Function Investigation Of A New Biofilm Regulator Serine/Threoine Protein Kinase, Stk In Staphylococcus Epidermidis

Staphylococcus epidermidis is an important nosocomial pathogen for its biofilm formation on implanted medical devices. Biofilm is of definition that bacteria embedded in secreted extra cellular matrix attach to organic or inorganic surface, then proliferate and accumulate, finally constitute the mature biofilm. Bacteria in biofilm makes them escaping from the immune system of host and disseminating to form new niche. Deep investigation of molecular mechanism of biofilm formation will be helpful to preclude and manage infections caused by Staphylococcus epidermidis efficiently. According to previous studies, serine/threoine protein kinase, stk plays an important role in bacterial biofilm formation. To study its function in S. epidermidis, we constructed a stk mutant strain of S. epidermidis. Compared with the isogenic wild-type strain, biofilm formation of the stk mutant strain decreased significantly. We cloned the S. epidermidis stk gene on a shuttle plasmid, and transformed the plasmid into the stk mutant strain, which restored the biofilm-forming ability in the resulted strain. These results indicated that the stk is essential for the biofilm formation of S. epidermidis. Compared with the isogenic wild-type strain, the attachment ability to polystyrene, the PIA [1] production of the stk mutant strain decreased significantly, and some biofilm regulator like ica operon reduced. These may account for the decreased biofilm formation of the stk mutant strain. Compared with the isogenic wild-type strain, the growth rate in minimum medium of the S. epidermidis stk mutant strain decreased, and the septum formation and cell wall structure was different. These results indicated that stk is needed for the metabolic pathway and cell wall structure of S. epidermidis. A rat model of intravascular catheter-associated infection beneath skin was used to compare the pathogenesis of the stk mutant strain and its isogenic wild-type strain in causing catheter-associated infections. The stk mutant strain was found less likely to cause catheter-associated infections.This study illuminated that stk is an important regulator gene of biofilm formation and virulence in S. epidermidis. And stk is likely regulated expression of ica to regulate biofilm formation and virulence in S. epidermidis. In this study, we also observed that stk plays an important role of bacterial metabolic pathway and cell wall formation in Staphylococcus epidermidis. Further more, it seems that stk may be potential drug target to prevent and treat infections caused by S. epidermidis.