University of the Ryukyus · Faculty of Medicine · 教授

Research keywords熱帯医学・下痢症疫学・Tropical Medicine・細菌学・Tropical microbiology・コレラ菌・レプトスピラ・バイオフィルム・分子疫学

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• Significant removal of bacterial biofilm induced by multiple-Short ranges of electric interventions*2024 · Taira, H; Yaga, M; Nakasone, S; Nishida, K; Yamashiro, T
• Significant removal of bacterial biofilm induced by multiple short ranges of electric interventions2023 · Hiroyuki Taira, Minoru Yaga, Satoshi Nakasone, Kotaro Nishida, Tetsu Yamashiro
• Fermentation products of the fungus Monascus spp. impairs the physiological activities of toxin-producing Vibrio cholerae2022 · Monascus spp. are filamentous fungi used in fermented foods. They are also natural colorants and food preservatives. Certain metabolites of Monascus spp. lower cholesterol and have other health-promoting effects in humans. In the present study, we demonstrated that the fermentation products of Monascus spp. inhibited ATP synthesis and motility in toxigenic Vibrio cholerae. Single-cell tracking and rotation assays on single flagella showed that Monascus fermentation extract (MFE) significantly impaired V. cholerae swimming by disrupting flagellar rotation. A membrane potential-sensitive carbocyanine dye revealed that MFE depolarized the V. cholerae cell membrane which, in turn, lowered the membrane potential and, by extension, restricted ATP synthesis and flagellar rotation. MFE also severely hindered the motility of other pathogenic bacteria such as V. parahaemolyticus, Pseudomonas aeruginosa, Salmonella enterica Typhimurium, and Leptospira interrogans. The foregoing findings indicate that Monascus fermentation extract could potentially preventing infection caused by multiple pathogenic bacteria as the conventional prophylaxes and slow their progression and lower mortality and morbidity.
• Analysis of human clinical and environmental Leptospira to elucidate the eco-epidemiology of leptospirosis in Yaeyama, subtropical Japan2022 · Background Leptospirosis, a zoonosis caused by species in the spirochete genus Leptospira, is endemic to the Yaeyama region in Okinawa, subtropical Japan. Species of the P1 subclade “virulent” group, within the genus Leptospira, are the main etiological agents of leptospirosis in Okinawa. However, their environmental persistence is poorly understood. This study used a combination of bacterial isolation and environmental DNA (eDNA) metabarcoding methods to understand the eco-epidemiology of leptospirosis in this endemic region. Findings Polymerase chain reaction (PCR) characterized twelve human clinical L. interrogans isolates belonging to the P1 subclade “virulent” subgroup and 11 environmental soil isolates of the P1subclade “low virulent” subgroup (genetically related to L. kmetyi, n = 1; L. alstonii, n = 4; L. barantonii, n = 6) from the Yaeyama region targeting four virulence-related genes (lipL32, ligA, ligB and lpxD1). Clinical isolates were PCR positive for at least three targeted genes, while all environmental isolates were positive only for lipL32. Analysis of infected renal epithelial cells with selected clinical and environmental strains, revealed the disassembly of cell-cell junctions for the Hebdomadis clinical strain serogroup. Comparison of leptospiral eDNA during winter and summer identified operational taxonomic units corresponding to the species isolated from soil samples (L. kmetyi and L. barantonii) and additional P2 subclade species (L. licerasiae, L. wolffii-related, among others) that were not detected by soil cultivation. Total Leptospira read counts were higher in summer than in winter and the analysis of leptospiral/animal eDNA relationship suggested Rattus spp. as a potential reservoir animal. Conclusion Our study demonstrated high environmental Leptospira diversity in the Yaeyama region, particularly during summer, when most of the leptospirosis cases are reported. In addition, several Leptospira species with pathogenic potential were identified that have not yet been reported in Yaeyama; however, the environmental persistence of P1 subclade species previously isolated from human clinical cases in this region was absent, suggesting the need of further methodology development and surveillance.

• 紅麹菌発酵物の動物細胞に対するコレラ毒素活性の減殺機序と原因物質解明に関する研究2022 · 基盤研究(C)
• ベトナムにおける下痢症の研究2016 · ベトナム北部ナムディン省地区における下痢性便検体2120検体を解析し、非下痢性便検体471検体と、下痢原性微生物の検出等を比較した。下痢原性微生物 の検出率は、下痢性便検体が13.1%、非下痢性便検体が8.4%と有意な差が見られた。下痢症の発生は、簡易水道利用者及び溜め込み式トイレ利用者に多い傾向が見られた。今回の解析では、サルモネラ、エロモナス、カンピロバクター、赤痢菌、コレラ菌は検出が少なく、赤痢アメーバ、ジアルジア及びクリプトスポルジウムが、幅広い年齢層で多く検出された。家畜便検体解析の結果、ジアルジア及クリプトスポリジウムはヒト・家畜間を伝播している可能性があると思われた。
• ベトナムにおける下痢症の研究2016 · 基盤研究(A)
• 北部ベトナムにおけるコミュニティを基盤とした網羅的下痢症の疫学的研究2013 · 研究期間中に北部ベトナムナムディン省ヒエンカインコミューン在住の300家屋、約1,600人を対象に、細菌、ウイルス、原虫を含む広範な下痢症の起炎微生物の分布状況の把および下痢症危険因子の解明を試みた。対象住民は1年間に約19%が下痢症を経験する事が示唆された。また、対象家屋において、非下痢性サンプルおよび下痢性サンプルをそれぞれ集積し解析した。その結果、ロタウイルス、アデノウイルス、全てのカテゴリーの下痢原性大腸菌、クロストリジウム、赤痢アメーバが下痢の起炎微生物として重要であることが示唆された。またウシ、ブタ、家禽等家畜の保有とジアルジア等下痢原性原虫感染症との関連が強く示唆された。

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