The Metapopulation Dynamics of an Infectious Disease: Tuberculosis in Possums

An SEI metapopulation model is developed for the spread of an infectious agent by migration. The model portrays two age classes on a number of patches connected by migration routes which are used as host animals mature. A feature of this model is that the basic reproduction ratio may be computed directly, using a scheme that separates topography, demography, and epidemiology. We also provide formulas for individual patch basic reproduction numbers and discuss their connection with the basic reproduction ratio for the system. The model is applied to the problem of spatial spread of bovine tuberculosis in a possum population. The temporal dynamics of infection are investigated for some generic networks of migration links, and the basic reproduction ratio is computed—its value is not greatly different from that for a homogeneous model. Three scenarios are considered for the control of bovine tuberculosis in possums where the spatial aspect is shown to be crucial for the design of disease management operations

Risk factors for Mycobacterium tuberculosis infection among children in Greenland

Objective To examine the risk factors for Mycobacterium tuberculosis infection (MTI) among Greenlandic children for the purpose of identifying those at highest risk of infection. Methods Between 2005 and 2007, 1797 Greenlandic schoolchildren in five different areas were tested for MTI with an interferon gamma release assay (IGRA) and a tuberculin skin test (TST). Parents or guardians were surveyed using a standardized self-administered questionnaire to obtain data on crowding in the household, parents’ educational level and the child’s health status. Demographic data for each child – i.e. parents’ place of birth, number of siblings, distance between siblings (next younger and next older), birth order and mother’s age when the child was born – were also extracted from a public registry. Logistic regression was used to check for associations between these variables and MTI, and all results were expressed as odds ratios (ORs) and 95% confidence intervals (CIs). Children were considered to have MTI if they tested positive on both the IGRA assay and the TST. Findings The overall prevalence of MTI was 8.5% (152/1797). MTI was diagnosed in 26.7% of the children with a known TB contact, as opposed to 6.4% of the children without such contact. Overall, the MTI rate was higher among Inuit children (OR: 4.22; 95% CI: 1.55–11.5) and among children born less than one year after the birth of the next older sibling (OR: 2.48; 95% CI: 1.33–4.63). Self-reported TB contact modified the profile to include household crowding and low mother’s education. Children who had an older MTI-positive sibling were much more likely to test positive for MTI themselves (OR: 14.2; 95% CI: 5.75–35.0) than children without an infected older sibling. Conclusion Ethnicity, sibling relations, number of household residents and maternal level of education are factors associated with the risk of TB infection among children in Greenland. The strong household clustering of MTI suggests that family sources of exposure are important.

Mycobacterium tuberculosis groE promoter controls the expression of the bicistronic groESL1 operon and shows differential regulation under stress conditions

Heat shock promoters of mycobacteria are strong promoters that become rapidly upregulated during macrophage infection and thus serve as valuable candidates for expressing foreign antigens in recombinant BCG vaccine. In the present study, a new heat shock promoter controlling the expression of the groESL1 operon was identified and characterized. Mycobacterium tuberculosis groESL1 operon codes for the immunodominant 10 kDa (Rv3418c, GroES/Cpn10/Hsp10) and 60 kDa (Rv3417c, GroEL1/Cpn60.1/Hsp60) heat shock proteins. The basal promoter region was 115 bp, while enhanced activity was seen only with a 277-bp fragment. No promoter element was seen in the groES-groEL1 intergenic region. This operon codes for a bicistronic mRNA transcript as determined by reverse transcriptase-PCR and Northern blot analysis. Primer extension analysis identified two transcriptional start sites (TSSs) TSS1 (-236) and TSS2 (-171), out of which one (TSS2) was heat inducible. The groE promoter was more active than the groEL2 promoter in Mycobacterium smegmatis. Further, it was found to be differentially regulated under stress conditions, while the groEL2 promoter was constitutive.

Characterization of novel immunodominant antigens of Mycobacterium tuberculosis

Seven novel antigens of Mycobacterium tuberculosis, which had previously been identified based on reactivity to sera from patients with tuberculosis, were characterized. Nucleotide sequence analysis of the genes encoding these seven antigens identified one of them as the FtsH and a second as the aminoimidazole ribotide synthase of M. tuberculosis. Antisera raised to the recombinant forms of each of these seven antigens were used to study the distribution of these proteins within mycobacterial species as well as to determine their subcellular localization and hydrophobicity. Four of the seven antigens were conserved only among pathogenic strains of mycobacteria. Of the seven proteins studied, FtsH and a second protein of unknown identity were localized in membranes. Two were cytosolic, while two others, which had a high proline content, were tightly associated with the cell wall. One protein was secreted. This secreted protein could be identified by serum from a majority of tuberculosis patients but not BCG-vaccinated individuals, suggesting its potential use in the immunodiagnosis of tuberculosis.

Analysis of a Genomic DNA Expression Library of Mycobacterium tuberculosis Using Tuberculosis Patient Sera: Evidence for Modulation of Host Immune Response

DNA obtained from a human sputum isolate of Mycobacterium tuberculosis, NTI-64719, which showed extensive dissemination in the guinea pig model resulting in a high score for virulence was used to construct an expression library in the lambda ZAP vector. The size of DNA inserts in the library ranged from 1 to 3 kb, and recombinants represented 60% of the total plaques obtained. When probed with pooled serum from chronically infected tuberculosis patients, the library yielded 176 recombinants with a range of signal intensities. Among these, 93 recombinants were classified into 12 groups on the basis of DNA hybridization experiments, The polypeptides synthesized by the recombinants were predominantly LacZ fusion proteins, Serum obtained from patients who were clinically diagnosed to be in the early phase of M. tuberculosis infection was used to probe the 176 recombinants obtained. interestingly, some recombinants that gave very strong signals in the original screen did not react with early-phase serum; conversely, others whose signals were extremely weak in the original screen gave very intense signals with serum from recently infected patients, This indicates the differential nature of either the expression of these antigens or the immune response elicited by them as a function of disease progression.

targetTB: A target identification pipeline for Mycobacterium tuberculosis through an interactome, reactome and genome-scale structural analysis

Background: Tuberculosis still remains one of the largest killer infectious diseases, warranting the identification of newer targets and drugs. Identification and validation of appropriate targets for designing drugs are critical steps in drug discovery, which are at present major bottle-necks. A majority of drugs in current clinical use for many diseases have been designed without the knowledge of the targets, perhaps because standard methodologies to identify such targets in a high-throughput fashion do not really exist. With different kinds of 'omics' data that are now available, computational approaches can be powerful means of obtaining short-lists of possible targets for further experimental validation. Results: We report a comprehensive in silico target identification pipeline, targetTB, for Mycobacterium tuberculosis. The pipeline incorporates a network analysis of the protein-protein interactome, a flux balance analysis of the reactome, experimentally derived phenotype essentiality data, sequence analyses and a structural assessment of targetability, using novel algorithms recently developed by us. Using flux balance analysis and network analysis, proteins critical for survival of M. tuberculosis are first identified, followed by comparative genomics with the host, finally incorporating a novel structural analysis of the binding sites to assess the feasibility of a protein as a target. Further analyses include correlation with expression data and non-similarity to gut flora proteins as well as 'anti-targets' in the host, leading to the identification of 451 high-confidence targets. Through phylogenetic profiling against 228 pathogen genomes, shortlisted targets have been further explored to identify broad-spectrum antibiotic targets, while also identifying those specific to tuberculosis. Targets that address mycobacterial persistence and drug resistance mechanisms are also analysed. Conclusion: The pipeline developed provides rational schema for drug target identification that are likely to have high rates of success, which is expected to save enormous amounts of money, resources and time in the drug discovery process. A thorough comparison with previously suggested targets in the literature demonstrates the usefulness of the integrated approach used in our study, highlighting the importance of systems-level analyses in particular. The method has the potential to be used as a general strategy for target identification and validation and hence significantly impact most drug discovery programmes.

Mycobacterium tuberculosis pantothenate kinase: possible changes in location of ligands during enzyme action

The crystal structures of complexes of Mycobacterium tuberculosis pantothenate kinase with the following ligands have been determined: (i) citrate; (ii) the nonhydrolysable ATP analogue AMPPCP and pantothenate (the initiation complex); (iii) ADP and phosphopantothenate resulting from phosphorylation of pantothenate by ATP in the crystal (the end complex); (iv) ATP and ADP, each with half occupancy, resulting from a quick soak of crystals in ATP (the intermediate complex); (v) CoA; (vi) ADP prepared by soaking and cocrystallization, which turned out to have identical structures, and (vii) ADP and pantothenate. Solution studies on CoA binding and catalytic activity have also been carried out. Unlike in the case of the homologous Escherichia coli enzyme, AMPPCP and ADP occupy different, though overlapping, locations in the respective complexes; the same is true of pantothenate in the initiation complex and phosphopantothenate in the end complex. The binding site of MtPanK is substantially preformed, while that of EcPanK exhibits considerabl plasticity. The difference in the behaviour of the E. coli and M. tuberculosis enzymes could be explained in terms of changes in local structure resulting from substitutions. It is unusual for two homologous enzymes to exhibit such striking differences in action. Therefore, the results have to be treated with caution. However, the changes in the locations of ligands exhibited by M. tuberculosis pantothenate kinase are remarkable and novel.

Immunointervention for patients with HIV and tuberculosis

Therapeutic options aimed at confronting the HIV pandemic face many obstacles. Current opinion on HIV-induced pathogenic immune activation and strategies aimed at eliminating HIV, including a potential role for non-neutralising antibodies as part of a therapeutic vaccine option, was elegantly reviewed by Martin Cadogan and Angus Dalgleish. 1 It is important to note that, for eliciting such antibody responses in patients, functionally fit antigen presenting cells and effector T and B cells are cruc.

Crystallographic and modelling studies on Mycobacterium tuberculosis RuvA: Additional role of RuvB-binding domain and inter species variability

RuvA, along with RuvB, is involved in branch migration of heteroduplex DNA in homologous recombination. The structures of three new crystal forms of RuvA from Mycobacterium tuberculosis (MtRuvA) have been determined. The RuvB-binding domain is cleaved off in one of them. Detailed models of the complexes of octameric RuvA from different species with the Holliday junction have also been constructed. A thorough examination of the structures presented here and those reported earlier brings to light the hitherto unappreciated role of the RuvB-binding domain in determining inter-domain orientation and oligomerization. These structures also permit an exploration of the interspecies variability of structural features such as oligomerization and the conformation of the loop that carries the acidic pin, in terms of amino acid substitutions. These models emphasize the additional role of the RuvB-binding domain in Holliday junction binding. This role along with its role in oligomerization could have important biological implications.

N-[2-naphthyl]-glycine hydrazide, a potent inhibitor of dna-dependent rna-polymerase of mycobacterium-tuberculosis h37rv

N-[2-Naphthyl]-glycine hydrazide has been shown for the first time as a potent inhibitor of the DNA-dependent RNA polymerase (EC 2.7.7.6) of Mycobacterium tuberculosis H37Rv. At a concentration of 10 to the power -9 M, the compound shows maximum inhibition of the enzyme, the inhibition being less at higher concentrations. It is suggested that the novel type of inhibition pattern may be due to hydrophobic interactions occurring between the molecules of the compound at higher concentrations. The finding that there is a shift in the max of the compound could also account for this phenomenon. The effect of this compound was also tested on DNA-dependent RNA polymerases from an eukaryotic fungus, Microsporum canis. At a concentration of 10 to the power-9 M it inhibits RNA polymerase II (32 percent) but not RNA polymerases I and III.

Pianist Hide Kosiwamuro shortly before her death from tuberculosis.

First wife of artist Rafaello Busoni