Ocular virulence of capsule-deficient streptococcus pneumoniae in a rabbit keratitis model

Area of Science:

• Microbiology
• Ophthalmology
• Infectious Diseases

Background:

• Streptococcus pneumoniae is a leading cause of bacterial keratitis.
• The role of the bacterial capsule in S. pneumoniae virulence is well-established.
• Nonencapsulated strains are often considered less virulent, but their ocular pathogenicity requires further investigation.

Purpose of the Study:

• To determine the ocular virulence of noncapsular Streptococcus pneumoniae.
• To compare the virulence of encapsulated and noncapsular S. pneumoniae strains in a rabbit keratitis model.
• To assess the role of the capsule in S. pneumoniae pathogenesis.

Main Methods:

• Infection of mice with encapsulated (Avery's strain) and noncapsular (strain R6) S. pneumoniae to monitor mortality.
• Intracorneal inoculation of rabbit eyes with both strains (10^5 CFUs).
• Quantification of bacterial loads in corneas at 20 and 48 hours post-infection.
• Slit-lamp examination (SLE) of rabbit eyes at 24, 36, and 48 hours to assess pathology.

Main Results:

• The noncapsular strain demonstrated significant ocular virulence in rabbits, causing similar pathological effects to the encapsulated strain.
• Bacterial loads were comparable between strains at 20 hours, but significantly higher for the encapsulated strain at 48 hours.
• In contrast, the encapsulated strain caused 100% mortality in mice, while the noncapsular strain was avirulent.

Conclusions:

• Noncapsular Streptococcus pneumoniae exhibits significant ocular virulence, comparable to its encapsulated counterpart in a rabbit keratitis model.
• The bacterial capsule is critical for systemic virulence in mice but not for establishing ocular infection in rabbits.
• These findings underscore the complex role of the S. pneumoniae capsule in host-specific pathogenesis.