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NAJRAN UNIVERSITY College of Applied Medical Sciences. General Microbiology Course Lecture No. 18. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. General properties of fungi

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NAJRAN UNIVERSITY

College of Applied Medical Sciences

General Microbiology Course

Lecture No. 18

By

Dr. Ahmed Morad Asaad

Associate Professor of Microbiology


  • 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



  • 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


Non-Septate hyphae

Mycelium

Septate hyphae


  • 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


  • 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:


  • 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


  • 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


  • 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


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