biofilms in mares with endometritis

Persistent bacterial communities covering a mare’s uterine surface spell trouble. These so-called “biofilms” cause inflammation, make it difficult for mares to get pregnant, and are highly tolerant of antimicrobial treatment, making them costly and time-consuming to treat. But one veterinarian has confirmed that a combination of drugs can disrupt these films in mares, potentially making the uterus a happier place for embryo attachment and pregnancy.

Ryan Ferris, DVM, Dipl. ACT, of Summit Equine, in Newberg, Oregon, has studied biofilms extensively, particularly in mares with endometritis (inflammation of the endometrium, or uterine lining). He presented his most recent findings at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

In previous in vitro (in the lab) studies, he’d found that a combination of the antibiotic ceftiofur and the buffering chelating agent tris-EDTA effectively killed bacteria living a biofilm lifestyle. Based on scanning electron microscopy the tris-EDTA broke up the biofilm material protecting the bacteria, allowing the antibiotic to better penetrate the plaques and kill them. So, he sought to confirm this finding in mares.

Ferris infected 20 mares with Pseudomonas aeruginosa, a common causative agent of endometritis. He split them into groups of five that received one of four different treatment protocols over three days (none [control group], ceftiofur, tris-EDTA, and ceftiofur/tris-EDTA combo). Fourteen days after the last treatment, he collected endometrial samples from each mare for culture and cytology and found that mares treated with the ceftiofur/tris-EDTA combo had significantly less intrauterine fluid and fewer white blood cells than did the mares treated with either ceftiofur or tris-EDTA alone; also, they had neither pathogenic (disease-causing) bacteria nor adherent material on the endometrial surface, whereas the other mares did.

“The combination is a more effective treatment against biofilm-associated endometritis than either one alone,” said Ferris. “This is exciting because it matched what we saw in vitro.”

He added, however, that not every case of bacterial endometritis involves a biofilm, and individual antibiotics can still clear those infections.

“If the bacteria are not cleared after the first round of antibiotic treatment, it’s highly indicative of biofilm-associated infection,” he added.