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Grace Tan

Publications and source records attributed to Grace Tan.

8 recordsLinked to original sources
PubMed2026

A tiled amplicon protocol for culture-free whole-genome sequencing of M. tuberculosis from clinical specimens.

Whole-genome sequencing of Mycobacterium tuberculosis can be a valuable tool for TB surveillance and treatment, providing insights into transmission patterns and comprehensive drug susceptibility testing. However, the slow growth of M. tuberculosis means traditional culture-based sequencing methods can take weeks to return results, which has limited the widespread adoption of these techniques and limited their use in clinical decision-making. Tiled amplicon sequencing is a fast, reliable, and cost-effective method of whole-genome sequencing that can be done directly on clinical specimens and has been implemented at scale in academic and public health laboratories across the world; it was the cornerstone of SARS-CoV-2 sequencing and has been adapted for a wide range of viral pathogens. However, similar methods are not yet available for far larger bacterial genomes. Extending this approach to M. tuberculosis would significantly reduce the cost, labor, and turnaround time for whole-genome sequencing. We designed a tiled amplicon panel consisting of 5,128 primers that covers the entire M. tuberculosis genome, the largest tiled amplicon sequencing panel we are aware of to date. Applying our amplicon panels to clinical samples of sputum, we show the ability to recover whole-genome bacterial sequences without the need for culture. The resulting sequence data can be used to determine M. tuberculosis lineage and reliably identify markers of drug resistance. Using this approach in clinical settings could reduce the time needed for comprehensive drug susceptibility testing from weeks to days and enable genomic epidemiology to be performed at scale, even in resource-limited settings.IMPORTANCEWe have developed and tested an amplicon panel, TB-seq, for the priority pathogen Mycobacterium tuberculosis, demonstrating recovery of near-full genomes directly from patient sputum, including mixed and low-concentration samples. This approach significantly reduces the turnaround time for this slow-growing bacterium while maintaining high accuracy in detecting clinically relevant mutations, including those associated with drug resistance. Given the global burden of tuberculosis and the critical need for faster diagnostic solutions, we believe our method has the potential to improve clinical decision-making and public health strategies.

Mycobacterium tuberculosis↗
PubMed2006

Nucleation and growth characteristics of a binary low-mass organogel.

The system of bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, when dissolved in a nonpolar organic solvent, forms an organogel. The fibers of this organogel are formed through a nucleation-growth phenomenon. By reducing evaporation of the pregel solution, the fibers can be directed to grow with extremely long persistence lengths. Alignment of multiple fibers is achieved by inducting growth at the air-solution interface. The interplay of two zones, one above the critical nucleation concentration and the other below, allows orientation to be accomplished as fiber growth proceeds. The observations have implications for the use of the organogel as a template for materials synthesis.

Journal Article↗
PubMed2005

Use of a self-assembling organogel as a reverse template in the preparation of imprinted porous polymer films.

The concept of reverse templating of an organogel to form imprinted porous divinylbenzene polymer films with submicrometer channels is demonstrated. The organogel comprising a 1:1 molar ratio of two organogelators, that is, bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, was formed in divinylbenzene. The gel was cast as a thin film before UV polymerization of the solvent, and the organogelators were later removed by simple washing with water and isooctane. The integrity of the fiber bundles of the organogel was preserved during polymerization, and an exact hollow replica was obtained after the organogelators were leached away. It is easily possible to imprint gel fiber bundle structures into polymeric films through this technique. The gel can also be formed on macroporous substrates to yield supported thin porous polymeric films. With the incorporation of functional nanoparticles in AOT inverse micelles and hence the organogel, nanoparticle-containing porous polymer films exhibiting luminescence or magnetic properties are envisioned.

Chlorophenols↗
PubMed2005

Urea and thiourea derivatives as low molecular-mass organogelators.

The properties of a series of organogels consisting of a urea or thiourea derivative with one or two n-alkyl substitutuents at the nitrogen atoms (a low molecular-mass organogelator (LMOG)) and an organic liquid are described. They include N,N'-dimethylurea, the LMOG of lowest molecular mass (M(W) 88) we are aware of. The efficiencies of the LMOGs, based the diversity of liquids gelated, the minimum amount required for gelation of a liquid at room temperature, and the temporal and thermal stabilities of the gels formed, have been investigated as a function of the number, length, and substitution pattern of their n-alkyl chains. The gels are thermally reversible and require generally very low concentrations (<2 wt %) of an LMOG. Some of the LMOGs with shorter chains are more efficient than their longer chained analogues. The structural and thermodynamic properties of the gels have been examined by IR, DSC, and X-ray diffraction techniques. Polarizing optical microscopic analyses of the gels show that the nature of gelator aggregates depends mainly on the alkyl chain length. Changes in the aggregation ability have been examined systematically by perturbing the molecular structure.

Journal Article↗
PubMed2004

Structural evolution of a two-component organogel.

Dry reverse micelles of AOT in isooctane spontaneously undergo a microstructural transition to an organogel upon the addition of a phenolic dopant, p-chlorophenol. This microstructural evolution has been studied through a combination of light scattering, small-angle neutron scattering (SANS), NMR, and rheology. Several equilibrium stages between the system of dry reverse micelles of AOT and a 1:1 AOT/p-chlorophenol (molar ratio) gel in isooctane have been examined. To achieve this, p-chlorophenol is added progressively to the dilute solutions of AOT in isooctane, and this concentration series is then analyzed. The dry micelles of AOT in isooctane do not undergo any detectable structural change up to a certain p-chlorophenol concentration. Upon a very small increment in the concentration of p-chlorophenol beyond this "threshold" concentration, large strandlike aggregates are observed which then evolve to the three-dimensional gel network.

Chlorophenols↗
PubMed2004

Langerhans cell histiocytosis of the cervical spine: a single institution experience in four patients.

When Langerhans cell histiocytosis (LCH) occurs at critical sites, such as in the cervical spine, there is a substantial risk for morbidity. Therefore, reports on clinical experiences with those patients remain important. We summarize the history of four patients with unifocal LCH at the cervical spine. All four patients received a biopsy to prove the histopathological diagnosis of LCH by demonstration of CD1a+cells. They were treated with oral prednisolone. All patients recovered completely and kept a normal function of the cervical spine. No reactivation of the disease occurred with an observation time of 3.4-7.3 years. This report contributes to the clinical experience for the treatment of LCH at critical sites.

Adolescent↗
PubMed2002

Comparison of two commercially available selective media to screen for vancomycin-resistant enterococci.

Campylobacter medium (CAMPY, Becton Dickinson [BD] Microbiology Systems, Cockeysville, MD) and Vancomycin Screen Agar (VSA, BD) were compared for their ability to screen for vancomycin-resistant Enterococcus (VRE) from primary plates. A microdilution minimal inhibitory concentration (MIC) assay (Pasco, BD) served as the reference vancomycin MIC. In the random sample of 200 enterococcal clinical isolates tested, the distribution of isolates was as follows: Enterococcus faecium, 113 (97 VRE); Enterococcus faecalis, 71(12 VRE); Enterococcus gallinarum, 10; and Enterococcus casseliflavus, 6. Of the 75 vancomycin-susceptible strains, none grew on CAMPY and 4 grew on VSA, whereas all 109 VRE isolates grew on both screen plates. Of the 16 strains with a Van C phenotype, ie, E. gallinarum and E. casseliflavus, 2 grew on CAMPY and 14 on VSA. Of the 899 clinical specimens plated onto both agars, 45 of 67 VRE were detected with both media, 20 were detected only with CAMPY and 2 were not detected by either screen plate. CAMPY compared with VSA as a primary plating medium was more sensitive and, when used to screen for VRE isolates from primary plates, was more specific for strains displaying Van A and B phenotypes.

Culture Media↗