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Biomedical subjects

A F Cheng

Publications and source records attributed to A F Cheng.

At least 37 records · Page 2Linked to original sources
PubMed2001

Bacteriologic analyses of bile and brown pigment stones in patients with acute cholangitis.

BACKGROUND: Bacteria play an important role in the formation of brown pigment stones through adherence and biofilm formation. Scanning electron microscopy of cross sections of these stones reveals a laminated appearance and various bacteria in the different layers. Our postulation was that different bacteria might be involved at different stages of stone formation. METHODS: By using standard bacteriologic cultures, the composition, morphology, and antibiotic sensitivity patterns of bacteria isolated from paired stone were compared with bile samples from 70 patients with acute cholangitis. A further comparison was made between bacteria isolated from the periphery and center of 3 randomly selected brown pigment stones. RESULTS: Ninety-one percent of bile and 99% of stone samples yielded positive cultures, with a total of 151 and 149 bacteria isolated from bile and stones, respectively. In 22 patients (33%), the bacteria isolated from the paired bile and stone samples were totally different. The mean percentage similarity of bacteria isolated from bile and stones was 39% (range 0%-100%). Of the 59 pairs of similar bacteria isolated, the antibiotic sensitivity patterns were different in 24 (41%) cases. Of the 3 brown stones studied, either different bacterial species or the same bacteria but different strains with different antibiotic sensitivities were isolated from the center and periphery of the stones. CONCLUSIONS: Bacteria present in the different layers of brown pigment stones may represent the bacterial flora in bile at different times. Simple bile culture may not identify bacteria trapped inside the stone.

Bile↗
PubMed2001

Epidemiological analysis of Salmonella enterica serotype typhimurium from Hong Kong by ribotyping and pulsed-field gel electrophoresis.

We investigated the antimicrobial susceptibilities and molecular epidemiology of 200 strains of Salmonella enterica serotype typhimurium isolated from 1989 to 1996 in Hong Kong. Only 22% of strains were susceptible to all 19 antibiotics tested but all were susceptible to second- and third-generation cephalosporins. Up to 9% of strains were resistant to 0.12 mg/l concentrations of ciprofloxacin or ofloxacin but none were resistant to 1 or 2 mg/l concentrations of these 2 drugs, respectively. The isolates were grouped into 15 types by ribotyping with restriction endonuclease EcoRI and into 53 types by pulsed-field gel electrophoresis of XbaI-restricted DNA fragments. When DNA fragments of the ribotypes and pulsotypes were pooled and analyzed 87 types resulted, 76 (87%) of which were of > 90% similarity and were grouped into 15 clusters. About 60% of the isolates belonged to 3 clusters, which probably represented 3 clones endemic in the community. The rest of the isolates were of a large variety of types or clusters. For epidemiological purposes analysis of pooled results from different molecular techniques would be more discriminative than results from individual techniques alone.

Anti-Bacterial Agents↗
PubMed2001

Clearance of TT virus after allogeneic bone marrow transplantation.

A 10-year-old girl with thalassemia underwent bone marrow transplantation. Before transplantation, she had persistent TT virus (TTV) DNAemia for at least 18 months. Interestingly, the viral DNAemia was cleared soon after transplant and remained undetectable at the latest follow-up at 28 months. The early clearance of TTV that had occurred before engraftment or initiation of any antiviral therapy, together with the absence of TTV DNA from the results of the liver biopsy performed before transplantation, led us to hypothesize that the hematologic compartment could have been the site for viral persistence. Thus, the conditioning regimen may have depleted the hemic cells and the hematologically compartmentalized TTV. The potential of hemic tropism of TTV and its role in hematologic diseases need to be considered.

Biopsy↗
PubMed2001

Postantibiotic effects of antituberculosis agents alone and in combination.

The postantibiotic effects (PAEs) of seven antimycobacterial agents, tested at their respective peak concentrations in serum alone and in different combinations, against Mycobacterium tuberculosis ATCC 27294 were studied with a radiometric culture system in parallel with the viable count method. Rifampin gave the longest PAE (67.8 h) among the drugs used alone, and combinations of first-line drugs generally gave PAEs longer than 120 h. The data obtained might help provide a better understanding of the scientific basis of intermittently administered antituberculosis chemotherapy.

Antitubercular Agents↗
PubMed2001

Macrolide resistance in Streptococcus pneumoniae in Hong Kong.

Erythromycin resistance rates among penicillin-susceptible Streptococcus pneumoniae were 38 and 92% among penicillin-intermediate and -resistant S. pneumoniae isolates from Hong Kong, respectively, and 27% (43 of 158) of the isolates showed the MLS(B) phenotype, and the majority carried the ermB gene; 73% (115 of 158) displayed the M phenotype, and all possessed the mef gene. The MLS(B) phenotype was predominant in penicillin-susceptible, macrolide-resistant isolates and in penicillin-nonsusceptible isolates of serotype 6B, whilst the M phenotype was predominant in penicillin-intermediate or -resistant isolates belonging to serotype 23F or 19F. Extensive spread of clones of drug-resistant pneumococci has led to the widespread presence of macrolide resistance in S. pneumoniae in Hong Kong.

Anti-Bacterial Agents↗
PubMed2001

Epidemiology and infection control implications of Acinetobacter spp. in Hong Kong.

In a previous study, we showed that Acinetobacter genomic DNA group 3 was the most common species among blood culture isolates and was commonly found on superficial carriage sites of the healthy and the sick, which are different findings from those reported in Europe and North America. We used amplified ribosomal DNA restriction analysis and pulsed-field gel electrophoresis to study further the molecular epidemiology of acinetobacters in our region. Over a study period of 6 weeks with 136 consecutive routine clinical isolates (1.33% of all specimens), genomic DNA groups 2 (Acinetobacter baumannii), 3, and 13TU were obtained from 59 of 69 positive patients. There is a significant difference in the specimen sources of the three genomic DNA groups, with group 13TU being significantly associated with the respiratory tract (chi-square exact test, P = 0.0064). Settle plates showed a significantly heavier environmental load from the intensive care unit (ICU) than from the four surgical wards examined (22 of 70 versus 76 of 120 plates with <5 colonies; chi-square test, P < 0. 0001). Genomic group 3 accounted for 6 of 12 clusters of possibly related strains among patients, between patients and the ICU environment, and in the ICU environment. Genomic groups 2 and 3 accounted for 21% of the 132 genomically identified isolates recovered from 21 of 41 local vegetables, 53 of 74 fish and meat samples, and 22 of 60 soil samples. Group 13TU was present only in patients' immediate surroundings. The role played by the environment and by human carriage should be evaluated in order to devise a cost-effective infection control program pertinent to our situation of acinetobacter endemicity.

Acinetobacter↗
PubMed2001

Evaluation of VITEK 2 rapid identification and susceptibility testing system against gram-negative clinical isolates.

A total of 281 strains of miscellaneous members of the family Enterobacteriaceae, Pseudomonas aeruginosa, and other gram-negative bacteria were evaluated by use of identification tests with the VITEK 2 system (bioMérieux) and an API identification system (bioMérieux). A total of 237 (95%) strains were correctly identified to the species level. Only six (2.1%) strains were misidentified, and eight (2.8%) strains were not identified. Among 14 strains with discrepant identifications, 8 (57.1%) strains were nonfermenters. The susceptibilities of 228 strains to 11 antibiotics including amikacin, netilmicin, tobramycin, gentamicin, ciprofloxacin, imipenem, meropenem, ceftazidime, cefepime, piperacillin, and piperacillin in combination with tazobactam were tested with the VITEK 2 AST-No. 12 card and by the broth microdilution (MB) method, according to NCCLS guidelines, as a reference. For the 2,508 organism-antibiotic combinations, the rates at which duplicate MICs correlated within +/-1 dilution ranged from 84.2 to 95.6%. Only 13 (0.5%) and 10 (0.4%) of the susceptibility tests gave major errors (resistant with the VITEK 2 system but sensitive by the MB method) and very major errors (sensitive with the VITEK 2 system but resistant by the MB method), respectively. Both VITEK 2 ID-GNB (an identification system) and VITEK 2 AST-No. 12 (a susceptibility testing system) card systems gave rapid, reliable, and highly reproducible results.

Anti-Bacterial Agents↗
PubMed2001

Randomised controlled study of oral erythromycin for treatment of gastrointestinal dysmotility in preterm infants.

AIM: To evaluate the effectiveness of oral erythromycin as a prokinetic agent for the treatment of moderately severe gastrointestinal dysmotility in preterm very low birthweight infants. METHODS: A prospective, double blind, randomised, placebo controlled study in a tertiary referral centre of a university teaching hospital was conducted on 56 preterm infants (< 1500 g) consecutively admitted to the neonatal unit. The infants were randomly allocated by minimisation to receive oral erythromycin (12.5 mg/kg, every six hours for 14 days) or an equivalent volume of placebo solution (normal saline) if they received less than half the total daily fluid intake or less than 75 ml/kg/day of milk feeds by the enteral route on day 14 of life. The times taken to establish half, three quarters, and full enteral feeding after the drug treatment were compared between the two groups. Potential adverse effects of oral erythromycin and complications associated with parenteral nutrition were assessed as secondary outcomes. RESULTS: Twenty seven and 29 infants received oral erythromycin and placebo solution respectively. The times taken to establish half, three quarters, and full enteral feeding after the drug treatment were significantly shorter in the group receiving oral erythromycin than in those receiving the placebo (p < 0.05, p < 0.05 and p < 0.0001 respectively). There was also a trend suggesting that more infants with prolonged feed intolerance developed cholestatic jaundice in the placebo than in the oral erythromycin group (10 v 5 infants). None of the infants receiving oral erythromycin developed cardiac dysrhythmia, pyloric stenosis, or septicaemia caused by multiresistant organisms. CONCLUSIONS: Oral erythromycin is effective in facilitating enteral feeding in preterm very low birthweight infants with moderately severe gastrointestinal dysmotility. Treated infants can achieve full enteral feeding 10 days earlier, and this may result in a substantial saving on hyperalimentation. However, until the safety of erythromycin has been confirmed in preterm infants, this treatment modality should remain experimental. Prophylactic or routine use of this medication for treatment of mild cases of gastrointestinal dysmotility is probably not warranted at this stage.

Double-Blind Method↗
PubMed2001

Association of human beta-herpesviruses with the development of cervical cancer: bystanders or cofactors.

BACKGROUND/AIM: Human papillomaviruses (HPVs) are important, but not sufficient, for the development of cervical cancer. All three human beta-herpesviruses--cytomegalovirus (CMV) and human herpesviruses (HHV) types 6 and 7--have been detected in the cervix. In addition, CMV and HHV-6 can interact with HPVs in vivo. This study examined the possible role of beta-herpesviruses in cervical cancer development. METHODS: HPV, CMV, HHV-6, and HHV-7 were detected by the polymerase chain reaction using cervical scrapes taken at colposcopy from 388 women. HPV types were identified using restriction fragment length polymorphisms. Colposcopy guided biopsies were taken from abnormal areas, and the histological findings were regarded as the final diagnoses. The associations between herpesvirus infection and the degree of cervical lesion were analysed with respect to HPV status. RESULTS: Of the 388 women, 51.8% had a normal cervix, 14.4% had cervical intraepithelial neoplasia grade 1 (CIN1), 8.2% had CIN2, 19.3% had CIN3, and 6.2% had invasive carcinoma. Overall, the positive rates for high, intermediate, and low risk HPVs were 18.8%, 21.4%, and 5.2%, respectively. Fifteen patients harboured HPVs for which the genotype could not be identified. Positive rates for CMV, HHV-6, and HHV-7 were 9.5%, 3.6%, and 3.4%, respectively. HPV positive patients carried a higher risk for high grade lesions (CIN2/3 or carcinoma) (odds ratio (OR), 5.24; 95% confidence interval (CI), 3.19 to 8.62; chi 2 = 51.79; p < 0.001), whereas those positive for CMV, HHV-6, or HHV-7 did not. Thirteen of 131 patients with high grade lesions had HPV/herpesvirus coinfections, but no association with the cervical lesion was noted. Furthermore, positive rates for herpesviruses among HPV negative, high/intermediate risk HPV negative, and high risk HPV negative subgroups were similarly low and without a significant association. CONCLUSIONS: The ubiquitous nature of herpesviruses may pose difficulty in elucidating their pathogenic role. These results indicate that CMV, HHV-6, and HHV-7 are bystanders rather than cofactors in the oncogenesis of cervical cancer.

Adolescent↗
PubMed2001

Evaluation of extraction methods from paraffin wax embedded tissues for PCR amplification of human and viral DNA.

AIM: To evaluate the efficiency of phenol/chloroform, microwave, and Qiagen spin column based DNA extractions from paraffin wax embedded tissue for use in the polymerase chain reaction (PCR). In addition, to assess the reliability of amplifying a housekeeping gene to indicate successful viral DNA extraction. METHODS: DNA samples extracted from 20 blocks of cervical carcinoma tissues using the three methods were subjected to PCRs targeting 509 bp and 355 bp of the beta globin gene, and 450 bp and 150 bp of human papillomavirus (HPV) DNA. RESULTS: Microwave extraction showed the highest positive rate for beta globin PCR, whereas the spin column method was the most efficient for HPV DNA extraction. When the 509 bp beta globin and 450 bp HPV PCR results were correlated, two of 10, eight of 12, and nine of 10 beta globin positive extractions prepared by means of the phenol/chloroform, microwave, and spin column methods, respectively, yielded HPV DNA of the expected size. For the beta globin negative samples, HPV was detected in three of 10, two of eight, and four of 10 samples. CONCLUSIONS: HPV DNA extraction was most efficient using the Qiagen spin column and had the highest positive predictive value when a housekeeping gene was used as an indicator of successful viral DNA extraction; the phenol/chloroform method was the least efficient. The potential drawbacks of some extraction methods when using a human housekeeping gene to assess the quality of viral DNA extraction need to be considered.

Carcinoma, Squamous Cell↗
PubMed2001

Rapid identification of mycobacterium tuberculosis complex from Bactec 12B broth cultures originating from non-respiratory secretion specimens: comparison between Accuprobe and in-house polymerase chain reaction.

The rapid identification of Mycobacterium tuberculosis complex from 161 consecutive positive Bactec 12B cultures originated from non-respiratory secretion specimens was evaluated by comparing Accuprobe and an in-house polymerase chain reaction method. Using conventional biochemical method as the gold standard, 85.7% of the isolates (n = 138) were identified as Mycobacterium tuberculosis. The sensitivities of Accuprobe and the in-house-polymerase chain reaction method in identifying Mycobacterium tuberculosis complex were 92.0% (127/138) and 93.5% (129/138), respectively. Specificities of both methods being 87.0% (20/23 for both tests). Using a batch system of performing identification once weekly, the average turnaround time for Accuprobe, from the time of primary inoculation, was 27 days, which was comparable with that of in-house polymerase chain reaction, which was 29 days. The average time required for a confirmatory result based on conventional biochemical identification method was 84 days. The estimated reagent cost of in-house polymerase chain reaction was only one-fifth of that of Accuprobe. Therefore, the choice of methodology will depend on the individual laboratory's availability of resources and clinical demand. In the event of discrepant results between rapid identification methods and conventional methods, histological examination and clinical assessment can provide guidance as to the nature of the infection.

Bacteriological Techniques↗
PubMed2000

Prevalence and distribution of human herpesvirus 7 in normal brain.

Although it has been recognised that human herpesvirus 7 (HHV-7) establishes latent infection in CD4+ T lymphocytes and productive infection in salivary glands, recent data suggest that its in vivo tropism may be more widespread. In this study, the prevalence and distribution of HHV-7 in brain tissues of 30 consecutive post-mortems were examined by nested polymerase chain reaction. For each post-mortem, 10 fresh autopsy tissue samples were collected respectively from the cerebellum, frontal, temporal, parietal, and occipital lobes of both cerebral hemispheres. These patients were aged from 20-95 years (mean = 61.4, SD = 20.2) with a male:female ratio of 2:1. Three patients died of intracranial haemorrhage, the others died of causes unrelated to the central nervous system. Overall, 5% (15/300) of the brain tissue samples were positive for HHV-7 DNA. The positive rates with respect to anatomical positions were similar (0-3/30). When analysed by patient, 36.7% (11/30) were HHV-7 DNA positive. The viral DNA-positive and -negative groups did not show a significant difference in gender or age distribution. The majority (81.8%) of viral DNA-positive patients had HHV-7 DNA detected at only one anatomical position; only two patients had viral DNA detected simultaneously at three anatomical sites. These results suggest that HHV-7 persists in brain tissues of a substantial proportion of the adult population, and in most individuals, its distribution is probably confined to one site rather than pervasive. Further studies to elucidate the role of this ubiquitous virus in neuropathology are warranted.

Adult↗
PubMed2000

Rapid identification of medically important Candida to species level by polymerase chain reaction and single-strand conformational polymorphism.

Invasive fungal disease has taken a great toll on immunocompromised patients. With the emergence of fluconazole and amphotericin B resistance, the rapid identification of fungi to species level is of clinical relevance in guiding appropriate antifungal therapy. Among these opportunistic fungi, Candida species are the most commonly encountered. We had developed a molecular method utilizing single-strand conformational polymorphism (SSCP) to delineate different patterns on a 260-bp amplicon from the 28S rRNA gene from six medically important Candida species. The SSCP banding patterns obtained from a total of 52 isolates were sufficiently unique to allow distinction between the species, thus indicated a high level of specificity. This method of PCR-SSCP can provide a simple and specific method for the rapid identification of medically important Candida to species level.

Candida↗
PubMed2000

Early attachment of anaerobic bacteria may play an important role in biliary stent blockage.

BACKGROUND: In vitro studies have demonstrated that ciprofloxacin suppresses Escherichia coli attachment on stents, and ciprofloxacin has been shown to prolong stent patency in cats. However, clinical studies with antibiotic prophylaxis have produced conflicting results. The aim of this study was to isolate and identify the bacteria that attach early on unblocked stents removed from patients and to study their enzyme activities. METHODS: Eighteen unblocked biliary stents were removed from 17 patients (benign obstruction in 14 and malignant obstruction in 4). All patients received antibiotic prophylaxis (mean of 6 days). Stents were in place for a mean of 33 days. The inside of stents was scraped and sludge was cultured aerobically and anaerobically. Identification of isolated bacteria and measurement of beta-glucuronidase and phospholipase C activities were performed by using standard techniques. Gastric and duodenal juice from 18 patients with no biliary diseases was used as control samples. RESULTS: All stents were patent and only 6 had visible sludge. There were 19 anaerobes isolated from 16 stents (Clostridium perfringens 13, Clostridium bifermentans 4 and Bacteroides fragilis 2). Phospholipase C was detected in all Clostridium species. beta-Glucuronidase was produced only by 12 of 13 C perfringens isolates. Sixteen aerobes including Enterococcus species and Bacillus species were isolated but none produced beta-glucuronidase or phospholipase C. There were no aerobic gram-negative bacteria isolated from stents. Clostridium species and B fragilis were not recovered from the control samples. CONCLUSIONS: In patients who had received antibiotic prophylaxis against gram-negative bacterial infection, anaerobic bacteria may play a role in initiating stent blockage.

Adult↗
PubMed2000

Aminoglycoside resistance in Mycobacterium kansasii, Mycobacterium avium-M. intracellulare, and Mycobacterium fortuitum: are aminoglycoside-modifying enzymes responsible?

Aminoglycoside acetyltransferase was detected in Mycobacterium kansasii and M. fortuitum but not in M. avium-M. intracellulare when they were screened by a radioassay. Aminoglycoside phosphotransferase and nucleotidyltransferase activities were absent from all three species tested. Acetyltransferases from both M. kansasii and M. fortuitum displayed relatively high K(m)s, all at the millimolar level, for substrates including tobramycin, neomycin, and kanamycin A. The K(m) of each substrate was well above the corresponding maximum achievable level in serum. The low affinities of these enzymes for their substrates suggested that drug modification in vivo was very unlikely. Among the various substrates tested, no apparent positive correlation was found between substrate affinity and resistance level. The presence of aminoglycoside-modifying enzymes in these mycobacterial species was therefore not shown to confer resistance to aminoglycosides.

Acetyltransferases↗
PubMed2000

Molecular methods for the epidemiological typing of Salmonella enterica serotype Typhi from Hong Kong and Vietnam.

A total of 217 and 73 strains of Salmonella enterica serotype Typhi isolated from 1985 to 1997 in Hong Kong and in 2 months of 1989 and 1990 in Vietnam, respectively, were studied. These isolates were typed by plasmid profile analysis, plasmid fingerprinting, ribotyping with PstI, and total DNA fingerprinting with NarI. There appeared to be no major outbreak of typhoid fever in Hong Kong during the study period since there was considerable heterogeneity among the isolates. Isolates from Hong Kong were different from those from Vietnam. Thirty-seven percent of Vietnamese isolates belonged to two predominant clones, with the rest being heterogeneous in nature. Total DNA fingerprinting supplemented with ribotyping could be a reliable and rapid method for epidemiological typing of S. enterica serotype Typhi.

Bacterial Typing Techniques↗
PubMed2000

Survey for the presence and distribution of human herpesvirus 8 in healthy brain.

Brain tissues from both sides of the cerebellum and frontal, temporal, parietal, and occipital lobes were collected postmortem from 30 patients for human herpesvirus 8 (HHV-8) detection by PCR. Overall, 42 of 300 (14.0%) samples were positive, with similar rates for each position. Nineteen patients (63.3%) were positive and showed a significant increase in positivity with age (P = 0.007). The results indicate a neuroinvasive and neuropersistent potential of HHV-8.

Adult↗