Fungi: Yeast vs. Mould Quiz

Fungi: Yeast vs. Mould

• Fungi are eukaryotic organisms. Candida is a key fungus in dentistry.
• Fungi exist in two forms: yeast (single-celled) and mould (multicellular). Some fungi are dimorphic (both forms).
• Yeast cells are unicellular, commonly found on fruit, in the oral cavity, and vagina. They appear white and thready, oval-shaped. They don't have true hyphae, but form pseudohyphae. They reproduce by budding or binary fission. They can grow aerobically or anaerobically. Overgrowth can cause infections in immunocompromised individuals.
• Moulds are multicellular, growing as tubular branches (hyphae). Hyphae form a mycelium. They're typically found in damp, dark areas. They appear fuzzy and come in various colours. They reproduce via spores (asexual or sexual reproduction). They require oxygen to grow and can cause allergic reactions and respiratory problems.

Fungal Commensal Flora

• Fungi are part of the commensal flora on skin, in the mouth, and gut.
• Candida albicans is found on the skin.
• Malassezia is found in the mouth.

Candida albicans Infections

• Candida albicans can cause superficial yeast infections (skin).
• Mucosal infections (thrush) involve the mouth, causing a cottony feeling, white coating, spots and taste loss.
• Skin infections commonly occur in areas with friction (e.g., nappy rash).
• Candidal paronychia affects the nail folds.
• Mucocutaneous candidiasis involves skin and oral/vaginal mucosa.
• Systemic candidiasis (deep candidiasis) arises from candidaemia (Candida in the bloodstream), affecting organs like the endocardium, meninges, bones, and kidneys. Untreated cases are fatal. Organ transplant recipients, heart surgery patients, and those on long-term steroid therapy are susceptible.

Predisposing Factors to Candida Infections

• Factors that increase the risk of Candida infections include decreased digestive secretions, nutrient deficiencies, impaired immune systems, underlying diseases, impaired liver function, drug use (including prolonged antibiotic use), and altered bowel flora.

Systemic Fungal Infections

Cryptococcosis

• Caused by inhaling spores of the yeast-like fungus Cryptococcus, found in soil.
• Spores germinate in the lungs, potentially causing disease.
• Symptoms include fever, headache, malaise, neck stiffness, meningitis, and lung infection. Central nervous system infection is fatal.
• Treatment involves antifungal medication (e.g., fluconazole or flucytosine) for at least six months.

Aspergillosis

• Caused by inhaling Aspergillus mold spores.
• Aspergillus is found in plants, decaying matter, soil, air, and on/in animals.
• Spores are inhaled and deposit in the bronchioles or alveoli.
• It can cause allergic reactions, lung bleeding, localized infections, endocarditis, endophthalmitis, gastrointestinal issues, and cerebral aspergillosis.
• Treatment includes corticosteroids and antifungal medication (oral or intravenous).

Zygomycosis

• Caused by Zygomycota fungi found in soil, leaves, compost, animal dung, and air.
• Spores are inhaled, ingested (contaminated food), or introduced via trauma/contaminated instruments.
• It can cause rhinocerebral and pulmonary disease.
• Treatment involves antifungal medication and sometimes surgery to remove infected tissue.