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NAJRAN UNIVERSITY College of Applied Medical Sciences

NAJRAN UNIVERSITY College of Applied Medical Sciences. General Microbiology Course Lecture No. 22. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. Laboratory diagnosis of fungal infections: 1- Microscopic examination of clinical samples

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NAJRAN UNIVERSITY College of Applied Medical Sciences

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  1. NAJRAN UNIVERSITY College of Applied Medical Sciences General Microbiology Course Lecture No. 22 By Dr. Ahmed Morad Asaad Associate Professor of Microbiology

  2. Laboratory diagnosis of fungal infections: • 1- Microscopic examination of clinical samples • -Potassium hydroxide (KOH) test: skin, hair or nail mounted with KOH to dissolve keratin and visualize fungal morphology microscopically • -Histological stains such as Haematoxylen and Eosin stain (H&E stain) in some fungal infections • -Gram’s stain in Candida infection • 2- Culture and isolation: • Culture media: • Sabouraud’s dextrose agar (slightly acidic pH 5.7 and does not favor bacterial growth) containing Penicillin or streptomycin (antibacterial agents) and cycloheximide (to inhibit saprophytic fungi contamination) • Technique: • 2 cultures are incubated: on at 22ºC and the other at 37ºC to detect dimporhic fungi

  3. Identification: It is based on the followings: • Macroscopic characters: Hyphae (septate or non-septate), spores or budding cells • Microscopic morphology: • Biochemical reactions • Detection of fungal antigens: for example by latex agglutination • 2 cultures are incubated: on at 22ºC and the other at 37ºC to detect dimporhic fungi • 3- Serological tests • Latex agglutination or complement fixation tests to detect antibodies (IgM or IgG antibodies). A major problem is the poor immunogenicity of fungal cell antigens • 4- Skin tests (delayed hypersensitivity testing): • Rarely used nowadays in diagnosis. Only to evaluate patients’ immunity

  4. Antifungal drugs • Fungi, like human cells, are eukaryotes, so selective toxicity in antifungal drugs is very limited • Mechanism of action of antifungal drugs: • 1- Binding to ergosterol in cell membrane • 2- Inhibit cell membrane synthesis • 3- Inhibit chitin synthesis in the cell wall • 4- Inhibit fungal DNA synthesis

  5. Examples of antifungal drugs: Amphotericin B - By binding to ergosterol in cell membrane - Used in sever systemic and opportunistic mycoses - Neprotoxic Flucytosine - Inhibit fungal DNA synthesis - In combination with Amphotericin B in treating candidiasis + cryptococcosis - Bone marrow supression – Liver affection – hair loss

  6. Azoles • - Including fluconazole, ketoconazole and itraconazole • - Inhibiting ergosterol synthesis • Systemic and local fungal infections • Inhibit testosterine synthesis (gynaecomastia, impotence and menstrual irregularity • Griseofulvin • - Inhibit hyphal growth • - In treating dermatophytosis

  7. Terbinafine • - Inhibit ergosterol synthesis • Treating dermatophytosis • Topical antifungal agents • - Nystatin for treating candidiasis • - Coltrimazole and miconazole for treating taniaversicolor and dermatophytosis

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