PM-250 Fungi 1: Medically Important Fungi

Fungi Kingdom Overview

• Mycology is the scientific study of fungi, a large and diverse kingdom.
• Most fungi are saprophytic, obtaining nutrients from dead organic matter.
• Fungi can be multicellular (e.g., mushrooms, truffles, moulds) or unicellular (e.g., yeasts).
• Significant contributors to toxins, antimicrobials, food production, and fermentation.

Ecological and Medical Significance

• Fungi inhabit air, soil, and various environments; they are also part of human microbiota.
• Generally, fungi are non-pathogenic and can be classified as commensal (endogenous) or environmental (exogenous).
• The rise of AIDS and the use of immunosuppressive therapies have increased the prevalence of fungal diseases.
• Annually, there are over 300 million serious fungal infections, surpassing malaria in mortality rates.

Medically Important Fungi Characteristics

• Fungi are eukaryotic organisms with rigid cell walls and are heterotrophic by nature.
• Fungi are non-motile and reproduce primarily asexually, though some can reproduce sexually.
• Certain fungi have the capacity to produce toxins.

Fungal Morphology

• Yeast typically measures around 3 μm in diameter, varying from 1 μm to 20 μm.
• Morphological structures include multinucleated hyphae, septate hyphae, and pseudohyphae.

Fungal Life Cycle

• Yeast undergoes a distinct life cycle involving the formation of sexual spores (n) followed by germination and asexual reproduction.
• Sexual reproduction forms structures like Ascus, while asexual reproduction leads to spore-producing structures such as conidiophores.

Asexual Spores Types

• Asexual spores can include:
  • Sporangiospores
  • Chlamydospores
  • Zoospores
  • Conidiospores

Fungal Cell Wall Composition

• The composition of fungal cell walls varies distinctly between species.
• Notable components include galactomannan in genera like Aspergillus and histoplasma, and GXM in Cryptococcus.

Fungal Cell Membrane Structure

• The fungal cell membrane consists of ergosterol, which is essential for membrane stability and permeability, differing from mammalian cholesterol.
• Ergosterol plays a critical role in maintaining the structural integrity of the cellular lipid membrane.

Fungi Kingdom Overview

• Study of fungi is called mycology.
• Fungi are a large and diverse kingdom, primarily saprophytic.
• Multicellular forms include mushrooms, truffles, and moulds; unicellular forms are mainly yeasts.
• Fungi are significant sources of:
  • Toxins
  • Antimicrobials
  • Food and food production.

Importance of Fungi in Medicine

• Fungi are present in air, soil, and as part of microbiota.
• Most fungi are non-pathogenic, classified as either commensal (endogenous) or environmental (exogenous).
• The rise of AIDS and immunosuppressive therapies has increased the visibility and impact of fungal diseases.
• Annually, over 300 million serious fungal infections occur, surpassing malaria in mortality.

Medically Important Fungi

• Fungi are eukaryotic organisms.
• Characterized by rigid cell walls and a heterotrophic lifestyle.
• Non-motile and reproduce asexually, with some also capable of sexual reproduction.
• Certain fungi produce toxins.

Fungal Morphology

• Yeasts typically measure around 3 μm, with diameters ranging from 1 μm to 20 μm.
• Fungal structures include multinucleated hyphae, septate hyphae, and pseudohyphae.

Life Cycle of Fungi

• Yeast and filamentous fungi have complex life cycles involving:
  • Sexual reproduction with spores (e.g., ascospores).
  • Asexual reproduction through structures like conidiophores and various types of asexual spores such as cladospores, sporangiospores, and zoospores.
• Mycelia formation occurs through the fusion of compatible cells.

Fungal Cell Structure

• Cell wall compositions vary by species, with components like:
  • Galactomannan in Aspergillus and histoplasma.
  • Capsular polysaccharides (GXM) in Cryptococcus.
• Fungi have unique cell membranes containing ergosterol, unlike mammals which contain cholesterol.
• Ergosterol stabilizes the cell membrane, affecting its stability and permeability.

Key Components of Fungal Cells

• Membrane parameters include:
  • Polar head groups
  • Sterol-stiffened regions
  • Fluid regions consisting of phospholipids.
• Ergosterol plays a critical role in maintaining the integrity of fungal cell membranes, essential for function and survival.