Candida Auris Explained: The Hospital Fungus That Copies Its Genome to Beat Our Last-Line Drugs

Some fungi live quietly on human skin and never cause trouble. Candida auris is not one of them. Since it was first identified in 2009, this yeast has spread through hospitals on every inhabited continent, caused outbreaks in more than 60 countries, and earned a place on the World Health Organization’s short list of critical-priority fungal pathogens. It survives on bed rails and medical equipment for weeks, shrugs off many disinfectants, and when it slips into the bloodstream of a seriously ill patient, roughly 45 out of every 100 of those patients die.

Doctors do have a drug class that usually works: the echinocandins, often described as the antifungals of last resort. But in October 2026, researchers at the University of Exeter and City St George’s, University of London reported something unsettling in Nature Communications: C. auris can defeat those last-resort drugs by copying its entire genome — carrying two to four complete sets of its DNA at once — and the standard laboratory tests doctors rely on cannot see it happening.

This guide explains, in plain language, what Candida auris is, why hospitals fear it, how the genome-copying trick works, why it hides from routine tests, and what scientists are doing about it. A companion expert guide goes deeper into the molecular evidence: Candida auris echinocandin resistance — the expert deep-dive.

1. What Is Candida Auris?

Candida auris (recently reclassified by some taxonomists as Candidozyma auris) is a yeast — a single-celled fungus related to the Candida species that cause thrush. The resemblance ends there. Most Candida species live as harmless passengers in the body and only cause problems opportunistically. C. auris behaves more like a hospital-adapted predator:

• It spreads between patients. It colonises skin — especially armpits and groin — and sheds onto bedding, rails, monitors and other equipment, where it can persist for weeks.
• It targets the most vulnerable. Infections strike people who are already critically ill: intensive-care patients, people on ventilators, patients with central venous lines or urinary catheters, and those with weakened immune systems.
• It resists drugs. Many strains resist fluconazole, the workhorse antifungal. Some resist two of the three main drug classes, and rare strains resist all three — leaving doctors with almost nothing to prescribe.
• It is expensive to fight. One British outbreak cost an estimated £1 million to control; another forced a hospital unit to close completely for refurbishment.

That combination — transmissibility, drug resistance, and lethality in the frailest patients — is why infection-control teams treat a single detected case as an emergency.

2. The Drugs of Last Resort

Antifungal medicine has only three main classes of drugs for invasive infections: azoles, polyenes and echinocandins. Echinocandins — drugs such as anidulafungin, caspofungin and micafungin — work by sabotaging the fungal cell wall. A fungal cell is wrapped in a wall built partly from a material called beta-glucan, which human cells do not have. Echinocandins block the enzyme that makes beta-glucan, so the wall weakens and the cell ruptures or cannot grow.

Because human cells have no wall to attack, these drugs are relatively safe; because so many C. auris strains already resist azoles, echinocandins became the default first treatment for serious infections. If they fail, the fallback is amphotericin B, an older polyene drug that is effective but much harder on the patient’s kidneys. There is no deep bench behind it. That is the context in which the new study matters: the drug class doctors trust most is the one the fungus has learned to beat.

3. The Mystery: The Tests Said the Drugs Should Work

The Exeter and City St George’s team began with a clinical puzzle. Two critically ill patients in London had bloodstream infections with C. auris. Both were treated with anidulafungin — and the treatment failed, even though laboratory susceptibility tests said the fungus was sensitive to the drug, and genetic sequencing found none of the well-known resistance mutations. Those classic mutations sit in genes called FKS1 and FKS2, which encode the very enzyme echinocandins target. Change the enzyme, and the drug can no longer bind. Neither patient’s fungus had them.

So the fungus was surviving the drug without the usual explanation. Something else was going on — and finding it took an accident.

4. The Accident in the Incubator

While running drug tests, a researcher left plates of fungal cells incubating far longer than the standard test period. On returning, the team found that a tiny population of cells had appeared over several days and kept growing despite very high concentrations of antifungal drug. “We were surprised to discover an entirely new mechanism for this fungus to survive — particularly with luck playing a big part of the discovery,” said Dr Sarah Murphy, a co-first author of the study. The surviving cells, it turned out, had rewritten the rules by copying themselves — all of themselves.

5. The Copying Trick

Every C. auris cell normally carries one set of chromosomes — one copy of its genome, the full instruction book of its DNA. The survivors of the drug exposure carried two to four copies of that entire book.

Why does that help? Think of mutation as buying lottery tickets. A drug kills almost every cell; the population’s only hope is that some cell, somewhere, randomly acquires a change that lets it survive. A cell with four genome copies is running four times as many experiments at once. Changes accumulate far faster in a population like that — and under the life-or-death pressure of a drug, the rare helpful change is found much sooner. Biologists call the temporary multiplication of chromosome sets a ploidy shift, and it is a known survival trick in other fungi — but, as study co-first author Dr Hugh Gifford put it, “not one that is well known in C. auris.”

The copying is temporary. It is an emergency measure, switched on under drug stress — a way to gamble aggressively while the house is on fire, then settle back once the danger passes.

6. Two Kinds of Survivors

The surviving population did not behave as one. It split into two kinds of colony:

• Small-colony variants — slow-growing, cautious cells that tolerate the drug’s presence and wait.
• Large-colony variants — fast-growing cells that thrive despite the drug.

Running two strategies at once is known as bet-hedging: if the drug pressure continues, the fast growers win; if conditions change, the patient slow growers endure. The fungus, in effect, refuses to put all its cells in one basket.

The fast growers carried the decisive weapon: a wide range of disabling mutations in a gene called CRZ1 — nicknamed “Crazy-one” — which normally helps govern the construction and repair of the cell wall. With CRZ1 knocked out and extra chitin (another wall material) packed into the wall, the cells’ walls emerged from drug exposure essentially unharmed. The drug arrived, attacked a wall it could no longer weaken, and the fungus lived.

7. Why the Standard Tests Missed It

Routine susceptibility testing grows the fungus taken from a patient, exposes it to a drug, and reports a single verdict: susceptible or resistant. That verdict describes the average population. But in these infections the population was not uniform — resistant cells were hiding as a minority among susceptible-looking ones. The test read the majority and reported “susceptible”. The patient, meanwhile, was being treated for an infection that contained cells the drug could not kill.

This phenomenon — a mostly susceptible population harbouring resistant sub-populations — is called heteroresistance, and it is treacherous precisely because every individual test result can look correct while the treatment fails. The study’s practical warning to clinicians follows directly: when a patient with C. auris is not improving on an echinocandin, repeat the cultures and repeat the susceptibility testing; a reassuring first result is not the whole story.

8. What This Means for Hospitals — and for the Rest of Us

For most healthy people, C. auris is not a personal threat; it preys on patients who are already fighting for their lives in intensive care. Its significance is institutional. It exposes three weak points in modern medicine at once: a shrinking arsenal of antifungal drugs (only three main classes exist), diagnostics that can be blind to mixed populations, and hospital environments where a hardy organism can persist on surfaces despite cleaning.

Professor Tihana Bicanic, the study’s senior author, frames the broader lesson bluntly: emerging fungal pathogens carry what she calls a “Swiss Army knife of innovation” within their own genomes, enabling step-by-step adaptation and drug resistance — and the new mechanism “weakens our antifungal drug arsenal”. Her conclusion is an alarm: better antifungal drugs are needed urgently, alongside better ways to prevent fungal deaths altogether.

9. What Scientists Are Doing Next

The most immediate line of attack is combination therapy — treating with two antifungal drugs at once, so that no single trick (a copied genome, a disabled gene) can rescue the fungus from both. That strategy is being tested through the Exeter-led, UKRI-funded Fungi-CARE programme, run with City St George’s colleagues. Alongside it, the study argues for diagnostics that look inside the population — checking genome copies and hunting for resistant sub-populations — rather than issuing a single verdict for a mixed crowd of cells.

Key Takeaways

• Candida auris is a WHO critical-priority hospital fungus, lethal to roughly 45% of intensive-care patients whose bloodstream it infects.
• Under echinocandin drug pressure it transiently copies its whole genome (2–4 copies), multiplying its chances of evolving resistance.
• Survivors split into slow- and fast-growing variants (“bet-hedging”); the fast growers disable the cell-wall gene CRZ1 and thicken their walls with chitin, so last-line drugs fail.
• Standard susceptibility tests report the population average, so resistant minorities stay invisible — a pattern called heteroresistance.
• The recommended responses: repeat cultures and testing when treatment stalls, and combination antifungal therapy, now under study by the Fungi-CARE programme.

Sources

• Gifford H, Murphy S, et al. “FKS1/2-variant independent mechanisms underlying the emergence of resistance in echinocandin-refractory Candida auris infections.” Nature Communications, 15 October 2026. doi.org/10.1038/s41467-026-76954-x
• University of Exeter (2026). “Unexpected discovery of new mechanism which helps deadly fungus Candida auris evade treatment.” news.exeter.ac.uk
• City St George’s, University of London (2026). “Researchers uncover new way deadly fungus Candida auris evades treatment.” citystgeorges.ac.uk

This guide is educational information about published research. It is not medical advice and is not a substitute for diagnosis or treatment by a qualified clinician.