A pneumococcal pilus influences virulence and host inflammatory responses

Area of Science:

• Microbiology
• Infectious Diseases
• Bacterial Pathogenesis

Background:

• Streptococcus pneumoniae causes significant global morbidity and mortality.
• Invasive pneumococcal disease begins with bacterial attachment to respiratory epithelial cells.
• The role of surface appendages in pneumococcal adherence and virulence was not fully understood.

Purpose of the Study:

• To investigate the presence and function of pili in Streptococcus pneumoniae.
• To determine if pili contribute to bacterial adhesion, colonization, and disease progression.
• To assess the impact of pili on the host inflammatory response.

Main Methods:

• Genetic analysis to identify pilus-encoding genes (rlrA islet).
• Introduction of the rlrA islet into non-piliated strains.
• In vitro adherence assays with lung epithelial cells.
• In vivo murine models for colonization, pneumonia, and bacteremia.
• Measurement of host TNF response during infection.

Main Results:

• Pili-like appendages were identified in some clinical isolates of Streptococcus pneumoniae, encoded by the rlrA islet.
• Introduction of the rlrA islet led to pilus expression, enhanced adherence to lung cells, and improved competitive colonization in mice.
• Piliated strains exhibited increased virulence in pneumonia and bacteremia models and out-competed non-piliated mutants.
• Piliated pneumococci induced a higher TNF response during systemic infection.

Conclusions:

• Pili are novel adhesive organelles in Streptococcus pneumoniae that enhance bacterial adherence and virulence.
• Pili contribute to the pathogenesis of invasive pneumococcal disease, including colonization, pneumonia, and bacteremia.
• Pneumococcal pili modulate the host inflammatory response, potentially influencing disease severity.