A fungus that sometimes causes serious infections appears to have a new way of resisting certain drugs: multiplying its chromosomes.
This fungus is called Candida auris. It can be difficult to eliminate in people already weakened by illness. Doctors commonly use antifungal drugs that weaken the cell wall protecting its cells. But some fungi eventually become resistant to these treatments.
Researchers studied fungi collected from two patients in London. Despite persistent infections, they did not have the usual mutations responsible for resistance.
To understand this phenomenon, the team cultured these fungi in the laboratory with a high concentration of anidulafungin, an antifungal drug. Some colonies changed in appearance. They formed small or large groups of cells and tolerated the presence of the drug better.
Analysis of their DNA revealed a surprise. Some cells had four or more sets of chromosomes, whereas this fungus normally has only one. In other words, they had multiplied the amount of genetic material contained in their cells.
The researchers also observed changes in the fungal cell wall, as well as in mechanisms that help it withstand difficult conditions. In some colonies, mutations affecting a gene linked to this stress response accompanied even greater resistance.
This adaptation therefore does not necessarily depend on a single change. The fungus could become increasingly resistant in stages, changing its DNA, cell wall and stress response at the same time. However, the study does not make it possible to determine precisely which change causes each effect.
It is also important to remember that these observations concern samples from two patients and laboratory experiments. They do not show that all Candida auris use this method. Nevertheless, they help explain why some treatments can fail without the usual genetic tests detecting the expected mutations.