No Effect of the vicK Deletion on Resistance of S. equi to Phagocytosis by PMNs 
To determine whether the DeltavicK deletion affects the resistance of S. equi to phagocytosis by PMNs, the phagocytosis of wild-type and DeltavicK bacteria by PMNs in non-immune horse and rabbit blood was compared. FITC-labeled wild-type S. equi, DeltavicK mutant, and S. pyogenes spy1718::aad mutant were incubated with heparinized horse or rabbit blood for 5 and 15 min, and percentages of PMNs associated with fluorescent bacteria were quantified using flow cytometry analysis. The spy1718::aad mutant of S. pyogenes, which is no longer resistant to phagocytosis by PMNs, was used as a positive control in the assay. The percentages of PMNs with associated wild-type S. equi and spy1718::aad were low and high, respectively, indicating that the assay worked well to evaluate resistance of the bacteria to phagocytosis. There was no significant difference in the percentages of PMNs associated with wild-type and DeltavicK bacteria at both time points and in both horse and rabbit blood (Fig. 3), indicating that the DeltavicK mutant retains the ability of S. equi to resist to phagocytosis by PMNs.
