A frenemy fungus provides clues about a new deadly one

It seems like every few years there’s a virus or bacterium that threatens human health in a new way. But a new fungus that is a threat to humans? That doesn’t happen very often. That’s why we in the medical mycology community – the people who study dangerous fungi – are so intrigued and concerned by news reports about a new, deadly fungus called Candida auris.

C. auris is believed to have been first identified in 2009 in the ear canal of a patient in Japan, but has taken the medical community by surprise with its rapid spread across the globe in the last decade. C. auris has now been detected in about 20 countries and shows no evidence of stopping.

What makes this well-traveled fungus fascinating and scary? Unlike other species of Candida, it is known to survive in hospital rooms for prolonged periods of time and is responsible for several outbreaks due to patient-to-patient transmission. The most concerning characteristic of this fungus, however, is its ability to withstand anti-fungal treatment.

We are a team of medical mycologists working at Tufts University and specializing in the study of a different fungus, Candida albicans, and how it affects human health. We have been interested in C. albicans for years because its interactions with humans are so complex: Sometimes it seems friendly and sometimes it is our enemy. The new fungus C. auris seems very mysterious but we believe we can use what we have learned from studying other fungi to deal with this new organism.

A formidable new adversary

Fungi are among the most successful, resilient and fascinating groups of organisms on Earth. In fact, the largest organism on Earth is believed to be a mushroom. We do not know exactly how long fungi have been around, but it is believed that they might be some of the oldest land dwellers on Earth.

During their existence, fungi have dealt with a multitude of global catastrophes, including five – and perhaps a coming sixth – mass extinctions. In order to survive and thrive during these extreme conditions, fungi have developed amazing strategies which have allowed them to conquer every environment imaginable. Out of the estimated 1.5 to 5 million fungal species on Earth, about 300 are able to cause disease in humans. In the case of C. auris, we know whom it is related to, but we do not know where it came from or how people acquire it.

Fungi are important in the natural environment as well as food and drug production. Rattiya Thongdumhyu/Shutterstock.com
Unlike anti-bacterials, the number of types of useful anti-fungal drugs is quite limited. There are only three main classes, and the chance of discovering new drugs is limited by the fact that fungi are in the group of organisms called eukaryotes, as humans are, which makes it difficult to find a drug that can kill a fungus but not a person. Additionally, anti-fungal resistance has been emerging over the past few decades in some fungi that cause disease in humans, but C. auris’ resistance to anti-fungals leaves other resistant fungi in the dust. Some C. auris strains are resistant to all classes of clinically used anti-fungals, which is extremely alarming.

C. auris is also able to form biofilms, which are microbial communities attached to a surface and protected by a “glue-like” layer. The architecture of the biofilm protects C. auris from anti-fungals and immune system attacks. In the context of health care, microbial biofilms often form on plastics such as catheters, pacemakers and other implanted devices. These biofilms have been well studied for many microbes, but we do not fully understand the importance of biofilms formed by C. auris in the context of human disease.

Where did this new pathogen come from? Why is it highly drug-resistant and able to spread so easily? How does it interact with our body and the other microbes in and on our body? While we don’t know much about C. auris yet, we know quite a bit more about its distant cousin, C. albicans.

Lessons from C. albicans

The fungus C. albicans was first described by Hippocrates in 400 B.C. when he was describing oral thrush, a disease characterized by white lesions that form in the oral cavity when there is overgrowth of C. albicans. Since then, C. albicans has become one of the most studied fungi next to Saccharomyces cerevisiae, the baker’s and brewer’s yeast.