriptome sequencing, we depicted the feature of two multi-drug resistant Mtb strains in resistance and virulence. Compared with H37Rv, the differential expressed genes (DEGs) of the MDR strains showed featured enrichment in arginine biosynthesis, fatty acid biosynthesis, and metabolism pathway. In the subset of virulence genes, the overlapping DEGs of the MDR strains exhibited downregulation of the cluster in type VII secretion system. In the mice experiment, the MDR strains showed attenuated but distinct virulence, both in survival rate and pathology. Taken together, the whole genome and transcriptome analysis could help understand the unique feature of the MDR strains both in resistance and virulence.

Genotyping, Assessment of Virulence and Antibacterial Resistance of the Rostov Strain of Mycobacterium tuberculosis Attributed to the Central Asia Outbreak Clade

The Central Asia Outbreak (CAO) clade is a growing public health problem for Central Asian countries. Members of the clade belong to the narrow branch of the Mycobacterium tuberculosis Beijing genotype and are characterized by multidrug resistance and increased transmissibility. The Rostov strain of M. tuberculosis isolated in Russia and attributed to the CAO clade based on PCR-assay and whole genome sequencing and the laboratory strain H37Rv were selected to evaluate the virulence on C57Bl/6 mice models by intravenous injection. All mice infected with the Rostov strain succumbed to death within a 48-day period, while more than half of the mice infected by the H37Rv strain survived within a 90-day period. Mice weight analysis revealed irreversible and severe depletion of animals infected with the Rostov strain compared to H37Rv. The histological investigation of lung and liver tissues of mice on the 30th day after injection of mycobacterial bacilli showed that the pattern of pathological changes generated by two strains were different. Moreover, bacterial load in the liver and lungs was higher for the Rostov strain infection. In conclusion, our data demonstrate that the drug-resistant Rostov strain exhibits a highly virulent phenotype which can be partly explained by the CAO-specific mutations.

Comparative Genomics and Transcriptomics Analyses Reveal a Unique Environmental Adaptability of Vibrio fujianensis

The genus Vibrio is ubiquitous in marine environments and uses numerous evolutionary characteristics and survival strategies in order to occupy its niche. Here, a newly identified species, Vibrio fujianensis, was deeply explored to reveal a unique environmental adaptability. V. fujianensis type strain FJ201301^T shared 817 core genes with the Vibrio species in the population genomic analysis, but possessed unique genes of its own. In addition, V. fujianensis FJ201301^T was predicated to carry 106 virulence-related factors, several of which were mostly found in other pathogenic Vibrio species. Moreover, a comparative transcriptome analysis between the low-salt (1% NaCl) and high-salt (8% NaCl) condition was conducted to identify the genes involved in salt tolerance. A total of 913 unigenes were found to be differentially expressed. In a high-salt condition, 577 genes were significantly upregulated, whereas 336 unigenes were significantly downregulated. Notably, differentially expressed genes have a significant association with ribosome structural component and ribosome metabolism, which may play a role in salt tolerance. Transcriptional changes in ribosome genes indicate that V. fujianensis may have gained a predominant advantage in order to adapt to the changing environment. In conclusion, to survive in adversity, V. fujianensis has enhanced its environmental adaptability and developed various strategies to fill its niche.

Efficient method for targeted gene disruption by homologous recombination in Mycobacterium avium subspecie paratuberculosis

Targeted gene disruption by homologous recombination, has been widely used in mycobacterium species to understand the genetic basis of virulence and persistence in the host and to develop efficacious potential live vaccines. However, in slow growing pathogenic mycobacteria as Mycobacterium avium subsp paratuberculosis (MAP), these methods have been inefficient, in part due to the low frequency of legitimate homologous recombination. Another feature of mycobacteria is the low efficiency of transformation; therefore, some years ago, a phage-mediated transduction process was developed to introduce DNA into mycobacteria. This strategy is very efficient, due to the high rate of infection of the phage. This report describes a genetic method for the generation of targeted deletion mutations in MAP by allelic exchange using in vitro-generated specialized transducing mycobacteriophages, which does not require the critical packaging step and that could also be applied to other mycobacteria. We provide a detailed gene deletion methodology and demonstrate the use of this genetic system by deleting the mce4 operon of MAP. Finally, our results showed that the deletion of mce4 in MAP induces triacylglycerol accumulation; alter morphology and aggregation in liquid culture.

A Phenotypic Characterization of Two Isolates of a Multidrug-Resistant Outbreak Strain of Mycobacterium tuberculosis with Opposite Epidemiological Fitness

Tuberculosis (TB) is an infectious disease, caused by Mycobacterium tuberculosis, primarily affecting the lungs. The M. tuberculosis strain of the Haarlem family named M was responsible for a large multidrug-resistant TB (MDR-TB) outbreak in Buenos Aires. This outbreak started in the early 1990s and in the mid 2000s still accounted for 29% of all MDR-TB cases in Argentina. By contrast, a clonal variant of strain M, named 410, has caused a single tuberculosis case since the onset of the outbreak. The molecular bases of the high epidemiological fitness of the M strain remain unclear. To assess its unique molecular properties, herein, we performed a comparative protein and lipid analysis of a representative clone of the M strain (Mp) and the nonprosperous M variant 410. We also evaluated their growth in low pH. The variant 410 had higher levels of latency proteins under standard conditions and delayed growth at low pH, suggesting that it is more sensitive to stress stimuli than Mp. Moreover, Mp showed higher levels of mycolic acids covalently attached to the cell wall and lower accumulation of free mycolic acids in the outer layer than the 410 strain. The low expression of latency proteins together with the reduced content of surface mycolic acids may facilitate Mp to evade the host immune responses.

Silver Nanoparticles for the Therapy of Tuberculosis

Rapid emergence of aggressive, multidrug-resistant Mycobacteria strain represents the main cause of the current antimycobacterial-drug crisis and status of tuberculosis (TB) as a major global health problem. The relatively low-output of newly approved antibiotics contributes to the current orientation of research towards alternative antibacterial molecules such as advanced materials. Nanotechnology and nanoparticle research offers several exciting new-concepts and strategies which may prove to be valuable tools in improving the TB therapy. A new paradigm in antituberculous therapy using silver nanoparticles has the potential to overcome the medical limitations imposed in TB treatment by the drug resistance which is commonly reported for most of the current organic antibiotics. There is no doubt that AgNPs are promising future therapeutics for the medication of mycobacterial-induced diseases but the viability of this complementary strategy depends on overcoming several critical therapeutic issues as, poor delivery, variable intramacrophagic antimycobacterial efficiency, and residual toxicity. In this paper, we provide an overview of the pathology of mycobacterial-induced diseases, andhighlight the advantages and limitations of silver nanoparticles (AgNPs) in TB treatment.

Insights into structures of imidazo oxazines as potent polyketide synthase XIII inhibitors using molecular modeling techniques

Tuberculosis, a major global health concern, and its drug development toward the disease are too devastating to meet the clinical demands. The present work emphasizes a detailed QSAR study using QSARINS which developed descriptors favoring an excellent model equation. The best model equation generated has four variables namely AlogP, ATSc4, mindssC, and MDEC23 with statistical values R² = 0.7406, LOF = 0.1858, CCC_tr = 0.8510, Q₂LOO = 0.6569, Q₂LMO = 0.6286, CCC_cv = 0.8037, R²_ext = 0.8600, and CCC_ext = 0.9252. The developed QSAR model justifies that the key structural fragments highly correlate with activity. Docking the designed compounds with PKS XIII, a novel target catalyzes the formation of mycolic acids and its results distinctly improve expected antitubercular activity showing all probable interactions. Compounds were further screened for ADME analysis and toxicity.

Infant Alveolar Macrophages Are Unable to Effectively Contain Mycobacterium tuberculosis

Infants are more likely to develop lethal disseminated forms of tuberculosis compared with older children and adults. The reasons for this are currently unknown. In this study we test the hypothesis that antimycobacterial function is impaired in infant alveolar macrophages (AMϕs) compared with those of adults. We develop a method of obtaining AMϕs from healthy infants using rigid bronchoscopy and incubate the AMϕs with live virulent Mycobacterium tuberculosis (Mtb). Infant AMϕs are less able to restrict Mtb replication compared with adult AMϕs, despite having similar phagocytic capacity and immunophenotype. RNA-Seq showed that infant AMϕs exhibit lower expression of genes involved in mycobactericidal activity and IFNγ-induction pathways. Infant AMϕs also exhibit lower expression of genes encoding mononuclear cell chemokines such as CXCL9. Our data indicates that failure of AMϕs to contain Mtb and recruit additional mononuclear cells to the site of infection helps to explain the more fulminant course of tuberculosis in early life.

Conformational flexibility of coenzyme A and its impact on the post-translational modification of acyl carrier proteins by 4'-phosphopantetheinyl transferases

One central question surrounding the biosynthesis of fatty acids and polyketide-derived natural products is how the 4'-phosphopantetheinyl transferase (PPTase) interrogates the essential acyl carrier protein (ACP) domain to fulfill the initial activation step. The triggering factor of this study was the lack of structural information on PPTases at physiological pH, which could bias our comprehension of the mechanism of action of these important enzymes. Structural and functional studies on the family II PPTase PptAb of Mycobacterium abscessus show that pH has a profound effect on the coordination of metal ions and on the conformation of endogenously bound coenzyme A (CoA). The observed conformational flexibility of CoA at physiological pH is accompanied by a disordered 4'-phosphopantetheine (Ppant) moiety. Finally, structural and dynamical information on an isolated mycobacterial ACP domain, in its apo form and in complex with the activator PptAb, suggests an alternate mechanism for the post-translational modification of modular megasynthases.

Draft Genome Sequence of a Mycobacterium porcinum Strain Isolated from a Pet Cat with Atypical Mycobacterial Panniculitis

A fast-growing Mycobacterium species was cultured from draining, purulent lesions on the caudal abdomen of a 12-year-old male domestic long-haired cat. Whole-genome sequencing identified the organism as Mycobacterium porcinum.

Differential determinants of virulence in two Mycobacterium tuberculosis Colombian clinical isolates of the LAM09 family

The heterogeneity of the clinical outcome of Mycobacterium tuberculosis (Mtb) infection may be due in part to different strategies used by circulating strains to cause disease. This heterogeneity is one of the main limitations to eradicate tuberculosis disease. In this study, we have compared the transcriptional response of two closely related Colombian clinical isolates (UT127 and UT205) of the LAM family under two axenic media conditions. These clinical isolates are phenotypically different at the level of cell death, cytokine production, growth kinetics upon in vitro infection of human tissue macrophages, and membrane vesicle secretion upon culture in synthetic medium. Using RNA-seq, we have identified different pathways that account for two different strategies to cope with the stressful condition of a carbon-poor media such as Sauton’s. We showed that the clinical isolate UT205 focus mainly in the activation of virulence systems such as the ESX-1, synthesis of diacyl-trehalose, polyacyl-trehalose, and sulfolipids, while UT127 concentrates its efforts mainly in the survival mode by the activation of the DNA replication, cell division, and lipid biosynthesis. This is an example of two Mtb isolates that belong to the same family and lineage, and even though they have a very similar genome, its transcriptional regulation showed important differences. This results in summary highlight the necessity to reach a better understanding of the heterogeneity in the behavior of these circulating Mtb strains which may help us to design better treatments and vaccines and to identify new targets for drugs.

Integrative proteomic and glycoproteomic profiling of Mycobacterium tuberculosis culture filtrate

Despite being the subject of intensive research, tuberculosis, caused by Mycobacterium tuberculosis, remains at present the leading cause of death from an infectious agent. Secreted and cell wall proteins interact with the host and play important roles in pathogenicity. These proteins are explored as candidate diagnostic markers, potential drug targets or vaccine antigens, and more recently special attention is being given to the role of their post-translational modifications. With the purpose of contributing to the proteomic and glycoproteomic characterization of this important pathogen, we performed a shotgun analysis of culture filtrate proteins of M. tuberculosis based on a liquid nano-HPLC tandem mass spectrometry and a label-free spectral counting normalization approach for protein quantification. We identified 1314 M. tuberculosis proteins in culture filtrate and found that the most abundant proteins belong to the extracellular region or cell wall compartment, and that the functional categories with higher protein abundance factor were virulence, detoxification and adaptation, and cell wall and cell processes. We could identify a group of proteins consistently detected in previous studies, most of which were highly abundant proteins. In culture filtrate, 140 proteins were predicted to contain one of the three types of bacterial N-terminal signal peptides. Besides, various proteins belonging to the ESX secretion systems, and to the PE and PPE families, secreted by the type VII secretion system using nonclassical secretion signals, were also identified. O-glycosylation was identified in 46 proteins, many of them lipoproteins and cell wall associated proteins. Finally, we provide proteomic evidence for 33 novel O-glycosylated proteins, aiding to the glycoproteomic characterization of relevant antigenic membrane and exported proteins. These findings are expected to collaborate with the research on pathogen derived biomarkers, virulence factors and vaccine candidates, and to provide clues to the understanding of the pathogenesis and survival strategies adopted by M. tuberculosis.

DMN-Tre Labeling for Detection and High-Content Screening of Compounds against Intracellular Mycobacteria

4-N,N-Dimethylamino-1,8-naphthalimide conjugate of trehalose (DMN-Tre) is a fluorogenic dye recently developed as a diagnostic tool for tuberculosis. DMN-Tre selectively labels the mycobacterial cell wall through the Ag85 enzymes. In this work, we disclose a protocol describing the total synthesis of DMN-Tre with more than 99% purity. We further developed a protocol for in vitro and intercellular labeling of various mycobacterial strains. DMN-Tre labeling was found to be a useful tool to study in vitro and intracellular Mycobacterium tuberculosis (Mtb) physiology and as an end-point readout system in high-content image-based screening (HCS) of drug molecules. Such uses of DMN-Tre labeling provide a simple, fast, and cheap alternative to the existing, time-consuming approach that requires Mtb strains to be genetically transformed with fluorescent reporter genes.

Granzyme B Attenuates Bacterial Virulence by Targeting Secreted Factors

Pathogenic bacteria secrete virulence factors that interact with the human host to establish infections. The human immune system evolved multiple mechanisms to fight bacterial invaders, including immune proteases that were demonstrated to contribute crucially to antibacterial defense. Here we show that granzyme B degrades multiple secreted virulence mediators from Listeria monocytogenes, Salmonella typhimurium, and Mycobacteria tuberculosis. Pathogenic bacteria, when infected in the presence of granzyme B or granzyme-secreting killer cells, fail to grow in human macrophages and epithelial cells owing to their crippled virulence. A granzyme B-uncleavable mutant form of the major Listeria virulence factor, listeriolysin O, rescued the virulence defect in response to granzyme treatment. Hence, we link the degradation of a single factor with the observed decrease in virulent bacteria growth. Overall, we reveal here an innate immune barrier function of granzyme B by disrupting bacterial virulence to facilitate bacteria clearance by bystander immune and non-immune cells.

CtpB is a plasma membrane copper (I) transporting P-type ATPase of Mycobacterium tuberculosis

BACKGROUND

The intracellular concentration of heavy-metal cations, such as copper, nickel, and zinc is pivotal for the mycobacterial response to the hostile environment inside macrophages. To date, copper transport mediated by P-type ATPases across the mycobacterial plasma membrane has not been sufficiently explored.

RESULTS

In this work, the ATPase activity of the putative Mycobacterium tuberculosis P1B-type ATPase CtpB was associated with copper (I) transport from mycobacterial cells. Although CtpB heterologously expressed in M. smegmatis induced tolerance to toxic concentrations of Cu2+ and a metal preference for Cu+, the disruption of ctpB in M. tuberculosis cells did not promote impaired cell growth or heavy-metal accumulation in whole mutant cells in cultures under high doses of copper. In addition, the Cu+ ATPase activity of CtpB embedded in the plasma membrane showed features of high affinity/slow turnover ATPases, with enzymatic parameters KM 0.19 ± 0.04 µM and Vmax 2.29 ± 0.10 nmol/mg min. In contrast, the ctpB gene transcription was activated in cells under culture conditions that mimicked the hostile intraphagosomal environment, such as hypoxia, nitrosative and oxidative stress, but not under high doses of copper.

CONCLUSIONS

The overall results suggest that M. tuberculosis CtpB is associated with Cu+ transport from mycobacterial cells possibly playing a role different from copper detoxification.

ClpB is an essential stress regulator of Mycobacterium tuberculosis and endows survival advantage to dormant bacilli

The ability to tolerate multiple host derived stresses, resist eradication and persist within the infected individuals is central to the pathogenicity of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). Mycobacterial survival is contingent upon sensing environmental perturbations and initiating a fitting response to counter them. Therefore, understanding of molecular mechanisms underlying stress tolerance and sensing in Mtb is critical for devising strategies for TB control. Our study aims to delineate the role of ClpB, a heat shock protein of Hsp100 family, in the general stress response and persistence mechanisms of Mtb. We demonstrate that Mtb requires ClpB to survive under stressful conditions. Additionally, we show that ClpB is necessary for the bacteria to persist in latency-like conditions such as prolonged hypoxia and nutrient-starvation. The disruption of ClpB results in aberrant cellular morphology, impaired biofilm formation and reduced infectivity of Mtb ex vivo. Our study also reports an alternative role of ClpB as a chaperokine which elicits inflammatory response in host. We conclude that ClpB is essential for Mtb to survive within macrophages, and plays a crucial part in the maintenance of dormant Mtb bacilli in latent state. The absence of ClpB in human genome makes it an attractive choice as drug target for TB.

Computational Identification of the Proteins Associated With Quorum Sensing and Biofilm Formation in Mycobacterium tuberculosis

With prolonged therapy and increased instances of drug resistance, tuberculosis is viewed as a serious infectious disease causing high mortality. Emerging concepts in Mycobacterium tuberculosis pathogenicity include biofilm formation, which endows bacterial survival in the host for a long time. To tackle chronic tuberculosis infection, a detailed understanding of the bacterial survival mechanisms is crucial. Using comparative genomics and literature mining, 115 M. tuberculosis proteins were shortlisted for their likely association with biofilm formation or quorum sensing. These include essential genes such as secA2, lpqY-sugABC, Rv1176c, and Rv0195, many of which are also known virulence factors. Furthermore, the functional relationship among these proteins was established by considering known protein-protein interactions, regulatory interactions, and gene expression correlation data/information. Graph centrality and motif analyses predicted the importance of proteins, such as Rv0081, DevR, RegX3, Rv0097, and Rv1996 in M. tuberculosis biofilm formation. Analysis of conservation across other biofilm-forming bacteria suggests that most of these genes are conserved in mycobacteria. As the processes, such as quorum sensing, leading to biofilm formation involve diverse pathways and interactions between proteins, these system-wide studies provide a novel perspective toward understanding mycobacterial persistence.

A Human Lung-Associated Streptomyces sp. TR1341 Produces Various Secondary Metabolites Responsible for Virulence, Cytotoxicity and Modulation of Immune Response

Streptomycetes, typical soil dwellers, can be detected as common colonizers of human bodies, especially the skin, the respiratory tract, the guts and the genital tract using molecular techniques. However, their clinical manifestations and isolations are rare. Recently they were discussed as possible "coaches" of the human immune system in connection with certain immune disorders and cancer. This work aimed for the characterization and evaluation of genetic adaptations of a human-associated strain Streptomyces sp. TR1341. The strain was isolated from sputum of a senior male patient with a history of lung and kidney TB, recurrent respiratory infections and COPD. It manifested remarkably broad biological activities (antibacterial, antifungal, beta-hemolytic, etc.). We found that, by producing specific secondary metabolites, it is able to modulate host immune responses and the niche itself, which increase its chances for long-term survival in the human tissue. The work shows possible adaptations or predispositions of formerly soil microorganism to survive in human tissue successfully. The strain produces two structural groups of cytotoxic compounds: 28-carbon cytolytic polyenes of the filipin type and actinomycin X2. Additionally, we summarize and present data about streptomycete-related human infections known so far.

Molecular epidemiological study of multidrug-resistant tuberculosis isolated from sputum samples in Eastern Cape, South Africa

Drug-resistant tuberculosis prevalence is still a global challenge. Making it imperative to examine the molecular epidemiology of drug resistant tuberculosis. Molecular epidemiology methods can evaluate transmission patterns and risk factors, ascertain transmission cases of multidrug-resistant tuberculosis (MDR-TB) and furthermore determine transmission patterns in a human populace. This work focuses on MDR-TB isolates in distinguishing them into several species and genotyping the MDR-TB isolates, mainly for epidemiological studies using the genomic regions of difference and the spoligotyping techniques. A total of 184 deoxyribonucleic acid isolated from sputum samples that showed resistance against the two major first-line anti-tuberculosis drugs (Rifampicin and Isoniazid) were examined. The deoxyribonucleic acid samples were amplified with primers specific for each flanking region of the genomic regions of difference for the identification of different MTBC species. Isolates were further characterized into different lineages using the spoligotyping commercial kit. The M. tuberculosis species was detected in 83.7% (154/184) of the deoxyribonucleic acid isolates, followed by the M. caprae in 8.7% (16/184) and the least detected species was the M. africanum in 2.2% (4/184). Nineteen spoligotype international types (SITs) were identified in this study. The pre-existing shared types were from 94.6% (174/184) isolates with 1.1% (2/184) isolates recognized as orphans and 4.3% (8/184) isolates were not found in the SITVIT database. The predominant family (spoligotype) was the Beijing with 67.4% (124/184) strains. This study gives a general overview of drug resistant strains and the circulating strains in the Eastern Cape, South Africa and it shows that the common Mycobacteria in the province is the Beijing strain.

Dynamic Characterization of Protein and Posttranslational Modification Levels in Mycobacterial Cholesterol Catabolism

Cholesterol assimilation is a critical step in mycobacterial chronic infection. However, knowledge from the dynamic characterization of cholesterol metabolism in mycobacteria at the protein expression and PTM levels remains limited. Our study uncovered the landscape of protein expression, lysine acetylation, lysine propionylation, and S/T/Y phosphorylation during the metabolic changes from glucose to cholesterol in mycobacteria. The data showed that cholesterol-induced carbon shift resulted in the elevation of protein expression and lysine acylation in diverse metabolic enzymes involved in cholesterol degradation and that the presence of cholesterol also promoted the perturbations at the phosphorylation level in the kinase system in mycobacteria. This study systematically characterized the regulation of cholesterol catabolism at several different levels, which provided the detailed references in mycobacterial proteome and potential antimycobacterial strategies.

Cholesterol of the host macrophage membrane is vital for mycobacterial infection, replication, and persistence. During chronic infection within host lung tissues, cholesterol facilitates the phagocytosis of mycobacteria into macrophages. Cholesterol degradation leads to increased flux of acetyl-coenzyme A (CoA) and propionyl-CoA, providing energy and building blocks for virulence macromolecules as well as donors for global protein acylation. Potential functions of lysine acylation are gradually revealed in bacterial survival and pathogenesis. However, the mycobacterial proteome and posttranslational modification (PTM) changes involved in the cholesterol catabolism bioprocess remain unclear. Here, we used nonpathogenic Mycobacterium smegmatis as a model and simultaneously monitored mycobacterial proteome and acetylome changes in the presence of glucose and cholesterol. We discovered that cholesterol metabolic enzymes were upregulated with respect to both protein expression levels and lysine acylation levels during the metabolic shift from glucose to cholesterol. After that, adenylating enzymes related to cholesterol metabolism were proven to be precisely regulated at the propionylation level by mycobacterial acyltransferase M. smegmatis Kat (MsKat) in response to cellular propionyl-CoA accumulation. Furthermore, the kinase expression and phosphorylation levels were also changed along with fluctuations in cholesterol levels. Our results expanded current knowledge of acylation regulation in the cholesterol catabolism of mycobacteria and provided references for possible antimycobacterium strategy.

IMPORTANCE Cholesterol assimilation is a critical step in mycobacterial chronic infection. However, knowledge from the dynamic characterization of cholesterol metabolism in mycobacteria at the protein expression and PTM levels remains limited. Our study uncovered the landscape of protein expression, lysine acetylation, lysine propionylation, and S/T/Y phosphorylation during the metabolic changes from glucose to cholesterol in mycobacteria. The data showed that cholesterol-induced carbon shift resulted in the elevation of protein expression and lysine acylation in diverse metabolic enzymes involved in cholesterol degradation and that the presence of cholesterol also promoted the perturbations at the phosphorylation level in the kinase system in mycobacteria. This study systematically characterized the regulation of cholesterol catabolism at several different levels, which provided the detailed references in mycobacterial proteome and potential antimycobacterial strategies.

Circulation of M. tuberculosis Beijing genotype in Latin America and the Caribbean

Lineage 2 (East Asian), which includes the Beijing genotype, is one of the most prevalent lineages of Mycobacterium tuberculosis (Mtb) throughout the world. The Beijing family is associated to hypervirulence and drug-resistant tuberculosis. The study of this genotype's circulation in Latin America is crucial for achieving total control of TB, the goal established by the World Health Organization, for the American sub-continent, before 2035. In this sense, the present work presents an overview of the status of the Beijing genotype for this region, with a bibliographical review, and data analysis of MIRU-VNTRs for available Beijing isolates. Certain countries present a prevalent trend of <5%, suggesting low transmissibility for the region, with the exception of Cuba (17.2%), Perú (16%) and Colombia (5%). Minimum Spanning Tree analysis, obtained from MIRU-VNTR data, shows distribution of specific clonal complex strains in each country. From this data, in most countries, we found that molecular epidemiology has not been a tool used for the control of TB, suggesting that the Beijing genotype may be underestimated in Latin America. It is recommended that countries with the highest incidence of the Beijing genotype use effective control strategies and increased care, as a requirement for public health systems.

Cloning, Expression and Purification of Espc, Espb and Espc/Espb Proteins of Mycobacterium tuberculosis ESX-1 Secretion System

BACKGROUND

It is estimated that one third of the world's population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of Tuberculosis (TB). The BCG vaccine is widely used to fight against TB; however, many question its ability to provide complete protection from Mtb. Recently, the "Region of Difference 1" (RD1) set of genes were shown to be involved in the pathogenesis of Mtb. Downstream of RD1 transcription region, two proteins are encoded, known as EspB and EspC, which were found to contribute to Mtb virulence.In this study these two proteins are targeted as potential vaccine candidates against TB.

METHODS

The EspB and EspC Mtb genes were codon-optimized for expression and synthesis in Escherichia coli (E. coli). The amplicons were cloned into a pET21a expression vector and transformed into E. coli BL21(DE3). The expression and purity of the expressed proteins (i.e. rEspC, rEspB and rEspC/EspB) were confirmed by SDS-PAGE and Western blotting. Moreover, BALB/c mice were immunized against Mtb using the recombinant proteins. Finally, the mice sera were analyzed via Western blotting.

RESULTS

EspC, EspB, and EspC/EspB fusion genes were cloned and expressed in E. coli. Both SDS-PAGE and Western blots confirmed the presence and successful purification of the desired proteins. Moreover, antisera produced against the purified recombinant proteins reacted with Mtb proteins.

CONCLUSION

rEspC, rEspB, and rEspC/EspB could be expressed and purified using an E. coli expression system. The recombinant proteins induced the production of antibodies in BALB/c mice that reacted with Mtb proteins.

Interplays between copper and Mycobacterium tuberculosis GroEL1

The chaperone GroEL1 enhances copper tolerance during Mycobacterium bovis BCG biofilm formation. The binding of copper ions to the GroEL1 histidine-rich region protects the chaperone from destabilization and increases its ATPase activity.

Chronic respiratory diseases: An introduction and need for novel drug delivery approaches

Globally, chronic respiratory diseases (CRDs), both communicable and noncommunicable, are among the leading causes of mortality, morbidity, economic and societal burden, and disability-adjusted life years (DALYs). CRDs affect multiple components of respiratory system, including the airways, parenchyma, and pulmonary vasculature. Although noncommunicable respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), cystic fibrosis (CF), and lung cancer (LC), account for enormous disease burden, the currently available therapies only focus on alleviating the symptoms of diseases rather than providing optimal treatment and/or prevention. Similarly a major respiratory communicable disease, that is, tuberculosis (TB), is associated with the challenge of increasingly developing antibiotic resistance in the bacterial pathogen Mycobacterium tuberculosis. In light of these challenges, we aim to summarize the underlying molecular and cellular mechanisms that lead to hallmark pathophysiology of CRDs. Moreover, we will also highlight the limitations of current therapeutic strategies and explore novel drug delivery options that may be potentially more effective in the management of CRDs.

Identifying the Structural Features of Diphenyl Ether Analogues for InhA Inhibition: A 2D and 3D QSAR Based Study

Background:

Enoyl acyl carrier protein reductase (InhA) is a validated target for Mycobacterium. It is an enzyme which is associated with the biosynthesis of mycolic acids in type II fatty acid synthase system. Mycobacterial cell wall majorly comprises mycolic acids, which are responsible for virulence of the microorganism. Several diphenyl ether derivatives have been known to be direct inhibitors of InhA.

Objective:

In the present work, a Quantitative Structure Activity Relationship (QSAR) study was performed to identify the structural features of diphenyl ether analogues which contribute to InhA inhibitory activity in a favourable way.

Method:

Both 2D and 3D QSAR models were built and compared. Several fingerprint based 2D QSAR models were generated and their relationship with the structural features was studied. Models which corroborated the inhibitory activity of the molecules with their structural features were selected and studied in detail.

Results:

A 2D-QSAR model, with dendritic fingerprints having regression coefficient, for test set molecules Q2 =0.8132 and for the training set molecules, R2 =0.9607 was obtained. Additionally, an atom-based 3D-QSAR model with Q2 =0.7697 and R2 =0.9159 was also constructed.

Conclusion:

The data reported by various models provides guidance for the designing of structurally new diphenyl ether inhibitors with potential activity against InhA of M. tuberculosis.

Mycobacterium tuberculosis Requires Cholesterol Oxidase to Disrupt TLR2 Signalling in Human Macrophages

This study tested the hypothesis that Mycobacterium tuberculosis (Mtb) uses a cholesterol oxidase enzyme (ChoD) to suppress a toll-like receptor type 2- (TLR2-) dependent signalling pathway to modulate macrophages' immune response. We investigated the impact of Mtb possessing or lacking ChoD as well as TBChoD recombinant protein obtained from Mtb on the expression and activation of two key intracellular proteins involved in TLR2 signalling in human macrophages. Finally, the involvement of TLR2-related signalling proteins in an inflammatory/immunosuppressive response of macrophages to Mtb was evaluated. We demonstrate that wild-type Mtb but not the ∆choD mutant decreased the cytosolic IRAK4 and TRAF6 protein levels while strongly enhancing IRAK4 and TRAF6 mRNA levels in macrophages. Our data show that the TLR2 present on the surface of macrophages are involved in disturbing the signalling pathway by wild-type Mtb. Moreover, recombinant TBChoD effectively decreased the cytosolic level of TRAF6 and lowered the phosphorylation of IRAK4, which strongly confirm an involvement of cholesterol oxidase in affecting the TLR2-related pathway by Mtb. Wild-type Mtb induced an immunosuppressive response of macrophages in an IRAK4- and TRAF6-dependent manner as measured by interleukin 10 production. In conclusion, ChoD is a virulence factor that enables Mtb to disturb the TLR2-related signalling pathway in macrophages and modulate their response.

Cytological diagnosis in a clinically unsuspected case of disseminated BCGosis: A case report

Bacille Calmette-Guerin (BCG) vaccine is administered worldwide to neonates and considered safe. Serious complications like disseminated BCGosis are extremely rare occurrences (<1 per million vaccinations). A 6 months male was brought to paediatric outpatient department with fever and swelling over the dorsum of the left hand for 5 days. On examination, he was febrile and had hepatosplenomegaly. X-ray of the hand showed lytic lesions in the first and second metacarpals. Provisional clinical diagnosis included Langerhans cell histiocytosis, congenital syphilis, and haematological malignancy. Fine Needle Aspiration Cytology (FNAC) was done from the swelling and showed diffuse sheets of histiocytes with both intracellular and extracellular rod-shaped unstained structures along with inflammatory cells. These ghost images stained positive with ZN stain. A cytological diagnosis of atypical mycobacteria vs leprosy was made. Child was revisited and found to have an active BCG scar. Further investigations showed low serum IgM and positive AFB culture. These bacilli were confirmed by GenoType MTBDR plus test as Mycobacterium bovis. Despite Antitubercular therapy, the patient succumbed to death. This case highlights the variable clinical presentation of BCGosis. Its occurrence may unmask any underlying immunodeficiency. If unfamiliar with the above cytological features and in absence of routinely performed special stains, the cytopathologist may miss these notorious organisms and treat such cases like suppurative lesions. To conclude, an early and definitive diagnosis of BCGosis can be established on FNAC which would ensure timely management and better outcome in this highly lethal entity.

Draft Genome Sequences of Mycobacterium tuberculosis Clinical Isolates from the Ural Region of Russia That Carry the pks15/1 Gene

Here, we report the draft genome sequences of 15 Mycobacterium tuberculosis isolates of the Beijing-B0/W-148 sublineage that carry a 7-bp insertion within the pks15 gene, which leads to the synthesis of Pks15/1 fusion protein. Pks15/1 is involved in phenolglycolipid synthesis and biofilm formation, thus potentially contributing to the B0/W-148 lineage's enhanced virulence and drug resistance.

Rv2617c and P36 are virulence factors of pathogenic mycobacteria involved in resistance to oxidative stress

In this study, we characterized the role of Rv2617c in the virulence of Mycobacterium tuberculosis. Rv2617c is a protein of unknown function unique to M. tuberculosis complex (MTC) and Mycobacterium leprae. In vitro, this protein interacts with the virulence factor P36 (also named Erp) and KdpF, a protein linked to nitrosative stress. Here, we showed that knockout of the Rv2617c gene in M. tuberculosis CDC1551 reduced the replication of the pathogen in a mouse model of infection and favored the trafficking of mycobacteria to phagolysosomes. We also demonstrated that Rv2617c and P36 are required for resistance to in vitro hydrogen peroxide treatment in M. tuberculosis and Mycobacterium bovis, respectively. These findings indicate Rv2617c and P36 act in concert to prevent bacterial damage upon oxidative stress.

Spoligotyping and drug sensitivity of Mycobacterium tuberculosis isolated from pulmonary tuberculosis patients in the Arsi Zone of southeastern Ethiopia

Tuberculosis (TB) is one of the leading causes of morbidity and mortality in different zones of Ethiopia. This study was undertaken to identify the strains of Mycobacterium tuberculosis and evaluate their drug sensitivity profiles in the Arsi Zone. A total of 111 isolates of M. tuberculosis from individuals with pulmonary TB were included and speciation and strain identification were performed using Region of difference 9 and spoligotyping, respectively. The drug sensitivity patterns were assessed using Bactec MGIT 960 SIRE and GenoType MTBDRplus line probe assays. Of 111 isolates, 83% were interpretable and 56 different spoligotype patterns were identified. From these, 22 patterns were shared types while the remaining 34 were orphans. The predominant shared types were spoligotype international type (SIT) 149 and SIT53, comprising 12 and 11 isolates, respectively. Euro-American lineage was the dominant lineage followed by East-African-Indian. Phenotypically, 17.2% of tested isolates were resistant to any first-line drugs and 3.1% were multidrug-resistant. Higher (6.2%) mono-resistance was observed to streptomycin, and no resistance was observed to rifampicin or ethambutol. Genotypically, five (5.4%) isolates were resistant to isoniazid and mutated at codon S315T1 of katG. In contrast, only 1.1% of the isolates were resistant to rifampicin and were mutated at codon S531L of rpoB gene. In this study, a high proportion of orphan strains were isolated, which could suggest the presence of new strains and a high percentage of mono-resistance, warranting the need to strengthen control efforts.

The conical shape of DIM lipids promotes Mycobacterium tuberculosis infection of macrophages

Phthiocerol dimycocerosate (DIM) is a major virulence factor of the pathogen Mycobacterium tuberculosis (Mtb). While this lipid promotes the entry of Mtb into macrophages, which occurs via phagocytosis, its molecular mechanism of action is unknown. Here, we combined biophysical, cell biology, and modeling approaches to reveal the molecular mechanism of DIM action on macrophage membranes leading to the first step of Mtb infection. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry showed that DIM molecules are transferred from the Mtb envelope to macrophage membranes during infection. Multiscale molecular modeling and ³¹P-NMR experiments revealed that DIM adopts a conical shape in membranes and aggregates in the stalks formed between 2 opposing lipid bilayers. Infection of macrophages pretreated with lipids of various shapes uncovered a general role for conical lipids in promoting phagocytosis. Taken together, these results reveal how the molecular shape of a mycobacterial lipid can modulate the biological response of macrophages.

Analysing nonsynonymous mutations between two Mycobacterium bovis strains with contrasting pathogenic profiles

Mycobacterium bovis (M. bovis) is the causative agent of bovine tuberculosis, a chronic infectious disease that can affect cattle, other domesticated species, wild animals and humans. This disease produces important economic losses worldwide. Two M. bovis strains (04-303 and 534) have been isolated in Argentina. Whereas the 04-303 strain was isolated from a wild boar, the 534 strain was obtained from cattle. In a previous study, six weeks after infection, the 04-303 strain induced 100% mortality in mice. By contrast, mice infected with the 534 strain survived, with limited tissue damage, after four months. In this study we compared all predictive proteins encoded in both M. bovis genomes. The comparative analysis revealed 141 polymorphic proteins between both strains. From these proteins, nine virulence proteins showed polymorphisms in 04-303, whereas five did it in the 534 strain. Remarkably, both strains contained a high level of polymorphism in proteins related to phthiocerol dimycocerosate (PDIM) synthesis or transport. Further experimental evidence indicated that only mutations in the 534 strain have an impact on PDIM synthesis. The observed reduction in PDIM content in the 534 strain, together with its low capacity to induce phagosome arrest, may be associated with the reported deficiency of this strain to replicate and survive inside bovine macrophages. The findings of this study could contribute to a better understanding of pathogenicity and virulence aspects of M. bovis, which is essential for further studies aiming at developing new vaccines and diagnostic techniques for bovines.

Rewiring of Metabolic Network in Mycobacterium tuberculosis During Adaptation to Different Stresses

Metabolic adaptation of Mycobacterium tuberculosis (M. tuberculosis) to microbicidal intracellular environment of host macrophages is fundamental to its pathogenicity. However, an in-depth understanding of metabolic adjustments through key reaction pathways and networks is limited. To understand how such changes occur, we measured the cellular metabolome of M. tuberculosis subjected to four microbicidal stresses using liquid chromatography-mass spectrometric multiple reactions monitoring (LC-MRM/MS). Overall, 87 metabolites were identified. The metabolites best describing the separation between stresses were identified through multivariate analysis. The coupling of the metabolite measurements with existing genome-scale metabolic model, and using constraint-based simulation led to several new concepts and unreported observations in M. tuberculosis; such as (i) the high levels of released ammonia as an adaptive response to acidic stress was due to increased flux through L-asparaginase rather than urease activity; (ii) nutrient starvation-induced anaplerotic pathway for generation of TCA intermediates from phosphoenolpyruvate using phosphoenolpyruvate kinase; (iii) quenching of protons through GABA shunt pathway or sugar alcohols as possible mechanisms of early adaptation to acidic and oxidative stresses; and (iv) usage of alternate cofactors by the same enzyme as a possible mechanism of rewiring metabolic pathways to overcome stresses. Besides providing new leads and important nodes that can be used for designing intervention strategies, the study advocates the strength of applying flux balance analyses coupled with metabolomics to get a global picture of complex metabolic adjustments.

Mycobacterium tuberculosis Rv0426c promotes recombinant mycobacteria intracellular survival via manipulating host inflammatory cytokines and suppressing cell apoptosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) is still a leading cause of death worldwide. M. tuberculosis has evolved multipronged strategies to subvert host immune defenses and establish an immunologically privileged niche in macrophages. Rv0426c has been predicted to be an effector involved in the Mtb-host interactions. To investigate the potential role played by Rv0426c, we constructed recombinant M. smegmatis strains with heterologous expression of Rv0426c. We observed that Rv0426c recombinants became more susceptible to various stresses by increasing cell wall permeability, however with elevated early survival rate within macrophages. This was accompanied by decreased levels of pro-inflammatory cytokines and host cell apoptosis. The data suggested that Rv0426c was a new player involved in the interactions between Mtb and macrophages.

In Vivo Methods to Study Protein-Protein Interactions as Key Players in Mycobacterium Tuberculosis Virulence

Studies on protein–protein interactions (PPI) can be helpful for the annotation of unknown protein functions and for the understanding of cellular processes, such as specific virulence mechanisms developed by bacterial pathogens. In that context, several methods have been extensively used in recent years for the characterization of Mycobacterium tuberculosis PPI to further decipher tuberculosis (TB) pathogenesis. This review aims at compiling the most striking results based on in vivo methods (yeast and bacterial two-hybrid systems, protein complementation assays) for the specific study of PPI in mycobacteria. Moreover, newly developed methods, such as in-cell native mass resonance and proximity-dependent biotinylation identification, will have a deep impact on future mycobacterial research, as they are able to perform dynamic (transient interactions) and integrative (multiprotein complexes) analyses.