Batterjee Medical College. Dr. Manal El Said Head of Microbiology Department Mycology

Batterjee Medical College


Dr. Manal El SaidDr. Manal El Said Head of Microbiology Department

Mycology


• Fungi are eukaryotic organisms that exist in two

basic forms: yeasts & molds.

• Yeasts are single cells & reproduce by budding

(daughter cells are unequal in size)

• Molds consist of long filaments of cells called

hyphae & reproduce by cell division (daughter

cells are equal in size).

Structure & Growth

Basic Mycology


Basic Mycology

Structure & Growth


Some fungi are dimorphic,

i.e., they can exist either as

yeasts or molds, depending

on temperature.

- Room temperature (25°C)

molds

- Body temperature (37°C)

yeasts

Basic Mycology

Structure & Growth


• Fungal cell wall is made of chitin

• Fungal cell membrane contains ergosterol.

Structure & Growth

Basic Mycology


• Infection with certain systemic fungi, such as

Histoplasma & Coccidioides, granulomatous

host defense response (composed of macrophages

& helper T cells) & can be detected by skin tests.

• Infection with Aspergillus, Mucor & Sporothrix

pyogenic response (composed of neutrophils).

Basic Mycology

Pathogenesis


• Ingestion of Amanita mushrooms liver

necrosis due to presence of two fungal toxins,

amanitin & phalloidin.Amanitin inhibits RNA

polymerase (synthesizes cellular mRNA).

Basic Mycology

Fungal Toxins & Allergies


• Ingestion of peanuts & grains contaminated with

Aspergillus flavus liver cancer due to

presence of aflatoxin.

• Aflatoxin epoxide mutation in p53 gene loss

of p53 tumor suppressor protein.

Basic Mycology



• Inhalation of spores of Aspergillus fumigatus can

cause allergic bronchopulmonary aspergillosis.

• This is IgE-mediated immediate hypersensitivity

response.

Basic Mycology



• Microscopic examination of KOH preparation can

reveal presence of fungal structures.

• KOH dissolve human cells, allowing visualization of

fungi.

Basic Mycology

Laboratory Diagnosis


• Sabouraud's agar is used to grow fungi because its

low pH inhibits growth of bacteria, allowing slower-

growing fungi to emerge.

Basic Mycology



• DNA probes can be used to identify fungi growing

in culture at much earlier stage, i.e., when colony

size is much smaller.

Basic Mycology



• Tests for presence of fungal antigens & for

presence of antibodies to fungal antigens are often

used.

• Two commonly used tests in patient's serum are:

- Cryptococcal antigen in spinal fluid

- Coccidioides antibodies.

Basic Mycology



• Amphotericin B binds to fungal cell membranes at

site of ergosterol disrupts integrity of membranes

Basic Mycology

Antifungal Therapy

• Azole drugs, such as itraconazole, fluconazole, &

ketoconazole inhibit synthesis of ergosterol.

• Echinocandins inhibit synthesis of D-glucan,

which (component of fungal cell wall).


Fungi Causing Cutaneous & Subcutaneous Mycoses


• Cutaneous (Superficial) mycoses are confined to outer

layers of skin, hair, & nails & do not invade living tissues.

• The fungi are called dermatophytes.

• Dermatophytes (keratinophilic fungi) , produce

extracellular enzymes (keratinases)

hydrolyzing keratin.

Dermatophytes Trichophyton, Microsporum, Epidermophyton Species



Characteristics

Transmission

Direct contact with skin scales.

• These fungi are molds that use keratin as nutritional

source.

• Habitat is human skin



DiseasesTinea means "ringworm" or "moth-like". Dermatologists use term to refer to variety of lesions of skin or scalp.•Tinea corporis - small lesions occurring anywhere on body•Tinea pedis - "athlete's foot". Infection of toe webs & soles of feet. •Tinea unguium (onychomycosis)- nails. Clipped are used for culture•Tinea capitis - head. Frequently found in children•Tinea cruris - "jock itch". Infection of groin, perineum or perianal area.•Tinea barbae - ringworm of bearded areas of face & neck


Tinea corporis


Tinea pedis (athlete's foot) Onychomycosis

"Tinea capitis Tinea faciei” Tinea cruris


Sporotrichosis.

Sporothrix schenckii

Disease

•Thermally dimorphic•Habitat is soil or vegetation.

Characteristics

Mold spores enter skin in puncture wounds caused

by rose thorns & other sharp objects in the garden.

Transmission


Sporothrix schenckii

Pathogenesis

Local abscess or ulcer with nodules in draining

lymphatics.


Fungi Causing Systemic Mycoses


Histoplasmosis.

1-Histoplasma capsulatum

Disease

Thermally dimorphic

Mold grows in soil enriched with bird droppings

Characteristics

Transmission

Inhalation of airborne asexual spores


Skin Test

•Histoplasmin (mycelial extract) is the antigen.

•Useful for epidemiologic purposes to determine incidence of

infection.

•Positive result indicates that infection has occurred

•It cannot be used to diagnose active disease.

•Skin testing can induce antibodies, so serologic tests must

be done first.

1-Histoplasma capsulatum



2-Coccidioides immitis

Disease

Characteristics

Transmission

Coccidioidomycosis.

•Thermally dimorphic.

•Natural habitat is the soil

Inhalation of airborne arthrospores.


Skin Test

•Coccidioidin, (mycelial extract) or spherulin, (extract of

spherules) is the antigen.

•Determining if the patient has been infected.

•Positive test indicates prior infection but not necessarily

active disease.

2-Coccidioides immitis



3-Blastomyces dermatitidis

Disease

Blastomycosis.

• Thermally dimorphic

• Yeast form has single, broad-based

bud & thick, refractile wall.

• Natural habitat is soil

Transmission

Inhalation of airborne spores (conidia).

Characteristics

Transmission


Disease

Paracoccidioidomycosis.

Characteristics

•Thermally dimorphic .

Transmission

Inhalation of airborne conidia.

4-Paracoccidioides brasiliensis

Disease

Characteristics

Transmission


Fungi Causing Opportunistic Mycoses


•Thrush,

•Disseminated candidiasis

• Chronic mucocutaneous candidiasis.

Fungi Causing Opportunistic Mycoses 1-Candida albicans

Disease

Characteristics

• Candida albicans is yeast when part of normal flora of

mucous membranes but forms pseudohyphae & hyphae

when it invades tissue.

• The yeast form produces germ tubes when

incubated in serum at 37°C.


• Part of the normal flora of skin, mucous membranes & GI

tract.

• No person-to-person transmission.


Transmission


• Predisposing factors include:

- Reduced cell-mediated immunity

- Altered skin & mucous membrane

- Suppression of normal flora

- Presence of foreign bodies.

• Thrush is common in:- Infants- immunosuppressed patients - persons receiving antibiotic therapy.


Pathogenesis


• Skin lesions occur on moisture-damaged skin.

• Disseminated infections, such as endocarditis and

endophthalmitis, occur in immunosuppressed patients and

intravenous drug users.

• Chronic mucocutaneous candidiasis occurs in children

with a T-cell defect in immunity to Candida.


Pathogenesis


Oral thrush. CDC


Candida albicans showing germ tube production in serum.


• Microscopic examination of tissue reveals yeasts &

pseudohyphae.

• The yeast is gram-positive.

• Germ tube formation & production of chlamydospores

distinguish C. albicans from other species of Candida.



Skin Test to determine competency of cell-

mediated immunity .

Out-pouching of cell wall that becomes tubular & does not have constriction at its base


•Heavily encapsulated yeast.

•Habitat is soil, enriched by pigeon droppings.

Fungi Causing Opportunistic Mycoses 2-Cryptococcus neoformans

Transmission

Inhalation of airborne yeast cells.

Disease

Cryptococcosis, especially cryptococcal meningitis.

Characteristics


• Organisms cause influenza-like syndrome or pneumonia.

• They spread via the bloodstream to the meninges.

• Reduced cell-mediated immunity severe disease

Fungi Causing Opportunistic Mycoses 2-Cryptococcus neoformans

Pathogenesis


•Invasive aspergillosis

• Allergic bronchopulmonary aspergillosis

• Aspergilloma (fungus ball).

Fungi Causing Opportunistic Mycoses 3-Aspergillus fumigatus

Disease

Characteristics

Transmission

• Inhalation of airborne spores (conidia).

• Mold with septate hyphae (branch at V-shaped angle) .

• Habitat is the soil.


• In immunocompromised patients, invasive disease occurs.

• It invades blood vessels thrombosis & infarction.

• Person with lung cavity, e.g., from tuberculosis, may

develop "fungal ball" (aspergilloma).

• Allergic person, can develop allergic bronchopulmonary

aspergillosis mediated by IgE antibody.

Fungi Causing Opportunistic Mycoses 3-Aspergillus fumigatus

Pathogenesis


Fungi Causing Opportunistic Mycoses 4-Mucor & Rhizopus Species

Disease

Characteristics

•Molds with nonseptate hyphae that typically branch at 90-

degree angle (wide-angle branching).

•Habitat is soil.

Mucormycosis.

Transmission

Inhalation of airborne spores.


• They cause disease primarily in ketoacidotic diabetic and

leukemic patients.

• Sinuses & surrounding tissue are typically involved.

• Hyphae invade mucosa & progress into underlying tissue &

vessels, leading to necrosis & infarction.

Fungi Causing Opportunistic Mycoses 4-Mucor & Rhizopus Species

Pathogenesis

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Batterjee Medical College. Dr. Manal El Said Head of Microbiology Department Mycology