Specific Involvement of Pilus Type 2a in Biofilm Formation in Group B Streptococcus

Abstract

Streptococcus agalactiae is the primary colonizer of the anogenital mucosa of up to 30% of healthy women and can infect newborns during delivery and cause severe sepsis and meningitis. Persistent colonization usually involves the formation of biofilm and increasing evidences indicate that in pathogenic streptococci biofilm formation is mediated by pili. Recently, we have characterized pili distribution and conservation in 289 GBS clinical isolates and we have shown that GBS has three pilus types, 1, 2a and 2b encoded by three corresponding pilus islands, and that each strain carries one or two islands. Here we have investigated the capacity of these strains to form biofilms. We have found that most of the biofilm-formers carry pilus 2a, and using insertion and deletion mutants we have confirmed that pilus type 2a, but not pilus types 1 and 2b, confers biofilm-forming phenotype. We also show that deletion of the major ancillary protein of type 2a did not impair biofilm formation while the inactivation of the other ancillary protein and of the backbone protein completely abolished this phenotype. Furthermore, antibodies raised against pilus components inhibited bacterial adherence to solid surfaces, offering new strategies to prevent GBS infection by targeting bacteria during their initial attachment to host epithelial cells.

CsrRS and Environmental pH Regulate Group B Streptococcus Adherence to Human Epithelial Cells and Extracellular Matrix

“…Biofilm assays were performed with 96-well polystyrene flat-bottom microtiter plates (Costar) essentially as described previously (18,30). GBS cultures grown overnight were diluted 1:20 in fresh LB medium containing 1% glucose.…”

“…Biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface, typically embedded within a self-produced matrix of exopolysaccharide, proteins, and nucleic acids. GBS bacteria have been isolated from the population of biofilm-forming bacteria on intrauterine devices (5) and have been shown to form biofilms on abiotic and cell surfaces in vitro (17,18,30). Biofilm formation by GBS appears to be associated with the production of PI-2a pili but not with the production of PI-1 or PI-2b (18,30).…”

“…Some enzymes and transport binding proteins also have been suggested to be involved in GBS adherence through various mechanisms (16,22,27,29,47). GBS pili also have been shown to contribute to adherence, although recent work suggests that adherence and biofilm formation may be exclusively functions of PI-2a pili and not of PI-1 or PI-2b pili (30).…”

Regulation and Function of Pilus Island 1 in Group B Streptococcus

“…A detailed investigation of the contribution of pili to biofilm formation concluded that PI-2a pili, but not PI-1 or PI-2b pili, mediate formation of biofilms on both abiotic and biotic surfaces (27). Another study, using the background of type III GBS strain NEM316, found no role for BP-2a (PilB) in resistance to phagocytosis and intracellular killing by macrophages, in contrast to earlier work (19,23).…”

Structure-based approach to rationally design a chimeric protein for an effective vaccine against Group B Streptococcus infections

“…The most promising protein vaccine candidates selected so far are the structural subunits of pili that are long filamentous structures protruding from the bacterial surface (5-8), which play a key role in bacterial virulence and pathogenesis (9)(10)(11)(12)(13). Extensive analysis of a large panel of GBS isolates has revealed the presence of three pilus islands, PI-1, PI-2a, and PI-2b.…”