title: Molecular characterization of nontypeable group B streptococcus.
abstract: Traditionally, the capsular polysaccharide (CPS) antigen has been used to distinguish between the nine known serotypes of group B streptococcus (GBS) by classical antibody-antigen reactions. In this study, we used PCR for all CPSs and selected protein antigens, multilocus sequencing typing (MLST), and pulsed-field gel electrophoresis (PFGE) to molecularly characterize 92 clinical isolates identified as nontypeable (NT) by CPS-specific antibody-antigen reactivity. The PCR and MLST were performed on blinded, randomly numbered isolates. All isolates contained the cfb gene coding for CAMP factor. While most (56.5%) contained a single CPS-specific gene, 40 isolates contained either two or three CPS-specific genes. Type V CPS-specific gene was present in 66% of the isolates, and all serotypes except types IV, VII, and VIII were represented. Most (44.5%) of the isolates contained a single protein antigen gene (bca, bac, rib, alp1, or alp3), and the remaining isolates had multiple protein antigen genes. Of the 61 isolates that had the V CPS-specific gene, 48 (78.6%) had the alp3 gene. PFGE analysis classified the isolates into 21 profile groups, while MLST analysis divided the isolates into 16 sequence types. Forty-two (69%) of 61 isolates with the V CPS-specific gene were in PFGE profile group 4; 41 of these 42 were sequence type 1 by MLST. These data shed new light on the antigenic complexity of NT GBS isolates, information that can be valuable in the formulation of an effective GBS vaccine.
authors.affiliation: Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, 221 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Srinivas V
authors.initials: SV
authors.lastname: Ramaswamy
authors.forename: Patricia
authors.initials: P
authors.lastname: Ferrieri
authors.forename: Aurea E
authors.initials: AE
authors.lastname: Flores
authors.forename: Lawrence C
authors.initials: LC
authors.lastname: Paoletti
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics; D016667:Bacterial Capsules / Q000235:genetics; D015373:Bacterial Typing Techniques; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000032:analysis* / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016133:Polymerase Chain Reaction; D011135:Polysaccharides, Bacterial / Q000235:genetics; D011247:Pregnancy; D011817:Rabbits; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000382:microbiology*; D013292:Streptococcus agalactiae / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D000942:Antigens, Bacterial; D004269:DNA, Bacterial; D011135:Polysaccharides, Bacterial