Genome-wide expression analysis of human plasma-regulated genes in Streptococcus mutans

• Main Authors: Chun-Ta Ho, 何俊達
• Other Authors: 賈景山
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/58923424925890896088

碩士 === 國立臺灣大學 === 微生物學研究所 === 97 === Streptococcus mutans which is a commensal in human oral cavity can metabolize various kinds of sugars and the end product of these metabolisms is the leading cause of dental caries. Being an opportunistic pathogen, S. mutans sneaks into blood steam through injury in oral cavity, circulates in the blood and adheres to damaged heart valve causing infective endocarditis. The pathogenesis of infective endocarditis of S. mutans relies on two important virulence factors: adhesins and carbohydrate-metabolic proteins. Genes transcribed adhesins help bacteria to bind to damaged valve and carbohydrate-metabolic genes sustain the growth of bacteria in human blood. In this study, two experimental strategies were used to elucidate the co-regulated virulence factors in S. mutans; identifying plasma-regulated genes by microarray and screening two component system ( TCS ) essential for in vivo survival. The microarray analysis indicated that among a total of 206 genes up- or down- regulated after 60 minutes exposure to human plasma, 30% of them were hypothetical proteins, 20% of genes involved in energy metabolism and 12% of them were putative virulence factors. Some plasma-regulated hypothetical proteins are predicted to be secreted or membrane anchored; most up-regulated genes of energy metabolism belong to sugar metabolism, transportation or fermentation; and some previously identified virulence factors, such as genes encoding putative adhesion protein, glucosyltransferase B and D were also identified. Prior-exposure of S. mutans to plasma for 30 or 60 minutes could enhance the ability of bacteria to survive killing in neutrophil or H2O2 treatment, suggesting that human plasma might alter phenotypical characteristics in S. mutans in addition to changes in gene transcription in order to survive in the blood circulation. The in vivo clearance screening identified three TCS mutants: RR6, RR8 and RR10 which are attenuated in survival. Among these mutants, only RR8 exhibited increased sensitivity to hydrogen peroxide. Some of the plasma-regulated genes, mainly citrate degradation related, are located near-by the TCS identified by the RR8 mutant. It is possible that S. mutans might utilize alternative carbon resources to generate ATP through fermentation when growing in plasma and bacteria could sense plasma components to enhance survival in neutrophil or ability to counteract H2O2.