Dynamics of Streptococcus agalactiae colonization in women during and after pregnancy and in their infants

Sortase A utilizes an ancillary protein anchor for efficient cell wall anchoring of pili in Streptococcus agalactiae

Pili are putative virulence factors and promising vaccine candidates in Streptococcus agalactiae (group B Streptococcus [GBS]) infection, a leading cause of neonatal sepsis and meningitis. The genes necessary for pilus synthesis and assembly are clustered in pilus islands (PI). Each gene encodes three structural subunits (a backbone and two ancillary proteins) bearing a C-terminal LPXTG motif and two subfamily C sortases (SrtC) involved in covalent polymerization of the subunits. GBS strains also possess the conserved "housekeeping" sortase A (SrtA), but its role in pilus assembly is unclear. To address this issue, pilus expression and cell wall anchoring were analyzed in srtA deletion mutants. Loss of SrtA did not affect pilus polymerization. However, pilus expression on the cell surface was reduced, and pili accumulated in the culture supernatant. Furthermore, cell-associated pili could be readily released by detergent treatment, indicating that SrtA is involved in covalent anchoring of pili to the cell wall. When each of the genes comprising PI-2a was systematically deleted, only the absence of ancillary subunit GBS150 or the SrtC required for incorporation of GBS150 into pili mimicked the srtA mutant phenotype. Thus, from these data a model for GBS pilus assembly can be proposed in which PI sortases are responsible for polymerization of the pilus structure, while SrtA is required to covalently attach it to the cell wall, utilizing ancillary pilus subunit GBS150 as the anchor protein.

Molecular typing of colonizing Streptococcus agalactiae strains by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) in a Chennai based hospital

Streptococcus agalactiae is reported to be an asymptomatic vaginal colonizer in Indian women, although it is considered one of the major causes of neonatal infections in many European countries. DNA based molecular typing methods are more reliable than the conventional serotyping method for identification and typing of this pathogen. In the present study, we have evaluated genetic diversity among colonizing S. agalactiae strains (n=86) by using a PCR-based genotyping method i.e. Enterobacterial Repetitive Intergenic Consensus PCR (ERIC-PCR). With ERIC-PCR fingerprinting at 60% similarity level in a dendrogram generated by UPGMA cluster analysis, 10 different ERIC groups were identified, which were subdivided into 62 distinct genotypes at ≥ 95% similarity level. Based on these findings, we demonstrate that ERIC-PCR is a simple, rapid, and inexpensive tool with sufficient discriminatory power and is applicable for characterization and genotyping of a large number of clinical isolates of S. agalactiae at molecular level.

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.

Group B streptococcal infections in a northern region of Italy

BACKGROUND

Group B streptococcus is a leading cause of neonatal bacterial infections. Despite adoption of preventive strategies, cases of infection continue to occur and there is concern that widespread antimicrobial prophylaxis might delay rather than prevent disease onset, increasing the rates of late-onset diseases.

OBJECTIVES

The purpose of this study was to determine the incidence and clinical features of early- and late-onset group B streptococcus disease in a northern region of Italy where a screening-based approach had been proposed.

METHODS

A population-based study was prospectively conducted in Emilia-Romagna, Italy. Infections that occurred during 2003-2005 in infants aged <3 months were analyzed.

RESULTS

Among 112,933 live births, 56 cases of invasive disease (30 early- and 26 late-onset disease) were observed, giving an annual group B streptococcus disease incidence of 0.50 per 1000 live births. Eleven infants with early-onset disease showed no signs of illness or were mildly ill, whereas 19 had moderate-to-severe symptoms, and culture-proven meningitis was found in 2. Risk factors were detected in 12 women. Twenty-two mothers had antenatal screening; 5 were group B streptococcus colonized, but 17 were culture-negative. Prophylaxis was administered in 3 women. Three infants with late-onset diseases were mildly ill, whereas 23 had moderate-to-severe symptoms. Risk factors were found in 7 mothers. Late-onset diseases were clinically more severe than early-onset diseases; meningitis was diagnosed in 12 infants, and 4 of 26 died.

CONCLUSIONS

The incidence of early-onset disease was low. Some early infections were still observed because of negative screening results or missed opportunity for prevention. Late-onset diseases accounted for most meningitis cases and deaths. Strict adherence to protocols and adoption of optimal culture methods would further improve prevention of early-onset disease, but the aim of future strategies should be the prevention of all invasive diseases.

Application of the French guidelines for preventing neonatal group B streptococcal disease in a university hospital

This study evaluated the application of the French guidelines for prevention of neonatal group B streptococcus (GBS) infections. The prevalence of GBS vaginal carriage by pregnant women during the study period was 6%. Less than 50% of pregnant women testing positive for GBS were treated with at least two doses of antibiotics during labour, and most received only one dose or no antibiotics. In addition, several neonates were colonised or infected by GBS although their mothers were GBS-negative. These results are consistent with vaginal screening having a poor sensitivity, as suggested by the low prevalence of GBS carriage.

Group B streptococcus prevalence in pregnant women from North-Eastern Italy: advantages of a screening strategy based on direct plating plus broth enrichment

AIMS

To assess the sensitivity of a combined selective broth enrichment technique plus selective plating for the detection of group B streptococcus (GBS) colonisation in a large cohort of pregnant women from North-Eastern Italy.

METHODS

During 2002-2005, 5020 pregnant women were screened between the 35th and the 37th week of gestation. A lower vaginal sample and a rectal sample were collected and inoculated onto LIM broth and a selective colistin aztreonam blood agar plate (CAP). Direct agar plates were examined after 18-24 hours and, if negative, after 48 hours. LIM broth was subcultured after 18-24 hours onto a Columbia blood agar plate. All colonies suggestive for GBS were submitted to phenotypic identification.

RESULTS

901 Women (17.9%) were positive for GBS. On 728 positive samples, corresponding to patients enrolled between 2003 and 2005, the results of selective direct plating and selective broth enrichment were compared. A total of 561 (77.1% of positive samples, corresponding to 13.9% of patients) were positive on direct selective agar; an additional 167 isolates (22.9% of samples, 4.1% of patients) were recovered from the LIM broth subculture.

CONCLUSIONS

The prevalence of GBS carriage in this population-based study is a reliable estimate considering the sensitivity of the microbiological methods used, the rate of attendance of pregnant women to clinical and laboratory settings and the compliance to the protocol. Results confirm that the combination of selective enrichment broth and selective direct plating is a time-saving and sensitive method.

Group B Streptococcus: global incidence and vaccine development

An ongoing public health challenge is to develop vaccines that are effective against infectious diseases that have global relevance. Vaccines against serotypes of group B Streptococcus (GBS) that are prevalent in the United States and Europe are not optimally efficacious against serotypes common to other parts of the world. New technologies and innovative approaches are being used to identify GBS antigens that overcome serotype-specificity and that could form the basis of a globally effective vaccine against this opportunistic pathogen. This Review highlights efforts towards this goal and describes a template that can be followed to develop vaccines against other bacterial pathogens.

Serotypes, genotypes, and antibiotic susceptibility profiles of group B streptococci causing neonatal sepsis and meningitis before and after introduction of antibiotic prophylaxis

We studied the characteristics of strains isolated from neonates with group B streptococci sepsis and meningitis, before and after the introduction of antibiotic prophylaxis in The Netherlands. In 1999, 1 year after this introduction the serotype and genotype distribution and the susceptibility patterns of the GBS strains had not changed. Penicillins remain drugs of first choice to prevent and treat neonatal GBS disease.

Rapid detection of the "highly virulent" group B Streptococcus ST-17 clone

Group B streptococcus (GBS) is a leading cause of neonatal morbidity and mortality. Multilocus sequence typing (MLST) revealed that the sequence type ST-17 defines a "highly virulent" serotype III clone strongly associated with neonatal invasive infections. Our aim was to identify a target sequence enabling rapid, simple, and specific detection of this clone by a real-time PCR assay. Conventional methods for DNA manipulation and gene analyses were used to characterize the gbs2018 gene variant specific for ST-17 clone and to design ST-17- and GBS-specific primers. Conventional and real-time PCR assays were developed to detect GBS and ST-17 clones in bacterial cultures and directly on clinical samples. One hundred and fifty-six French GBS strains from various geographical areas in France isolated between 1990 and 2005 were screened by PCR with ST-17-specific primers. Forty strains were positive, and all were validated by MLST as ST-17. A representative sampling of 49 ST-17-PCR-negative strains was confirmed by MLST as non-ST-17. Real-time PCR was further used to directly test 85 vaginal samples. Among these, 13 were GBS-positive, and one was identified as ST-17. The association between strain invasiveness and ST-17 lineage in neonates with late onset disease was highly significant: 78% (P<0.0001) of strains isolated were ST-17. In conclusion, an ST-17-specific gbs2018 allele was identified and used to develop a sensitive and specific rapid-screening molecular assay for identifying ST-17 "highly virulent" GBS. Using this technique, accurate identification of women and neonates colonized by ST-17 can be readily achieved within less than 2 h.

Genomic diversity and evolution within the species Streptococcus agalactiae

Streptococcus agalactiae is a leading cause of invasive infections in neonates, and responsible for bovine mastitis. It is also a commensal bacterium adapted to asymptomatic colonization of the mammalian gut and of the genitourinary tract. Here, we report the analysis of a collection of 75 strains of human and animal origin by using serotyping, multilocus sequence typing, whole genome DNA-array hybridizations and sequence comparison of putatively virulence-associated loci. Although the most variable parts of the genome are the previously predicted genomic islands, significant genetic variations were present in the genome backbone. Evolution within genes encoding surface and secreted proteins and those involved in the biosynthesis of different capsular types is mainly due to recombination events leading to the replacement of a locus of several genes or to the allelic exchange of the internal part of a gene. These two processes, which led to a broad diversity of surface protein patterns, are probably involved in the diversity of interactions with the host and its immune system. According to gene content comparisons and phylogeny, recent gene replacements by horizontal gene transfer may occur but are rare events. Although specific gene patterns, with respect to the origin of the strains and the epidemiological characteristics, were not identified, we show that the recently described hypervirulent ST-17 lineage is a homogeneous group. The study highlights for the first time that this lineage contains a specific and conserved set of surface proteins, probably accounting for its high capacity to cause infections in newborns.

Intragenomic recombination in the highly leukotoxic JP2 clone of Actinobacillus actinomycetemcomitans

The highly leukotoxic JP2 clone of Actinobacillus actinomycetemcomitans is strongly associated with aggressive periodontitis in adolescents of African descent. DNA fingerprinting using the frequently cutting restriction enzyme MspI and multilocus sequence typing (MLST) showed that five strains of this clone were genetically virtually identical, although ribotyping of the six rrn genes and EcoRI RFLP analysis of the seven IS150-like elements revealed differences. PCR analyses demonstrated that these multi-copy sequences are subject to intragenomic homologous recombination, resulting in translocations or large inversions. The genome rearrangements were reflected in differences among 25 strains representing the JP2 clone in DNA fingerprinting using the rare-cutting restriction enzyme XhoI and resolved by PFGE. XhoI DNA fingerprinting provides a tool for studying local epidemiology, including transmission of this particularly pathogenic clone of A. actinomycetemcomitans.