aureus RN4220 and transduced into strain Newman clfA clfB isdA sdrCDE selecting for chloramphenicol
resistance. Primers FpKisdA (5′-CGCTGATCAAACATTATTTAAACAGTAAGTATC-’3) and RpKisdA (5′-CGCTGATCATTATTTAGATTCTTTTCTTTTGA-’3) which incorporate a 5′ and a 3′ BclI site, respectively, were used to amplify the isdA coding sequence from genomic DNA. The PCR product was digested with BclI and cloned into BclI digested pKS80. This resulted in the open reading frame of isdA being fused to the ATG codon of the expression cassette to optimize Proteasome inhibitor translation and created the plasmid pKS80isdA +. The plasmid was sequenced, screened by restriction mapping and electroporated into competent L. lactis strain MG1363. Western immunoblot analysis Cell wall-associated proteins of S. aureus and L. lactis were prepared as previously described [35, 22]. For S. aureus exponential phase cultures were grown to an OD600 of 0.6. Stationary phase cultures were grown for 16 – 24 h. Cells were harvested, washed in PBS and resuspended to an OD600 of 1 in lysis buffer (50 mM
Tris/HCl, 20 mM MgCl2, pH 7.5) supplemented with 30% (w/v) raffinose and 40 μl ml-1 protease inhibitors (Roche). Cell wall proteins were solubilized by incubation with lysostaphin (200 μgml-1) for 10 minutes at 37°C. Cell wall fractions were separated on 7.5% (w/v) polyacrylamide gels, electrophoretically transferred onto PVDF membranes (Roche), blocked in 10% (w/v) skimmed milk (Marvel) and DNA Damage inhibitor probed with anti-ClfB Tobramycin antibodies (1:5,000; [31], anti-IsdA antibodies (1:2,000; a gift from Prof. P. Speziale, Department of Biochemistry, University of Pavia, Pavia, Italy) and anti-SdrC, anti-SdrD, anti-SdrE or anti-Sdr region B antibodies (1:2,000) [22]. The specificity of each antibody is indicated by the fact that no immnocrossreactive bands appeared in mutant strains lacking the relevant antigen. Membranes were washed three times with gentle agitation for 15 min
in TS-Tween (10 mM Tris-HCl pH 7.4, 150 mM NaCl, 0.05% (v/v) Tween 20 (Sigma)). Bound antibodies were detected using horseradish peroxidase-conjugated protein A-peroxidase (1:500; Sigma). Proteins were visualised using the LumiGLO™ Reagent and peroxide detection system (Cell Signalling Technology®). Membranes were detected using Kodak X-ray film. The exposed films were fixed and developed using a Kodak X-OMAT 1000 Processor developing machine. Bacterial adherence to desquamated epithelial cells Bacterial adherence assays were performed as previously described [13]. Briefly desquamated nasal epithelial cells were harvested from three healthy donors by vigorous swabbing of the anterior nares. One donor was a carrier of S. aureus while the other two were not. After washing in PBS, cells were adjusted to 1 × 105cell ml-1. Bacterial cells were washed with PBS and adjusted to 1 × 109cells ml-1.