Difference Between Dermatophytes and Yeast
Dermatophytes are filamentous fungi that require keratin for growth and invade keratinized tissues (skin, hair, nails), while yeasts are single-celled organisms that typically cause opportunistic infections of skin and mucous membranes without the same keratinolytic properties. 1, 2
Structural and Growth Characteristics
Morphology:
- Dermatophytes are filamentous fungi that grow as branching hyphae and produce specialized spores (macroconidia, microconidia, arthroconidia) 3, 1
- Yeasts are single-celled organisms that reproduce by budding, though some species like Candida can form pseudohyphae 4, 5
Keratin Requirement:
- Dermatophytes possess keratolytic enzymes (hydrolases, keratinases, cysteine dioxygenase) that allow them to break down and invade keratinized tissue, making them obligate keratinophiles 6, 2
- Yeasts lack keratinolytic properties and are generally considered secondary invaders rather than primary pathogens of keratinized structures 4
Clinical Infection Patterns
Dermatophyte Infections:
- Cause "tinea" or "ringworm" infections with characteristic patterns: tinea pedis, tinea capitis, tinea corporis 4, 3
- In onychomycosis, dermatophytes typically cause distal and lateral subungual onychomycosis (DLSO), spreading proximally along the nail bed with significant subungual hyperkeratosis 4, 6
- Common causative species include Trichophyton rubrum, T. mentagrophytes, Microsporum canis, and Epidermophyton species 4, 2
Yeast Infections:
- Candida species typically cause proximal nail infections starting at the nail fold (paronychia), associated with chronic water immersion and wet occupations 4
- Distal Candida nail infection is uncommon and typically occurs only in patients with vascular insufficiency or on corticosteroids 4
- Malassezia species cause pityriasis versicolor (tinea versicolor) with characteristic hypopigmented or hyperpigmented macules 7, 2
Inflammatory Response
Dermatophytes induce a higher level of tissue damage and inflammatory reaction compared to yeasts, which elicit relatively low levels of host tissue damage during infection 5. This explains why dermatophyte infections often present with more pronounced erythema and inflammation.
Diagnostic Distinctions
Microscopic Appearance:
- Dermatophytes appear as branching septate hyphae on KOH preparation 3, 1
- Candida yeasts show budding yeast cells with pseudohyphae 4
- Malassezia demonstrates the characteristic "spaghetti and meatballs" appearance (short hyphae and round yeast cells) 7
Clinical Clues:
- Absence of toenail involvement and lesser degree of subungual hyperkeratosis suggest yeast rather than dermatophyte infection 4
- Presence of nail fold inflammation (paronychia) strongly suggests Candida infection 4
- Associated skin lesions are more common with dermatophyte infections 4
Treatment Implications
The distinction is clinically critical because dermatophytes respond well to allylamines (terbinafine) and azoles, while Candida infections require different management including addressing predisposing factors like water exposure and may need azole therapy specifically 1, 8. Non-dermatophyte molds have little to no activity against most standard antifungals, with particularly high resistance seen in Fusarium species 8.