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Use of antifungals in agriculture may increase resistance in an infectious yeast

Genomic changes in the infectious yeast Candida tropicalis may play a role in its resistance to antifungals, according to a study in PLOS Biology. The work, led by Guanghua Huang at Fudan University, China, and colleagues, shows that these genomic changes can be brought on by a common antifungal, TBZ. The study demonstrates that the use of TBZ in agriculture may contribute to the increasing problem of antifungal resistance.

C. tropicalis is one of the most common fungi to infect humans, and while many infections are treatable, some can be life-threatening, especially among people who are immunocompromised. Infections by C. tropicalis and other fungi are of growing concern as many of these pathogens are becoming increasingly resistant to antifungal medicines. However, the biological mechanisms underlying this resistance are not well understood.

The researchers surmised that these yeasts may be developing resistance from exposure to antifungal agents and one of the most common uses of these agents is in agriculture. When C. tropicalis was exposed to the agricultural fungicide TBZ, the researchers found that the yeast cells' genomes became unstable, losing half their DNA.

It was previously thought that C. tropicalis required two copies of each chromosome to survive, known as being diploid. However, these cells with one copy of each chromosome—or haploid cells—persisted and were resistant to TBZ and similar antifungals used in medicine.

How exactly this change in chromosomes creates antifungal-resistance is a question that remains to be answered. This study, however, provides evidence that the use of antifungals in agriculture is likely a key factor in the increasing levels of resistance seen among C. tropicalis and perhaps even other infectious yeast, such as the recently emerged "superbug" fungal pathogen Candida auris.

The authors add, "The human fungal pathogen Candida tropicalis is widely distributed in natural environments and often exposed to agricultural fungicides. This study reports that tebuconazole, a triazole fungicide, can induce the formation of haploid cells (having one set of chromosomes) and promote genetic diversity in this fungus, which has long been thought to be an 'obligate' diploid organism (having two sets of chromosomes)."