Efficient suilysin-mediated invasion and apoptosis in porcine respiratory epithelial cells after streptococcal infection under air-liquid interface conditions

Meng, Fandan; Wu, Nai-Huei; Seitz, Maren; Herrler, Georg; Valentin-Weigand, Peter

Aim of this study was to establish the ALI culture system as an infection model for analyzing bacterial infection of porcine well-differentiated respiratory epithelial cells. ALI cultures from porcine airway cells have only recently been described for infection studies with viruses such as influenza virus and adenovirus 23, 38 but not yet for bacterial infections. S. suis had been analyzed using a variety of immortalized respiratory epithelial cells 12,31,32,39,42 , PBEC were apically infected with approximately 1 × 10 7 CFU of S. suis wt, 10Δ sly, 10Δ cpsΔ sly, cW461F or cS148 respectively. After 4 h, cells were washed thoroughly to remove non-adherent bacteria, and then further incubated until 48 hpi under air-liquid interface conditions. The infection of PBEC (A-E) were immunostained for streptococci both before permeabilization to visualize adherent bacteria (yellow/green) and after permeabilization to visualize invasive bacteria (red). Nuclei were stained by DAPI (blue). Bars represent 25 μ m. To quantify invasive S. suis in PBEC (F), the percentage of intracellular bacteria was determined by comparing the red fluorescent bacterial signals from panels A to the total bacteria number. Results are expressed as means ± SEM and significance, indicated by ***(P < 0.0001), was determined using one-way-ANOVA and Tukey multiple comparison test. Experiments were performed at least three times.