| Summary: | 碩士 === 義守大學 === 生物技術與化學工程研究所碩士班 === 95 === Streptococcus pyogenes (Group A streptococcus, GAS) is an important human pathogen that causes pharyngitis, toxic shock syndrome and many infections on human respiratory tract and tissue. Although there are many virulence factors involved in GAS infection, the actual pathogenic mechanism of GAS is far from clear. Almost GAS strains produce Streptolysin S (SLS) is an oxygen-stable cytolysin. The gene of Streptococcal pyrogenic exotoxin B (SPE B) is widely exits in all GAS and encoded a cysteine protease. The SPE B protease is the important virulence factor of GAS infection; it does not only induce apoptosis in cell, but also helps bacteria to resist phagocytosis of macrophage.
In order to investigate the relationships between SLS and SPE B during GAS infected period, we constructed sagB－ (NpASC) and sagB－/speB－ (JM4) mutant strains of GAS and we found that the growth curves were not different between the wild-type and mutants strains. We used the A549 cells to determine the roles of SLS and SPE B on bacterial invasion and cell lethality first. The data obviously showed that the ability of invasion and killing cells of double mutant strain was weaker than wild type and single mutant strains. When wild-type strain and mutants incubated with whole blood for 1 h, the results indicated that the sagB－/speB－ double mutant were less resistant to phagocytosis than wild type, sagB－ and speB－ single mutants. On BALB/c animal model, wild type and mutants were inoculated by air-pouch method, after six days later, the mice all dead by wild type GAS infections, the sagB－ mutant caused 40% survival rate, but the speB－ and sagB－/speB－ mutants maintained 100% survival rate. Compared with the lesions of these mice at the same time, the double mutant strain resulted in very small lesion area (<40 mm2), but the lesions would recover later. After air-pouch infection for 48 hrs, we aspirated the body fluid from the air pouch to detect the bacterium concentrations. The mice that were infected by sag－/speB－ double mutant showed the lowest bacterium concentrations than any other strains infections. From tissue slices observations, the neutrophiles influx of mice that were infected by wild type or single mutants showed more serious than the double mutant strain did.
Our result suggested that SLS and SPE B have the interaction relations in the pathogenesis of group A streptococcal infection, but the SPE B play more special roles than SLS in the streptococcal infection process.
|
|---|
