Chapter 10 General Mycology PDF Qassim University

Kingdom of Saudi Arabia ‫المملكة العربية السعودية‬ Ministry of Education ‫وزارة التعليم‬ Qassim University ‫جامعة القصيم‬...

Kingdom of Saudi Arabia ‫المملكة العربية السعودية‬ Ministry of Education ‫وزارة التعليم‬ Qassim University ‫جامعة القصيم‬ College of Medical Rehabilitation ‫كلية التاهيل الطبى‬ Microbiology [EDPT 211] Prof. Dr. Noha Mohammed Afifi Chapter 10 General Mycology Mycology is the study of Fungi. Medical Mycology is the science that deals with pathogenic Fungi that cause disease. Fungi differ from bacteria in the following: Fungi Bacteria Size Larger Smaller Nucleus Eukaryotic Prokaryotic Mitochondria Present Absent Sterols in cell Present (Ergesterol) Absent in all bacteria membrane (target of action of anti- (Except Mycoplasma) fungal agents) Cell wall content Chitin (a derivative of Peptidoglycan glucose)(target of action of anti-fungal agents) Spores For reproduction For survival Metabolism - All Fungi are - Hetero & Autotrophic Heterotrophic - Many obligate anerobes - All Fungi are Aerobes. No obligate anerobes All Fungi are Non-Motile Prof. Noha Afifi 100  Morphological Forms of Fungi Fungi are Unicellular or Multicellular 1) Moulds (Filamentous Fungi):  Are fungi that grow in the form of long, multicellular filaments (hyphae) which may be: - Septate (with cross walls) - Non-septate (without cross walls).  They grow by branching and tip elongation forming a mass called mycelium on culture media.  Examples of moulds: Aspergillus, Penicillum & the Dermatophytes. 2) Yeasts:  They grow as single cells "Unicellular" (round or oval). Prof. Noha Afifi 101   They reproduce asexually by budding and may form pseudohyphae (hyphae with constrictions; sausage-like chain).  Examples of Yeasts: Candida, and Cryptococcus. Pseudohyphae Yeast Clinical Classification (A) Mycotic infections: 1. Superficial mycoses: limited to the outermost keratinized horny layer of the skin + Skin Appendadges” hair and nails e.g. Tinea Versicolor; a fungus that causes areas of either hypopigmentation or hyperpigmentation of the skin of the chest, back and upper arms and legs. They secrete keratinase enzyme which helps them to invade keratinized tissues Tinea Versicolor Tinea Versicolor 102 2. Cutaneous mycoses: Infections extending deeper affecting ALL layers of the skin, e.g. (Dermatophytes causing dermatophytosis (Tinea or Ringworm) and Cutaneous Candidiasis. 3. Subcutaneous mycoses: Chronic infections that involve dermis, subcutaneous tissue, muscle and facsia. These infections are initiated by piercing trauma to the skin which allows fungi present in the soil to enter; mainly the foot, called Madura foot (e.g. mycetoma). These infections are difficult to treat and may require surgical intervention (debridement). 4. Systemic mycoses: affecting internal organs. These fungi fall into 2 groups:  True Pathogens infecting normal healthy individuals (e.g. Histoplasma and Blastomyces).  Opportunistic Pathogens infecting immunocompromized individuals (e.g. Crytococcus & Candida). 103  (B) Mycotoxicosis: It is produced by consumption of food containing fungal toxins, e.g.  Mushroom poisoning: causes damage to liver, kidney and bone marrow.  Aflatoxin of Aspergillus flavus: may cause chronic liver damage and cancer. (C) Allergic disorders: Spores of free-living fungi as Aspergillus, may be the allergen in some cases of atopy (asthma, hay fever, urticaria……etc.) Pathogenesis  Infection with certain systemic fungi (e.g. Histoplasma) elicits a granulomatous host defense response (composed of macrophages and Helper T cells).  Infection with other fungi (notably Aspergillus) elicits a pyogenic response (composed of Neutrophils). Diagnosis of Fungal Infections Laboratory diagnosis of Fungal infection involves 2 main diagnostic methods: A) Direct methods: which depend on either the detection of fungi and/or their antigens in the patient's specimens, OR on isolation of Fungi. B) Indirect methods: which depend mainly on the detection of serum antibodies against the suspected fungus in systemic mycosis, OR less frequently on Skin tests. Prof. Noha Afifi 104 The different techniques used in diagnosis of fungal infections are discussed in the practical lab. Anti- Fungal Drugs  Because fungi are Eukaryotes, the range of non-toxic systemically active drugs is still limited.  The Selective toxicity of antifungal drugs is based on the presence of Ergosterol in fungal cell membranes, in contrast to the cholesterol found in bacterial cell membranes.  The most commonly used drugs are Mycostatin (nystatin) and azole drugs (e.g. fluconazole, ketoconazole). Prof. Noha Afifi 105