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

The invasion of epithelial cells by streptococci involves bacterial uptake by a dynamic process of membrane reorganization, possibly related to the formation of membrane ruffles that have been observed in S. suis infected HEp-2 cells 39 . This uptake mechanism is suilysin-dependent. As suilysin is a soluble protein, the high efficiency of this process in the case of ALI cultures can be explained by the higher local concentration of this protein in the absence of apical medium. In the case of immortalized cells, suilysin produced by S. suis is immediately diluted by the medium and, thus, a homogeneous and low concentration of the protein is available for interaction with the cell surface. By contrast, suilyin released from S. suis to the apical side of airway epithelial cells in ALI cultures will not be diluted by the culture medium and, thus, can accumulate and be active on the site where it is released from the bacteria.