Methods Bacterial strains, plasmids and growth media All the bacterial strains and plasmid used in the present study are listed in Table 3. E. coli were cultivated in Luria-Bertani broth (LB), whereas Staphylococcus were grown in B-Medium or Tryptic soy broth (TSB, Oxoid, Basingstoke, England). PSI-7977 supplier Unless otherwise stated, all bacterial cultures were incubated at 37 °C, and aerated at 220 rpm with a flask-to-medium ratio of 5:1. SYTO 9 and propidium iodide (PI) (Live_Dead reagents, Molecular Probes, Eugene, OR) were used at a concentration Selleckchem Belnacasan of 1 mM for staining live or dead bacteria

in biofilms. Antibiotics were used at the following concentrations: erythromycin, 10 μg ml-1, chloramphenicol, 10 μg ml-1, ampicillin, 100 μg ml-1. Table 3 Bacterial Strains and plasmids used in this study Strain or plasmid Relevant

characteristic(s) Source or reference Strains     S. aureus RN4220 Restriction-negative, intermediate host for plasmid transfer from E. coli to S. epidermidis [54] selleck chemicals S. epidermidis        1457 Biofilm-positive laboratory strain [55]    1457 ΔlytSR lytSR: : erm derivative of S. epidermidis 1457 This study    1457ΔlytSR (pNS-lytSR) lytSR complementary strain This study    1457 ΔlytSR (pNS) lytSR mutant containing the empty cloning vector This study    1457 ΔatlE atlE: : erm derivative of S. epidermidis 1457 [29]    12228 Biofilm-negative standard strain [6] Plasmids     pBT2 Temperature-sensitive E. coli-Staphylococcus shuttle vector. Apr (E. coli) Cmr (Staphylococcus) [49] pEC1 pBluescript KS+ derivative. Source of ermB gene (Emr). Apr [49] pBT2-ΔlytSR Deletion vector for lytSR; ermB fragment flanked by fragments upstream and downstream of lytSR in pBT2 This study pNS E. coli-Staphylococcus shuttle cloning vector. Apr (E. coli) Spcr (Staphylococcus) This study pNS-lytSR Plasmid pNS containing lytSR fragment and its native

promoter This study *Abbreviations: Ap, ampicillin; Cm, chloramphenicol; Em, erythromycin; Spc, spectinomycin Construction of the S. epidermidis lytSR knockout mutant In S. epidermidis 1457 strain inactivation of the lytSR operon via homologous recombination using temperature sensitive SSR128129E shuttle vector pBT2 was carried out as described by Bruckner [49]. An XbaI/HindIII-digested erythromycin-resistance cassette (ermB) from plasmid pEC1 was inserted into the pBT2 plasmid, named as pBT2-ermB. The regions flanking lytSR operon amplified by PCR were then ligated into the plasmid pBT2-ermB. Primers for PCR were designed according to the genomic sequence of S. epidermidis RP62A (GenBank accession number CP000029). Sequences of the primers are listed in Table 4. The homologous recombinant plasmid, designated pBT2-ΔlytSR, was first transformed by electroporation into S. aureus RN4220 and then into S. epidermidis 1457.