Vero E6 cells were cultured in Dulbecco's modified Eagle medium (DMEM) containing sodium pyruvate, 2 mM l -glutamine, 1% penicillin-streptomycin (Gibco) and 10% Fetal Bovine Serum (Gibco). Adherent Spodoptera frugiperda 9 (Sf9) cells from Life Technologies (USA) were cultured in Grace's Insect Cell Culture medium (Gibco) with 10% Fetal Bovine Serum and 1% penicillin-streptomycin at 27 °C; Sf9 suspension cells were cultured in SIM SF Expression Medium (Sino Biological) with 1% penicillin-streptomycin at 27 °C. Lactobacillus MG1363 was cultured in M17 medium (Cat: HB0391, Qingdao Hope Biotechnology Company) with 1% glucose at 30 °C and was stored in our laboratory.
The isolated SARS-CoV-2 virus (BetaCoV/Beijing/IME-BJ05-2020, abbreviated as BJ05, GenBank accession No. MT291835) and a SARS-CoV-2 mouse-adapted strain (C57MA14) were grown in Vero E6 cells for 3 days at 37 °C and 5% CO2. The C57MA14 strain was passaged 14 times in aged C57BL/6 N mice. Furthermore, BJ05 and C57MA14 were cultured as described previously (Yan et al., 2022 ).
The isolated SARS-CoV-2 virus (BetaCoV/Beijing/IME-BJ05-2020, abbreviated as BJ05, GenBank accession No. MT291835) and a SARS-CoV-2 mouse-adapted strain (C57MA14) were grown in Vero E6 cells for 3 days at 37 °C and 5% CO2. The C57MA14 strain was passaged 14 times in aged C57BL/6 N mice. Furthermore, BJ05 and C57MA14 were cultured as described previously (Yan et al., 2022 ).