For the first time, researchers have isolated the fungus Candida auris a sandy beach and tidal swamp in a remote coastal wetland ecosystem. The discovery, 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 limited to mammalian hosts. C. auris can cause infections resistant to major antifungal drugs, and since its identification in clinical patients 10 years ago, scientists have sought to understand its origins.
A commentary accompanying the study, published simultaneously in the journal, hailed the work as a “historic 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, coastal swamps and mangroves around the Andaman Islands, a remote archipelago with a tropical climate in the Bay of Bengal. they isolated C. auris in samples from two sites, an intertidal salt marsh bay and a beach.
In samples from the salt marsh, which was rich in seagrass and low human activity, the researchers found 2 isolates, one of which was found to be multidrug resistant when tested against antifungals. In samples taken from the beach, with high human activity, the team identified 22 isolates, all multidrug-resistant. Whole genome sequencing of the isolates revealed that they were closely related to pathogenic strains found in Southeast Asia.
âThe isolates found in the area where there was human activity were more related to the strains we see in the clinical setting,â Chowdhary said. Future studies, she said, might be able to explain this link. “It can come from plants or can come from human skin, which we know C. auris can colonize. We need to explore more environmental niches for the pathogen. “
Although cases of C. auris trace until the mid-1990s, the fungus was not named until 2009.
The new work also provides evidence for a hypothesis recently introduced by the microbiologists who wrote the new commentary, including Arturo Casadevall, Ph.D, of the Johns Hopkins Bloomberg School of Public Health in Baltimore; Dimitrios Kontoyiannis, Ph.D, of the MD Anderson Cancer Center at the University of Texas at Houston; and Vincent Robert, Ph.D, Westerdijk Fungal Biodiversity Institute, Utrecht, The Netherlands.
The trio proposed that C. auris, which is tolerant to a range of temperatures and salinity, is native to wetlands, and its emergence as a pathogen in humans has resulted from the effects of global warming on these environments. Chowdhary, who studied C. auris for nearly a decade, said the hypothesis inspired her to explore ecological niches where the fungus could live.
“This study takes the first step towards understanding how the pathogen survives in the wetland,” Chowdhary said, “but it’s only a niche.” Future studies, she said, could reveal more about how the fungus thrives in nature and better explain why it is such a threat to humans.