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Chronic wound healing impaired by fungal/bacterial combined biofilms

Fungal communities in chronic wounds appear to form mixed biofilms with bacteria, leading to poor patient outcomes and longer healing times, according to findings published in mBio (Sept. 6, 2016; 7(5):e1058–16).

The authors followed 100 patients with non-healing diabetic foot ulcers over a period of 26 weeks or until the wound had either healed or required amputation. Deep wound fluid was sampled every two weeks and underwent genetic sequencing.

Some 80% of the wounds were found to harbour fungi, which was significantly higher than previous estimates. Fungi were identified belonging to 284 different species, with the most abundant—Cladosporium herbarum—identified in 41% of the samples. The second most commonly found fungus was Candida albicans which was identified in approximately one-fifth of the samples.

“Chronic wounds are a silent epidemic,” said Elizabeth Grice, PhD, assistant professor of dermatology and microbiology at University of Pennsylvania in Philadelphia and senior author on the study, in a press release. “They usually occur in conjunction with another disorder such as diabetes or obesity, but once a chronic wound occurs, it requires a lot of healthcare and has a devastating effect on a patient’s quality of life.”

However, no single species of fungi the authors identified was associated with poor outcomes. Instead, mixed microbial communities were associated with slow healing or complications including bone infection and amputation.

Higher levels of ascomycetes—sac fungi—at the first swabbing were associated with wounds that took longer than eight weeks to heal, however. The authors said this suggests that a wound swab may be a means of quickly predicting how long it will take a wound to heal.

To determine if the microbial communites of two patients could form biofilms, the investigators isolated the C. albicans yeast and Citrobacter freundii bacteria from a patient whose wound eventually healed, and fungus Trichosporon asahii and bacteria Staphylococcus simulans from a patient whose wound resulted in an amputation. The bacterial-fungal pairs were co-cultured, and both pairs were found to form mixed biofilms.

Postdoctoral researcher at the University of Pennsylvania and co-author Lindsay Kalan, PhD, “showed very nicely that the fungi interact with the bacteria, potentially making biofilms within wounds,” said Dr. Grice. “You can’t properly target treatment if you are missing that critical interaction.”

Dr. Kalan says the study is a first step toward better understanding of chronic wounds and developing better ways to treat them. “There are polymicrobial interactions within these wounds. It’s important to look at the fungal and bacterial communities and how they interact with each other and the immune system to impair or promote healing.”

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