Fungal Morphology Review

Impact on treatment of onychomycosis

Fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and moulds. Unlike plants, animals, protists and bacteria, fungal cells have cell walls that contain chitin (not cellulose). Fungi feed by absorption, they do not ingest their food. They accomplish this by growing through and within the substrate on which they are feeding. Numerous hyphae network through the flesh (or wood, cheese, bread, leather, vegetation, etc) from which they are growing. The hyphae secrete complex digestive enzymes which break down the substrate, making it easier for the fungus to absorb the nutrients which the
substrate contains.

Fig 1: Typical mycelium of a fungus

Reproductive hyphae produce spores, which differ by size, shape and structure and are used in the classification and identification of fungi. The tube-like hyphae are responsible for the fluffy appearance of the macroscopic mould colony. Spores are very resistant to cold but easily killed at high temperatures. Fungi grow well under the same conditions that favour the growth of bacteria – warmth and moisture.

Fungi are classified according to biological taxonomy based upon the type of hypha, spore and reproduction. The ‘Class Deuteromyceters’ or Fungi imperfecti, are a heterogeneous collection of fungi with asexual reproduction (spores branch off from hyphae at the point called a conidiophore and create new colonies) and most of the pathogens encountered in medical mycology belong to this class.

Fig 2: Fungal nail infection with visible ‘streaks’ indicating presence of fungal spores and deeply embedded fungal hyphae throughout nail bed.

Different types of fungi will produce different-looking colonies in biological systems. As such, when examining onychomycosis, fungal colonies with patches or streaks signify the presence of a high number of fungal spores, indicating that the hyphae are well established and embedded through the nail and nail bed structure. Clinically, this can impact treatment success as progress may take longer. It is important to manage patient expectations, as nails with only 40% fungal infection may require only 8 treatments with ToeFX, however those with 30% infection but visible streaks may require close to double the treatments to achieve the same amount of clearance. If you need assistance with nail morphology or managing patient progress, please don’t hesitate to reach out to us at

Source: Morphology and General Properties of Fungi. Section 51.1 in Microbiology Module. Accessed March 21, 2022.