Molecular microbiologic studies have suggested that the human endometrium has a resident microbiota dominated by Lactobacillus spp., similar to the vagina microbiota. However, these findings were primarily derived from endometrial samples obtained through a transcervical catheter and thus prone to contamination from the vaginal microbiota. Therefore, the existence of a resident endometrial microbiota and its structure, if indeed present, is still controversial.
PRB researchers investigated the molecular microbial profiles of mid-endometrial samples obtained from non-pregnant women undergoing hysterectomy, and compared them with those of the cervix, vagina, rectum, oral cavity, and controls for background DNA contamination. The bacterial burden and bacterial profiles of samples were examined through 16S rRNA gene quantitative real-time PCR and sequencing, respectively. Sixty percent of endometrial samples had a bacterial load exceeding that of background technical controls. The bacterial profiles of endometrial samples differed from those of the oral cavity, rectum, vagina, and background technical controls, but not of the cervix. The bacterial profiles of endometrial and cervical samples were dominated by Acinetobacter, Pseudomonas, Cloacibacterium, and Comamonadaceae. Both 16S rRNA gene sequencing and Lactobacillus species-specific (L. iners and L. crispatus) quantitative real-time PCR showed that Lactobacillus was rare in the endometrium. Therefore, if there is a microbiota in the mid-endometrium outside pregnancy, it is not dominated by Lactobacillus.