Abstract
BackgroundStaphylococci belong to the most important pathogens causing implant-associated infections. Colonization of the implanted medical devices by the formation of a three-dimensional structure made of bacteria and host material called biofilm is considered the most critical factor in these infections. To form a biofilm, bacteria first attach to the surface of the medical device, and then proliferate and accumulate into multilayered cell clusters. Biofilm accumulation may be mediated by polysaccharide and protein factors.Methology/Principal FindingsThe information on Staphylococcus aureus protein factors involved in biofilm accumulation is limited, therefore, we searched the S. aureus Col genome for LPXTG-motif containing potential surface proteins and chose the so far uncharacterized S. aureus surface protein C (SasC) for further investigation. The deduced SasC sequence consists of 2186 amino acids with a molecular mass of 238 kDa and has features typical of Gram-positive surface proteins, such as an N-terminal signal peptide, a C-terminal LPXTG cell wall anchorage motif, and a repeat region consisting of 17 repeats similar to the domain of unknown function 1542 (DUF1542). We heterologously expressed sasC in Staphylococcus carnosus, which led to the formation of huge cell aggregates indicative of intercellular adhesion and biofilm accumulation. To localize the domain conferring cell aggregation, we expressed two subclones of sasC encoding either the N-terminal domain including a motif that is found in various architectures (FIVAR) or 8 of the DUF1542 repeats. SasC or its N-terminal domain, but not the DUF1542 repeat region conferred production of huge cell aggregates, higher attachment to polystyrene, and enhanced biofilm formation to S. carnosus and S. aureus. SasC does not mediate binding to fibrinogen, thrombospondin-1, von Willebrand factor, or platelets as determined by flow cytometry.Conclusions/SignificanceThus, SasC represents a novel S. aureus protein factor involved in cell aggregation and biofilm formation, which may play an important role in colonization during infection with this important pathogen.
Highlights
In the past two decades, Staphylococcus aureus has emerged one of the most important pathogens causing infections with indwelling medical devices, such as prosthetic joints, prosthetic heart valves, intravascular catheters, and cerebrospinal fluid shunts, which creates an increasing health care problem [1]
Nucleotide sequence of sasC and amino acid sequence analysis of the deduced protein The nucleotide sequence of the cloned sasC gene from S. aureus 4074 was determined on both strands. sasC consists of 6558 nucleotides and encodes a deduced protein of 2186 amino acids with a predicted molecular mass of 237.9 kDa
S. aureus surface protein C (SasC) shares 31% identical aa with Mrp and FmtB proteins from strain Col that have been implicated in methicillinresistance [32,33]
Summary
In the past two decades, Staphylococcus aureus has emerged one of the most important pathogens causing infections with indwelling medical devices, such as prosthetic joints, prosthetic heart valves, intravascular catheters, and cerebrospinal fluid shunts, which creates an increasing health care problem [1]. The pathogenesis of device-associated infections with staphylococci is mainly characterized by the pathogens ability to colonize the surfaces of the implanted medical device by the formation of a three-dimensional structure of microorganisms embedded in a thick extracellular matrix composed of polysaccharides, proteins, extracellular DNA, and host factors, known as biofilm [3,4,5]. The first step involves the adherence of the bacteria to artificial surfaces that can occur either directly or via host factors acting as bridging molecules, such as the extracellular matrix and plasma proteins fibrinogen (Fg) and fibronectin (Fn) or platelets [6]. SasC or its N-terminal domain, but not the DUF1542 repeat region conferred production of huge cell aggregates, higher attachment to polystyrene, and enhanced biofilm formation to S. carnosus and S. aureus. SasC does not mediate binding to fibrinogen, thrombospondin-1, von Willebrand factor, or platelets as determined by flow cytometry
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