The Other Resistance Crisis: Fungal AMR

Antibiotic resistance dominates the headlines. Drug-resistant bacteria are a crisis that kills 1.27 million people per year and threatens the foundation of modern medicine. But there is another resistance crisis — quieter, less funded, and in some ways more dire — unfolding in parallel. Drug-resistant fungi now kill an estimated 3.8 million people annually. And where bacteria face a shrinking but still substantial pipeline of new drugs, fungi face something closer to a void. For most of the modern antifungal era, clinicians have had access to only three classes of drugs: polyenes (amphotericin B, introduced in the 1950s), azoles (fluconazole, 1990), and echinocandins (caspofungin, 2001). Three classes across 50 years. By comparison, antibacterial medicine has produced more than 20 distinct classes. The reasons are structural: fungi are eukaryotes, like human cells. The molecular targets that distinguish fungal biology from ours are few, and hitting them without toxicity is hard. This biological kinship is not an excuse for neglect — it is an explanation for why the neglect has been so consequential. In 2022, the WHO published its first-ever Fungal Priority Pathogens List, ranking four species as critical threats: Cryptococcus neoformans, Candida auris, Aspergillus fumigatus, and Candida albicans. Each tells a different story about how fungi are outpacing the drugs meant to stop them. Together, they describe a crisis that mirrors bacterial AMR in its drivers — agricultural misuse, climate change, market failure, diagnostic gaps — while differing in ways that make it harder to solve. Cryptococcus neoformans: The Silent Catastrophe Cryptococcus neoformans sits atop the WHO Fungal Priority Pathogens List — the single highest-ranked fungal pathogen in the world. Its ranking reflects a body count that most people outside infectious disease have never heard of: 152,000 to 220,000 cases of cryptococcal meningitis per year, killing between 112,000 and 181,000. In sub-Saharan Africa alone, more than 130,000 die annually. Cryptococcal meningitis accounts for roughly 20 percent of all HIV-related mortality worldwide. The cruelty of Cryptococcus is compounded by what it resists. C. neoformans is intrinsically resistant to echinocandins — the newest and, for Candida infections, often the most reliable antifungal class. This means the entire toolkit against Cryptococcus consists of drugs from the 1950s (amphotericin B, which is nephrotoxic and requires IV infusion), the 1990s (fluconazole, to which resistance is increasing), and the 1960s (flucytosine, which is unavailable in most of the countries where Cryptococcus kills the most people). The standard regimen for cryptococcal meningitis in well-resourced settings — two weeks of amphotericin B plus flucytosine, followed by fluconazole — is inaccessible to most patients in sub-Saharan Africa. And Cryptococcus is not only a disease of HIV. Rising numbers of non-HIV patients — those with liver disease, renal failure, diabetes, organ transplants — are developing cryptococcal infections, often with higher mortality than their HIV-positive counterparts. The pipeline has glimmers. Fosmanogepix, Basilea's first-in-class Gwt1 inhibitor now in Phase 3, has activity against Cryptococcus — one of the few new agents that does. ATI-2307, a mitochondrial respiratory chain inhibitor, has completed Phase 1. And butyrolactol A, a phospholipid flippase inhibitor discovered by Gerard Wright's lab at McMaster University, can restore echinocandin activity against Cryptococcus — potentially opening up an entire drug class that the pathogen has historically ignored. The WHO published its first-ever Target Product Profile for new anti-cryptococcal agents in late 2025, formally acknowledging the void. But none of these are approved. None are close. The world's number-one fungal killer is being fought with 70-year-old drugs. Candida auris: The Pathogen That Climate Change May Have Created If Cryptococcus represents the deepest humanitarian crisis, Candida auris represents the most alarming trajectory. First identified in 2009 from a patient's ear canal in Japan, C. auris appeared simultaneously on three continents in genetically distinct clades — an emergence pattern that defied conventional epidemiology. It was not spreading from a single source. It seemed to be arising independently, everywhere at once. The leading hypothesis for how this happened is climate change. Most Candida species cannot survive sustained human body temperature — the mammalian thermal barrier has historically protected us from environmental fungi. C. auris is thermotolerant to 42 degrees Celsius. Its closest relatives are not. Each degree of global warming reduces the thermal gap between environmental fungi and human hosts by an estimated five percent. C. auris may be the first human pathogen created by a warming planet — a fungus that evolved to bridge the temperature gap that once kept us safe. Once inside healthcare facilities, C. auris behaves unlike any Candida species before it. It persists on surfaces for weeks. It colonizes skin and spreads between patients through contact and contaminated equipment. In 2024, the CDC recorded 6,304 clinical cases in the United States — and 21,195 patients who screened positive for colonization between 2016 and 2023, of whom 6.9 percent progressed to clinical infection. Mortality in invasive C. auris infections ranges from 30 to 60 percent. The resistance profile is the defining feature. Ninety-five percent of clinical isolates are resistant to fluconazole. Fifteen percent are resistant to amphotericin B. One percent are resistant to echinocandins — still low, but increasing. Pan-resistance, while under one percent, exists. For a pathogen that has been in clinical awareness for less than two decades, the speed of resistance accumulation is extraordinary. Recent research has revealed the biological machinery behind C. auris's success. A cover article in Nature Microbiology (February 2026) by Karl Kuchler's group at the Medical University of Vienna showed that C. auris uses carbonic anhydrase Nce103 to convert CO2 into bicarbonate, sustaining energy metabolism on the nutrient-poor human skin surface. The CO2 comes from bacterial skin colonizers — their urease activity generates the carbon dioxide that feeds C. auris. This means C. auris is not just colonizing skin; it is exploiting the skin microbiome as infrastructure. Targeting bacterial urease could potentially starve C. auris of the CO2 it needs — a microbiome-level intervention that would not require killing the fungus directly. A complementary study from the University of Exeter, published in Communications Biology (December 2025), used Arabian killifish larvae — which survive at human body temperature — to study C. auris gene expression during infection. They found that C. auris activates iron-scavenging genes as a primary survival strategy in the host. Iron dependence may be an Achilles heel: the iron chelator deferiprone synergizes with echinocandins against C. auris in vitro. Aspergillus fumigatus: The Agricultural Mirror If C. auris is the poster child for emergence, Aspergillus fumigatus azole resistance is the clearest One Health story in mycology — and the most direct parallel to how livestock antibiotic use drives bacterial resistance. A. fumigatus causes invasive aspergillosis primarily in immunocompromised patients. Azoles — voriconazole, itraconazole, isavuconazole — are the first-line treatment. But 15.6 percent of clinical A. fumigatus isolates now carry resistance mutations, based on surveillance of 12,679 isolates. Of those resistant isolates, 67.6 percent carry the TR34/L98H mutation — a tandem repeat in the gene promoter plus a leucine-to-histidine amino acid change. This is not a mutation that arose in patients taking azoles. It is an environmental mutation, selected by agricultural triazole fungicides used on crops. The mechanism is the same as in bacterial AMR: agricultural chemicals with the same molecular targets as medical drugs create a resistance reservoir in the environment. Composting generates the warm, azole-contaminated conditions where A. fumigatus thrives and evolves. The resistant spores become airborne. Patients inhale them. By the time they develop invasive aspergillosis, the first-line drugs are already compromised. The clinical consequences are severe. TR34/L98H confers pan-azole resistance in 68.5 percent of carriers. Ninety-seven percent of resistant isolates are voriconazole-resistant. Patients with azole-resistant invasive aspergillosis have 33 percent higher mortality than those with susceptible disease. This is the same pattern — agricultural use driving clinical resistance — that the AMR community has documented with colistin (mcr-1 from livestock), fluoroquinolones (poultry), and third-generation cephalosporins (ESBL-producing Enterobacteriaceae from animal agriculture). The fungal version receives a fraction of the attention. Trichophyton indotineae: The Superficial Superbug Not all drug-resistant fungi kill. Trichophyton indotineae — a dermatophyte that causes tinea corporis and tinea cruris (ringworm and jock itch) — does something arguably worse for the AMR narrative: it makes resistant fungal infection ordinary. First recognized as a distinct species in India, T. indotineae has spread to at least 20 countries across five continents. A multinational genomic study published in The Lancet Microbe (February 2026) traced its single evolutionary origin and mapped its rapid transcontinental spread. By mid-2024, T. indotineae accounted for 38 percent of dermatophyte isolates in the United Kingdom — surpassing the previously dominant T. rubrum. In India, it has already done so. Seventy percent of T. indotineae isolates are resistant to terbinafine, the mainstay of dermatophyte treatment worldwide. The resistance is driven by mutations in the SQLE gene (squalene epoxidase, the terbinafine target). But emerging azole resistance — via CYP51B gene duplication — threatens the backup options as well. Some isolates are resistant without any known mutations, suggesting undiscovered mechanisms. The driver is over-the-counter misuse of fixed-dose combination creams containing a corticosteroid, an antifungal, and an antibiotic. Widely available without prescription in India and other countries, these creams suppress symptoms (the corticosteroid masks inflammation) while providing sub-therapeutic antifungal exposure that selects for resistance. It is the topical equivalent of agricultural antibiotic misuse — and it has created a global pandemic of resistant skin infection. T. indotineae is not lethal. But it is debilitating, stigmatizing, and increasingly untreatable. And it demonstrates that fungal resistance is not confined to ICUs. It is in dermatology clinics, pharmacies, and homes. Mucormycosis: The Albumin Revelation Mucormycosis — the "black fungus" — entered public consciousness during India's devastating COVID-19 second wave, when more than 47,000 cases were reported in a single year. The explanation at the time focused on corticosteroids: immunosuppressive treatment for severe COVID created the vulnerability that Mucorales exploited. A January 2026 paper in Nature, from Ashraf Ibrahim's group at the Lundquist Institute, reframes this entirely. The study showed that albumin — the most abundant protein in human blood — has direct antifungal activity against Mucorales through a fatty acid-dependent mechanism. Low serum albumin emerged as the single strongest predictor of severe mucormycosis outcomes across multicontinental data. This changes the causal story. COVID-19 inflammation suppresses albumin production (hypoalbuminemia is a hallmark of severe COVID). The corticosteroids contributed, but the underlying mechanism may have been the loss of a natural antifungal defense that had been hiding in plain sight in the most common blood protein. A Phase 2 clinical trial is being planned to test whether albumin supplementation in cancer patients with hypoalbuminemia can prevent mucormycosis. The simplicity is striking. Not a new molecule. Not a new drug class. A protein we already know how to measure and supplement, potentially repurposed as antifungal prophylaxis. If validated, it would be one of the most cost-effective interventions in all of mycology. Mucorales remain intrinsically resistant to both azoles (except posaconazole and isavuconazole) and echinocandins. First-line treatment is liposomal amphotericin B plus surgical debridement — a regimen that is toxic, expensive, and inaccessible in the settings where mucormycosis kills the most people. The expanded access data for fosmanogepix — showing greater than 70 percent response rates in fusariosis and mucormycosis — suggest that the pipeline may eventually reach these patients. But eventually is not soon enough. Candida albicans: The Old Enemy Evolving C. albicans remains the most common Candida species globally. It does not carry the headlines of C. auris or the mortality of Cryptococcus. But it is evolving in ways that matter. Fluconazole resistance in C. albicans has reached 32 percent in some institutional cohorts, based on a 19-year retrospective study. The trend is driven by the same selection pressure — widespread azole use in prophylaxis and treatment — that is reducing susceptibility across all Candida species. The rise of non-albicans species (C. glabrata, C. krusei, C. parapsilosis, C. auris) in clinical cultures is itself partly a consequence of azole selection pressure favoring species with intrinsic or acquired resistance. A 2025 finding revealed a molecular mechanism linking temperature and drug tolerance. Human body temperature — 37 degrees Celsius — increases C. albicans azole tolerance by inhibiting autophagy-mediated degradation of Erg11, the azole drug target. At 37 degrees, C. albicans retains more of the protein that azoles are trying to block, making the drugs less effective. This is a thermotolerance-resistance link at the cellular level — distinct from C. auris's thermotolerance story but part of the same climate-biology intersection. Biofilm-forming C. albicans presents a separate challenge. Biofilm persistence is driven by the HSP90-calcineurin signaling pathway. Pharmacological inhibition of HSP90 — using geldanamycin, an existing research compound — re-sensitizes C. albicans biofilms to both azoles and echinocandins. Biofilm infections on catheters, prostheses, and mucosal surfaces are among the most difficult Candida infections to treat, and adjuvant strategies targeting the persistence machinery could be transformative. Perhaps most concerning is the evidence that resistance genes are flowing across Candida species boundaries. Horizontal gene transfer, long considered rare in fungi, is now documented as a mechanism for spreading azole resistance determinants between species — meaning the resistance crisis is not confined to individual species but is a pan-Candida phenomenon. The Pipeline: Four New Mechanisms and an Adjuvant The antifungal pipeline is more active than it has been in decades. For the first time, genuinely novel mechanisms — not derivatives of existing classes — are advancing through clinical trials. Fosmanogepix is the first Gwt1 inhibitor. By blocking the glycosylphosphatidylinositol (GPI) anchor biosynthesis pathway, it disrupts fungal cell wall integrity through a mechanism entirely distinct from echinocandins. Basilea has two Phase 3 trials running: FAST-IC for candidemia (450 patients) and FORWARD-IM for invasive mold infections. The BARDA commitment — up to 268 million dollars in potential milestones — reflects the strategic importance. Fosmanogepix's broad spectrum (Candida, Aspergillus, Cryptococcus, Mucorales, Fusarium) makes it the closest thing to a universal antifungal in the pipeline. Olorofim, from F2G, is the first orotomide — inhibiting dihydroorotate dehydrogenase (DHODH) in the pyrimidine biosynthesis pathway. It received an FDA Complete Response Letter in June 2023, raised 100 million dollars, and is now in a Phase 3 trial (OASIS) with results expected late 2026. Its strength is against molds, particularly Aspergillus and the rare molds (Scedosporium, Lomentospora) that resist everything else. Its weakness: no meaningful activity against yeasts, limiting its use in candidemia. SCY-247, from SCYNEXIS, is a second-generation triterpenoid — the successor to ibrexafungerp, which was approved for vulvovaginal candidiasis. Where ibrexafungerp's development has been complicated by a legal dispute between SCYNEXIS and GSK over the MARIO Phase 3 trial, SCY-247 is starting fresh. Oral Phase 1 data (September 2025) showed that 200 and 300 milligrams once daily achieved target exposure against MDR C. auris and echinocandin-resistant C. glabrata. IV Phase 1 dosing began in February 2026. QIDP and Fast Track designations (January 2026) signal FDA recognition of the need. Active against the pathogens that other drugs struggle with. Mandimycin represents the most radical departure. Discovered by mining 316,000 bacterial genomes for novel polyene biosynthetic gene clusters, this compound from Streptomyces netropsis targets phospholipids in the fungal membrane — not ergosterol, the target of every polyene since amphotericin B was introduced in 1959. A 38-membered macrolactone with unique dideoxysaccharides, mandimycin is 9,700 times more soluble than amphotericin B, less nephrotoxic, and showed no resistance development in serial passage experiments. MICs of 0.125 to 2 micrograms per milliliter against Candida, Cryptococcus, and Aspergillus. Published in Nature (March 2025). Still preclinical, but the first genuinely new polyene mechanism in more than six decades. The adjuvant approach adds a fifth dimension. Butyrolactol A, from the Wright lab at McMaster — the same group that discovered lariocidin, one of the most promising new antibacterial classes — inhibits the phospholipid flippase Apt1-Cdc50 in fungal membranes. It does not kill fungi alone. Instead, it disrupts membrane asymmetry and vesicular trafficking, making echinocandins dramatically more potent against resistant organisms. The fractional inhibitory concentration index (FICI) was below 0.5 against both C. auris and Cryptococcus — the definition of synergy. In a mouse skin infection model, subtherapeutic butyrolactol A combined with caspofungin significantly reduced C. auris fungal burden. The "helper molecule" concept — making existing drugs work against resistant fungi — could extend the life of echinocandins by decades if it translates to clinical use. Eleven years of research from initial screen to Cell publication (2025). The Diagnostic Void If antifungal therapeutics are 30 years behind antibacterials, antifungal diagnostics are further still. In March 2025, the WHO published its first-ever report on fungal diagnostics — a "Landscape Analysis of Commercially Available and Pipeline In Vitro Diagnostics for Fungal Priority Pathogens." The conclusions were bleak: existing tests work for a limited range of fungi, are insufficiently accurate, require equipped laboratories and trained staff, and are inaccessible to most patients in low- and middle-income countries — precisely where fungal infections kill the most people. The only true point-of-care fungal diagnostics are lateral flow assays for cryptococcal antigen and galactomannan (Aspergillus). These are valuable but limited to specific species. Antifungal susceptibility testing — determining whether a patient's isolate is resistant to available drugs — is essentially non-existent at the point of care. While the bacterial diagnostics revolution is producing 36-minute phenotypic AST devices and culture-free pathogen identification, fungal diagnostics remain tethered to culture-based methods that take days. The EU has committed 13 million euros through HERA for development of point-of-care AST devices that work for bacteria or fungi. LAMP-based assays and electrochemical biosensors have been identified as the most promising emerging technologies. But the gap between the bacterial diagnostic frontier and the fungal diagnostic reality is measured in decades, not years. The Parallel Crisis The structural parallels between fungal and bacterial antimicrobial resistance are striking. Both are driven by the same forces: agricultural chemical use selecting for resistance in environmental organisms (triazole fungicides for Aspergillus, livestock antibiotics for Enterobacteriaceae); climate change accelerating pathogen evolution and expanding geographic range; market failure discouraging pharmaceutical investment in drugs that save lives but generate inadequate returns; diagnostic gaps that force clinicians into empiric prescribing; and access inequities that concentrate mortality in the countries least able to afford new treatments. But the differences matter. Fungi are eukaryotes. They share fundamental biology with human cells — cell membranes, protein synthesis, DNA replication — which means that the number of drug targets unique to fungi is small, and hitting them without toxicity requires extraordinary molecular precision. This is why three classes took 50 years. This is why the new mechanisms emerging now — Gwt1 inhibition, DHODH inhibition, phospholipid targeting, flippase disruption — are so significant. Each represents a needle threaded through the narrow space between fungal vulnerability and human safety. There is no fungal equivalent of phage therapy. Bacteriophages — viruses that kill bacteria — have no analog in mycology. Mycoviruses exist but are poorly characterized and have no therapeutic development path. The evolutionary medicine strategies I wrote about recently — phage steering, collateral sensitivity, CRISPR gene drives — are bacterial concepts with no fungal translation. What fungi do have, uniquely, is a set of host biology interventions that bacteria lack. Albumin supplementation for mucormycosis prevention. Urease inhibition to starve C. auris of CO2 on skin. Iron chelation to synergize with echinocandins. HSP90 inhibition to break biofilm persistence. These are not antifungals in the traditional sense. They are interventions in the ecology of infection — changing the host environment rather than attacking the pathogen directly. Whether this ecological approach can scale to match the burden — 3.8 million deaths per year, a number that competes with tuberculosis and exceeds malaria — depends on whether the world decides fungal resistance is worth the same urgency it has begun to give bacterial resistance. The WHO's Fungal Priority Pathogens List was a start. The pipeline is more active than it has been in a generation. But the gap between what fungi are doing and what medicine can do about it remains vast, and it is growing. Three classes in 50 years was never going to be enough. The fungi have known this longer than we have.