title: Capsular gene typing of Streptococcus agalactiae compared to serotyping by latex agglutination.
abstract: We evaluated three different PCR-based capsular gene typing methods applied to 312 human and bovine Streptococcus agalactiae (group B Streptococcus [GBS]) isolates and compared the results to serotyping results obtained by latex agglutination. Among 281 human isolates 27% could not be typed by latex agglutination. All 312 isolates except 5 could be typed by the three PCR methods combined. Two of these methods were multiplex assays. Among the isolates that were typeable by both latex agglutination and capsular gene typing, 94% showed agreement between the two methods. However, each of the PCR methods showed limitations. One of the methods did not include all 10 recognized serotypes, one misidentified eight isolates of serotypes Ib and IV as serotype Ia, and one did not distinguish between serotypes VII and IX. For five isolates that showed aberrant patterns in the capsular gene typing, long-range PCR targeting the cps operon disclosed large insertions or deletions affecting the cps gene cluster. A sensitive flow cytometric assay based on serotype-specific antibodies applied to 76 selected isolates that were nontypeable by latex agglutination revealed that approximately one-half of these did express capsular polysaccharide. A procedure for convenient and reliable capsular gene typing to be included in epidemiological and surveillance studies of S. agalactiae is proposed.
authors.affiliation: Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark.
authors.forename: Kaihu
authors.initials: K
authors.lastname: Yao
authors.forename: Knud
authors.initials: K
authors.lastname: Poulsen
authors.forename: Domenico
authors.initials: D
authors.lastname: Maione
authors.forename: C Daniela
authors.initials: CD
authors.lastname: Rinaudo
authors.forename: Lucilla
authors.initials: L
authors.lastname: Baldassarri
authors.forename: John L
authors.initials: JL
authors.lastname: Telford
authors.forename: Uffe B Skov
authors.initials: UB
authors.lastname: Sørensen
authors.forename: Mogens
authors.initials: M
authors.lastname: Kilian
mesh_terms: D000818:Animals; D016667:Bacterial Capsules / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D005260:Female; D005434:Flow Cytometry; D056426:Genetic Loci; D006801:Humans; D007841:Latex Fixation Tests; D058889:Molecular Typing; D011247:Pregnancy; D012703:Serotyping; D013290:Streptococcal Infections / Q000175:diagnosis / Q000382:microbiology; D013292:Streptococcus agalactiae / Q000145:classification* / Q000235:genetics* / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors