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Lactobacillus iners and Genital Health: Molecular Clues to an Enigmatic Vaginal Species

  • Female Genital Tract Infections (JD Sobel, Section Editor)
  • Published:
Current Infectious Disease Reports Aims and scope Submit manuscript

Abstract

Purpose of Review

Vaginal lactobacilli are recognized as important drivers of genital health including protection against bacterial vaginosis and sexually transmitted infections. Lactobacillus iners is distinct from L. crispatus, L. gasseri, and L. jensenii by its high global prevalence in vaginal microbiomes, relatively small genome, production of only L-lactic acid, and inconsistent associations with genital health outcomes. In this review, we summarize our current understanding of the role of L. iners in the vaginal microbiome, highlight the importance of strain-level consideration for this species, and explain that while marker gene-based characterization of the composition of the vaginal microbiota does not capture strain-level resolution, whole metagenome sequencing can aid in expanding our understanding of this species in genital health.

Recent Findings

L. iners exists in the vaginal microbiome as a unique combination of strains. The functional repertoires of these strain combinations are likely wide and contribute to the survival of this species in a variety of vaginal microenvironments. In published studies to date, strain-specific effects are aggregated and may yield imprecise estimates of risk associated with this species.

Summary

The worldwide high prevalence of Lactobacillus iners warrants more research into its functional roles in the vaginal microbiome and how it may directly impact susceptibility to infections. By incorporating strain-level resolution into future research endeavors, we may begin to appreciate L. iners more thoroughly and identify novel therapeutic targets for a variety of genital health challenges.

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Acknowledgements

The authors acknowledge Lindsay Rutt and Breanna Shirtliff for providing images of Gram-stained cultures.

Funding

This review article was supported in part by the National Institute of Allergy and Infectious Diseases under award numbers K01-AI163413 (JH), R01-AI116799 (RB), T32-AI162579 (KC) and R01-AI119012 (RB) and the National Institute for Nursing Research under award number R01-NR015495 (JR).

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Authors and Affiliations

  1. Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD, USA

    Johanna B. Holm, Kayla A. Carter, Jacques Ravel & Rebecca M. Brotman

  2. Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, USA

    Johanna B. Holm & Jacques Ravel

  3. Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA

    Rebecca M. Brotman

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All authors contributed to writing and revision of the manuscript. All authors agreed and approved the final manuscript.

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Correspondence to Johanna B. Holm.

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JR is co-founder of LUCA Biologics, a biotechnology company focusing on translating microbiome research into live biotherapeutics drugs for women’s health. Dr. Holm reports personal fees from Intralytix Inc., outside the submitted work. All other authors declare that they have no competing interests.

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Holm, J.B., Carter, K.A., Ravel, J. et al. Lactobacillus iners and Genital Health: Molecular Clues to an Enigmatic Vaginal Species. Curr Infect Dis Rep 25, 67–75 (2023). https://doi.org/10.1007/s11908-023-00798-5

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