Evaluating SARS-CoV-2 Infectious Dose via Plaque Assay

L2 cells (ATCC CCL-149TM) were used for the MHV plaque assay. In addition, the mouse asterocytoma-derived cell line (DBT), was used to propagate MHV (generously provided by Julian Leibowitz, Texas A&M Health Science Center, College Station, TX). All cells used in this study were cultured at 37°C in 5% CO₂ in Dulbecco’s modified Eagle’s medium (DMEM; Cellgro) supplemented with 10% fetal bovine serum (FBS), penicillin (50 IU/mL), and streptomycin (50 μg/mL). MHV strain A59 (ATCC VR-764) was used for all the experiments in this study. The virus stocks used for this study were produced as previously described (59 (link)). The MHV viral titer used for all experiments was ~1.0 × 10⁴ PFU/mL. We chose 100 μL (1.0 × 10³ virus particles) to inoculate on each of our samples because 1.0 × 10² – 2.0 × 10³ virus particles is the predicted minimal amount of virus particles needed in order to infect someone (60 (link), 61 (link)). In addition, we chose 1.0 × 10³ virus particles because according to a recent publication modeling the SARS-CoV-2 viral titer when sneezing or coughing on a surface, the range of virus particles for a cough or sneeze was ~1.0 × 10³ – 1.0 × 10⁵, which is in this range (62 (link)).