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Dive into the research topics where Masatomo Hirasawa is active.

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Featured researches published by Masatomo Hirasawa.


Caries Research | 1991

Anticaries effects of polyphenolic compounds from Japanese green tea.

Shigeo Otake; M. Makimura; T. Kuroki; Y. Nishihara; Masatomo Hirasawa

The dental caries inhibiting effect of the extract from Japanese green tea, one of the most popular drinks in Japan, was studied both in vitro and in vivo. The crude tea polyphenolic compounds (designated Sunphenon) from the leaf of Camellia sinensis were found to effectively inhibit the attachment of Streptococcus mutans strain JC-2 (serotype c) to saliva-coated hydroxyapatide discs. Sunphenon was also inhibitory to water-insoluble glucan formation from sucrose by crude glucosyltransferase of S. mutans JC-2 (c). Among the tea catechins tested, (-)-epigallocatechin gallate and (-)-epicatechin gallate showed the most potent inhibition of the glucosyltransferase activity. Finally, significantly lower caries scores were observed in specific pathogen free rats infected with S. mutans JC-2 (c) and fed a cariogenic diet and/or drinking water containing 0.05% Sunphenon as compared with control rats not receiving polyphenolic compounds.


International Journal of Antimicrobial Agents | 1999

Three kinds of antibacterial substances from Lentinus edodes (Berk.) Sing. (Shiitake, an edible mushroom)

Masatomo Hirasawa; Naoto Shouji; Tomotake Neta; Kazuo Fukushima; Kazuko Takada

Three kinds of antibacterial substances were extracted by chloroform, ethylacetate or water from dried Shiitake mushrooms (Lentinus edodes). These substances possess efficient antibacterial activities against Streptococcus spp., Actinomyces spp., Lactobacillus spp., Prevotella spp., and Porphyromonas spp. of oral origin. In contrast, other general bacteria, such as Enterococcus spp., Staphylococcus spp., Escherichia spp., Bacillus spp., and Candida spp. were relatively resistant to these substances. Chloroform extracts had bactericidal activity against both growing and resting bacterial cells of S. mutans and P. intermedia, whereas the other two extracts showed bacteriostatic activity against both growing and resting bacterial cells of S. mutans and resting bacterial cell of P. intermedia. The antibacterial activity of chloroform extracts and ethylacetate extracts were relatively heat-stable. The water extract was heat-labile.


International Journal of Systematic and Evolutionary Microbiology | 1994

Porphyromonas gingivicanis sp. nov. and Porphyromonas crevioricanis sp. nov., Isolated from Beagles

Masatomo Hirasawa; Kazuko Takada

Two new species, Porphyromonas gingivicanis and Porphyromonas crevioricanis, are proposed for black-pigmented, asaccharolytic, anaerobic, nonmotile, non-spore-forming, gram-negative, rod-shaped organisms. These organisms were isolated from the gingival crevicular fluids of beagles. P. gingivicanis and P. crevioricanis do not grow in the presence of 20% bile. They exhibit less than 5% DNA-DNA homology with the type strains of Porphyromonas gingivalis (strain ATCC 33277), Porphyromonas endodontalis (strain ATCC 35406), and Porphyromonas asaccharolytica (strain ATCC 25260), which were isolated from humans, or with the type strains of Porphyromonas salivosa (strain NCTC 11632) and Porphyromonas circumdentaria (strain NCTC 12469), which were isolated from cats. The major cellular fatty acid of P. gingivicanis and P. crevioricanis is 13-methyltetradecanoic acid (iso-C15:0 acid). Glutamate and malate dehydrogenases are present in both species, and 6-phosphogluconate and glucose-6-phosphate dehydrogenases are absent; neither organism exhibits trypsin activity. P. gingivicanis and P. crevioricanis produce large amounts of acetic and isovaleric acids and minor amounts of isobutyric and succinic acids as end products of metabolism in GAM medium. P. gingivicanis also produces large amounts of butyric acid and small amounts of propionic acid, while P. crevioricanis produces large amounts of propionic acid and minor amounts of butyric and phenylacetic acids. The G+C contents of the DNA of P. gingivicanis is 41 to 42 mol%; the G+C content of the DNA of P. crevioricanis is 44 to 45 mol%. Catalase is produced by P. gingivicanis but not by P. crevioricanis; strains of P. crevioricanis agglutinate sheep erythrocytes, but strains of P. gingivicanis do not.(ABSTRACT TRUNCATED AT 250 WORDS)


Caries Research | 2006

Inhibition of Acid Production in Dental Plaque Bacteria by Green Tea Catechins

Masatomo Hirasawa; Kazuko Takada; Shigeo Otake

The inhibition of acid production from dental plaque and mutans streptococci by epigallocatechin gallate (EGCg), one of the green tea catechins, was examined. The effect of EGCg solution on dental plaque pH was investigated.Subjects rinsed their mouths with 2 mg/ml EGCg solution and then, after 30-min interval, rinsed their mouths with 10% sucrose. Plaque samples were collected at appropriate times and the pH was measured. The pH values of plaque samples from 15 volunteers were significantly higher after treatment with catechin than after treatment with water. EGCg inhibited pH fall when cariogenic bacteria grown in medium with or without sucrose were incubated with sugar. In medium without sucrose, cultured cells were killed time-dependently by EGCg treatment. However, EGCg did not kill cells cultured in medium containing sucrose. Also, EGCg did not kill oral streptococci adhering to a saliva-coated hydroxyapatite disk. EGCg and epicatechin gallate inhibited lactate dehydrogenase activity much more efficiently than epigallocatechin, epicatechin, catechin or gallocatechin. These results suggest that EGCg is effective in reducing acid production in dental plaque and mutans streptococci.


Caries Research | 1992

Noncariogenicity of Erythritol as a Substrate

J. Kawanabe; Masatomo Hirasawa; Takeo Takeuchi; T. Oda; Tadashi Ikeda

Erythritol is a sugar alcohol produced by Aureobasidium sp. from glucose. It is 75-80% as sweet as sucrose and is also nonhygroscopic. The aim of this study was to evaluate this sugar substitute from a cariological point of view. Erythritol was neither utilized as a substrate for the lactic acid production nor for plaque formation of mutans streptococci (serotypes a-h) and certain oral microorganisms. It was not utilized for water-insoluble glucan synthesis or cellular adherence by glucosyltransferase from Streptococcus mutans PS-14 (c) and Streptococcus sobrinus 6715 (g). Finally, a significantly lower caries score (3.1 +/- 0.5; mean +/- SEM) was observed in specific pathogen-free rats infected with S. sobrinus 6715 and fed with a diet containing 26% erythritol, as compared to control rats fed with a diet containing 26% sucrose (60.5 +/- 2.0). Also, rats provided a diet containing 56% erythritol chocolate (23.8% erythritol) and challenged with S. mutans PS-14 exhibited a significantly lower caries score (6.7 +/- 0.8) compared to the sucrose chocolate group (82.8 +/- 2.8). The main conclusion from this study is therefore that erythritol is a promising sugar substitute from a cariological point of view.


Caries Research | 2002

Susceptibility of Streptococcus mutans and Streptococcus sobrinus to Cell Wall Inhibitors and Development of a Novel Selective Medium for S. sobrinus

Masatomo Hirasawa; Kazuko Takada

Representative strains of Streptococcus mutans and Streptococcus sobrinus showed differences in susceptibility to members of the monobactam group of β-lactam antibiotics: S. sobrinus was less sensitive than S. mutans. The minimum inhibitory concentrations of aztreonam (AZT) and carumonam, both of which belong to this group, were 2,000 µg/ml for S. sobrinus and 125 µg/ml for S. mutans. Further addition of fosfomycin, bacitracin and sodium chloride to Mitis Salivarius agar (MS) supplemented with AZT resulted in growth inhibition of S. mutans and oral streptococci other than S. sobrinus, and was therefore used as a selective medium for S. sobrinus (MS-SOB medium). The average growth recovery of laboratory and clinically isolated strains of S. sobrinus on MS-SOB medium was 74.1% compared to that on MS medium. Seventy-eight percent of clinical samples in which S. sobrinus was detected yielded pure growth of S. sobrinus on MS-SOB medium.


Caries Research | 2000

Anticaries effect of a component from shiitake (an edible mushroom).

N. Shouji; Kazuko Takada; Kazuo Fukushima; Masatomo Hirasawa

The caries–inhibiting effect of the extract from shiitake (Lentinus edodes), the most popular edible mushroom in Japan, was studied both in vitro and in vivo. Shiitake extract showed an inhibitory effect on water–insoluble glucan formation from sucrose by crude glucosyltransferases of Streptococcus mutans JC–2 and Streptococcus sobrinus OMZ–176. The firmly adherent plaque in the artificial plaque formation test was strongly inhibited by shiitake extract. The reduction of firmly adherent plaque caused an increase in the incidence of non– and loosely adherent plaque and a decrease in total plaque formation. A significantly lower caries score was observed in specific pathogen–free rats infected with S. mutans JC–2 and fed with a cariogenic diet containing 0.25% shiitake extract as compared with controls fed the cariogenic diet without shiitake extract.


Journal of Dentistry | 2000

Low-cariogenicity of trehalose as a substrate.

Tomotake Neta; Kazuko Takada; Masatomo Hirasawa

OBJECTIVES The effects of trehalose on cariogenesis by mutans streptococci were investigated. METHODS Inhibited effect of trehalose on water-insoluble glucan (WIG) synthesis from sucrose by glucosyltransferase (GTase) of mutans streptococci was assayed. The acid fermentability of trehalose by mutans streptococci was determined by the measurements of pH, and amounts of lactic acid production. Plaque pH was determined by the measurements of collected plaque from volunteers after sugar mouth-rinse. Rat experimental caries was investigated by feeding a sucrose and/or trehalose diet. RESULTS Trehalose was not utilized as a substrate for GTase. In addition, trehalose inhibited synthesis of WIG by GTase in the presence of sucrose. Trehalose showed weaker and slower acid fermentation than sucrose by mutans streptococci. The levels of lactic acid production from trehalose by Streptococcus mutans and Streptococcus sobrinus were 24.2 and 59.8% of those from sucrose, respectively. The minimum plaque pH after sucrose mouth-rinse was lower than those after trehalose mouth-rinse in all subjects. Plaque pH after trehalose mouth-rinse never reached critical pH. The substitution of trehalose for sucrose in the rat diet significantly reduced caries scores. Furthermore, rats fed diets containing sucrose and trehalose had significantly lower caries scores than those fed a sucrose diet. CONCLUSIONS These results suggested that trehalose might be not only lowly cariogenic but also anti-cariogenic, and is promising as a sugar substitute.


Molecular Oral Microbiology | 2010

Characterization of a new serotype g isolate of Aggregatibacter actinomycetemcomitans

Kazuko Takada; Masanori Saito; Osamu Tsuzukibashi; Y. Kawashima; S. Ishida; Masatomo Hirasawa

Aggregatibacter actinomycetemcomitans is usually isolated from the oral cavity where it is associated with active periodontitis. The species can be divided into six serotypes (a-f) according to their surface carbohydrate antigens. However, some clinical isolates cannot be grouped within these six serotypes. Gram-negative, facultative anaerobic, catalase-positive coccobacilli were isolated from a patient with periodontitis and identified by employing genetic, biochemical and serological analyses. Phenotypic data identified the isolate as A. actinomycetemcomitans. Serotype-specific polysaccharide antigen from the isolate was untypeable by immunodiffusion testing in comparison with reference A. actinomycetemcomitans serotype a to f strains. Biofilm formation by the isolate was strong but cytotoxic activity was low. Gas chromatography/mass spectroscopy analysis of partially methylated alditol acetates from surface polysaccharide showed the presence of 2,4-di-O-methyl-rhamnose and 2,3,6-tri-O-methyl-glucose, with a 1 : 1 m ratio. The (1)H- and (13)C-nuclear magnetic resonance spectra of the antigen showed that both constituent glycoses had alpha-anomeric configuration. It is proposed that the untyped strain is a new A. actinomycetemcomitans serotype, designated serotype g.


Caries Research | 2003

A New Selective Medium for Streptococcus mutans and the Distribution of S. mutans and S. sobrinus and Their Serotypes in Dental Plaque

Masatomo Hirasawa; Kazuko Takada

A new selective medium (MS-MUT) was developed for the isolation of Streptococcus mutans from clinical specimens. The average growth recovery of S. mutans on MS-MUT medium was 72.4% of that on MS medium. Growth of Streptococcus sobrinus was significantly inhibited on the medium with an average recovery of 0.034%. In 103 subjects, S. mutans was detected at 58.3, 75.0 and 95.7% in the dental plaque of caries-free (CF), caries-inactive (CI) and caries-active (CA) subjects, respectively. S. sobrinus was detected in 8.3, 13.6 and 38.3% of CF, CI and CA subjects, respectively. S. sobrinus alone was detected in only 4.3% of CA subjects. The subjects in whom neither S. mutans nor S. sobrinus were detected were 41.6% in CF and 25.0% in CI. The most predominant serotype was c with a 67% detection rate. S. sobrinus, serotypes d or g were usually found together with S. mutans.

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Jerry R. McGhee

University of Alabama at Birmingham

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Tetsuo Shiota

University of Alabama at Birmingham

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