創傷弧菌為一伺機感染性病原菌，主要生存於海水內，會經由傷口或胃腸道而造成感染。目前推測創傷弧菌的毒力因子主要有莢膜、胞外產物、細菌競爭宿主體內鐵的能力等，但關於創傷弧菌的致病機制仍不清楚。近年來，已有許多研究顯示quorum-sensing system會調控某些致病菌的毒力，如霍亂弧菌、綠膿桿菌及金黃色葡萄球菌等。創傷弧菌的基因體序列已於2002年全部定序完成，且經由annotation的結果得知參與AI-2 quorum-sensing system的基因都可在創傷弧菌中被比對出來。本研究的目的在於了解創傷弧菌於感染小鼠的過程中，其毒力因子的表現是否受到quorum-sensing system的調控。藉由分離及分析此系統調控子LuxO的兩種表現型，一為luxO缺失（LD）突變，另一為LuxO持續活化的luxOD47E突變，我們發現LuxO不但會負調控創傷弧菌蛋白酶的表現同時也會正調控細胞溶解毒素的表現。在測定不同luxO突變株以皮下感染模式對實驗小鼠的半致死劑量的實驗中，我們觀察到LD突變株的致死力比野生株或luxOD47E突變株下降近100倍，顯示LuxO的突變確實會影響創傷弧菌的毒力。進一步測試luxO突變株對HEp-2細胞的毒性時，發現luxOD47E突變株的細胞毒性與野生株並沒有明顯差異，但LD突變株的細胞毒性已喪失。此外，我們也發現LD突變株由感染部位侵入小鼠循環系統的散播能力遠比野生株或是luxOD47E突變株差，並且觀察各突變株由皮下感染小鼠之上皮組織的病理變化時，亦發現受LD突變株感染後，只有大量吞噬細胞遍布於真皮層及皮下層，而無細菌的聚集。但受luxOD47E突變株感染的結果則與野生株相彷，均可見到大量吞噬細胞及細菌聚集於感染部位的真皮層及皮下層。另一方面，分析各突變株所產生siderophore的表現量，在小鼠全血內的生長情形，及對人體血清抗性的實驗，其結果均顯現各突變株的表現與野生株並無明顯差異。因此，根據以上實驗結果，我們推測LuxO調控創傷弧菌的毒力表現可能是藉由活化某一細胞毒素，且此毒素對於此菌抵抗免疫細胞的攻擊或是侵入小鼠循環系統的能力扮演了相當重要的角色。

　　Vibrio vulnificus, a halophilic gram-negative marine bacterium, is an opportunistic pathogen causing septicemia and wound infection in humans. A few virulence factors, such as the capsule, a few extracellular products, and iron-acquisition ability, have been proposed; however, the pathogenesis mechanism of this organism remains unclear. It has been shown previously that the quorum-sensing system can regulate the virulence of pathogens, such as V. cholerae, Pseudomonas aeruginosa, and Staphylococcus aureus. In the whole genome sequence of V. vulnificus completed in 2002, most genes required for AI-2 quorum-sensing signaling were identified. To understand whether the quorum-sensing system is involved in the regulation of V. vulnificus, a mutant (LD mutant) deficient in LuxO, the quorum-sensing regulator, and a luxOD47E mutant expressing constitutively active LuxO were isolated and characterized. We found that LuxO regulates not only the extracellular protease activity negatively but also the cytolysin activity positively. The virulence of LD mutant in mice infected by subcutaneous injection was 100-fold less than that of the wild-type strain or the luxOD47E mutant, suggesting that quorum-sensing system may be involved in regulating the virulence of V. vulnificus. The cytotoxicity to HEp-2 cells was not affected in the luxOD47E mutant, but has diminished in the LD mutant. Furthermore, the spread of bacteria from subcutaneous tissue to bloodstream was remarkably slower in mice infected with the LD mutant than those infected with the wild-type strain or luxOD47E mutant. In the histological examination, we found abundant infiltrating cells but few bacteria in the infection site with the LD mutant. However, a large number of infiltrating cells and bacteria were found clustered together with the wild-type strain and the luxOD47E mutant. On the other hand, the amount of siderophore produced, growth in murine blood, and resistance to serum bactericidal effect were not affected in either the LD or luxOD47E mutant. In conclusion, these results suggest that LuxO may be involved in regulating the virulence of V. vulnificus, probably via activating the expression of an unknown cytotoxin important for escaping the attack from the phagocytes and/or invasion of this organism to the bloodstream, where the organism multiplies and causes septic shock and death.

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