horse skin wound
Move over antibiotics. Equine platelet lysate might hinder bacterial growth just as well—and without causing antimicrobial resistance.

Researchers at the University of Georgia have discovered that platelet lysate pooled from donor horses significantly slowed bacterial growth rates in the laboratory. The results pertained to both Gram-positive and Gram-negative bacteria, including Escherichia coli and pathogens responsible for certain kinds of endometritis and joint infections, said John Peroni, DVM, MS, of the Department of Large Animal Medicine in the University’s College of Veterinary Medicine, in Athens.

“Our findings demonstrate the potential value of platelet lysate as a broad-spectrum antimicrobial that would offer an alternative to traditional antibiotics for the treatment of bacterial infection in equine species,” Peroni and his colleagues stated in their recent publication in Frontiers in Veterinary Science.

Researchers have already determined that pooled platelet-rich plasma lysate (pPRP-L) appears to help reduce inflammation in cases of equine osteoarthritis and can contribute to lower bacterial counts in joint infections when associated with systemic antibiotics and anti-inflammatories.

Peroni, however, suspected the donor-derived compound might have antimicrobial properties itself, he said. That’s because scientists have already shown that platelets kill bacteria by producing superoxide, hydrogen peroxide, hydroxyl-free radicals, and other oxygen metabolites. Platelets also facilitate antibody-mediated killing of pathogenic bacterial cells, possibly through a direct interaction between platelets and the bacteria or through peptides released by the platelets.

So Peroni and his fellow researchers used plateletpheresis to manufacture platelet lysate from plasma donated from healthy adult mixed-breed horses belonging to the University of Georgia. They cultured strains of E. coli and Pseudomonas aeruginosa—both Gram-negative—and of Staphylococcus aureus and Enterococcus faecalis—both Gram-positive—in their laboratory. Then, they measured bacterial growth over 24 hours, in the presence and absence of platelet lysate.

In general, the researchers found that the bacteria grew approximately 10 times more without the platelet lysate during that 24-hour period, Peroni said.

Encouraged by those results, the scientists then measured hourly growth of bacteria at different platelet lysate concentrations.

The more platelet lysate in the test dish, the slower the growth for E. coli and P. aeruginosa, he said. The compound even delayed the start of exponential growth in these bacterial species.

For S. aureus and E. faecalis, however, the higher concentrations of platelet lysate did not matter: The reduction in bacterial growth remained stable.

This suggests platelet lysate might help overcome current issues with antibiotics: Few new antibiotic agents are being discovered; bacteria are developing strong resistance to antibiotics; and veterinarians must select antibiotics according to the type of bacteria.

Platelet lysate, however, appears to offer a new, broad-spectrum approach toward managing pathogenic bacteria, with no signs of resistance, he said. In addition, platelet lysate is “very versatile,” formulated as a liquid or a gel that could potentially be used systemically or locally. Platelet lysate would be “ideal” for use in joint infections, orthopedic implant failure, and skin grafts, for example, where veterinarians want to stave off local infections without affecting the gut microbiota, Peroni explained.

While he refrains from touting platelet lysate as a “miracle” drug, Peroni said its possibilities are nonetheless “super exciting” and offer many avenues of study.

While platelet lysate is not a replacement for standard antibiotics, it does provide hope for a much-needed alternative. “I’m not knocking the effectiveness of the antibiotic,” he told The Horse. “I’m saying that the quest for an alternative is a really big deal worldwide (across multiple species), so why not do a good job in the equine space as well?”

Although still in experimental stages, platelet lysate as an antimicrobial could reach veterinary markets within a few years, said Peroni.

“Our findings highlight the potential value of platelet lysate as a broad-spectrum antimicrobial deserving further and more detailed analysis,” the research team stated. “This, together with its known anti-inflammatory effects, could define it as a multifunctional treatment, helping to control both inflammation and infection to promote the healing process.”

The study was published in the August 2021 issue of Frontiers in Veterinary Science.