The role of Srv in group A streptococcal pathogenesis

• Main Authors: Cheng-Chan Lo, 羅晟展
• Other Authors: Jiunn-Jong Wu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/29994683225356981692

碩士 === 國立成功大學 === 醫學檢驗生物技術學系碩博士班 === 97 === Group A streptococcus (GAS) is a common pathogen that can cause a wide-spectrum of human diseases. Several global regulators have been extensively studied in GAS such as mga, rgg, covR etc. However, there still have a lot of controversy and unknown mechanisms that are involved in virulence regulation. Srv is a Crp/Fnr family transcriptional regulator and involved in a complex regulatory network of GAS. The aim of this study was to understand how Srv affected the downstream genes. The northern blot, western blot, SpeB activity assay and luciferase speB promoter assay all showed Srv is a negative regulator of speB, Streptococcal pyrogenic exotoxin B, a cysteine proteinase, which plays an important role in GAS infection. However, the highly expressed speB in a srv mutant strain showed low virulence in mice model reported previously, suggesting some other virulence factors may be involved. In order to find out which virulence factors can be regulated by Srv, the putative Srv binding box in GAS whole genome was searched. Two genes, mga and slo had the Srv putative binding box. Mga is an important global regulator, which has shown a regulation of M protein (emm) and C5a peptidase (scpA). RT-PCR, Northern blot and real time RT-PCR showed mga, emm, scpA, and slo decreased expression in srv mutant, and restored in a complementary strain. Luciferase assay also showed that the mga activity in srv mutant was two times lower than that of wild-type strain. In addition, Srv showed a highly expression in log phase by real time RT-PCR and western blot which is correlated with the expression pattern of mga. SLO hemolysin activity decreased in the srv mutant. The human whole blood killing assay was also confirmed that the relative resistant to bactericidal effect was 80% decrease in mutant. Based on these results suggest that Srv plays an important role in blood survival, it not only positively regulate mga to resistant the bactericidal effect but also regulate streptolysin O to evade phagocytosis.