Most bacterial pathogens have long filamentous structures known as pili or fimbriae extending from their surface. These structures are often involved in the initial adhesion of the bacteria to host tissues during colonization. In gram-negative bacteria, pili are typically formed by non-covalent interactions between pilin subunits. By contrast, the recently discovered pili in gram-positive pathogens are formed by covalent polymerization of adhesive pilin subunits. Evidence from studies of pili in the three principal streptococcal pathogens of humans indicates that the genes that encode the pilin subunits and the enzymes that are required for the assembly of these subunits into pili have been acquired en bloc by the horizontal transfer of a pathogenicity island.
olate dispersal behavior to the landscape level (17, 21,27,28). Explicit tests of such models are needed (18). The tight fit between observed and predicted patterns of seed rain in our habitat patches provides strong support for the key assumption that small-scale behavioral responses can drive landscape-scale distributional patterns. From a conservation perspective, impacts of corridors can be predicted on the basis of behaviors that are relatively simple to measure (29).
The 2,160,267 bp genome sequence of Streptococcus agalactiae, the leading cause of bacterial sepsis, pneumonia, and meningitis in neonates in the U.S. and Europe, is predicted to encode 2,175 genes. Genome comparisons among S. agalactiae, Streptococcus pneumoniae, Streptococcus pyogenes, and the other completely sequenced genomes identified genes specific to the streptococci and to S. agalactiae. These in silico analyses, combined with comparative genome hybridization experiments between the sequenced serotype V strain 2603 V͞R and 19 S. agalactiae strains from several serotypes using whole-genome microarrays, revealed the genetic heterogeneity among S. agalactiae strains, even of the same serotype, and provided insights into the evolution of virulence mechanisms. Streptococcus agalactiae, or group B Streptococcus, is the leading cause of bacterial sepsis, pneumonia, and meningitis in neonates in the U.S. and Europe. Although S. agalactiae usually behaves as a commensal organism that colonizes the gastrointestinal or genital tract of 25-40% of healthy women, it can cause life-threatening invasive infection in susceptible hosts: newborn infants, pregnant women, and nonpregnant adults with underlying chronic illnesses (1, 2). Since guidelines recommending intrapartum antibiotic prophylaxis for high-risk or colonized women were issued in 1996 (3), the incidence of neonatal infections has decreased, and invasive S. agalactiae infections in immunocompromised adults have become more common. Adult disease now accounts for the majority of serious S. agalactiae infections. First recognized as a pathogen in bovine mastitis, S. agalactiae is distinguished from other pathogenic streptococci by the cell wall-associated group B carbohydrate.Another polysaccharide constitutes the organism's capsule, an important S. agalactiae virulence determinant. S. agalactiae strains of capsular serotype V were rarely isolated before the mid-1980s but now account for approximately one-third of clinical isolates in the U.S. (4-6). Type V is the most common capsular serotype associated with invasive infection in nonpregnant adults, and the emergence of type V strains over the past decade has been temporally linked to an increase in S. agalactiae disease in this population (7). As a species, S. agalactiae shares certain features with other pathogenic streptococci; however, the precise repertoire of shared and unique attributes that account for the emergence of S. agalactiae as a major pathogen for specific human populations remains undefined. To elucidate the molecular basis for S. agalactiae virulence, we determined the complete genome sequence (8) of the recent clinical type V isolate 2603 V͞R (www.tigr.org) and performed comparative analyses with other S. agalactiae strains and with other species of pathogenic streptococci. Methods ORF Prediction and Gene Identification.ORFs were predicted by GLIMMER (9, 10) trained with ORFs larger than 600 bp from the genomic sequence and S. agalactiae genes available in GenBank. All predicted proteins la...
SummaryWe have recently reported the presence of covalently linked pilus-like structures in the human pathogen, Group B Streptococcus (GBS). The pilus operon codes for three proteins which contain the conserved amino acid motif, LPXTG, associated with cell wall-anchored proteins together with two genes coding for sortase enzymes. Analysis of the eight sequenced genomes of GBS has led to the identification of a second, related genomic island of which there are two variants, each containing genes coding for proteins with LPXTG motifs and sortases. Here we show that both variant islands also code for pilus-like structures. Furthermore, we provide a thorough description and characterization of the genomic organization of the islands and the role of each protein in the assembly of the pili. For each pilus, polymerization of one of the three component proteins is essential for incorporation of the other two proteins into the pilus structure. In addition, two sortases are required for complete pilus assembly, each with specificity for one of the pilus components. A component protein of one of the newly identified pili is also a previously identified protective antigen and a second component of this pilus is shown to confer protection against GBS challenge. We propose that pilus-like structures are important virulence factors and potential vaccine candidates.
International audienceStreptococcus agalactiae (Group B Streptococcus, GBS) is a commensal of the digestive and genitourinary tracts of humans that emerged as the leading cause of bacterial neonatal infections in Europe and North America during the 1960s. Due to the lack of epidemiological and genomic data, the reasons for this emergence are unknown. Here we show by comparative genome analysis and phylogenetic reconstruction of 229 isolates that the rise of human GBS infections corresponds to the selection and worldwide dissemination of only a few clones. The parallel expansion of the clones is preceded by the insertion of integrative and conjugative elements conferring tetracycline resistance (TcR). Thus, we propose that the use of tetracycline from 1948 onwards led in humans to the complete replacement of a diverse GBS population by only few TcR clones particularly well adapted to their host, causing the observed emergence of GBS diseases in neonates
Pili are essential virulence factors in many Gram-negative bacteria; however, they have not been described in most important Gram-positive pathogens. While screening the sequence of multiple genomes of Group B Streptococcus , we identified protective antigens that formed high molecular weight polymers. Immunogold electron microscopy revealed that the structures have a pilus-like form. These large structures have gone unrecognized in decades of studies of Group B Streptococcus .
SummaryGroup A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive human pathogen responsible for several acute diseases and autoimmune sequelae that account for half a million deaths worldwide every year. GAS infections require the capacity of the pathogen to adhere to host tissues and assemble in cell aggregates. Furthermore, a role for biofilms in GAS pathogenesis has recently been proposed. Here we investigated the role of GAS pili in biofilm formation. We demonstrated that GAS pilusnegative mutants, in which the genes encoding either the pilus backbone structural protein or the sortase C1 have been deleted, showed an impaired capacity to attach to a pharyngeal cell line. The same mutants were much less efficient in forming cellular aggregates in liquid culture and microcolonies on human cells. Furthermore, mutant strains were incapable of producing the typical three-dimensional layer with bacterial microcolonies embedded in a carbohydrate polymeric matrix. Complemented mutants had an adhesion and aggregation phenotype similar to the wild-type strain. Finally, in vivo expression of pili was indirectly confirmed by demonstrating that most of the sera from human patients affected by GASmediated pharyngitis recognized recombinant pili proteins. These data support the role of pili in GAS adherence and colonization and suggest a general role of pili in all pathogenic streptococci.
We recently described the presence of 3 pilus variants in the human pathogen group B streptococcus (GBS; also known as Streptococcus agalactiae), each encoded by a distinct pathogenicity island, as well as the ability of pilus components to elicit protection in mice against homologous challenge. To determine whether a vaccine containing a combination of proteins from the 3 pilus types could provide broad protection, we analyzed pili distribution and conservation in 289 clinical isolates. We found that pilus sequences in each island are conserved, all strains carried at least 1 of the 3 islands, and a combination of the 3 pilus components conferred protection against all tested GBS challenge strains. These data are the first to indicate that a vaccine exclusively constituted by pilus components can be effective in preventing infections caused by GBS, and they pave the way for the use of a similar approach against other pathogenic streptococci.
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