PubMed Health⌕ Search

Biomedical subjects

W C Yam

Publications and source records attributed to W C Yam.

47 records · Page 3Linked to original sources
PubMed1993

Examination of archetypal strains of enteropathogenic Escherichia coli for properties associated with bacterial virulence.

Nine strains of Escherichia coli isolated from infants with diarrhoea between 1947 and 1960 and designated "enteropathogenic" were examined for phenotypic and genetic characters associated with virulence. Each strain belonged to a different serotype. All the isolates were historically significant in that they were amongst the first strains of E. coli reported to be causally associated with infantile diarrhoea. Five strains possessed the virulence properties of class I enteropathogenic E. coli (EPEC). All these strains were isolated originally from symptomatic children during outbreaks of diarrhoea. Two isolates from sporadic cases of diarrhoea fulfilled the criteria for classification as class II EPEC. One strain was identified as enteroaggregative E. coli and the other carried no known virulence-associated properties. These findings indicate that most early isolates of E. coli which were designated "enteropathogenic" were indeed EPEC, as currently defined.

Bacterial Adhesion↗
PubMed1992

Cloning of a functional Burkitt's lymphoma polypeptide-binding protein/78 kDa glucose-regulated protein (BiP/GRP78) gene promoter by the polymerase chain reaction, and its interaction with inducible cellular factors.

The promoter of the human gene encoding the stress-responsive protein polypeptide-binding protein/78 kDa glucose-regulated protein (BiP/GRP78) was isolated from Burkitt's lymphoma cells by PCR. This promoter DNA segment (termed BiP670) or one of its 5' deletion derivatives was fused to the bacterial chloramphenicol acetyltransferase gene and introduced into HeLa cells for transient expression. BiP670 retained transcriptional activity at both the basal and Ca2+ ionophore A23187-inducible levels. However, there was no significant increase in promoter activity following a 5 h induction with 7 microM-A23187, and less than 5-fold induction at 15 h. In contrast, the steady-state mRNA level was induced by 18-fold at 5 h. The in vivo transactivation assays with BiP670 5' deletion derivatives indicate that the putative A23187-inducible element is located within a 70 bp DNA segment (i.e. spanning -39 to -107 bp upstream of the transcriptional initiation site). Using an in vitro gel mobility shift assay, A23187-inducible nuclear factors were identified from HeLa cell extracts. DNA-binding competition experiments also suggest that the 70 bp DNA segment contains a potential sequence motif for the binding of the A23187-inducible nuclear factors.

Base Sequence↗
PubMed1992

Evaluation and optimization of a latex agglutination assay for detection of cholera toxin and Escherichia coli heat-labile toxin.

The effectiveness of a latex agglutination assay kit for the detection of Escherichia coli heat-labile toxin and cholera toxin was determined for the identification of natural isolates of the corresponding enteric pathogens in Southeast Asia. By selection of the appropriate culture media, the sensitivity of the assay was improved from 90.6% (for the detection of heat-labile toxin) and 75% (for the detection of cholera toxin) to 100%, and the results were confirmed with bioassays and DNA hybridization assays for both clinical and environmental isolates.

Agglutination Tests↗
PubMed1991

Restriction fragment length polymorphism analysis of Vibrio cholerae strains associated with a cholera outbreak in Hong Kong.

We studied Vibrio cholerae El Tor isolates associated with an outbreak of cholera among Vietnamese refugees interned in Hong Kong. The restriction fragment length polymorphism of the enterotoxin gene was used as an epidemiological marker. All outbreak strains were indistinguishable. They were distinct from strains isolated in Hong Kong prior to the outbreak.

Cholera↗
PubMed1990

Coordinated induction of two unrelated glucose-regulated protein genes by a calcium ionophore: human BiP/GRP78 and GAPDH.

The induction of human BiP/GRP78 and GAPDH protein genes by the calcium ionophore A23187 was determined. Steady-state levels of mRNA for both the glucose starvation-responsive BiP/GRP78 gene and the glucose-responsive GAPDH gene were dramatically induced in a variety of human cells. There is a homologous palindromatic sequence GCCGTTAACGGC in the active promoter region of the two genes that is known to be required for the induction of mammalian BiP/GRP78 by A23187. The evidence confirms in general the function of this element in the regulation of calcium-associated gene activity.

Base Sequence↗
PubMed1989

Molecular epidemiology of Vibrio cholerae in Hong Kong.

We studied restriction fragment length polymorphism of the enterotoxin genes of isolates of Vibrio cholerae El Tor, indistinguishable by bacteriophage typing, which were collected in Hong Kong since 1978. Using this approach, we could distinguish indigenous and exogenous strains obtained from different sources and epidemiological settings.

Autoradiography↗
PubMed1988

Clonal origin, restricted natural distribution, and conservation of virulence factors in isolates of enterotoxigenic Escherichia coli serogroup O126.

Enterotoxigenic Escherichia coli serogroup O126 isolates have been isolated in Hong Kong since 1982 from sporadic cases of infantile diarrhea and from one outbreak in a neonatal ward. A 64-megadalton plasmid encoding colonization factor antigen I and heat-stable enterotoxin was identified in all 23 isolates. Enterotoxigenic E. coli strains producing heat-stable enterotoxin from different regions of Southeast Asia were collected and compared by biotyping, antibiotic resistance patterns, and plasmid profiles. Restriction endonuclease digestion of plasmids and subsequent Southern blot analysis with the heat-stable enterotoxin gene probe of representative strains showed a unique plasmid was harbored by all heat-stable enterotoxin-producing O126 strains tested. These results are consistent with conservative inheritance of enterotoxin plasmids within enterotoxigenic E. coli strains over a 2-year period in Hong Kong.

Antigens, Bacterial↗
PubMed1987

Escherichia coli associated with childhood diarrheas.

We studied 2,246 episodes of childhood diarrhea over a 2-year period in a general hospital serving a population of about one million on the island of Hong Kong. Rotavirus (24%) and nontyphoid salmonellas (23%) were the most common causal agents, followed by Campylobacter sp. (9%). Rotavirus occurred largely during winter, whereas salmonellas and Campylobacter sp. occurred more commonly during summer and autumn, respectively. Enterotoxigenic Escherichia coli was rarely isolated (1%), and the isolates were clonally diverse. A small percentage (2.8%) of E. coli had serological specificities commonly associated with enteropathogenic E. coli, but only two of the isolates were also positive for HEp-2 adhesive factor. Pure or heavy and predominant growth of E. coli was obtained in repeated stool cultures of 432 (19%) of these episodes, which did not yield any of the above-mentioned pathogens. Although associated with diarrhea, these E. coli isolates possess neither the pathogenic attributes of enterotoxigenic E. coli nor the properties commonly associated with enteropathogenic E. coli. Enteroinvasive E. coli and enterohemorrhagic E. coli were considered unlikely causes on clinical grounds.

Campylobacter Infections↗
PubMed1984

The bacteriology and septic complication of patients with appendicitis.

A detailed bacteriologic study was done on 161 patients operated for appendicitis. Aerobic and anaerobic cultures were taken from the blood, the appendicular lumen, mucosa, serosa, fossa, and from the wound after closure of the peritoneum. There is no correlation between the degree of appendicitis and the incidence of positive blood culture. The infection spread through the appendicular wall as the disease progressed. Aerobic infection was common in early appendicitis but a mixed aerobic and anaerobic infection was predominant in late cases. Late appendicitis, a positive wound culture at the end of the operation, the duration of symptoms of over 36 hours before operation and the age of the patient over 50 years were all associated with an increased incidence of septic complication. From the antibiotic sensitivity on the bacteria isolated, the most effective agent against anaerobes was metronidazole. Effective agents against the aerobes were aminoglycosides and cephalosporins. The best single agent against both anaerobes and aerobes was moxalactum.

Anti-Bacterial Agents↗
PubMedDate not supplied

Fluoroquinolone resistance among Streptococcus pneumoniae in Hong Kong linked to the Spanish 23F clone.

Serotypes 6A/B, 19F, and 23F accounted for 73% of 140 mucosal isolates of Streptococcus pneumoniae from Hong Kong. In pulsed-field gel electrophoresis analysis, a group of related patterns was shared by 14 of 15 ciprofloxacin-resistant and 12 of 16 ciprofloxacin-susceptible isolates. These strains exhibited capsular switching and were highly similar to the Spanish 23F clone.

Adolescent↗