each dilution step with 50 µL virus suspension containing 100 plaque-forming units, followed by an incubation for 1 h at 37 °C. The cells were washed with phosphate-buffered saline (Bio&SELL), inoculated with 100 μL of these virus serum dilutions, and incubated for one hour at room temperature on a rocking shaker. Then, 100 µL of the cell culture medium supplemented with 20% (v/v) fetal calf serum (FCS) was added to each well to achieve a FCS concentration of 10% (v/v). After four to five days, cells were fixed with 4% (w/v) paraformaldehyde in phosphate-buffered saline and stained with an aqueous solution of 0.1% (w/v) crystal violet and 20% (v/v) methanol. The stained