, 2004b). Unexpectedly, data on fibronectin-binding adhesins and invasins of S. lugdunensis are scarce. Binding to fibronectin has previously been

investigated in a small collection of strains, but all of eleven isolates showed only weak binding to fibronectin compared with that of strain Cowan I of S. aureus (Paulsson et al., 1993). S. lugdunensis has been described as being part of several niches of the human skin flora (Bieber & Kahlmeter, 2010). The clinical presentation of S. lugdunensis-caused infections is similar to infections caused by S. aureus. Staphylococcus lugdunensis can cause potentially fatal endocarditis, osteomyelitis, and skin and soft tissue infections (Vandenesch et al., 1993; Pareja et al., 1998; Patel et al., 2000; Hellbacher et al., 2006; Frank et al., 2008). Staphylococcus lugdunensis is thought to be rarely see more isolated; nevertheless, the low prevalence of S. lugdunensis in skin infection has recently been questioned (Bocher et al., 2009). We therefore sought to analyze the invasion of epithelial and endothelial cells (human urinary bladder carcinoma cell line 5637 and the endothelial cell line EA.hy 926) using a previously described fluorescence-activated cell-sorting (FACS)-based invasion assay. We correlated these results

with the binding of clinical isolates of S. lugdunensis to fibronectin. The bacteria used were S. aureus Cowan I, Staphylococcus carnosus TM 300 and eight clinical isolates of S. lugdunensis: Stlu 12, Stlu 30, Stlu 33, Stlu 35, Stlu 36, Stlu 39, Stlu 50, and Stlu 108 and the isogenic knockout mutant selleck inhibitor Stlu 108Δfbl::ermB (Table 1).

All S. lugdunensis isolates used in this study were confirmed by two reference methods: S. lugdunensis specific tanA and fbl PCRs and by MALDI-TOF MS, as described previously (Noguchi et al., 2009; Szabados et al., 2010; Szabados et al., 2011). Human urinary bladder carcinoma cell line 5637 (DSMZ, Braunschweig, Germany) and endothelial cell line EA.hy 926 (DMSZ) were used throughout this study. Bacteria were grown until the mid-logarithmic phase, as described previously (Szabados et al., 2008). The mutagenesis construct for the homologous recombination cloned into pBT2, and named pMB2503, has previously been described (Marlinghaus only et al., 2011). The homologous recombination of the fbl gene in strain Stlu 108 was also performed as previously described (Marlinghaus et al., 2011). The Δ fbl knockout mutant was confirmed by sequencing (data not shown). Human urinary bladder carcinoma cell line 5637 was cultured in RPMI 1640 with phenol red (PAA, Pasching, Austria). The endothelial cell line EA.hy 926 was cultured in HAT medium (Invitrogen) with addition of HAT medium supplement (hypoxanthine, aminopterin, and thymidine). Both media were also supplemented with 10% heat-inactivated fetal calf serum (PAA) and 1 g L−1 pyruvate (Invitrogen) and 1.5 g L−1 glucose (Invitrogen).