Detection of VtaA8 and VtaA9 on the surface of H. parasuis . Phagocytosis-resistant strain PC4-6P was incubated with monoclonal antibody 69C6 directed against VtaA8 and VtaA9. Reaction was detected with a FITC-conjugated anti-mouse antibody and analyzed by flow cytometry (bold line). Phagocytosis- susceptible strain F9 was included as a negative control (shown in gray). As an additional control, PC4-6P incubated only with the secondary antibody is also shown (fine line).