Bacterial Load and Molecular Markers Associated With Early-onset Group B Streptococcus: A Systematic Review and Meta-analysis

Inferring longitudinal patterns of group B Streptococcus colonization during pregnancy

Maternal colonization by Group B Streptococcus (GBS) can lead to severe infection in neonates and has also been associated with prematurity and stillbirth. Better quantitative understanding of the trajectories of GBS carriage during pregnancy is essential for the design of informative epidemiological studies. Here, we describe analyses of published longitudinal data using Bayesian hidden Markov models, which involve the estimation of parameters related to the succession of latent states (infection status) and observations (culture positivity). In addition to quantifying infection acquisition and clearance probabilities, the statistical approach also suggests that for some longitudinal patterns of culture results, pregnant women were likely to have been GBS-colonized despite a negative diagnostic result. We believe this method, if used in future longitudinal studies of maternal GBS colonization, would improve our understanding of the pathologies linked to this bacterium and could also inform maternal GBS vaccine trial design.

Group B Streptococcus and the vaginal microbiome among pregnant women: a systematic review

BACKGROUND

Vaginal microbiome studies frequently report diversity metrics and communities of microbiomes associated with reproductive health outcomes. Reports of Streptococcus agalactiae (also known as Group B Streptococcus or GBS), the leading cause of neonatal infectious morbidity and mortality, are notably lacking from the studies of the vaginal microbiome, despite being a known contributor to preterm birth and other complications. Therefore, the purpose of this systematic review was to explore the frequency of GBS reporting in vaginal microbiome literature pertaining to pregnancy and to examine methodological bias that contributes to differences in species and genus-level microbiome reporting. Lack of identification of GBS via sequencing-based approaches due to methodologic or reporting bias may result incomplete understanding of bacterial composition during pregnancy and subsequent birth outcomes.

METHODOLOGY

A systematic review was conducted following the PRISMA guideline. Three databases (PubMed, CINAHL, and Web of Science) were used to identify papers for review based on the search terms "vaginal microbiome", "pregnancy", and "16S rRNA sequencing". Articles were evaluated for methods of DNA extraction and sequencing, 16S region, taxonomy classification database, number of participants or vaginal specimens, and pregnancy trimester.

RESULTS

Forty-five research articles reported employing a metagenomic approach or 16S approach for vaginal microbiome analysis during pregnancy that explicitly reported taxonomic composition and were included in this review. Less than 30% of articles reported the presence of GBS (N = 13). No significant differences in methodology were identified between articles that reported versus did not report GBS. However, there was large variability across research methods used for vaginal microbiome analysis and species-level bacterial community reporting.

CONCLUSION

Considerable differences in study design and data formatting methods may contribute to underrepresentation of GBS, and other known pathogens, in existing vaginal microbiome literature. Previous studies have identified considerable variation in methodology across vaginal microbiome studies. This study adds to this body of work because in addition to laboratory or statistical methods, how results and data are shared (e.g., only analyzing genus level data or 20 most abundant microbes), may hinder reproducibility and limit our understanding of the influence of less abundant microbes. Sharing detailed methods, analysis code, and raw data may improve reproducibility and ability to more accurately compare microbial communities across studies.

Performance of PhenoMatrix for the detection of Group B Streptococcus from recto-vaginal swabs

We assessed the performance of PhenoMatrix digital imaging software in detection of Group B Streptococcus from recto-vaginal swabs plated on a specific chromogenic medium, using the WASP automated processor. PhenoMatrix algorithm showed a sensitivity of 100% and a specificity of 64.5%. False-positive results were mainly due to commensal viridans streptococci.

Polymerase chain reaction for Group B Streptococci (GBS) at labor highly correlates with vaginal GBS load

OBJECTIVE

To explore factors associated with a high vaginal GBS load during labor considering (1) the recto-vaginal GBS load at 35-37 weeks' gestation determined by culture and (2) the vaginal GBS colonization determined by a polymerase chain reaction (PCR) assay during labor.

METHODS

From an unselected cohort of 902 pregnant women, we obtained (1) recto-vaginal swabs for culture of GBS at 35-37 weeks' gestation (GBS_rectovag-36), (2) vaginal swabs for GBS PCR detection at labor (PCR_vag-labor), and (3) vaginal swabs for culture of GBS at labor (GBS_vag-labor). The GBS load was classified semi quantitatively according to a culture protocol without prior broth enrichment of the swab samples: none (0), few (+), some (++), or many (+++) GBS colonies.

RESULTS

Among 902 unselected pregnant women, 859 (95%) had a vaginal swab culture taken at labor, which was classified semi quantitatively. High load GBS_vag-labor (+++) were found in 31 participants. GBS_rectovag-36 showed a sensitivity of 90% (28/31) and a PPV of 23% (28/121), whereas PCR_vag-labor had a sensitivity of 98% (30/31, non-significant difference) and a PPV of 42% (30/71, p < .01). PCR at labor had a lower sensitivity (78%) for detection of vaginal colonization with GBS at labor (any load) compared to recto/vaginal colonization with GBS at 36 weeks (92%). Vaginal colonization with GBS at 36 weeks seemed to have a lower sensitivity for detecting GBS in vagina at labor for high load (48%) and for any load (39%).

CONCLUSION

PCR at labor has higher detection rate (non-significant) and PPV in identification of laboring women with a high load of vaginal GBS compared with recto-vaginal culture at 36 weeks' gestation.

Association of Group B streptococcus serum serotype-specific anti-capsular IgG concentration and risk reduction for invasive Group B streptococcus disease in South African infants: an observational birth-cohort, matched case-control study

BACKGROUND

Licensure of a Group B streptococcus (GBS) polysaccharide-protein conjugate vaccine for protecting infants against invasive GBS disease (IGbsD) will likely need to be based on demonstrating vaccine safety in pregnant women, and benchmarking immunogenicity against a serological threshold associated with risk reduction of IGbsD. We investigated the association between naturally-derived GBS serotype-Ia and III IgG and risk reduction of IGbsD in infants' ≤90 days of age.

METHODS

In a matched case-control study (ClinicalTrials.gov NCT02215226), IGbsD cases were identified from a cohort of 38,233 mother-newborn dyads. Mothers colonized vaginally with serotype-Ia or III at birth, and their healthy infants were eligible as matched controls. GBS serotype-specific anti-capsular IgG was measured on maternal and cord blood/infant sera by multiplex Luminex assay; and the IgG threshold associated with 90% risk reduction of IGbsD derived by estimating absolute disease risk.

RESULTS

In infants born ≥34 weeks gestational age, cord-blood IgG geometric mean concentrations (GMC) were lower in cases than controls for serotype-Ia (0.05 vs. 0.50µg/ml; p=0.004) and III (0.20 vs. 0.38µg/ml; p=0.078). Cord-blood IgG concentration ≥1.04 and ≥1.53µg/ml were associated with 90% risk reduction of serotype-Ia and III IGbsD, respectively. The maternal sera IgG threshold associated with 90% risk reduction was ≥2.31 and ≥3.41µg/ml for serotype-Ia and III, respectively.

CONCLUSIONS

The threshold associated with a reduced risk for serotype-Ia and III IGbsD identified on infant sera supports the case for licensure of a GBS polysaccharide-protein conjugate vaccine based on immunogenicity evaluation benchmarked against the defined thresholds.

Improvement of selection of pregnant women for intrapartum polymerase chain reaction screening for vaginal Group B Streptococci (GBS) colonization by adding GBS urine screening at 35-37 weeks of pregnancy

OBJECTIVE

To evaluate whether systematic antepartum screening for Group B Streptococci (GBS) by urine culture improves the risk factor-based selection of pregnant women for intrapartum GBS screening with a rapid polymerase chain reaction (PCR) assay.

METHODS

A prospective observational study was conducted between April 2013 and June 2014. GBS colonization judged by urine culture at 35-37 weeks of gestation was compared with the result of a vaginal GBS PCR test at labor as outcome. The results of urine culture were used as exposure variable. The PCR test was performed on intrapartum vaginal samples.

RESULTS

Screening for urine GBS in 902 unselected pregnant Danish women at 35-37 weeks of gestation predicted intrapartum PCR GBS status with a sensitivity of 33.6%. A positive predictive value of 41.2% was seen among women with low GBS counts (<104 CFU/mL) and 83.3% among women with high GBS counts (≥104 CFU/mL). Systematic GBS screening of urine at 35-37 weeks of gestation added 30.9% extra women for intrapartum GBS PCR screening in the study group.

CONCLUSION

Systematic antepartum GBS screening of urine should be implemented in order to improve risk stratification for early onset GBS by offering laboring women an intrapartum GBS PCR test.

Uncertainties in Screening and Prevention of Group B Streptococcus Disease

In autumn 2016, the UK Department of Health (now Department of Health and Social Care) convened 2 meetings to discuss how to address research evidence gaps in order to minimize the impact of infant group B streptococcus (GBS) disease in the United Kingdom. At that meeting, a number of research priorities were highlighted, including improving the screening for GBS colonization in pregnant women, offering intrapartum antibiotic prophylaxis and point-of-care testing, and understanding the effect of widespread intrapartum antibiotic use on long-term infant health. Further discussions involved investigating the feasibility of a large prospective study of pregnant women and their infants in order to understand the role of antibodies in the protection against GBS disease in infancy following maternal exposure to GBS colonization. Here, we summarize the research uncertainties identified at that meeting.

In-vitro effect of vaginal lactobacilli against group B Streptococcus

Streptococcus agalactiae(GBS) is a leading cause of infection during pregnancy, preterm birth and neonatal infection, with a significant clinical and socio-economic impact. To prevent maternal GBS vaginal colonization, new antibiotic-free approaches, based on lactobacilli probiotics, are advisable. The aim of this study was to assess the anti-GBS activity of 14 vaginal Lactobacillus strains, belonging to different species (L. crispatus, L. gasseri, L. vaginalis), isolated from healthy pre-menopausal women. In particular, we performed 'inhibition' experiments, evaluating the ability of both Lactobacillus cells and culture supernatants in reducing Streptococcus viability, after 60 min contact time. First, we demonstrated that the acidic milieu, produced by vaginal lactobacilli metabolism, is crucial in counteracting GBS growth in a pH-dependent manner. Experiments with organic/inorganic acid solutions confirmed the strict correlation between pH levels and the anti-GBS activity. GBS was more sensitive to lactic acid than to hydrochloric acid, indicating that the presence of H⁺ ions is necessary but not sufficient for the inhibitory activity. Moreover, experiments with Lactobacillus pH-adjusted supernatants led to exclude a direct role in the anti-GBS activity by other bioactive molecules. Second, we found that only a few Lactobacillus strains were able to reduce Streptococcus viability by means of cell pellets. The anti-GBS effect displayed by Lactobacillus cells was related to the their ability to interact and aggregate with Streptococcus cells. We found that the anti-GBS activity was retained after methanol/proteinase K treatment, but lost after lysozyme exposure of Lactobacillus cells. Therefore, we supposed that non-proteinaceous components of Lactobacillus cell wall could be responsible for the anti-GBS activity. In conclusion, we identified specific Lactobacillus strains able to interfere with GBS viability by multiple strategies and we elucidated some of the mechanisms of action. These strains could serve as probiotic formulations for the prevention of GBS vaginal colonization.

Group B Streptococcus DNA Copy Numbers Measured by Digital PCR Correlates with Perinatal Outcomes

Group B Streptococcus (GBS) is a one of the main causes of perinatal disease, yet the method for GBS detection, broth-enriched culture, is time-consuming and has low sensitivity and accuracy. We aimed to develop a GBS digital PCR (GBS-dPCR) assay for detecting GBS colonization. More rapid and accurate detection of GBS colonization could increase GBS diagnosis and treatment closer to delivery. A single-center, retrospective, case-controlled study was performed. A total of 182 rectovaginal swabs from pregnant women, who were undergoing prenatal screening by broth-enriched culture, were evaluated using GBS-dPCR targeting the cfb gene of GBS. Pregnant women with GBS colonization were followed up for correlation analysis between GBS DNA copy numbers and perinatal outcomes. The results of the GBS-dPCR assay were compared to those from the broth-enriched culture, which is the gold standard for GBS detection. The sensitivity and specificity of GBS-dPCR were 98% and 92.5%, respectively. By discrepant result analysis, the specificity of GBS-dPCR was raised to 97.4%. The incidence of premature rupture of membrane (PROM) and neonatal infection were statistically significantly positively correlated with GBS DNA copy numbers. GBS-dPCR has the advantage of directly detecting GBS colonization from swabs with high specificity and sensitivity, while reducing turnaround time (<4 h). Analysis of clinical samples with GBS-dPCR shows that GBS DNA copy numbers are positively correlated with the incidence of PROM and neonatal infection, suggesting that dPCR is a promising method for detection of GBS colonization during pregnancy.

Emerging serotype III sequence type 17 group B streptococcus invasive infection in infants: the clinical characteristics and impacts on outcomes

BACKGROUND

Group B Streptococcus (GBS) is an important pathogen that causes high mortality and morbidity in young infants. However, data on clinical manifestations between different GBS serotypes and correlation with molecular epidemiology are largely incomplete. The aim of this study was to determine the serotype distribution, antimicrobial resistance, clinical features and molecular characteristics of invasive GBS isolates recovered from Taiwanese infants.

METHODS

From 2003 to 2017, 182 non-duplicate GBS isolates that caused invasive disease in infants less than one year of age underwent serotyping, multilocus sequence typing (MLST) and antibiotic susceptibility testing. The clinical features of these infants with GBS disease were also reviewed.

RESULTS

Of the 182 patients with invasive GBS disease, 41 (22.5%) were early-onset disease, 121 (66.5%) were late-onset disease and 20 (11.0%) were late late-onset disease (> 90 days of age). All these patients were treated with effective antibiotics on time. Among them, 51 (28.0%) had meningitis, 29 (16.0%) had neurological complications, 12 (6.6%) died during hospitalization, and 15 (8.8%) out of 170 patients who survived had long-term neurological sequelae at discharge. Serotype III GBS strains accounted for 64.8%, followed by serotype Ia (18.1%) and Ib (8.2%). MLST analysis revealed 11 different sequence types among the 182 isolates and ST-17 was the most dominant sequence type (56.6%). The correlation between serotype III and ST17 was evident, as ST17 accounted for 87.3% of all serotype III isolates. There was an obvious increasing trend of type III/ST-17 GBS that caused invasive disease in infants. All isolates were susceptible to penicillin, cefotaxime, and vancomycin, while 68.1 and 65.9% were resistant to erythromycin and clindamycin, respectively.

CONCLUSIONS

Despite timely and appropriate antibiotic treatment, a significant proportion of invasive GBS disease still inevitably causes adverse outcomes. Further study to explore preventive strategies and development of serotype-based vaccines will be necessary in the future.