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

PTEC and PBEC were infected with S. suis strains from the apical side at an multiplicity of infection (MOI) of 20. After 4 hours, cells were washed thoroughly to remove non-adherent bacteria, and from then on, cells were kept under ALI conditions for at least 72 hours. As shown in Figure S1 , at the indicated times colonizing bacteria on the apical side of cells were quantified by plating. The wt strain and all mutant strains were able to colonize the apical side of PBEC, since the bacterial numbers remained constant over the whole observation period of 72 hours. Similar results were obtained with PTEC (results not shown). No differences in bacterial growth were observed between the parental strain and the different mutants incubated with either of the two cell types (shown for PBEC in Figure S1 ). These results showed that S. suis can efficiently colonize the apical side of PTEC and PBEC under ALI conditions with similar kinetics. Our findings indicate that this culture system for well-differentiated airway epithelial cell can be applied to analyze S. suis infection in vitro.