The Role Of SarZ And Hln In Biofilm Formation And Virulence In Staphylococcus Epidermidis

Staphylococcus epidermidis is an important nosocomial pathogen for its biofilmformation on implanted medical devices. Biofilm is of definition that bacteriaembedded in secrated excellular matix attach to orgnic or unorganic surface, thenproliferate and accumulate, finally constitute the mature biofilm. Bacteria in biofilmmakes them escaping from the immune system of host and disseminating to form newniche. Deep investigation of molecular mechenism of biofilm formation will behelpful to preclude and manage infections caused by Staphylococcus epidermidisefficiently. In this study, we screened out three mutants deficient in biofilm formationfrom Tn917 transposon random mutagenesis library derived from biofilm-formationS.epidermidis1457 and identified the insertion sites by Tn917 which were all in thesame gene, sarZ. In comparison between sarZ mutant and wild type strain S.epidermidis1457, we found that sarZ mutant showed decreased biofilm formation,decreased ability in the primary attachment, decreased production of PIA in the laterstep and less pathogenicity both in a rat CVC related infection model and a micesubcutaneous infection model. Genetic complementation of sarZ mutant restored thewild type phenotype. It demonstrated that sarZ is a novel gene important for biofilmformation in both the steps in S. epidermidis. DNA Microarray results showed 79genes were up and down regulted in sarZ mutant compared with wild type, includingdownregulated biofilm gene icaADBC and its negative regulator gene, icaR andupregulated putative hemolysin gene hln (SERP2258) and organic hydroperoxideresistance gene (ohr) . Part of the results were confirmed by TaqMan Real TimePCR. According to the results above, we also observed that sarZ mutant was moresusceptible to t-BOOH and showed significant hemolysis compared with wild type.Besides, strain overexpressing sarZ showed increased hemolytic activity. It impliedthat hln is a new hemolysin gene in S. epidermidis and regulated by sarZ. Interestingly,overexpression of sarZ made 1457 deficient in biofilm formation and the primaryadherence. It seems sarZ also repressed biofilm formation in S. epidermidis. We alsoemployed the silkworm infection model to compare the virulence of overexpression strain and wild type. As a result, it showed no significant virulence difference between them.This study illuminated that sarZ is an important regulator gene of biofilm formation and virulence in S. epidermidis. Most likely in IcaR-independent pattern, sarZ regulated expression of ica and it implied that there existed new pathway in SarZ-dependent way to regulate biofilm formation and virulence in S. epidermidis. In this study, we also identified a noval hemolysin gene hln in S. epidermidis and observed that its overexpression led to decreased biofilm formation. Besides, we firstly employed the silkworm infection model in S. epidermidis. Further more, it seems that sarZ and hln may be potential drug target to prevent and treat infections caused by S. epidermidis.