Molecular Diagnosis of Cladosporium sp. and Fusarium equiseti Fungal Infection for Zoonotic Otitis externa from Formalin-fixed Samples

Abstract

A total of thirty otitis externa samples from the pet Shirazi cats and nineteen skin swab samples were collected from children who had direct hand contact with them between October 2024 and March 2025. Macroscopic Potato dextrose agar (PDA) cultures and microscopic characteristics were used to identify filamentous fungal species, and DNA was extracted from seven formalin-fixed fungal cultures using commercial purification kits for PCR-based phylogenetic analysis. Cultures initially developed fluffy white colonies, which turned brown to dark brown by the seventh day. Microscopic analysis displayed the presence of filamentous mycelia, hyphae, and conidia. Fungal species were isolated from 26.31 % (5 out of 19) of the children's samples and 33.3% (10 out of 30) of the pet cat samples. PCR enabled the identification of several fungal species, including Cladosporium cladosporioides, Cladosporium limoniforme, Fusarium equiseti, Cladosporium cucumerinum, Cladosporium tenellum, and Stemphylium paludiscirpi. All sequences matched identically with those listed in the NCBI GenBank database. In conclusion, this study demonstrates that Cladosporium and Fusarium species isolated from pet cats may pose a zoonotic risk to children, underscoring the importance of pet hygiene and public health awareness. Cladosporium species and Fusarium equiseti were found in six samples of otitis externa in cats kept as pets. Given that most children have close experiences with cats in their homes, which are typically infected with diseases in their pet cats, the results of this study have highlighted the importance of considering pet cats as an infectious source of this disease in 26.31% of patients.