“Wounds on the distal limbs of horses heal more slowly than wounds on other parts of the body because of a comparatively decreased blood supply, poor soft tissue coverage, and an increased incidence of bacterial contamination because of proximity to the ground,” explained Isabelle Kilcoyne, MVB, Dipl. ACVS, assistant professor in the University of California Davis School of Veterinary Medicine, during her presentation at the 2019 Annual Convention of the American Association of Equine Practitioners, held Dec. 7-11 in Denver.
Without appropriate infection control, even small traumatic wounds can be career-limiting or even life-threatening.
Polyhexamethylene biguanide (PHMB) is a synthetic compound with a chemical structure similar to broad-spectrum antimicrobial agents. This antibiotic kills bacteria by binding to the bacterial cell membrane causing lysis (disintegration by cell wall or membrane rupture) of the cells.
“Cotton roll gauze impregnated with 0.2% PHMB was developed as a means of reducing bacterial growth within bandaged wounds in humans,” said Kilcoyne, who previously confirmed a 0.2% PHMB-impregnated dressing could help reduce the incidence of colic surgery incisional infections. “In experimental trials conducted by the manufacturer, the PHMB-impregnated dressing was effective in reducing numbers of penicillin-resistant staphylococcal species within the bandage and preventing colonization of the organism on human skin beneath the dressing.”
To compare the efficacy of 0.2% PHMB-impregnated gauze and nontreated gauze in reducing the growth of bacteria , Kilcoyne, together with Charlene Noll, DVM, and other veterinary specialists at UC Davis, collected and isolated samples of bacteria from wounds, draining tracts, and incisional infections of horses previously examined at the hospital.
They created petri dishes of those bacterial colonies and placed 0.2% PHMB gauze squares on the colonies for 24 hours. They measured zones of inhibition and compared treated and untreated (control) gauze squares.
“We found that the 0.2% PHMB-impregnated gauze squares significantly inhibited the growth of staphylococcal species and Escherichia coli species compared with the untreated gauze squares,” relayed Kilcoyne.
The PHMB squares inhibited Staphlococcus spp, growth by 33-83.1% and E. coli growth by 6.5-37%. They saw no inhibitory effect on the growth of Pseudomonas aeruginosa or Enterococcus spp.
“Based on the results of this study, the use of 0.2% PHMB-impregnated gauze reduced the growth of underlying bacteria commonly implicated in orthopedic wounds and infections of horses,” Kilcoyne concluded.