Genomic analysis reveals the molecular basis for capsule loss in the group B Streptococcus population

The human and bovine bacterial pathogen Streptococcus agalactiae (Group B Streptococcus, GBS) expresses a thick polysaccharide capsule that constitutes a major virulence factor and vaccine target. GBS can be classified into ten distinct serotypes differing in the chemical composition of their capsular polysaccharide. However, non-typeable strains that do not react with anti-capsular sera are frequently isolated from colonized and infected humans and cattle. To gain a comprehensive insight into the molecular basis for the loss of capsule expression in GBS, a collection of well-characterized non-typeable strains was investigated by genome sequencing. Genome based phylogenetic analysis extended to a wide population of sequenced strains confirmed the recently observed high clonality among GBS lineages mainly containing human strains, and revealed a much higher degree of diversity in the bovine population. Remarkably, non-typeable strains were equally distributed in all lineages. A number of distinct mutations in the cps operon were identified that were apparently responsible for inactivation of capsule synthesis. The most frequent genetic alterations were point mutations leading to stop codons in the cps genes, and the main target was found to be cpsE encoding the portal glycosyl trasferase of capsule biosynthesis. Complementation of strains carrying missense mutations in cpsE with a wild-type gene restored capsule expression allowing the identification of amino acid residues essential for enzyme activity

Dynamics of Streptococcus agalactiae Colonization in Women during and after Pregnancy and in Their Infants

The population dynamics of Streptococcus agalactiae (group B streptococci [GBS]) colonization of the vagina and anorectal area was investigated in a cohort of 77 Danish women during and after their pregnancy by a new sensitive method. The mean carriage rate among individual observations was 36%, and the cumulative carriage rate over the entire observation period was 54%. Examination of more than 1,500 GBS isolates by pulsed-field gel electrophoresis demonstrated that the GBS population was remarkably homogeneous and stable in each carrier. Virtually all carriers were colonized by a single GBS clone on all occasions spanning up to 2 years. Repeated detection of the same clone even in women who were recorded as intermittent carriers suggests that the actual carrier rate exceeds 50% but that fluctuations in the GBS proportions of the flora occasionally preclude their detection. Newborns and young infants usually carried the same GBS clone as their mothers. However, only twice were identical clones of GBS detected in different women in contrast to the observed clonal relationships of clinical isolates. These observations strongly suggest differences in the properties and epidemiology of virulent GBS clones compared to clones commonly carried by healthy individuals

Effect of Capsulation of Opportunistic Pathogenic Bacteria on Binding of the Pattern Recognition Molecules Mannan-Binding Lectin, L-Ficolin, and H-Ficolin

Mannan-binding lectin (MBL), L-ficolin, and H-ficolin are pattern recognition molecules of the innate immune system. We investigated their ability to bind to different serotypes and noncapsulated variants of two gram-positive bacterial species, Streptococcus pneumoniae and Staphylococcus aureus. MBL did not bind to capsulated S. aureus or capsulated S. pneumoniae but did bind to a noncapsulated S. aureus variant (Wood). L-ficolin bound to some capsulated S. aureus serotypes (serotypes 1, 8, 9, 11, and 12) and capsulated S. pneumoniae serotypes (11A, 11D, and 11F) but not to noncapsulated strains. H-ficolin did not bind to any of the S. pneumoniae and S. aureus serotypes included in this study but did bind to one strain of Aerococcus viridans. The concentrations of the three proteins in 97 plasma samples were estimated. The median concentrations were 0.8 μg per ml for MBL, 3.3 μg per ml for L-ficolin, and 18.4 μg per ml for H-ficolin

Ascariasis Is a Zoonosis in Denmark

A preliminary epidemiological survey indicated an association between Ascaris infections in Danish patients and contact with pigs or pig manure. In the present study, we compared Ascaris worms collected from humans and Ascaris worms collected from pigs by amplified fragment length polymorphism (AFLP) analysis, a technique for whole-genome fingerprinting, and by PCR-linked restricted fragment length polymorphism (PCR-RFLP) analysis of the internal transcribed spacer region of nuclear rDNA. The AFLP data were analyzed by distance- and model-based clustering methods. These results assigned Ascaris worms from Danish patients to a cluster different from that for worms from humans in other geographic areas. In contrast, worms from humans and pigs in Denmark were assigned to the same cluster. These results were supported by the PCR-RFLP results. Thus, all of the examined Danish patients had acquired Ascaris infections from domestic pigs; ascariasis may therefore be considered a zoonotic disease in Denmark

Genomic Analysis Reveals the Molecular Basis for Capsule Loss in the Group B <i>Streptococcus</i> Population

<div><p>The human and bovine bacterial pathogen <i>Streptococcus agalactiae</i> (Group B Streptococcus, GBS) expresses a thick polysaccharide capsule that constitutes a major virulence factor and vaccine target. GBS can be classified into ten distinct serotypes differing in the chemical composition of their capsular polysaccharide. However, non-typeable strains that do not react with anti-capsular sera are frequently isolated from colonized and infected humans and cattle. To gain a comprehensive insight into the molecular basis for the loss of capsule expression in GBS, a collection of well-characterized non-typeable strains was investigated by genome sequencing. Genome based phylogenetic analysis extended to a wide population of sequenced strains confirmed the recently observed high clonality among GBS lineages mainly containing human strains, and revealed a much higher degree of diversity in the bovine population. Remarkably, non-typeable strains were equally distributed in all lineages. A number of distinct mutations in the <i>cps</i> operon were identified that were apparently responsible for inactivation of capsule synthesis. The most frequent genetic alterations were point mutations leading to stop codons in the <i>cps</i> genes, and the main target was found to be <i>cpsE</i> encoding the portal glycosyl trasferase of capsule biosynthesis. Complementation of strains carrying missense mutations in <i>cpsE</i> with a wild-type gene restored capsule expression allowing the identification of amino acid residues essential for enzyme activity.</p></div