Pili distribution among invasive pneumococci in Portugal after 7valent conjugate vaccine

Abstract number: O156

Aguiar S.I., Melo-Cristino J., Ramirez M.

Objective: Evaluate the distribution of the pilus islets among Streptococcus pneumoniae recovered from invasive infections after 7-valent vaccine availability.

Methods: Two pilus-like structures (PI-1 and PI-2) have been recently recognized in pneumococci. These have been implicated in virulence and suggested as potential vaccine targets. However these pilus-like structures are not universally distributed among pneumococcal strains. We had previously demonstrated that carrying PI-1 was a clonal property of S. pneumoniae and that only 27% of the invasive strains carried the rlrA islet. Furthermore, 83% of these piliated strains expressed vaccine serotypes. Similar findings were reported for the PI-2 islet which was shown to be present in 16% of a convenience sample of strains. PI-2 positive clonal complexes were associated with serotypes 1, 2, 7F, 19A, and 19F. The introduction of the 7-valent conjugate vaccine (PCV7) resulted in changes in serotype frequency that can also affect pili prevalence. To evaluate this effect we determined the presence of PI-1 and PI-2 among a collection of 475 invasive isolates recovered from children after PCV7 introduction (2003–2008). The results were analyzed in terms of pilus islet association with antibiotic resistance, serotype, pulsed-field gel electrophoretic profile (PFGE) and multilocus sequence type.

Results: Overall, 46.7% of the strains presented one of the pilus islet. As observed in previous studies serotype distribution analysis showed a high correspondence between serotype and the presence and type of pili (Wallace coefficient, W = 0.85). This association was even higher when considering pili and PFGE cluster (W = 0.98). The rlrA islet was identified in 13% of the strains most of them expressing serotype 6B, 9V, 14, 19A and 19F. PI-2 islet was found to be present in 37% of the pneumococcal strains and was identified mainly among serotypes 1 and 7F.

Conclusion: A decrease in the presence of the rlrA islet among invasive pneumococcal strains was observed after PCV7 availability. This change is associated with the decrease of vaccine serotypes since the majority of the strains carrying PI-1 expressed vaccine serotypes. In contrast, PI-2 islet was more prevalent due to the predominance of serotypes 1 and 7F. Since most of the strains carrying pili presented serotypes that are included either in current or future conjugate vaccine formulations, their potential use in a vaccine would offer limited additional benefits.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
Back to top