Pneumolysin Produced By Streptococcus-Pneumoniae Damages Human Respiratory Epithelium Invitro

Streptococcus pneumoniae is an important human pathogen responsible for lower respiratory tract infections, septicemia, and meningitis. It elaborates a number of proteins, including a hemolytic thiol-activated toxin called pneumolysin. We studied the effect of S pneumoniae culture filtrates on biopsy specimens of human respiratory epithelium in vitro by a photometric technique which measures ciliary beat frequency (CBF), and by transmission electron microscopy. Broth culture filtrates from 11 of 15 clinical isolates caused significant (p<0.001) slowing (16 to 48% control) of CBF. This slowing was associated with disruption of the integrity of epithelium structure, cell vacuolation, and death. The cilioinhibitory activity was heat labile and was absent from broth during log phase growth but then increased, reaching a maximum after 16 h, when the hemolytic titer of the filtrate was also maximal. Gel filtration of a culture filtrate, which had been concentrated by dialysis against propylene glycol, yielded a single peak of cilioinhibitory activity corresponding to the fractions containing hemolytic activity. Recombinant pneumolysin purified from Escherichia coli harboring a plasmid carrying the pneumolysin gene, caused dose-dependent (5-50 μg/ml) slowing of CBF and the same ultrastructural changes observed with culture filtrate. The addition of serum from a rabbit immunized with pneumolysin to a culture filtrate neutralized its cilioinhibitory properties, while the addition of serum obtained prior to immunization had no effect.