New clues to origin of mysterious deadly antibiotic-resistant pathogen


 

About a decade ago a new fungal pathogen was detected in a Tokyo hospital. It was resistant to most known antibiotics and it was subsequently named Candida auris. This pathogen was detected nearly simultaneously in hospitals across several continents and presented a major mystery for scientists. What was driving the emergence of this novel pathogen in geographically separate sites at virtually the same time?


A new study, published in the journal mBio, is offering clues to the origins of this deadly fungal pathogen. Researchers have, for the first time, discovered Candida auris in a natural environment.


Anuradha Chowdhary, from the University of Delhi, has studied Candida auris for nearly as long as we have known it existed. Chowdhary was inspired to look for the pathogen in natural environments after an article hypothesized global warming to be responsible for its emergence.


Candida auris was unusually tolerant of high temperatures and salinity, unlike its other close relatives. The hypothesis suggested particular coastal wetlands with ecosystems very susceptible to global warming, could serve as unique ecological niches for this new kind of fungus to evolve.


Exploring that hypothesis Chowdhary and a team of researchers collected a variety of environmental samples from eight different sites around the tropical Andaman Islands in the Bay of Bengal. Candida auris isolates were detected across two separate sites, a beach high in human activity and a more isolated salt marsh wetland.


Chowdhary said, the isolates found in the area where there was human activity were more related to strains we see in the clinical setting. It might be coming from plants, or might be shed from human skin, which we know C. auris can colonize. We need to explore more environmental niches for the pathogen.


The trio of researchers behind the original global warming hypothesis article call the findings a landmark discovery. They suggests it is conceivable the samples found on the public beach could have been carried there by people from health care environments but the two samples found in the remote wetlands were much more interesting.


The two isolates discovered in the wetlands were quite genetically distinct from each other. One of the strains in particular presented with a reduced heat tolerance compared to clinical strains of Candida auris. This suggests it may be a wild ancestor strain of the deadly pathogen found in hospitals, adding weight to the global warming emergence hypothesis.


Chowdhary said, this study takes the first step in toward understanding how pathogen survives in the wetland, but this is just one niche.


The new research does not wholly validate the global warming emergence hypothesis, but it does at the very least suggest Candida auris existed as an environmental fungus in nature before it appeared in hospitals as a superbug a decade ago. More natural samples of the fungus will need to be uncovered and studied before a clearer insight can be garnered into how this pathogen developed.


The researchers said, validating or refuting the global warming emergence hypothesis for C. auris will require a deeper exploration of the environmental isolates and closely related species. Support for the hypothesis would consist of finding more C. auris isolates with borderline mammalian thermotolerance and perhaps that these isolates can be adapted to grow at higher temperatures through laboratory selection for growth at higher temperatures.

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