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Ionic Liquids Shown to Combat Bacterial Biofilms

Pseudomonas aeruginosa bacteria (NIH)

Pseudomonas aeruginosa bacteria (NIH)

27 August 2014. Researchers at Los Alamos National Lab in New Mexico developed a way to harness ionic liquids — salts in a liquid state — that in lab tests disrupt biofilms, antibiotic-resistant bacterial colonies, and boost treatments for skin infections. The team led by Los Alamos Lab’s David Fox and Samir Mitragotri at University of California in Santa Barbara published their results appearing in yesterday’s issue of Proceedings of the National Academy of Sciences (paid subscription required).

Biofilms are communities of microbes that connect and expand through a matrix of organic matter. These microbe colonies also stick tightly to surfaces, including the skin, making them difficult to treat, because of their persistence and ability to resist conventional antibiotics. When biofilms cause skin infections, the bacteria are further protected by the outermost layer of the skin. The authors cite data showing biofilms are responsible for some 80 percent of bacterial infections in humans, including wounds in the skin such as those developed at surgical incisions.

Fox and Mitragotri, with colleagues from their institutions as well as Dixie State University in Utah and Northern Arizona University, synthesized and tested ionic liquids as treatments for skin infections caused by biofilms. Ionic liquids are salt materials that form a liquid state below the boiling point, 100 degrees C, and are often used in industry as solvents, electrolytes, and lubricants.

The team tested a range of synthesized ionic liquids for their ability to break up biofilms, yet still deliver antibiotics through multiple skin layers and not irritate a patient’s skin. For these tests, they build a model wound with multiple skin layers in the lab, and tested the ionic liquid candidates on biofilms of two common bacteria: Salmonella enterica and Pseudomonas aeruginosa found in skin infections, including those acquired in health care settings.

The tests also included the ability to deliver cefadroxil, an antibiotic to treat skin infections through the multiple skin layers in the model. In addition, ionic liquids were tested against household bleach, already known to disrupt biofilms.

The tests show choline-geranate as the optimal ionic liquid for battling biofilms. The researchers report choline-geranate at least as effective as bleach in killing of more than 95 percent of the bacteria after a 2-hour treatment. In addition, choline-geranate was able to increase delivery of cefadroxil through 16 skin layers in the model, and did not appear to cause skin irritation.

“If the bacterial biofilm can be disrupted, delivery of antibiotics is greatly enhanced, and any dispersed pathogens are generally restored to normal antibiotic susceptibility,” says Fox in a Los Alamos Lab statement. “These materials are able to penetrate through the skin and effectively carry antibiotics to the deepest layers.”

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