2.2. Preparation of Bacterial Suspensions

The lyophilized preparations of five strains transferred into 5 mL de Man–Rogosa–Sharpe (MRS) medium were firstly activated at 37°C, respectively. Then, they were inoculated into the MRS medium at 37°C for 12 hr incubation with 4% inocula. Their cells were collected by centrifugation (4°C, 5000 rpm, and 10 min) and washed twice with sterile water. The cell concentrations of these tested strains were finally adjusted to 5 × 10⁹ cfu/mL prior to use.