Bio 348: Mycology Yeasts&Molds

Transition from Prokaryotes to Eukaryotes

• Introduction to Eukaryotes

  • Shift from discussing prokaryotic bacteria to eukaryotic organisms.

  • Eukaryotic cells possess a nuclear membrane.

  • Humans are eukaryotes.

Fungal Infections

• Treatment Challenges

  • Fungal infections are harder to treat due to similarity to human cells.

  • Increased risk of toxicity from antifungal treatments.

  • Duration of treatment may be longer compared to bacterial infections.

• Nutritional Mechanisms

  • Fungi lack chlorophyll and therefore do not perform photosynthesis.

  • Nutritional acquisition through absorption; fungi metabolize organic matter.

  • Hyphal structures (mycelia) penetrate substrates to absorb nutrients.

• Cell Wall Composition

  • Composed of chitin, mannan, and glucan.

  • Contains ergosterol, analogous to cholesterol in human cells, making antifungal treatments risky due to cross-reactivity.

Reproduction in Fungi

• Reproductive Methods

  • Fungi can reproduce sexually and asexually.

  • Historical classification included two names for organisms based on reproductive method, now typically simplified to one, often the asexual name.

• Diversity of Fungi

  • Fungi can be unicellular (yeasts) or multicellular (molds).

  • Examples of infections: ringworm, thrush, sporotrichosis, and systemic infections like histoplasmosis, blastomycosis, candidiasis, and aspergillosis.

Common Fungal Infections

• Superficial vs. Systemic Infections

  • Common superficial infections include athlete's foot, scalp infections, and ringworm.

  • Severe conditions involve lymphatic spread and systemic issues.

• Specific Fungal Infections

  • Pityriasis: Characterized by scaly skin rashes, often with pigmentation changes.

  • Ringworm: Rarely strictly circular; may present more patchily with growth from the center outwards.

• Dermatophytes and Other Molds

  • Dermatophytes: Infect keratinized tissues (e.g., hair, skin).

  • White Piedra: Affects hair shafts, presenting as soft white nodules, spreads both externally and internally.

  • Aspergillus Fumigatus: Causes invasive aspergillosis; can form fungal balls (aspergilloma) in lung cavities, especially dangerous for immunocompromised patients.

Lab Techniques for Fungal Identification

• Specimen Types and Processing Techniques

  • Some molds are fragile, such as Mucor, while others like Calcofluor White stain are used for fungal identification in cultures.

  • Potassium hydroxide (KOH) is utilized to dissolve tissues, aiding in slide preparation.

Fungal Culture Techniques

• Fungal Media Preparation

  • Various media types:

  • Sabadour Dextrose: General purpose.

  • Dermatophyte Test Media (DTM): Selective media that changes from orange to red in the presence of dermatophytes.

  • Incubation period for fungi typically lasts up to four weeks at room temperature for optimal growth.

Yeasts and Their Characteristics

• Yeast Characteristics

  • Yeasts are unicellular and can form pseudohyphae, contributing to virulence.

  • Yeast can reproduce via budding, creating mother and daughter cells, resulting in uneven size distribution.

• Candida Albicans and Other Candida Species

  • Commonly associated with infections (thrush, skin infections).

  • Can lead to sepsis and is often an opportunistic pathogen.

  • Different Candida species vary in antifungal susceptibility, with C. glabrata being resistant to fluconazole.

Emerging Pathogens

• Candida Auris

  • An emergent multi-drug resistant pathogen posing significant global health risks.

  • Cases have become prevalent in healthcare settings, particularly in immunocompromised patients.

Cryptococcus Neoformans

• General Characteristics

  • Encapsulated yeast associated with pigeon droppings; inhalation can cause serious infections, particularly in immunocompromised patients.

• Clinical Significance

  • Cryptococcal infections include meningitis and bloodstream involvement.

  • Diagnosed using India ink preparations to visualize the capsule, with antigen testing indicating immune response.

Other Fungi and Their Infections

• Malassezia Furfur

  • Part of normal skin flora but can cause clinical issues, like dandruff or seborrheic dermatitis.

  • Requires lipids for growth and can cause tinea versicolor (pityriasis).

• Trichosporon

  • Causes white piedra characterized by soft nodules attached to hair shafts.

Final Notes on Fungal Diagnostics

• Diagnostic Approaches

  • Identification methods such as Gram stains, culture methods, and PCR testing are critical for accurate diagnosis of fungal infections.

  • Special attention is needed for opportunistic pathogens and resistant species to ensure appropriate treatment.

• Pneumocystis Jirovecii

  • Once thought to be a parasite, it can cause pneumonia in severely immunocompromised individuals.

The distinctive features, reproductive mechanisms, and pathogenic potential of various fungal species underscore the necessity for accurate diagnosis and effective treatment strategies against fungal infections.