Beware biofilm formation on horse wounds

Groups of microorganisms that stick to each other to form colonies in a slimy layer covering living or non-living surfaces, biofilms can slow or halt healing.

A study from Denmark underscores the dangers of biofilm formation in equine lower leg wounds.

Biofilms are groups of microorganisms that stick to each other to form colonies in a slimy layer covering living or non-living surfaces. “Everyone knows biofilms,” says Elin Jørgensen, DVM, of the University of Copenhagen. “They are a part of the plaque forming on our teeth every day.”

A primary characteristic of biofilms is their resilience: Neither the host’s immune system nor antimicrobial medications are effective against them. The best way to eradicate a biofilm is to physically remove it. In the case of dental plaque, brushing accomplishes this, but it’s not always that simple.

Biofilms are groups of microorganisms that stick to each other to form colonies in a slimy layer covering living or non-living surfaces. Research has shown that biofilms can slow healing on limb wounds.

“The first ‘medical’ biofilm was described in 1982 in a pacemaker patient, where biofilm was detected on the pacemaker and kept seeding bacteria into the bloodstream of the patient, and antibiotics didn’t help, as biofilms are extremely tolerant towards antibiotics,” says Jørgensen. “The patient was not cured until the pacemaker (and thereby the biofilm) was removed.”

In most cases, biofilm in a wound must be surgically removed through debridement of the affected tissues. “It’s far better,” says Jørgensen, “to prevent a biofilm from forming in the first place than to have to remove one.”

What was not known was whether biofilms inhibit the wound healing process or are a byproduct of the disruption. Jørgensen and her fellow researchers set out to answer that question by devising a study to track biofilm formation in surgically created wounds on the lower forelimbs and shoulders of nine horses. To allow for comparison, wounds on one lower limb of each horse were left uncovered, while wounds on the other were bandaged using a gauze material known to inhibit wound healing by promoting the growth of excessive granulation tissue (“proud flesh”).

Click here to learn the phases of equine wound healing.

The researchers closely tracked the wounds over a 15-day period, regularly taking biopsies of the tissue for microscopic examination and grading of biofilm formation by size. They found that none of the shoulder wounds developed biofilm, while all leg wounds did between days seven and 10. By day 15 of the study, the biofilms in the bandaged limb wounds had increased significantly in size and depth compared to those in uncovered leg wounds. On the final day of the study, all bandaged limb wounds had biofilm formation, while only 57 percent of the bare leg wounds did.

Wound location and treatment also seemed to affect healing rates. By the final day of the study, the shoulder wounds were 28 percent of their original size, while uncovered limb wounds were 84 percent of their original size. Bandaged leg wounds actually grew larger, measuring 120 percent of their original size by the end of the study period. This data, the researchers say, demonstrates that biofilm and proud flesh are related to slow healing on lower limb wounds.

Just to be clear, says Jørgensen, bandaging of limb wounds is not a bad idea and it will improve healing if done correctly.

“Seek veterinary help for limb wounds,” she says. “The right management and treatment from the start is crucial for providing the best conditions for the wounds to heal.” Bandaging materials, particularly of the “primary” layer that comes in contact with the wound, are a crucial consideration, she adds, but the best choice depends on the characteristics of a specific wound and changes at each stage of the healing process, making guidance from a veterinarian extremely important.

Reference: “The occurrence of biofilm in an equine experimental wound model of healing by secondary intention,” Veterinary Microbiology, May 2017

This article first appeared in the September 2017 issue of EQUUS (Volume #480)

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