Washington, DC – March 16, 2021 – For the first time, researchers have isolated the fungus Candida auris from a sandy beach and tidal marsh in an isolated coastal wet ecosystem. The find, reported this week in mBio, an open access journal of the American Society for Microbiology, represents the first evidence that the pathogen thrives in a natural environment and is not restricted to mammalian hosts. C. auris can cause infections that are resistant to major antifungal drugs, and since it was identified in clinical patients 10 years ago scientists have tried to understand where it came from.
A statement accompanying the study, published at the same time in the journal, said the work was a “unique discovery.”
Medical mycologist Anuradha Chowdhary, Ph.D, at the University of Delhi, India, led the new study. She and her colleagues analyzed 48 soil and water samples collected from 8 sites including rocky shores, sandy beaches, tidal bogs and mangrove swamps around the Andaman Islands, a remote island with a tropical climate in the Bay of Bengal. They removed C. auris in the samples from two sites, sea salt marsh wetland and beach.
In samples from the salt marsh, which was rich in seagrass and low in human activity, the researchers found 2 isolates, one of which tended to be multi-rub when tested against antifungals. In samples from the beach, which were high in human activity, the team identified 22 individuals, all of whom were versatile. A whole genome sequence of the isolated islands showed a close association with pathogenic strains found in Southeast Asia.
“The loneliness? Found in the area where human activity was more linked to sequences we see in the clinical setting,” Chowdhary said. Future studies, she said, may be able to explain that connection. “It may come from plants, or it may be peeled from human skin, which we know C. auris can colonize. We need to study more environmental areas for the pathogen.”
Although cases of C. auris went into the mid-1990s, the fungus was not named until 2009. The new work also provides evidence for a hypothesis recently introduced by the microbes that wrote the new report, including Arturo Casadevall, Ph.D, of the Johns Hopkins Bloomberg School of Public Health in Baltimore; Dimitrios Kontoyiannis, Ph.D, of Texas MD University Cancer Center in Houston; and Vincent Robert, Ph.D, Westerdijk Fungal Biodiversity Institute, in Utrecht, the Netherlands.
The tripod suggested that C. auris, which is tolerant to temperature and salinity range, is native to bogs, and is emerging as a pathogen in humans due to the effects of global warming on these environments. Chowdhary, who has been studying C. auris for nearly a decade, said her hypothesis prompted her to study ecological areas where the fungus might live.
“This study takes the first step toward understanding how a pathogen survives in the wetlands,” Chowdhary said, “but this is just one specific place.” Future studies, she said, could reveal more about how the fungus thrives in the country – and a better explanation of why it poses a threat to humans.
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