Development of an Antibiotic-Gene Free Live Attenuated Vaccine of Salmonellae

沙氏桿菌除能夠感染多種經濟動物外，亦是人畜共通傳染病之主要病原之一，特別在公共衛生上，更可藉由污染的畜產食品導致宿主之消化道疾病甚至引起全身性敗血症，雖然沙氏桿菌被認為是一種機會性病原，但其對人類健康與農業經濟影響則相當鉅大。且從診斷中心之病例統計中發現有70%以上皆為沙氏桿菌之併發感染症，加上病原已具多重抗藥特性，造成防疫與公共衛生上極大的困擾。由於沙氏桿菌均經由消化道黏膜而感染，當病原與黏膜接觸後再侵入深層組織造成全身性感染。目前許多的沙氏桿菌之研究都致力於改善或增加沙氏桿菌在黏膜部位激起免疫反應的能力，在眾多的模式中主要以減毒活菌之免疫方式或黏膜免疫佐劑的研發及利用減毒的活菌作為其它免疫抗原攜帶者為最普遍。本計畫為新辦計畫，將嘗試開發構築一沙門氏桿菌過度減毒株(phoQ基因缺損株)，並利用此過度減毒候選株，單獨或同時配合先前所構築之crp基因缺損株，來開發更安全及更具有免疫保護效力之沙門氏桿菌活菌疫苗。The diarrheagenic disease Salmonellosis caused by Salmonella choleraesuis and S. typhimurium is among the most important bacterial diseases worldwide and both pathogen can induce gastroenteritis, interstitial pneumonia and systemic septicemia in swine. After infection, pathogenic Salmonella serovars will encounter the intracellular killing by host phagocytic cells during internalization, but Salmonella has been proved to be able to survive and even replicate in phagocytic cells to cause systemic infection. Although Salmonella is thought to be an opportunistic pathogen in pig farm, it will induce serious economic problem after outbreak and hard to eradicate from a contaminated farm. According to the survey of Animal disease diagnostic center, 70% from the submitted swine cases were identified to be affected or associated with Salmonella co-infection. Those Salmonella isolates also showed multi-drugs resistance from the affected clinical cases. Because Salmonella invasion always start from the mucosal surfaces of gastrointestinal tract and microorganisms will transit across the mucosa during the early steps of the infections. Therefore, to elicit the local immune response to block the virulence determinants of Salmonella on mucus is extremely important to prevent both infection and the following disease development. However, most of these virulence factors are poorly immunogenic by mucosal administered route. Recently, a number of strategies have been developed to overcome this problem, including suitable mucosal adjuvant and vector vaccine delivers used. One of the approaches that can be pursued to elicit efficient mucosal immunity is the use of attenuated strains to deliver heterologous antigens by the mucosal route. Recent studies indicate that the attenuated Salmonella is a good candidate for immunization and also could be utilized for a potential vaccine vector to deliver multivalent heterologous antigens at mucosal administered routes. But the antibiotic gene inserted into the attenuated Salmonella Choleraesuis genome may raise a public health concern. Therefore, the purpose of this project is to develope an antibiotic gene-free Salmonella choleraesuis knockout strain and an over attenuated phoQ mutant. And we wish to develope a safe and immuno-protective live attenuated Salmonella vaccine in the near furture