Novel Research Shedding Light on Fungal Infections BY DAVID WILD A Candida tropicalis fungal colony. Source: CDC/ Dr. Hardin
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ovel diagnostics are helping clinicians identify fungal infections where conventional methods have proven insufficient, and new technologies are revealing that fungi interact with pathogenic bacteria in ways that can exacerbate infections. “There is an increased understanding that while many types of chronic wounds, including diabetic foot ulcers, are polymicrobial in nature, traditional culture methods might underrepresent the vast diversity of chronic wound microbiomes, including fungal populations,” explained Lindsay Kalan, PhD, an assistant professor, Departments of Medical Microbiology and Immunology and Medicine, Division of Infectious Disease, University of Wisconsin–Madison. Advanced techniques have uncovered fungi in roughly 80% of diabetic foot ulcers, whereas traditional culturing methods identify fungi in only 5% of wounds, Dr. Kalan noted (mBio 2016;7[5]:e0158-16. doi:10.1128/mBio.01058-16). Better understanding of the role that fungal populations play in these infections could help pinpoint those patients who are most likely to develop nonhealing foot wounds, she said, noting that the presence of other organisms, such as Staphylococcus aureus, has not been a very good prognostic marker in this regard.
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“We have found some interesting things by studying microbial communities instead of a single pathogen within a single wound sample and looking at how community diversity changes before and after an intervention,” Dr. Kalan said. For example, she and her colleagues found that diabetic foot wounds that heal after debridement exhibit a significant drop in the overall microbial diversity, while unhealed or amputated wounds have a much larger proportion of fungi on a community level (mBio 2016;7[5]:e0158-16. doi:10.1128/mBio.01058-16). “Additionally, looking at highly necrotic tissue, we’ve seen a really striking increase in the proportion of pathogenic fungi that grow alongside anaerobic bacteria, suggesting there are bacterial–fungal networks forming within these wounds and leading to poor outcomes,” she said. Indeed, using a diabetic foot ulcer lab model, her team demonstrated that bacteria and fungi “jointly synergize to contribute to pathogenesis,” she said. They cultured Candida albicans along with S. aureus and Citrobacter freundii, a species of anaerobic gram-negative bacteria, and found that when C. albicans colonized first, C. freundii outcompeted S. aureus by inducing growth of fungal hyphae and binding to C. albicans (ISME J 2021;15:2012-2027). They also found significantly
