Biomedical subjects

Chi Wai Yip

Publications and source records attributed to Chi Wai Yip.

9 recordsLinked to original sources

PubMed2006

Naturally occurring anti-Escherichia coli protein antibodies in the sera of healthy humans cause analytical interference in a recombinant nucleocapsid protein-based enzyme-linked immunosorbent assay for serodiagnosis of severe acute respiratory syndrome.

We reported the analytical interference of anti-Escherichia coli protein (EP) antibodies in human sera and residual EP in a recombinant nucleocapsid protein-based enzyme-linked immunosorbent assay as a possible source of false positives in severe acute respiratory syndrome serodiagnosis. The rate of false positives was significantly reduced by adding mouse anti-EP antiserum in the blocking step.

Antibodies, Bacterial↗

PubMed2006

Quantitative comparison of the efficiency of antibodies against S1 and S2 subunit of SARS coronavirus spike protein in virus neutralization and blocking of receptor binding: implications for the functional roles of S2 subunit.

Neutralizing effects of antibodies targeting the C-terminal stalk (S2) subunit of the spike protein of severe acute respiratory syndrome coronavirus have previously been reported, although its mechanism remained elusive. In this study, high titered mouse antisera against the N-terminal globular (S1) and S2 subunits of the S protein were generated and total immunoglobulin G (IgG) was purified from these antisera. The efficiency of these purified IgGs in virus neutralization and blocking of receptor binding were compared quantitatively using virus neutralization assay and a previously developed cell-based receptor binding assay, respectively. We demonstrated that anti-S1 IgG neutralizes the virus and binds to the membrane associated S protein more efficiently than anti-S2 IgG does. Moreover, both anti-S1 and anti-S2 IgGs were able to abolish the binding between S protein and its cellular receptor(s), although anti-S1 IgG showed a significantly higher blocking efficiency. The unexpected blocking ability of anti-S2 IgG towards the receptor binding implied a possible role of the S2 subunit in virus docking process and argues against the current hypothesis of viral entry. On the other hand, the functional roles of the previously reported neutralizing epitopes within S2 subunit were investigated using an antigen specific antibody depletion assay. Depletion of antibodies against these regions significantly diminished, though not completely abolished, the neutralizing effects of anti-S2 IgG. It suggests the absence of a major neutralizing domain on S2 protein. The possible ways of anti-S2 IgGs to abolish the receptor binding and the factors restricting anti-S2 IgGs to neutralize the virus are discussed.

Animals↗

PubMed2006

Demonstration of receptor binding properties of VP2 of very virulent strain infectious bursal disease virus on Vero cells.

Tissue culture adaptation of infectious bursal disease virus (IBDV) results in alternation of three residues on its major capsid protein VP2 and these residues may engage in receptor binding. Although the key of successful infection of tissue culture adapted IBDV in tissue cultures was defined as the virus entering steps, mechanism of the adaptation is poorly understood. In this study, recombinant VP2s of an attenuated strain (D78) and a very virulent strain (HK46) of IBDV tagged with rabbit immunoglobulin G heavy chain were expressed in mammalian cells, generating RAVP2 and RVVP2, respectively, in high purity. Using flow cytometry, both RAVP2 and RVVP2 were demonstrated to bind with Vero cells while these bindings were blocked by D78 viral particles, implying both very virulent IBDVs (vvIBDVs) and attenuated IBDVs bind to Vero cells through the same receptor(s). Since vvIBDVs cannot be propagated directly in tissue cultures, the specific binding between RVVP2 and Vero cells suggests the barrier for tissue culture adaptation may be beyond the virus attachment process.

Adaptation, Physiological↗

PubMed2006

Stepwise decrease in moxifloxacin susceptibility amongst clinical isolates of multidrug-resistant Mycobacterium tuberculosis: correlation with ofloxacin susceptibility.

To study the effectiveness of moxifloxacin (MOX) against multidrug-resistant (MDR) Mycobacterium tuberculosis (MTB), in vitro drug susceptibility tests on MOX and ofloxacin (OFX) using the MGIT system against 132 nonduplicate MDR MTB isolates (108 OFX-sensitive and 24 OFX-resistant) were performed. Eleven OFX-resistant non-MDR MTB isolates were also included. All strains that were susceptible to OFX were shown to be also susceptible to MOX. For OFX-resistant isolates, regardless of their MDR status, a 4- to 8-fold decrease in MIC was observed for MOX when compared to OFX. On the basis of similarities in mode of action and pharmacokinetic data between MOX and OFX, a breakpoint MIC of 2 mg/L was suggested for MOX in the MGIT system. All but two OFX-resistant isolates possessed MIC of MOX of 2 mg/L or lower and were considered to be susceptible to MOX; however, all OFX-resistant strains studied had mutations involved in resistance to quinolones. DNA sequence analysis for the gyrase A mutation, which was an indicator for OFX resistance, correlated with MOX susceptibility changes. Significant decreases in MOX susceptibility amongst MDR-MTB strains were observed that correlated with OFX susceptibility. The Asp94Gly mutation appeared to be associated with a higher level of MICs to both OFX and MOX. These findings on the stepwise decline of in vitro susceptibility to MOX suggest that clinical usage of MOX should be accompanied by careful monitoring of susceptibility to this important anti-MDR MTB drug.

Anti-Bacterial Agents↗

PubMed2006

Optimization of variable number tandem repeat typing set for differentiating Mycobacterium tuberculosis strains in the Beijing family.

Variable number tandem repeat (VNTR) typing of Mycobacterium tuberculosis, as presently used, has often failed to differentiate clonal strains especially in areas where the Beijing family genotype is predominant. We have evaluated mycobacterial interspersed repetitive units (MIRUs), Queen's University of Belfast (QUB) loci and exact tandem repeat (ETR) loci individually for their abilities to differentiate the Beijing and non-Beijing genotype families of M. tuberculosis. The best locus was QUB 3232 followed by QUB 11b. Available MIRU, QUB and ETR loci were then consecutively arranged in declining order of discriminatory power, and combined to form an optimal set of 12-loci VNTR typing (MIRU 10, 26, 39, 40; QUB 11a, 11b, 15, 18, 26, 3232, 3336; ETR A) that possessed comparable discriminatory ability to IS6110 restriction fragment length polymorphism. This optimized 12-loci VNTR typing set can become an important tool for tracking M. tuberculosis of the Beijing family.

Bacterial Typing Techniques↗

PubMed2005

Utility of mycobacterial interspersed repetitive unit typing for differentiating multidrug-resistant Mycobacterium tuberculosis isolates of the Beijing family.

Mycobacterial interspersed repetitive unit (MIRU) typing has been found to allow rapid, reliable, high-throughput genotyping of Mycobacterium tuberculosis and may represent a feasible approach to study global M. tuberculosis molecular epidemiology. To evaluate the use of MIRU typing in discriminating drug-resistant M. tuberculosis strains of the Beijing genotype family, 102 multidrug-resistant (MDR) clinical isolates and 253 randomly selected non-MDR isolates collected from 2000 to 2003 in Hong Kong were subjected to 12-locus MIRU typing, spoligotyping, and IS6110 restriction fragment length polymorphism (RFLP) typing. Spoligotyping showed that 243 (68.5%) of 355 isolates belonged to Beijing family genotype. MIRU typing showed lower discrimination in differentiating between the Beijing family strains (Hunter-Gaston discriminative index [HGI] of 0.8827) compared with the IS6110 RFLP method (HGI = 0.9979). For non-Beijing strains, MIRU typing provided discrimination (HGI = 0.9929) comparable to that of the RFLP method (HGI = 0.9961). There was no remarkable difference in discrimination power between the two methods in differentiating both within and between MDR and non-MDR strains of M. tuberculosis. Dendrograms constructed with the MIRU typing data showed a clear segregation between the Beijing and non-Beijing genotype. Addition of RFLP to MIRU typing offered a higher discrimination ability (92.6%) than did addition of MIRU typing to RFLP (40.0%). This supported the potential use of this method to analyze the global genetic diversity of MDR M. tuberculosis strains that may be at different levels of evolutionary divergence.

Bacterial Typing Techniques↗

PubMed2004

Characterization of humoral responses in mice immunized with plasmid DNAs encoding SARS-CoV spike gene fragments.

The immunological characteristics of SARS-CoV spike protein were investigated by administering mice with plasmids encoding various S gene fragments. We showed that the secreting forms of S1, S2 subunits and the N-terminus of S1 subunit (residues 18-495) were capable of eliciting SARS-CoV specific antibodies and the region immediate to N-terminus of matured S1 protein contained an important immunogenic determinant for elicitation of SARS-CoV specific antibodies. In addition, mice immunized with plasmids encoding S1 fragment developed a Th1-mediated antibody isotype switching. Another interesting finding was that mouse antibodies elicited separately by plasmids encoding S1 and S2 subunits cooperatively neutralized SARS-CoV but neither the S1 nor S2 specific antibodies did, suggesting the possible role of both S1 and S2 subunits in host cell docking and entry. These results provide insights into understanding the immunological characteristics of spike protein and the development of subunit vaccines against SARS-CoV.

Animals↗

PubMed2003

Molecular advances in severe acute respiratory syndrome-associated coronavirus (SARS-CoV).

The sudden outbreak of severe acute respiratory syndrome (SARS) in 2002 prompted the establishment of a global scientific network subsuming most of the traditional rivalries in the competitive field of virology. Within months of the SARS outbreak, collaborative work revealed the identity of the disastrous pathogen as SARS-associated coronavirus (SARS-CoV). However, although the rapid identification of the agent represented an important breakthrough, our understanding of the deadly virus remains limited. Detailed biological knowledge is crucial for the development of effective countermeasures, diagnostic tests, vaccines and antiviral drugs against the SARS-CoV. This article reviews the present state of molecular knowledge about SARS-CoV, from the aspects of comparative genomics, molecular biology of viral genes, evolution, and epidemiology, and describes the diagnostic tests and the anti-viral drugs derived so far based on the available molecular information.

Animals↗

PubMed2001

Trends in multidrug-resistant Mycobacterium tuberculosis in relation to sputum smear positivity in Hong Kong, 1989-1999.

We studied retrospectively the territory-wide occurrence and trends of multidrug-resistant tuberculosis (MDR-TB) in Hong Kong over an 11-year period during which a short-course directly observed therapy ("DOTS-Plus") strategy has been in operation. The overall MDR rate was 2.1% (primary, 1.4% and acquired, 9.5%) and declined at 0.08% per year: smear-positive primary MDR cases declined at yearly rate of -0.065% (R2=.23), and smear-negative primary MDR cases increased at 0.035% yearly. With declining rates of smear positivity, sputum culture has become the mainstay of detection of MDR-TB. Although the overall notification rates showed the elderly (age >65 years) age group to be most affected, the occurrence of MDR-TB has been consistently highest in the 35-65 year age group (60.4% of MDR caseload). We demonstrated declining rates of sputum smear positivity of MDR-TB in a DOTS-plus environment and that a centralized laboratory database is essential in gathering epidemiological information for identifying particular risk groups and monitoring trends of MDR-TB in a community.

Age Distribution↗