Interaction of pneumolysin-sufficient and -deficient isogenic variants of Streptococcus pneumoniae with human respiratory mucosa

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, and pneumolysin, a hemolytic toxin, is thought to be an important virulence factor. We have studied the interaction of a pneumolysin-sufficient type II S. pneumoniae strain (PL+) and an otherwise identical pneumolysin-deficient derivative (PL-) with human respiratory mucosa in an organ culture with an air interface for up to 48 h. Ciliary beat frequency (CBF) was measured by a photometric technique, and adherence to and invasion of the epithelium were assessed by scanning and transmission electron microscopy. PL+ and PL- caused a progressive fall in CBF compared with the control which became significant (P < 0.01) at 24 h for PL+ and at 48 h for PL-. At 24 h, there was a significant increase in the percentage of the mucosa of the organ culture that was damaged for PL+ compared with the control (P < 0.01) and PL- (P < 0.02). At 48 h, there was a significant increase in mucosal damage for both PL+ (P < 0.005) and PL- (P < 0.05) compared with the control. At 24 and 48 h, PL+ and PL- adhered predominantly to mucus and damaged cells. PL+ infection alone caused separation of tight junctions between epithelial cells, and at 48 h PL+ cells were adherent to the separated edges of otherwise healthy unciliated cells. PL+ and PL- both caused damage to the epithelial cell ultrastructure. S. pneumoniae infection caused patchy damage to the respiratory mucosa and a lowered CBF. These changes were more severe and occurred earlier with the pneumolysin-sufficient variant.