Population‑Specific Diversity of Dominant Vaginal Lactobacillus Species in Healthy Iranian Women and Those with Vaginitis: A Molecular Case‑Control Study

Background: Lactobacillus species play a key role in maintaining vaginal microbial homeostasis and protecting against genital infections. Disruption of this microbial balance can increase susceptibility to vaginitis. Population-specific variations in the composition of vaginal Lactobacillus communities may influence disease risk and therapeutic responses. This study aimed to evaluate the distribution of major vaginal Lactobacillus species in healthy Iranian women and those with vaginitis using species-specific molecular assays. Methods: In this case–control study, 100 women with clinically confirmed vaginitis and 100 healthy controls were enrolled. Vaginal swabs were examined by Gram staining, followed by DNA extraction and PCR amplification using universal and species-specific 16S rRNA primers targeting L. iners, L. crispatus, L. acidophilus, L. gasseri , and L. jensenii . Associations between bacterial species and clinical status were evaluated using Odds Ratio (OR), Relative Risk (RR), Phi coefficient (Φ), and Chi-square tests. Results: Lactobacillus spp. were detected in 97% of healthy women compared with 53% of symptomatic participants. L. jensenii and L. acidophilus were significantly more prevalent in healthy individuals, demonstrating strong protective associations with vaginal health. In contrast, L. iners was more frequently detected in women with vaginitis, consistent with its proposed role as a transitional species associated with microbiome instability. Although L. crispatus is often reported as protective in other populations, it did not show a statistically significant protective association in this study population. Conclusion: Our findings highlight the protective association of dominant Lactobacillus species, particularly L. jensenii and L. acidophilus , in maintaining vaginal microbial balance. The higher prevalence of L. iners among symptomatic women further supports its association with disturbed vaginal microbiota. These results suggest the presence of population-specific microbial patterns and underscore the importance of considering regional microbiome characteristics when developing diagnostic approaches and probiotic-based interventions. Keywords: Lactobacillus , vaginal microbiota, vaginitis L. iners, L. jensenii , case–control study