Attenuation of a Highly Pathogenic Porcine Deltacoronavirus Strain CZ2020 by a Serial Passage In Vitro

Figure 1

Biological characterization of PDCoV CZ2020 and its high passages, CZ2020-F80 and CZ2020-F100. (a) LLC-PK1 cells were infected with PDCoV CZ2020, CZ2020-F80, and CZ2020-F100 for 12 h; then, PDCoV was detected with immunofluorescence assay (IFA). Porcine polyclonal antibodies were used to detect PDCoV (green), and cell nuclei were stained with DAPI (blue). Scale bar, 100 μm. (b) LLC-PK1 cells were infected with PDCoV strains at an MOI of 0.1. The cell culture supernatants were collected at the indicated time points (6, 12, 24, 36, 48, and 72 hpi). Growth curves were drawn based on the viral titers determined by the TCID50 assay in LLC-PK1 cells. (c) Monolayers of LLC-PK1 cells were infected with PDCoV CZ2020, CZ2020-F80, and CZ2020-F100 for 3 days; then, the plaques were stained with 0.1% crystal violet.

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