Lactobacillus Salivarius

If you have been trying to conceive without success, dealing with recurrent miscarriage, or preparing for IVF, the bacteria living in your vagina may be doing more than you think. Specific lactic-acid-producing bacteria appear to shape whether pregnancies take hold and whether your body wards off infections that complicate delivery.

This swab looks for Lactobacillus salivarius, one of several beneficial vaginal bacteria. Its presence and abundance offer a window into the health of your vaginal ecosystem, with the strongest links to fertility outcomes and to protection against pathogens like Group B Strep.

What This Bacterium Does

L. salivarius (now reclassified as Ligilactobacillus salivarius) is a Gram-positive bacterium that lives naturally in the human gut, mouth, genitourinary tract, and breast milk. When it colonizes the vagina, it produces lactic acid, which lowers vaginal pH and creates an environment hostile to many harmful microbes.

In laboratory studies, specific L. salivarius strains have shown the ability to slow the growth of Gardnerella vaginalis and Streptococcus agalactiae (Group B Strep). Lactobacillus species more broadly have also been studied against Candida and Ureaplasma urealyticum, though the strain-specific evidence for L. salivarius against those two is weaker. The swab measures whether this bacterium is detectable and how abundant it is, typically through species-specific genetic testing of vaginal swab samples.

This is an exploratory, research-stage marker. There are no standardized clinical cutpoints for what counts as a normal or healthy L. salivarius level on a vaginal swab. The science is still defining what specific quantities mean for individual decision-making.

Fertility and Pregnancy

One of the most direct signals in the research links L. salivarius to fertility outcomes. In a single randomized, triple-blind, placebo-controlled trial of 70 women with unexplained infertility undergoing IVF, oral supplementation with the L. salivarius CECT5713 strain raised vaginal L. salivarius prevalence. About 89.5% of women in the probiotic group had detectable vaginal L. salivarius compared with 7.7% in the placebo group. Pregnancy success was 48.1% in the probiotic group versus 20.0% with placebo. Because this is a single small trial, the effect size should be interpreted cautiously, broader meta-analytic data on Lactobacillus probiotics in assisted reproduction suggest a more modest pooled benefit.

A separate open-label study in women with recurrent abortion or unexplained infertility found that those who became pregnant after L. salivarius CECT5713 supplementation showed high vaginal levels of the bacterium, lower vaginal pH, improved Nugent scores (a standard measure of vaginal flora health), and a term pregnancy rate of 56%. In women with reproductive failure, roughly one third had virtually no detectable L. salivarius DNA at baseline, compared with higher levels in fertile controls.

What this means for you: if you are working through unexplained infertility or repeat pregnancy loss, knowing whether L. salivarius is present in your vaginal flora gives you a concrete piece of microbial data that has been linked to reproductive outcomes in early trials. The single best-established use is to monitor whether a targeted probiotic strain is actually colonizing the vagina.

Protection Against Group B Strep

Group B Strep colonization in late pregnancy is a leading reason women receive antibiotics during labor, given to protect newborns. In a small non-randomized pilot, 25 Group B Strep-positive pregnant women received the L. salivarius CECT 9145 strain, with rectal carriage eradicated in 72% and vaginal carriage in 68% by week 38 of pregnancy. The 136 figure sometimes cited refers to the broader screening pool, not the probiotic arm itself.

For women who carry Group B Strep, this is an early but encouraging signal that a targeted strain may reduce colonization before delivery. Because the pilot was small and uncontrolled, and a separate randomized trial of a different probiotic for Group B Strep found no significant eradication benefit, results should be interpreted cautiously. Knowing your vaginal L. salivarius status during pregnancy can help you and your clinician decide whether to pursue a targeted probiotic approach as part of a broader plan.

Where L. salivarius Fits in the Vaginal Microbiome

In broad population studies, the vaginal microbiomes most strongly linked to health are dominated by Lactobacillus species, especially L. crispatus, with low overall diversity. L. salivarius is one of several beneficial Lactobacillus species that can be present, but it is rarely the single dominant species in most women.

In a clustering analysis of 436 Ecuadorian women, L. salivarius appeared as part of a multi-microbial consortium of Lactobacillus species that together protected against bacterial vaginosis and aerobic vaginitis. In cervical swabs from 88 women undergoing assisted reproduction, L. salivarius was among the species whose abundance differed between favorable and unfavorable pregnancy outcomes.

In one randomized trial of 66 perimenopausal women with bacterial vaginosis, higher vaginal L. salivarius after a multi-Lactobacillus suppository was inversely associated with the vaginal health index. This is a statistical association in one specific population using one specific product, not evidence that L. salivarius itself is harmful. It points to the fact that strain and context matter and that this marker should not be read in isolation.

Why One Reading Is Not Enough

The vaginal microbiome is dynamic. It shifts with hormones, menstrual cycle phase, sexual activity, antibiotic use, douching, and pregnancy. A single swab captures a snapshot. To make this number useful, you need at least two readings: a baseline and a follow-up after any intervention or significant life change.

A practical cadence: get a baseline, retest 6 to 12 weeks after starting a targeted probiotic or after antibiotic treatment, and consider rechecking at key transitions like before IVF transfer, in early pregnancy, or in late pregnancy if Group B Strep is a concern. Trend matters more than a single value, especially because no validated reference ranges exist.

When Results Can Be Misleading

A single vaginal swab can be distorted by a number of factors that do not reflect a real change in your underlying flora:

• Recent antibiotics: standard bacterial vaginosis treatments like metronidazole mainly reduce harmful bacteria; other antibiotics and antifungals do not consistently lower Lactobacillus species, but recent antibiotic use can shift results either direction.
• Hormonal phase and pregnancy: estrogen and progesterone strongly shape Lactobacillus abundance. The same person can look quite different in early pregnancy, postpartum, or different menstrual cycle phases.
• Douching, recent sex, or hygiene products: these can transiently change the bacteria sampled.
• Sampling technique: the volume of secretions on the swab and the depth of sampling affect quantitative genetic test results.

There is also no published intra-individual variability estimate specifically for L. salivarius, which means biological variability is meaningful and not precisely quantified. Treat a single reading as a starting point, not a verdict.

What to Do With an Unexpected Result

If L. salivarius is absent or very low and you are working on fertility, recurrent miscarriage, or Group B Strep colonization, this finding is most useful as part of a broader workup, not as a standalone diagnosis. Pair it with a full vaginal microbiome assessment to characterize overall Lactobacillus dominance, screen for bacterial vaginosis and pathogens like Gardnerella, Candida, and Trichomonas, and consider testing for Group B Strep in late pregnancy.

If you are pursuing IVF or addressing unexplained infertility, a reproductive endocrinologist familiar with vaginal microbiome data is the right specialist. For Group B Strep concerns in pregnancy, your obstetrician can guide whether a targeted probiotic strategy makes sense. If the result is high after starting a probiotic, that confirms colonization and supports continuing the regimen during the relevant window.

Because this is still an emerging marker, your decisions should rest on the pattern across multiple tests and on how the result fits with your symptoms, history, and other lab findings. Do not treat a single L. salivarius number as a diagnosis on its own.