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The effect of Streptococcus pneumoniae pneumolysin on human respiratory epithelium in vitro
C Feldman1, T J Mitchell, P W Andrew
1Department of Thoracic Medicine, National Heart and Lung Institute, London, U.K.
Abstract:
Streptococcus pneumoniae culture filtrates and pneumolysin both slow human ciliary beating and damage respiratory epithelium in vitro. A polyclonal pneumolysin antibody bound to sepharose beads removed pneumolysin from culture filtrates and showed that pneumolysin alone was responsible for the effects on epithelium. In a 48-h organ culture pneumolysin caused ciliary slowing and epithelial disruption in a dose-dependent manner down to 5 ng/ml. Comparison of the ciliary slowing activity and pneumolysin concentration in filtrates in a continuous broth culture showed a maximal effect at 16 h (pneumolysin 7.5 micrograms/ml). Later the activity decreased while the pneumolysin concentration increased (8.8 micrograms/ml). This loss of activity was prevented by neutralisation of the acid pH of the culture medium. Eight different culture filtrates produced significant (P less than 0.05) ciliary slowing which correlated (r = 0.95) with simultaneously measured haemolytic (pneumolysin) activity. Substitution of tryptophan (position 433) by phenylalanine reduced the haemolytic and ciliary slowing activity of pneumolysin, but did not affect its ability to activate complement. There was no correlation between the ciliary slowing produced by the culture filtrate and that produced by the autolysate of a particular strain, nor between ciliary slowing and the extent of autolysis or the serotype of the strain.
Insights
Pneumolysin, a toxin from Streptococcus pneumoniae, damages respiratory epithelium and slows ciliary beating. This study confirms pneumolysin is the sole cause of these effects, crucial for understanding lung infections.
Area of Science:
- Microbiology
- Respiratory Medicine
- Toxicology
Background:
- Streptococcus pneumoniae is a major cause of respiratory infections.
- Pneumolysin is a key virulence factor produced by S. pneumoniae.
- The effects of pneumolysin on respiratory epithelium and ciliary function are not fully understood.
Purpose of the Study:
- To investigate the role of pneumolysin in damaging respiratory epithelium and affecting ciliary beating.
- To quantify the dose-dependent effects of pneumolysin on ciliary function.
- To explore the relationship between pneumolysin activity, pH, and other bacterial factors.
Main Methods:
- In vitro organ culture of human respiratory epithelium.
- Use of polyclonal pneumolysin antibody for toxin neutralization.
- Measurement of ciliary beating frequency.
- Quantification of pneumolysin concentration and hemolytic activity.
- pH monitoring of culture medium.
Main Results:
- Pneumolysin alone, isolated from culture filtrates, caused dose-dependent ciliary slowing and epithelial damage.
- Significant effects were observed at concentrations as low as 5 ng/ml.
- Loss of ciliary slowing activity at later time points was linked to acidic pH, which was reversible upon neutralization.
- Ciliary slowing activity strongly correlated with hemolytic activity (r=0.95).
- A specific mutation (Trp433Phe) reduced toxin activity but not complement activation.
Conclusions:
- Pneumolysin is the primary virulence factor responsible for ciliary dysfunction and epithelial damage caused by Streptococcus pneumoniae.
- The activity of pneumolysin is pH-dependent, with acidic conditions reducing its impact on ciliary beating.
- Specific structural features of pneumolysin influence its hemolytic and ciliary slowing activities.