Hyperosmotic agents help clear biofilms in unexpected ways

Medical-grade honey and cadexomer iodine are hyperosmotic agents that have been shown to have antimicrobial activity. A new study reports that they may also clear biofilms by promoting wound healing.

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The medical benefits of honey have been espoused for centuries and in early 2000, a wave of academic literature began saying that certain types of honey can be used to treat infection.

While the real world application of honey as an antimicrobial is debatable, in the lab, it certainly has antimicrobial activity against a wide range of bacteria. This has been attributed to a cocktail of compounds found naturally in honey, but also the the fact that the thick, sticky substance is hyperosmotic ie. very, very sugary.

Well no wonder it kills bacteria and can be used to treat infection. Case closed.

Not so fast. A team of researchers at Washington State University lead by Haluk Beyenal have found evidence that hyperosmotic agents have additional benefits when it comes to clearing an infection. They saw that applying medical-grade honey or cadexomer to biofilms increased the dissoved oxygen and decreased the pH which are important factors in wound healing and general skin health. They also found that applying these agents improved the activity of some antibiotics.

Read the abstract from Applied and Environmental Microbiology below.

Hyperosmotic agents and antibiotics affect dissolved oxygen and pH concentration gradients in Staphylococcus aureus biofilms


Biofilms on wound surfaces are treated topically with hyperosmotic agents such as medical-grade honey and cadexomer iodine; in some cases, these treatments are combined with antibiotics. Tissue repair requires oxygen, and a low pH is conducive to oxygen release from red blood cells and epithelialization. We investigated the variation of dissolved oxygen concentration and pH with biofilm depth, and the variation in oxygen consumption rates when biofilms are challenged with medical-grade honey or cadexomer iodine combined with vancomycin or ciprofloxacin. Dissolved oxygen and pH depth profiles in Staphylococcus aureus biofilms were measured using microelectrodes. The presence of cadexomer iodine with vancomycin or ciprofloxacin on the surface of the biofilm permitted a measurable concentration of oxygen at greater biofilm depths (101.6 ± 27.3 μm, P = 0.02 and 155.5 ± 27.9 μm, P = 0.016, respectively) than in untreated controls (30.1 μm). Decreases in pH of ∼0.6 and ∼0.4 units were observed in biofilms challenged with medical-grade honey alone and combined with ciprofloxacin, respectively (P < 0.001 and P = 0.01, respectively); the number of bacteria recovered from biofilms was significantly reduced (1.26 log) by treatment with cadexomer iodine and ciprofloxacin (P = 0.002) compared to the untreated control. Combining cadexomer iodine and ciprofloxacin improved dissolved oxygen concentration and penetration depth into the biofilm, while medical-grade honey was associated with a lower pH; not all treatments established a bactericidal effect in the time frame used in the experiments.

Importance Reports about using hyperosmotic agents and antibiotics against wound biofilms focus mostly on killing bacteria, but the results of these treatments should additionally be considered in the context of how they affect physiologically important parameters such as oxygen concentration and pH. We confirmed that the combination of a hyperosmotic agent and an antibiotic results in greater dissolved oxygen and reduced pH within a S. aureus biofilm.


2017. Hyperosmotic agents and antibiotics affect dissolved oxygen and pH concentration gradients in Staphylococcus aureus biofilms

Mia Mae Kiamco, Erhan Atci, Abdelrhman Mohamed, Douglas R. Call and Haluk Beyenal. Appl. Environ. Microbiol. doi:10.1128/AEM.02783-16

Ben Libberton

Science Communicator, Freelance

I'm a freelance science communicator, formerly a Postdoc in the biofilm field. I'm interested in how bacteria cause disease and look to technology to produce novel tools to study and ultimately prevent infection.