Streptococcus suis is a frequent early colonizer of the upper respiratory tract of pigs, but it can also cause life-threatening diseases in pigs and humans. Despite its importance for pigs and as an emerging zoonotic pathogen, it is still unclear which mechanisms contribute to the invasive activity of colonizing S. suis strains in the respiratory tract. The cholesterol-dependent pore-forming toxin suilysin seems to be a major factor mediating streptococcal adherence to and bacterial invasion through epithelial cell barriers. However, it is still under debate how suilysin contributes to pathogenesis of S. suis infections in the respiratory tract, since most studies have been done with cell lines. Thus, we attempted to dissect the role of suilysin in pathogen interactions with primary respiratory cells using porcine precision-cut lung slices (PCLS). We infected PCLS with wild type and mutant strains or treated them with recombinant suilysin. Furthermore, we analysed effects of co-infections with Bordetella bronchiseptica, a common primary pathogen in S. suis infections. Our results clearly showed that suilysin contributes to bacterial adherence and invasion, and that it was essential for cytotoxicity. Furthermore, we found that suilysin was the key factor in induction of COX-2 and production of its metabolite prostaglandin E2, which are important in modulation of inflammation and immune activation. Finally, we could show that pre-infection with B. bronchiseptica promoted the cytotoxic effects of S. suis, probably by paving the way for its colonization. Currently, we investigate how the pore-forming and other activities of suilysin contribute to these effects.