Introduction Flashcards by fatima usman

What is mycology

The study of fungi and diseases they cause

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Difference btw bacteria and fungi

1 their cell wall contain chitin which is not sensitive to antibiotics
2 the fungal cell membrane contain ergosterol on which anti fungal drugs act
3 they have true nucleus

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Benefits of fungi

Production of antibiotics
Fermentation of carbohydrate
Decomposition of dead animals
Uses as food in some society

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Harmful effects of fungi

Spoils food
Mycotoxins infection
Produce toxin and cause disease(mycotoxicosis)

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Fungi maybe what and what

Saprophyte in dead animals
Parasite cause disease in animals and human

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Anatomy of fungi

Hyphae: elongated unit and multicellular which either be separate or non septate
Mycelium- group of hyphae
Divided into 2 parts
Aerial for reproduction and growth
Vegetative- for absorption of nutrition

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What are the medically important cell structures of fungi

Cell wall composed of chitin instead of bacterial peptidoglycan
Cell membrane contains ergosterol instead of cholesterol(a human cell membrane thing)

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Explain chitin

Is a polysaccharide,B-glucagon is one of the medical importance as the site of action at caspofungin(antifungal drug)

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Selective action of amphotericin b and azole drugs

The selective action of amphotericin b and azole drugs such as fluconazole and ketoconazole on fungi is based on the differences in membrane sterols

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types of fungi

Yeast
Molds
Medically important fungi are thermally dimorphic ( forms different structure at different temperature)

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Yeast fungi

Grows as single cell(unicellular fungus)that reproduce be asexual budding

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Molds

Relatively simple multicellular fungi they grow as long filaments(hyphae) and form a mat (mycelium), forming either ;
Septate with transverse walls

Non septate are mulnucleated(coenocytic) without transverse wall

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Medically important fungi

They exist as molds in environment at ambient temp and yeast in human tissues at body temp

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Temperature of fungi

It grows btw 0-70C
But pathogenic fungi from 20-40(mesophlic) some superficial grow on the surface of body at 25 other grow systematically inside the body at 37
Above 50 thermophilic

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Oxygen requirement of fungi

Most are obligate aerobes
Some are facultative anaerobes
No fungi are obligate anaerobes

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Nutrition of fungi

All fungi require a preformed organic source of carbon(associated with decaying matter)

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Natural habitat of fungi

therefore the natural of most fungi is environment except candida albicans which is part of human normal flora

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Reproduction of fungi

Sexually
Asexually

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Sexual reproduction of fungi

By mating and forming sexual spores as follows
-zygospores
-ascospores
-basidiospores

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Zygospores

Are single spores with thick walls(phycomycete non separated hyphae- they can reproduce asexually by spotangiospores)

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Ascospores

Are formed in a sac called as us forming from 4 to 8 ascus(ascomycete septated hyphae- they reproduce asexually forming conidia)

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Basidiospores

Are formed externally on the tip of a pedestal called a basidium no asexual reproduction and non pathogenic

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Asexually explanation

Most of medical interest propagate asexually and they form conidia by the sides or ends of specialized structures

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According to their shape color and arrangement conidia is identified into

Arthrospores
Chlamydospores
Blastospores
Sporangiospores

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Arthrospores

arise by fragmentation of the ends of hyphae and are mode of transmission of coccidioides immitis

Chlamydospheres

Rounded thick walled and quite resistant( the terminal chlamydospores of candida Albicans aid in its identification)

Sporangiospores

Are formed within a sac (sporangium) on a stalk by molds such as rhizopus amd mucor

The response of the immune sysatem to fungal infection lead to formation of what And what are the major systemic fungal diseases it produces

Formation of Granulomas Coccidioidomycosis Histoplasmosis Blastomycosis

Cell mediated immune response is invoked in

Granuloma formation

Activation of cell mediated immune response results in what

Delayed hypersensitivity skin test response to certain fungal antigens injected intradermally

Acute suppuration characterized by presence of neutrophils in the exudate also occurs in certain fungal disease such as

Aspergillosis and sporotrichosis

A positive skin test indicates what

Exposure to fungal antigen but it doesn’t imply current infection because the exposure may have occurred in the oasty

A negative skin test means

Unlikely diagnosis unless the patient is immunocompromised

Skin test for candida is used to determine

If cell mediated immunity is normal or not because most people carry candida as normal flora

Candida and deematophyte née what to establish

Damage skin so Intact skin is host defense against them

What inhibits dermatophytes growth

Fatty acids in skin

Hormone associated skin changes at puberty limit what

Ringworm of the scalp

Ring worm of the scalp is caused by

Trichophyton

Can normal flora of the skin and mucous membranes suppress fungi

Yes

Inhibition of normal flora eg by antibiotics lead to what

Overgrowth of fungi such as c albicans

Fungal

Fungal disease are

Mycotoxicoses Mycotic infection Allergies to fungal spores

Mycotoxicoses Caused by ingesting which toxins

a amanitin and phalloidin by amanita mushrooms,most potent hepatotoxins b ergotism by mold claviceps purpurea cause pronounced vascular and neurological effects C aflatoxins by aspergillus flavus, causing hepatic carcinoma

Allergies to fungal spores lead to

So especially aspergillus they lead to immediate hypersensitivity response

Allergies to fungal spores cause which clinical manifestation

A asthmatic reaction B eosinophilia Cc skin test reaction( wheel and fire)

4 approaches to The lab diagnosis of fungal disease

Direct microscopic examination of clinical specimens 2 culture of organism on sabourauds agar 3 DNA probe test 4 serologic test

Direct microscopic exam of clinical specimens

Such as sputum lung biopsy material and skin scrapings depends on finding characteristic asexual spores hyphae or yeasts in the light microscope ( stained with 10% KOH India pink fluorescent dye or methanamine silver)

Culture of org on sabourauds agar

It facilitates the appearance of slow growing fungi by inhibiting the growth of bacteria in the specimen by 1 the low ph of the medium 2 chloramphenicol and cyclohexamide that are frequently added

Dna probe test

Can identify colonies at an earlier (rapid)stage of growth than visual detected test of colonies

Seeologic test

For presence of antibodies in the patients serum or spinal fluid and useful in diagnosing systemic mycoses but less in diagnosing other fungal infection Significant rise in antibody tiger confirm the diagnosis

Complement fixation test is the most frequently used in suspected cases of

Coccioiodomycosis Histoplasmosis Blastomycosis

Latex agglutination test is used to detect

The presence of the polysaccharide capsular antigens of c.neoformans in spinal fluid in streptococcal meningitis

What are the most effective antifungal drugs

Amphotericin b and azoles

Amphotericin b mechanism of action

Disrupts fungal cell memebranes at the site of ergosterol

Amphotericin b mechanism of action

Disrupts fungal cell memebranes at the site of egosterol

Amphotericin b is Also called

Fungizone

Caspofungin (cancidas) drugs mechanism of action

Inhibit the sysnthesis of beta glucan which found in fungal cell walls but not in the bacterial cell walls( human cells do not have a cell wall)

Azole drugs mechanismof action

Inhibit the synthesis of ergosterol which is essential component of fungal membranes