Enterococci were determined on KFS agar (KF Streptococcus agar, Becton Dickinson AG, Allschwil, Switzerland) incubated at 42°C for 3 days, and Listeria on Palcam agar (Oxoid, Pratteln, Switzerland) incubated at 37°C for 2 days, all under aerobic conditions. Lactic acid bacteria were counted on MRS agar with Tween 80 (De

Man et al., 1960, Biolife, Milano, Italy) incubated at 37°C for 6 days, OICR-9429 mw under anaerobic conditions which were generated using GENbox anaerobic systems (Biomérieux, Geneva, Switzerland). At the end of ripening, the presence or absence of Listeria was assessed using a three-step enrichment procedure that was previously validated against the reference method ISO 11290-1 for use

on smear samples by Selleckchem SIS 3 ALP (Bern, Switzerland). 10 g (~2000 cm2) of smear were homogenized in 90 g tryptic soy broth supplemented with 0.6% (w/v) yeast extract, 0.02% (w/v) Delvocid® (DSM, Heerlen, Netherlands), 0.001% (w/v) acriflavin (Fluka, Buchs, Switzerland), and 0.004% (w/v) nalidixic acid (Fluka, Buchs, Switzerland) for 4 min using a Stomacher and incubated at 30°C for 24 h. After this step, 1% (v/v) of enriched sample was inoculated to supplemented tryptic soy broth and incubated again at 30°C for 24 h. Presence or absence of Listeria was then checked by streaking a loopful of the second enrichment media on ALOA agar (Biolife, Pero, Italy) that was incubated at 37°C for 24 h. DNA extraction of complex consortia and single isolates Total DNA extraction of cheese surface consortia was carried out with 1 ml homogenate containing 107 to 109 CFU ml-1 that was centrifuged at 18’000 × g for 5 min. The resulting pellet was stored at -20°C until further use. The DNA extraction protocol was modified from Chavagnat et al. [50]. The frozen pellet was resuspended in 1 ml 0.1 M NaOH, incubated at room temperature for 15 min and centrifuged at 18’000 × g for 5 min. The pellet was resuspended in 1 ml TES buffer (10 mM EDTA, 0.1. M tris(hydroxymethyl)-aminomethane, 25% (w/v) saccharose)

containing Montelukast Sodium 0.25% (w/v) lysozyme (50000 U mg-1, Merck, PU-H71 research buy Dietikon, Switzerland), incubated at 37°C for 1 h, and centrifuged at 18’000 × g for 5 min. The pellet was resuspended in 190 μl G2 Buffer (EZ1 DNA Tissue Kit, Qiagen, Basel, Switzerland) and 10 μl proteinase K (EZ1 DNA Tissue Kit; Qiagen, Basel, Switzerland) were added. This suspension was incubated at 56°C for 1 h after which DNA was further purified by BioRobot® EZ1 (Qiagen, Basel, Switzerland) and analyzed by TTGE, as described below. DNA extraction of single isolates was carried out by dissolving one colony of a pure culture in 0.2 ml tris-K buffer (0.01 M tris(hydroxymethyl)-aminomethane (Merck, Dietikon, Switzerland)) containing 0.5 μl ml-1 Tween 20 (Fluka, Buchs, Switzerland) and 0.24 mg ml-1 proteinase K (Sigma-Aldrich, St. Louis, USA).