The cytotoxic effects of PA-MSHA were examined using CCK-8 assays (Cell Counting Kit-8, Dojindo Molecular Technologies Inc., USA). Cells were treated with 0, 0.125, 0.25, 0.5, 1.0, 2.0, 4.0, or 8.0 × 109/mL PA-MSHA and then maintained at 37°C for 24, 48, or 72 hours. The IC50 values were calculated using CalcuSyn (Biosoft, USA).