轉糖鏈球菌抑制吞噬細胞毒殺作用之機轉與基因調控

Abstract

轉糖鏈球菌(Streptococcus mutans) 為人類齲齒的致病菌，並也是人類感染性心內膜炎的機會致病菌之一。在感染性心內膜炎發展的初期，轉糖鏈球菌必須由口腔進入血液循環之中，而暴露在血漿之中。血漿是一成份複雜的豐富培養基。一旦轉糖鏈球菌進入血液中後，細菌必須面對新環境所產生的壓力；而環境中壓力所產生的訊號也會刺激細菌特別基因的表現來適應與生存於改變的環境中。 在本實驗的第一部份，我們利用微陣列分析來探討轉醣鏈球菌受血漿刺激後之基因的表現。在本篇研究中，我們著重於轉糖鏈球菌內與氧化還原相關的基因及一個two component system response regulator, scnR 二者間的關係。經過胺基酸序列比對後，我們發現到scnR 與Streptococcus pyogenes 內用以抵抗吞噬細胞毒殺作用的irr response regulator 有35 % 的一致性。爾後，我們建構了轉糖鏈球菌scnR 的突變株，並分析在抵抗Raw264.7 吞噬作用以及細胞毒殺作用能力上，與轉糖鏈球菌野生株的差異。我們發現scnR 突變株在消弭經由Raw264.7 所產生的反應性含氧物種之能力上較野生株降低許多。我們也發現，轉糖鏈球菌野生株在經過血漿刺激後，可以增加經過Raw264.7 毒殺作用後的存活率；然而，此現象卻沒有在scnR突變株中發現。因此，我們認為轉糖鏈球菌利用two component system response regulator scnR 調控下游與氧化還原相關基因的表現，對於抵抗Raw264.7 的毒殺作用是重要的；並且在經由血漿刺激後，是可以增加細菌scnR與氧化還原相關基因的表現。

Streptococcus mutans, being the principal etiological agent of dental caries, is also one of the most common opportunistic pathogens isolated from patients with infective endocarditis (IE). As an early step in the development of infective endocarditis, S. mutans gains access to the bloodstream from the oral cavity, and exposes in human plasma. We hypothesized that plasma as a complex medium could trigger S. mutans cells to adapt to different stresses through inducing specific gene expression upon sensing of signals from the plasma components. In the first part of this study, we used oligonucleotide DNA microarray to analyze the expression of the genes after plasma stimulation. We focused on the function of redox genes and one of the two component system response regulator, scnR, in this study. We found that the amino acid sequence of scnR showed 35% identify to irr response regulator, which is associated with ability against phagocytic killing in Streptococcus pyogenes. Furthermore, an isogenic scnR deletion mutant exhibited decreased ability to eliminate the reactive oxygen species (ROS) produced in Raw264.7 in comparison with wild-type S. mutans strain. In addition, plasma-induced resistance to phagocytic killing was significantly reduced in scnR deletion mutant. We hypothesize that the two component system response regulator, scnR, is important for S. mutans against phagocytic killing in Raw264.7 through stimulating redox genes expression.