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Biomedical subjects

Kwok-Yung Yuen

Publications and source records attributed to Kwok-Yung Yuen.

At least 55 records · Page 3Linked to original sources
PubMed2005

Typhoid fever associated with acute appendicitis caused by an H1-j strain of Salmonella enterica serotype Typhi.

While most strains of Salmonella enterica serotype Typhi, the etiologic agent of typhoid fever, have only a phase 1 flagellar antigen, H1-d, variations of the flagellar antigen have been observed. Although H1-j strains (one of the flagellar antigen variants) account for 10 to 50% of S. enterica serotype Typhi strains found in Indonesia, there have been no published data to suggest its existence in other parts of the world. We describe a case of typhoid fever associated with acute appendicitis caused by an S. enterica serotype Typhi H1-j strain in a Chinese woman in Hong Kong. A gram-negative, motile rod was recovered from her blood and stool cultures. Conventional biochemical tests and the Vitek system (GNI+) showed that the bacterium was S. enterica serotype Typhi. The isolate agglutinated with poly(O), 9O, Vi and H1-j Salmonella antisera but not with poly(H) antisera. The patient developed antibodies against only S. enterica serotype Typhi O antigens but not against H1-d antigen by the Widal test. Flagellin C gene (fliC) sequencing showed a 261-bp deletion in the fliC gene of the isolate, confirming that the isolate possessed the H1-j antigen. The patient had no past history of travel to Indonesia or personal contact with any Indonesian. She recovered with appendectomy and antibiotic treatment. Further studies should be performed to determine the prevalence of this unusual S. enterica serotype Typhi strain in our locality.

Acute Disease↗
PubMed2005

Differential sensitivities of severe acute respiratory syndrome (SARS) coronavirus spike polypeptide enzyme-linked immunosorbent assay (ELISA) and SARS coronavirus nucleocapsid protein ELISA for serodiagnosis of SARS coronavirus pneumonia.

The use of recombinant severe acute respiratory syndrome-coronavirus (SARS-CoV) nucleocapsid protein (N) enzyme-linked immunosorbent assay (ELISA)-based antibody and antigen tests for diagnosis of SARS-CoV infections have been widely reported. However, no recombinant SARS-CoV spike protein (S)-based ELISA is currently available. In this article, we describe the problems and solutions of setting up the recombinant SARS-CoV S-based ELISA for antibody detection. The SARS-CoV S-based immunoglobulin M (IgM) and IgG ELISAs were evaluated and compared with the corresponding N-based ELISA for serodiagnosis of SARS-CoV pneumonia, using sera from 148 healthy blood donors who donated blood 3 years ago as controls and 95 SARS-CoV pneumonia patients in Hong Kong. Results obtained by the recombinant S (rS)-based IgG ELISA using the regenerated S prepared by dialysis with decreasing concentrations of urea or direct addition of different coating buffers, followed by addition of different regeneration buffer, identified 4 M urea and 1 M sarcosine for plate coating and no regeneration buffer as the most optimal conditions for antibody detection. The specificities of the S-based ELISA for IgG and IgM detection were 98.6% and 93.9%, with corresponding sensitivities of 58.9% and 74.7%, respectively. The sensitivity of the rN IgG ELISA (94.7%) is significantly higher than that of the rS IgG ELISA (P < 0.001), whereas the sensitivity of the rS IgM ELISA is significantly higher than that of the rN IgM ELISA (55.2%) (P < 0.01). An ELISA for detection of IgM against S and N could be more sensitive than one that detects IgM against N alone for serodiagnosis of SARS-CoV pneumonia.

Antibodies, Viral↗
PubMed2005

Human parainfluenza virus 4 outbreak and the role of diagnostic tests.

Owing to the difficulties in isolating the virus and the lack of routine surveillance, the clinical significance of human parainfluenza virus 4 (HPIV-4) is less well defined than that of the other human parainfluenza viruses. We describe the first outbreak of HPIV-4 infection in a developmental disabilities unit, involving 38 institutionalized children and three staff members, during a 3-week period in autumn 2004. Most subjects had upper respiratory tract infections (URTI), while lower respiratory tract infections (LRTI) occurred in three children (7%), one complicated by respiratory failure requiring ventilation support. All patients recovered. Nasopharyngeal aspirates tested for HPIV-4 were positive by reverse transcriptase PCR (RT-PCR) in all 41 cases (100%), by direct immunofluorescence in 29 of 39 tested cases (74%), and by cell cultures in 6 of 37 cases (16%), and serum was positive for antibodies against HPIV-4 in all 35 cases (100%) with serum samples available. In addition, RT-PCR detected HPIV-4 in four children (three LRTI and one URTI) out of 115 patients with community-acquired respiratory tract infection. Molecular analysis of the 1,198-bp phosphoprotein sequences showed that HPIV-4 isolates among the cases were genetically similar, whereas the community controls were more genetically distant, supporting nosocomial transmission of a single HPIV-4 genotype during the outbreak. Moreover, the HPIV-4 causing the outbreak is more closely related to HPIV-4A than HPIV-4B. HPIV-4 may be an important cause of more severe respiratory illness in children. The present RT-PCR assay is a sensitive, specific, and rapid method for the diagnosing HPIV-4 infection. To better define the epidemiology and clinical spectrum of disease of HPIV-4 infections, HPIV-4 should be included in the routine panels of respiratory virus detection on respiratory specimens.

Adolescent↗
PubMed2005

Comparative host gene transcription by microarray analysis early after infection of the Huh7 cell line by severe acute respiratory syndrome coronavirus and human coronavirus 229E.

The pathogenesis of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) at the cellular level is unclear. No human cell line was previously known to be susceptible to both SARS-CoV and other human coronaviruses. Huh7 cells were found to be susceptible to both SARS-CoV, associated with SARS, and human coronavirus 229E (HCoV-229E), usually associated with the common cold. Highly lytic and productive rates of infections within 48 h of inoculation were reproducible with both viruses. The early transcriptional profiles of host cell response to both types of infection at 2 and 4 h postinoculation were determined by using the Affymetrix HG-U133A microarray (about 22,000 genes). Much more perturbation of cellular gene transcription was observed after infection by SARS-CoV than after infection by HCoV-229E. Besides the upregulation of genes associated with apoptosis, which was exactly opposite to the previously reported effect of SARS-CoV in a colonic carcinoma cell line, genes related to inflammation, stress response, and procoagulation were also upregulated. These findings were confirmed by semiquantitative reverse transcription-PCR, reverse transcription-quantitative PCR for mRNA of genes, and immunoassays for some encoded proteins. These transcriptomal changes are compatible with the histological changes of pulmonary vasculitis and microvascular thrombosis in addition to the diffuse alveolar damage involving the pneumocytes.

Apoptosis↗
PubMed2005

Cytokine responses in severe acute respiratory syndrome coronavirus-infected macrophages in vitro: possible relevance to pathogenesis.

The pathogenesis of severe acute respiratory syndrome (SARS) remains unclear. Macrophages are key sentinel cells in the respiratory system, and it is therefore relevant to compare the responses of human macrophages to infections with the SARS coronavirus (SARS-CoV) and other respiratory viruses. Primary human monocyte-derived macrophages were infected with SARS-CoV in vitro. Virus replication was monitored by measuring the levels of positive- and negative-strand RNA, by immunofluorescence detection of the SARS-CoV nucleoprotein, and by titration of the infectious virus. The gene expression profiles of macrophages infected with SARS-CoV, human coronavirus 229E, and influenza A (H1N1) virus were compared by using microarrays and real-time quantitative reverse transcriptase PCR. Secreted cytokines were measured with an enzyme-linked immunosorbent assay. SARS-CoV initiated viral gene transcription and protein synthesis in macrophages, but replication was abortive and no infectious virus was produced. In contrast to the case with human coronavirus 229E and influenza A virus, there was little or no induction of beta interferon (IFN-beta) in SARS-CoV-infected macrophages. Furthermore, SARS-CoV induced the expression of chemokines such as CXCL10/IFN-gamma-inducible protein 10 and CCL2/monocyte chemotactic protein 1. The poor induction of IFN-beta, a key component of innate immunity, and the ability of the virus to induce chemokines could explain aspects of the pathogenesis of SARS.

Animals↗
PubMed2005

Recombinant modified vaccinia virus Ankara expressing the spike glycoprotein of severe acute respiratory syndrome coronavirus induces protective neutralizing antibodies primarily targeting the receptor binding region.

Immunization with a killed or inactivated viral vaccine provides significant protection in animals against challenge with certain corresponding pathogenic coronaviruses (CoVs). However, the promise of this approach in humans is hampered by serious concerns over the risk of leaking live severe acute respiratory syndrome (SARS) viruses. In this study, we generated a SARS vaccine candidate by using the live-attenuated modified vaccinia virus Ankara (MVA) as a vector. The full-length SARS-CoV envelope Spike (S) glycoprotein gene was introduced into the deletion III region of the MVA genome. The newly generated recombinant MVA, ADS-MVA, is replication incompetent in mammalian cells and highly immunogenic in terms of inducing potent neutralizing antibodies in mice, rabbits, and monkeys. After two intramuscular vaccinations with ADS-MVA alone, the 50% inhibitory concentration in serum was achieved with reciprocal sera dilutions of more than 1,000- to 10,000-fold in these animals. Using fragmented S genes as immunogens, we also mapped a neutralizing epitope in the region of N-terminal 400 to 600 amino acids of the S glycoprotein (S400-600), which overlaps with the angiotensin-converting enzyme 2 (ACE2) receptor-binding region (RBR; S318-510). Moreover, using a recombinant soluble RBR-Fc protein, we were able to absorb and remove the majority of the neutralizing antibodies despite observing that the full S protein tends to induce a broader spectrum of neutralizing activities in comparison with fragmented S proteins. Our data suggest that a major mechanism for neutralizing SARS-CoV likely occurs through blocking the interaction between virus and the cellular receptor ACE2. In addition, ADS-MVA induced potent immune responses which very likely protected Chinese rhesus monkeys from pathogenic SARS-CoV challenge.

Angiotensin-Converting Enzyme 2↗
PubMed2005

SARS coronavirus detection methods.

Using clinical samples from patients with severe acute respiratory syndrome, we showed that the sensitivities of a quantitative reverse transcription-polymerase chain reaction (80% for fecal samples and 25% for urine samples) were higher than those of the polyclonal (50% and 5%) and monoclonal (35% and 8%) antibody-based nucleocapsid antigen capture enzyme-linked immunosorbent assays.

Enzyme-Linked Immunosorbent Assay↗
PubMed2005

Viral load distribution in SARS outbreak.

An unprecedented community outbreak of severe acute respiratory syndrome (SARS) occurred in the Amoy Gardens, a high-rise residential complex in Hong Kong. Droplet, air, contaminated fomites, and rodent pests have been proposed to be mechanisms for transmitting SARS in a short period. We studied nasopharyngeal viral load of SARS patients on admission and their geographic distribution. Higher nasopharyngeal viral load was found in patients living in adjacent units of the same block inhabited by the index patient, while a lower but detectable nasopharyngeal viral load was found in patients living further away from the index patient. This pattern of nasopharyngeal viral load suggested that airborne transmission played an important part in this outbreak in Hong Kong. Contaminated fomites and rodent pests may have also played a role.

Adult↗
PubMed2005

Synthetic peptides outside the spike protein heptad repeat regions as potent inhibitors of SARS-associated coronavirus.

A novel severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) has been identified as the aetiological agent of SARS. We previously isolated and characterized SARS-CoV and SARS-CoV-like viruses from human and animals, respectively, suggesting that SARS could be transmitted from wild/farmed animals to humans. Comparison of the viral genomes indicated that sequence variation between animal and human isolates existed mainly in the spike (S) gene. We hypothesized that these variations may underlie a change of binding specificity of the S protein to the host cells, permitting viral transmission from animals to humans. Here we report that four 20-mer synthetic peptides (S protein fragments), designed to span these sequence variation hotspots, exhibited significant antiviral activities in a cell line. SARS-CoV infectivity was reduced over 10 000-fold through pre-incubation with two of these peptides, while it was completely inhibited in the presence of three peptides. Molecular modelling of the SARS-CoV peplomer suggests that three of these antiviral peptides map to the interfaces between the three monomers of the trimeric peplomer rather than the heptad repeat region from which short peptides are known to inhibit viral entry. Our results revealed novel regions in the spike protein that can be targeted to inhibit viral infection. The peptides identified in this study could be further developed into antiviral drugs.

Amino Acid Sequence↗
PubMed2004

Initial viral load and the outcomes of SARS.

BACKGROUND: Severe acute respiratory syndrome (SARS) is caused by a novel coronavirus. It may progress to respiratory failure, and a significant proportion of patients die. Preliminary data suggest that a high viral load of the SARS coronavirus is associated with adverse outcomes in the intensive care unit, but the relation of viral load to survival is unclear. METHODS: We prospectively studied an inception cohort of 133 patients with virologically confirmed SARS who were admitted to 2 general acute care hospitals in Hong Kong from Mar. 24 to May 4, 2003. The patients were followed until death or for a minimum of 90 days. We used Cox proportional hazard modelling to analyze potential predictors of survival recorded at the time of presentation, including viral load from nasopharyngeal specimens (measured by quantitative reverse transcriptase polymerase chain reaction [PCR] of the SARS-associated coronavirus). RESULTS: Thirty-two patients (24.1%) met the criteria for acute respiratory distress syndrome, and 24 patients (18.0%) died. The following baseline factors were independently associated with worse survival: older age (61-80 years) (adjusted hazard ratio [HR] 5.24, 95% confidence interval [CI] 2.03-13.53), presence of an active comorbid condition (adjusted HR 3.36, 95% CI 1.44-7.82) and higher initial viral load of SARS coronavirus, according to quantitative PCR of nasopharyngeal specimens (adjusted HR 1.21 per log10 increase in number of RNA copies per millilitre, 95% CI 1.06-1.39). INTERPRETATION: We found preliminary evidence that higher initial viral load is independently associated with worse prognosis in SARS. Mortality data for patients with SARS should be interpreted in light of age, comorbidity and viral load. These considerations will be important in future studies of SARS.

Adult↗
PubMed2004

Characterization of SARS-CoV main protease and identification of biologically active small molecule inhibitors using a continuous fluorescence-based assay.

Severe acute respiratory syndrome associated coronavirus main protease (SARS-CoV Mpro) has been proposed as a prime target for anti-SARS drug development. We have cloned and overexpressed the SARS-CoV Mpro in Escherichia coli, and purified the recombinant Mpro to homogeneity. The kinetic parameters of the recombinant SARS-CoV Mpro were characterized by high performance liquid chromatography-based assay and continuous fluorescence-based assay. Two novel small molecule inhibitors of the SARS-CoV Mpro were identified by high-throughput screening using an internally quenched fluorogenic substrate. The identified inhibitors have Ki values at low microM range with comparable anti-SARS-CoV activity in cell-based assays.

Base Sequence↗
PubMed2004

Identification of novel small-molecule inhibitors of severe acute respiratory syndrome-associated coronavirus by chemical genetics.

The severe acute respiratory syndrome-associated coronavirus (SARS-CoV) infected more than 8,000 people across 29 countries and caused more than 900 fatalities. Based on the concept of chemical genetics, we screened 50,240 structurally diverse small molecules from which we identified 104 compounds with anti-SARS-CoV activity. Of these 104 compounds, 2 target the SARS-CoV main protease (M(pro)), 7 target helicase (Hel), and 18 target spike (S) protein-angiotensin-converting enzyme 2 (ACE2)-mediated viral entry. The EC(50) of the majority of the 104 compounds determined by SARS-CoV plaque reduction assay were found to be at low micromolar range. Three selected compounds, MP576, HE602, and VE607, validated to be inhibitors of SARS-CoV M(pro), Hel, and viral entry, respectively, exhibited potent antiviral activity (EC(50) < 10 microM) and comparable inhibitory activities in target-specific in vitro assays.

Angiotensin-Converting Enzyme 2↗
PubMed2004

Eggerthella hongkongensis sp. nov. and eggerthella sinensis sp. nov., two novel Eggerthella species, account for half of the cases of Eggerthella bacteremia.

Eggerthella, one of the human gut flora, was rarely reported to cause bacteremia in the literature. We describe the application of 16S ribosomal RNA gene sequencing in defining the epidemiology and clinical significance of Eggerthella bacteremia during a 4-year period. Among 55 clinically significant blood culture isolates of anaerobic Gram-positive bacilli, 5 were identified as E. lenta and 5 belonged to 2 novel Eggerthella species, proposed as E. hongkongensis and E. sinensis, respectively. The 10 patients with Eggerthella bacteremia were adults, and 9 had underlying diseases. In all cases, the source of the bacteremia was likely from endogenous flora. Septic shock was a complication in 4 patients, and 3 patients died. The present study suggests that Eggerthella bacteremia is much more common than expected and is associated with significant morbidity and mortality. Moreover, the 2 novel species account for half of the cases of Eggerthella bacteremia.

Actinobacteria↗
PubMed2004

Bacteremia in a patient with colonic carcinoma caused by a novel Sedimentibacter species: Sedimentibacter hongkongensis sp. nov.

A bacterium was isolated from the blood culture of a 91-year-old patient with colonic carcinoma. The cells were strict anaerobic, motile, Gram-negative, sporulating, straight, or slightly curved rods. The bacterium grew on agar using the BACTEC anaerobic blood culture broth or buffered charcoal yeast extract agar as pinpoint colonies after 72 h of incubation at 37 degrees C in anaerobic conditions. It did not grow on blood agar, chocolate agar, MacConkey agar, nutrient agar or broth, brain heart infusion agar or broth, Brucella agar, or cooked meat medium. It produces catalase but not cytochrome oxidase. 16S rRNA gene sequencing and phylogenetic analysis showed that it is closely related to Sedimentibacter hydroxybenzoicus and Sedimentibacter saalensis, with 10.5% and 11.9% differences between the 16S rRNA gene sequence of the bacterium and those of S. hydroxybenzoicus and S. saalensis respectively. A new species, Sedimentibacter hongkongenesis sp. nov., is proposed, for which HKU2(T) is the type strain.

Adenocarcinoma↗
PubMed2004

Clinical deterioration in community acquired infections associated with lymphocyte upsurge in immunocompetent hosts.

Clinical deterioration during the course of community-acquired infections can occur as a result of an exaggerated immune response of the host towards the inciting pathogens, leading to immune-mediated tissue damage. Whether a surge in the peripheral lymphocyte count can be used as a surrogate marker indicating the onset of immunopathological tissue damage is not known. In this study, we report the clinical presentations and outcomes of a cohort of immunocompetent patients with non-tuberculous community acquired infections who experienced clinical deterioration during hospital stay (n=85). 12 (14.1%) patients had a surge in lymphocyte count preceding their clinical deteriorations, and their diagnoses included viral pneumonitis , viral encephalitis , scrub typhus , leptospirosis , brucellosis , and dengue haemorrhagic fever . The clinical manifestations during deterioration ranged from interstitial pneumonitis , airway obstruction , CNS disturbances , and systemic capillary leak syndrome , all of which were thought to represent immunopathological tissue damages. When compared with patients without lymphocyte surge, these patients were more likely to be infected with fastidious/viral pathogens (0 vs 12; p<0.05), in addition to having lower mean baseline lymphocyte counts (403+/-181 vs 1143+/-686 cells/microl; p<0.05). We postulate that the peripheral lymphocyte count may be a useful surrogate marker indicating the presence of immunopathological damage during clinical deterioration in certain infectious diseases.

Adult↗
PubMed2004

Streptococcus sinensis may react with Lancefield group F antiserum.

Lancefield group F streptococci have been found almost exclusively as members of the 'Streptococcus milleri' group, although they have been reported very occasionally in some other streptococcal species. Among 302 patients with bacteraemia caused by viridans streptococci over a 6-year period, three cases were caused by Streptococcus sinensis (type strain HKU4T, HKU5 and HKU6). All three patients had infective endocarditis complicating their underlying chronic rheumatic heart diseases. Gene sequencing showed no base differences between the 16S rRNA gene sequences of HKU5 and HKU6 and that of HKU4T. All three strains were Gram-positive, non-spore-forming cocci arranged in chains. All grew on sheep blood agar as alpha-haemolytic, grey colonies of 0.5-1 mm in diameter after 24 h incubation at 37 degrees C in ambient air. Lancefield grouping revealed that HKU5 and HKU6 were Lancefield group F, but HKU4T was non-groupable with Lancefield groups A, B, C, D, F or G antisera. HKU4T was identified by the Vitek system (GPI), API system (20 STREP) and ATB system (ID32 STREP) as 99 % Streptococcus intermedius, 51.3 % S. intermedius and 99.9 % Streptococcus anginosus, respectively. Using the same tests, HKU5 was identified as 87 % Streptococcus sanguinis/Streptococcus gordonii, 59 % Streptococcus salivarius and 99.6 % S. anginosus, respectively, and HKU6 as 87 % S. sanguinis/S. gordonii, 77 % Streptococcus pneumoniae and 98.3 % S. anginosus, respectively. The present data revealed that a proportion of Lancefield group F streptococci could be S. sinensis. Lancefield group F streptococci should not be automatically reported as 'S. milleri'.

Bacteremia↗
PubMed2004

Anaerobic, non-sporulating, Gram-positive bacilli bacteraemia characterized by 16S rRNA gene sequencing.

Owing to the difficulties in identifying anaerobic, non-sporulating, Gram-positive bacilli in clinical microbiology laboratories, the epidemiology and clinical spectrum of disease of many of these bacteria have been poorly understood. The application of 16S rRNA gene sequencing in characterizing bacteraemia due to anaerobic, non-sporulating Gram-positive bacilli during a 4-year period is described. The first case of Olsenella uli bacteraemia, in a patient with acute cholangitis, is also reported. Among 165 blood culture isolates of anaerobic, Gram-positive bacilli, 75 were identified as Propionibacterium acnes by phenotypic tests and 21 as members of other anaerobic, non-sporulating Gram-positive bacilli by 16S rRNA gene sequencing. Of these 96 isolates, 16 (17 %) were associated with cases of clinically significant bacteraemia, among which 10 (63 %) were caused by Eggerthella, four (25 %) by Lactobacillus and one (6 %) by each of Eubacterium tenue and O. uli. Five of the 10 Eggerthella isolates were Eggerthella lenta, whereas the other five belonged to two novel Eggerthella species, with Eggerthella hongkongensis being almost as prevalent as Eggerthella lenta. Underlying disease in the gastrointestinal tract, isolation of Eggerthella and Lactobacillus, and monomicrobial bacteraemia were associated with clinically significant bacteraemia, whereas isolation of P. acnes and polymicrobial bacteraemia were associated with pseudobacteraemia. Most patients with clinically significant bacteraemia had underlying diseases, with diseases in the gastrointestinal tract being most common. The overall mortality rate was 31 %. Immunocompromised patients with clinically significant bacteraemia due to anaerobic, non-sporulating, Gram-positive bacilli other than P. acnes should be treated with appropriate antibiotics. The unexpected frequency of isolation of Eggerthella from blood cultures and its association with clinically significant disease suggest that this genus is probably of high pathogenicity. Further studies to look for specific virulence factors are warranted.

Adult↗