Virulence potential of polysaccharide dependent biofilm forming methicillin resistant Staphylococcus epidermidis: A differential proteomics approach.

Biofilm is the most significant virulence factor in Staphylococcus epidermidis bacteremia. The major biofilm determinants are the polysaccharide intercellular adhesin (PIA) and the Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs). S. epidermidis can potentially contaminate blood cultures, leading to significant misdiagnosis. Moreover, the prevalence of polysaccharide-dependent biofilm-forming S. epidermidis is non-significant in paediatric bacteremia, which might indicate a lower virulence potential or culture contamination by less virulent strains. Therefore, to rule out possible contamination, the virulence potential of S. epidermidis having different background biofilm-forming mechanisms was checked through a differential proteomics approach. 20 S. epidermidis isolated from paediatric bacteremia were characterized by multiplex PCR. Polysaccharide synthesis was assessed using a Congo red assay, and biofilm formation was checked through the 96-well microtiter plate well assay. The differentially expressed proteins were identified through LC-MS/MS analysis, and virulence association of differentially expressed proteins were analyzed by adopting different in-silico approaches coupled with extensive literature mining. All isolates were encoding the mecA, major MSCRAMMs and were strong biofilm producers. Ten strains of S. epidermidis isolates were found to be synthesizing the PIA. The LC-MS/MS identified 498 upregulated and 416 downregulated proteins. 55 upregulated and 11 downregulated virulence-associated proteins, were identified in the polysaccharide-dependent biofilm-forming S. epidermidis. Therefore, it is concluded that instead of non-pathogenic culture contaminants, the polysaccharide-dependent biofilm-forming S. epidermidis is encoding and expressing potential virulence determinants, hence representing an infectious origin. The study will help in the diagnosis and management of S. epidermidis paediatric bacteremia.