Tuberculosis - Articles in Press

Effects of immunomodulators on liquefaction and ulceration in the rabbit skin model of tuberculosis - Corrected Proof

2012-05-07

Summary: To better control tuberculosis (TB) epidemics in developing countries a real need exists to study the liquefaction and cavity formation that occur in pulmonary TB lesions. This report is the first to evaluate the effects of immunomodulators on these two processes in a rabbit skin model. The effects of recombinant human interferon-γ (rIFN-γ), recombinant human interleukin-2 (rIL-2), dexamethasone and cyclophosphamide (CTX) were evaluated in TB lesions produced by intradermal injection of 5 × 106 viable BCG bacilli. Recombinant IL-2 and rIFN-γ accelerated the liquefaction and healing of the lesions, and reduced the bacterial load. In contrast, dexamethasone inhibited the liquefaction of the lesions, and increased the bacterial load. The effect of CTX was similar to dexamethasone but not as pronounced. Serum levels of IL-2 were higher during the liquefaction and healing phases in the rIL-2 and rIFN-γ groups. Therefore, immunomodulators affect both the development of TB lesions and the survival of the mycobacteria within them. This study suggests that the rabbit skin model can be a valuable method to select therapeutic agents that could inhibit liquefaction and cavity formation in pulmonary tuberculosis.

A novel assay detecting recall response to Mycobacterium tuberculosis: Comparison with existing assays - Corrected Proof

2012-04-30

Summary: A strategy to reduce the burden of active TB is isoniazid preventive therapy for latent TB infection (LTBI). However, current assays used to diagnose LTBI all have limitations.In these proof of concept studies, we compared the agreement of a novel flow cytometry assay detecting CD25/CD134 co-expression with QuantiFERON-TB Gold In-Tube (QFN-GIT) and Tuberculin skin test (TST) in the detection of recall immune response to TB.The CD25/CD134 assay, QFN-GIT and TST were performed on 74 participants referred for TB screening in Sydney and on 50 participants with advanced HIV infection (CD4 ≤ 350 × 106 cells/L) in Bangkok.The agreement between CD25/CD134 assay and QFN-GIT was 93.2% (Kappa 0.631 95% CI 0.336–0.926) in Sydney and 90% (Kappa 0.747 95% CI 0.541–0.954) in Bangkok. Discordant results occurred around the cut off of both tests.The agreement between CD25/CD134 assay and TST was 73.6% (Kappa 0.206 95% CI 0.004–0.409) in Sydney and 84% (Kappa 0.551 95% CI 0.296–0.806) in Bangkok.The CD25/CD134 assay showed good agreement with QFN-GIT in detecting recall response to TB both in well and less resourced setting as well as in persons with advanced HIV infection. Further study into the performance of this assay is thus warranted.

Low rates of synonymous mutations in sequences of Mycobacterium tuberculosis GyrA and KatG genes - Corrected Proof

2012-04-23

Summary: Partial sequences of KatG and GyrA genes have been obtained from multi and extensively drug-resistant (MDR and XDR) clinical isolates of Mycobacterium tuberculosis. Nonsynonymous (DN) and synonymous (DS) distances between those sequences have been calculated by Kumar method. Results revealed that DN is significantly higher than DS between some pairs of partial GyrA sequences. We found out that DN is higher than DS in many other partial and complete sequences of KatG and GyrA coding regions deposited in GenBank. The cause of the DN > DS situation is in several nonsynonymous substitutions occurrence (which may be associated with drug-resistance or not) in the absence of synonymous substitutions. Low rates of synonymous mutations occurrence is a consequence of the strong mutational GC-pressure. Due to the high saturation of third codon positions by guanine and cytosine (78.81 ± 0.17% for all the genes from M. tuberculosis H37Rv genome), the probability to be synonymous for the nucleotide mutation of preferable (AT to GC) direction is low. Fixation of a single nonsynonymous mutation leading to drug-resistance is a consequence of Darwinian selection. This clear example of Darwinian selection on the molecular level can be confirmed by selection test (DN > DS) only in case of DN and DS calculation in pairs of sequences possessing at least two additional nonsynonymous mutations which may be neutral or excessive.

Non-acid-fastness in Mycobacteriumtuberculosis ΔkasB mutant correlates with the cell envelope electron density - Corrected Proof

2012-04-20

Summary: The acid-fastness is the most important and the most specific characteristics in mycobacteria, the mechanism of which is not clear but may be attributed to the lipid rich cell wall of this bacterium. While the exact component(s) responsible for this staining method remained unidentified, a Mycobacterium tuberculosis mutant, attenuated strain that produced shorter mycolic acids with defects in trans-cyclopropanation was shown to be acid fast negative. In this study, we examined the ultrastructure of the cell envelope (CE) of the mutant strain ΔkasB (missing a beta-ketoacyl-ACP synthase involved in mycolic acid biosynthesis), the parental CDC1551 (wild type strain) and kasB complemented strain, and compared ultrastructural differences among them with conventional transmission electron microscopy (TEM) and cryo-transmission electron microscopy (CEM). Conventional TEM revealed that there were no detectable differences in the thickness of the cell envelope among three strains (wild-type: 43.35 ± 6.13 nm; ΔkasB: 45.98 ± 11.32 nm; complement: 40.71 ± 6.3 nm). However, CEM data demonstrated that the region between the inner and outer membranes of the mutant strain, which is composed mainly of cell wall anchored mycolic acids (MA), showed a significant decrease in electron density as compared to the wild type and kasB complement strain (567.1 ± 372.7 vs. 301.4 ± 262.1, or vs. 235.2 ± 174.9, p < 0.02 or p < 0.001, respectively). These results suggested that altered MA patterns in the kasB mutant may have affected the packing of the lipid rich layer of the M. tuberculosis cell envelope, resulting in a reduced electron density of this layer as seen by CEM and loss of acid-fastness in light microscopical observation, and we propose a novel model of the cell envelope structure in tubercle bacilli.

The unsurprising story of MDR-TB resistance in India - Corrected Proof

Giridhara R. Babu, Ramanan Laxminarayan — 2012-04-16

Summary: W.H.O. defines Totally Drug-Resistant Tuberculosis (TDR-TB) as Tuberculosis caused due to a virulent strain of tuberculosis that seems to be resistant to all known treatments. In a recent correspondence, Zarir F. Udwadia and others described what they termed as “first patients from India with TDR tuberculosis”. The processes and weakness ingrained in the vastness of Indian society and health system leading to drug resistance reveal multitude layers of weakness. This review aims at listing some of the important factors and levels responsible for the development of resistance in TB. The review identifies access issues, poor adherence to short-course chemotherapy, poor knowledge, practices and quality TB drugs in the private sector, resistance against some of second-line drugs prevalent in India and poor utilization of diagnostic services as the factors for causing TB resistance in India.

Chronobiology: Relevance for tuberculosis - Corrected Proof

2012-04-16

Summary: Despite the knowledge concerning the pathogenesis of tuberculosis, this disease remains one of the most important causes of mortality worldwide. Several risk factors are well-known, such poverty, HIV infection, and poor nutrition, among others. However, some issues that may influence tuberculosis warrant further investigation. In particular, the chronobiological aspects related to tuberculosis have garnered limited attention. In general, the interface between tuberculosis and chronobiology is manifested in four ways: variations in vitamin D bioavailability, winter conditions, associated infections, and circannual oscillations of lymphocytes activity. Moreover, tuberculosis is related to the following chronobiological factors: seasonality, latitude, photoperiod and radiation. Despite the relevance of these topics, the relationship between them has been weakly reviewed. This review aims to synthesize the studies regarding the association between tuberculosis and chronobiology, as well as urge critical discussion and highlight its applicability to health policies for tuberculosis.

Improved signal peptide predictions in mycobacteria? - Corrected Proof

Nils Anders Leversen, Harald G. Wiker — 2012-04-09

In a correspondence in the October issue in 2011 of Nature Methods, Petersen and colleagues presented SignalP 4.0; an updated version of a widely used algorithm for predicting the presence of an N-terminal signal peptide in proteins of eukaryotes, Gram-positive and Gram-negative organisms. The authors state that the new version was primarily developed to improve the ability of the algorithm to distinguish between signal peptides and N-terminal transmembrane regions, and shows this version to perform better than previous versions and other signal peptide prediction algorithms. They note that a downside to the new version is a decreased ability to identify the presence of a signal peptide and the correct cleavage site in proteins without transmembrane regions. Here, we want to contribute with the perspectives of the end-users of such prediction algorithms by sharing our experiences on signal peptide prediction of mycobacterial proteins. Mycobacteria have a cell wall structure that is different from Gram-positives and Gram-negatives, but mycobacterial proteins are normally included in the training sets used for developing algorithms for Gram-positive organisms.

Mycobacterium tuberculosis WhiB1 represses transcription of the essential chaperonin GroEL2 - Corrected Proof

2012-04-05

Summary: A central feature of TB pathogenesis is the formation of Mycobacterium tuberculosis latent infections that can persist for decades. Nitric oxide produced by infected lung macrophages promotes expression of genes associated with dormancy, and impaired nitric oxide production can lead to reactivation of latent disease. Recently, WhiB1 was identified as a nitric oxide-responsive transcription factor. Here it is shown that apo-WhiB1 binds to groEL2 (Rv0440) promoter DNA. Apo-WhiB1 inhibited transcription from the groEL2 promoter in vitro and the transcript start was located ∼181 bases upstream of the groEL2 start codon. Electrophoretic mobility shift assays with sub-fragments of the groEL2 promoter indicated that the complete Rv0439c-Rv0440 intergenic region was required for WhiB1 binding, suggesting that this region possessed more than one WhiB1-binding site. DNase I footprinting identified a WhiB1-binding region that overlapped the −35 element of the groEL2 promoter. The CRP-family transcription factor Cmr (Rv1675c) was shown to bind the groEL2 promoter and activate transcription in vitro in the presence or absence of cAMP. Therefore, it is suggested that WhiB1 acts to oppose Cmr-mediated cAMP-independent activation of groEL2 expression in the presence of nitric oxide by promoter occlusion.

Sudden cardiac death and tuberculosis – How much do we know? - Corrected Proof

Alexander Liu, Yanmin Hu, Anthony Coates — 2012-03-14

Summary: Tuberculosis (TB), caused by Mycobacterium tuberculosis, is a major killer in the world and pulmonary infections are well characterised. It is not widely known that TB myocarditis leads to sudden cardiac deaths (SCD), especially in young people. Unlike other causes of SCD, risk factors such as family history are absent and patients are asymptomatic. This makes risk stratification and interventions with implantable cardiac defibrillators extremely difficult. Only a few cases of TB myocarditis SCD have been reported since 1977 and all of which were diagnosed at autopsy. The majority of reports showed extensive TB infiltration of the myocardium with no systemic symptoms. Concurrent miliary or systemic TB was postulated to be the source of TB myocarditis. The mechanism of death has been hypothesized to be ventricular tachyarrhythmia. Pulmonary TB has also been reported to cause sudden death. However, ventricular arrhythmias have not been recorded, suggesting a different mechanism to TB myocarditis SCD, which centres upon cardiopulmonary collapse leading to bradycardia. Although anti-tuberculous chemotherapy is efficacious in the treatment of TB myocarditis, there is no evidence to suggest that it is effective in the prevention of SCD. It remains to be seen whether better global control of TB disease burden will result in reductions in SCD. Furthermore, no experimental data exist on the link between TB myocarditis SCD and arrhythmias. We propose a unifying diagnostic system for TB myocarditis based on the current data and molecular techniques. This is likely to require updates as more evidence becomes available.

WITHDRAWN: Stimulation of the Mycobacterium tuberculosis transcription elongation by MtbMfd - Corrected Proof

Swayam Prabha, Arnab China, Desirazu N. Rao, Valakunja Nagaraja — 2011-11-30

This article has been withdrawn at the request of the author(s). The Publisher apologizes for any inconvenience this may cause.The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Mouse and guinea pig models for testing new tuberculosis vaccines - Corrected Proof

Ian M. Orme — 2005-01-17

Summary: In this brief review I will discuss some of the more interesting [and in some cases, confusing] aspects that have arisen from the current NIH-funded TB vaccine screening program at Colorado State University, how they affect our understanding of the vaccination process, and how this may influence the rational vaccine design in the near future.