Role of anaerobic bacteria in equine endometritis.

The research article discusses a study done over three horse breeding seasons that investigated the presence and significance of anaerobic and aerobic bacteria on the reproductive health of Thoroughbred mares and stallions.

Study Overview

• The study took samples from 362 clitoral and endometrial swabs, and uterine washes, across 263 Thoroughbred mares of various reproductive statuses: maiden, foaling, post-foaling heat, and barren.
• Furthermore, 113 samples were collected from male parts (urethra, urethral fossa, prepuce and pre-ejaculatory fluid) of 29 Thoroughbred stallions.

Significance of Bacterial Isolates

• The researchers determined the significance of isolated bacteria by their association with acute endometritis (inflammation of the inner lining of the uterus), which was confirmed by concurrent endometrial test results.
• Other factors for consideration were the age and reproductive status of the horses before and after the study.

Results and Findings

• The research findings suggest that the horse uterus may have obligate anaerobes as surface commensals, meaning these bacteria usually live on the external genital surfaces of mares and stallions without causing disease.
• However, these bacteria may become pathogenic under specific circumstances, such as during injury or damage to the reproductive organs, or post-partum involutionary period.
• Often, there’s a synergism with aerobic bacteria resulting in mixed infections and active endometritis.

Notable Uterine Bacterial Species

• The study identified Bacteroides fragilis as the most notable anaerobic species in the uterus of mares. Noteworthy is this bacterium’s resistance to penicillin and aminoglycosides, two common types of antibiotics.

Implications for Treatment

• The research suggests that the nature of these bacteria needs careful consideration during treatment because they tend to resist common antibiotics.
• Diagnostic procedures focusing on anaerobic bacteria are inherently time-consuming, and since mixed infections are frequent, using nitrofurantoin or metronidazole in antibiotic mixtures is recommended.
• Failure to include these antibiotics in the treatment regimen may account for some cases of aerobe-negative persistent endometritis, a condition where inflammation in the uterus continues despite negative tests for aerobic bacteria.