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Journal of Bacteriology, August 2008, p. 5480-5492, Vol. 190, No. 15
0021-9193/08/$08.00+0     doi:10.1128/JB.00384-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

A Second Pilus Type in Streptococcus pneumoniae Is Prevalent in Emerging Serotypes and Mediates Adhesion to Host Cells

Fabio Bagnoli,^1, Monica Moschioni,^1, Claudio Donati,¹ Valentina Dimitrovska,¹ Ilaria Ferlenghi,¹ Claudia Facciotti,¹ Alessandro Muzzi,¹ Fabiola Giusti,² Carla Emolo,¹ Antonella Sinisi,¹ Markus Hilleringmann,¹ Werner Pansegrau,¹ Stefano Censini,¹ Rino Rappuoli,¹ Antonello Covacci,¹ Vega Masignani,¹ and Michele A. Barocchi^1*

Department of Cellular Microbiology and Bioinformatics, Novartis Vaccines,¹ Department of Evolutionary Biology, University of Siena, Siena 53100, Italy²

Received 17 March 2008/ Accepted 21 May 2008

Analysis of publicly available genomes of Streptococcus pneumoniae has led to the identification of a new genomic element containing genes typical of gram-positive pilus islets (PIs). Here, we demonstrate that this genomic region, herein referred to as PI-2 (consisting of pitA, sipA, pitB, srtG1, and srtG2) codes for a second functional pilus in pneumococcus. Polymerization of the PI-2 pilus requires the backbone protein PitB as well as the sortase SrtG1 and the signal peptidase-like protein SipA. Presence of PI-2 correlates with the genotype as defined by multilocus sequence typing and clonal complex (CC). The PI-2-positive CCs are associated with serotypes 1, 2, 7F, 19A, and 19F, considered to be emerging serotypes in both industrialized and developing countries. Interestingly, strains belonging to CC271 (where sequence type 271 is the predicted founder of the CC) contain both PI-1 and PI-2, as revealed by genome analyses. In these strains both pili are surface exposed and independently assembled. Furthermore, in vitro experiments provide evidence that the pilus encoded by PI-2 of S. pneumoniae is involved in adherence. Thus, pneumococci encode at least two types of pili that play a role in the initial host cell contact to the respiratory tract and are potential antigens for inclusion in a new generation of pneumococcal vaccines.

Published ahead of print on 30 May 2008.

F.B. and M.M. contributed equally to this work.