IIP technique for determining the percentage of the epithelial surface covered by adherent P. multocida. (a) Normal fetal rabbit respiratory nasal epithelium of IIP, negative control; light microscopy (LM), scale bar = 20 μm. (b) Respiratory epithelium of the nasal septa of rabbit fetus preincubated with PNA plus P. multocida (sparse focal immunostaining (arrows); >0–30% of the epithelial surface); LM, scale bar = 20 μm. (c) Tissue preincubated with VVA and P. multocida showing multifocal immunostaining (>30–60% of the surface covered with bacteria); LM, scale bar = 20 μm. (d) Tissue incubated with P. multocida without lectins (positive control) showing generalized immunostaining (>60% of the epithelial surface covered by bacteria); LM, scale bar = 20 μm.