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

well-differentiated airway epithelial cells by S. suis was first analyzed by determining bacterial adherence and colonization under ALI conditions. PTEC and PBEC were infected with encapsulated wt strain 10, its isogenic suilysin-deficient mutant strain 10Δ sly and the nonencapsulated suilysin-deficient mutant 10Δ cpsΔ sly. In addition we tested two complemented strains expressing suilysin with single amino-acid substitutions, one of which carried a silent mutation (suilysin derivative S148) and the other one which resulted in lack of cytolytic macropore formation (suilysin derivative W461F). The strains were generated by complementation of strain 10Δ sly with either of two point-mutated suilysin genes, designated strain cS148, and strain cW461F, respectively. We included those strains to confirm possible effects of suilysin by complementation (strain cS148) and to elucidate whether effects might require cytolyctic activity of the toxin or not (strain cW416F). In previous studies we observed that suilysin derivative W461F does not induce any cytolytic pores 39 , and that suilysin derivative S148 is similarly active as the wt suilysin (unpublished results).