Related Experiment Videos
Growth and virulence of a complement-activation-negative mutant of Streptococcus pneumoniae in the rabbit cornea
M K Johnson1, M C Callegan, L S Engel
1Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, LA 70112, USA.
Abstract:
Our previous work has demonstrated the importance of pneumolysin in the virulence of S. pneumoniae in a rabbit intracorneal model. This was accomplished by showing that deletion of the gene encoding pneumolysin resulted in reduced virulence, whereas restoration of the wild-type gene resulted in restoration of the virulent phenotype. To assess the importance of a particular domain in the pneumolysin molecule, we have now constructed a strain which produces a pneumolysin molecule which is hemolytic but which bears a site-specific mutation in the domain known to be associated with the complement-activating properties of this molecule. Comparison of the virulence of this strain with that of a strain bearing the wild-type gene showed statistically significantly lower total slit lamp examination (SLE) scores at 12, 18, 24, and 36 h (particularly with respect to fibrin formation), but no difference at 48 h. Determination of colony forming units (CFU) in eyes infected with the two strains showed approximately 10(6) bacteria per cornea until 36 h. Between 36 and 48 h, the bacteria were almost completely cleared with very few bacteria recoverable at the later time point. The loss of virulence observed with this mutation in the complement-activation domain of pneumolysin, though less than that observed with the gene deletion mutant, suggests that complement activation by pneumolysin has a significant role in the pathology observed in this model of corneal infection.
Insights
Pneumolysin
Area of Science:
- Microbiology
- Immunology
- Ophthalmology
Background:
- Pneumolysin is a key virulence factor in Streptococcus pneumoniae infections.
- Previous studies confirmed pneumolysin's role in a rabbit intracorneal model.
Purpose of the Study:
- To investigate the role of the complement-activation domain of pneumolysin in S. pneumoniae virulence.
- To assess the impact of a specific mutation within this domain on disease pathology.
Main Methods:
- Constructed a mutant S. pneumoniae strain producing hemolytic pneumolysin with a mutation in the complement-activation domain.
- Compared the virulence of the mutant strain to the wild-type strain in a rabbit intracorneal model.
- Assessed disease severity using slit lamp examination (SLE) scores and quantified bacterial load via colony-forming units (CFU).
Main Results:
- The mutant strain showed significantly reduced virulence, indicated by lower SLE scores, particularly concerning fibrin formation, at early time points (12-36 h).
- Bacterial load (CFU) remained high until 36 h for both strains, with significant clearance occurring between 36 and 48 h.
- No difference in virulence was observed at 48 h.
Conclusions:
- Complement activation by pneumolysin plays a significant role in the pathology of S. pneumoniae corneal infections.
- While a mutation in the complement-activation domain reduces virulence, the effect is less pronounced than complete gene deletion.
- This highlights the specific contribution of complement activation to S. pneumoniae-induced eye disease.