Understanding Fungal Versus Bacterial Foot Infections in Dermatology, with William Scherer, DPM, MS

A talk presented at the 2025 SDPA Annual Summer Dermatology Conference in Washington, DC, featured speaker William Scherer, DPM, MS, who spoke about an often under-discussed topic in dermatology: interdigital foot skin infections.

Scherer, a Senior Podiatric Medical Advisor for Bako Diagnostics, interviewed on-site with the HCPLive editorial team, providing a list of important takeaways from his SDPA session on foot web space infections, fungal versus bacterial infections, methicillin-resistant Staphylococcus aureus (MRSA), and more. Scherer was asked about the most common misdiagnoses seen in this area, given the portion of his talk distinguishing fungal from bacterial infections in the foot’s web spaces.

“First things first, for any type of infection of the foot, and especially in patients wearing tight fitting shoes in the summer months where it's really hot and humid, the shoe is a perfect environment for bacteria to grow or fungus to grow,” Scherer explained. “What happens is that when you kind of cram your foot into a in a shoe, you're out walking around all day long, and there's the friction between the digits that it can cause a little maceration, breaking down the skin barrier, and that allows both a fungal infection or even a bacterial infection to kind of invade.”

Scherer noted that at first, this can feel like a small amount of pain, with a bit of redness. Then, he added, patients may ignore it and a condition can then fester and grow.

“But in the grand scheme of things, as a physician, we're always worried about bacterial infection,” Scherer said. “The misconception of this is that most patients, and even most physicians, think that it's a fungal infection…So the initial emphasis is that patients and doctors jump into the assumption that this is not a big deal. ‘It's athlete's foot or it's a fungus infection, so let's just treat it with some over the counter medications.’ And the truth is yes, in some patients, they're going to get better. But in a lot of patients, they do not. So in weighing the 2, I always emphasize, don't miss the bacterial infection by thinking that it's only a fungal infection.”

In his session, Scherer had highlighted the importance of DNA-based diagnostics. He was asked about how, in his experience, the use of PCR assays transformed the accuracy and speed of diagnosing interdigital infections compared to traditional methods like fungal culture.

“PCR is a huge game changer for all of medicine, this is now looking at the DNA specimens,” he said. “Number one, it's rapid, it's quick, and it's super accurate. So your sensitivity is quite high and your specificity is quite high, compared to, say, KOH or even fungal cultures. Historically, again, you're going back 10, 20, 30 years. Those were our classic diagnostic tests. What we're finding out is that when you compare them head-to-head, DNA does offer a superior identification of both the genus and the species in a rapid, high-sensitivity, high-specificity [manner]. So it's a perfect new test that you can apply, not only to things like COVID, and we all remember the importance of PCR testing for COVID, but also for skin and nails, especially bacterial and fungal infections, because now we can identify the genes and species of what we think are the most common organisms causing that infection.”

For any additional information on Scherer’s topic, and on differentiating these conditions, view Scherer’s full interview video posted above. For more from SDPA, view the latest conference coverage.

The quotes used in this interview summary were edited for clarity.

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