Vaginal Microbiome Analysis with PaRTI-Seq mNGS Workflow
Why Vaginal Microbiome Profiling Matters
The vaginal microbiome plays a central role in reproductive health outcomes, from natural conception to assisted reproductive technologies like IVF. An optimal microbial environment in both the vaginal and endometrial compartments is associated with improved embryo implantation success rates and fewer pregnancy complications. Conversely, microbial imbalances — including bacterial vaginosis (BV) — are linked to adverse outcomes such as preterm birth, implantation failure, and recurrent pregnancy loss.
Current vaginal microbiome characterization relies primarily on 16S rRNA gene sequencing, which identifies bacterial taxa but lacks the resolution necessary for species-level differentiation. This limitation obscures clinically meaningful distinctions between commensal and pathogenic strains. Metagenomic next-generation sequencing (mNGS) offers a more comprehensive approach by sequencing all genetic material in a sample, enabling simultaneous detection of bacteria, viruses, fungi, and parasites at species-level precision.
However, vaginal samples present a specific challenge for mNGS: the overwhelming proportion of human host DNA. Without host depletion, the vast majority of sequencing reads map to the human genome rather than microbial organisms, severely limiting detection sensitivity. The PaRTI-Seq workflow addresses this directly by combining host DNA depletion with ultralow-input library construction and dedicated bioinformatics analysis.
PaRTI-Seq vs Generic mNGS: Head-to-Head Results
Two vaginal lavage samples were processed using both the PaRTI-Seq workflow (with host depletion via the Devin Microbial DNA Enrichment Kit) and a generic mNGS workflow without host depletion. Each sample included ZymoBIOMICS Spike-in Control I as internal quality control. Sequencing was performed on an Illumina platform, with data analyzed using the PaRTI-Seq RUO Analysis pipeline.
The host depletion results were striking:
- Sample A human DNA: 22.55% with PaRTI-Seq versus 99.91% with generic mNGS.
- Sample A microbial reads: 47.35% with PaRTI-Seq versus 0.03% with generic mNGS.
- Sample B human DNA: 61.18% with PaRTI-Seq versus 99.82% with generic mNGS.
- Sample B microbial reads: 14.86% with PaRTI-Seq versus 0.06% with generic mNGS.
Sample A showed a reduction in host DNA from 99.91% to 22.55% — a nearly complete inversion of the host-to-microbe ratio. Microbial reads increased from 0.03% to 47.35%, representing a greater than 1,500-fold enrichment. Sample B demonstrated a similar pattern, with host DNA reduced from 99.82% to 61.18% and microbial reads increasing from 0.06% to 14.86%.
This level of host depletion transforms vaginal lavage from a sample type dominated by uninformative human reads into one where nearly half the sequencing output provides actionable microbial data.
Species Diversity Comparison
The enrichment in microbial reads translated directly into dramatically expanded species detection. PaRTI-Seq identified organisms across all four microbial kingdoms — bacteria, fungi, viruses, and parasites — while the generic workflow detected only a fraction of the community.
- Bacteria: Sample A PaRTI-Seq detected 399 bacterial taxa versus 31 with generic mNGS, a 12.9x increase.
- Fungi: Sample A PaRTI-Seq detected 121 fungal taxa versus 5 with generic mNGS, a 24.2x increase.
- Viruses: Sample A PaRTI-Seq detected 2 viral taxa versus 0 with generic mNGS.
- Parasites: Sample A PaRTI-Seq detected 3 parasite taxa versus 0 with generic mNGS.
Sample B showed a comparable pattern, with 364 bacterial taxa, 127 fungi, 1 virus, and 0 parasites detected via PaRTI-Seq, versus 52 bacteria, 16 fungi, 0 viruses, and 0 parasites via the generic workflow.
The detection of 399 bacterial species versus 31 represents more than a 12-fold increase in taxonomic resolution. For fungi, the gap widens further — 121 species versus 5, a 24-fold improvement. Critically, viruses and parasites were entirely undetected by the generic workflow, meaning clinically relevant organisms such as HPV or Trichomonas would be missed without host depletion.
Library Construction from Ultra-Low Input
Host depletion inherently reduces the total DNA available for library construction. After processing with the Devin Microbial DNA Enrichment Kit, both vaginal lavage samples yielded DNA concentrations below the detection limit of Qubit fluorometry — effectively undetectable input.
Despite this challenge, the Unison Ultralow DNA NGS Library Preparation Kit produced successful libraries from all samples:
- Sample A: PaRTI-Seq input DNA was undetected by Qubit, yet library concentration reached 0.31 ng/µl with a 495 bp fragment size.
- Sample B: PaRTI-Seq input DNA was undetected by Qubit, yet library concentration reached 0.66 ng/µl with a 495 bp fragment size.
- System control: PaRTI-Seq input DNA was undetected by Qubit, yet library concentration reached 0.59 ng/µl with a 456 bp fragment size.
By comparison, the generic workflow samples — which had measurable inputs of 0.576 ng/µl and 0.284 ng/µl — produced libraries of 2.22 ng/µl and 6.02 ng/µl respectively. The Unison kit’s ability to generate sequenceable libraries from sub-detection-limit inputs is what makes the PaRTI-Seq workflow viable for host-depleted clinical specimens. Without a library prep kit engineered for ultralow inputs, the benefits of host depletion would be negated by library construction failure.
Vaginal Microbiome Analysis Software and Bioinformatics
Vaginal microbiome analysis does not end with sequencing. The bioinformatics layer determines whether low-abundance organisms are reported clearly, whether host background is separated from microbial signal, and whether species-level results are usable for reproductive-health research.
PaRTI-Seq Analysis connects the wet-lab workflow to downstream reporting. After host depletion and ultralow-input library preparation, the analysis pipeline classifies reads across bacteria, fungi, viruses, and parasites, then presents the microbial profile at species-level resolution. This matters for vaginal microbiome studies because clinically relevant differences often sit below the genus level or outside bacteria-only 16S workflows.
For laboratories comparing vaginal microbiome analysis software, the practical requirement is not only taxonomic classification. The software must fit the sample-preparation reality: low biomass after host depletion, matched system controls, and the need to interpret organisms that generic mNGS may miss entirely.
Implications for Clinical Reproductive Health
These results have direct relevance for reproductive medicine. Current IVF protocols increasingly recognize the vaginal and endometrial microbiome as a modifiable factor in treatment success. However, the standard 16S approach detects only bacterial taxa and cannot distinguish between species with different clinical implications within the same genus.
The PaRTI-Seq workflow enables comprehensive vaginal microbiome profiling that can inform targeted interventions before embryo transfer. With species-level resolution across bacteria, fungi, viruses, and parasites, clinicians gain a complete view of the microbial environment rather than a bacterial-only snapshot. The detection of organisms missed entirely by generic mNGS — including viruses and parasites — could reveal previously unrecognized contributors to implantation failure or pregnancy complications.
The combination of the Devin Microbial DNA Enrichment Kit for host depletion, the Unison Ultralow DNA NGS Library Preparation Kit for robust library construction, and PaRTI-Seq Analysis for bioinformatics provides an end-to-end solution purpose-built for this application — from sample to actionable microbial profile.
