PubMed Health⌕ Search

Biomedical subjects

John Chan

Publications and source records attributed to John Chan.

34 records · Page 2Linked to original sources
PubMed2003

Detection and drug-susceptibility testing of M. tuberculosis from sputum samples using luciferase reporter phage: comparison with the Mycobacteria Growth Indicator Tube (MGIT) system.

Rapid diagnosis of drug-resistant M.tuberculosis (Mtb) is desirable worldwide. We (i) describe a new luciferase reporter phage (LRP), phAE142 for this purpose; (ii) compare it to the automated MGIT 960 for time-to-detection of Mtb in clinical specimens; and (iii) evaluate its use for species confirmation and antibiotic susceptibility testing(AST) of Mtb. Twenty sputum samples were inoculated for testing by LRP, or by MGIT 960. After "positives" were identified by either method, the LRP was used for confirmation of Mtb complex (TBC) and for AST. The LRP method proved comparably efficient to MGIT 960 at detecting Mtb. Using an antibiotic uniquely inhibiting TBC with LRP provided species assignment, concurrently with AST, in a median of 3 days, with a sensitivity of 97%. Overall agreement in susceptibility results was 96%. Reliable susceptibility results and identification of TBC can be completed in a median of 12 days (range 8 to 16d) with LRP applied to sputum samples.

Antibiotics, Antitubercular↗
PubMed2003

Immune evasion by Mycobacterium tuberculosis: living with the enemy.

Mycobacterium tuberculosis is successful as a pathogen because of its ability to persist in an immunocompetent host. This bacterium lives within the macrophage, a cell whose function is the elimination of microbes. Recent advances have improved our understanding of how M. tuberculosis evades two major antimicrobial mechanisms of macrophages: phagolysosome fusion and the production of toxic reactive nitrogen intermediates. M. tuberculosis also modulates antigen presentation to prevent the detection of infected macrophages by CD4(+) T cells.

Animals↗
PubMed2003

Chemokines and tuberculosis.

Mycobacterium tuberculosis is a respiratory pathogen responsible for tuberculosis. A primary pathologic feature of M. tuberculosis infection is the formation of a granuloma. Immune cells migrate to the lung and then through the lung to the site of infection to form a granuloma. This structure contains the infection, and is often maintained for a long period of time. The signals responsible for granuloma formation and maintenance are largely unknown. Since chemokines and chemokine receptors direct cells to specific sites within the tissues, it is plausible that these cells participate in granuloma formation. In this review, the current literature on chemokines and M. tuberculosis infection, as well as the specific role that tumor necrosis factor alpha (TNF-alpha) plays in granuloma formation and chemokine expression are discussed.

Animals↗
PubMed2003

Latent tuberculosis: mechanisms of host and bacillus that contribute to persistent infection.

Most people infected with Mycobacterium tuberculosis contain the initial infection and develop latent tuberculosis. This state is characterised by evidence of an immune response against the bacterium (a positive tuberculin skin test) but no signs of active infection. It can be maintained for the lifetime of the infected person. However, reactivation of latent infection occurs in about 10% of infected individuals, leading to active and contagious tuberculosis. An estimated 2 billion people worldwide are infected with M tuberculosis--an enormous reservoir of potential tuberculosis cases. The establishment and reactivation of latent infection depend on several factors, related to both host and bacterium. Elucidation of the host immune mechanisms that control the initial infection and prevent reactivation has begun. The bacillus is well adapted to the human host and has a range of evasion mechanisms that contribute to its ability to avoid elimination by the immune system and establish a persistent infection. We discuss here current understanding of both host and bacterial factors that contribute to latent and reactivation tuberculosis.

Animals↗
PubMed2003

Cognitive-behavioral group treatment program for adults with epilepsy in Hong Kong.

A subjective sense of uncertainty is a common theme in the experience of patients with epilepsy. Lack of control has also been implicated as an etiologic factor in the development of psychosocial problems in epilepsy. Cognitive-behavioral interventions emphasizing the mediating role of thoughts and self-control appear to be particularly relevant for patients with epilepsy because anxiety and depression are the most common problems. Despite its apparent importance, very little systematic research has been published on the effectiveness of psychological treatment of epilepsy. The purpose of the present study was to conduct a seminal outcome evaluation of psychological intervention for adult patients in Hong Kong. Using a waitlist control group, the treatment program focused particularly on cognitive restructuring and seizure control. Results indicated significant gains by the treatment group in overall quality of life and self-efficacy. In particular, marked improvements were noted for emotional well-being, seizure, and stress management. The clinical implications are discussed in the context of developing specific intervention programs and outcome measures specific to the various needs of adult patients with epilepsy.

Adult↗
PubMed2003

SecA2 functions in the secretion of superoxide dismutase A and in the virulence of Mycobacterium tuberculosis.

Tuberculosis remains a severe worldwide health threat. A thorough understanding of Mycobacterium tuberculosis pathogenesis will facilitate the development of new treatments for tuberculosis. Numerous bacterial pathogens possess specialized protein secretion systems that are dedicated to the export of virulence factors. Mycobacterium tuberculosis is part of a developing group of pathogenic bacteria that share the uncommon property of possessing two secA genes (secA1 and secA2). In mycobacteria, SecA1 is the essential 'housekeeping' SecA protein whereas SecA2 is an accessory secretion factor. Here we demonstrate that SecA2 contributes to the pathogenesis of M. tuberculosis. A deletion of the secA2 gene in M. tuberculosis attenuates the virulence of the organism in mice. By comparing the profile of proteins secreted by wild-type M. tuberculosis and the DeltasecA2 mutant, we identified superoxide dismutase A (SodA) as a protein dependent on SecA2 for secretion. SodA lacks a classical signal sequence for protein export. Our data suggests that SecA2-dependent export is a new type of secretion pathway that is part of a virulence mechanism of M. tuberculosis to elude the oxidative attack of macrophages.

Adenosine Triphosphatases↗
PubMed2003

Gene expression in the tuberculous granuloma: analysis by laser capture microdissection and real-time PCR.

We have assessed the kinetics of host gene expression in granulomas of mice infected with virulent Mycobacterium tuberculosis, using an approach that incorporates the laser capture microdissection (LCM) and real-time PCR technology in conjunction with a newly derived mathematical equation. The results have provided evidence indicating that conventional use of whole infected lungs to study granuloma-specific gene expression can yield data that may not genuinely reflect intralesional events. Significantly, the expression of nine host genes known to regulate the inflammatory response to M. tuberculosis, as determined by real-time PCR analysis of microdissected granuloma-derived cDNAs, was downregulated (up to 27-fold) at around the time when the rapid growth phase of the bacilli in the lungs of infected mice ends. This downregulation was masked when whole infected lungs were used for the studies. The data suggest that the host immune system can adjust and respond to, or can be modulated by specific physiological states of the tubercle bacillus in vivo. The LCM/real-time PCR-based system described in this study can be applied to safely and accurately evaluate gene expression in any lesions that can be microscopically visualized, including those contained in biohazardous tissues.

Animals↗
PubMed2003

The effects of reactive nitrogen intermediates on gene expression in Mycobacterium tuberculosis.

Nitric oxide (NO) and related reactive nitrogen intermediates (RNI) are effective antimycobacterial agents and signal-transducing molecules. The present study uses microarray analysis to examine the effects of RNI on Mycobacterium tuberculosis gene expression. A common set of 53 genes was regulated by two chemically distinct nitric oxide donors. For a subset of the RNI-inducible genes, evidence exists suggesting that they may play a role in promoting survival of the tubercle bacillus in the host. Results obtained from studies based on a murine experimental tuberculosis model involving nos2-deficient mice suggest that RNI could regulate M. tuberculosis gene expression in vivo. Finally, there is a remarkable overlap between the RNI-inducible regulon and that previously reported to be regulated by hypoxia; and both reactive nitrogen species and anaerobicity upregulate the expression of one and the same putative two-component regulatory response system. Together, the results of this study provide evidence suggesting that (i) RNI play a role in regulating M. tuberculosis gene expression in vivo; (ii) the reactive nitrogen species upregulate genes that may be conducive to the survival of the tubercle bacillus in the infected host; and (iii) RNI and hypoxia may regulate mycobacterial gene expression via overlapping signal transduction pathways.

Animals↗
PubMed2003

Activation of transcription factors AP-1 and NF-kappa B in murine Chagasic myocarditis.

The myocardium of CD1 mice was examined for the activation of signal transduction pathways leading to cardiac inflammation and subsequent remodeling during Trypanosoma cruzi infection (Brazil strain). The activity of three pathways of the mitogen-activated protein kinases (MAPKs) was determined. Immunoblotting revealed a persistent elevation of phosphorylated (activated) extracellular-signal-regulated kinase (ERK), which regulates cell proliferation. During infection there was a transient activation of p38 MAPK but no activation of Jun N-terminal kinase. Early targets of activated ERK, c-Jun and c-Fos, were elevated during infection, as demonstrated by semiquantitative reverse transcription-PCR. Immunostaining revealed that the endothelium and the interstitial cells were most intensely stained with antibodies to c-Jun and c-Fos. Soon after infection, AP-1 and NF-kappa B DNA binding activity was increased. Protein levels of cyclin D1, the downstream target of ERK and NF-kappa B, were induced during acute infection. Immunostaining demonstrated increased expression of cyclin D1 in the vascular and endocardial endothelium, inflammatory cells, and the interstitial areas. Increased expression of the cyclin D1-specific phosphorylated retinoblastoma protein (Ser780) was also evident. Immunoblotting and immunostaining also demonstrated increased expression of proliferating cellular nuclear antigen that was predominantly present in the inflammatory cells, interstitial areas (i.e., fibroblasts), and endothelium. These data demonstrate that T. cruzi infection results in activation of the ERK-AP-1 pathway and NF-kappa B. Cyclin D1 expression was also increased. These observations provide a molecular basis for the activation of pathways involved in cardiac remodeling in chagasic cardiomyopathy.

Animals↗
PubMed2002

Significance of inducible nitric oxide synthase in acute myocarditis caused by Trypanosoma cruzi (Tulahuen strain).

Chagas' disease, caused by Trypanosoma cruzi, is associated with myocarditis and expression of myocardial cytokines and inducible nitric oxide synthase (NOS2). To assess the functional significance of NOS2 in murine Chagas' disease, we infected NOS2 knockout (NOS2(-/-)) and C57BL/6x129sv (wild type) mice with the Tulahuen strain of T. cruzi. Serial transthoracic echocardiography was performed to assess the progression of left and right ventricular dysfunction in infected mice. Uninfected wild type and NOS2(-/-) mice served as controls. At day 10 post-infection (p.i.), infected wild type mice had larger left ventricular end-diastolic diameter (2.52+/-0.14-vs-2.11+/-0.06 mm, P<0.02) and right ventricle (0.6+/-0.2-vs-0 visual grade, P<0.02) as compared with uninfected wild type mice. At day 19 p.i., compared with uninfected controls, infected wild type mice had larger left ventricular end-diastolic diameter (3.30+/-0.29-vs-2.11+/-0.07 mm), left ventricular end-systolic diameter (1.86+/-0.29-vs-0.88+/-0.05 mm), right ventricle (1.6+/-0.2-vs-0 visual grade), lower heart rate (413+/-27-vs-557+/-25 beats per min), left ventricular relative wall thickness (0.44+/-0.05-vs-0.64+/-0.03) and fractional shortening (45+/-4-vs-57+/-2%) [P<0.05 for all]. In contrast, no differences in left ventricular end-diastolic diameter or fractional shortening were noted among infected and uninfected NOS2(-/-) mice at day 19 p.i. Compared with uninfected controls, infected NOS2(-/-) mice had significantly lower heart rate (272+/-23-vs-512+/-31 beats per min, P<0.01) and larger right ventricle (0.6+/-0.2-vs-0, P<0.05 visual grade). The magnitude of right ventricular dilation in NOS2(-/-) mice was less than that observed in infected wild type mice. At necropsy, the heart weight was greater (129+/-16-vs-109+/-7 mg, P=0.02) and myocardial inflammation more severe in infected wild type compared with infected NOS2(-/-) mice. Myocardial interleukin (IL)-1beta, IL-6, tumour necrosis factor-alpha, and interferon-gamma were induced in all infected mice. These data indicate that nitric oxide derived from NOS2 plays an important role in the development and progression of ventricular dilation and systolic dysfunction in acute murine chagasic myocarditis caused by infection with the Tulahuen strain.

Animals↗
PubMed2002

Mycobacterium tuberculosis induces differential cytokine production from dendritic cells and macrophages with divergent effects on naive T cell polarization.

Th1-mediated cellular responses are important for protection in tuberculosis. However, the mechanisms and APC types responsible for initiating Th1 responses are not well understood. These studies show that macrophages and dendritic cells, albeit both being APC, respond differently following Mycobacterium tuberculosis infection and thereby have different consequences for the development of naive T cells. We report that M. tuberculosis-infected dendritic cells bias the polarization of OVA peptide-specific naive transgenic T cells to the Th1 phenotype, and, in contrast, in the presence of infected macrophages naive T cells do not develop a Th1 phenotype. Comparison of the cytokine profile expressed by the infected dendritic cells and macrophages revealed several differences, the most striking being that infected macrophages did not express the Th1-promoting cytokine IL-12. These studies also show that IL-10 is responsible for the failure of IL-12 production by M. tuberculosis-infected macrophages, and that the effects of IL-10 can be overcome by IFN-gamma priming. We speculate that the observed difference in response of the two APC types to M. tuberculosis infection may be a reflection of their respective roles in immune initiation and granuloma regulation.

Animals↗
PubMed2002

Predicting the quality of life in Hong Kong Chinese adults with epilepsy.

Epilepsy is both a medical diagnosis and a social label. The traditional care of patients with epilepsy tends to focus on seizure control and drug treatment. There is a growing concern in the West about the importance of the influence of psychosocial factors on the quality of life. The main purpose of the present study is to explore and delineate the relationships between biomedical and psychosocial predictors and the health-related quality-of-life outcomes of Chinese patients in Hong Kong. Independent measures consisted of two types of predictors: biomedical and psychosocial variables. The biomedical variables included seizure frequency and the number of years since diagnosis. The psychosocial variables included locus of control, social support, and mood. The Quality of Life in Epilepsy Scale was used as the outcome measure. Correlation and hierarchical regression techniques were used. Results showed that psychosocial variables did make a significantly independent contribution to the prediction of the quality of life of patients with epilepsy. Furthermore, results suggested that mood could act as a mediator between seizure characteristics and psychosocial factors, on the one hand, and quality of life, on the other. The statistical significance of the health locus of control and the satisfaction with social support confirmed the importance of the influence of the subjective sense of mastery of condition on quality of life. The clinical implication was discussed in the context of developing psychological interventions in increasing the self-efficacy and resourcefulness of the patients.

Journal Article↗
PubMed2002

Specialized transduction: an efficient method for generating marked and unmarked targeted gene disruptions in Mycobacterium tuberculosis, M. bovis BCG and M. smegmatis.

The authors have developed a simple and highly efficient system for generating allelic exchanges in both fast- and slow-growing mycobacteria. In this procedure a gene of interest, disrupted by a selectable marker, is cloned into a conditionally replicating (temperature-sensitive) shuttle phasmid to generate a specialized transducing mycobacteriophage. The temperature-sensitive mutations in the mycobacteriophage genome permit replication at the permissive temperature of 30 degrees C but prevent replication at the non-permissive temperature of 37 degrees C. Transduction at a non-permissive temperature results in highly efficient delivery of the recombination substrate to virtually all cells in the recipient population. The deletion mutations in the targeted genes are marked with antibiotic-resistance genes that are flanked by gammadelta-res (resolvase recognition target) sites. The transductants which have undergone a homologous recombination event can be conveniently selected on antibiotic-containing media. To demonstrate the utility of this genetic system seven different targeted gene disruptions were generated in three substrains of Mycobacterium bovis BCG, three strains of Mycobacterium tuberculosis, and Mycobacterium smegmatis. Mutants in the lysA, nadBC, panC, panCD, leuCD, Rv3291c and Rv0867c genes or operons were isolated as antibiotic-resistant (and in some cases auxotrophic) transductants. Using a plasmid encoding the gammadelta-resolvase (tnpR), the resistance genes could be removed, generating unmarked deletion mutations. It is concluded from the high frequency of allelic exchange events observed in this study that specialized transduction is a very efficient technique for genetic manipulation of mycobacteria and is a method of choice for constructing isogenic strains of M. tuberculosis, BCG or M. smegmatis which differ by defined mutations.

Alleles↗