社區性抗甲氧苯青黴素金黃色葡萄球菌在皮膚及軟組織感染的致病機轉: Panton-Valentine Leukocidin的角色

Abstract

Staphylococcus aureus is a leading cause of human infections. The pathogen is able to cause a wide range of diseases of varied severity. Skin and soft tissue infections (SSTIs) caused by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) have emerged as major health problems throughout the world. CA-MRSA infection has been attributed to several virulence factors. Epidemiological reports demonstrate that most SSTI CA-MRSA strains produce Panton-Valentine leukocidin (PVL), but its contribution to CA-MRSA pathogenesis is poorly defined. In this thesis I used an endemic PVL-positive SSTI-causing CA-MRSA strain from Taiwan, together with an isogenic PVL-knockout mutant (Δpvl) and complemented PVL-positive derivative to evaluate the role of PVL in the pathogenesis of CA-MRSA in the RHEK-1 human keratinocyte cell line and a rabbit skin infection model. I found that both PVL-positive CA-MRSA and isogenic Δpvl strains attached and were engulfed into endosomes of RHEK-1 cells within 1h following infection. However, by 2h post-infection PVL-positive CA-MRSA more effectively disrupted endosomes, escaped into the cytoplasm, and replicated intracellularly. Additionally, PVL-positive CA-MRSA induced higher reactive oxygen species (ROS) production than the isogenic Δpvl mutant strains after 2h of infection. By 6h post-infection the PVL-positive strain caused significantly more caspase-dependent keratinocyte apoptosis than the isogenic Δpvl mutant. In rabbit infection model, one week following infection the wild type strain produced significantly more widespread lesions and cell apoptosis than the isogenic Δpvl mutant. Moreover, the expressions of mRNA of proinflammatory cytokines, chemokines, and receptors at the skin lesions were significantly increased by infected with wild type PVL-positive CA-MRSA isolate than the isogenic Δpvl mutant. These findings indicate that PVL is an important virulence factor that enables CA-MRSA to produce necrotizing skin infections by allowing the bacteria to escape from endosomes, replicate intracellularly, trigger ROS production, induce apoptosis, and increase the expression of proinflammatory mediators. The significant contribution of PVL to CA-MRSA virulence in both human keratinocytes and animal infection models suggests that PVL is not only a marker of CA-MRSA, but also a potential therapeutic target to control the inappropriate inflammation and cell death at the infection sites.