Isolation of human pathogenic Candida species colonising plastic wastes: environmental screening for drug resistance, thermotolerance, and virulence of ‘WHO Priority Fungal Pathogens’

Abstract Plastic pollution can provide an important substrate for the survival and dissemination of a range of human pathogens, and could increase potential transfer routes to humans. Recently, five species of the pathogenic yeast Candida have been classified as priority fungal pathogens by the WHO, yet viable pathogenic species of Candida have never before been isolated from environmental plastic pollution. Therefore, we tested whether plastic pollutants in freshwater, estuarine, and marine environments were colonised by Candida. We successfully isolated five species (C. glabrata, C. tropicalis, C. krusei, C. sojae, C. pseudolambica), which includes two that are on the WHO fungal priority pathogens list. All environmental isolates were resistant to at least one antifungal drug, thermotolerant to human body temperature, and in many cases more pathogenic than comparable clinical isolates (when virulence was assessed in a Galleria mellonella model of infection). The incidence of candidiasis, particularly by drug resistant strains, is globally increasing, and it is therefore critical that we increase our focus on the environmental persistence of these pathogens, and the role of environmental plastic pollution as novel transfer routes for enhanced human exposure.