title: RrgA is a pilus-associated adhesin in Streptococcus pneumoniae.
abstract: Adherence to host cells is important in microbial colonization of a mucosal surface, and Streptococcus pneumoniae adherence was significantly enhanced by expression of an extracellular pilus composed of three subunits, RrgA, RrgB and RrgC. We sought to determine which subunit(s) confers adherence. Bacteria deficient in RrgA are significantly less adherent than wild-type organisms, while overexpression of RrgA enhances adherence. Recombinant monomeric RrgA binds to respiratory cells, as does RrgC with less affinity, and pre-incubation of epithelial cells with RrgA reduces adherence of wild-type piliated pneumococci. Non-adherent RrgA-negative, RrgB- and RrgC-positive organisms produce pili, suggesting that pilus-mediated adherence is due to expression of RrgA, rather than the pilus backbone itself. In contrast, RrgA-positive strains with disrupted rrgB and rrgC genes exhibit wild-type adherence despite failure to produce pili by Western blot or immunoelectron microscopy. The density of bacteria colonizing the upper respiratory tract of mice inoculated with piliated RrgA-negative pneumococci was significantly less compared with wild-type; in contrast, non-piliated pneumococci expressing non-polymeric RrgA had similar numbers of bacteria in the nasopharynx as piliated wild-type bacteria. These data suggest that RrgA is central in pilus-mediated adherence and disease, even in the absence of polymeric pilus production.
authors.affiliation: Swedish Institute for Infectious Disease Control and Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: A L
authors.initials: AL
authors.lastname: Nelson
authors.forename: J
authors.initials: J
authors.lastname: Ries
authors.forename: F
authors.initials: F
authors.lastname: Bagnoli
authors.forename: S
authors.initials: S
authors.lastname: Dahlberg
authors.forename: S
authors.initials: S
authors.lastname: Fälker
authors.forename: S
authors.initials: S
authors.lastname: Rounioja
authors.forename: J
authors.initials: J
authors.lastname: Tschöp
authors.forename: E
authors.initials: E
authors.lastname: Morfeldt
authors.forename: I
authors.initials: I
authors.lastname: Ferlenghi
authors.forename: M
authors.initials: M
authors.lastname: Hilleringmann
authors.forename: D W
authors.initials: DW
authors.lastname: Holden
authors.forename: R
authors.initials: R
authors.lastname: Rappuoli
authors.forename: S
authors.initials: S
authors.lastname: Normark
authors.forename: M A
authors.initials: MA
authors.lastname: Barocchi
authors.forename: B
authors.initials: B
authors.lastname: Henriques-Normark
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001422:Bacterial Adhesion / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D004847:Epithelial Cells / Q000382:microbiology; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D016253:Microscopy, Immunoelectron; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D018829:Adhesins, Bacterial; D011994:Recombinant Proteins; D036781:Fimbriae Proteins