Browsing by Author "Yoshimasa Yamamoto"

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    Analysis of risk factors for a high prevalence of extended-spectrum β-lactamase-producing Enterobacteriaceae in asymptomatic individuals in rural Thailand
    (2011-05-01) Ulzii Orshikh Luvsansharav; Itaru Hirai; Marie Niki; Tadahiro Sasaki; Kiyoko Makimoto; Chalit Komalamisra; Wanna Maipanich; Teera Kusolsuk; Surapol Sa-Nguankiat; Somchit Pubampen; Yoshimasa Yamamoto; Osaka University Faculty of Medicine; Kobe University School of Medicine; Mahidol University
    The prevalence of and risk factors associated with extended-spectrum β-lactamase (ESBL)-producing micro-organisms have not been well studied in healthy individuals. The aim of this study was to determine this in healthy individuals in Thailand. Stool samples and questionnaires obtained from 445 participants from three provinces in Thailand were analysed. The antimicrobial susceptibility of the isolates was assessed using phenotypic and genotypic methods. PCR analysis was performed to detect and group the bla CTX-M genes. The prevalence of CTX-M-type ESBL-producing Enterobacteriaceae in the three provinces was as follows: 29.3% in Nan (43/147), 29.9% in Nakhon Si Thammarat (43/144) and 50.6% in Kanchanaburi (78/154) (P < 0.001). Of the 445 samples, 33 (7.4%), 1 (0.2%) and 127 (28.5%) isolates belonged to the bla CTX-M gene groups I, III and IV, respectively. Escherichia coli was the predominant member of the Enterobacteriaceae producing CTX-M-type ESBLs (40/43, 39/43 and 70/78 isolates in Nan, Nakhon Si Thammarat and Kanchanaburi, respectively). No statistically significant association was observed between the presence of ESBL-producing bacteria and gender, age, education, food habits or antibiotic usage. However, the provinces that had the highest prevalence of ESBLproducing Enterobacteriaceae also had the highest prevalence of use and purchase of antibiotics without a prescription. Thus, this study revealed that faecal carriage of ESBL-producing Enterobacteriaceae is very high in asymptomatic individuals in Thailand, with some variations among the provinces. This high prevalence may be linked to antibiotic abuse. © 2011 SGM.
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    High prevalence of CTX-M β-lactamase-producing enterobacteriaceae in stool specimens obtained from healthy individuals in Thailand
    (2010-01-27) Tadahiro Sasaki; Itaru Hirai; Marie Niki; Tatsuya Nakamura; Chalit Komalamisra; Wanna Maipanich; Teera Kusolsuk; Surapol Sa-nguankiat; Somchit Pubampen; Yoshimasa Yamamoto; Osaka University Faculty of Medicine; Kobe University School of Medicine; Kansai Medical University; Mahidol University
    Objectives: To determine the prevalence of CTX-M β-lactamase-producing Enterobacteriaceae in stool specimens obtained from healthy individuals in a rural area of Thailand. Methods: Bacteria in stool specimens were screened for extended-spectrum β-lactamase (ESBL) production on McConkey agar with cefotaxime and confirmed by the double-disc synergy test. Genetic detection and genotyping of CTX-M-type ESBL was performed by PCR with bacterial DNA extracted from isolates. Results: A markedly high number (82 of 141, 58.2%) of the specimens showed the presence of CTX-M β-lactamase-producing Enterobacteriaceae, as confirmed by both phenotypic and genetic examinations. The majority of the CTX-M β-lactamase-producing bacteria were Escherichia coli (85.1%). Conclusions: The study revealed the wide dissemination of CTX-M β-lactamase-producing Enterobacteriaceae in the healthy population. © The Author 2010. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy.
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    Nano-matrix structure formed by graft-copolymerization of styrene onto natural rubber
    (2007-08-01) Nanthaporn Pukkate; Toshiaki Kitai; Yoshimasa Yamamoto; Tetsuji Kawazura; Jitladda Sakdapipanich; Seiichi Kawahara; Nagaoka University of Technology; Mahidol University
    Nano-matrix structure was formed by graft-copolymerization of styrene onto urea-deproteinized natural rubber (U-DPNR) latex. The grafted U-DPNR was characterized by FT-IR spectroscopy,1H NMR spectroscopy and transmission electron microscopy. Conversion and grafting efficiency of styrene were more than 90% under the best condition of the graft-copolymerization. In transmission electron micrograph of film specimen stained by OsO4, it was found that natural rubber particle of about 0.5 μm in diameter was dispersed in polystyrene matrix of about 15 nm in thickness. The conversion and grafting efficiency for the grafted U-DPNR were compared with those for a control sample prepared from enzymatic deproteinized natural rubber (E-DPNR) with styrene. © 2007 Elsevier Ltd. All rights reserved.
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    Preparation and characterization of natural rubber with soft nanomatrix structure
    (2012-01-01) Kenichiro Kosugi; Ratchaniwan Sutthangkul; Oraphin Chaikumpollert; Yoshimasa Yamamoto; Jitladda Sakdapipanich; Yoshinobu Isono; Seiichi Kawahara; Nagaoka University of Technology; Mahidol University; Thailand National Metal and Materials Technology Center; Tokyo National College of Technology
    Abstract Preparation of natural rubber (NR) with a soft nanomatrix structure was made by graft-copolymerization of butyl acrylate (BA) onto deproteinized natural rubber with tert-butyl hydroperoxide/tetraetylenepentamine in latex stage. The resulting graft-copolymer of deproteinized natural rubber and poly (butyl acrylate) (DPNR-graft-PBA) was characterized by Fourier-transforminfrared spectroscopy. Conversion and grafting efficiency of BA were dependent upon BA concentration, which were more than 90 mol% under a suitable condition of the graft-copolymerization. Morphology of DPNR-graft-PBA was observed by transmission electron microscopy after staining film specimens with I2 vapor for 5min. TheNR particles of about 0.5 μm in diameter were dispersed in PBA matrix of about 15 nm in thickness. Storage modulus and loss tangent of DPNR-graft-PBA were measured, and they were related with the soft nanomatrix structure. The tensile strength and elongation at break decreased as monomer concentration increased. © Springer-Verlag 2012.
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    Preparation and characterization of protein-free natural rubber
    (2012-04-01) Oraphin Chaikumpollert; Yoshimasa Yamamoto; Krisda Suchiva; Phan Trung Nghia; Seiichi Kawahara; Nagaoka University of Technology; Mahidol University; Thailand National Metal and Materials Technology Center; Hanoi University of Science and Technology
    Protein-free natural rubber was prepared by incubation of natural rubber latex with urea and polar organic solvent in the presence of surfactant. Effect of the polar organic solvent on the removal of the proteins was investigated with respect to chemical affinity and concentration of the solvents. Under a suitable condition, nitrogen content of the deproteinized natural rubber (DPNR) was 0.000wt%, which was less than that of natural rubber deproteinized with proteolytic enzyme or urea in the presence of surfactant. The removal of all proteins from natural rubber was proved through FT-IR spectroscopy. Changes in morphology of the DPNR were also investigated by transmission electron microscopy. © 2011 John Wiley & Sons, Ltd.
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    Prevalence of and risk factors associated with faecal carriage of CTX-M β-lactamase-producing enterobacteriaceae in rural Thai communities
    (2012-07-01) Ulzii Orshikh Luvsansharav; Itaru Hirai; Arisa Nakata; Kaori Imura; Kou Yamauchi; Marie Niki; Chalit Komalamisra; Teera Kusolsuk; Yoshimasa Yamamoto; Osaka University Faculty of Medicine; Mahidol University; Osaka Prefectural Institute of Public Health
    Objectives: To determine the prevalence of CTX-M β-lactamase-producing Enterobacteriaceae and to study the risk factors associated with faecal carriage in asymptomatic rural Thai people. Methods: In all, 417 stool samples were obtained from rural Thai people and screened for extended-spectrum β-lactamases (ESBLs) using MacConkey agar supplemented with 2 mg/L cefotaxime. Results were confirmed using cefotaxime and ceftazidime with and without clavulanic acid. The bla CTX-M genes were identified and genotyped using PCR with bacterial DNA samples. Multivariate analysis was performed to investigate risk factors associated with the faecal carriage of CTX-M producers. Results: The prevalence of CTX-M-type ESBL-producing Enterobacteriaceae was 65.7%. The CTX-M-9 group (60.6%) was dominant, followed by the CTX-M-1 group (38.7%). Most of the bacteria were Escherichia coli (85.4%) and Klebsiella pneumoniae (4.7%). Of a total of 234 E. coli strains, 48.7% belonged to phylogenetic group A, 28.6% to group B1, 15.8% to group D and 6.8% to group B2. Most CTX-M producers were susceptible to carbapenems and amikacin, but resistant to tetracycline and gentamicin. In a multivariate logistic regression model, better education status (OR 2.245; 95% CI 1.297-3.884), history of hospitalization (OR 1.643; 95% CI 1.036-2.603) and the use of antibiotics within the last 3 months (OR 1.883; 95% CI 1.221-2.903) were independently associated with faecal carriage. Conclusions: Faecal carriage of CTX-M-type ESBL-producing Enterobacteriaceae among asymptomatic individuals in rural Thailand remains alarmingly high, and previous antibiotic use and a history of hospitalization may contribute to its dissemination. © The Author 2012. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
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    Wide dissemination of extended-spectrum ß-lactamase-producing Escherichia coli in community residents in the indochinese peninsula
    (2015-01-23) Tatsuya Nakayama; Shuhei Ueda; Bui Thi Mai Huong; Le Danh Tuyen; Chalit Komalamisra; Teera Kusolsuk; Itaru Hirai; Yoshimasa Yamamoto; Osaka University; University of the Ryukyus; National Nutrition Institute; Mahidol University; Osaka Public Health Institute
    © 2015 Nakayama et al. Recent studies have reported a widespread distribution of extended-spectrum P-lactamase (ESBL)-producing bacteria, not only in the nosocomial setting, but also in the community; some local communities in Southeast Asia have been reported to show a high prevalence of ESBL-producing bacteria. However, the details regarding the quantitative/qualitative state of ESBL-producing bacterial spread in Southeast Asia are currently unclear. Thus, the aim of this study was to assess the state of ESBL-producing bacterial spread in community residents from the Indochinese peninsula, as a representative region of Southeast Asia. In order to achieve this aim, local community residents in Laos and Vietnam were examined for fecal carriage of ESBL-producing Enterobacteriaceae, and the findings were compared with data from a previous study in Thailand which was conducted in the same manner as this study. Between 47.0%-70.2% of the Laotian and Vietnamese residents carried ESBL-producing CTX-M genotype Enterobacteriaceae. The most common sub-genotypes of CTX-M were CTX-M-1 (33.0%—17.5%) and CTX-M-9 (47.5%-64.1%), and these rates were similar among all three countries. Taken together, these results confirmed that ESBL-producing Enterobacteriaceae are widely disseminated in Indochinese countries, such as Thailand, Laos, and Vietnam.