Soybean peptone

S. boulardii CNCM I-745 (Biocodex, Gentilly, France) was cultured for 18 h in 20 ml of liquid YPD medium (1% (w/v) yeast extract, 2% (w/v) soybean peptone and 2% (w/v) glucose, Sigma-Aldrich, St. Louis, MO, USA) at 30 °C in an orbital shaker MaxQ 6000 (Thermo Fisher Scientific, Waltham, MA, USA) with a rotation speed of 170 rpm. S. salivarius (Andrewes and Horder) strain K12 (ATCC BAA-1024) was purchased from American Type Culture Collection (Manassas, VA, USA). Bacterial cells were cultured for 24 h in 20 ml liquid brain heart infusion (BHI) medium (Sigma-Aldrich) at 37 °C in an atmosphere of 5% CO₂, without shaking. To prepare cultures on appropriate agar plates (YPD broth with 1.5% (w/v) agar for yeasts and BHI broth with 1.5% (w/v) agar for bacteria), cells were centrifuged for 5 min (3000 × g for S. boulardii and 5000 × g for S. salivarius); the cell pellet was suspended in sterile Dulbecco’s phosphate-buffered saline (DPBS) containing 8.1 mM sodium phosphate, 136.9 mM sodium chloride, 2.68 mM potassium chloride, and 1.47 mM potassium phosphate, pH 7.50 ± 0.30 (Biowest, Nuaillé, France); and the number of cells was estimated using the OD measurement at 600 nm and 3 × 10⁸ yeast cells or 3 × 10⁹ bacterial cells were spread on the agar plates and cultured for 24 h at 37 °C, additionally in an atmosphere of 5% CO₂ in the case of S. salivarius.

Candida glabrata (Anderson) Meyer et Yarrow strain CBS138 (ATCC^® 2001™), C. tropicalis (Castellani) Berkhout strain T1 (ATCC^® MYA-3404™), and C. parapsilosis (Ashford) Langeron et Talice strain CDC 317 (ATCC^® MYA-4646™) were purchased from the American Type Culture Collection (Manassas, VA, USA) and cultured at 30°C for 18 h in YPD medium (1% yeast extract, 2% soybean peptone, and 2% glucose, Sigma, St. Louis, MO, USA) on an orbital shaker MaxQ 6000 (170 rpm) (Thermo Fisher Scientific, Waltham, MA, USA). Then, cells were harvested by centrifugation (3,000g, 5 min); the cell pellets were washed twice with sterile phosphate-buffered saline (PBS), pH 7.4 (Biowest, Nuaillé, France); and 10⁸ C. tropicalis and 10⁹ C. glabrata or C. parapsilosis cells were inoculated into 100 ml of RPMI 1640 medium (Biowest) and cultured in roller bottles (Corning Inc., New York, NY, USA) at 37°C with roller rack speed 3 rpm for 48 h (with medium exchange after 24 h).