Effect of plate passage of strain ER-6P. Strain ER-6P and the same strain after 14 passages on agar plates (ER-6Pp14) were tested with PAM for their susceptibility to phagocytosis. Both strains were FITC-labelled and incubated with PAM. Extracellular bacteria were detected with a H. parasuis-specific antiserum coupled with a PE-secondary antibody. Percentages of macrophages with FITC and PE fluorescence were detected by flow cytometry. Figure shows representative results of three independent experiments.