Viability Of Mycobacterium Tuberculosis Research Articles

Evolutionarily divergent Mycobacterium tuberculosis CTP synthase filaments are under selective pressure.

The final and rate-limiting enzyme in pyrimidine biosynthesis, CTP synthase (CTPS) , is essential for the viability of Mycobacterium tuberculosis and other mycobacteria. Its product, CTP, is critical for RNA, DNA, lipid and cell wall synthesis, and is involved in chromosome segregation. In various organisms across the tree of life, CTPS assembles into higher-order filaments, leading us to hypothesize that M. tuberculosis CTPS (mtCTPS) also forms higher-order structures. Here, we show that mtCTPS does assemble into filaments but with an unusual architecture not seen in other organisms. Through a combination of structural, biochemical, and cellular techniques, we show that polymerization stabilizes the active conformation of the enzyme and resists product inhibition, potentially allowing for the highly localized production of CTP within the cell. Indeed, CTPS filaments localize near the CTP-dependent complex needed for chromosome segregation, and cells expressing mutant enzymes unable to polymerize are altered in their ability to robustly form this complex. Intriguingly, mutants that alter filament formation are under positive selection in clinical isolates of M. tuberculosis, pointing to a critical role needed to withstand pressures imposed by the host and/or antibiotics. Taken together, our data reveal an unexpected mechanism for the spatially organized production of a critical nucleotide in M. tuberculosis, which may represent a vulnerability of the pathogen that can be exploited with chemotherapy.

M. tuberculosis PrrA binds the dosR promoter and regulates mycobacterial adaptation to hypoxia

The PrrAB two-component system (TCS) is essential for Mycobacterium tuberculosis viability. Previously, it was demonstrated that PrrA binds DNA in the absence of PrrB-mediated transphosphorylation and that non-cognate serine/threonine-kinases phosphorylate PrrA threonine-6 (T6). Therefore, we investigated the differential binding affinity and regulatory properties of the M. tuberculosis-derived wild-type PrrA, PrrA phosphomimetic (D58E, T6E), and PrrA phosphoablative (D58A, T6A) proteins with the prrAMtb, dosRMtb, and cydAMtb genes. While we hypothesized greater DNA binding affinity and more pronounced regulation by PrrA phosphomimetic variants, recombinant, wild-type PrrAMtb bound DNA with greatest affinity. Collectively, wild-type PrrAMtb recombinant protein displayed the highest binding affinity to the dosRMtb promoter (KD 3.46 ± 2.09 nM), followed by the prrAMtb promoter (KD 9.00 ± 2.66 nM). To establish PrrAMtb regulatory activity, we constructed M. smegmatis ΔprrABMsmeg::prrAMtb strains with each of the PrrAMtb variants and extrachromosomal prrAMtb, dosRMtb, and cydAMtb promoter-mCherry reporter fusions. Our findings showed that PrrAMtb is autoregulatory and induces dosRMtb expression only during in vitro, hypoxic growth. Combined expression of prrABMtb in M. smegmatis ΔprrAB significantly induced cydAMtb promoter-mCherry expression. Our studies advanced the understanding of PrrA function and PrrAB phosphorylation-mediated regulatory mechanisms and control of mycobacterial dosR and cydA hypoxic and low-oxygen responsive genes.

Structure of the M. tuberculosis DnaK−GrpE complex reveals how key DnaK roles are controlled

The molecular chaperone DnaK is essential for viability of Mycobacterium tuberculosis (Mtb). DnaK hydrolyzes ATP to fold substrates, and the resulting ADP is exchanged for ATP by the nucleotide exchange factor GrpE. It has been unclear how GrpE couples DnaK’s nucleotide exchange with substrate release. Here we report a cryo-EM analysis of GrpE bound to an intact Mtb DnaK, revealing an asymmetric 1:2 DnaK−GrpE complex. The GrpE dimer ratchets to modulate both DnaK nucleotide-binding domain and the substrate-binding domain. We further show that the disordered GrpE N-terminus is critical for substrate release, and that the DnaK−GrpE interface is essential for protein folding activity both in vitro and in vivo. Therefore, the Mtb GrpE dimer allosterically regulates DnaK to concomitantly release ADP in the nucleotide-binding domain and substrate peptide in the substrate-binding domain.

Cryo-EM structures for the Mycobacterium tuberculosis iron-loaded siderophore transporter IrtAB.

The adenosine 5'-triphosphate (ATP)-binding cassette (ABC) transporter, IrtAB, plays a vital role in the replication and viability of Mycobacterium tuberculosis (Mtb), where its function is to import iron-loaded siderophores. Unusually, it adopts the canonical type IV exporter fold. Herein, we report the structure of unliganded Mtb IrtAB and its structure in complex with ATP, ADP, or ATP analogue (AMP-PNP) at resolutions ranging from 2.8 to 3.5 Å. The structure of IrtAB bound ATP-Mg2+ shows a "head-to-tail" dimer of nucleotide-binding domains (NBDs), a closed amphipathic cavity within the transmembrane domains (TMDs), and a metal ion liganded to three histidine residues of IrtA in the cavity. Cryo-electron microscopy (Cryo-EM) structures and ATP hydrolysis assays show that the NBD of IrtA has a higher affinity for nucleotides and increased ATPase activity compared with IrtB. Moreover, the metal ion located in the TM region of IrtA is critical for the stabilization of the conformation of IrtAB during the transport cycle. This study provides a structural basis to explain the ATP-driven conformational changes that occur in IrtAB.

PPE51 mediates uptake of trehalose across the mycomembrane of Mycobacterium tuberculosis

The disaccharide trehalose is essential for viability of Mycobacterium tuberculosis, which synthesizes trehalose de novo but can also utilize exogenous trehalose. The mycobacterial cell wall encompasses two permeability barriers, the cytoplasmic membrane and the outer mycolic acid-containing mycomembrane. The ABC transporter LpqY–SugA–SugB–SugC has previously been demonstrated to mediate the specific uptake of trehalose across the cytoplasmic membrane. However, it is still unclear how the transport of trehalose molecules across the mycomembrane is mediated. In this study, we harnessed the antimycobacterial activity of the analogue 6-azido trehalose to select for spontaneous resistant M. tuberculosis mutants in a merodiploid strain harbouring two LpqY–SugA–SugB–SugC copies. Mutations mediating resistance to 6-azido trehalose mapped to the proline–proline–glutamate (PPE) family member PPE51 (Rv3136), which has recently been shown to be an integral mycomembrane protein involved in uptake of low-molecular weight compounds. A site-specific ppe51 gene deletion mutant of M. tuberculosis was unable to grow on trehalose as the sole carbon source. Furthermore, bioorthogonal labelling of the M. tuberculosis Δppe51 mutant incubated with 6-azido trehalose corroborated the impaired internalization. Taken together, the results indicate that the transport of trehalose and trehalose analogues across the mycomembrane of M. tuberculosis is exclusively mediated by PPE51.

Radiological and functional evidence of the bronchial spread of tuberculosis: an observational analysis

SummaryBackgroundDirect bronchial spread of tuberculosis was extensively described in pre-antibiotic human pathology literature but this description has been overlooked in the post-antibiotic era, in which most pathology data come from animal models that emphasise the granuloma. Modern techniques, such as [18F]2-fluoro-2-deoxy-D-glucose (FDG) PET-CT scans, might provide further insight. Our aim was to understand normal early tuberculosis resolution patterns on pulmonary PET-CT scans in treated patients with tuberculosis who were subsequently cured.MethodsIn this observational analysis, we analysed data from PredictTB, an ongoing, prospective, randomised clinical trial that examined sequential baseline and week 4 FDG-PET-CT scans from participants successfully treated (sputum culture negative 18 months after enrolment) for drug-susceptible pulmonary tuberculosis in South Africa and China. Participants who were aged 18–75 years, GeneXpert MTB/RIF positive for tuberculosis and negative for rifampicin resistance, had not yet started tuberculosis treatment, had not been treated for active tuberculosis within the previous 3 years, and met basic safety laboratory criteria were included and participants with diabetes, HIV infection, or with extrapulmonary tuberculosis including pleural tuberculosis were excluded. Scans were assessed by two readers for the location of tuberculosis lesions (eg, cavities and consolidations), bronchial thickening patterns, and changes from baseline to week 4 of treatment.FindingsAmong the first 124 participants (enrolled from June 22, 2017, to Sept 27, 2018) who were successfully treated, 161 primarily apical cavitary lesions were identified at baseline. Bronchial thickening and inflammation linking non-cavitary consolidative lesions to cavities were observed in 121 (98%) of 124 participants' baseline PET-CT scans. After 4 weeks of treatment, 21 (17%) of 124 participants had new or expanding lesions linked to cavities via bronchial inflammation that were not present at baseline, particularly participants with two or more cavities at baseline and participants from South Africa.InterpretationIn participants with pulmonary tuberculosis who were subsequently cured, the location of cavitary and non-cavitary lesions at baseline and new lesions at week 4 of treatment suggest a cavitary origin of disease and bronchial spread through the lungs. Bronchial spread from cavities might play a larger role in the spread of pulmonary tuberculosis than has been appreciated. Elucidating cavity lesion dynamics and Mycobacterium tuberculosis viability within cavities might better explain treatment outcomes and why some patients are cured and others relapse.FundingBill & Melinda Gates Foundation, European and Developing Countries Clinical Trials Partnership, China Ministry of Science and Technology, National Natural Science Foundation of China, and National Institutes of Health.TranslationsFor the Chinese, Afrikaans and Xhosa translations of the abstract see Supplementary Materials section.

Population Pharmacokinetic Analyses of Isoniazid in Tuberculosis Treatment: a Systematic Review

The aims of this systematic review are to provide knowledge concerning population pharmacokinetics of isoniazid (INH) and to identify factors influencing INH pharmacokinetic variability. Pubmed and Embase databases were systematically searched from inception to July, 2017. Relevant articles from reference lists were also included. All population pharmacokinetic studies of INH written in English, conducted in human (either healthy subjects or pulmonary tuberculosis patients) were included in this review. Ten studies were included in this review. Most studies characterized a two-compartment model with first-order kinetics for INH with a transit-compartment model for absorption suggested. Frequently reported significant predictors for INH clearance is NAT2 acetylator types (slow/intermediate/fast), while weight is a significant covariate for INH volume of distribution (both central and peripheral). In children, enzyme maturation had a profound affect on INH clearance.
 Keywords:
 Population pharmacokinetics, Isoniazid.
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Everolimus-induced effector mechanism in macrophages and survivability of Erdman, CDC1551 and HN878 strains of Mycobacterium tuberculosis infection.

With a disease as widespread and destructive as tuberculosis, more effective drugs and healthcare strategies, in addition to the current antibiotics regimen, are crucial for the enhanced well-being of millions of people suffering from the disease. Host-directed therapy is a new and emerging concept in treating chronic infectious diseases, such as tuberculosis. Repurposing of anti-cancer drugs, such as everolimus, may be an effective way to supplement the standard antibiotic treatment. Individuals with type 2 diabetes are increasingly susceptible to co-morbidities and co-infections including Mycobacterium tuberculosis, the causative agent of tuberculosis. We demonstrated in this study that in vitro everolimus treatment of granulomas from individuals with type 2 diabetes caused significant reduction in the viability of Mycobacterium tuberculosis.Further investigations revealed the effects of everolimus in targeting foamy macrophages, a macrophage phenotype that forms around granulomas, and is characterized by a higher lipid accumulation inside the cells. These foamy macrophages are thought to harbor dormant bacilli, which are potential sources of disease reactivation. Therefore, blocking foamy macrophage formation would help better killing of intracellular bacteria. Here, we report the potential of everolimus treatment to downregulate lipid content within the foamy macrophages of in vitro granulomas, thus leading to a potential decrease in the number of foamy macrophages and a more robust response to Mycobacterium tuberculosis.

Discovery of a Novel Mycobacterial F-ATP Synthase Inhibitor and its Potency in Combination with Diarylquinolines.

The F1 FO -ATP synthase is required for growth and viability of Mycobacterium tuberculosis and is a validated clinical target. A mycobacterium-specific loop of the enzyme's rotary γ subunit plays a role in the coupling of ATP synthesis within the enzyme complex. We report the discovery of a novel antimycobacterial, termed GaMF1, that targets this γ subunit loop. Biochemical and NMR studies show that GaMF1 inhibits ATP synthase activity by binding to the loop. GaMF1 is bactericidal and is active against multidrug- as well as bedaquiline-resistant strains. Chemistry efforts on the scaffold revealed a dynamic structure activity relationship and delivered analogues with nanomolar potencies. Combining GaMF1 with bedaquiline or novel diarylquinoline analogues showed potentiation without inducing genotoxicity or phenotypic changes in a human embryonic stem cell reporter assay. These results suggest that GaMF1 presents an attractive lead for the discovery of a novel class of anti-tuberculosis F-ATP synthase inhibitors.

Discovery of a Novel Mycobacterial F‐ATP Synthase Inhibitor and its Potency in Combination with Diarylquinolines

AbstractThe F1FO‐ATP synthase is required for growth and viability of Mycobacterium tuberculosis and is a validated clinical target. A mycobacterium‐specific loop of the enzyme's rotary γ subunit plays a role in the coupling of ATP synthesis within the enzyme complex. We report the discovery of a novel antimycobacterial, termed GaMF1, that targets this γ subunit loop. Biochemical and NMR studies show that GaMF1 inhibits ATP synthase activity by binding to the loop. GaMF1 is bactericidal and is active against multidrug‐ as well as bedaquiline‐resistant strains. Chemistry efforts on the scaffold revealed a dynamic structure activity relationship and delivered analogues with nanomolar potencies. Combining GaMF1 with bedaquiline or novel diarylquinoline analogues showed potentiation without inducing genotoxicity or phenotypic changes in a human embryonic stem cell reporter assay. These results suggest that GaMF1 presents an attractive lead for the discovery of a novel class of anti‐tuberculosis F‐ATP synthase inhibitors.

Type III interferons are expressed in tuberculosis granulomas and promote an inflammatory phenotype in macrophages that differs from type I interferon

Abstract Humans and non-human primates express four subtypes of type III interferons (IFNλs; IFNλ1-IFNλ4). Unlike type I interferons, which have been thoroughly investigated in tuberculosis (TB), the role of IFNλs and their effects on immunity in TB remain unknown, especially at the disease site. To better understand the role of IFNλs in TB, we examined IFNλ1 and IFNλ4 expression in cynomolgus macaques with TB and investigated the effects of IFNα/β, IFNλ1 and IFNλ4 signaling on macaque macrophages. Using IHC, we identified differential IFNλ1 and IFNλ4 expression in macrophages and neutrophils, including IFNλ4 localization in the nuclei of epithelioid macrophages. CD206+ macrophages and CD3+ cells in the airway expressed IFNλR while CD11c+ macrophages in the lymphocyte cuff of the granuloma expressed IFNλR. To measure IFNλ1 and IFNλ4’s effect on macrophage gene expression and compare these cytokines against IFNα/β, we used NanoString transcriptional profiling and Ingenuity Pathway Analysis (IPA) on cytokine-stimulated macrophages to identify differentially regulated pathways. We found that IFNα/β upregulated the greatest number of ISGs, followed by IFNλ1, whereas IFNλ4 stimulation had minimal effect on gene expression. Interestingly, pro-inflammatory genes including IL-1β, IL-8, TLR1, BATF were upregulated by IFNλ1 while IL-1β and TLR1 were downregulated by IFNα/β. To determine the effects of IFNλs on anti-mycobacterial macrophage responses, we used a reporter Mtb strain to determine how IFNλ1 and IFNλ4 effect the viability of Mycobacterium tuberculosis. Our data suggest that IFNλs have non-redundant properties with type 1 interferons that may promote macrophage activation, inflammation, and antibacterial activity in TB.

Ultrasensitive enzyme-linked immunosorbent assay for the detection of MPT64 secretory antigen to evaluate Mycobacterium tuberculosis viability in sputum

ObjectivesThis study examined Mycobacterium tuberculosis (MTB)-secreted MPT64 as a surrogate of bacterial viability for the diagnosis of active pulmonary TB (PTB) and for follow-up treatment. MethodsIn this proof-of-concept prospective study, 50 PTB patients in the Tokyo metropolitan region, between 2017 and 2018, were consecutively included and 30 healthy individuals were also included. Each PTB patient submitted sputum on days 0, 14 and 28 for diagnosis and follow-up, and each healthy individual submitted one sputum sample. The following were performed: smear microscopy, Xpert MTB/RIF, MGIT and solid culture, and MPT64 detection on the sputum samples. Ultrasensitive ELISA (usELISA) was used to detect MPT64. The receiver operating characteristic analyses for diagnosis and follow-up revealed the optimal cut-off value of MPT64 absorbance for detecting culture positivity at multiple intervals. ResultsThe sensitivity of MPT64 for diagnosing PTB was 88.0% (95% CI 75.7–95.5) and the specificity was 96.7% (95% CI 82.8–99.9). The specificity of MPT64 for predicting negative culture results on day 14 was 89.5% (95% CI 66.9–98.7). The sensitivity of MPT64 for predicting positive culture results on day 28 was 81.0% (95% CI 58.1–94.6). ConclusionsThis study revealed that MPT64 is useful for diagnosing active PTB in patients and predicting treatment efficacy at follow-up.

Innate immune receptors in development of Mycobacterium tuberculosis infection

According to the World Health Organization, over 10 million new tuberculosis cases are reported annually worldwide. According to the 2017 Federal State Statistics Service Report, incidence rate for active TB infection in the Russian Federation was 109.8 cases per 100,000 population, of which 41.3% accounted for chronic disease form. Regardless of climatic conditions, high prevalence of TB infection, is not only due to high Mycobacterium tuberculosis viability, but also its ability for long persistence in human body and reactivation after an unlimited period of dormancy. The outcome of infection is largely determined by host immunoreactivity and its ability to develop protective immune response. In addition, status of immune system also underlies tuberculosis course after the onset: either as a localized form, or as a form with extensive damage to the lungs and even other organs observed in generalized infection. In recent decades, a great attention was paid to examining mechanisms of adaptive cell immunity played in pathogenesis of TB infection. No doubt, adaptive immunity is a powerful defense system providing a targeted specific immune response, but now it is becoming clear that it represents solely an effector arm of innate immunity. Innate immunity is a phylogenetically more ancient, inherited system largely aimed at ensuring rapid pathogen elimination and preventing development of infection at early stages when adaptive immunity ongoing antigen-specific maturation. Mechanisms of innate immunity mediated by cells, diverse receptors, molecules and their complexes, found on various cells. Activation of innate immunity begins with recognition of conserved molecular groups present in various pathogens called pathogen-associated molecular patterns (PAMPs), which are sensed by pathogen recognition receptors (PRRs). Here, we review current data on the role of innate receptors in recognizing M. tuberculosis-derived PAMPs, production of immunoregulatory cytokines and activation of signaling pathways playing a crucial role in the regulation of necroptosis, apoptosis and autophagy of infected macrophages. Significance of innate mucosal factors in implementing immune response to M. tuberculosis is discussed. In particular, Toll-like receptors, scavenger-receptors, mannose receptor, DC-SIGN etc. were described to participate in development of M. tuberculosis immunity. The data on single nucleotide polymorphic variants for innate genes are shown, which predispose to developing tuberculosis and affecting its course.

Plasticity of the Mycobacterium tuberculosis respiratory chain and its impact on tuberculosis drug development

The viability of Mycobacterium tuberculosis (Mtb) depends on energy generated by its respiratory chain. Cytochrome bc1-aa3 oxidase and type-2 NADH dehydrogenase (NDH-2) are respiratory chain components predicted to be essential, and are currently targeted for drug development. Here we demonstrate that an Mtb cytochrome bc1-aa3 oxidase deletion mutant is viable and only partially attenuated in mice. Moreover, treatment of Mtb-infected marmosets with a cytochrome bc1-aa3 oxidase inhibitor controls disease progression and reduces lesion-associated inflammation, but most lesions become cavitary. Deletion of both NDH-2 encoding genes (Δndh-2 mutant) reveals that the essentiality of NDH-2 as shown in standard growth media is due to the presence of fatty acids. The Δndh-2 mutant is only mildly attenuated in mice and not differently susceptible to clofazimine, a drug in clinical use proposed to engage NDH-2. These results demonstrate the intrinsic plasticity of Mtb’s respiratory chain, and highlight the challenges associated with targeting the pathogen’s respiratory enzymes for tuberculosis drug development.

КОМПЛЕКСНОЕ ИССЛЕДОВАНИЕ МОКРОТЫ ВПЕРВЫЕ ВЫЯВЛЕННЫХ БОЛЬНЫХ ТУБЕРКУЛЁЗОМ ЛЁГКИХ С ИСПОЛЬЗОВАНИЕМ ПОЛИМЕРАЗНОЙ ЦЕПНОЙ РЕАКЦИИ И МИКРОБИОЛОГИЧЕСКОГО КОНТРОЛЯ ЖИЗНЕСПОСОБНОСТИ МИКОБАКТЕРИЙ ТУБЕРКУЛЁЗА

Objective: The use of polymerase chain reaction (PCR) in a comprehensive study of sputum in newly diagnosed patients with pulmonary tuberculosis (PTB) in the control of mycobacterium tuberculosis (MTB) viability by the microbiological method. Methods: The object of the study – 59 newly diagnosed patients with PTB in admission for treatment and 28 patients with PTB two months after the start of anti-tuberculosis chemotherapy. The study material is the sputum of PTB patients. Identification of the dead and persistent MTB was noted with the positive result of PCR (PCR+) and the absence of growth of MTB on the dense of nutritional environment of Levenstein-Jensen. The DNASorb-B and Litekh sets were used for DNA extraction of Mycobacterium tuberculosis complex. For amplification, Politub and AmpliSens MBT kits were used. Detection of amplification products was carried out with electrophoresis in 1.7% agarose gel in the presence of bromide ethidium Results: Before treatment, PCR was detected in 52 (88.1%) of the 59 PTB patients examined, 34 (57.6%) tested positive for inoculation (culture+). 25 (42.4%) of patients, lack of growth of MTB out of 59 PTB patients. After 2 months of chemotherapy, PCR+ was detected in 23 (82.1%) out of 28 patients with PTB, culture+ – in 13 (46.4%), no growth of MTB was revealed in 15 (53.6%). Conclusion: Before treatment, PCR was detected in 52 (88.1%) of the 59 PTB patients examined, 34 (57.6%) tested positive for inoculation (culture+). 25 (42.4%) of patients, lack of growth of MTB out of 59 PTB patients. After 2 months of chemotherapy, PCR+ was detected in 23 (82.1%) out of 28 patients with PTB, culture+ – in 13 (46.4%), no growth of MTB was revealed in 15 (53.6%). Keywords: Pulmonary tuberculosis, polymerase chain reaction, microbiological method, mycobacterium tuberculosis viability, chemotherapy.

Identifying drug-like inhibitors of Mycobacterium tuberculosis H37Rv Seryl tRNA synthetase based on bioassay dataset: homology modelling, docking and molecular dynamics simulation

Resistance to existing drugs of tuberculosis bacteria demands an immediate requirement to develop effective new chemical entities acting on emerging targets. Seryl-tRNA synthetase (SerRS) is essential for the viability of Mycobacterium tuberculosis (MTB). In this study, we have attempted to develop the tertiary structure of SerRS through homology modelling and to elucidate the active site interactions of inhibitor compounds aided by docking. Homology modelling using PDB ID: '2DQ3: A' chain as template and validation of the model was carried out with Modeller V9.13 and SAVES online server respectively. About 1248 compounds from a putative kinase compound library of PubChem database found active in whole cell bioassay (AID2842) on MTB - H37Rv was used in docking studies using 'AutoDock'. Out of the tested molecules, nine showed docking scores ≤-10 kcal/mol with good drug-like properties were further subjected to molecular dynamics (MD) simulations and found three of the compounds have stable interactions.

Identifying drug-like inhibitors of Mycobacterium tuberculosis H37Rv Seryl tRNA synthetase based on bioassay dataset: homology modelling, docking and molecular dynamics simulation

Resistance to existing drugs of tuberculosis bacteria demands an immediate requirement to develop effective new chemical entities acting on emerging targets. Seryl-tRNA synthetase (SerRS) is essential for the viability of Mycobacterium tuberculosis (MTB). In this study, we have attempted to develop the tertiary structure of SerRS through homology modelling and to elucidate the active site interactions of inhibitor compounds aided by docking. Homology modelling using PDB ID: '2DQ3: A' chain as template and validation of the model was carried out with Modeller V9.13 and SAVES online server respectively. About 1248 compounds from a putative kinase compound library of PubChem database found active in whole cell bioassay (AID2842) on MTB - H37Rv was used in docking studies using 'AutoDock'. Out of the tested molecules, nine showed docking scores ≤-10 kcal/mol with good drug-like properties were further subjected to molecular dynamics (MD) simulations and found three of the compounds have stable interactions.

LtpA, a CdnL-type CarD regulator, is important for the enzootic cycle of the Lyme disease pathogen

Little is known about how Borrelia burgdorferi, the Lyme disease pathogen, adapts and survives in the tick vector. We previously identified a bacterial CarD N-terminal-like (CdnL) protein, LtpA (BB0355), in B. burgdorferi that is preferably expressed at lower temperatures, which is a surrogate condition mimicking the tick portion of the enzootic cycle of B. burgdorferi. CdnL-family proteins, an emerging class of bacterial RNAP-interacting transcription factors, are essential for the viability of Mycobacterium tuberculosis and Myxococcus xanthus. Previous attempts to inactivate ltpA in B. burgdorferi have not been successful. In this study, we report the construction of a ltpA mutant in the infectious strain of B. burgdorferi, strain B31-5A4NP1. Unlike CdnL in M. tuberculosis and M. xanthus, LtpA is dispensable for the viability of B. burgdorferi. However, the ltpA mutant exhibits a reduced growth rate and a cold-sensitive phenotype. We demonstrate that LtpA positively regulates 16S rRNA expression, which contributes to the growth defects in the ltpA mutant. The ltpA mutant remains capable of infecting mice, albeit with delayed infection. Additionally, the ltpA mutant produces markedly reduced spirochetal loads in ticks and was not able to infect mice via tick infection. Overall, LtpA represents a novel regulator in the CdnL family that has an important role in the enzootic cycle of B. burgdorferi.

Performance of OMNIgene•SPUTUM (DNA Genotek) and cetylpyridinium chloride for sputum storage prior to mycobacterial culture.

Purpose. The aim was to assess the performance of both cetylpyridinium chloride (CPC) and OMNIgene•SPUTUM (OMNI) reagents for the maintenance of Mycobacterium tuberculosis viability in sputum prior to recovery by culture.Methodology. Using 312 sputa, we evaluated the performance of the two reagents using culture on Löwenstein-Jensen medium after sputum storage in CPC or OMNI for up to 28 days. In addition, the viability of M. tuberculosis isolates stored in both reagents was assessed.Results. The contamination rates for freshly processed samples and those stored in CPC were not statistically different, while the contamination rate for OMNI was significantly lower than that for fresh sputa (P=0.026 for 8 days and P=0.002 for 28 days of storage). The culture positivity for fresh sputa (81.7 %) was similar to that for samples stored in CPC, regardless of the storage time (89.8 % for CPC-8 and 73.0 % for CPC-28). For OMNI-preserved samples, the culture positivity was similar after 8 days of storage (84.2 %), but decreased significantly after 28 days (42.7 %; P<0.0001) compared to fresh sputa, CPC-8, CPC-28 and OMNI-8. There was a significant loss of viability for the H37Rv strain when it was stored in OMNI at room temperature beyond 8 days compared to CPC, but storage at 37 °C decreased recovery from both CPC- and OMNI-stored suspensions.Conclusion. Culture from sputum stored for 8 days at room temperature in OMNI or CPC gave comparable culture positivity rates to culture from fresh sputum, but after 28 days of storage the performance of OMNI decreased significantly compared to CPC.

Viability, biofilm formation, and MazEF expression in drug-sensitive and drug-resistant Mycobacterium tuberculosis strains circulating in Xinjiang, China.

BackgroundTuberculosis (TB) caused by Mycobacterium tuberculosis (MTB) is one of the most common chronic infectious amphixenotic diseases worldwide. Prevention and control of TB are greatly difficult, due to the increase in drug-resistant TB, particularly multidrug-resistant TB. We speculated that there were some differences between drug-sensitive and drug-resistant MTB strains and that mazEF3,6,9 toxin–antitoxin systems (TASs) were involved in MTB viability. This study aimed to investigate differences in viability, biofilm formation, and MazEF expression between drug-sensitive and drug-resistant MTB strains circulating in Xinjiang, China, and whether mazEF3,6,9 TASs contribute to MTB viability under stress conditions.Materials and methodsGrowth profiles and biofilm-formation abilities of drug-sensitive, drug-resistant MTB strains and the control strain H37Rv were monitored. Using molecular biology experiments, the mRNA expression of the mazF3, 6, and 9 toxin genes, the mazE3, 6, and 9 antitoxin genes, and expression of the MazF9 protein were detected in the different MTB strains, H37RvΔmazEF3,6,9 mutants from the H37Rv parent strain were generated, and mutant viability was tested.ResultsEx vivo culture analyses demonstrated that drug-resistant MTB strains exhibit higher survival rates than drug-sensitive strains and the control strain H37Rv. However, there was no statistical difference in biofilm-formation ability in the drug-sensitive, drug-resistant, and H37Rv strains. mazE3,6 mRNA-expression levels were relatively reduced in the drug-sensitive and drug-resistant strains compared to H37Rv. Conversely, mazE3,9 expression was increased in drug-sensitive strains compared to drug-resistant strains. Furthermore, compared with the H37Rv strain, mazF3,6 expression was increased in drug-resistant strains, mazF9 expression was increased in drug-sensitive strains, and mazF9 exhibited reduced expression in drug-resistant strains compared with drug-sensitive strains. Protein expression of mazF9 was increased in drug-sensitive and drug-resistant strains compared to H37Rv, while drug-resistant strains exhibited reduced mazF9 expression compared to drug-sensitive strains. Compared to H37Rv, H37RvΔmazEF3,6,9-deletion mutants grew more slowly under both stress conditions, and their ability to survive in host macrophages was also weaker. Furthermore, the host macrophage-apoptosis rate was higher after infection with any of the H37RvΔmazEF3,6,9 mutants than with the H37Rv strain.ConclusionThe increased viability of MTB drug-resistant strains compared with drug-sensitive strains is likely to be related to differential MazEF mRNA and protein expression. mazEF3,6,9 TASs contribute to MTB viability under stress conditions.