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Drug-resistant fungi, notorious for making ICU patients sicker, found in nature for first time

The Print logo The Print 19-03-2021 Mohana Basu
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New Delhi: A drug-resistant fungus that was so far known to only dwell in hospitals, and even co-infect Covid-19 patients, has been discovered in the natural environment for the first time in the Andamans.

Candida auris (C. auris) is notorious for lurking in ICUs across the world and worsening the health of patients who are already ill. In September, a small study in Delhi ICUs found that 60 per cent of Covid-19 patients who also got infected with Candida auris died. 

The discovery of C. auris at a sandy beach and tidal swamp in the Andaman Islands has been made by a team of researchers from Vallabhbhai Patel Chest Institute in Delhi. The team was led by researcher Anuradha Chowdhary, who has been working on C. auris for almost a decade and is credited with making a significant contribution to understanding the fungus.  

For their study, Chowdhary and team collected 48 soil and water samples from eight sites in the “virgin habitats” of the Andamans, including rocky shores, sandy beaches, tidal marshes and mangrove swamps. The samples were then put through mass spectroscopy (that helps identify the mass of tiny particles suspended in a solution) and genome sequencing, which revealed the presence of C. auris in samples from two sites — a beach and a marsh.

The C. auris samples isolated from the beach were drug-resistant, and may have been left there by an infected person. Genetic sequencing revealed the fungi were closely related to the yeast found in clinical settings. 

The samples from the salty marsh, however, were not drug-resistant, showing that there are environmental niches that naturally harbour C. auris. 

According to the researchers, these need to be explored in the future to understand how the transmission is occurring in humans. 

The research was published in the journal mbio on 16 March. A group of US researchers also involved in studying the fungus has hailed the study, describing its findings as a “landmark discovery” in the pursuit of exploring a potential link between C. auris infections in humans and climate change.

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Chasing the fungus

In 2013, Chowdhary’s team became the first in the world to describe a large series of C. auris bloodstream infections from two hospitals in Delhi.

“Before our findings, only one report from Korea was published in 2011 with three cases,” she told ThePrint. 

In 2015, her team’s work was the first to draw attention to the fact that this yeast is misidentified in routine microbiology laboratory as C. haemulonii or other yeasts. 

“After that, many commercially available databases were upgraded to correctly identify this yeast in identification systems. We also brought attention that this yeast is multidrug-resistant and pan-drug resistant by documenting antifungal data of a large series of isolates,” she added.

C. auris infections are not restricted to coronavirus patients. According to Chowdhary, C. auris causes invasive infections — specifically bloodstream infections — in patients who are admitted in ICUs and are plugged into invasive devices.

According to the researchers, patients with comorbidities such as diabetes, coronary heart disease, and chronic heart disease are at increased risk of being infected with C. auris.

Candida auris was first described in 2009, Chowdhury said. Widespread use of antifungal medication such as Fluconazole may have contributed to selective pressures on the evolution of the fungi, causing C. auris to become drug-resistant, she said.

“The closest related species of C. auris have been isolated from a variety of marine and terrestrial environments, in addition to human sources,” Chowdhary added. 

However, its natural reservoir in the environment was not known. 

Before their 2013 paper was published, Chowdhary said, none of the countries recognised C. auris infections as a global phenomenon. “It was thought to be a problem of India.”

But afterwards, research teams in several other countries also found isolates of the yeast.

Link to climate change

In 2019, a group of scientists from Johns Hopkins Bloomberg School of Public Health and the University of Texas in the US hypothesised that the rise of fungal infections caused by Candida auris were a consequence of climate change. 

Arturo Casadevall, a professor of at Johns Hopkins, had predicted that these fungi were naturally present in the environment, and that global warming had pushed the yeast to adapt to infect humans. 

It was Casadevall’s hypothesis that inspired Chowdhary to explore ecological niches where the fungus might live.

“We already know that species related to C. auris are found in marine environments in other parts of the world,” she said.

In a linked commentary in the same journal where the study was published, Casadevall and his team hailed the team’s “landmark discovery”, adding that the work provides the first evidence to the global warming hypothesis.

(Edited by Sunanda Ranjan)

Also read: Drug-resistant fungi lurking in ICUs are infecting Covid patients, study in Delhi finds

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