Composition of endometrial microbiota and chronic endometritis severity in patients with in vitro fertilization failures. Is there any connection

Background . Pelvic inflammatory disease (PID), including chronic endometritis (CE), is a factor leading to endometrial receptivity disorder and in vitro fertilization (IVF) failures. The role of microorganisms in colonizing the endometrium, the pathogenesis of chronic inflammation, and associated infertility require further study. Aims : To determine the taxonomic profile of the endometrial microbiota in different grades of CE in patients with a history of IVF failure. Materials and methods . This study included 107 patients with ≥ 1 IVF failures. Depending on the severity of CE, and according to the morphological analysis of endometrial biopsy, the patients were categorized into three groups: group I (n = 14), patients without signs of CE; group II (n= 20); patients with signs of mild CE; and group III (n = 73),patients with signs of moderate and severe CE. All the patients underwent Pipelle biopsy of the endometrium according to our modified technique on days 18–23 of the menstrual cycle. Species and quantitative composition of the endometrial microbiota were investigated using real-time polymerase chain reaction (PCR). Results . Compared to groups II and III, Lactobacillus spp. (50% and 46.6% versus 85.7%) and Eubacterium spp. (25% and 35.6% versus 78.6%) were detected significantly more frequently in the endometrial microflora of group I patients, respectively. Simultaneously, significantly more bacteria of the families Enterobacteriaceae (50% and 64.4% versus 35.7%, respectively) and Streptococcus spp. (55% and 56.2% versus 7.1%, respectively) were found in the patients of groups II and III compared to group I. The abundance of lactobacilli and Eubacterium spp. have also been shown to be significantly higher in the endometrial samples of women in group I than in those of the women in groups II and III, whereas the abundance of enterobacteria and streptococci are significantly higher in women with CE than in women without CE. Conclusions . In patients without signs of CE, Lactobacillus spp. and Eubacterium spp. prevail in the endometrial microbiota. Chronic inflammation in the endometrium is associated with an increase in the frequency and abundance of Streptococcus spp., Staphylococcus spp., and bacteria of the family Enterobacteriaceae.