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 of 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 requires 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 yeasts, 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)."