Genotyping of the capsule gene cluster (cps) in nontypeable group B streptococci reveals two major cps allelic variants of serotypes III and VII

GBS-SBG - GBS Serotyping by Genome Sequencing

Group B Streptococcus (GBS; Streptococcus agalactiae) is the most common cause of neonatal meningitis and a rising cause of sepsis in adults. Recently, it has also been shown to cause foodborne disease. As with many other bacteria, the polysaccharide capsule of GBS is antigenic, enabling its use for strain serotyping. Recent advances in DNA sequencing have made sequence-based typing attractive (as has been implemented for several other bacteria, including Escherichia coli, Klebsiella pneumoniae species complex, Streptococcus pyogenes, and others). For GBS, existing WGS-based serotyping systems do not provide complete coverage of all known GBS serotypes (specifically including subtypes of serotype III), and none are simultaneously compatible with the two most common data types, raw short reads and assembled sequences. Here, we create a serotyping database (GBS-SBG, GBS Serotyping by Genome Sequencing), with associated scripts and running instructions, that can be used to call all currently described GBS serotypes, including subtypes of serotype III, using both direct short-read- and assembly-based typing. We achieved higher concordance using GBS-SBG on a previously reported data set of 790 strains. We further validated GBS-SBG on a new set of 572 strains, achieving 99.8% concordance with PCR-based molecular serotyping using either short-read- or assembly-based typing. The GBS-SBG package is publicly available and will hopefully accelerate and simplify serotyping by sequencing for GBS.

Dual and divergent transcriptional impact of IS1548 insertion upstream of the peptidoglycan biosynthesis gene murB of Streptococcus agalactiae

Fourteen different insertion sequences belonging to seven families were identified in the genome of Streptococcus agalactiae. Among them, IS1548, a mobile element of the ISAs1 family, was linked to clonal complex (CC) 19 strains associated with neonatal meningitis and endocarditis. IS1548 impacts S. agalactiae in two reported ways: i) inactivation of virulence genes by insertion in an open reading frame (e.g. hylB or cpsD), ii) positive modulation of the expression of a downstream gene by insertion in an intergenic region (e.g. lmb). We previously identified an unknown integration site of IS1548 in the intergenic region between the folK and the murB genes involved in folate and peptidoglycan biosynthesis, respectively. In this work, we analyzed the prevalence of IS1548 in a large collection of nine hundred and eleven S. agalactiae strains. IS1548 positive strains belong to twenty-nine different sequence types and to ten CCs. The majority of them were, however, clustered within sequence type 19 and sequence type 22, belonging to CC19 and CC22, respectively. In contrast, IS1548 targets the folK-murB intergenic region exclusively in CC19 strains. We evaluated the impact of the insertion of IS1548 on the expression of murB by locating transcriptional promoters influencing its expression in the presence or absence of IS1548 and by comparative β-galactosidase transcriptional fusion assays. We found that in the absence of IS1548, genes involved in folate biosynthesis are co-transcribed with murB. As it was postulated that a folic acid mediated reaction may be involved in cell wall synthesis, this co-transcription could be necessary to synchronize these two processes. The insertion of IS1548 in the folK-murB intergenic region disrupt this co-transcription. Interestingly, we located a promoter at the right end of IS1548 that is able to initiate additional transcripts of murB. The insertion of IS1548 in this region has thus a dual and divergent impact on the expression of murB. By comparative β-galactosidase transcriptional fusion assays, we showed that, consequently, the overall impact of the insertion of IS1548 results in a minor decrease of murB gene transcription. This study provides new insights into gene expression effects mediated by IS1548 in S. agalactiae.

Emergence of a Streptococcus dysgalactiae subspecies equisimilis stG62647-lineage associated with severe clinical manifestations

Increasing incidence rates of invasive Streptococcus dysgalactiae subspecies equisimilis (SDSE) infections have been reported worldwide, but the evolutionary mechanisms underlying this development remain elusive. Through prospective surveillance of invasive SDSE infections in western Norway, we observed the emergence of a novel and virulent SDSE genotype, stG62647. This emm-type, rarely encountered as a cause of invasive disease during 1999–2012, emerged in 2013 as the predominant SDSE-genotype. The stG62647-infections were associated with an aggressive clinical course, including the occurrence of streptococcal toxic shock syndrome, necrotizing soft-tissue infections and endocarditis. All the invasive stG62647-isolates were subjected to whole genome sequencing, attempting to explore the genetic events underpinning its epidemicity. Although 10% of the genomes was unique for stG62647-genotype, notably 18 out of 19 isolates contained a disrupted streptococcal invasive locus (sil) due to the insertion of a transposase, IS1548, into the silB-gene. We postulate that the virulence of stG6267-isolates could be partly attributable to the abrogation of the attenuating control normally exerted by this regulon, although experimental verification was not performed. To the best of our knowledge, this is the first study employing large scale whole genome sequencing to illuminate the genetic landscape of epidemic lineages in SDSE.

Identification of Group B Streptococcus Capsule Type by Use of a Dual Phenotypic/Genotypic Assay

The group B streptococcus (GBS) capsular polysaccharide (CPS) is an important virulence factor which is also used for GBS typing. There are 10 CPS types (Ia, Ib, and II to IX). GBS that do not phenotypically type are considered nontypeable. All genes required for CPS synthesis are found on the GBS cps operon, which contains a highly variable CPS-determining region (cpsG-cpsK). The objective of this study was development of an assay to detect sialic acid on the GBS cell surface, followed by a genotypic PCR CPS typing assay. Sialic acid is located at the terminal end of the side chain of all known GBS CPS types. Sialic acid can be bound to commercially available lectins such as slug Limax flavus lectin. Biotinylated L. flavus-streptavidin-peroxidase complex was used in an enzyme immunoassay and dot blot assay to detect sialic acid. This was followed by a PCR typing scheme that was developed to target the serotype-determining region of the cps locus for Ia, Ib, and II to IX. Sialic acid from the CPS types Ia, Ib, and II to IX was detectable on the GBS cell surfaces of all previously identified CPS-typed GBS strains assayed. This was followed by the real-time PCR typing assay which successfully identified CPS Ia, Ib, and II to IX types. The combination of phenotypic and genotypic assays provides an accurate tool for detection of CPS expression and assignment of CPS typing. These assays have the potential to be used for CPS typing in large-scale epidemiological studies.

Comparison of molecular serotyping approaches of Streptococcus agalactiae from genomic sequences

BACKGROUND

Group B streptococcus (GBS) capsular polysaccharide is one of the major virulence factors underlying invasive GBS disease and a component of forthcoming vaccines. Serotype classification of GBS is based on the capsule polysaccharide of which ten variants are known to exist (Ia, Ib, II-IX). Current methods for GBS serotype assignment rely on latex agglutination or PCR while more recently a whole genome sequencing method was reported. In this study, three distinct algorithms for serotype assignment from genomic data were assessed using a panel of 790 clinical isolates.

METHODS

The first approach utilised the entire capsular locus coupled with a mapping methodology. The second approach continues from the first and utilised a SNP-based methodology across the conserved cpsD-G region to differentiate serotypes Ia-VII and IX. Finally the third approach used the variable cpsG -K region coupled with a mapping methodology. All three approaches were assessed for typeability (percentage of isolates assigned a serotype) and concordance to the latex agglutination methodology.

RESULTS

Following comparisons, the third approach using the variable cpsG-K region demonstrated the best performance with 99.9% typeability and 86.7% concordance. Overall, of the 105 discordant isolates, 71 were resolved following retesting of latex agglutination and whole genome sequencing, 20 failed to assign a serotype using latex agglutination and only 14 were found to be truly discordant on re-testing. Comparison of this final approach with the previously described assembly-based approach returned identical results.

CONCLUSIONS

These results demonstrated that molecular capsular typing using whole genome sequencing and a mapping-based approach is a viable alternative to the traditional, latex agglutination-based serotyping method and can be implemented in a public health microbiology setting.

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 transferase 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.

Physiological impact of transposable elements encoding DDE transposases in the environmental adaptation of Streptococcus agalactiae

We have referenced and described Streptococcus agalactiae transposable elements encoding DDE transposases. These elements belonged to nine families of insertion sequences (ISs) and to a family of conjugative transposons (TnGBSs). An overview of the physiological impact of the insertion of all these elements is provided. DDE-transposable elements affect S. agalactiae in a number of aspects of its capability to adapt to various environments and modulate the expression of several virulence genes, the scpB–lmB genomic region and the genes involved in capsule expression and haemolysin transport being the targets of several different mobile elements. The referenced mobile elements modify S. agalactiae behaviour by transferring new gene(s) to its genome, by modifying the expression of neighbouring genes at the integration site or by promoting genomic rearrangements. Transposition of some of these elements occurs in vivo, suggesting that by dynamically regulating some adaptation and/or virulence genes, they improve the ability of S. agalactiae to reach different niches within its host and ensure the ‘success’ of the infectious process.

Polymerase chain reaction with insertion sequence-specific and -unrelated primers: a new tool for the identification of IS1548 insertion targets in Streptococcus agalactiae

We developed a PCR method with outward insertion sequence-specific and -unrelated primers to identify IS1548 targets in the genome of unsequenced Streptococcus agalactiae strains. Our rapid and easy method allowed the identification of previously known but also of yet unnoticed integration sites in the three clinical isolates tested.

Identification and molecular characterization of a S. agalactiae strain lacking the capsular locus

During a national surveillance program on Group B streptococci (GBS) maternal carriage and neonatal infections, a GBS strain isolated from a pregnant woman's vagino-rectal swab was non typable by either serological or molecular methods. Further molecular characterization demonstrated that the strain lacked the entire capsular locus, possibly by a recombination event that excised a 14,1 Kbase pairs genomic fragment extending from the regulatory protein cpsX gene to the neuA gene. The natural loss of the capsular locus by GBS isolated from a human has never been described so far. Such an event, while possibly a dead-end from the evolutionary point of view, leaves a still able-to-colonize organism unrecognizable by the vaccines currently under development.

Group B streptococcus serotype prevalence in reproductive-age women at a tertiary care military medical center relative to global serotype distribution

Background

Group B Streptococcus (GBS) serotype (Ia, Ib, II-IX) correlates with pathogen virulence and clinical prognosis. Epidemiological studies of seroprevalence are an important metric for determining the proportion of serotypes in a given population. The purpose of this study was to evaluate the prevalence of individual GBS serotypes at Madigan Healthcare System (Madigan), the largest military tertiary healthcare facility in the Pacific Northwestern United States, and to compare seroprevalences with international locations.

Methods

To determine serotype distribution at Madigan, we obtained GBS isolates from standard-of-care anogenital swabs from 207 women of indeterminate gravidity between ages 18-40 during a five month interval. Serotype was determined using a recently described molecular method of polymerase chain reaction by capsular polysaccharide synthesis (cps) genes associated with pathogen virulence.

Results

Serotypes Ia, III, and V were the most prevalent (28%, 27%, and 17%, respectively). A systematic review of global GBS seroprevalence, meta-analysis, and statistical comparison revealed strikingly similar serodistibution at Madigan relative to civilian-sector populations in Canada and the United States. Serotype Ia was the only serotype consistently higher in North American populations relative to other geographic regions (p < 0.005). The number of non-typeable isolates was significantly lower in the study (p < 0.005).

Conclusion

This study establishes PCR-based serotyping as a viable strategy for GBS epidemiological surveillance. Our results suggest that GBS seroprevalence remains stable in North America over the past two decades.

Evidence for rare capsular switching in Streptococcus agalactiae

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.

Analysis of group B streptococcal isolates from infants and pregnant women in Portugal revealing two lineages with enhanced invasiveness

The populations of group B streptococcus (GBS) associated with vaginal carriage in pregnant women and invasive neonatal infections in Portugal were compared. GBS isolates were characterized by serotyping, pulsed-field gel electrophoresis (PFGE) profiling, and multilocus sequence typing (MLST). Serotypes III and V accounted for 44% of all colonization isolates (n = 269), whereas serotypes III and Ia amounted to 69% of all invasive isolates (n = 64). Whereas serotype Ia was associated with early-onset disease (EOD), serotype III was associated with late-onset disease (LOD). Characterization by PFGE and MLST identified very diverse populations in carriage and invasive disease. Serotype Ia was represented mainly by a single PFGE cluster defined by sequence type 23 (ST23) and the infrequent ST24. In contrast, serotype III was found in a large number of PFGE clusters and STs, but a single PFGE cluster defined by ST17 was found to be associated with invasive disease. Although serotype III was associated only with LOD, ST17 showed an enhanced capacity to cause both EOD and LOD. Our data reinforce the evidence for enhanced invasiveness of ST17 and identify a lineage expressing serotype Ia capsule and represented by ST23 and ST24 as having enhanced potential to cause EOD.

Serotype IX, a Proposed New Streptococcus agalactiae Serotype

We identified three isolates of Streptococcus agalactiae (group B streptococcus [GBS]), of human origin, which failed to react with antisera against any of the nine known GBS serotypes. Polyclonal rabbit antisera raised against these isolates and standard GBS typing sera were used in capillary precipitation and Ouchterlony tests to compare the strains with known GBS serotype reference strains. All three previously nontypeable isolates reacted with all three new antisera, producing lines of identity in the Ouchterlony test. Weak cross-reactions with antisera against several GBS serotypes were observed but were removed by absorption with corresponding antigens. The new antisera were used to test 227 GBS isolates that had been nontypeable or difficult to type using standard antisera. Of these, five reacted with the new antisera. These results suggested that all eight isolates belong to the previously unrecognized GBS serotype. They were tested by Western blotting for the Calpha and Cbeta proteins and by PCR to identify molecular serotypes and surface protein antigen genes. Two segments of the cps gene cluster (3' end of cpsE-cpsF and 5' end of cpsG, approximately 700 bp; 3' end of cpsH and 5' end of cpsM, approximately 560 bp) were sequenced. All eight isolates expressed Calpha, and seven expressing the Cbeta protein and the corresponding genes, bca and bac, respectively, were identified. They all share the same, unique partial cps sequence. These results indicate that these eight isolates represent a new S. agalactiae serotype, which we propose should be designated serotype IX.

Reevaluating the serotype II capsular locus of Streptococcus agalactiae

We report a novel sequence of the serotype II capsular locus of group B streptococcus that resolves inconsistencies among the results of various groups and the sequence in GenBank. This locus was found in diverse lineages and presents genes consistent with the complete synthesis of the type II polysaccharide.

Multiplex PCR assay for rapid and accurate capsular typing of group B streptococci

We developed a simple, specific, and sensitive two-multiplex-PCR assay that enabled the detection of all known group B streptococcal (GBS) capsular polysaccharides. This test is well adapted for GBS capsular polysaccharide typing in large-scale epidemiological studies.

Identification of novel cps locus polymorphisms in nontypable group B Streptococcus

Group B Streptococcus (GBS) is an important pathogen responsible for a variety of diseases in newborns and the elderly. A clinical GBS isolate is considered nontypable (NT) when serological methods fail to identify it as one of nine known GBS serotypes. Eight clinical isolates (designated A1-A4, B1-B4) showed PFGE profiles similar to that of a GBS serotype V strain expressing R1, R4 surface proteins. These unique isolates were further characterized by immunologic and genetic methods. Rabbit sera to isolates A1 and A2 reacted weakly with concentrated HCl extracts of A1-A4 isolates, but not with those of B1-B4 isolates. In addition, a type V capsular polysaccharide (CPS) inhibition ELISA revealed that cell wall extracts from isolates A1-A4, but not from B1-B4, expressed low but measurable amounts of type V CPS. Molecular serotyping with PCR analysis showed that all eight isolates contained a type V-specific CPS gene (cpsO) and harboured the gene encoding the surface protein Alp3. Multilocus sequence typing identified isolate A1 as belonging to a new sequence type (ST) designated ST-173, whereas the other seven isolates keyed to ST-1. Sequencing of the 18 genes (17 736 bp) in the cps locus showed that each NT isolate harboured one to three unique polymorphisms, and also identified an IS1381 element in cpsE of the B4 isolate. Collectively, genetic and immunologic analyses revealed that these NT isolates expressing R1, R4 proteins have a genetic profile consistent with that of type V, an emergent, antigenically diverse and increasingly prevalent GBS serotype.

Molecular characterization of nontypeable group B streptococcus

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.

DNA polymorphism and molecular subtyping of the capsular gene cluster of group B streptococcus

Serotyping and other phenotypic methods are often used to characterize the capsular polysaccharide of group B streptococci (GBS). We describe a capsular genotyping method that utilizes PCR of capsular polysaccharide synthesis genes (cps) and restriction enzyme digestion. This method facilitates the detection of DNA polymorphism in cps genes and correlates well with serotyping.

Acquisition of insertion sequences and the GBSi1 intron by Streptococcus agalactiae isolates correlates with the evolution of the species

The prevalence of insertion sequences IS1548, IS861, IS1381, and ISSa4 and of the group II intron GBSi1 within Streptococcus agalactiae human isolates strongly correlates with the genetic lineages obtained by multilocus sequence typing. Our results yielded an evolutionary scheme for the acquisition of these genetic elements linked to the ecosystems from which the isolates were obtained.

Comparison of a 3-set genotyping system with multilocus sequence typing for Streptococcus agalactiae (Group B Streptococcus)

Group B streptococcus (GBS; Streptococcus agalactiae) is the most common cause of neonatal and obstetric sepsis and is an increasingly important cause of septicemia in elderly individuals and immunocompromised patients. Epidemiological studies of GBS infections require comprehensive typing systems that provide information about variable characteristics, such as antigenic type, virulence, or antibiotic resistance, as well as the "backbone" structure or the genetic lineage of isolates. We have previously described a 3-set genotyping system that identifies the molecular serotype (MS) or molecular serosubtype (msst), the protein gene profile, and the presence of several mobile genetic elements (F. Kong, D. Martin, G. James, and G. L. Gilbert, J. Med. Microbiol. 52:337-344, 2003). In this study, 83 clinical GBS isolates which had been previously studied by multilocus sequence typing (MLST) (N. Jones, J. F. Bohnsack, S. Takahashi, K. A. Oliver, M. S. Chan, F. Kunst, P. Glaser, C. Rusniok, D. W. Crook, R. M. Harding, N. Bisharat, and B. G. Spratt, J. Clin. Microbiol. 41:2530-2536, 2003) were examined by using the 3-set genotyping system. Genotypes were assigned to five isolates that were nontypeable by conventional serotyping. There were 27 "3-set" genotypes, 24 multilocus sequence types (STs), and 35 unique combinations (or strains), of which the 4 most common, msst III-2 (ST-17), msst III-1 (ST-19), Ia-1 (ST-23), and V-1 (ST-1), accounted for more than 60% of isolates. The 83 isolates were grouped into seven clusters, with a good correlation between the multilocus STs and the genotypes. The combination of 3-set genotyping and MLST adds discriminatory power to strain typing of GBS, which will be useful for future studies of the epidemiology and pathogenesis of GBS disease.

Multilocus sequence typing of Swedish invasive group B streptococcus isolates indicates a neonatally associated genetic lineage and capsule switching

Streptococcus agalactiae, also designated group B streptococcus (GBS), is an important pathogen in neonates, pregnant women, and nonpregnant adults with predisposing conditions. We used multilocus sequence typing (MLST) to characterize 158 GBS isolates that were associated with neonatal and adult invasive disease and that were collected in northern and western Sweden from 1988 to 1997. Five major genetic lineages (sequence type [ST] 19, ST-17, ST-1, ST-23, and ST-9 complexes) were identified among the isolates, including serotype Ia, Ib, and II to V isolates, indicating a highly clonal population structure among invasive GBS isolates. A number of STs were found to contain isolates of different serotypes, which indicates that capsule switching occurred rather frequently. Two distantly related genetic lineages were identified among isolates of serotype III, namely, clonal complex 19 (CC19), and CC17. CC19 was equally common among isolates from adult and neonatal disease (accounting for 10.3% of GBS isolates from adult disease and 18.7% from neonatal disease), whereas CC17 significantly appeared to be associated with neonatal invasive disease (isolated from 21.9% of neonatal isolates but only 2.6% of adult isolates). The distribution of the mobile elements GBSi1 and IS1548 reveals that they can act as genetic markers for lineages CC17 and CC19, respectively.

Multilocus sequence typing of Swedish invasive group B streptococcus isolates indicates a neonatally associated genetic lineage and capsule switching

Streptococcus agalactiae, also designated group B streptococcus (GBS), is an important pathogen in neonates, pregnant women, and nonpregnant adults with predisposing conditions. We used multilocus sequence typing (MLST) to characterize 158 GBS isolates that were associated with neonatal and adult invasive disease and that were collected in northern and western Sweden from 1988 to 1997. Five major genetic lineages (sequence type [ST] 19, ST-17, ST-1, ST-23, and ST-9 complexes) were identified among the isolates, including serotype Ia, Ib, and II to V isolates, indicating a highly clonal population structure among invasive GBS isolates. A number of STs were found to contain isolates of different serotypes, which indicates that capsule switching occurred rather frequently. Two distantly related genetic lineages were identified among isolates of serotype III, namely, clonal complex 19 (CC19), and CC17. CC19 was equally common among isolates from adult and neonatal disease (accounting for 10.3% of GBS isolates from adult disease and 18.7% from neonatal disease), whereas CC17 significantly appeared to be associated with neonatal invasive disease (isolated from 21.9% of neonatal isolates but only 2.6% of adult isolates). The distribution of the mobile elements GBSi1 and IS1548 reveals that they can act as genetic markers for lineages CC17 and CC19, respectively.

Recurrent endocarditis caused by beta-haemolytic streptococci group B

Recurrent endocarditis was diagnosed in a 73-y-old woman by echocardiography and positive blood cultures with beta-haemolytic streptococci group B. All 3 episodes were treated intravenously with a combination of antibiotics for at least 4 weeks, and after the second recurrence a 3-month course of rifampicin and clarithromycin was given orally.

Comparison of DNA dot blot hybridization and lancefield capillary precipitin methods for group B streptococcal capsular typing

Group B streptococci (GBS) (Streptococcus agalactiae) are a major cause of sepsis and meningitis in neonates and infants and of invasive disease in pregnant women, nonpregnant, presumably immunocompromised adults, and the elderly. Nine GBS serotypes based on capsular polysaccharide antigens have been described. The serotype distributions among invasive and colonizing isolates differ between pediatric and adult populations and have changed over time. Thus, periodic monitoring of GBS serotype distributions is necessary to ensure the proper formulation and application of an appropriate GBS vaccine for human use and to detect the emergence of novel serotypes. Since the mid-1990s, the proportion of GBS isolates that are nontypeable by standard serologic methods has increased, creating a need for more sensitive typing methods. We describe a typing method that uses DNA dot blot hybridization with probes generated by PCR from the GBS capsular genes for serotypes Ia, Ib, and II to VIII. PCR primers were designed to amplify type-specific GBS capsular gene sequences. Gene probes were constructed from the PCR products and used to classify isolates based on hybridization profiles. A total of 306 previously serotyped invasive and colonizing isolates were used to compare our dot blot capsular typing (DBCT) identification method with Lancefield serotyping (LS). A dot blot capsular type was assigned to 99% (303 of 306) of the isolates, whereas 273 of 306 isolates (89%) were assigned a Lancefield serotype. The overall agreement between the methods was 95% (256 of 270 isolates typeable by both methods). We conclude that the DBCT method is a specific and useful alternative to the commonly used LS method.

An inserted DNA fragment with plasmid features is uniquely associated with the presence of the GBSi1 group II intron in Streptococcus agalactiae

The group II intron (GBSi1) identified downstream of the C5a-peptidase gene (scpB) in a subpopulation of Streptococcus agalactiae isolates is a suggested marker for a separate genetic lineage of serotype III isolates. In the present study two additional copies of GBSi1, one of which not previously described, were identified among serotype III isolates. All intron copies shared a common target site motif. A single copy of GBSi1 was found in a subgroup of serotype II and V isolates. In these isolates, the intron had inserted downstream of scpB, which suggests that this is the primary insertion site for GBSi1. Most bacterial group II introns described to date reside in transposable elements. The scpB locus was found to be flanked by insertion sequences similar to what has been described in an intronless serotype Ia isolate. However, this region contained an additional 2.1 kb DNA fragment present only in intron carrying isolates. This DNA fragment contained a partial transposase and putative plasmid related proteins. This may suggest that GBSi1 once was brought into the S. agalactiae genome by an integrated plasmid.

Serotype identification of group B streptococci by PCR and sequencing

Group B streptococcus (GBS; Streptococcus agalactiae) is the most common cause of neonatal and obstetric sepsis and is an increasingly important cause of septicemia in elderly individuals and immunocompromised patients. Ongoing surveillance to monitor GBS serotype distribution will be needed to guide the development and use of GBS conjugate vaccines. We designed sequencing primers based on the previously published sequences of the capsular polysaccharide (cps) gene clusters to further define partial cps gene clusters for eight of the nine GBS serotypes (serotypes Ia to VII). Subsequently, we designed and evaluated primers to identify serotypes Ia, Ib, III, IV, V, and VI directly by PCR and all eight serotypes (serotypes Ia to VII) by sequence heterogeneity. A total of 206 clinical GBS isolates were used to compare our molecular serotype (MS) identification method with conventional serotyping (CS). All clinical isolates were assigned an MS, whereas 188 of 206 (91.3%) were assigned a serotype by use of antisera. A small number of isolates (serosubtypes III-3 and III-4) showed different serotype specificities between PCR and sequencing, but the PCR results correlated with those obtained by CS. The overall agreement between the MS identification method and CS for isolates for which results of both tests were available was 100% (188 of 188 isolates). The MS identification method is a specific and practical alternative to conventional GBS serotyping and will facilitate epidemiological studies.

Serotyping group B streptococci in a small community hospital: an analysis of distribution and site of isolation

OBJECTIVE

To determine the prevalence and site of isolation of different serotypes of group B streptococcus (GBS) colonization or infection at a small community hospital.

METHODS

GBS isolates were obtained from a small community hospital and were then serotyped as la, Ib, II, III, IV, V or nontypeable. Hospital records were reviewed for patient sex, age and pregnancy status as well as the site of GBS isolation.

RESULTS

GBS serotypes Ia, III and V were most common and accounted for over 60% of the total number of isolates. Serotype Ia was most prevalent in reproductive-age females, while serotypes V and III were most prevalent in non-reproductive-age females and males, respectively. Serotype la was most frequent in both pregnant and nonpregnant females. Serotype IV was more common in this study population than in those from other locations.

CONCLUSIONS

The GBS serotype distribution in this small community did not differ significantly from distributions described in larger North American centers. A GBS vaccine designed against multiple serotypes would be protective for most of this population.