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Medical Mycology

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Title: Medical Mycology


1
MEDICAL MYCOLOGY Arthur F. Di Salvo, MD Reno,
Nevada
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Medical Mycology Outline
  • HOUR SUBJECT
  • Introduction, Actinomycetes
  • Yeasts, Dermatophytes
  • Filamentous Fungi, Dimorphic Fungi
  • Dimorphic Fungi
  • Opportunistic Fungi

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OBJECTIVES
  • To impart sufficient basic science of the
    medically important fungi to assist you in
    diagnosing mycotic diseases.
  • To impart sufficient clinical knowledge
  • to raise your index of suspicion for mycotic
    diseases.

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INTRODUCTION
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Fairy Ring Mushrooms
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What is Mycology?
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Mycology is the study of
  • Beer
  • Wine
  • Bread
  • Cheese
  • Gourmet mushrooms
  • Environmental toxins
  • Biodegradation
  • Disease

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BIOREMEDIATION
  • Oil spills
  • Cyanide in mining operations
  • Dioxins and pesticides
  • Produce organic acids, sugars
  • Other commercial products

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A. Classification
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What is a Fungus ?
  • Eukaryotic a true nucleus
  • Do not contain chlorophyll
  • Have cell walls
  • Produce filamentous structures
  • Produce spores

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Species of Fungi
  • 100,000 200,000 species
  • About 300 pathogenic for man

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Kingdom Fungi Eukaryocytes
  • Ascomycota
  • Basidiomycota
  • Zygomycota
  • Mitosporic Fungi
  • (Fungi Imperfecti)

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SIZE COMPARISON OF PATHOGENS
Cocci 0.8 u
Bacilli 4-6 u
Spirochetes 8 - 10 u
Viruses 0.08 u
Protozoa 15 u
Nematodes 10 mm
Fungi 10 15 u

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Actinomyces(True Bacteria)
  • Tradition
  • Clinical infection resembles mycoses
  • Actinomyces grow on mycotic media
  • Actinomyces grow slowly (24-48 h)
  • Gross colonies resemble fungi
  • (rough,heaped, short aerial filaments)
  • Resemble mycelia microscopically, with branched
    mycelia in tissue and smears.

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What is Medical Mycology ?
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MYCOTIC DISEASES(Four Types)
  • Hypersensitivity
  • Allergy
  • Mycotoxicosis
  • Production of toxin
  • Mycetismus (mushroom poisoning)
  • Pre-formed toxin
  • Infection

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PATHOGENIC FUNGI
  • NORMAL HOST
  • Systemic pathogens - 25 species
  • Cutaneous pathogens - 33 species
  • Subcutaneous pathogens - 10 species
  • IMMUNOCOMPROMISED HOST
  • Opportunistic fungi - 300 species

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PARASITIC STATE
  • Increased metabolic state
  • Modified metabolic pathways
  • Modified cell wall structure
  • Carbohydrate content
  • Lipid structure
  • RNA aggregates

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PATHOGENICITY OF FUNGI
  1. Thermotolerance
  2. Ability to survive in tissue environment
  3. Ability to withstand host defenses

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REVIVED INTEREST IN MYCOLOGY
  • Increased frequency of mycotic diseases
  • Increased awareness by physicians
  • Better trained laboratory personnel
  • More invasive procedures used on patients
  • Increased use of immunosuppressive drugs
  • Increase in immunosuppressive disease
  • 7. Better laboratory diagnostic tools

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B. MORPHOLOGY
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MORPHOLGY
  • Yeasts
  • Hyphae (filamentous fungi, mycelium)
  • Septate
  • Coenocytic (non-septate)
  • Dimorphic
  • Yeast
  • Mycelium

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Dimorphic Fungi
  • Yeast Form
  • Parasitic form
  • Tissue form
  • Cultured at 37 C
  • Mycelial Form
  • Saprophytic form
  • Cultured at 25 C

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SPORES
  • SEXUAL
  • ASEXUAL
  • Arthrospore
  • Blastospore
  • Chamydospore
  • Conidia
  • Microconidia
  • Macroconidia

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By their fruits ye shall know them
  • Mathew 720

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C. EPIDEMIOLOGY
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  • MOST MYCOTIC AGENTS
  • ARE SOIL SAPRPHYTES

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ECOLOGICAL ASSOCIATION
  • PATHOGEN HUMAN SOIL
  • _________________________________________
  • Blastomyces dermatitidis 1898 1964
  • Cryptococcus neoformans 1894 1951
  • Coccidioides immitis 1900 1932
  • Histoplasma capsulatum 1934 1949

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Mycotic Diseases Are NOTContagious
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ESTABLISHMENT OF INFECTION WITH A MYCOTIC AGENT
DEPENDS ON
  1. Inoculum size
  2. Resistance of the host

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THE CLINICIAN MUST DISTINGUISH BETWEEN
  • COLONIZATION
  • FUNGEMIA
  • INFECTION

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PORTAL OF ENTRY
MOUTH
RESPIRATORY TRACT
EYE
  • SKIN
  • HAIR
  • NAILS
  • RESPIRATORY TRACT
  • GASTROINTESTINAL TRACT
  • URINARY TRACT

SKIN
UROGENITAL TRACT
ANUS
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COLONIZATION
MOUTH
RESPIRATORY TRACT
EYE
Multiplication of an organism at a given site
without harm to the host
SKIN
UROGENITAL TRACT
ANUS
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INFECTION
MOUTH
RESPIRATORY TRACT
EYE
Invasion and multiplication of organisms in body
tissue resulting in local cellular injury.
SKIN
UROGENITAL TRACT
ANUS
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GEOGRAPHIC DISTRIBUTION
  • The present ease and frequency of world-wide
    travel make it more likely that physicians in the
    United States will be confronted with a variety
    of unfamiliar mycoses acquired in distant parts
    of the country or of the world.

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PATIENT HISTORY
  • Medical
  • Travel
  • Occupation
  • Avocation

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D. DIAGNOSIS
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA
probes
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA
probes
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DIRECT MICROSCOPIC OBSERVATION
  • 10 KOH
  • Gentle Heat

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KOH Wet Mount
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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SKIN TESTING(DERMAL HYPERSENSTIVITY)
  • Use is limited to
  • Determine cellular defense mechanisms
  • Epidemiologic studies

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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FUNGI ARE POOR ANTIGENS
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FUNGAL SEROLOGYANTIBODIES
  • Latex Agglutination IgM
  • Immunodiffusion IgG
  • Complement Fixation IgG

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Most serological tests for fungi measure
antibody. Newer tests to measure antigen are now
being developed
  • ANTIGEN DETECTION PRESENTLY AVAILABLE
  • Cryptococcosis
  • Histoplasmosis

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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DIRECT FLUORESCENT ANTIBODYCAN BE APPLIED TO
  • HISTOLOGIC SECTIONS
  • CULTURE
  • Viable organisms
  • Non-viable organisms

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probe
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INFLAMMATORY REACTION
  • Normal host
  • Pyogenic
  • Granulomatous
  • Immunodeficient host
  • Necrosis

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Polymorphic Nuclear Leukocytes
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Giant Cell
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GMS
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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ISOLATION MEDIA
  • SABOURAUD DEXTROSE AGAR
  • (pH 5.6)
  • Plain
  • With antibiotics
  • With cycloheximide

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INCUBATION TEMPERATURE
  • 37 C - Body temperature
  • 25 C - Room temperature

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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DNA Probes
  • Rapid (1 Hour)
  • Species specific
  • Expensive

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E. TREATMENT
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THERAPY
  • Because they are eukaryotic, fungi are
    biochemically similar to the human host.
    Therefore it is difficult to develop
    chemotherapeutic agents that will destroy the
    invading fungus without harming the patient.

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A BASIC TENET OF PATHOLGY IS
  • A CAUSE OF IRREVERSIBLE CELL INJURY IS CELL
    MEMBRANE DAMAGE.

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IN FUNGAL THERAPY
  • We attempt to induce cell injury by causing
    the cell membrane of the fungus to become
    permeable.

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PROBLEM
  • Finding an agent that will selectively injure
    fungal cell walls without damaging the host cell.

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ALL EUKARYOTIC CELLS CONTAIN STEROLS
  • Mammalian cells cholesterol
  • Fungal cells - ergosterol

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PRIMARY ANTI-FUNGAL AGENTS
  • Polyene derivatives
  • Amphotericin B
  • Nystatin
  • Azoles
  • Ketoconazole
  • Fluconazole
  • Itraconazole
  • Voriconazole

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AMPHOTERICIN BMechanism of Action
  • Amphotericin B binds to sterols
  • Ergosterol is a constituent of the fungal cell
    wall
  • AMB has a greater avidity for ergosterol than for
    the cholesterol in the human cell wall
  • Binding to the fungal cell wall alters the
    permeability and the intracellular contents leak

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AMPHOTERICIN BDisadvantages
  • Intravenous administration
  • Thrombophlebitis
  • Nephrotoxic
  • Fever
  • Chills
  • Anemia
  • Long term administration

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Azoles
  • There are a few rare serious side effects from
    Itraconazole and Fluconazole

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PRIMARY ANTI-FUNGAL AGENTS
  • 3. Griseofulvin
  • 4. 5-fluorocytosine (5-FC)
  • 5. Allylamines
  • -Terbinafine (Lamasil)
  • 6. Echinocandins
  • - Caspofungin

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Griseofulvin
  • A slow acting drug used for skin and nail
    infections. It accumulates in the stratum
    corneum and prevent hyphal penetration through
    these layers

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5-fluorocytosine(5-FC)
  • Interferes With RNA Synthesis

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MECHANISMS OF ACTION
  • Polyenes
  • Azoles
  • Griseofulvin
  • 5 - FC
  • Ergosterol in cell membrane
  • Interfere with ergosterol synthesis
  • Forms a barrier to fungal growth
  • Inhibits RNA synthesis

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F. Clinical Classification of Mycoses
  • Cutaneous
  • Subcutaneous
  • Systemic
  • Opportunistic

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Cutaneous Mycoses
  • Skin, hair and nails
  • Rarely invade deeper tissue
  • Dermatophytes

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Subcutaneous Mycoses
  • Confined to subcutaneous tissue and rarely spread
    systemically. The causative agents are soil
    organisms introduced into the extremities by
    trauma

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Systemic Mycoses
  • Involve skin and deep viscera
  • May become widely disseminated
  • Predilection for specific organs

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OPPORTUNISTIC FUNGI
  • Ubiquitous saprophytes and occasional pathogens
    that invade the tissues of those patients who
    have
  • Predisposing diseases
  • Diabetes, cancer, leukemia, etc.
  • Predisposing conditions
  • Agammaglobulinemia, steroid or
    antibiotic therapy.

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Medical Mycology Iceberg
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THE ESSENTIAL ELEMENT OF DIAGNOSIS IS
  • A HIGH INDEX OF SUSPICION !

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End
  • Introduction
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