Mycology: Study of Fungi

Mycology: Study of Fungi

• Mycology is the study of fungi, including yeasts and molds.
• Yeasts are unicellular, rounded fungi.
• Molds are multicellular, filamentous fungi.
• Fungi reproduce via budding (yeasts) or spores (molds).
• Fungi have rigid cell walls containing chitin, glucan, mannans.
• Cell membranes contain ergosterol.
• Fungi are eukaryotic organisms with a nucleus, nuclear membrane, endoplasmic reticulum, and mitochondria.

Characteristics of Fungi

• Fungi are important as plant, human, and animal pathogens.
• Over 70% of plant diseases are fungal.
• Many fungi are saprophytes (consuming dead matter).
• Other fungi are parasites.
• Most fungi are multicellular, but yeasts are unicellular.
• Fungi are aerobes or facultative anaerobes.
• Cell walls are primarily composed of chitin.
• Many human fungal infections are nosocomial (hospital-acquired) or occur in immunocompromised individuals (opportunistic infections).

Morphological Classification of Medically Important Fungi

• Yeasts: Unicellular, non-filamentous, oval/spherical cells. Reproduce by budding.
  • Example: Candida albicans (yeast-like), Cryptococcus neoformans (true yeast, capsulated).
• Yeast-like fungi: Grow partly as yeast cells and partly as elongated cells resembling hyphae (pseudohyphae). Reproduce by budding.
  • Example: Candida albicans
• Molds/Filamentous fungi: Multicellular, filamentous. Form a mycelium composed of hyphae. Reproduce via spore formation.
  • Identified by appearance, colony characteristics, and spore types.
  • Examples: Aspergillus, Penicillium, dermatophytes.
  • Hyphae can be septate (divided by cross-walls) or aseptate (uninterrupted).
  • Mycelium is the visible filamentous mass.
  • Penicillium: Brush-like arrangement of conidia, initially velvety/white, later powdery/blue-green.
  • Aspergillus: Green-colored colonies on SDA/PFA, conidiophores, sterigmata, conidia visible with Lactophenol Cotton Blue stain.
• Dimorphic fungi: Can exist as both molds and yeasts, depending on growth conditions.
  • Mold form produces hyphae; yeast form reproduces by budding.
  • Primarily infect the lungs.
  • Dimorphism often temperature-dependent (e.g., yeast at 37°C and mold at 25°C).
  • Examples: Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, Sporothrix schenckii, Penicillium marneffei, Paracoccidioides brasiliensis.

Reproduction and Life Cycle of Fungi

• Yeasts and yeast-like fungi reproduce by budding.
• Filamentous fungi reproduce asexually (fragmentation of hyphae).
• Spores are for both sexual and asexual reproduction.
• Asexual spores (e.g., conidiospores, chlamydospores, sporangiospores) are produced by aerial hyphae.
• Sexual spores are produced by fusion of nuclei from opposite mating strains.

Divisions of Fungi (Systematic Classification)

• Deuteromycota (Fungi Imperfecti): Unknown to produce sexual spores. Reproduce asexually.
  • Example: Candida albicans (vaginal yeast infections; opportunistic in AIDS), Malassezia furfur, Sporothrix schenckii.

Explore the fascinating world of mycology, focusing on the characteristics, classifications, and importance of fungi. Learn about yeasts, molds, and their various roles as pathogens, saprophytes, and members of ecosystems. This quiz will deepen your understanding of fungal biology and its medical significance.