Complete genome sequence and comparative genomic analysis of an emerging human pathogen, serotype VStreptococcus agalactiae

Abstract

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...

Variation in the Group BStreptococcusCsrRS Regulon and Effects on Pathogenicity

“…GBS strains used in this study included type Ia strain 515 (32) and type V strain 2603 (2603V/R) (30) and their derivative ⌬csrR and ⌬csrS mutants (12). GBS was grown in liquid culture in Todd-Hewitt broth (THB; Difco), on trypticase soy agar (TSA) supplemented with 5% defibrinated sheep blood (PML Microbiologicals), or on Todd-Hewitt agar supplemented with antibiotics and 5% defibrinated sheep blood.…”

“…In keeping with the adaptation of GBS to diverse host environments, the genome sequences of GBS strains 2603V/R (hereafter referred to as 2603) and NEM316 revealed 17 and 20 predicted TCS, respectively (9,30). Of these, the CsrRS (or CovRS) system has been investigated most thoroughly.…”

Complete sequence and comparative genome analysis of the dairy bacterium Streptococcus thermophilus

“…The dairy streptococcus must have followed a divergent evolutionary path from that of its pathogenic congeners, as it has adapted to a rather narrow, well-defined and constant ecological niche, milk. To obtain insight into this path and to assess the potential for virulence of this bacterium, we sequenced the genomes of two yogurt strains of S. thermophilus, and compared them to those of previously sequenced pathogenic streptococci [4][5][6][7][8][9] .…”

The staphylocoagulase family of zymogen activator and adhesion proteins

“…Domain organization of ZAAPs. SC homologs are S. agalactiae proteins CAD46494 [34]; NP_687847 [33]; SfbX, Streptococcus pyogenes fibronectin (FN)-binding protein [37]; and vWbp [32]. The sequence that directs cell-wall sorting of SfbX is indicated by a diamond; the RGD triplet is also indicated.…”

“…The ZAAPs, NP_687847 and CAD46494, are produced by strains of S. agalactiae which originated from neonatal infections and were initially identified by genome sequencing as novel proteins [33,34]. Preliminary results indicate that NP_687847 is a prothrombin activator with an unknown mechanism of activation [P. Panizzi and P. E. Bock, unpublished observations].…”