Marilen Benner

MICROBIOTA AND ENDOMETRIAL HEALTH 149 6 species of the genera Clostridium, Megasphaera, Parvimonas, Prevotella, Sphingomonas or Sneathia ). Eighteen of the 22 women presented with stable microbiota profiles when comparing pre-receptive and receptive phase, of which 12 women were continuously categorized in the Lactobacillus -dominated group, and six women categorized in the non- Lactobacillus group independent from sampling time point. This indicates that bacterial community composition was relatively stable in most women. Contradictory to the results by Franasiak et al. (2006), Moreno et al. (2016) found an association between Lactobacillus abundance and pregnancy outcome. Implantation was decreased (23.1% versus 60.7%), and pregnancy rates declined (13.3% versus 58.8%) when the women showed a non- Lactobacillus dominated endometrial phenotype at the time of ET. An especially negative impact on reproductive outcome was observed when G. vaginalis and Streptococcus species were present in abundance. These results were independent of pH of the sample, known to be affected by Lactobacillus species (58). Unlike the other transcervical sampling approaches, Walther-Antonio et al. (2016) studied samples taken from the uterus, Fallopian tubes, and ovaries removed during hysterectomy (n=31), in addition to pre-operative vaginal and cervical swabs and scrapes. Their results showed Shigella and Barnesiella as dominant species of the endometrial microbiome in accordance with earlier culture-based observations (36). High abundance of Staphylococcus, Blautia and Parabacteroides was found in benign uterine conditions (n=10), and Bacteroides , and Faecalibacterium were associated with women who presented with cancer as reason for hysterectomy (n=17). Miles and colleagues (2017) also took samples from various tissue types obtained during hysterectomy. Their data on 10 women, comprising a wide range of uterine pathologies, shows high variability. Species such as Lactobacillus, Acinetobacter, Blautia, Corynebacterium and Staphylococcus were abundantly found in some of the women. The authors also note that even after various attempts, no sequencing data could be obtained for endometrium from a patient with atrophic endometrium. Similarly, Chen and colleagues investigated the microbiota of different sites of the female reproductive tract accessed through surgery (23). Tissue was obtained during laparoscopy or laparotomy, therefore not reflecting healthy, fertile women of reproductive age but the patients enrolled had conditions known not to involve infection. In these conditions, Lactobacillus, Pseudomonas, Acinetobacter, Vagococcus, and Sphingobium were frequently detected. When evaluating the results of the recent 16S endometrial studies, certain species were found in more than one study (Table I). Some of the described findings are addressed in two recent reviews (4, 59), neither including a concluding summary of the species found in the different studies, nor a meta-analysis.