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T K Ng

Publications and source records attributed to T K Ng.

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

Target site modifications and efflux phenotype in clinical isolates of Streptococcus pneumoniae from Hong Kong with reduced susceptibility to fluoroquinolones.

Ciprofloxacin-susceptible (n = 7) and -resistant (MIC >or=4 mg/L) (n = 15) clinical isolates of Streptococcus pneumoniae from diverse sources in Hong Kong were studied for target site modifications and efflux phenotype. Reserpine-inhibited efflux of ciprofloxacin and/or levofloxacin was common in both susceptible and non-susceptible isolates. The ParC substitutions K137N and/or S79F or Y were associated with increased ciprofloxacin MICS. The GyrA substitution S81F was only found in isolates with full resistance to ciprofloxacin (MIC >or=16 mg/L) and levofloxacin (MIC >or=8 mg/L). Among clinical isolates of S. pneumoniae, accumulation of target site mutations in strains with an efflux mechanism was associated with increasing MICs of fluoroquinolones.

Amino Acid Substitution↗
PubMed2001

Increasing resistance of Streptococcus pneumoniae to fluoroquinolones: results of a Hong Kong multicentre study in 2000.

The MICs of 13 antimicrobial agents including seven fluoroquinolones (ciprofloxacin, levofloxacin, sparfloxacin, grepafloxacin, gatifloxacin, moxifloxacin and clinafloxacin) for Streptococcus pneumoniae isolates obtained from all regions of Hong Kong in the year 2000 were determined by the Etest. Overall, 39.4% of 180 isolates were susceptible to penicillin, 11.7% were intermediate and 48.9% were resistant. The overall prevalence of fluoroquinolone non-susceptibility (levofloxacin MIC > or = 4 mg/L) was 13.3% but increased to 27.3% among the penicillin-resistant isolates. For the fluoroquinolone non-susceptible isolates, within-class cross-resistance was common. For the fluoroquinolone non-susceptible isolates, the median MICs of clinafloxacin, gatifloxacin, moxifloxacin, sparfloxacin and grepafloxacin were, respectively, six-, 24-, 32- 84- and 128-fold higher than those for the susceptible isolates. All fluoroquinolone non-susceptible strains were derived from adults. The prevalence of fluoroquinolone resistance was higher in isolates from older patients (17.1% among those > or = 65 years of age versus 9.1% among those 18-64 years of age, P < 0.001) and from adults with chronic obstructive pulmonary disease (24.6% versus 9.3%, P = 0.01). All fluoroquinolone non-susceptible strains were non-susceptible to penicillin (MIC range 2-4 mg/L), cefotaxime (MIC range 1-4 mg/L) and erythromycin (MIC range 4- > or = 256 mg/L). The fluoroquinolone non-susceptible isolates were genetically related to the Spain(23F)-1 clone when analysed by pulse-field gel electrophoresis and multilocus sequence typing. In conclusion, a rapid increase in the prevalence of fluoroquinolone resistance among S. pneumoniae was found in Hong Kong. Typing analysis suggests that this is due to the pan-regional dissemination of a fluoroquinolone-resistant variant (designated Hong Kong(23F)-1) of the globally distributed Spain(23)F-1 clone.

Adolescent↗
PubMed2001

Detection of RTX toxin gene in Vibrio cholerae by PCR.

A PCR that amplifies a recently discovered Vibrio cholerae RTX (repeat in toxin) toxin gene was developed. Among 166 clinical and environmental isolates of V. cholerae causing epidemics and sporadic cases of cholera in various parts of the world, all were found to be toxigenic by both PCR and HEp-2 cell cytotoxicity assay. Standard strains of the classical biotype containing a deletion within the gene cluster exhibited negative results by both assays. This is the first rapid genotyping method for differentiation of V. cholerae O1 classical biotype strains from El Tor biotype strains as well as strains of other non-O1 serogroups including serogroup O139. The PCR assay that was developed also specifically detects RTX toxin genes in V. cholerae, as clinical isolates of Vibrio parahaemolyticus, diarrheagenic Escherichia coli, Aeromonas species, and Plesiomonas species were all negative by the RTX toxin-specific PCR as well as the HEp-2 cytotoxicity assay. These findings highlight the characteristics of the RTX toxins in V. cholerae. Their role in the pathogenicity of the bacterium requires further investigation.

Acyltransferases↗
PubMed2000

Probing superconducting phase fluctuations from the current noise spectrum of pseudogapped metal-superconductor tunnel junctions.

We study the current noise spectra of a tunnel junction of a metal with strong pairing phase fluctuation and a superconductor. It is shown that there is a characteristic peak in the noise spectrum at the intrinsic Josephson frequency omega(J) = 2eV when omega(J) is smaller than the pairing gap but larger than the pairing scattering rate. In the presence of an ac voltage, the tunneling current noise shows a series of characteristic peaks with increasing dc voltage. Experimental observation of these peaks will give direct evidence of the pair fluctuation in the normal state of high- T(c) superconductors and the pair decay rate can be estimated from the half width of the peaks.

Journal Article↗
PubMed2000

Distinct cellular distribution of GABA(B)R1 and GABA(A)alpha1 receptor immunoreactivity in the rat substantia nigra.

GABA is one of the most important inhibitory neurotransmitters in the substantia nigra. Functions of GABA are mediated by two major types of GABA receptors, namely the GABA(A) and GABA(B) receptors. Subunits of both the GABA(A) and GABA(B) receptors have been cloned and functional characteristics of the receptors depend on their subunit compositions. In order to characterize the cellular localization of GABA(B)R1 and GABA(A)alpha1 subunit immunoreactivity in subpopulations of neurons in the rat substantia nigra, double and triple immunofluorescence was employed. Over 90% of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta were found to display immunoreactivity for GABA(B)R1. In contrast, immunoreactivity for GABA(A)alpha1 was found to be primarily displayed by neurons in the substantia nigra pars reticulata. Around 85% of the GABA(A)alpha1-immunoreactive reticulata neurons were found to display parvalbumin immunoreactivity and some GABA(A)alpha1-positive reticulata neurons were found to be parvalbumin negative. In addition, triple-labeling experiments revealed that at the single cell level, the tyrosine hydroxylase-positive, i.e. the dopaminergic neurons in the compacta displayed intense immunoreactivity for GABA(B)R1 but not GABA(A)alpha1 receptors. The parvalbumin-positive neurons in the reticulata displayed intense immunoreactivity for GABA(A)alpha1 but not GABA(B)R1 receptors. The present results demonstrate in the same sections that there is a distinct pattern of localization of GABA(B)R1 and GABA(A)alpha1 receptor immunoreactivity in different subpopulations of the rat substantia nigra and provide anatomical evidence for GABA neurotransmission in the subpopulations of nigral neurons.

Animals↗
PubMed2000

Bacteremia due to Staphylococcus aureus with reduced susceptibility to vancomycin.

Four cases of bacteremia caused by Staphylococcus aureus with heteroresistance to vancomycin (hetero-VRSA) were described. In at least two of these four mortalities, the cause of death was temporally related to the hetero-VRSA bacteremia. The vancomycin and teicoplanin MICs of the resistant subpopulations of these four hetero-VRSA were 8 and 24 microg/ml, respectively. All isolates were producers of beta-lactamase, produced penicillin-binding protein PBP2a, and possessed the mecA gene accounting for methicillin resistance. Thickening of the peptidoglycan cell wall was observed by electron microscopy. When ampicillin was combined with vancomycin, in vitro synergism was detected using the checkerboard titration method (epsilonFIC = 0.13). The use of vancomycin plus ampicillin-sulbactam could be a viable option in treating severe hetero-VRSA infection in view of the higher affinity of ampicillin toward PBP2a.

Aged↗
PubMed2000

Plesiomonas shigelloides infection in Hong Kong: retrospective study of 167 laboratory-confirmed cases.

OBJECTIVE: To study the epidemiological, clinical, and microbiological features of Plesiomonas shigelloides infection in Hong Kong. DESIGN: Retrospective study. SETTING: Infectious Disease Unit of a district hospital, Hong Kong. PATIENTS: Patients with laboratory-confirmed cases of Plesiomonas shigelloides infection between 1 January 1995 and 31 December 1998. MAIN OUTCOME MEASURES: Epidemiological and clinical data, antibiotic sensitivity, and clinical outcome. RESULTS: There was an increasing trend in the number of isolates of Plesiomonas shigelloides obtained and the prevalence of the bacterium. A total of 197 isolates were obtained from 188 patients, and most isolates (172; 87.3%) were obtained during the summer. Clinical and epidemiological data were available for 167 patients (85 males, 82 females). Patient age ranged from 1 month to 95 years; the mean and median ages of the patients older than 15 years were 51.0 and 40.5 years, respectively (n=132). Only 35 (21.0%) of the 167 patients had a history of travel outside Hong Kong, whereas 21 (12.6%) had a history of consuming seafood or uncooked food; 39 (23.4%) had underlying medical conditions. Most patients (165; 98.8%) had symptoms of Plesiomonas shigelloides infection. Nine (5.4%) patients had had chronic diarrhoea for more than 2 weeks; watery and bloody diarrhoea was discharged by 122 (73.1%) and 42 (25.1%) of the patients, respectively. All 197 Plesiomonas shigelloides isolates were sensitive to ofloxacin, or levofloxacin and ceftriaxone. Resistance or partial resistance was recorded for ampicillin (72%), tetracycline (67%), co-trimoxazole (12%), and chloramphenicol (5%). The majority of patients (142/167; 85.0%) had self-limiting cases of infection, but 25 patients were given antibiotics for more severe symptoms at the time of presentation; there were two deaths. CONCLUSIONS: The occurrence of Plesiomonas shigelloides infection in Hong Kong is increasing, although most cases of are self-limiting.

Adolescent↗
PubMed2000

Abdominal pregnancy presenting as a missed abortion at 16 weeks' gestation.

We report on an abdominal pregnancy that presented as a missed abortion at 16 weeks' gestation and review the literature on the management of abdominal pregnancy. The clinical presentation of abdominal pregnancy varies, and the diagnosis depends on a high index of suspicion. Ultrasonography is useful for early diagnosis of the condition. The management depends on the gestation at presentation; for advanced abdominal pregnancy, surgical intervention is recommended. The treatment of the placenta is a matter of controversy. In general, expectant management is suggested. When the placenta is left behind, the use of prophylactic methrotrexate is not advocated. An awareness of abdominal pregnancy is very important for reducing associated morbidity and mortality.

Abortion, Missed↗
PubMed1999

Subpopulations of neurons in the rat neostriatum display GABABR1 receptor immunoreactivity.

Immunoreactivity for gamma aminobutyric acid BR1 receptor (GABABR1) was detected in the neuropilar elements as well as in the perikarya of neurons in the neostriatum. Many of the GABABR1-immunoreactive perikarya were medium-sized with a thin rim of cytoplasm. They resembled the morphology of medium spiny neurons, the projection neurons of the neostriatum. In addition, some GABABR1-immunoreactive neurons were densely labeled and were of medium to large in size. These neurons were characterized by double immunofluorescence using their neurochemicals as markers. Over 90% of the parvalbumin- and choline acetyltransferase-immunoreactive neurons and about 80% of the nitric oxide synthase-immunoreactive neurons displayed GABABR1 immunoreactivity. The present results show for the first time that the major four subpopulations of striatal neurons express GABABR1 receptor and may have a functional implication in the GABA neurotransmission in the microcircuitry of the neostriatum.

Animals↗
PubMed1999

Minihernia repair.

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Cohort Studies↗
PubMed1999

A cervical ectopic pregnancy managed by medical treatment and angiographic embolization.

Medical treatment in the form of systemic methotrexate with or without local methotrexate/potassium chloride is effective for early cervical pregnancy. It should be the treatment of choice in suitable cases. Haemorrhagic complications can be effectively managed by angiographic embolization. A case report illustrating these points is presented.

Abortifacient Agents, Nonsteroidal↗
PubMed1999

Emergence of fluoroquinolone resistance among multiply resistant strains of Streptococcus pneumoniae in Hong Kong.

The MICs of 17 antimicrobial agents for 181 Streptococcus pneumoniae strains were determined by the E-test. Overall, 69.1% were penicillin resistant (MIC > 0.06 microgram/ml). Resistance to ciprofloxacin (MIC > 2 microgram/ml), levofloxacin (MIC > 2 microgram/ml), or trovafloxacin (MIC > 1 microgram/ml) was found in 12.1, 5.5, or 2.2% of the strains, respectively. These high rates of resistance raise concerns for the future.

Adolescent↗
PubMed1998

Antimicrobial resistance in Shigella flexneri and Shigella sonnei in Hong Kong, 1986 to 1995.

Three hundred and thirty-three Shigella isolates obtained in 1986 to 1995 were tested for their susceptibilities to 19 antimicrobial agents. Nalidixic acid resistance had emerged in 59.6% of Shigella flexneri isolates during 1994 to 1995, with all tested resistant isolates having the mutation in gyrA encoding the Ser-83 alteration. Multiresistance (resistance to four or more agents) was more common in S. flexneri than in Shigella sonnei.

Anti-Infective Agents↗