Detection of tetracycline-resistance determinants by multiplex polymerase chain reaction in Edwardsiella tarda isolated from fish farms in Korea

To determine and discriminate the types of tetracycline (Tc)-resistance determinants (tet), we developed a multiplex polymerase chain reaction (PCR). With minimized numbers of primers derived from the variable and conserved regions of six different types of tet genes, tet(A)–(E) and (G), the multiplex PCR was sensitive and specific enough to discriminate the various types of tet genes, even multiple tet genes in an individual resistant isolate, by the different sizes of the resulting PCR products. Each of 20 Tc-resistant Edwardsiella tarda (Ed. tarda) isolates from diseased fish from aquatic farms in Korea carrying either one or two tet genes of types (A), (D), (B), or (G) gave PCR products of the appropriate lengths. Among the four types of tet genes found in Ed. tarda, two types, tet(A) and (D), were always present on mobile plasmids, and the other two types, tet(B) and (G), were located on the nonmobile nucleic acids. This is the first time that either of these two genes, type (B) or (G), have been found in Ed. tarda isolates. The two most common types of Tc-resistance determinant were, tet(A) and (D), occurring in 55% and 45% of total Tc-resistant Ed. tarda isolates, respectively.     

Field investigations and multi‐indicators for shallow water lagoon management: perspective for societal benefit

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Current status of freshwater prawn culture in Vietnam and the development and transfer of seed production technology

ABSTRACT:   In Vietnam, the giant freshwater prawn Macrobrachium rosenbergii is becoming an increasingly important targeted species, as its culture, especially in rice fields, is considered to have the potential to raise income among impoverished farmers. The production of M. rosenbergii based on aquaculture reached over 10 000 tons per year in 2002, having increased from about 2500 tons since the 1990s. Until recently, lack of a stable supply of seed had been an important obstacle to the further expansion and development of M. rosenbergii culture, but cumulative research on larval rearing, especially in the 1990s, has led to the development of new seed production technology based on the 'modified stagnant green water system'. Following its dissemination by the efforts of provincial authorities, hatchery operators, and farmers, the freshwater prawn seed production industry developed rapidly in the Mekong Delta with over 90 hatcheries producing 76.5 million postlarvae in 2003. This is considered to have affected the expansion of rice–prawn farming in the Mekong Delta, leading to increased aquacultural production in the region. This paper reviews the current status of freshwater prawn culture in Vietnam and background history, and presents a socioeconomic evaluation of seed production technology implementation.     

Preparation of high molecular weight poly(methyl methacrylate) with high yield by room temperature suspension polymerization of methyl methacrylate

To obtain high molecular weight (HMW) poly(methyl methacrylate) (PMMA) with high conversion, methyl methacrylate (MMA) was polymerized in suspension using a room temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior of MMA and the molecular parameters of PMMA were investigated. On the whole, the experimental results well corresponded to the theoretically predicted tendencies. These effects could be explained by a kinetic order of ADMVN concentration calculated by an initial rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 25 °C by adopting ADMVN proved to be successful in obtaining PMMA of HMW (number-average degree of polymerization (P_n): 30,900–36,100) and of high yield (ultimate conversion of MMA into PMMA: 83–93 %) with diminishing heat generated during polymerization. The P_n and lightness were higher and polydispersity index was lower with PMMA polymerized at lower temperatures.     

棉花生产使用包衣种子好

优良品种和优质种子是棉花生产的基础 ,种子质量的好坏直接影响棉花生产的丰歉 ,为了保证增产增收 ,建议棉花生产上使用包衣种子 ,其好处在于 :1、使用包衣种子有利于棉花机械化播种 ,加快播种进度 ,提高播种质量。2、使用包衣种子可节省用种。经过脱绒包衣的种子可实行精量半精量播种 ,同棉花毛籽相比 ,单位面积用种量可节省一半左右。3、使用包衣种子可防治棉花苗期病虫害 ,提高棉苗素质。由于种子包衣所使用的包衣剂是由杀虫剂、杀菌剂、微肥、植物生长调节剂、缓释剂等经科学配制而成 ,所以包衣后的棉花种子可有效地防治立枯病、炭疽病…     

Preparation and properties of crosslinkable waterborne polyurethanes containing aminoplast

In order to improve the water swelling, thermal/mechanical and adhesion properties of waterborne polyurethane (WBPU), a series of the crosslinkable WBPUs containing hydrophilic ionic component, dimethylol propionic acid (20 mole%), were prepared by in-situ polymerization using a cross-linker hexakis (methoxymethyl) melamine (HMMM). Effects of the HMMM content (2, 4, and 6 wt%) and curing temperature on these properties of the crosslinked WBPUs samples were investigated. All properties were found to increase with increasing HMMM content. It was found that the optimum curing temperature of the WBPU films and adhesives was near 120°C, which was not dependent on the HMMM content.     

Evaluation of a canine small intestinal submucosal xenograft and polypropylene mesh as bioscaffolds in an abdominal full-thickness resection model of growing rats

We evaluated the biological scaffold properties of canine small intestinal submucosa (SIS) compared to a those of polypropylene mesh in growing rats with full-thickness abdominal defects. SIS is used to repair musculoskeletal tissue while promoting cell migration and supporting tissue regeneration. Polypropylene mesh is a non-resorbable synthetic material that can endure mechanical tension. Canine SIS was obtained from donor German shepherds, and its porous collagen fiber structure was identified using scanning electron microscopy (SEM). A 2.50-cm² section of canine SIS (SIS group) or mesh (mesh group) was implanted in Sprague-Dawley rats. At 1, 2, 4, 12, and 24 weeks after surgery, the implants were histopathologically examined and tensile load was tested. One month after surgery, CD68+ macrophage numbers in the SIS group were increased, but the number of CD8+ T cells in this group declined more rapidly than that in rats treated with the mesh. In the SIS group, few adhesions and well-developed autologous abdominal muscle infiltration into the SIS collagen fibers were observed. No significant differences in the tensile load test results were found between the SIS and mesh groups at 24 weeks. Canine SIS may therefore be a suitable replacement for artificial biological scaffolds in small animals.     

Modelling rice competition with <Emphasis Type="Italic">Echinochloa crus-galli</Emphasis> and <Emphasis Type="Italic">Eleocharis kuroguwai</Emphasis> in transplanted rice cultivation

Field experiments were conducted to investigate rice — Echinochloa crus-galli and rice — Eleocharis kuroguwai competition under transplanted rice cultivation in four major rice production areas; Suwon, Daejeon, Iksan, and Naju in Korea. Rice yield data were used to predict rice yield as a function of plant densities of E. crus-galli and E. kuroguwai using a rectangular hyperbola and to determine economic threshold (ET) levels of the weeds. Both weed species significantly reduced number of tillers at early rice growth stage, resulting in significant reduction in number of spikes, and the other yield components such as number of grains, maturity and 1,000-grain weight at later growth stage. The weed competitivity represented by parameter ranged from 0.0145 to 0.0346 for E. crus-galli and from 0.0037 to 0.0187 for E. kuroguwai, indicating that the competition effect of E. crus-galli on rice yield was slightly greater than that of E. kuroguwai. The ET values of E. crus-galli were between 0.298 and 1.078 plants m⁻², while those of E. kuroguwai were between 0.848 and 5.298 plants m⁻², depending on weed competitivity and herbicide price. Therefore, our results can be used to support decision-making on herbicide application for E. crus-galli and E. kuroguwai management in transplanted rice cultivation.