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Model of Chronic Equine Endometritis Involving a Pseudomonas aeruginosa Biofilm
Ryan A Ferris1, Patrick M McCue2, Grace I Borlee3
1Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado, USA rferris@colostate.edu brad.borlee@colostate.edu.
Abstract:
Bacteria in a biofilm community have increased tolerance to antimicrobial therapy. To characterize the role of biofilms in equine endometritis, six mares were inoculated with lux-engineered Pseudomonas aeruginosa strains isolated from equine uterine infections. Following establishment of infection, the horses were euthanized and the endometrial surfaces were imaged for luminescence to localize adherent lux-labeled bacteria. Samples from the endometrium were collected for cytology, histopathology, carbohydrate analysis, and expression of inflammatory cytokine genes. Tissue-adherent bacteria were present in focal areas between endometrial folds (6/6 mares). The Pel exopolysaccharide (biofilm matrix component) and cyclic di-GMP (biofilm-regulatory molecule) were detected in 6/6 mares and 5/6 mares, respectively, from endometrial samples with tissue-adherent bacteria (P < 0.05). A greater incidence (P < 0.05) of Pel exopolysaccharide was present in samples fixed with Bouin's solution (18/18) than in buffered formalin (0/18), indicating that Bouin's solution is more appropriate for detecting bacteria adherent to the endometrium. There were no differences (P > 0.05) in the number of inflammatory cells in the endometrium between areas with and without tissue-adherent bacteria. Neutrophils were decreased (P < 0.05) in areas surrounding tissue-adherent bacteria compared to those in areas free of adherent bacteria. Gene expression of interleukin-10, an immune-modulatory cytokine, was significantly (P < 0.05) increased in areas of tissue-adherent bacteria compared to that in endometrium absent of biofilm. These findings indicate that P. aeruginosa produces a biofilm in the uterus and that the host immune response is modulated focally around areas with biofilm, but inflammation within the tissue is similar in areas with and without biofilm matrix. Future studies will focus on therapeutic options for elimination of bacterial biofilm in the equine uterus.
Insights
Equine endometritis involves Pseudomonas aeruginosa biofilms, which modulate the local immune response. This study highlights biofilm presence and immune modulation in mares, suggesting new therapeutic targets for uterine infections.
Area of Science:
- Veterinary Microbiology
- Equine Reproductive Health
- Bacterial Pathogenesis
Background:
- Biofilms confer increased antimicrobial tolerance to bacteria.
- Equine endometritis is a significant concern in mare reproductive health.
- The role of bacterial biofilms in equine uterine infections remains incompletely understood.
Purpose of the Study:
- To characterize the role of Pseudomonas aeruginosa biofilms in equine endometritis.
- To investigate the localization and host immune response to biofilms in the equine uterus.
- To evaluate diagnostic methods for detecting endometrial biofilms.
Main Methods:
- Inoculation of mares with lux-engineered P. aeruginosa strains.
- Imaging of endometrial surfaces for bacterial luminescence.
- Cytology, histopathology, and cytokine gene expression analysis of endometrial samples.
- Comparison of Bouin's solution and buffered formalin for biofilm detection.
Main Results:
- Tissue-adherent P. aeruginosa biofilms were detected in all infected mares.
- Biofilm matrix components (Pel exopolysaccharide, cyclic di-GMP) were identified.
- Bouin's solution was superior to buffered formalin for detecting adherent bacteria.
- Increased interleukin-10 expression was observed around biofilm sites, indicating focal immune modulation.
- No significant difference in overall inflammation, but decreased neutrophils near biofilms.
Conclusions:
- P. aeruginosa forms biofilms in the equine uterus, contributing to endometritis.
- The host immune response is focally modulated around endometrial biofilms.
- Diagnostic techniques require optimization for biofilm detection in uterine tissues.
- Understanding biofilm dynamics is crucial for developing effective treatments for equine endometritis.
