Antibiotic-resistant bacterial infections are a growing threat, as researchers estimate a high probability of them killing an estimated 10 million people per year by 2050. Of particular concern are infections with bacteria that form biofilms, which require 100 - 1,000 times more antibiotics than other bacteria, and being significantly more likely to become multidrug resistant. A team of researchers recently uncovered a surprisingly effective treatment - one that dates back as far as 1,000 years.

Biofilms are like cities for microbes - large deposits containing high concentrations of multiple microorganisms that work in coordination to produce and share resources. These microorganisms produce a variety of polymer substances that form an extracellular matrix that has a sticky texture and protects the inside layers of the biofilm from the external environment, including antibiotic treatments. Before the discovery of antibiotics in the 20th century, remedies such as Bald’s eyesalve (a combination of onion or leek, garlic, wine, and bile salts) were used to treat infection. Given recent evidence of its efficacy in killing Staphylcoccus aureus biofilms, and the current lack of success in creating novel antibiotics, researchers are now turning to the question of whether ancient remedies may guide the development of new treatments.

The researchers prepared the Bald’s eyesalve according to instructions from a 10th century Anglo-Saxon leechbook - an Old English medical text. The ingredients were mixed and left to brew for nine days. Then the researchers prepared cultures of non-biofilm bacteria and mature biofilms of eight strains of bacteria that commonly cause chronic wound infections. The biofilms were deposited in a synthetic soft-tissue wound model made to mimic bodily infection. The researchers then measured the number of live bacteria remaining after 24 hours of exposure to Bald’s eyesalve. They found that the medieval treatment eradicated six of the eight non-biofilm cultures, while the two species that were not eradicated, (Staphylococcus aureus and Staphylococcus maltophilia), were exponentially reduced. The treatment’s success was similar in treating biofilm-producing cultures, with five of eight of them being exponentially reduced. There was, however, no consistent killing of biofilms containing Pseudomonas aeruginosa, Escherichia cloacae, or Staphylococcus maltophilia.

Having documented the effectiveness of the remedy in a variety of bacterial strains, the researchers then repeated their experiment with various preparations of the salve that omitted one ingredient at a time, in order to determine whether any one of them was responsible for any antimicrobial effects. They found that garlic, which contains the antimicrobial compound allicin, was independently effective in killing non-biofilm cultures. However, all four ingredients were necessary to produce the anti-biofilm effects.

These results indicate that ancient remedies containing multiple coordinating ingredients may have a crucial role in the fight against antibiotic resistance.

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