Population structure of Streptococcus agalactiae reveals an association between specific evolutionary lineages and putative virulence factors but not disease

Genomic Insights Into the Distribution and Evolution of Group B Streptococcus

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is a bacteria with truly protean biology. It infects a variety of hosts, among which the most commonly studied are humans, cattle, and fish. GBS holds a singular position in the history of bacterial genomics, as it was the substrate used to describe one of the first major conceptual advances of comparative genomics, the idea of the pan-genome. In this review, I describe a brief history of GBS and the major contributions of genomics to understanding its genome plasticity and evolution as well as its molecular epidemiology, focusing on the three hosts mentioned above. I also discuss one of the major recent paradigm shifts in our understanding of GBS evolution and disease burden: foodborne GBS can cause invasive infections in humans.

Group B Streptococcus vaccine development: present status and future considerations, with emphasis on perspectives for low and middle income countries

Globally, group B Streptococcus (GBS) remains the leading cause of sepsis and meningitis in young infants, with its greatest burden in the first 90 days of life. Intrapartum antibiotic prophylaxis (IAP) for women at risk of transmitting GBS to their newborns has been effective in reducing, but not eliminating, the young infant GBS disease burden in many high income countries. However, identification of women at risk and administration of IAP is very difficult in many low and middle income country (LMIC) settings, and is not possible for home deliveries. Immunization of pregnant women with a GBS vaccine represents an alternate pathway to protecting newborns from GBS disease, through the transplacental antibody transfer to the fetus in utero. This approach to prevent GBS disease in young infants is currently under development, and is approaching late stage clinical evaluation. This manuscript includes a review of the natural history of the disease, global disease burden estimates, diagnosis and existing control options in different settings, the biological rationale for a vaccine including previous supportive studies, analysis of current candidates in development, possible correlates of protection and current status of immunogenicity assays. Future potential vaccine development pathways to licensure and use in LMICs, trial design and implementation options are discussed, with the objective to provide a basis for reflection, rather than recommendations.

Characterization of invasive group B streptococcus strains from the greater Toronto area, Canada

We determined the capsular polysaccharide (CPS) type of 600 group B Streptococcus (GBS) (also known as Streptococcus agalactiae) strains recovered from patients with invasive infections in the greater Toronto area, Canada, between 2009 and 2012. GBS strains of CPS type III were the most prevalent among infants (44% in those with early-onset disease, 75% in those with late-onset disease), while type V strains were most frequently isolated from adult patients (26% in patients≥19 years old). We next investigated the presence in our collection of GBS strains belonging to the hypervirulent multilocus sequence typing clonal complex 17 (CC17). We used a PCR test described as specific for the detection of CC17 strains, which targets the gene encoding the major virulence factor HvgA. We identified 91 hvgA-positive strains; of these, 88 were CPS type III, 2 were CPS type IV, and 1 was CPS type V. Using whole-genome sequencing, we showed that the two hvgA-positive CPS type IV strains are CC17 strains which underwent capsular switching. However, sequence analysis revealed that the hvgA-positive CPS type V strain does not belong to CC17 but instead is a bona fide CC1 strain which acquired hvgA, probably by recombination from a CC17 donor. Our findings underline the importance of recombination in GBS pathogenesis and caution against the use of single-gene-based PCR tests to detect CC17 GBS strains.

Comparative genomics of oral isolates of Streptococcus mutans by in silico genome subtraction does not reveal accessory DNA associated with severe early childhood caries

Comparative genomics is a popular method for the identification of microbial virulence determinants, especially since the sequencing of a large number of whole bacterial genomes from pathogenic and non-pathogenic strains has become relatively inexpensive. The bioinformatics pipelines for comparative genomics usually include gene prediction and annotation and can require significant computer power. To circumvent this, we developed a rapid method for genome-scale in silico subtractive hybridization, based on blastn and independent of feature identification and annotation. Whole genome comparisons by in silico genome subtraction were performed to identify genetic loci specific to Streptococcus mutans strains associated with severe early childhood caries (S-ECC), compared to strains isolated from caries-free (CF) children. The genome similarity of the 20 S. mutans strains included in this study, calculated by Simrank k-mer sharing, ranged from 79.5% to 90.9%, confirming this is a genetically heterogeneous group of strains. We identified strain-specific genetic elements in 19 strains, with sizes ranging from 200 to 39 kb. These elements contained protein-coding regions with functions mostly associated with mobile DNA. We did not, however, identify any genetic loci consistently associated with dental caries, i.e., shared by all the S-ECC strains and absent in the CF strains. Conversely, we did not identify any genetic loci specific with the healthy group. Comparison of previously published genomes from pathogenic and carriage strains of Neisseria meningitidis with our in silico genome subtraction yielded the same set of genes specific to the pathogenic strains, thus validating our method. Our results suggest that S. mutans strains derived from caries active or caries free dentitions cannot be differentiated based on the presence or absence of specific genetic elements. Our in silico genome subtraction method is available as the Microbial Genome Comparison (MGC) tool, with a user-friendly JAVA graphical interface.

International external quality assurance for laboratory identification and typing of Streptococcus agalactiae (Group B streptococci)

We report the results from the first international multicenter external quality assessment (EQA) studies for molecular and serological typing of group B streptococcus (GBS) strains as part of DEVANI (Design of a Vaccine against Neonatal Infections), a pan-European program. A questionnaire-based surveillance was undertaken among eight laboratories participating in DEVANI and six laboratories not participating in DEVANI from 13 countries in order to assess their current microbiological procedures for GBS screening, diagnosis, and typing. GBS strains from three EQA distributions were characterized using molecular and serological methods based on GBS capsular polysaccharide typing. Participants were asked to test the first distribution using their current serotyping and genotyping methods. The Strep-B-Latex agglutination method was the most widely used method, with a typeability value of >90%. A multiplex PCR assay for GBS capsular gene typing was also used by 2 of 14 centers, which achieved a typeability value of 93%; this assay detected only 9 of 10 GBS capsular polysaccharide genes. From the second and third EQA studies, standardized protocols were prepared for serological and molecular typing of GBS strains based on the Strep-B-Latex agglutination method and a novel multiplex PCR assay that detected all 10 GBS capsular types (Ia to IX). These standardized protocols are being used by many European laboratories, and as the use of these methods increases, it is imperative to continuously improve and assess laboratory performance and offer training to any laboratories that have technical difficulties.

Distribution of putative virulence genes in Streptococcus mutans strains does not correlate with caries experience

Streptococcus mutans, a member of the human oral flora, is a widely recognized etiological agent of dental caries. The cariogenic potential of S. mutans is related to its ability to metabolize a wide variety of sugars, form a robust biofilm, produce copious amounts of lactic acid, and thrive in the acid environment that it generates. The remarkable genetic variability present within the species is reflected at the phenotypic level, notably in the differences in the cariogenic potential between strains. However, the genetic basis of these differences is yet to be elucidated. In this study, we surveyed by PCR and DNA hybridization the distribution of putative virulence genes, genomic islands, and insertion sequences across a collection of 33 strains isolated from either children with severe early childhood caries (S-ECC) or those who were caries free (CF). We found this genetically diverse group of isolates to be remarkably homogeneous with regard to the distribution of the putative virulence genes and genetic elements analyzed. Our findings point to the role of other factors in the pathogenesis of S-ECC, such as uncharacterized virulence genes, differences in gene expression and/or enzymatic activity, cooperation between S. mutans strains or with other members of the oral biota, and host factors.

Emergence and global dissemination of host-specific Streptococcus agalactiae clones

To examine the global diversity of Streptococcus agalactiae (group B streptococci [GBS]) and to elucidate the evolutionary processes that determine its population genetics structure and the reported changes in host tropism and infection epidemiology, we examined a collection of 238 bovine and human isolates from nine countries on five continents. Phylogenetic analysis based on the sequences of 15 housekeeping genes combined with patterns of virulence-associated traits identified a genetically heterogeneous core population from which virulent lineages occasionally emerge as a result of recombination affecting major segments of the genome. Such lineages, like clonal complex 17 (CC17) and two distinct clusters of CC23, are exclusively adapted to either humans or cattle and successfully spread globally. The recent emergence and expansion of the human-associated and highly virulent sequence type 17 (ST17) could conceivably account, in part, for the increased prevalence of neonatal GBS infections after 1960. The composite structure of the S. agalactiae genome invalidates phylogenetic inferences exclusively based on multilocus sequence typing (MLST) data and thereby the previously reported conclusion that the human-associated CC17 emerged from the bovine-associated CC67.

Group B streptococci (GBS) (Streptococcus agalactiae) have long been recognized as important causes of mastitis in cattle. After 1960, GBS also became the most prevalent cause of invasive and often fatal infections in newborns. At the same time, GBS are carried by a substantial proportion of healthy individuals. The aims of this study were to elucidate the genetic mechanisms that lead to diversification of the GBS population and to examine the relationship between virulence and host preference of evolutionary lineages of GBS. Genetic analysis of GBS isolates from worldwide sources demonstrated epidemic clones adapted specifically to either the human or bovine host. Such clones seem to emerge from a genetically heterogeneous core population as a result of recombination affecting major segments of the genome. Emergence and global spread of certain clones explain, in part, the change in epidemiology of GBS disease and may have implications for prevention.

Selection, recombination, and virulence gene diversity among group B streptococcal genotypes

Transmission of group B Streptococcus (GBS) from mothers to neonates during childbirth is a leading cause of neonatal sepsis and meningitis. Although subtyping tools have identified specific GBS phylogenetic lineages that are important in neonatal disease, little is known about the genetic diversity of these lineages or the roles that recombination and selection play in the generation of emergent genotypes. Here, we examined genetic variation, selection, and recombination in seven multilocus sequence typing (MLST) loci from 94 invasive, colonizing, and bovine strains representing 38 GBS sequence types and performed DNA sequencing and PCR-based restriction fragment length polymorphism analysis of several putative virulence genes to identify gene content differences between genotypes. Despite the low level of diversity in the MLST loci, a neighbor net analysis revealed a variable range of genetic exchange among the seven clonal complexes (CCs) identified, suggesting that recombination is partly responsible for the diversity observed between genotypes. Recombination is also important for several virulence genes, as some gene alleles had evidence for lateral gene exchange across divergent genotypes. The CC-17 lineage, which is associated with neonatal disease, is relatively homogeneous and therefore appears to have diverged independently with an exclusive set of virulence characteristics. These data suggest that different GBS genetic backgrounds have distinct virulence gene profiles that may be important for disease pathogenesis. Such profiles could be used as markers for the rapid detection of strains with an increased propensity to cause neonatal disease and may be considered useful vaccine targets.

Epidemiology of and prenatal molecular distinction between invasive and colonizing group B streptococci in The Netherlands and Taiwan

The identification of markers for virulent group B streptococci (GBS) could guide prenatal prevention and intervention strategies. We compared the distribution of serotypes and potential pathogenicity islands (PPIs) between invasive and colonizing GBS. Colonizing and invasive strains from The Netherlands and Taiwan were serotyped. We used polymerase chain reaction (PCR) for the amplification of several new PPI markers. Several combinations of PPI-specific markers and serotypes were associated with invasiveness. For Dutch neonatal strains, a receiver operating characteristic (ROC) curve with serotype and five PPI markers showed an area under the curve (AUC) of 0.963 (95% confidence interval [CI] 0.935-0.99). For Taiwanese neonatal strains, serotype and four different PPI markers resulted in an ROC curve with an AUC of 0.894 (95% CI 0.826-0.963). PPI-specific and serological markers can distinguish local neonatal invasive GBS strains from colonizing ones. Apparently, there are clear regional differences in the GBS epidemiology and infection potential of clones.

Different sequence strains of Streptococcus agalactiae elicit various levels of cytokine production

Group B streptococcus (GBS) is the most common cause of neonatal and obstetric sepsis and an increasingly important cause of septicemia in elderly subjects and immunocompromised patients. Our aim was to evaluate whether different genotypes of GBS may induce a different production of pro-inflammatory and anti-inflammatory cytokines. We used multilocus sequence typing to identify 71 clones isolated from asymptomatic healthy carriers and symptomatic individuals. All these clinical isolates were used to infect purified human monocytes. TNF-alpha, IL-6, IL-8 and IL-10 secretion was measured. Fifteen allelic sequence types (STs) were identified. The MLST (multilocus sequence typing) analysis grouped the bacteria into four different lineages (clonal cluster) and two of these were closely involved in the infection of symptomatic subjects: CC17 and CC19. Furthermore, CC17 and CC19 stimulated TNF-alpha, IL-6 and IL-8 production significantly more than the other lineages, while CC17 induced a decreased IL-10 production. These results suggest the existence of differences in immune response to infection with particular genotypes of GBS.

Combining microarray technology and molecular epidemiology to identify genes associated with invasive group B streptococcus

Many bacterial species function as both commensals and pathogens; we used this dual nature to develop a high-throughput molecular epidemiological approach to identifying bacterial virulence genes. We applied our approach to Group B Streptococcus (GBS). Three representative commensal and one invasive GBS isolates were selected as tester strains from a population-based collection. We used microarray-based comparative genomic hybridization to identify open reading frames (ORFs) present in two sequenced invasive strains, but absent or divergent in tester strains. We screened 23 variable ORFs against 949 GBS isolates using a GBS Library on a Slide (LOS) microarray platform. Four ORFs occurred more frequently in invasive than commensal isolates, and one appeared more frequently in commensal isolates. Comparative hybridization using an oligonucleotide microarray, combined with epidemiologic screening using the LOS microarray platform, enabled rapid identification of bacterial genes potentially associated with pathogenicity.

Population structure of invasive and colonizing strains of Streptococcus agalactiae from neonates of six U.S. Academic Centers from 1995 to 1999

The purpose of this study was to describe the population structure of group B streptococci (GBS) isolated from infected and colonized neonates during a prospective active-surveillance study of early-onset disease in six centers in the United States from July 1995 to June 1999 and to examine its relationship to bovine strains of GBS. The phylogenetic lineage of each GBS isolate was determined by multilocus sequence typing, and isolates were clustered into clonal complexes (CCs) using the eBURST software program. A total of 899 neonatal GBS isolates were studied, of which 129 were associated with invasive disease. Serotype Ia, Ib, and V isolates were highly clonal, with 92% to 96% of serotype Ia, Ib, and V isolates being confined to single clonal clusters. In contrast, serotype II and III isolates were each comprised of two major clones, with 39% of serotype II and 41% of serotype III isolates in CC 17 and 41% of serotype II and 54% of serotype III isolates in CC 19. Further analysis demonstrates that the CC 17 serotype II and III GBS are closely related to a previously described "ancestral" lineage of bovine GBS. While 120 (93%) of invasive GBS were confined to the same lineages that colonized neonates, 9 (7%) of the invasive GBS isolates were from rare lineages that comprised only 2.7% of colonizing lineages. These results are consistent with those for other geographic regions that demonstrate the highly clonal nature of GBS infecting and colonizing human neonates.

Distribution of virulence-associated genes inYersinia enterocoliticabiovar 1A correlates with clonal groups and not the source of isolation

Yersinia enterocolitica, an important food- and water-borne enteric pathogen, is represented by six biovars viz. 1A, 1B and 2-5. Some biovar 1A strains, despite lacking virulence plasmid (pYV) and chromosomal virulence genes, have been reported to cause symptoms similar to that produced by isolates belonging to known pathogenic biovars. Virulence-associated genes viz. ail, virF, inv, myfA, ystA, ystB, ystC, tccC, hreP, fepA, fepD, fes, ymoA and sat were studied in 81 clinical and nonclinical strains of Y. enterocolitica biovar 1A by PCR amplification. All strains lacked ail, virF, ystA and ystC genes. The distribution of other genes with respect to clonal groups revealed that four genes viz. ystB, hreP, myfA and sat were associated exclusively with strains belonging to clonal group A. The clonal groups A and B were differentiated previously based on rep (REP-/ERIC) - PCR genomic fingerprinting. The distribution of virulence-associated genes, however, did not differ significantly between clinical and nonclinical strains. In strains of Y. enterocolitica biovar 1A, clonal groups seem to reflect virulence potential better than the source (clinical vs. nonclinical) of isolation.

High-virulence clone of group B streptococci unable to grow at high temperatures is present in serotypes other than type III

Highly virulent clonotypes of serotype III seem to cause much of the perinatal morbidity and mortality attributed to Streptococcus agalactiae (group B streptococci, GBS), One of these clonal types, designated the "high-virulence clone" (HVC), was identified by its inability to grow at 40 degrees C in a chemically defined medium. In the present study, this inability to grow at high temperatures was used as a marker to identify HVC in a sample of 286 Mexican GBS isolates. Forty-three isolates (15%) were identified as belonging to this clone: 15 were invasive isolates, 33 were serotype III (77%), and 10 were of serotypes other than type III (23%). These results demonstrate that HVC is more prevalent in Mexico than previously reported and that this clone is not restricted to serotype III isolates.

Distribution of novel and previously investigated virulence genes in colonizing and invasive isolates of Streptococcus agalactiae

Although Streptococcus agalactiae has emerged as an important cause of invasive disease, relatively little is known regarding the genetic basis of virulence of this organism. Three novel genes with characteristics suggesting a role in virulence were identified via comparison of sequenced genomes of S. agalactiae. The presence of these genes and of the previously identified genes bac, bca, rib, and spb1 was determined, and isolates were assigned a binary genetic signature. It was found that isolates containing spb1, previously suggested to be limited to serotype III-3, were represented by 18 different genetic signatures and several serotypes, and that the presence of both sbp1 and rib was more predictive of invasive disease than spb1 alone. Additionally, bac-positive isolates, reported to be genetically homogeneous, were represented by 14 different genetic signatures. Finally, the majority of serotype V isolates examined contained zero or only one of the genes tested, suggesting that much remains undiscovered regarding important virulence factors in isolates of this serotype.

Phylogenetic lineages of invasive and colonizing strains of serotype III group B Streptococci from neonates: a multicenter prospective study

This study compares the phylogenetic lineages of invasive serotype III group B streptococci (GBS) to those of colonizing strains in order to determine lineages associated with invasive disease. Isolates from 29 infants with early-onset disease (EOD) and from 196 colonized infants, collected in a prospective, multicenter study, were assigned a sequence type (ST) by multilocus sequence typing. Overall, 54.5% of the isolates were in the ST-19 complex, and 40.4% were in the ST-17 complex. Invasive strains were more likely to be in the ST-17 complex than were colonizing strains (59% versus 38%, P = 0.03). After we adjusted for potential confounders, the ST-17 complex was more likely to be associated with EOD than were other lineages (odds ratio = 2.51, 95% confidence interval = 1.02 to 6.20). These data support the hypothesis that ST-17 complex GBS are more virulent than other serotype III GBS.

Enhanced Invasiveness of Bovine-Derived Neonatal Sequence Type 17 Group B Streptococcus Is Independent of Capsular Serotype

BACKGROUND

A defined geographical area (Oxford, United Kingdom) was investigated for the role of group B Streptococcus (GBS) as a human pathogen.

METHODS

GBS carriage in pregnant women and invasive disease in neonates and adults >60 years of age was studied over a 3-year period. Multilocus sequence typing and capsular serotyping were used to study 369 isolates of GBS from carriage in pregnant women (n=190) and invasive disease in neonates (n=109) and adults >60 years of age (n=70).

RESULTS

A total of 20.3% of pregnant women carried GBS. Invasive GBS disease occurred at a rate of 0.9 cases per 1000 live births and 11 cases per 100,000 population >60 years of age per annum. Four sequence types (STs) (ST-17, ST-19, ST-23, and ST-1) that were identified with use of multilocus sequence typing accounted for >50% of carried and invasive strains. A single sequence type (ST-17), previously shown to be phylogenetically of bovine origin, was significantly associated with increased invasiveness in neonates (P=.00002), and this was independent of capsular serotype III. In contrast, among adults >60 years of age, no STs exhibited increased invasiveness, compared with STs carried in pregnant women.

CONCLUSIONS

Enhanced invasiveness associated with ST-17 is specific to neonates and is independent of capsular serotype.

Distribution of serotypes and antimicrobial resistance genes among Streptococcus agalactiae isolates from bovine and human hosts

To better understand the emergence and transmission of antibiotic-resistant Streptococcus agalactiae, we compared phenotypic and genotypic characteristics of 52 human and 83 bovine S. agalactiae isolates. Serotypes found among isolates from human hosts included V (48.1%), III (19.2%), Ia and Ib (13.5% each), and II (5.8%). Among isolates from bovine hosts, molecular serotypes III and II were predominant (53 and 14.5%, respectively). Four and 21 different ribotypes were found among human and bovine isolates, respectively. A combination of ribotyping and serotyping showed that two bovine isolates were indistinguishable from human isolates. Resistance to tetracycline and erythromycin was more common among human (84.6% and 26.9%, respectively) than bovine (14.5% and 3.6%, respectively) isolates. tetM was found in all tetracycline-resistant human isolates, while tetO was the predominant resistance gene among bovine isolates. tet genes were found among various ribotypes. ermB, ermTR, and mefA were detected among erythromycin-resistant human isolates, while ermB was the only erythromycin resistance determinant among isolates from bovine hosts. For isolates from human hosts, erythromycin resistance genes appeared to be associated with specific ribotypes. We conclude that (i) human and bovine S. agalactiae isolates represent distinct populations; (ii) human host-associated S. agalactiae subtypes may occasionally be transmitted to bovines; (iii) while emergence of erythromycin and tetracycline resistance appears to largely occur independently among human and bovine isolates, occasional cross-species transfer of resistant strains or transmission of resistance genes between human- and bovine-associated subtypes may occur; and (iv) dissemination of antibiotic-resistant S. agalactiae appears to include both clonal spread of resistant strains as well as horizontal gene transfer.

Distribution of serotypes and antimicrobial resistance genes among Streptococcus agalactiae isolates from bovine and human hosts

To better understand the emergence and transmission of antibiotic-resistant Streptococcus agalactiae, we compared phenotypic and genotypic characteristics of 52 human and 83 bovine S. agalactiae isolates. Serotypes found among isolates from human hosts included V (48.1%), III (19.2%), Ia and Ib (13.5% each), and II (5.8%). Among isolates from bovine hosts, molecular serotypes III and II were predominant (53 and 14.5%, respectively). Four and 21 different ribotypes were found among human and bovine isolates, respectively. A combination of ribotyping and serotyping showed that two bovine isolates were indistinguishable from human isolates. Resistance to tetracycline and erythromycin was more common among human (84.6% and 26.9%, respectively) than bovine (14.5% and 3.6%, respectively) isolates. tetM was found in all tetracycline-resistant human isolates, while tetO was the predominant resistance gene among bovine isolates. tet genes were found among various ribotypes. ermB, ermTR, and mefA were detected among erythromycin-resistant human isolates, while ermB was the only erythromycin resistance determinant among isolates from bovine hosts. For isolates from human hosts, erythromycin resistance genes appeared to be associated with specific ribotypes. We conclude that (i) human and bovine S. agalactiae isolates represent distinct populations; (ii) human host-associated S. agalactiae subtypes may occasionally be transmitted to bovines; (iii) while emergence of erythromycin and tetracycline resistance appears to largely occur independently among human and bovine isolates, occasional cross-species transfer of resistant strains or transmission of resistance genes between human- and bovine-associated subtypes may occur; and (iv) dissemination of antibiotic-resistant S. agalactiae appears to include both clonal spread of resistant strains as well as horizontal gene transfer.

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.

Molecular subtyping and characterization of bovine and human Streptococcus agalactiae isolates

Streptococcus agalactiae causes severe invasive disease in humans and mastitis in cattle. Temporally matched bovine milk isolates and clinical human invasive isolates (52 each) collected in New York State over 18 months were characterized by molecular subtyping and phenotypic methods to probe the interspecies transmission potential of this species. EcoRI ribotyping differentiated 17 ribotypes, and DNA sequencing of the housekeeping gene sodA and the putative virulence gene hylB differentiated 7 and 17 allelic types, respectively. Human and bovine isolates were not randomly distributed between ribotypes or hylB and sodA clusters. The combined analysis of all subtyping data allowed the differentiation of 39 clonal groups; 26 groups contained only bovine isolates, and 2 groups contained both human and bovine isolates. The EcoRI ribotype diversity among bovine isolates (Simpson's numerical index of discrimination [mean +/- standard deviation], 0.90 +/- 0.05) being significantly higher than that among human isolates (0.42 +/- 0.15) further supports that these isolates represent distinct populations. Eight human isolates, but no bovine isolates, showed an IS1548 transposon insertion in hylB, which encodes a hyaluronidase. Based on data for 43 representative isolates, human isolates, on average, showed lower hyaluronidase activities than bovine isolates. Isolates with the IS1548 insertion in hylB showed no hyaluronidase activity. Human and bovine isolates did not differ in their abilities to invade HeLa human epithelial cells. Our data show that (i) EcoRI ribotyping, combined with hylB and sodA sequencing, provides a discriminatory subtype analysis of S. agalactiae; (ii) most human invasive and bovine S. agalactiae isolates represent distinct subtypes, suggesting limited interspecies transmission; and (iii) hyaluronidase activity is not required for all human infections.

Surface proteins of Streptococcus agalactiae and related proteins in other bacterial pathogens

Streptococcus agalactiae (group B Streptococcus) is the major cause of invasive bacterial disease, including meningitis, in the neonatal period. Although prophylactic measures have contributed to a substantial reduction in the number of infections, development of a vaccine remains an important goal. While much work in this field has focused on the S. agalactiae polysaccharide capsule, which is an important virulence factor that elicits protective immunity, surface proteins have received increasing attention as potential virulence factors and vaccine components. Here, we summarize current knowledge about S. agalactiae surface proteins, with emphasis on proteins that have been characterized immunochemically and/or elicit protective immunity in animal models. These surface proteins have been implicated in interactions with human epithelial cells, binding to extracellular matrix components, and/or evasion of host immunity. Of note, several S. agalactiae surface proteins are related to surface proteins identified in other bacterial pathogens, emphasizing the general interest of the S. agalactiae proteins. Because some S. agalactiae surface proteins elicit protective immunity, they hold promise as components in a vaccine based only on proteins or as carriers in polysaccharide conjugate vaccines.

Serotype III Streptococcus agalactiae from bovine milk and human neonatal infections

Although largely unrelated, many bovine type III GBS appear to share a common ancestor with an important human clone.

Streptococcus agalactiae (group B streptococcus [GBS]) causes invasive human infections and bovine mastitis. This study examined the genetic relationship between bovine and human serotype III GBS by using molecular techniques that classify human serotype III GBS into four distinct phylogenetic lineages. Bovine serotype III GBS were largely contained in two lineages, which are distinct from the two major lineages (restriction digest types III-2 and III-3) that infect human neonates. One of the bovine lineages closely resembles the human III-1 lineage, whose members occasionally cause human neonatal infections. The bovine strains in the other lineage characteristically have an initiation factor IF2 gene (infB) H allele and multilocus sequence types that are not found in human GBS strains. Evidence suggests that this “H allele” lineage is related to the human III-3 lineage. These results support the assertion that human and bovine GBS are largely unrelated and provide further insight into the genetic relation between human and bovine GBS.

Molecular epidemiology of group B streptococcal infections

Streptococcus agalactiae (GBS) is a causative agent of sepsis and meningitis in newborns and diseases in pregnant women and nonpregnant adults. Various approaches, including both nongenetic and genetic techniques, are currently used for the study of epidemiology of GBS infections. In the present paper the different methods of molecular epidemiology of GBS infections are reviewed, and several novel approaches are introduced. The advantages and disadvantages of molecular methods are discussed and compared with traditional serotyping technique. The possible use of the molecular approaches for identification of different genetic lineages in GBS as well as for identification and control of the epidemiologically actual clones is discussed.

Streptococcus agalactiae in a large Portuguese teaching hospital: antimicrobial susceptibility, serotype distribution, and clonal analysis of macrolide-resistant isolates

Group B streptococci are emerging as a cause of serious infection worldwide. The capsular polysaccharides are not only important virulence factors but also the target of vaccine development efforts. Serotypes III (24.6%), V (23.4%), Ia (17.8%), and II (16.3%) were the most prevalent among 252 Streptococcus agalactiae isolates collected during 1999-2002 in the largest hospital of Lisbon, Portugal. The substantial proportion of bacteremic patients (17 neonates and 21 adults) in this period illustrates the present importance of S. agalactiae as a cause of invasive disease. All isolates were fully susceptible to penicillin (MIC(50) = 0.064 microg/ml; MIC(90) = 0.094 microg/ml, range 0.008-0.094), cefotaxime, chloramphenicol, ofloxacin, and vancomycin. Resistance was found to tetracycline (75.4%), erythromycin (10.7%), and clindamycin (9.9%). Of the 27 erythromycin-resistant isolates, 70.4% had the cMLS(B), 22.2% the iMLS(B), and 7.4% the M phenotype. All isolates presenting the M phenotype carried the mef(A) gene, whereas the erm(B) gene was found in a large fraction of MLS(B) isolates (n = 17) and only a small proportion (n = 7) the erm(A) gene [erm(TR) variant]. All isolates carried a single macrolide-resistance determinant. Macrolide resistance was not attributable to a single clone as evidenced by distinct serotype and pulsed-field gel electrophoretic profiles. Careful surveillance of S. agalactiae invasive infections in Portugal is essential, and the treatment or intrapartum prophylaxis of patients who are allergic to penicillin should be guided by contemporary resistance patterns observed in the country.

ISSa4-based differentiation of Streptococcus agalactiae strains and identification of multiple target sites for ISSa4 insertions

A collection of 113 epidemiologically unrelated Streptococcus agalactiae strains were studied (group B streptococcus; GBS): they belonged to different serotypes and were isolated from pregnant women in China and Russia. The insertion sequence ISSa4 was found in 21 of 113 strains (18,6%). All of the strains with ISSa4 belonged to serotypes II and II/c and were characterized by the presence of IS1381 and IS861 as well as the absence of IS1548 and GBSi1. All of the strains with ISSa4 possessed both bca and bac virulence genes coding for alpha and beta antigens, respectively. Among 21 ISSa4-positive strains, 13 different HindIII patterns (D1 to D13) hybridizing with an ISSa4 probe were found. One of them (D13) contained a single HindIII hybridization fragment 6.5 kb in size that was found to be specific for all ISSa4-positive GBS strains. Multiple target sites for insertions of ISSa4 were identified and included a putative pathogenicity island, "housekeeping" genes, and intergenic regions, as well as the genes for hypothetical proteins. No significant similarity was observed in the sequences of the target genes for ISSa4 insertions, in the relative location of the target genes on the chromosome, or the biological functions of the encoded proteins. The possible significance of ISSa4-based differentiation of the strains and the presence of possible "hot spots" for insertions of ISSa4 in GBS genome are discussed.

The presence of insertion elements IS861 and IS1548 in group B streptococci

The presence of insertion elements (IS) IS861 and IS1548 in the collection of 211 Streptococcus agalactiae strains isolated from pregnant women and dairy cows was assayed. IS861 was found in 67 human strains (59%) and 36 bovine strains (37%), IS1548 in 13 human strains (12%) and 16 bovine strains (16%). Two combinations, IS861+ IS1548- and IS861- IS1548-, were widely distributed in both human and bovine strains. The copy number and the restriction fragment length polymorphism (RFLP) of the two IS were determined in human group B streptococcus (GBS) strains. A minimum of 8 copies of IS1548 were detected in GBS strains while the copy number of IS861 varied from 1 to 9. The number of different hybridizing patterns with IS861 and IS1548 probes was 9 and 6, respectively. These hybridization patterns were divided into several clusters. All strains with IS were also clustered according to pulsed field-gel electrophoresis (PFGE) patterns. A correlation was found between the results of PFGE- and IS-based clustering.

Multilocus sequence typing system for group B streptococcus

A multilocus sequence typing (MLST) system was developed for group B streptococcus (GBS). The system was used to characterize a collection (n = 152) of globally and ecologically diverse human strains of GBS that included representatives of capsular serotypes Ia, Ib, II, III, V, VI, and VIII. Fragments (459 to 519 bp) of seven housekeeping genes were amplified by PCR for each strain and sequenced. The combination of alleles at the seven loci provided an allelic profile or sequence type (ST) for each strain. A subset of the strains were characterized by restriction digest patterning, and these results were highly congruent with those obtained with MLST. There were 29 STs, but 66% of isolates were assigned to four major STs. ST-1 and ST-19 were significantly associated with asymptomatic carriage, whereas ST-23 included both carried and invasive strains. All 44 isolates of ST-17 were serotype III clones, and this ST appeared to define a homogeneous clone that was strongly associated with neonatal invasive infections. The finding that isolates with different capsular serotypes had the same ST suggests that recombination occurs at the capsular locus. A web site for GBS MLST was set up and can be accessed at http://sagalactiae.mlst.net. The GBS MLST system offers investigators a valuable typing tool that will promote further investigation of the population biology of this organism.

Towards a genotyping system for Streptococcus agalactiae (group B streptococcus): use of mobile genetic elements in Australasian invasive isolates

This study forms part of the development of an integrated genotyping system for Streptococcus agalactiae (group B streptococcus, GBS) that can be used to study the population genetics of the organism and the pathogenesis and epidemiology of GBS disease. In recent previous studies, two sets of markers, the capsular polysaccharide synthesis (cps) gene cluster and surface protein antigen genes, have been used to assign molecular serotypes (MS) and protein-gene profiles (PGP) to more than 200 isolates. In the present study, five mobile genetic elements (MGE) have been used as a third set of markers, to characterize further 194 invasive isolates, recovered from blood or cerebrospinal fluid (CSF). Of these, 97 % contained one or more of the five MGE, the distribution of which was related to MS and PGP, as illustrated by MS III, which is divisible into four serosubtypes with different combinations of the MGE (or none). Fifty-six different genotypes and eight genetic clusters were identified, each with different combinations of the three sets of molecular markers. Five predominant genotypes (Ia-1, Ib-1, III-1, III-2 and V-1) contained 62 % of the isolates and five of the eight genetic clusters contained 92 % of the isolates. The 17 CSF isolates were relatively widely distributed between 10 genotypes and across seven of the eight clusters. Further study is needed to determine whether these genotypes or clusters share common markers of increased virulence. In future, comparison of invasive with colonizing strains of GBS may elucidate the significance of these findings.

Chromosomal analysis of group B streptococcal clinical strains; bac gene-positive strains are genetically homogenous

A collection of 45 epidemiologically unrelated Streptococcus agalactiae strains (group B Streptococcus, GBS), belonging to different serotypes, isolated from pregnant women in China and Russia was studied. Strains were characterized by pulsed-field gel electrophoresis (PFGE) employing hybridization with nine genes potentially involved in virulence. Molecular sizes of GBS genomes varied from 2030 to 2290 kb. Location of the genes under study bac, bca, glnA, scpB, cyl, hylB, lmb, scaA and cfb on the GBS genomes was found to be conserved irrelevant to the serotype. Potential virulence genes scpB, hylB, lmb were located on a 91-kb SmaI fragment that is equal to 4.5% of total genome. Ribotyping of the strains under study revealed three different HindIII, nine EcoRI and 12 PvuII ribotypes among 45 strains. A strong correlation between the PvuII ribotype and the presence of the bac gene was observed, with 21 of 22 bac-positive strains belonging to the same PvuII ribotype P1. PFGE patterns of bac-positive strains were also similar. The possibility of close genetic relatedness of all bac-positive strains is discussed.

Molecular profiles of group B streptococcal surface protein antigen genes: relationship to molecular serotypes

The study of surface protein antigens of group B streptococci (GBS) is important for understanding of the pathogenesis and epidemiology of infection, and several of these antigens have been proposed as components of GBS conjugate vaccines. In a previous study, we developed a novel PCR-and-sequencing system for identification of GBS serotypes and serosubtypes based on the capsular polysaccharide synthesis (cps) gene cluster. In this study, we used published sequences to develop PCR assays for identification of genes encoding GBS surface proteins including C alpha (bca), C alpha-like proteins 2 and 3 (alp2 and alp3), Rib (rib), and C beta (bac). We showed that the prototype R reference strain, Prague 25/60, contained a novel alpha-like protein antigen gene (the proposed alp4), which presumably encodes an atypical, but antigenically similar, R-like protein. Initial evaluation of these gene-specific assays showed excellent specificity. By combining cps serotypes, serosubtypes, and surface protein gene profiles, we were able to divide 224 GBS isolates into 31 serovariants. GBS bac-positive strains could be further subtyped into 11 groups and 20 subgroups. Our results confirmed and extended reported associations between some cps serotypes and serosubtypes, on the one hand, and surface protein genes, on the other: serosubtypes III-1 and III-2 were associated with rib, serosubtype III-3 with alp2, serotype Ib with bca and bac, and serotype V with alp3. The associations between serotype Ia and bca, bca repetitive unit, and bca repetitive unit-like sequence-containing genes need to be studied further. These PCR-based methods will provide an alternative and objective tool for subtyping of GBS based on surface protein antigen genes.

Long-range mapping of the Streptococcus agalactiae phylogenetic lineage restriction digest pattern type III-3 reveals clustering of virulence genes

Human isolates of serotype III Streptococcus agalactiae (group B streptococcus [GBS]) can be divided into three separate phylogenetic lineages based on analysis of the restriction digest patterns (RDPs) of chromosomal DNA. Nine DNA sequences that are present in all isolates of the RDP III-3 phylogenetic lineage, but not in the other lineages, were identified by genomic subtractive hybridization. A complete physical map of a III-3 chromosome was constructed. Six of the nine III-3-specific sequences mapped to a 340-kb Sse8387I fragment which contains or is located close to known GBS virulence genes. One of the III-3-specific probes, AW-10, encodes part of GBSi1, a group II intron that is inserted at two sites within the GBS genome. The second chromosomal site for GBSi1 was isolated, sequenced, and mapped to a location near the locus responsible for hemolysin production. These findings suggest that the genetic variation that distinguishes the RDP type III-3 strains from other serotype III strains occurs largely within localized areas of the genome containing known or putative virulence genes.

Mutually exclusive distribution of IS1548 and GBSi1, an active group II intron identified in human isolates of group B streptococci

The present study shows that active, self-splicing group II intron GBSi1 is located downstream of the C5a-peptidase gene, scpB, in some group B streptococcus (GBS) isolates that lack insertion sequence IS1548. IS1548 was previously reported to be often present at the scpB locus in GBS isolated in association with endocarditis. Since none of 67 GBS isolates examined, 40 of which were of serotype III, harbored both IS1548 and GBSi1, these two elements are suggested to be markers for different genetic lineages in GBS serotype III. The DNA region downstream of scpB in GBS isolates harboring either GBSi1, IS1548, or none of these mobile elements was found to encode the laminin binding protein, Lmb, which shows sequence similarities to a family of streptococcal adhesins. IS1548 is inserted 9 bp upstream of the putative promoter for lmb, while the insertion site for GBSi1 is located 88 bp further upstream. Sequences highly similar to GBSi1 exist also in Streptococcus pneumoniae. An inverted repeat sequence, with features typical of transcription terminators, was identified immediately upstream of the insertion site for the group II intron both in the GBS and S. pneumoniae sequences. This motif is suggested to constitute a target for the GBS intron as well as for rather closely related introns in Bacillus halodurans, Pseudomonas alcaligenes, and Pseudomonas putida. When transcripts containing the GBSi1 intron were incubated at high concentrations of ammonium and magnesium, a major product with the expected length and sequence for the ligated exons was generated. Unlike, however, all members of group II investigated so far, the excised intron was in linear, rather than in a branched (lariat), form.

Antibacterial properties of human amnion and chorion in vitro

OBJECTIVE

The purpose of the present study was to explore the direct effects of amnion and chorion on bacterial growth in vitro including the antibacterial spectrum. Chorioamniotic membranes were obtained under sterile conditions from 13 healthy women undergoing elective cesarean section at term. Likewise, chorioamniotic membranes were obtained from 10 healthy women with spontaneous vaginal delivery at term. Five strains of Hemolytic streptococci group B (GBS) were tested and one clinical isolate of the following species or bacterial groups: Hemolytic streptococcus group A, Staphylococcus aureus, Staphylococcus saprophyticus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter calcoaceticus and Lactobacillus species. Bacteriological media included (1) blood-agar medium; (2) a transparent agar medium for submerged cultures; and (3) a nutrient broth medium.

RESULTS

An inhibitory effect of fetal membranes against a range of bacteria was found. Consistent results were obtained in experiments with cultures on agar and cultures suspended in agar (membranes from eight women in both studies). In experiments with liquid cultures (seven women) only chorion showed a marginal inhibitory effect. All strains were inhibited, but the most pronounced inhibition was obtained for streptococcus group A, S. aureus and S. saprophyticus by both chorion and amnion.

CONCLUSION

This study demonstrated an inhibitory effect of the fetal membranes on a diverse panel of bacteria

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

Forty group B Streptococcus (GBS) isolates obtained from Europe and the United States previously reported to be nontypeable (NT) by capsule serotype determination were subjected to buoyant density gradient centrifugation. From nearly half of the isolates capsule-expressing variants could be selected. For characterization of the remaining NT-GBS isolates, the capsule operon (cps) was amplified by the long-fragment PCR technique and compared by restriction fragment length polymorphism (RFLP) analysis. The patterns from serotype reference isolates (n = 32) were first determined and used as a comparison matrix for the NT-GBS isolates. Using two restriction enzymes, SduI and AvaII, cluster analysis revealed a high degree of similarity within serotypes but less than 88% similarity between serotypes. However, serotypes III and VII were each split in two distant RFLP clusters, which were designated III(1) and III(2) and VII(1) and VII(2), respectively. Among the isolates that remained NT after repeated Percoll gradient selections, two insertional mutants were revealed. Both were found in blood isolates and harbored insertion sequence (IS) elements within cpsD: one harbored IS1548, and the other harbored IS861. All other NT-GBS isolates could, by cluster analysis, be referred to different serotypes by comparison to the RFLP reference matrix. In pulsed-field gel electrophoresis of SmaI-restricted chromosomal DNA, patterns from allelic type 1 and 2 isolates were essentially distributed in separate clusters in serotypes III and VII. A covariation with insertion sequence IS1548 in the hylB gene was suggested for serotype III, since allelic type III(1) harboring IS1548 in hylB, clustered separately. The variation in serotype VII was not dependent on the presence of IS1548, which was not detected at any position in the type VII chromosome.

Investigation of the translation-initiation factor IF2 gene, infB, as a tool to study the population structure of Streptococcus agalactiae

The sequence of infB, encoding the prokaryotic translation-initiation factor 2 (IF2), was determined in eight strains of Streptococcus agalactiae (group B streptococcus) and an alignment revealed limited intraspecies diversity within S. agalactiae. The amino acid sequence of IF2 from S. agalactiae and from related species were aligned and revealed an interspecies conserved central and C-terminal part, and an N-terminal part that is highly variable in length and amino acid sequence. The diversity and relationships in a collection of 58 genetically distinct strains of S. agalactiae were evaluated by comparing a partial sequence of infB. A total of six alleles were detected for the region of infB analysed. The alleles correlated with the separation of the same strains of S. agalactiae into major evolutionary lineages, as shown in previous work. The partial sequences of infB were furthermore used in phylogenetic analyses of species closely related to S. agalactiae, yielding an evolutionary tree which had a topology similar to a tree constructed using 16S rRNA sequences from the same species.

Action pattern and substrate specificity of the hyaluronan lyase from group B streptococci

The hyaluronan lyase of group B streptococci rapidly cleaves hyaluronan by an elimination mechanism to yield the unsaturated disaccharide 2-acetamido-2-deoxy-3-O-(beta-D-gluco-4-enepyranosyluronic acid)-D-glucose. Additionally, it has been shown that the enzyme has limited specificity for achondroitin sulphate and cleaves the chain at unsulphated sites [Baker,Yu, Morrison, Averett and Pritchard (1997) Biochem. J. 327,65-71]. In the present extension of that study it was found that 6-sulphated regions of chondroitin sulphate are also susceptible to cleavage by this hyaluronan lyase. Of the four 6- and/or 4-sulphated tetrasaccharides which can be isolated from testicular hyaluronidase digests of chondroitin sulphate, only those two tetrasaccharides with a6-sulphated disaccharide at the reducing end were cleaved. From thisand other data, a model is proposed for the cleavage specificity of hyaluronan lyase on a chondroitin sulphate. Evidence is presented in support of an action pattern for hyaluronan lyase which involves aninitial random endolytic cleavage followed by rapid exolytic and processive release of unsaturated disaccharide. Since the on lyoligosaccharides which tend to accumulate in near-complete digests of hyaluronan are unsaturated, it is argued that the processive cleavage occurs from the non-reducing to the reducing end of a hyaluronan chain. This detailed knowledge of substrate specificity contributes to our understanding of the enzyme's role in Group B streptococcal pathogenesis. In addition, the hyaluronan lyase may find application in sequence studies of chondroitin sulphates.

Chorioamniotic membranes constitute a competent barrier to group b streptococcus in vitro

OBJECTIVE

To study the penetration of group B streptococcus (GBS) through human chorioamniotic membranes in vitro.

STUDY DESIGN

Chorioamniotic membranes from seventeen healthy women were mounted onto glass cylinders and placed in tissue culture trays constituting a two-compartment system with a maternal compartment internally and a fetal compartment externally. GBS from healthy pregnant women and from newborn babies with sepsis were added to the maternal compartment at densities from 10(7) to 10(9) colony forming units (cfu) per ml.

RESULTS

Irrespective of inoculum density, GBS was not recovered from the fetal compartment within a 20 h incubation period. By histology, micro-colonies of GBS were found on the maternal surface after 8 h, but invasion of the morphologically intact membranes was not observed. A five log reduction in cfu occurred in the maternal compartment with amnion when GBS were suspended in saline.

CONCLUSION

In this in vitro model the membranes appear to constitute an effective barrier against ascending infection.

Physical and genetic chromosomal maps of Streptococcus agalactiae, serotypes II and III; rRNA operon organization

A detailed analysis of two Streptococcus agalactiae (group B streptococcus, GBS) strains was performed by pulsed field gel electrophoresis (PFGE). Digestion of the chromosomal DNA with SmaI and SgrAI endonucleases, followed by separation and analysis of fragments by PFGE was carried out. Physical chromosomal maps of serotype II/(alpha + beta) and III/alpha strains of S. agalactiae were constructed. The GBS genome size was estimated to be 2200 kb. Sixteen GBS genes were used as probes and were located on the restriction maps of both strains by DNA-DNA hybridization. Six copies of ribosomal operons were found in the genome of the analyzed strains. Significant differences in the restriction patterns of chromosomal DNA and DNA-DNA hybridization between the two analyzed strains were detected so that DNA restriction patterns may be used to trace outbreaks of disease. The overall GBS chromosomal organization as determined is fairly conserved.

Identification of a histidine residue essential for enzymatic activity of group B streptococcal hyaluronate lyase

Hyaluronate lyase produced by group B streptococci (GBS) degrades hyaluronan completely to unsaturated disaccharide units and also cleaves unsulfated regions of chondroitin sulfate. The enzyme is rapidly inactivated by diethyl pyrocarbonate and enzymatic activity is restored by treatment with hydroxylamine, suggesting that a histidine residue is present in the active site. Amino acid sequence comparisons of GBS hyaluronate lyase and four other related enzymes revealed that one of the 16 histidine residues of the enzyme (His-479) is present in a highly conserved region. Conversion of His-479 to a glycine by site-directed mutagenesis resulted in a complete loss of enzymatic activity of the modified protein. We propose that His-479 is in the active site of GBS hyaluronate lyase and participates in the initial abstraction of hydrogen ions from the glucuronic acid residues of hyaluronan.

Genetic diversity of rRNA operons of unrelated Streptococcus agalactiae strains isolated from cerebrospinal fluid of neonates suffering from meningitis

The genetic diversity of a collection of 54 unrelated Streptococcus agalactiae strains isolated from the cerebrospinal fluid of neonates and of 60 unrelated carrier strains was evaluated by investigating the restriction fragment length polymorphism of the rRNA gene region. Three restriction enzymes were selected for use: PstI, HindIII, and CfoI. Clustering analysis revealed two phylogenetic groups of strains with 40% divergence. Group I contained two clusters, A and B, and group II contained three clusters, C, D, and E. Strains of serotype Ia were mostly distributed in cluster A, and strains of serotype Ib were mostly distributed in cluster E. Serotype III isolates did not cluster. Nevertheless, 37 of 39 isolates belonging to cluster B were serotype III. With HindIII, two rRNA gene banding patterns characterized 38 of the 39 strains of cluster B, which represents a high-virulence group. In addition, two rRNA gene banding patterns with each enzyme and/or a pair of CfoI fragments of 905 and 990 bp identified 81% of the invasive strains. On account of the genetic homogeneity of the cerebrospinal fluid strains, ribotyping is a powerful typing method for investigation of nosocomial or epidemic invasive infections only when all three enzymes are used or when PstI and HindIII or PstI and CfoI are combined with serotyping (index of discrimination, > 0.95).