感染伤口的处理导论.pptVIP

* Elastase is a collagen degrading protease and an important virulence factor in the wound pathogen Pseudomonas aeruginosa. This is one of the reasons why P aeruginosa delays wound healing. * Yet another important virulence strategy, that has been recognized lately also for bacteria colonizing wounds, is the ability of bacteria to form so called biofilms. Biofilm is composed of microorganisms enclosed in slime made of polysaccharides. Both our own immune system and antimicrobial agents have poor effect on bacteria within biofilms. It is believed that the slime inhibit penetration of antimicrobial agents. Furthermore, bacteria within biofilm are metabolically less active rendering them even more resistant to antimicrobial agents. Knowledge about the biofilm life style of bacteria is well accepted in some research areas but less in others, also from one medical dicipline to another the awareness may be very different. Dental plaque, which actually is the same as biofilm, has been known for very long. The problems with bacterial biofilms on for example hip implants or pace makers as well as bacterial biofilm causing severe problems in the lung disease cystic fibrosis has also been well documented since several years. There is no defined reason why biofilms should not be present in chronic wounds however their existens have not been addressed until recently. Following steps describe how a biofilm is formed: Planktonic cells adhere to a surface. Adherent cells start to multiply. - 5. At a certain cell density they produce slime and form clustered (mushroom) structures. This behaviour is controlled by cell-to-cell communication called quorum sensing. * Here is a nice scanning electron microscopy image on a biofilm with more than one bacteria species. Centers for Disease Control and Prevention (CDC) stated last year that 67% of all infections are caused by biofilms. Recently, Patricia Mertz (Miami) has shown the existence of biofilm in wounds. (P Mertz’s group has a