A Medieval Potion Proves Its Worth as an Effective Bacteria Killer

Bald's eyesalve recipe, as found in an early Anglo-Saxon medical text.  (Image: University of Warwick)
Bald's eyesalve recipe, as found in an early Anglo-Saxon medical text. (Image: University of Warwick)

A 1,000-year-old recipe to treat eye infections could lead to an unorthodox way of combating antibiotic resistance.

Garlic, onion, wine, and a dash of bovine bile. It’s a veritable witch’s brew, but as a new Scientific Reports paper shows, this medieval recipe, called “Bald’s eyesalve,” is effective at staving off several nasty strains of bacteria, including those that have evolved to resistant antibiotics.

Indeed, the new paper, led by Freya Harrison from the School of Life Sciences at the University of Warwick, highlights an under-appreciated way of sourcing antibacterial compounds. Many previously effective antibiotic drugs no longer work, as germs are evolving new defences against them, so it’s important to develop alternative strategies. Medieval texts, while a seemingly weird source for medical information, could help in this regard.

“Plants have been used as medicines against infection for millennia, and we’ve only scratched the surface in understanding their true potential,” said Cassandra Quave, an ethnobotanist at Emory University who wasn’t involved in the new research. “This study is exciting because it demonstrates how mixtures of specific plant ingredients, such as those found in Bald’s eyesalve, can sometimes work better than individual components in fighting infection.”

Indeed, as the new research shows, the potency of Bald’s eyesalve couldn’t be whittled down to a single ingredient. For it to work, all ingredients had to be present, highlighting the importance of studying combinations of compounds.

The new study is a continuation of previous research conducted by Christina Lee from the School of English at the University of Nottingham. Lee had been studying Bald’s Leechbook, an early Anglo-Saxon medical textbook containing advice and recipes for medicines, lotions (or salves), and treatments. The book, written around 905 CE, was found in the British Library. Intrigued by Bald’s eyesalve, Lee, with the help from other experts, discovered that the lotion was surprisingly effective as an antibacterial compound against Staphylococcus aureus (MRSA) — a staph that can cause serious, and even fatal, infections.

The recreated Bald's eyesalve. (Image: University of Warwick)

For the new study, Harrison and her co-authors recreated the brew, testing it against five bacterial strains, including planktonic bacteria and biofilms, the latter being a complex bacterial colony often equipped with antibacterial-resistant attributes.

Specifically, Bald’s eyesalve was applied to soft-tissue models of infection, including infections of Acinetobacter baumanii (often found in war wounds), Stenotrophomonas maltophilia (commonly linked to lung infections), Staphylococcus aureus (often linked to surgical infections), and Staphylococcus epidermidis (associated with infections like tonsillitis, scarlet fever, cellulitis, and rheumatic fever). These bacteria are also found in diabetic foot ulcers, and all have shown varying degrees of resistance to standard antibiotics.

Tests of Bald’s eyesalve demonstrated “promising antibacterial activity” against these bacteria, whether in planktonic or biofilm form, according to the paper. The medieval mixture wasn’t harmful to human cells or to mice, which is good news, as it suggests the compound could be reconstituted as an effective treatment for infections.

That a mixture of onion, garlic, wine, and bovine bile can work so well in this context is pretty amazing, and it’s clear the inventor of this brew was onto something. As to how it works, that now presents a bit of a mystery.

Garlic contains allicin, which, while effective against planktonic forms of bacteria, is not very effective at tackling biofilms, like the kind of bacteria seen in foot ulcers. Accordingly, the researchers say Bald’s eyesalve is the sum of its total parts.

“We have found the potent anti-biofilm activity of Bald’s eyesalve cannot be attributed to a single ingredient and requires the combination of all ingredients to achieve full activity,” wrote the researchers.

Indeed, the new research shows the importance of sourcing antibacterial compounds with multiple ingredients, as Harrison explained in a University of Warwick press release.

“Most antibiotics that we use today are derived from natural compounds, but our work highlights the need to explore not only single compounds but mixtures of natural products for treating biofilm infections,” explained Harrison. “We think that future discovery of antibiotics from natural products could be enhanced by studying combinations of ingredients, rather than single plants or compounds. In this first instance, we think this combination could suggest new treatments for infected wounds, such as diabetic foot and leg ulcers.”

This isn’t the first time that scientists have found value in old-timey medicines. Last year, Quave co-authored a paper investigating medical plants used during the U.S. Civil War. The remedies, found in a Confederate Civil War field guide, described three plant-based topical remedies, all of which exhibited antimicrobial potential.