轉糖鏈球菌雙分子訊息調控系統參與感染性心內膜炎的致病機轉

Abstract

轉糖鏈球菌（Streptococcus mutans）主要存在於人體口腔中，是造成齲齒的主要病原菌。轉糖鏈球菌可藉由傷口，或口腔外科手術的過程進入到血流中，造成暫時性的菌血症，存在於血流中的細菌黏附到受損的心臟瓣膜上，形成贅疣（vegetation）引發感染性心內膜炎（infective endocarditis）。細菌中最常見一種訊息傳遞系統是雙分子訊息調控系統（two component regulatory systems; TCS），由histidine kinase（HK）和response regulator（RR）兩個蛋白質所組成。該系統可以使細菌面對外界環境改變，可活化或抑制某些基因的表現，調整細菌的結構組成或毒性因子的表現。目前已知S. mutans具有14對TCS。本實驗利用實驗性心內膜炎老鼠模型進行篩選，試圖找出具有調控S. mutans引起心內膜炎相關毒性因子能力的HK或RR。實驗發現將rr11剔除後，RR11突變株黏附在贅疣上的能力，和其它突變株比較相對減弱許多。進一步研究，比較野生株UA159和突變株RR11的毒性差異，利用活體螢光影像系統和共軛焦顯微鏡可以觀察到轉糖鏈球菌野生株在受損的心臟瓣膜上會形成生物膜，相對地RR11突變株無法在受損的心臟瓣膜上形成生物膜，可能是造成RR11突變株引起心內膜炎能力降低的原因。此外，將野生株UA159和突變株RR11培養於富血小板血漿(platelet rich plasma)中，在體外試驗中觀察兩菌株形成生物膜能力的差異，結果發現RR11突變株利用血小板形成生物膜的能力比野生株UA159差。由實驗結果推測rr11的基因產物在S. mutans中參與與生物膜之形成有關的毒性因子之訊息傳遞路徑，而調控S. mutans引起感染性心內膜炎的致病機制。

Streptococcus mutans is one of the principle causative agents of dental caries, and an opportunistic pathogen of infective endocarditis (IE). Bacteremia is caused by S. mutans following common dental procedures or oral trauma. In blood circulation, S. mutans can escape from immune surveillance and adhere on damaged valve surface to form vegetation（platelet-fibrin biofilm）, which is a decisive pathogenic process in IE. S. mutans has 14 two component systems（TCSs） which is composed of a histidine kinase sensor（HK）and a response regulator（RR）to sense and respond to environmental change. The bacterial virulence factors are commonly regulated through TCSs. We used a PCR-dependent detection assay to assess in vivo the role of individual hk or rr mutant strains potential affecting pathogenesis of IE, particularly focusing on the biofilm formation in a rat (experimental endocarditis model). One of deletion mutants rr11 was reduced in the colonization on vegetations of catheterized rats when coinfected with a pool of hk or rr mutant strains, respectively. Furthermore, we identified biofilm formation in situ on the vegetation by Ultra Sensitive Imaging System and confocal laser scanning microscope approaches. Both systems revealed that the biofilms formed by rr11 deletion mutant in the vegetation had altered architecture. Deletion of rr11 also resulted in reduced biofilm formation in the platelet rich plasma (PRP). Together, these results indicated that the new response regulator participate in the pathogenesis of IE through regulating biofilm formation in situ on vegetation.