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

Sungju Lim, Shilpa Rajagopal, Ye Ryn Jeong, Dumebi Nzegwu, Michelle L Wright

Journal: PeerJ 2021;9():e11437

PMID: 34046261

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Plain Language Summary

Variations within the vaginal microbiome have been associated with higher risk for preterm birth and other pregnancy complications. For example, there is a notable lack of discussion of S. agalactiae, commonly referred to as Group B Streptococcus (GBS), a known pathogen associated with poor maternal, foetal, and neonatal outcomes in amplicon-based metagenomic vaginal microbiome studies during pregnancy. The main aim of this study was to determine how often GBS is reported in studies of the vaginal microbiome during pregnancy. This study is a systematic review of forty-five studies. Out of the forty-five studies, 13 (28.9%) reported GBS. Results show that no systematic differences in factors previously known to introduce bias in microbiome studies were associated with the lack of GBS reporting. However, there was considerable heterogeneity in research methods employed across studies. Authors conclude that future studies evaluating the presence of GBS may need to adopt both confirmatory testing for GBS via culture and parallel comparison with results obtained from metagenomic/meta-taxonomic approaches.

Abstract

BACKGROUND

Vaginal microbiome studies frequently report diversity metrics and communities of microbiomes associated with reproductive health outcomes. Reports of (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 ( = 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.

Address: School of Nursing, The University of Texas at Austin, Austin, TX, United States of America.; College of Natural Sciences, Biology Instructional Office, The University of Texas at Austin, Austin, TX, United States of America.; College of Liberal Arts, Department of Health and Society, The University of Texas at Austin, Austin, TX, United States of America.; Dell Medical School, Department of Women's Health, University of Texas at Austin, Austin, TX, United States of America.

DOI: 10.7717/peerj.11437