AAEP Reproduction Coverage: Battling Bacteria—Biofilms Within the Uterus

Akhal-teke mare protecting her foal on a summer pasture

Biofilm-associated endometritis causes refractory infectious disease in mares and frustration for equine practitioners. When uterine infections associated with biofilms are suspected, numerous treatment options exist. Practitioners should use these treatments in conjunction with culturing and sensitivity testing.  

“The vast majority of bacteria are capable of producing biofilm by moving from a single (planktonic) bacterium to a community of bacteria trying to survive and live,” explained Ryan Ferris, DVM, DACT, from Summit Equine Inc., in Gervais, Oregon, during a presentation at the 2022 AAEP Convention. “Biofilms allow tolerance to antibiotics and protection from the host’s immune system. When bacteria move from a single cell organism to a community, the established infection is much more difficult to eradicate.” 

When acute uterine infections become chronic and fail to resolve with traditional treatment regimens, the practitioner should consider the presence of biofilms.

Treatment Options for Biofilm-Associated Uterine Infections

“How do we treat these? Do we just put more antibiotics into the uterus? No,” stated Ferris. 

He said that bacteria living in biofilms can be up to 1,000 times more tolerant to treatment with antibiotics compared to planktonic bacteria. Thus, antibiotics alone are not as effective for infections believed to be associated with biofilms. 

Antibiotic and Non-Antibiotic Combinations

In vitro laboratory studies identified a number of antibiotic and non-antibiotic combinations that seemed effective. For Gram-negative bacteria, for example, a combination of antibiotics and non-antibiotics replaced daily for three consecutive days resolved the biofilm-associated infection. This suggests that the combination of non-antibiotics and antibiotics infused into the uterus for three consecutive days might provide similar results in the mare.

Ceftiofur and Tris-EDTA

Ferris then relayed the results of a study that involved inoculating mares with bacteria and allowing biofilm to form. The mares were then treated with tris-EDTA, ceftiofur, or the combination of ceftiofur and tris-EDTA. Clinically, the combination therapy improved clinical outcomes with scant uterine fluid compared with the control group. Additionally, the mares after treatment remained negative for detection of bacteria as compared to the control or antibiotic-treated mares, which remained chronically infected. 

“Other studies identified a whole host of ineffective treatments,” Ferris Noted. “N-acetylcysteine for example, when combined with ceftiofur, was rather useless. We might as well have just used saline.” 

Hydrogen Peroxide and Dimethylsulfoxide

Other therapies that helped clear biofilm-associated endometritis were 1% hydrogen peroxide and dimethylsulfoxide (30%, which is a high concentration). 

In Ferris’ hands, combination therapies involving appropriate antibiotics (selected based on culture and sensitivity testing) can be quite advantageous when treating an infection involving a suspected biofilm

“Be aware, though, that not all compounds can be mixed together. Don’t just start randomly making concoctions at home,” he advised. 

For recipes, Ferris recommended the following link: https://equinerepro.colostate.edu/formulary/Formulary/Uterine

Diagnosing Biofilm-Associated Infections

Currently, diagnosing a biofilm-associated infection can be difficult. The best methodology is detection of bacteria that are not eliminated when treated appropriately. To directly evaluate biofilm, practitioners need to perform an endometrial biopsy or hysteroscopy with biopsy of suspected areas. Even these diagnostics will only be able to determine there is a strong suspicion of a biofilm-associated infection. 

“If performing biopsies to diagnose biofilm-associated infection, they should be fixed with Bouin’s solution, not formalin,” Ferris emphasized. 

Despite biofilms being an important cause of chronic uterine infection, Ferris warned practitioners not to over-diagnose biofilms. 

“Biofilm-associated infections are still not a top differential for subfertility in mares,” he said. 

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