Biofilm-Associated Endometritis in Mares

Bacterial endometritis that is refractory to traditional antimicrobial treatment is a significant challenge to the equine breeding industry. Fortunately, several therapeutic options are currently available to clinicians for the treatment of biofilm-associated endometritis in horses.

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Biofilm-Associated Endometritis in Mares
A biofilm is a group of bacteria surrounded by a matrix that is protected from the host immune system and antibiotic treatment. | Photo: Courtesy Dr. Ryan Ferris

Bacterial endometritis (infection of the uterine mucosa) that is refractory to traditional antimicrobial treatment is a significant challenge to the equine breeding industry. A common survival strategy employed by bacterial pathogens is the formation of a biofilm—a complex and dynamic structure composed of aggregates of bacteria surrounded by a thick protective layer of exopolysaccharide (a polymer composed of sugar residues).

Biofilms confer resistance to immune-mediated clearance by reducing the host’s ability to recognize infection. Additionally, biofilms protect bacteria from antibiotics by providing a diffusion barrier and creating a microenvironment that slows down bacterial metabolism and replication, which makes them more tolerant to antimicrobial agents. Using a model of equine infectious endometritis, we have clearly identified the ability of the bacterium Pseudomonas aeruginosa to form a biofilm within the uterus of the mare.

The biofilm forms in multiple locations with the greatest number of adherent bacteria occurring between the tissue folds and in the uterine horns. This suggests that a traditional guarded culture swab might not be ideal for detecting biofilm-associated infections; a low-volume lavage might be a better diagnostic tool. The bacteria are in greater numbers deep within the endometrial glands as compared to the luminal surface. To be successful in clearing these infections, treatment options need to be capable of penetrating deeper into the glands and tissue. For microscopic visualization of biofilms within endometrial biopsies, Bouin’s solution provides significantly better preservation of the biofilm matrix on the surface of the endometrium as compared to traditional formalin fixation

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