Streptococcus agalactiae (GBS) is a leading cause of invasive neonatal infection. Serotyping of GBS is important in following epidemiological trends and vaccine development. Capsular serotyping of GBS by latex agglutination has been the predominant typing method, but more recently capsular genotyping has been introduced as an alternative method. The purpose of this study was to compare the relative performance of these methods in a contemporary population of pregnant women. We typed isolates from an unselected population of 426 colonized women at delivery using latex agglutination and a combination of four PCR methods. Antibiotic resistance was tested in 449 isolates. Capsular genotyping gave a result in all except three of 426 isolates. Fifty-nine of 426 isolates could not be typed by latex agglutination. Agreement between serotyping and genotyping was shown in 303 (71.1%) of the isolates. 10.2% of the isolates were resistant to erythromycin, 9.6% to clindamycin, 76.6% to tetracycline and none to penicillin. In conclusion, a substantial proportion of the colonizing strains were non-typeable by serotyping, but typeable by genotyping. This suggests that a diagnostic genotyping strategy is preferable to serotyping of the GBS polysaccharide capsule in colonized, pregnant women.

bNearly all Streptococcus agalactiae (group B streptococcus [GBS]) strains express a protein which belongs to the so-called alphalike proteins (Alps), of which C␣, Alp1, Alp2, Alp3, Rib, and Alp4 are known to occur in GBS. The Alps are chimeras which form mosaic structures on the GBS surface. Both N-and C-terminal stretches of the Alps possess immunogenic sites of dissimilar immunological specificity. In this review, we have compiled data dealing with the specificity of the N-and C-terminal immunogenic sites of the Alps. The majority of N-terminal sites show protein specificity while the C-terminal sites show broader cross-reactivity. Molecular serotyping has revealed that antibody-based serotyping has often resulted in erroneous Alp identification, due to persistence of cross-reacting antibodies in antisera for serotyping. Retrospectively, this could be expected on the basis of sequence analysis results. Some of the historical R proteins are in fact Alps. The data included in the review may provide a basis for decisions regarding techniques for the preparation of specific antisera for serotyping of GBS, for use in other approaches in GBS research, and for decision making in the context of GBS vaccine developments.

The majority of group B streptococcus (GBS) isolates express one or more of a family of surface-anchored proteins that vary by strain and that form ladder-like patterns on Western blotting due to large repeat units. These proteins, which are important as GBS serotype markers and as inducers of protective antibodies, include the alpha C (C␣) and R4 proteins and the recently described alpha-like protein 2 (Alp2), encoded by alp2, and Alp3, encoded by alp3. In this study, we examined antigenic determinants possessed by Alp2 and Alp3 by testing of antibodies raised in rabbits, mainly by using enzyme-linked immunosorbent assays (ELISA) and an ELISA absorption test. The results showed that Alp2 and Alp3 shared an antigenic determinant, which may be a unique immunological marker of the Alp variants of GBS proteins. Alp2, in addition, possessed an antigenic determinant which showed specificity for Alp2 and a third determinant which showed serological crossreactivity with C␣. Alp3, in addition to the determinant common to Alp2 and Alp3, harbored an antigenic site which also was present in the R4 protein, whereas no Alp3-specific antigenic site was detected. These ELISAbased results were confirmed by Western blotting and a fluorescent-antibody test. The results are consistent with highly complex antigenic structures of the alpha-like proteins in a fashion which is in agreement with the recently described structural mosaicism of the alp2 and alp3 genes. The results are expected to influence GBS serotyping, immunoprotection studies, and GBS vaccine developments. Streptococcus agalactiae (group B streptococcus [GBS]) has been classified into nine serotypes based on the capsular polysaccharide antigens Ia, Ib, and II through VIII. In addition, several surface-anchored protein antigens that vary by strain have been described for GBS, and these antigens can be used to define serosubtypes (11,18). The proteins include the immunoglobulin A-binding beta C protein (C␤) (4) encoded by bac (8), the alpha C protein (C␣) (4) encoded by bca (16), and the proteins R1, R3, and R4 (5, 6, 14). C␣ and the R proteins belong to a family of so-called ladder-forming proteins (25), a designation based on the banding patterns generated on Western blotting. More recently, other laddering GBS proteins, including protein Rib (24) encoded by rib (25) and the alphalike proteins 2 and 3 (Alp2 and Alp3) (12, 13), which are gene products of alp2 and alp3, respectively (12), have been described. The relationship between the recently described proteins and the classic R proteins has been uncertain, but evidence that the proteins Rib and R4 may be identical (2; B. Smith, A. Flores, J. Dechaine, J. Krepela, A. Bergdall, and P. Ferrieri, Abstr. 15th Lancefield Int. Symp. Streptococci Streptococcal Dis., abstr. P4. 07,2002) and that Alp2 and Alp3 may be variants of the R1 protein (J. Maeland and R. V. Lyng, Abstr. 13th Eur. Congr. Clin. Microbiol. Infect. Dis., abstr. P611, 2003) has been provided.Stretches of the ladder-forming proteins show sequence homology ...

This study focuses on immunological markers of R4, an important Streptococcus group B (GBS) protein. The results obtained by using rabbit antisera and purified proteins for antigens in enzyme-linked immunosorbent assay-based experiments provided evidence that R4 possesses two antigenic determinants. One of the determinants is shared with the alpha-like protein 3 (Alp3) of GBS, was named R4/Alp3 common, and was expressed by GBS, which possessed the Alp3-encoding gene alp3 or the R4-encoding gene rib. The other antigenic determinant was detected only in rib-positive GBS organisms and was named R4 specific. This determinant probably is an immunological marker unique to the R4 protein. Neither of the antigenic R4 determinants showed serological cross-reactivity with the GBS proteins C␣, C␤, and R3 or with alpha-like protein 2. Of 60 clinical serotype III GBS strains, 56 (93%) isolates possessed the rib gene and 50 (89%) of the rib-positive isolates expressed levels of R4 detectable by antibody-based tests, consistent with R4 expression failure or low-level expression in ϳ10% of rib-positive GBS. alp3 was not detected in type III GBS but was possessed by six of eight type V strains and six of six type VIII strains. All alp3-positive strains were recognized by the R4/Alp3 common antibodies, but none of them were recognized by the R4-specific antibodies. NCTC 9828, a reference strain for R3 and R4, expressed the determinant R4/Alp3 common but not R4 specific. A monoclonal R4 antibody, previously considered to be R4 specific and used in GBS serotyping, targeted R4/Alp3 common and is thus not R4 specific. The results show that failure to discriminate between R4 specific and R4/Alp3 common by antisera designed for GBS serotyping can result in the false identification of Alp3 as R4 or vice versa, whereas anti-R4 antibodies targeting only the determinant R4 specific will detect only R4. Both R4 and Alp3 need further evaluation with respect to the immunobiological function of each distinct antigenic determinant, for instance, with regard to their potential as GBS vaccine components.Streptococcus agalactiae (group B streptococci [GBS]) is an important cause of infections in humans, notably in neonates. Serotyping based on the capsular polysaccharide antigens Ia, Ib, and II through VIII has been used extensively in epidemiological classification of GBS, sometimes supplemented by serosubtyping on the basis of strain-variable and surface-anchored protein antigens. These proteins include the C proteins C␣ (3) (encoded by bca [22]) and C␤ (3) (encoded by bac [10]) and the classical R proteins R1, R3, and R4 (8, 18, 35 P611, 2003). These proteins, except for C␤, belong to a protein family characterized among other things by similarity in primary structure, with up to 100% homology for some of the protein stretches (16,34), and by their generation of ladder-like patterns on Western blots, probably due to large and identical repeat units which vary in number from strain to strain (9,22,34). Horizontal transfer of genetic elements be...

Multilocus sequence typing of an almost complete collection of invasive group B streptococcus (GBS) strains from infants in Norway, conducted in 2006-2007, revealed 27 sequence types (ST), of which 23 clustered into five clonal complexes. The case fatality rate of invasive GBS disease in infants was 16/98 (16.3%). Type V strains were predominant among strains resistant to erythromycin and clindamycin (11/18; 61.1%). All type V strains from fatal cases (5/16) were ST1, resistant to erythromycin and clindamycin, and belonged to three pulsed-field gel electrophoresis-clusters. Further analysis of virulence characteristics of these apparently highly virulent subtypes of type V, ST1 GBS strains is warranted.

The streptococcal R1 protein was studied by means of anti-R1 antibodies prepared by appropriate cross-absorption of rabbit antiserum raised against the group B streptococcal (GBS) strain ATCC 12403 (D136C), serotype III/R1. The protein was a ladder-forming antigen according to banding patterns in immunoblotting, similar to several other GBS proteins, and was susceptible to digestion by both pepsin and trypsin. Antibody-based testing revealed that 10% of Norwegian GBS isolates expressed the R1 protein, most frequently capsular antigen type V strains (72%) and less frequently type III strains (3%). None of 132 GBS strains from Zimbabwe, including 39 type V strains, expressed the R1 protein. R1-specific rabbit antibodies showed protective activity in mice challenged with a GBS type V/R1 strain. The results show that the R1 protein is an important GBS serotype marker in strains from certain geographical areas, notably for the subtyping of capsular type V strains, and that this protein is a target of protective antibodies.

Streptococcus agalactiae (group B streptococci, GBS) are important human and animal pathogens, which can be subdivided based on different capsular polysaccharides and surface-anchored alpha-like proteins (Alps), as well as other proteins. Nearly all GBS strains possess an Alp (Alp GBS), although Alp-negative GBS (non-Alp GBS) do occur. In this study, 10 (1.1 %) of 932 clinical human GBS tested lacked an Alp encoding gene. All 10 strains were from patients with bloodstream infection, confirming that non-Alp GBS can be highly virulent. All non-Alp GBS expressed one or more of the surface-anchored proteins R3, Z1 and Z2, while less than 10 % of unselected clinical strains express any of these proteins. In contrast to Alp GBS, all non-Alp strains tested were PCR negative for the upstream sequence of the insertion site of the Alp encoding gene of Alp GBS. Genome sequencing showed that all but one of the 10 clinical non-Alp strains and the non-Alp reference strain CNCTC 10/84 lacked a region surrounding the Alp gene commonly present in Alp GBS strains. These strains instead harboured an 849 bp region not present in the Cα prototype strain A909. We have shown that non-Alp GBS differ from Alp GBS in the region surrounding the insertion site of Alp genes of Alp GBS as well as in their content of other surface proteins and that PCR for the upstream flanking region of the Alp gene may be useful for differentiation between Alp and non-Alp GBS.

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