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.
Highlights
A number of studies have revealed that many bacteria and fungi exist predominantly as surface-attached multicellular communities, commonly referred to as biofilms, embedded in bacterialderived extracellular matrix typically containing exopolysaccharides, proteins and nucleic acids
Since growth medium composition influences the capacity to form biofilm in other streptococci [31,32], GBS strain 515 was cultured under static conditions in Todd Hewitt Broth (THB), a standard streptococcal growth medium, and in THB supplemented with increasing concentrations of glucose and biofilm formation was assessed after 18 hours of growth
Since asymptomatic colonization of maternal vaginal mucosa by GBS is the major risk factor for sepsis and meningitis in newborns, and since GBS is decorated with pili, it was of interest to investigate the possible role of pili in GBS colonization and biofilm formation
Summary
A number of studies have revealed that many bacteria and fungi exist predominantly as surface-attached multicellular communities, commonly referred to as biofilms, embedded in bacterialderived extracellular matrix typically containing exopolysaccharides, proteins and nucleic acids. Biofilm development is a multistep process, in which component cells acquire phenotypes that are distinct from their planktonic (or free-floating) counterparts, and is considered critical for numerous bacterial infections [1]. To switch from the planktonic to sessile lifestyle bacteria have to undergo a series of genetically regulated events and several studies have indicated that biofilm formation proceeds through a five-stage developmental program. The study of bacteria residing in biofilms as an interactive community rather than free-living planktonic cells has recently gained much attention as a result of a recent estimate by the Centers for Disease Control and Prevention that more than 65% of human bacterial infections involve biofilms [3]. Many species of streptococci are known to form biofilms [4]
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