Diversity of Culturable Yeasts in the Feces of Mew Gulls Breeding in Natural and Urban Habitats, with Insights into the Antifungal Susceptibility of the Observed Pathogens

Abstract

Migratory birds play an important role in the spread of yeasts in the environment over long distances and in different geographical regions. Human activities, in turn, have a major impact on the biology of wild birds and, consequently, on the microbial communities for which birds act as carriers and disseminators. We sought to assess the “response” of the diversity of culturable yeasts in the feces of Mew Gulls to the type of nesting site (natural/anthropogenic) during the breeding season from April to October 2023. We isolated and molecularly identified 26 yeast species. The species composition in the feces of birds from the natural habitat was more diverse, and the diversity increased from April to October. In contrast, the diversity in the feces of birds from the urban habitat decreased from April to October. Analysis of susceptibility to conventional antibiotics (fluconazole, voriconazole, and amphotericin B) using the CLSI BMD (Clinical and Laboratory Standards Institute broth microdilution) method in isolated strains of opportunistic Candida (C. parapsilosis and C. tropicalis) and strains of the emerging pathogen Rhodotorula mucilaginosa showed that the proportion of resistant strains was higher in strains isolated from the feces of birds from the anthropogenic population. Mew Gulls that spent their breeding season near a landfill and flew away for wintering appear to be a source for the spread of pathogenic yeasts with resistance against antifungal agents.