O-252 Unravelling the endometrial microbiome: relationship between pathogen prevalence and the presence of Lactobacillus species

Abstract Study question Are all Lactobacillus species equally associated with the prevalence of pathogenic bacteria in the endometrium? Summary answer The incidence of pathogenic bacteria is significantly higher when Lactobacillus gasseri is the only Lactobacillus species detected, as compared to the presence of Lactobacillus crispatus. What is known already Multiple factors influence female infertility; however, emerging evidence suggests that the composition of the endometrial microbiome plays a critical role in reproductive health, requiring a delicate balance between the presence of pathogenic microorganisms and beneficial Lactobacillus species. Studies have linked the presence of Lactobacillus to favourable reproductive outcomes by protecting against pathogenic colonization of the reproductive tract; however, no consensus exists regarding which Lactobacillus species provides the most effective protective role. This study aims to explore the interactions between the four Lactobacillus species and pathogenic bacteria, providing insights into their potential as therapeutic targets in managing female infertility. Study design, size, duration Retrospective observational study evaluating the association between the presence of pathogenic bacteria and Lactobacillus species. Endometrial microbiome assessment was performed on 7,795 endometrial biopsies carried out between May 2023 and December 2024. The mean age of patients was 38.3 ± 4.9 years. Samples were divided into two groups depending on the detection of Lactobacillus species. In-depth analysis was performed by extracting samples with just one of the four Lactobacillus species analysed. Participants/materials, setting, methods Endometrial biopsies were processed using RealTime-PCR (OpenArray, Thermo Fisher Scientific) to determine the presence of DNA in a custom bacterial panel that included four Lactobacillus species and twenty-six potential reproductive tract pathogens. Reference ranges were established during test development, evaluating patients with live births to determine values of clinical relevance. Bacterial presence was expressed in percentage and compared using the Chi-Square test. Multivariate logistic regression was used for analysis, adjusting for demographic variables. Main results and the role of chance Among 7,795 patients, we detected at least one pathogen outside the reference range in 1,992 (25.6%). The four most prevalent pathogens were Gardnerella vaginalis (10.6%), Atopobium vaginae (7.6%), Ureaplasma urealyticum (4.7%), and Prevotella bivia (4.6%). 5,546 (71.2%) patients possessed at least one Lactobacillus species present, with Lactobacillus crispatus the most abundant (39.6%), followed by Lactobacillus iners (27.5%), Lactobacillus jensenii (21.7%), and Lactobacillus gasseri (12.9%). Patient stratification by Lactobacillus presence revealed a significantly lower prevalence of pathogens in those possessing (23.3%) compared to those lacking Lactobacillus species (31.1%) (p < 0.001). We performed additional analyses to determine the Lactobacillus species most strongly associated with pathogen presence. Samples with only one Lactobacillus species possessed the following distribution: L. crispatus (21.8%), L. gasseri (6.7%), L. iners (14.0%), and L. jensenii (4.0%). Notably, only 11.9% of samples containing L. crispatus contained pathogens, compared to 45.8% for L. gasseri (p < 0.001). Samples containing L. iners and L. jensenii displayed intermediate pathogen values of 28.7% and 24.2%. Multivariate logistic regression revealed a positive correlation for L. gasseri (aOR 2.3, 95% CI 1.8-2.9) and a negative correlation for L. crispatus (aOR 0.5, 95% CI 0.4-0.6) with regard to the presence of pathogens. Limitations, reasons for caution The methodology applied ensured an adequate assessment at the species level; however, we could not correlate the results with clinical outcomes in this retrospective study despite validating the test with clinical outcome data to establish the reference ranges for each pathogen. Wider implications of the findings Our findings reveal differences in pathogen prevalence according to the presence of distinct Lactobacillus species; we observed lower and higher prevalence of pathogens in the presence of Lactobacillus crispatus and Lactobacillus gasseri, respectively. These results reinforce the need for adequate methodologies for microbiome evaluations at the species level. Trial registration number No