Association of the pneumococcal pilus with certain capsular serotypes but not with increased virulence

Area of Science:

• Microbiology
• Vaccinology
• Genetics

Background:

• A mobile genetic element encoding a pilus-like structure in Streptococcus pneumoniae has been discovered.
• This pilus has demonstrated a role in virulence in mouse models.
• The pilus has been proposed as a candidate for a pneumococcal vaccine.

Purpose of the Study:

• To determine the frequency of the pneumococcal pilus (rrgC gene) in Streptococcus pneumoniae.
• To analyze the association of the pilus with virulence, capsular serotypes, and multilocus sequence types.
• To assess the impact of the pneumococcal conjugate vaccine on pilus prevalence.

Main Methods:

• Analysis of the rrgC gene frequency in the American Indian pneumococcal collection and isolates from Children's Hospital Boston.
• Comparison of rrgC prevalence between nasopharyngeal and sterile site isolates.
• Association analysis with capsular serotypes and multilocus sequence types.
• Evaluation of rrgC frequency changes before and after the introduction of the pneumococcal conjugate vaccine.

Main Results:

• The rrgC gene was present in 21.4% of strains in the American Indian collection, with no difference between nasopharyngeal and sterile site isolates.
• Vaccine-type strains were significantly more likely to possess the pilus gene (P < 0.001).
• High concordance (95%) was observed between multilocus sequence type and the presence or absence of rrgC.
• The frequency of rrgC significantly decreased after 2000 in isolates from Children's Hospital Boston (42.8% before vs. 21.3% after, P = 0.019).

Conclusions:

• The pneumococcal pilus is present in a minority of Streptococcus pneumoniae strains.
• The pilus is associated with specific serotypes and exhibits high genetic linkage with multilocus sequence types.
• The prevalence of the pneumococcal pilus has been reduced by the conjugate pneumococcal vaccine.