Candida on urinary catheters can be more than contamination, patient samples suggest

Relying on a urinary catheter is a standard part of medical care for hundreds of thousands of patients each year. Unfortunately, the device carries the risk of catheter-associated urinary tract infections (CAUTIs), for which bacteria are widely recognized as the primary cause. And yet, many patients face a growing threat from another pathogen: a fungus, Candida albicans.

Research published in Proceedings of the National Academy of Sciences by University of Notre Dame associate professors of biological sciences Ana Flores-Mireles and Felipe Santiago-Tirado shows how the fungus works in the bladder, potentially changing the way doctors treat and diagnose CAUTIs.

A master switch in the bladder

Their work continues foundational research the team previously published. They mapped a critical protein called Efg1, which serves as a “master switch” in C. albicans. Without this protein, the fungus cannot cause disease in a catheterized bladder. However, Flores-Mireles and Santiago-Tirado did not know which specific target genes Efg1 commanded inside a catheterized bladder.

“This protein has been really well described in other infections, but not in the bladder,” Flores-Mireles said.

The research team sequenced the genetic activity of Candida strains, identifying 75 target genes that are turned on in the bladder. Twenty-six had never been characterized before, demonstrating how unique the bladder environment is.

To verify their laboratory findings, Flores-Mireles and Santiago-Tirado, along with their doctoral student and first author, Alyssa La Bella, evaluated urinary catheters collected from patients with C. albicans by analyzing fungal RNA directly from those devices. The fungal gene network they saw in the laboratory was nearly identical to the one they detected in patient samples.

“When we got the samples from humans, and saw the exact same results, we knew this was ‘real,'” Flores-Mireles said.

Evidence from patient catheters

Physicians often characterize fungus found on catheters as potential contamination rather than part of the active infection within the bladder, Santiago-Tirado said. This is because current diagnostic tools are designed to detect “swimming” bacteria in urine samples rather than biofilms attached to catheters.

“For us to be able to get these catheters and show that, yes, this factor is critical, that this fungus is a colonizer, and not contamination, is important,” Flores-Mireles said. “It’s actually a virulent process.”

Their study also described how C. albicans behaves when sharing space with bacteria on a catheter. When researchers examined catheters containing both Candida and E. coli, the virulence of the Candida decreased because it is often killed by the bacteria.

“People will study these infections as monomicrobial, as like, pure infection from one pathogen,” Santiago-Tirado said. “But now we realize that in reality, in hospitals, in real life, almost all of the infections are polymicrobial, so people are starting to look more carefully at interactions between microbes and how they might have positive or negative contributions to the person’s symptoms.”

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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