Medical Mycology Overview

Fungal Cell Structure

• Fungal cell walls contain glucan and chitin.
• Cell membranes are characterized by the presence of sterols.
• Fungi are classified into yeast, mold, yeast-like, and dimorphic forms.
• Fungi reproduce via sexual and asexual means.

Fungal Metabolism

• Aerobic metabolism is present in all fungi; some can also survive as facultative anaerobes.
• Optimal growth temperature ranges from 25 to 30 ºC, aligning with their saprophytic lifestyle.
• Fungi can thrive in a wide range of pH (2–9), generally favoring acidic environments.

Classification of Fungi

• Yeasts are unicellular and reproduce by budding, resulting in pseudohyphae.
• Examples include Cryptococcus neoformans for yeasts and Candidiasis for candida.
• Moulds are filamentous fungi, with hyphae being either septated or non-septated.
• Dimorphic fungi exhibit two morphological forms: yeast and hyphae, like Histoplasma capsulatum.

Fungal Reproduction

• Sexual reproduction involves the fusion of two nuclei or gametes.
• Asexual reproduction is predominant and occurs via fragmentation of hyphae or budding, leading to individual fungi.

Mycosis Naming

• Mycosis is named after the causative organism, e.g., Candidiasis, Aspergillosis, Cryptococcosis, and Histoplasmosis.
• Mycosis can also be categorized based on the site of infection, such as pulmonary mycosis.

Types of Human Mycosis

• Categories include superficial, cutaneous, subcutaneous, systemic, and opportunistic infections.
• Opportunistic infections primarily affect immunocompromised individuals, usually entering through inhalation of spores or direct implantation.

Diagnosis of Fungal Infections

• Samples are collected based on infection sites such as skin, hair, and nails.
• Direct microscopic preparation uses KOH (10-30%) for unstained samples and lactophenol cotton blue for stained preparations.
• Fungi can be isolated through culture on media such as Sabouraud's dextrose agar (SDA) or SDA supplemented with chloramphenicol and cyclohexamide to inhibit contaminants.

Diagnosis Techniques

• Woods light examination detects fungal infections via fluorescent reactions to ultraviolet rays.
• Serological diagnosis, including ELISA, is utilized for candidal infections.

Source and Predisposing Factors of Infection

• Endogenous sources arise from normal flora present in the oral cavity, gastrointestinal tract, and skin.
• Exogenous sources can occur through sexual contact.
• Predisposing factors include age extremes, immunosuppression (due to pregnancy, diabetes, or immunosuppressive drugs), and traumatic conditions like catheterization.

Clinical Manifestations of Candidiasis

• Mucocutaneous infections may include oral thrush and vaginitis.
• Cutaneous infections manifest in areas like the napkin region in babies and can include nail infections.
• Systemic infections can affect urinary tracts, lead to endocarditis, CNS infections like meningitis, and systemic placements like septicemia and fungemia.

Laboratory Diagnosis of Candidiasis

• Microscopic examination is done using KOH for unstained samples or lactophenol cotton blue for stained samples to detect yeast cells and pseudohyphae.
• Culturing on SDA helps isolate candida.