Intracellular localization of two different H. parasuis strains: F9 (non-virulent strain) and PC4-6P (virulent strain) within the endosomal network of PAM. After 1 h of incubation with PAM, bacteria were labelled with a rabbit anti-H. parasuis hyperimmune serum followed by an anti-rabbit-FITC (green signal) and nuclei were counterstained with DAPI (blue signal). The upper panels show the co-localization between F9 (left panel) or PC4-6P (right panel) and the early endosomal marker EEA1. EEA1 was stained with goat anti-EEA1 and anti-goat-Cy3 (red) antibodies. The lower panels show the co-localization between F9 (arrow in the left panel) or PC4-6P (detail in the inset in the right panel) and the acidic lysosomes stained with LysoTracker Red DND-99 (red signal). Percentages of co-localization are indicated in each panel. Scale bars, 5 μm. The images showing the individual fluorescences are presented in Additional file 1: Figure S1.