| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 107 === Staphylococcus pseudintermedius is an opportunistic pathogen for causing pyoderma in dogs. The number of human cases with S. pseudintermedius infection, mainly acquired from dogs, is also increasing during recent years. S. pseudintermedius-induced soft tissue infection (STI) is a typical biofilm-related infectious disease, which is refractory to routine antibiotic treatment. In addition, methicillin resistance S. pseudintermedius-induced STIs in dogs and human are also rapidly emerging recently. Therefore, to understand the pathogenesis of S. pseudintermedius infection for developing the effective strategies for the prevention and treatment of S. pseudintermedius-induced infections is imperative. The biochemical properties of S. pseudintermedius are similar to those of Staphylococcus aureus, but the current understanding of the pathogenesis of S. pseudintermedius is still limited. In S. aureus, accessory gene regulator (agr) system, which is a quorum sensing and a two-component system, mediate S. aureus virulence for causing diseases, but the role of agr in the pathogenesis of S. pseudintermedius is still unknown. Therefore, in this study, the virulence of different agr types of S. pseudintermedius for causing STI was characterized. To investigate the pathogenesis of S. pseudintermedius-induced skin infection, the mouse pyoderma model was established. Fourty-seven clinical MRSP isolates were classified into four types by agr classification, namely type I (52%), type II (2%), type III (35%) and type IV (10%). The agr type III and type IV of MRSP isolates showed stronger ability to cause skin infection in vivo. The abilities of MRSP to resist neutrophil killing and to form the biofilm are not correlated to the virulence of MRSP for causing skin abscesses. The results of cytotoxicity assay, cell adhesion and cell invasion tests showed that agr type III and type IV isolates perform significantly better than other agr types of MRSP for causing skin infection. Taken together, agr type III and type IV of S. pseudintermedius isolates show greater abilities to adhere, invade and damage host cells, which contribute to bacterial virulence for causing pyoderma.
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