Characterization of the follicular fluid microbiota based on culturomics and sequencing analysis

Introduction. The human oocyte microenvironment is follicular fluid, which is important for follicle growth, ovulation and maturation of the oocyte. The micro-organisms present in follicular fluid could be a predictor of in vitro fertilization outcomes. Hypothesis/Gap Statement. Women with follicular fluid colonized with micro-organisms can be asymptomatic, but the presence of some genera in the follicular fluid correlates with in vitro fertilization. Aim. To confirm the existence of micro-organisms in follicular fluid, and to profile the micro-organisms present in follicular fluid sampled from women undergoing in vitro fertilization with different outcomes. Methodology. Women undergoing in vitro fertilization (n=163) were divided into different subgroups according to their in vitro fertilization outcomes. Their follicular fluid samples were collected, and among them, 157 samples were analysed by 16S rDNA sequencing, and 19 samples were analysed using culturomics. Results. The culturomics results suggested that the 19 follicular fluid samples were not sterile. The isolation rates for Streptococcus, Finegoldia and Peptoniphilus were >50% in the 19 samples. Linear discriminant analysis effect size analysis showed differential bacteria abundance according to the pregnancy rate, the rate of normal fertilization, the rate of high-quality embryos and the rate of available oocytes. The sequencing results showed that micro-organisms could be detected in all 157 samples. Pseudomonas, Lactobacillus, Comamonas, Streptococcus and Acinetobacter were detected in all of the samples, but with a wide range of relative abundance. Pseudomonas, Lactobacillus, Ralstonia and Vibrio constituted a notable fraction of the microbiota. Conclusions. Follicular fluid is not sterile. Micro-organisms in follicular fluid could be a predictor of in vitro fertilization outcomes.