title: Evidence for rare capsular switching in Streptococcus agalactiae.
abstract: The polysaccharide capsule is a major antigenic factor in Streptococcus agalactiae (Lancefield group B streptococcus [GBS]). Previous observations suggest that exchange of capsular loci is likely to occur rather frequently in GBS, even though GBS is not known to be naturally transformable. We sought to identify and characterize putative capsular switching events, by means of a combination of phenotypic and genotypic methods, including pulsed-field gel electrophoretic profiling, multilocus sequence typing, and surface protein and pilus gene profiling. We show that capsular switching by horizontal gene transfer is not as frequent as previously suggested. Serotyping errors may be the main reason behind the overestimation of capsule switching, since phenotypic techniques are prone to errors of interpretation. The identified putative capsular transformants involved the acquisition of the entire capsular locus and were not restricted to the serotype-specific central genes, the previously suggested main mechanism underlying capsular switching. Our data, while questioning the frequency of capsular switching, provide clear evidence for in vivo capsular transformation in S. agalactiae, which may be of critical importance in planning future vaccination strategies against this pathogen.
authors.affiliation: Instituto de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisbon, Portugal.
authors.forename: Elisabete Raquel
authors.initials: ER
authors.lastname: Martins
authors.forename: José
authors.initials: J
authors.lastname: Melo-Cristino
authors.forename: Mário
authors.initials: M
authors.lastname: Ramirez
mesh_terms: D000328:Adult; D016667:Bacterial Capsules / Q000235:genetics* / Q000378:metabolism*; D015373:Bacterial Typing Techniques; D016000:Cluster Analysis; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007231:Infant, Newborn; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D012703:Serotyping; D013290:Streptococcal Infections / Q000382:microbiology; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000378:metabolism*; D014169:Transformation, Bacterial; D055815:Young Adult
chemical_list: D004269:DNA, Bacterial