FIGURE 6.

Genetic switching of CovS in AP53 cells. AP53/CovS^WT cells (7 × 10⁹ cfu) were injected subcutaneously into C57Bl/6 mice. Skin lesions were harvested after 3 days and homogenized. Dilutions were plated on THY/milk medium, and production of aSpeB from individual colonies was observed by the lytic zones surrounding the cells. A total of 1,500 colonies/mouse was screened for each of three mice. The unpassaged cells were prepared similarly to the injected cells. A, unpassaged AP53/CovS^M (WT-AP53) cells. No aSpeB was observed. B, unpassaged AP53/CovS^WT cells. aSpeB was produced in all clones. C, passaged AP53/CovS^WT cells. aSpeB was produced in all clones, suggesting that CovR/CovS remained as WT proteins and stimulated aSpeB production.