For anaerobic incubations we used a DG250 Anaerobic Workstation (Don Whitley Scientific Ltd., Shipley, West Yorkshire, UK), with a gas mixture consisting of 10% H2-10% CO2-80% N2. GlucoseeYeast Extract Agar supplemented with oxytetracycline (0.1 g/L) (OGYE; Mossel et al., 1962) was incubated aerobically at 30 C for 2 days.