Antibacterial efficacy of metals in preventative and therapeutic equine podiatry applications

Summary Background Thrush, abscesses, white line disease and cankers are life‐threatening infections common in equine hooves. Copper has a history of medicinal use on equine hooves. There is a paucity of scientific evidence supporting the use of metals as antimicrobial agents in equine podiatry. Additionally, there is growing interest in discovering alternatives to copper. This report describes the process through which various metals inhibit the growth of bacterial pathogens using an equine hoof model. Objectives To report the results of exposure of clinically relevant hoof pathogens to various metals and determine the best method of application (i.e. route of exposure) of these metals to the pathogens. Study Design In vitro culturing of bacteria exposed to various metals. Methods Lawns of Escherichia coli were cultured anaerobically at 24°C for 1–8 weeks on the surface of nutrient agar with silicone padding placed on top. The silicone padding either encapsulated the metal (copper, zinc and silver) or allowed it to come into contact with the bacteria. After the initial incubation, the agar was moved to glass beakers containing 200 mL nutrient broth and incubated at 26°C and 95 rpm for 24 h. Then, the broth cultures were serially diluted and plated onto fresh nutrient agar plates to determine the survival of E. coli underneath the silicone padding. Any growth indicated the survival of E. coli after it came into contact with the metal. Results Growth of the bacteria was inhibited if the metal was free to diffuse away from the silicon padding or was in direct physical contact with the bacteria. Main Limitations Escherichia coli is a model pathogen representing Treponema sp. and Fusobacterium necrophorum . This work was conducted entirely in vitro. Conclusions Metals are efficacious antimicrobial agents in equine podiatry. Diffusion of the metal away from the padding is crucial for antimicrobial activity.