Thermotolerance, virulence, and drug resistance of human pathogenic Candida species colonising plastic pollution in aquatic ecosystems

Recently, six species of the pathogenic yeast Candida have been classified as priority fungal pathogens by the World Health Organisation (WHO), yet the persistence and niches of pathogenic species of Candida in the environment remains unclear. And despite the ability of Candida to form strong biofilms on plastics in clinical settings, the potential for plastics in the environment to facilitate survival and dissemination of Candida as has not been determined. Here, we have collected plastic pollutants from freshwater, estuarine, and marine environments and successfully isolated five pathogenic species of Candida, including three that are on the WHO Fungal Priority Pathogens list (C. glabrata, C. tropicalis, Pichia kudriavzevii (formerly known as Candida krusei). All environmental isolates were resistant to at least one antifungal drug, thermotolerant to human body temperature, and showed pathogenicity in a Galleria mellonella model of infection. In addition, polyethylene (PE) plastic pellets were deployed upstream and downstream of a wastewater discharge pipe in a small freshwater stream. Although all pellets became colonised by pathogenic species of Candida, there were clear differences in species prevalence upstream and downstream of the effluent, indicating a clear point source for Candida discharge into surface waters. The global incidence of candidiasis, particularly by drug resistant strains, is increasing, and it is therefore critical that we increase our focus on the environmental reservoirs of these pathogens and continue to improve our understanding of their environmental persistence and subsequent transfer routes to humans.