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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. 21 By Dr. Ahmed Morad Asaad Associate Professor of Microbiology

  2. General properties of fungi • They are eukaryotic organisms consisting of microscopic branched filaments called hyphae carrying spores • The hyphae interlace to form a visible mass called mycelium • They are unicellular or multicellular • Classification of fungi • They are classified by several methods: • 1- Morphological classification • 2- Systematic classification • 3- Clinical classification

  3. Differences between fungi and bacteria

  4. Morphological classification • Based on morphology of fungi into: • 1- Filamentous fungi (molds) • They grow as hyphae and reproduce by asexual spores (conidia) which may be unicellular (microconidia) or multicellular (macroconidia) • 2-yeast • They are single cells and reproduce by budding. They may form chains f elongated cells called pseudohyphae • 3- Dimorphic fungi: They have 2 forms of growth: • A filamentous form (saprophytic phase): At 22ºC or room temperature, they grow as filaments (hyphae) • A yeast form (parasitic phase): At 37ºC or body temperature, they grow as yeast

  5. Non-Septate hyphae Mycelium Septate hyphae

  6. Systematic classification • Based on type of hyphae and sporulation into: • 1- Ascomycetes • Septate hyphae and sexual spores in a sac (ascus) • 2-Basidiomycetes • Septate hyphae and sexual spores in club-shaped cells (basidium) • 3- Phycomycetes • Non-septatehyphae and sexual spores • 4- Deutromycetes • Asexual spores. Most pathogenic fungi belong to this type

  7. Clinical classification • The most important classification for clinicians into: • 1- Superficial (cutaneous) mycosis • Infection of keratinized tissues (skin, hair or nail): • Tineaversicolor • Dermatophytosis • 2-Subcutaneous mycosis • Infection of subcutaneous tissues (deep ulcerated skin lesion) and rarely spread to systemically • Chromomycosis • Sporotrichosis • 3- Systemic (deep) mycosis • Infection of viscera involoving different body organs. It is divided into:

  8. A)- Pathogenic fungai infection: • Histoplasmosis • Blastomycosis • B)- Opportunistic fungi infection: • Candidiasis • Aspergillosis • Cryptococcosis • 4- Mycotoxicosis: by fungal toxins in food • Mushroom poisoning • Aflatoxin by Aspergillusflavus

  9. 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

  10. 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