Phosphate buffered saline pbs ph 7.1

Three different commonly used reference strains of L. monocytogenes (LO28, EGD-e and 10403S) were used in this study. LO28 is a serotype 1/2c, while EGD-e and 10403S both belong to serotype 1/2a. All bacterial strains were kept in cryovials supplemented with 7.0 % (vol/vol) dimethyl sulfoxide (DMSO; Sigma-Aldrich, Dorset, UK) at -80 o C. Before experiments, strains were streaked onto Brain Heart Infusion (BHI) agar (LABM, Lancashire UK) and incubated overnight at 37 o C. A single colony from each plate was transferred with a sterile loop in 3 mL of BHI (LAB M, Lancashire UK) and incubated overnight at 37 o C without shaking. To prepare the final working cultures, 20 mL sterile BHI were inoculated with the overnight culture and left for incubation at 37 o C for 24 h without shaking. Cultures from stationary phase were harvested by centrifugation (Heraeus™ Multifuge™ X 3 Centrifuge, Thermo Scientific, UK) at 9000 ×g for 5 min (room temperature), washed twice using sterile Phosphate-buffered saline (PBS pH 7.1; Oxoid, Basingstoke, UK) and re-suspended in the same medium. Further serial decimal dilutions were prepared for direct plating on BHI agar. The plates were incubated for 24 h at 37°C and viable cell number was expressed as log CFU/mL.