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Pili distribution among Streptococcus pneumoniae associated with invasive disease in Portugal

Abstract number: P2002

Aguiar S., Serrano I., Pinto F.R., Melo-Cristino J., Ramirez M.

Objective: Evaluate the distribution of the pilus islet among Streptococcus pneumoniae isolated from invasive infections

Methods: Pilus-like structures were recently recognised in pneumococci and implicated in the virulence of this bacterium. These structures are encoded by the genes of the rlrA islet, and signature tagged mutagenesis studies implicated the rlrA gene, encoding a putative transcriptional regulator, as an essential virulence gene in murine models of infection. Nevertheless, the rlrA islet is not universally distributed among pneumococcal strains.

To evaluate the distribution of the pilus islet, we determined the presence of the rlrA gene as a marker for the locus, among a collection of invasive isolates recovered in Portugal between 1999 and 2002, and analysed its association with antibiotic resistance, capsular serotypes, clusters defined by pulsed-field gel electrophoretic profiles (PFGE) and multilocus sequence types.

Results: A minority of the isolates were positive for the presence of the rlrA gene (27%). Nevertheless, serotype distribution analysis showed a high correspondence between the serotype and the presence or absence of the rlrA gene (Wallace coefficient, W=0.778). Additionally, even within serotypes, variation of the presence of the pilus islet between PFGE clones was observed. A higher Wallace coefficient between PFGE clones and the presence of the locus (W=0.939) indicates that the presence of the islet is a clonal property of S. pneumoniae. Analysis of rlrA negative isolates revealed heterogeneity in the genomic region downstream of the pfl gene, the region where the islet is found in other isolates, compatible with recent loss of the islet in some lineages.

Conclusion: The low prevalence of the rlrA islet in our collection of invasive isolates indicates that pili are not essential virulence factors in human infections and that their potential use in a vaccine would offer limited benefits. However, its association with a widely disseminated pneumococcal clone (Spain9V-3) may indicate that pili could facilitate dissemination or colonisation of the host, as suggested recently. Nevertheless, since serotype prevalence is changing as a consequence of vaccine introduction, the acquisition of the pilus islet by emerging clones or the increase in incidence of clones carrying the rlrA islet may clarify the role of this surface structure in human infections.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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