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Biomedical subjects

H C Lim

Publications and source records attributed to H C Lim.

At least 19 recordsLinked to original sources
PubMed2006

Determination of molecular types and genetic heterogeneity of Cryptococcus neoformans and C. gattii in Malaysia.

The molecular types and genetic heterogeneity of Cryptococcus neoformans and C. gattii clinical isolates in Malaysia were determined in this study. Of 44 C. neoformans collected between 1980 and 2003, 42 (95.5%) were molecular type VNI, 2 (4.5%) were molecular type VNII. Of 17 C.gattii isolates, 13 (76.5%) were molecular type VGI, and 4 (23.5%) were molecular type VGII. A difference was noted when comparing the molecular types of cryptococcal isolates in the earlier and recent cases of cryptococcosis. While both molecular types VNI and VGI were equally predominant in the earlier cases of cryptococcosis, VNI was the most predominant molecular type isolated from the recent cases. VNII was a new molecular type, isolated from 5.1% of the recent cases. All the bird dropping isolates were molecular type VNI. The genetic heterogeneity of the two predominant molecular types, i.e., VNI, VGI clinical isolates and bird dropping isolates of C. neoformans were further determined by polymerase chain reaction (PCR) fingerprinting method, using (GTG)5 as single primer. Two clusters of cryptococcal isolates were distinguished at 68.5% of similarity, with cluster I consisting of VNI isolates and cluster II consisting of VGI isolates. Each cluster was further subdivided into three subtypes at >/=80% of similarity. Fourteen bird dropping isolates were grouped into a subtype within VN1, sharing 82.7% of similarity with the clinical isolates. A higher degree of similarities, ranging from 93.4-97.6% was noted between 3 bird dropping isolates with the clinical isolates in another subtype. This study demonstrated the existence of various molecular types of C. neoformans isolates in Malaysia and the genetic heterogeneity within the predominant molecular types. The study also provides evidence for genetic relatedness of clinical isolates with bird dropping isolates in the environment.

Cryptococcosis↗
PubMed2003

Kinetics of L-lysine fermentation: a continuous culture model incorporating oxygen uptake rate.

For process design and optimization, it is essential to have a mathematical model that represents the system well. Many past studies do not go beyond empirically fitting experimental data. In the present study, an unstructured model incorporating oxygen uptake and dissolved oxygen concentration was developed for a continuous culture of L-lysine. Specific rate expressions of cell growth, substrate consumption, product formation, and oxygen uptake were developed and incorporated in the model. The model predicts very well the effects of operational parameters, such as the dilution rate and the feed substrate concentration. It is also able to predict the unsteady-state dynamics of continuous L-lysine fermentation.

Bioreactors↗
PubMed2001

Intra-articular ganglion cysts of the knee: clinical and MR imaging features.

The purpose of this study was to present clinical and MR imaging features of intra-articular ganglion cysts of the knee. Retrospective review of 1685 consecutive medical records and MR examinations of the knee performed at three imaging centers allowed identification of 20 patients (13 men and 7 women; mean age 35 years), in whom evidence of intra-articular ganglion cyst was seen. Of the 20 ganglion cysts, 5 were found in the infrapatellar fat pad, 10 arose from the posterior cruciate ligament, and 5 from the anterior cruciate ligament. Three of five patients with ganglion cyst in the infrapatellar fat pad had a palpable mass. In 7 of 15 patients with ganglion cyst in the intercondylar notch, exacerbation of pain occurred in a squatting position. On four MR arthrographies, ganglion cysts were an intra-articular round, lobulated, low signal intensity lesion. Five cases of fat-suppressed contrast-enhanced T1-weighted SE images demonstrated peripheral thin rim enhancement. The clinical presentation of intra-articular ganglion cyst is varied according to its intra-articular location. The MR appearance of intra-articular ganglion cyst is characteristic and usually associated with the cruciate ligament or the infrapatellar fat pad. Magnetic resonance arthrography has no definite advantage over conventional MR in the evaluation of the lesion. For intra-articular ganglion cyst in the infrapatellar fat pad, fat-suppressed contrast-enhanced MR imaging could be useful, because a thin, rim-enhancing feature of intra-articular ganglion cyst allows it to be distinguished from synovial hemangioma and synovial sarcoma.

Adolescent↗
PubMed2001

Out of hospital cardiac arrests--the experience of one hospital in Singapore.

In Singapore, all public emergency ambulances are equipped with semi-automatic external defibrillators and the crew is trained in their use. This is the first paper from Singapore reporting the survival rate in patients presenting to an urban public hospital with acute coronary syndrome (ACS) who developed out-of-hospital cardiac arrest (OHCA). All consecutive patients who presented to the ED of a public hospital with OHCA or ACS were surveyed from 1 April 1999 to 30 September 1999. There were 392 patients among whom 115 (28.5%) had OHCA. There was no significant difference in age and gender distribution between the OHCA and non-OHCA patients. More than 2/3 of the OHCA patients had no report of chest pain or breathlessness before they collapsed. Forty five (39.1%) of the 115 OHCA patients were noted to have initial rhythms of ventricular tachycardia (VT) or ventricular fibrillation (VF) and received pre-hospital defibrillation. The mean time from collapse to first DC shock was 12.07+/-7.2 min. Twenty (17.4%) of the OHCA patients had return of spontaneous circulation after resuscitation in the ED. Four patients (3.5%), all with an initial rhythm of VF were discharged alive from the hospital. Much remains to be done to reduce the time interval to first DC shock for the OHCA group.

Aged↗
PubMed2000

Meniscal flounce on MR: correlation with arthroscopic or surgical findings.

The purpose of this study was to investigate the frequency of the meniscal flounce on MR imaging in patients who underwent arthroscopy or open surgery due to symptoms related to internal derangement of the knee, and to investigate associated findings in patients with meniscal flounce by comparing and analyzing the findings from MR imaging and surgery. MR images obtained from 116 knees before surgery were reviewed retrospectively. Seven medial menisci showed buckled, wavy flounce on sagittal MR images. None of the lateral menisci showed flounce. We reviewed the surgical records of all seven patients and the videotapes of six of the patients undergoing arthroscopy or open surgery. The frequency of flounce on sagittal MR images was 6.0% in the medial meniscus and was completely absent in the lateral meniscus. On coronal MR images, the truncated appearance of the affected meniscus was demonstrated in five patients, and a valgus deformity was seen in three patients. Five patients showed a moderate to large amount of joint effusion. On MR imaging and in surgery, ligament injuries were found in six patients (six medial collateral ligament injuries, five anterior cruciate ligament injuries, and two posterior cruciate ligament injuries). Non-specific synovitis was found in the one remaining patient. In the surgery of all seven patients, no tears were found at the meniscus itself showing flounce. In conclusion, the meniscal flounce seen on sagittal MR imaging can be a rare appearance of a transient distortion of a normal meniscus due to a valgus deformity caused by a MCL tear and/or due to an external rotation induced by cruciate ligament injury or positioning of knee joint within the magnet. The meniscal flounce should be interpreted carefully because it frequently appears truncated on the coronal scan and can simulate a meniscal tear.

Arthroscopy↗
PubMed2000

Vision screening of 4-year-old children in Singapore.

AIM OF THE STUDY: To evaluate the feasibility of an improved visual acuity screening program for Singapore 4-year-old preschool children and to draw up an appropriate referral criteria as well as evaluating the rates and outcomes of these referrals. METHOD: A total of 450 children aged 4 to 4 1/2 years, who attended 3 polyclinics of the Family Health Service (FHS) for their 4-year-old Developmental Health Screening during the study period from 1/4/1997 to 30/6/1997 were recruited for the study. Children who were tested with Snellen (or Sloan) visual acuity chart resulting in visual acuity of 6/9 or worse, or failed to pass the 3 mm medium plate at 30 cm distance (300 seconds of arc) in the Frisby Stereotest, or were found to have strabismus, or were untestable in either visual acuity test or stereotest were offered referral to ophthalmologists in the hospitals for specialist assessment. RESULT: 82.7% of the 450 children were successfully screened with Snellen (or Sloan) chart while 91.6% were successfully screened with Frisby Stereotest. In all, 180 children were evaluated by ophthalmologists. Majority of the children were referred because of their abnormal visual acuity test while only 2 children were referred for failing stereotest alone. Among the 180 children referred, 63 (35.0%) were found to have refractive errors for which spectacles were prescribed. Eight children had amblyopia and 2 children had strabismus which were not detected at the polyclinic screening. The untestable children evaluated had significantly higher abnormality rate (37.5%) than that of children who had 6/9 vision (8.8%) therefore they should be offered referral for further evaluation. There was high "refused referral" rate of 39.0%. Parents of children who were untestable or had 6/9 vision were found to be more likely to refuse offer of referral. If these two groups of children were excluded, the "refused referral" rate dropped to 13.3%. When the referral criteria for visual acuity was reset at 6/12 instead of 6/9, the referral rate dropped from 39.6% to a more manageable 26.7% and the positive predictive value improved from 35.4% to 48.3% and none of the children with amblyopia were missed being screened-out. CONCLUSION: The study confirmed the feasibility of doing visual acuity screening at 4 to 41/2 year-old. The referral criteria for abnormal visual acuity should be set at 6/12. The efficacy of adding Frisby stereotest needs further evaluation.

Age Factors↗
PubMed1998

Characterization of bacteriophage lambda Q- mutant for stable and efficient production of recombinant protein in Escherichia coli system.

We previously demonstrated that the lambda system integrated into the host chromosome can overcome the instability encountered in continuous operations of unstable plasmid-based expression vectors. High stability of a cloned gene in a lysogenic state and a high copy number in a lytic state provide cloned-gene stability and overexpression in a two-stage continuous operation. But the expression by the commonly used S- mutant lambda was only twice as high as that of the single copy. To increase the expression in the lambda system, we constructed a Q- mutant lambda vector that can be used in long-term operations such as a two-stage continuous operation. The Q- mutant phage lambda is deficient in the synthesis of proteins involved in cell lysis and lambda DNA packaging, while the S- mutant is deficient in the synthesis of one of two phage proteins required for lysis of the host cell and liberation of the progeny phage. Therefore, it is expected that the replicated Q- lambda DNA containing a cloned gene would not be coated by a phage head and would remain naked for ample expression of the cloned gene and host cells would not lyse easily and consequently would produce larger amounts of cloned-gene products. The beta-galactosidase expression per unit cell by the Q- mutant in a lytic state was about 30 times higher than that in a lysogenic state, while the expression by the commonly used S- mutant in a lytic state was twice as high as that in a lysogenic state. The optimal switching time of the Q- mutant from the lysogenic state to the lytic state for the maximum production of beta-galactosidase was 5.3 h, which corresponds to an early log phase in the batch operation.

Bacteriophage lambda↗
PubMed1998

Why do patients complain? A primary health care study.

BACKGROUND/AIM OF STUDY: Patient complaints are indications of their dissatisfaction with the service received. With increasing patient expectations, we need to address this issue for a more satisfying relationship between healthcare provider and user. The objective of this study was to analyse the basis of patients' complaints and to make recommendations to reduce its incidence. METHOD: This is a retrospective descriptive study of all complaints to the Family Health Service between January 1994 and December 1995. All complaints, investigations and replies to complainants were examined and analysed by the authors to determine the reasons for complaints and their justification. RESULTS: There were 226 complaint cases out of 5,620,834 attendances in two years, giving the complaints rate of 4 per 100,000 attendances per year. The complaint rate was highest for the 20-59-year age group and lowest in the 10-19-year age group (3.7 and 2.0 per 100,000 attendances respectively). Sixty-four percent of complaints were verbal and the rest were written. Forty-seven percent of the complaints were made by relatives and 46% were self-complaints. The main reasons for complaints were related to attitude/conduct (28.8%), professional skills (17.8%), patient expectations (16.2%), waiting time (10.0%) and communication (7.8%). Forty-three percent of complaints were evaluated as justifiable, 38% not justifiable and 19% inconclusive. There were no particular sex or ethnic group differences. CONCLUSION: The rate of complaints in Family Health Service was low. Healthcare personnel need to pay attention to areas related to attitude/conduct, professional skills, patient expectations, waiting time and communication.

Communication↗
PubMed1997

Computerised prostate boundary estimation of ultrasound images using radial bas-relief method.

A new method is presented for automatic prostate boundary detection in ultrasound images taken transurethrally or transrectally. This is one of the stages in the implementation of a robotic procedure for prostate surgery performed by a robot known as the robot for urology (UROBOT). Unlike most edge detection methods, which detect object edges by means of either a spatial filter (such as Sobel, Laplacian or something of that nature) or a texture descriptor (local signal-to-noise ratio, joint probability density function etc.), this new approach employs a technique called radial bas-relief (RBR) to outline the prostate boundary area automatically. The results show that the RBR method works well in the detection of the prostate boundary in ultrasound images. It can also be useful for boundary detection problems in medical images where the object boundary is hard to detect using traditional edge detection algorithms, such as ultrasound of the uterus and kidney.

Humans↗
PubMed1996

Bioreactor studies on temperature induction of the Q- mutant of bacteriophage lambda in Escherichia coli.

The parasite-host interactions between bacteriophage lambda (denoted as lambda) and Escherichia coli bacteria were studied in different bioreactor systems. Although the replicated lambda-DNA of Q- mutant remains naked for a longer time to reach a high gene expression, the epidemic of lambda-infection and the coevolutionary host-phage relations limit the temperature induction efficiency. The temperature induction is strongly dependent upon the susceptible population density at which lambda-infection is activated. Maximum beta-galactosidase expression occurs at the threshold of the infection system. According to this concept, the lethal level of parasitic lambda to hosts is approx. 5 x 10(6) pfu/ml. Since a higher phage lambda burden is exerted upon host cells at a low ODsh, the system moves towards virulence reduction for total survival. Prey-predator isocline analysis is used to consider the stability of the outcome of infection. The host growth has a destabilizing effect at lower population densities and a stabilization effect at higher population. Based upon the predictions, a substrate enrichment enhances bacterial growth and reporter protein production. However, the operations still need to follow the trajectory of threshold tie line to guarantee maximal productivity. Since the washout of infected cells reduces induction performance in continuous cultures, a batch mode of operation is better than continuous stirred tank reactor (CSTR) mode to achieve high gene expression. The threshold cell density regulates induction performances and therefore produces the optimal gene expression by maintaining maximal viable cells that provide sufficient resources for lambda expression.

Bacteriophage lambda↗
PubMed1996

The field testing of Denver Developmental Screening Test Singapore: a Singapore version of Denver II Developmental Screening Test.

The Denver Developmental Screening Test, Singapore (DDST, Singapore), a Singapore version of the Denver II Developmental Screening Test, was field-tested, using trained staff nurses as testers, on 2459 children (known cases excluded), in 5 key ages of 3 months, 9 months, 17 months, 37 months and 60 months. Only 2.6% (65) of the parents suspected developmental problems in their children before screening. Taking children with "questionable" (7.2%), "abnormal" (3.7%) and "untestable" (1.7%) scores as the screened-out cases, the DDST, Singapore had a screened-out rate of 12.6%. A total of 171 screened-out cases and 168 "normal" children were also evaluated by the Development Assessment Clinic (DAC) of the Singapore General Hospital and the results were compared in these 2 groups of children. Among the screened-out cases, 16.6% were confirmed or suspected to have neuro-developmental disorders (NDDs) by the DAC. The computed NDD rate in the study sample was 5.3%. Based on a single DDST, Singapore test result, there was a high false positive rate of 83.5% and lower false negative rate of 3.7% compared to the DAC assessment. However, the high false positive rate would be significantly reduced by doing a repeat screening test on the "questionable" cases and having the screened-out cases assessed by trained primary health care doctors. In conclusion, no major revision is needed in the scoring criteria suggested in the current version of DDST, Singapore. It is a useful tool in identifying children who will otherwise be missed without formal screening.

Child, Preschool↗
PubMed1995

Temperature induction of bacteriophage lambda mutants in Escherichia coli.

The paper presents temperature induction in Escherichia coli cells with phage lambda on the target-protein production and cell growth. Replicated lambda-DNA particles in the Q- and S- mutants remain naked for a longer time by preventing DNA packaging and cell lysis, and therefore the expression of the foreign genes is high. However, the parasitic infection of phage-lambda causes on significant losses of host cell viability in the induction phase. The temperature effects on cell growth and targeted-gene product formation were investigated. Gene amplification was found to be growth phase dependent for both Qam73 (Q mutation) and Sam100 (S mutation) mutants. Maximum induction occurs in the early exponential phase and under the optimal cell density. The total beta-galactosidase activity at this optimal induction condition increases roughly 8-10-fold with respect to that without thermal induction. To maximize the induction efficiency for the gene-product beta-galactosidase activity, several operating parameters were investigated. In this study, temperature induction is strongly dependent upon the population density of 'susceptible' cells at which time the temperature is shifted to 38-42 degrees C. This may be due to the 'threshold' population density to regulate the infection of lambda to hosts and control the productivity of target gene expression.

Bacteriophage lambda↗
PubMed1994

cAMP, ethanol, and CO2 production with the addition of D-glucose anomer to starved yeast cells.

cAMP, ethanol, and CO2 production in starved yeast cells after the addition of D-glucose anomer was measured and compared over a wide range of anomer concentrations. At 1.0 g/l or higher concentrations, the addition of beta-D-glucose resulted in a higher cAMP peak. beta-D-glucose was more rapidly metabolized to ethanol and CO2 than alpha-D-glucose, although there was no notable difference in the uptake rates of the two anomers. At 0.4 g/l D-glucose anomer, the differences in cAMP and ethanol production rates for the two anomers were not significant. At 0.2 g/l D-glucose anomer or lower concentrations, ethanol production with alpha-D-glucose was higher than that with beta-D-glucose. The uptake rate of alpha-D-glucose was higher than that of beta-D-glucose at this low concentration.

Carbon Dioxide↗
PubMed1994

Tyrosinase production in recombinant E. coli containing trp promoter and ubiquitin sequence.

We have successfully expressed the active tyrosinase of Streptomyces antibioticus in Escherichia coli under the control of the trp promoter by fusing the sequence to the ORF438 gene. Because our attempt to connect the polycistronic gene of ORF438 and tyrosinase directly to the trp promoter of E. coli resulted in the expression of functionally inactive tyrosinase, we decided to fuse the COOH-terminus of ubiquitin sequence to the NH2-terminus of ORF438. Ubiquitin fusion has been shown to augment the yield of cloned gene products in E. coli by increasing the stability or translational efficiency of the fusion proteins. As a result, E. coli transformants harboring a plasmid pTRUBF that contains the ubiquitin-fused ORF438 and the tyrosinase gene produced the strong black pigment of melanin. About 300 units of tyrosinase per liter of batch culture were detected when cultivated in M9 medium containing casamino acids, L-tyrosine, and copper supplements. The black pigment, however, was not seen when grown in LB medium, suggesting that the trp promoter is well regulated. When recombinant E. coli cells grown in LB medium were transferred to a tryptophan-deficient minimal medium with phenol, we observed that phenol was removed from the solution, and the color of the medium turned black. This is due to the fact that the tyrosinase has polyphenol oxidase properties. We expect to use this recombinant E. coli for the waste treatment of phenolic compounds.

Base Sequence↗
PubMed1994

Standardisation and adaptation of the Denver Developmental Screening Test (DDST) and Denver II for use in Singapore children.

OBJECTIVE: To modify and standardise the Denver Developmental Screening Test (DDST) and Denver II for developmental screening of children in Singapore. METHOD: The study used a quota sample of 2,194 Singapore children aged 4 weeks to 6 years. Logistic regression analysis established the 25th, 50th, 75th, and 90th percentile passing age for achieving the test tasks. Subgroup differences in Sex, Ethnicity, Social Class and Mother's Education were analysed by stepwise logistic regression; the composite norms for items with statistically significant subgroup differences (p < or = 0.10), were then adjusted by weighting based on the composition of Singapore children. The study protocol was based on the DDST (1975) and Denver II (1990), the latest version of the DDST. Modifications were introduced to improve on the sensitivity of the test and to make the test more suited to Singapore culture. MAIN FINDINGS: Out of the 215 items studied, 115 items were selected to form the new test, DDST, Singapore, DDST, Singapore shares 63% of the items with DDST (1975) and 67% of the items with Denver II. Among the comparable items, differences between the norms of Singapore and Denver children greater than 10% were demonstrated in more than 30 items, and differences of greater than 20% in 10 items. Within the study sample of Singapore children, there were relatively smaller differences among the subgroups studied. Only 10 items had clinically significant subgroup differences of more than 10%. None had more than 20% difference. CONCLUSION: DDST, Singapore is substantially different from the DDST (1975) and Denver II (1990). The use of the local standardised version for developmental screening of Singapore children is justified.

Child↗
PubMed1992

Nitrazepam-induced cricopharyngeal dysphagia, abnormal esophageal peristalsis and associated bronchospasm: probable cause of nitrazepam-related sudden death.

Nitrazepam was used in the treatment of resistant myoclonic epilepsy in 38 children. After the occurrence of nitrazepam-associated swallowing incoordination, high-peaked esophageal peristalsis and related bronchospasm in one patient, we initiated a prospective study of esophageal manometry using a station pull-through technique with a pediatric 4-channel continuous perfusing system. Three more patients were found to have delayed cricopharyngeal relaxation and high-peaked esophageal peristaltic waves. The initial patient developed severe respiratory distress and bronchospasm necessitating ventilatory support while on nitrazepam and improved dramatically with subsequent normal manometric study following nitrazepam discontinuation. Nitrazepam was reintroduced for its anticonvulsant and cognitive benefits and was tolerated at a reduced dosage. We postulate a central nervous system effect of nitrazepam promoting parasympathetic overactivity or vagotonia which can cause potentially fatal respiratory distress. Care must be exercised in nitrazepam use and esophageal manometry may be helpful in defining patients at greater risk for sudden death.

Adolescent↗
PubMed1988

Concomitant hypotensive and antinociceptive effects of guanabenz in conscious rats: involvement of nucleus reticularis gigantocellularis.

Subcutaneous administration of guanabenz (1, 2, 5, or 8 mg/kg) in conscious Sprague-Dawley rats exerted concomitant suppressive actions on systolic pressure (tail-cuff sphygmomanometric measurement) and pain responses (hot-plate algesio-metric assay) that varied both in degree (antinociception much greater than hypotension) and response pattern. Furthermore, both depressive effects were appreciably attenuated by bilateral lesions of the nucleus reticularis gigantocellularis in the medulla oblongata. It is speculated that separate subpopulations of neurons within this reticular nucleus may be involved in the expression of hypotension and antinociception by this amino-guanidine derivative.

Analgesia↗