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      The frequency of genes encoding three putative group B streptococcal virulence factors among invasive and colonizing isolates

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          Abstract

          Background

          Group B Streptococcus (GBS) causes severe infections in very young infants and invasive disease in pregnant women and adults with underlying medical conditions. GBS pathogenicity varies between and within serotypes, with considerable variation in genetic content between strains. Three proteins, Rib encoded by rib, and alpha and beta C proteins encoded by bca and bac, respectively, have been suggested as potential vaccine candidates for GBS. It is not known, however, whether these genes occur more frequently in invasive versus colonizing GBS strains.

          Methods

          We screened 162 invasive and 338 colonizing GBS strains from different collections using dot blot hybridization to assess the frequency of bca, bac and rib. All strains were defined by serotyping for capsular type, and frequency differences were tested using the Chi square test.

          Results

          Genes encoding the beta C protein ( bac) and Rib ( rib) occurred at similar frequencies among invasive and colonizing isolates, bac (20% vs. 23%), and rib (28% vs. 20%), while the alpha ( bca) C protein was more frequently found in colonizing strains (46%) vs, invasive (29%). Invasive strains were associated with specific serotype/gene combinations.

          Conclusion

          Novel virulence factors must be identified to better understand GBS disease.

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          Most cited references32

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          Genome analysis of multiple pathogenic isolates of Streptococcus agalactiae: implications for the microbial "pan-genome".

          The development of efficient and inexpensive genome sequencing methods has revolutionized the study of human bacterial pathogens and improved vaccine design. Unfortunately, the sequence of a single genome does not reflect how genetic variability drives pathogenesis within a bacterial species and also limits genome-wide screens for vaccine candidates or for antimicrobial targets. We have generated the genomic sequence of six strains representing the five major disease-causing serotypes of Streptococcus agalactiae, the main cause of neonatal infection in humans. Analysis of these genomes and those available in databases showed that the S. agalactiae species can be described by a pan-genome consisting of a core genome shared by all isolates, accounting for approximately 80% of any single genome, plus a dispensable genome consisting of partially shared and strain-specific genes. Mathematical extrapolation of the data suggests that the gene reservoir available for inclusion in the S. agalactiae pan-genome is vast and that unique genes will continue to be identified even after sequencing hundreds of genomes.
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            Genome sequence of Streptococcus agalactiae, a pathogen causing invasive neonatal disease.

            Streptococcus agalactiae is a commensal bacterium colonizing the intestinal tract of a significant proportion of the human population. However, it is also a pathogen which is the leading cause of invasive infections in neonates and causes septicaemia, meningitis and pneumonia. We sequenced the genome of the serogroup III strain NEM316, responsible for a fatal case of septicaemia. The genome is 2 211 485 base pairs long and contains 2118 protein coding genes. Fifty-five per cent of the predicted genes have an ortholog in the Streptococcus pyogenes genome, representing a conserved backbone between these two streptococci. Among the genes in S. agalactiae that lack an ortholog in S. pyogenes, 50% are clustered within 14 islands. These islands contain known and putative virulence genes, mostly encoding surface proteins as well as a number of genes related to mobile elements. Some of these islands could therefore be considered as pathogenicity islands. Compared with other pathogenic streptococci, S. agalactiae shows the unique feature that pathogenicity islands may have an important role in virulence acquisition and in genetic diversity.
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              Complete genome sequence and comparative genomic analysis of an emerging human pathogen, serotype V Streptococcus agalactiae.

              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 V/R 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.
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                Author and article information

                Journal
                BMC Infect Dis
                BMC Infectious Diseases
                BioMed Central (London )
                1471-2334
                2006
                17 July 2006
                : 6
                : 116
                Affiliations
                [1 ]National Food Safety and Toxicology Center and Department of Pediatrics and Human Development, Michigan State University, East Lansing, Michigan, USA
                [2 ]Department of Preventive Medicine, Eulji University School of Medicine, Daejeon, Korea
                [3 ]Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, Michigan, USA
                [4 ]Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, Bacterial Zoonoses Branch, Fort Collins, Colorado, USA
                [5 ]Fargo Veterans Administration Medical Center, Fargo, North Dakota, USA
                [6 ]Department of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
                Article
                1471-2334-6-116
                10.1186/1471-2334-6-116
                1559624
                16846499
                7f93e096-7c0d-498d-a432-fb0779289cea
                Copyright © 2006 Manning et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 7 March 2006
                : 17 July 2006
                Categories
                Research Article

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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