Sortase A promotes virulence in experimental Staphylococcus lugdunensis endocarditis

Staphylococcus lugdunensis is a commensal of humans and an opportunistic pathogen. It can cause an aggressive form of infective endocarditis in healthy humans akin to Staphylococcus aureus. Here we compared the virulence of the genome-sequenced S. lugdunensis strain N920143 to S. aureus in an experimental rat endocarditis model. N920143 caused a milder course of disease with lower levels of bacteraemia and smaller endocardial vegetations than S. aureus strain Newman. However, vegetations were comparable to those produced by S. aureus MRSA strain COL. Little is known about virulence factors of S. lugdunensis as systems to manipulate the bacterium genetically are currently limited. Here, we report a method for electroporation of S. lugdunensis with plasmid DNA and demonstrate that the low efficiency of transformation is due to the activity of a conserved type I restriction modification system. To streamline the transformation process, we constructed SL01B, an E. coli strain expressing the hsdM/hsdS genes of N920143. Modified plasmid DNA isolated from SL01B transformed S. lugdunensis strains from clonal complexes 1 and 2 efficiently. A deletion mutant of N920143 lacking sortase A was significantly less virulent than the wild-type in the endocarditis model. Mutants defective in single surface proteins Fbl or vWbl were not significantly different from the wild-type but showed trends towards reduced virulence.