ARE BACTERIAL LYSOZYME INHIBITORS IMPORTANT IN BACTERIA-HOST INTERACTIONS?

摘要

Lysozymes are key effectors of the animal innate immunity system. They catalyse the hydrolysis of the P(l-4) glycosidic bond between the N-acetylglucosamine and N-acetylmuramic acid residues in the main chain of peptidoglycan, the major constituent ofbacterial cell walls. In the animal kingdom the main lysozyme families are chicken (c-), goose (g-) and invertebrate (i-) type lysozyme. Recently, at least four families of specific lysozyme inhibitors have been discovered in Gram-negative bacteria, andit has been proposed that these are produced as a mechanism to evade lysozyme mediated lysis. Three different inhibitors have been reported in Escherichia coli, of which two are specific for c-type lysozyme (Ivy, Inhibitor of vertebrate lysozyme; MliC,membrane bound lysozyme inhibitor of c-type lysozyme), and one specific for g-type lysozyme (PliG, periplasmic lysozyme inhibitor of g-type lysozyme) [1-3]. In vitro experiments have shown that they protect E. coli against the corresponding lysozyme whenthe outer membrane is permeabi-lised by lactoferrin or EDTA [2-4]. In addition, knockout of ivy or pliG reduced survival of E. coli in respectively chicken and goose egg albumen, thus demonstrating a possible ecological significance for these inhibitors[5, 6]. These results indicate that a highly specific one-to-one interaction between host lysozymes and bacterial lysozyme inhibitors exists that may affect bacteria-host interactions, but in vivo studies to demonstrate such a role are still lacking todate. Therefore, the objective of this work was to investigate the role of lysozyme inhibitors in the pathogenesis of Avian Pathogenic E. coli (APEC) using chickens and zebrafish as infection model systems.