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Reprod Med Biol. 2018 Jan 18;17(2):125-133. doi: 10.1002/rmb2.12083. eCollection 2018 Apr.

Bacterial contamination hypothesis: a new concept in endometriosis.

Author information

Graduate School of Medical Science Department of Obstetrics and Gynecology Kyoto Prefectural University of Medicine Kyoto Japan.
Department of Gynecology Saiseikai Nagasaki Hospital Nagasaki Japan.
Department of Obstetrics and Gynecology Nagasaki University Graduate School of Biomedical Sciences Nagasaki Japan.
Department of Tumor and Diagnostic Pathology Atomic Bomb Disease Institute Nagasaki Japan.
Center for Quality Assurance in Research and Development Kyoto Prefectural University of Medicine Kyoto Japan.



Endometriosis is a multifactorial disease that mainly affects women of reproductive age. The exact pathogenesis of this disease is still debatable. The role of bacterial endotoxin (lipopolysaccharide, LPS) and Toll-like receptor 4 (TLR4) in endometriosis were investigated and the possible source of endotoxin in the pelvic environment was examined.


The limulus amoebocyte lysate test was used to measure the endotoxin levels in the menstrual fluid and peritoneal fluid and their potential role in the growth of endometriosis was investigated. Menstrual blood and endometrial samples were cultured for the presence of microbes. The effect of gonadotrophin-releasing hormone agonist (GnRHa) treatment on intrauterine microbial colonization (IUMC) and the occurrence of endometritis was investigated.

Main findings Results:

Lipopolysaccharide regulates the pro-inflammatory response in the pelvis and growth of endometriosis via the LPS/TLR4 cascade. The menstrual blood was highly contaminated with Escherichea coli and the endometrial samples were colonized with other microbes. A cross-talk between inflammation and ovarian steroids or the stress reaction also was observed in the pelvis. Treatment with GnRHa further worsens intrauterine microbial colonization, with the consequent occurrence of endometritis in women with endometriosis.


For the first time, a new concept called the "bacterial contamination hypothesis" is proposed in endometriosis. This study's findings of IUMC in women with endometriosis could hold new therapeutic potential in addition to the conventional estrogen-suppressing agent.


Toll‐like receptor; bacterial endotoxin; endometriosis; gonadotrophin‐releasing hormone agonist; menstrual blood

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