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Experimental group A rotaviral infection in cynomolgus monkeys raised on formula diet

Leong YK, Awang A

Microbiol. Immunol., 1990;34(2):153-62.
PMID: 2161071

Rotaviral infections in cynomolgus monkeys (Macaca fasicularis) were studied to ascertain its suitability as a model of infection and diarrhea caused by group A human rotaviruses. Formula-fed monkeys were used as they could be observed closely. Experimental rotaviral infection of cynomolgus monkeys was age-dependent; only young monkeys were readily infected. Formula-fed newborns were readily infected with cell-culture-adapted human (WA) and simian (SA11) viruses and with a rotavirus from a human fecal specimen. However, diarrhea was detected only in very young animals. A number of rotaviral shedding patterns as a function of time were observed. Although there was no typical viral shedding pattern which represented exclusive association of viral infection with diarrhea, the initial level of viral excretion and the maximum level of viral shedding attained were much higher in animals with diarrhea. Seroconversion occurred in less than half of the inoculated animals. The presence of maternal rotaviral antibodies did not prevent infection or diarrhea.
Fulltext SVC obstruction and cardiac tamponade

Leong YK, Ong HS

Heart Asia, 2012;4(1):56.
PMID: 27326031 DOI: 10.1136/heartasia-2012-010101
Survival of SA11 rotavirus in fresh fruit juices of pineapple, papaya, and honeydew melon

Leong YK, Xui OC, Chia OK

J Food Prot, 2008 May;71(5):1035-7.
PMID: 18522042

Survival of rotavirus in fresh fruit juices of papaya (Caraca papaya L.), honeydew melon (Cucumis melo L.), and pineapple (Ananas comosus [L.] Merr.) was studied. Clarified juices were prepared from pulps of ripe fruits and sterilized by ultrafiltration. One milliliter of juice from each fruit was inoculated with 20 microl of 1 x 10(6) PFU of SA11 rotavirus and sampled immediately (0-h exposure) and 1 and 3 h later at 28 degrees C. Mean viral titers in juices of papaya (pH 5.1) and honeydew melon (pH 6.3) at 1 and 3 h were not significantly different from titers at 0-h exposure. Mean viral titers in juices from pineapples with ripening color indices of 3 (pH 3.6) and 6 (pH 3.7) at 1-h exposure (color index 3: 4.0 +/- 1.7 x 10(4); color index 6: 2.3 +/- 0.3 x 10(5)) and 3-h exposure (color index 3: 1.1 +/- 0.4 x 10(4); color index 6:1.3 +/- 0.6 x 10(5)) were significantly lower than titers at 0-h exposure (color index 3: 5.7 +/- 2.9 x 10(5); color index 6: 7.4 +/- 1.3 x 10(5)). Virus titers in pineapple juices of color index 3 were significantly lower than titers of the virus in juices of index 6. In cell culture medium (pH 7.4), SA11 titer remained stable over 3 h at 28 degrees C. However, at pH 3.6, the virus titer was reduced to a level not significantly different from that of the virus in pineapple juice of color index 6 (pH 3.7). In conclusion, papaya and honeydew melon juices, in contrast to pineapple juice, have the potential to transmit rotavirus. Inactivation of SA11 virus in pineapple juice can be possibly attributed to low pH and constituent(s) in the juice.
Microstructure of Sodium Montmorillonite Gels with Long Aging Time Scale

Leong YK, Du M, Au PI, Clode P, Liu J

Langmuir, 2018 08 21;34(33):9673-9682.
PMID: 30053778 DOI: 10.1021/acs.langmuir.8b00213

Purified sodium montmorillonite (SWy-2) gels of a few percent solids displayed pronounced time-dependent rheological or aging behavior with a long time scale. The aging behavior was characterized by an increasing yield stress with rest time. This increase continued even after a week of rest. An open sponge-like cellular microstructure of the aged gels was captured by cryo-SEM with samples prepared at high pressure. The size of the openings of the cellular structure is small, generally less than 1 μm formed by thin flexible platelet with curling edges. This structure was formed by strong attractive and repulsive forces. The rapid yield stress increase in the early stage of aging is due to rapid bond formation occurring between network platelets and free individual platelet, isolated aggregates, and platelet particles in network with free edges. Over time, all platelets are bonded in the network. During aging, the platelets in the structure would have to adjust continually in response to a net force acting on it by its neighbors. The high concentration of platelets responding to this force imbalance is the cause of the long aging time scale. The operation of the attractive and repulsive forces, and the shape and charge properties of the platelets are responsible for the cellular structure being built. At complete structural recovery, the structure should attain the state of lowest free energy. The repulsive force regulates the development of the microstructure. The aging data of the 3.3 wt % gel were fitted by different aging models.
Laboratory study of Vibrio cholerae O1 survival on three types of boiled rice (Oryza sativa L.) held at room temperature

Huat JT, Leong YK, Lian HH

J Food Prot, 2008 Dec;71(12):2453-9.
PMID: 19244898

This study examined whether the survival of Vibrio cholerae O1 on contaminated cooked rice was influenced by the type of rice. Vibrios survived unchanged on clumps of glutinous white rice (wet, grains adhered) held at room temperature for 24 h. On nonglutinous white rice (slightly moist, grains separate), 30% viable vibrios remained at 24 h. On nonglutinous brown rice (moist, separate, covered with a mucus-like substance), the number of vibrios increased 2.7-fold at 24 h. Survival rates of vibrios on the surfaces of a row of five cooked rice grains after 2 h of exposure at room temperature were 86, 29, 12, and 4% for glutinous rice, white rice, and the endosperm and pericarp of brown rice, respectively. (Each boiled brown rice grain surface was partly pericarp and partly endosperm, which became exposed by a rupture of the pericarp.) Covering each inoculated grain with a similar cooked rice grain surface increased the corresponding figures to 93, 99, 60, and 94%. Scanning electron microscopy revealed that each type of cooked grain surface possessed a distinct microtopography. For example, the surfaces of glutinous rice grains consisted of separated overlapping strips with many holes, while the pericarps of brown rice were flat interspersed with small pits. In conclusion, each type of boiled rice produced a distinct survival pattern of V. cholerae O1 caused by both the distinct gross features and the fine surface characteristics of the rice. The significance of this finding is that the type of rice consumed can be a factor in cholera transmission by contaminated rice.
Bleomycin, etoposide and cisplatinum (BEP) chemotherapy for metastatic germ cell tumours: treatment outcomes at UKM medical centre, Malaysia

Azrif M, Leong YK, Aslan NM, Fong KV, Ismail F

Asian Pac J Cancer Prev, 2012;13(6):2467-71.
PMID: 22938405

INTRODUCTION: Although bleomycin/etoposide/cisplatinum (BEP) chemotherapy is established as the standard treatment for germ cell tumours, it requires significant experience in administration and toxicity management to maintain optimal dose intensity. A retrospective review of 30 patients was conducted at UKMMC to study treatment outcomes.
METHODS AND MATERIALS: Patients with GCTs and treated with at least two cycles of BEP chemotherapy between January 2003 and Oct 2009 were eligible for this study. Patients received 4-6 cycles of bleomycin 30,000IU IV D1, D8 and D15 and either etoposide 100mg/m2 IV D1- D5 and cisplatin 20mg/m2 IV D1- D5 (5 day BEP regimen) or etoposide 165 mg/m2 D1- D3 and cisplatin 50mg/m2 D1-3 (3 day BEP regimen) every three weeks per cycle. All patients received prophylactic granulocyte colony-stimulating factor (GCSF) from days 6 to 10 of each cycle. The overall response rates, 2 year progression-free survival and overall survival of the whole cohort were assessed.
RESULTS: Thirty patients fulfilled the inclusion criteria. Non-seminomatous GCTs comprised 93.3% of cases and gonadal and mediastinal primary sites were the most common. Sixty percent were classified as IGCCCG poor risk disease. Median follow-up was 26.6 months. The overall response rate (CR+PR) was 70%. The two year PFS and OS were 70% and 66%. There was a significant difference in terms of the overall response rate (85% vs 40%, p = 0.03) and in PFS (94.7% vs 50%, p = 0.003) between gonadal and extragonadal primary sites.
CONCLUSION: It is possible to achieve outcomes similar to those in international clinical trials with close monitoring and good supportive care of patients undergoing BEP chemotherapy. There is a strong argument for patients with IGCCCG poor prognosis disease to be treated in specialist tertiary centres to optimize treatment outcomes.
Thermoseparating aqueous two-phase systems: Recent trends and mechanisms

Leong YK, Lan JC, Loh HS, Ling TC, Ooi CW, Show PL

J Sep Sci, 2016 Feb;39(4):640-7.
PMID: 26447739 DOI: 10.1002/jssc.201500667

Having the benefits of being environmentally friendly, providing a mild environment for bioseparation, and scalability, aqueous two-phase systems (ATPSs) have increasingly caught the attention of industry and researchers for their application in the isolation and recovery of bioproducts. The limitations of conventional ATPSs give rise to the development of temperature-induced ATPSs that have distinctive thermoseparating properties and easy recyclability. This review starts with a brief introduction to thermoseparating ATPSs, including its history, unique characteristics and advantages, and lastly, key factors that influence partitioning. The underlying mechanism of temperature-induced ATPSs is covered together with a summary of recent applications. Thermoseparating ATPSs have been proven as a solution to the demand for economically favorable and environmentally friendly industrial-scale bioextraction and purification techniques.
Fulltext Statistical Design of Experimental and Bootstrap Neural Network Modelling Approach for Thermoseparating Aqueous Two-Phase Extraction of Polyhydroxyalkanoates

Leong YK, Chang CK, Arumugasamy SK, Lan JC, Loh HS, Muhammad D, et al.

Polymers (Basel), 2018 Jan 30;10(2).
PMID: 30966168 DOI: 10.3390/polym10020132

At present, polyhydroxyalkanoates (PHAs) have been considered as a promising alternative to conventional plastics due to their diverse variability in structure and rapid biodegradation. To ensure cost competitiveness in the market, thermoseparating aqueous two-phase extraction (ATPE) with the advantages of being mild and environmental-friendly was suggested as the primary isolation and purification tool for PHAs. Utilizing two-level full factorial design, this work studied the influence and interaction between four independent variables on the partitioning behavior of PHAs. Based on the experimental results, feed forward neural network (FFNN) was used to develop an empirical model of PHAs based on the ATPE thermoseparating input-output parameter. In this case, bootstrap resampling technique was used to generate more data. At the conditions of 15 wt % phosphate salt, 18 wt % ethylene oxide⁻propylene oxide (EOPO), and pH 10 without the addition of NaCl, the purification and recovery of PHAs achieved a highest yield of 93.9%. Overall, the statistical analysis demonstrated that the phosphate concentration and thermoseparating polymer concentration were the most significant parameters due to their individual influence and synergistic interaction between them on all the response variables. The final results of the FFNN model showed the ability of the model to seamlessly generalize the relationship between the input⁻output of the process.
Current trends in polyhydroxyalkanoates (PHAs) biosynthesis: insights from the recombinant Escherichia coli

Leong YK, Show PL, Ooi CW, Ling TC, Lan JC

J Biotechnol, 2014 Jun 20;180:52-65.
PMID: 24698847 DOI: 10.1016/j.jbiotec.2014.03.020

Pursuing the current trend, the "green-polymers", polyhydroxyalkanoates (PHAs) which are degradable and made from renewable sources have been a potential substitute for synthetic plastics. Due to the increasing concern towards escalating crude oil price, depleting petroleum resource and environmental damages done by plastics, PHAs have gained more and more attractions, both from industry and research. From the view point of Escherichia coli, a microorganism that used in the biopolymer large scale production, this paper describes the backgrounds of PHA and summarizes the current advances in PHA developments. In the short-chain-length (scl) PHAs section, the study of poly[(R)-3-hydroxybutyrate] [P(3HB)] as model polymer, ultra-high-molecular-weight P(3HB) which rarely discussed, and P(3HB-co-3HV), another commercialized PHA polymer are included. Other than that, this review also shed some light on the new members of PHA family, lactate-based PHAs and P(3HP) with topics such as block copolymers and invention of novel biopolymers. Flexibility of microorganisms in utilizing different carbon sources to accumulate medium-chain-length (mcl) PHAs and lastly, the promising scl-mcl-PHAs with interesting properties are also discussed.
Reuniting the Biogeochemistry of Algae for a Low-Carbon Circular Bioeconomy

Leong YK, Chew KW, Chen WH, Chang JS, Show PL

Trends Plant Sci, 2021 07;26(7):729-740.
PMID: 33461869 DOI: 10.1016/j.tplants.2020.12.010

Given their advantages of high photosynthetic efficiency and non-competition with land-based crops, algae, that are carbon-hungry and sunlight-driven microbial factories, are a promising solution to resolve energy crisis, food security, and pollution problems. The ability to recycle nutrient and CO2 fixation from waste sources makes algae a valuable feedstock for biofuels, food and feeds, biochemicals, and biomaterials. Innovative technologies such as the bicarbonate-based integrated carbon capture and algae production system (BICCAPS), integrated algal bioenergy carbon capture and storage (BECCS), as well as ocean macroalgal afforestation (OMA), can be used to realize a low-carbon algal bioeconomy. We review how algae can be applied in the framework of integrated low-carbon circular bioeconomy models, focusing on sustainable biofuels, low-carbon feedstocks, carbon capture, and advances in algal biotechnology.
Cloud-point extraction of green-polymers from Cupriavidus necator lysate using thermoseparating-based aqueous two-phase extraction

Leong YK, Lan JC, Loh HS, Ling TC, Ooi CW, Show PL

J Biosci Bioeng, 2017 Mar;123(3):370-375.
PMID: 27745851 DOI: 10.1016/j.jbiosc.2016.09.007

Polyhydroxyalkanoates (PHAs), a class of renewable and biodegradable green polymers, have gained attraction as a potential substitute for the conventional plastics due to the increasing concern towards environmental pollution as well as the rapidly depleting petroleum reserve. Nevertheless, the high cost of downstream processing of PHA has been a bottleneck for the wide adoption of PHAs. Among the options of PHAs recovery techniques, aqueous two-phase extraction (ATPE) outshines the others by having the advantages of providing a mild environment for bioseparation, being green and non-toxic, the capability to handle a large operating volume and easily scaled-up. Utilizing unique properties of thermo-responsive polymer which has decreasing solubility in its aqueous solution as the temperature rises, cloud point extraction (CPE) is an ATPE technique that allows its phase-forming component to be recycled and reused. A thorough literature review has shown that this is the first time isolation and recovery of PHAs from Cupriavidus necator H16 via CPE was reported. The optimum condition for PHAs extraction (recovery yield of 94.8% and purification factor of 1.42 fold) was achieved under the conditions of 20 wt/wt % ethylene oxide-propylene oxide (EOPO) with molecular weight of 3900 g/mol and 10 mM of sodium chloride addition at thermoseparating temperature of 60°C with crude feedstock limit of 37.5 wt/wt %. Recycling and reutilization of EOPO 3900 can be done at least twice with satisfying yield and PF. CPE has been demonstrated as an effective technique for the extraction of PHAs from microbial crude culture.
Application of thermo-separating aqueous two-phase system in extractive bioconversion of polyhydroxyalkanoates by Cupriavidus necator H16

Leong YK, Show PL, Lan JC, Krishnamoorthy R, Chu DT, Nagarajan D, et al.

Bioresour Technol, 2019 Sep;287:121474.
PMID: 31122870 DOI: 10.1016/j.biortech.2019.121474

Polyhydroxyalkanoates (PHAs), a family of biodegradable and renewable biopolymers show a huge potential as an alternative to conventional plastics. Extractive bioconversion (in situ product recovery) is a technique that integrates upstream fermentation and downstream purification. In this study, extractive bioconversion of PHAs from Cupriavidus necator H16 was performed via a thermo-separating aqueous two-phase system to reduce the cost and environmental impacts of PHAs production. Key operating parameters, such as polymer concentration, temperature, and pH, were optimized. The strategy achieved a yield and PF of 97.6% and 1.36-fold, respectively at 5% EOPO 3900 concentration, 30 °C fermentation temperature and pH 6. The PHAs production process was also successfully scaled up in a 2 L bioreactor. To the best of our knowledge, this is the first report on extractive fermentation of PHAs from Cupriavidus necator utilizing a thermo-separation system to achieve a better productivity and purity of the target product.

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