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A study published in Science Translational Medicine on 16 September 2026 reports that the fungus Pneumocystis jirovecii has evolved resistance to mycophenolic acid, a drug given to humans to suppress the immune system after an organ transplant.
Researchers led by the Critical Care Medicine Department of the NIH Clinical Center analysed 163 samples from six countries across Asia, Europe and North America.
Six mutations were found in the fungus's impdh gene, four of them never reported before, arising independently in 11 separate strains between 2005 and 2019.
The mutations were far commoner in transplant recipients exposed to the drug (4-21%) than in non-transplant controls (0-1%).
The case is unusual because resistance was driven by a drug never intended to kill the pathogen, widening what antimicrobial resistance is understood to mean.
Antimicrobial resistance is usually blamed on overuse of antimicrobials. Here a human-targeted immunosuppressant hit an enzyme the fungus also possesses, so patients on the drug unintentionally selected for fungal mutants that could survive it.
Simple Analogy: Weeding a garden with a chemical meant for insects, and breeding tougher weeds by accident.
The research hospital of the US National Institutes of Health; its Critical Care Medicine Department led the study
Released the first Fungal Priority Pathogens List on 25 October 2022, ranking 19 fungi in critical, high and medium priority groups, with Pneumocystis jirovecii in the medium group
GS Paper 3 > Science and Technology > Health, biotechnology and antimicrobial resistance
General Awareness > General Science and current affairs
An organism that causes disease only when the host's defences are weakened; it is harmless in people with normal immunity.
A drug that deliberately damps down the immune response, used after organ transplants to prevent rejection.
Inosine monophosphate dehydrogenase, an enzyme in the guanine nucleotide pathway; mycophenolic acid blocks it in humans, and the fungus carries its own version.