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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

NAJRAN UNIVERSITY

College of Applied Medical Sciences

General Microbiology Course

Lecture No. 18

By

Dr. Ahmed Morad Asaad

Associate Professor of Microbiology


Najran university college of applied medical sciences

  • 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


Najran university college of applied medical sciences

Differences between fungi and bacteria


Najran university college of applied medical sciences

  • 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


Najran university college of applied medical sciences

Non-Septate hyphae

Mycelium

Septate hyphae


Najran university college of applied medical sciences

  • 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


Najran university college of applied medical sciences

  • 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:


Najran university college of applied medical sciences

  • 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


Najran university college of applied medical sciences

  • 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


Najran university college of applied medical sciences

  • 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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