Lab no 8Lab no 8

Definition:

Fungi are eukaryotic organisms and

include the yeasts, fleshy fungi & molds

which include dimorphic fungi.

Yeasts are microscopic, unicellular fungi;

molds are multinucleated, filamentous

fungi and the fleshy fungi include

mushrooms.

All fungi are chemoheterotrophs, requiring organic compounds as an energy and carbon source. They obtain nutrients by absorbing them from their environment.

Most of them survive by decaying organic material and are termed saprophytes. Some are parasitic, getting their nutrients from living plants or animals.

The study of fungi is termed mycology and the diseases caused by fungi are

called mycotic infections or mycoses.

Uses of fungi

In general, fungi are beneficial to humans. They are involved in :

1. The decay of dead plants and animals (resulting in the recycling of nutrients in nature).

2. The manufacturing of various industrial and food products.

3. the production of many common antibiotics,

4. and may be eaten themselves for food.

MouldsYeast

Dimorphic

FungiFungi

Fungi

Classification of fungi

.

It is classified according to morphology into:

1. Yeasts:1. Yeasts: oval or round cells that reproduce by

budding e.g: Cryptococcus

neoformans . Some yeasts produce chains of

elongated budding cells (Pseudohyphae)

e.g: Candida albicans.

2. 2. Filamentous fungi Filamentous fungi (Moulds):(Moulds):

• Grow as branching filaments (hyphae).

• Reproduce by spores

e.g.: Aspergillus, Penicillium and rhizopus species

33. . Dimorphic fungi:Dimorphic fungi: They grow either in tissue or in

culture at 37 oC in yeast form but when cultures are incubated at 22 oC they appear in mould forms.

e.g.: histoplasma and blastomyces.

Specific Cultivation Medium

Sabaroud’s Dextrose Agar: It has acidic PH. It contains relatively high concentrations of sugars

e.g; dextrose and maltose. enhanced SDA with the addition of cycloheximide,

streptomycin, and penicillin to produce an excellent medium for the primary isolation of fungi.

Culture of pathogenic yeasts are incubated at 37 oC

Candida albicans

it is an oval budding yeast which produces pseudohyphea.

It is a normal inhabitant of the mouth, vagina and intestine .

It may predominate and cause super infection. It causes oral or vaginal thrush .

Candida albicans..

Laboratory diagnosis:1. Direct microscopic examination : Gram stain that show large gram positive

budding cells with pseudohyphea.2. Culture on sabouraud’s dextrose agar :

large cream colonies with yeasty odour which can be identified by Gram stain

Filamentous Fungi

Structure of Filamentous Fungi:Structure of Filamentous Fungi:Structure of Filamentous Fungi:Structure of Filamentous Fungi:

1. Hyphae:• It is a tube or filament that could be septate or non septate

Filamentous Fungi ,cont..

2 .Mycelium:

Macroscopic collection of branching hyphae

Divided into:

* Vegetative: diffuses into the medium to absorb nutrients.

* Aerial: projects above the substrate and contains spores.

Filamentous Fungi ,cont..

3. Spores:• More resistant to unfavorable environmental condition.• reproductive elements produced on the aerial mycelium.• produced by asexual cell division or as a result of sexual reproduction.

Filamentous Fungi ,cont..

• Asexual spores could be classified according to their relation to the parent hyphae into:

*Conidiospores(never enclosed in a

sac)Eg. Aspergillus, Penicillium

Sporangiospores

(formed inside a sac

“sporangium)”Eg. Mucor sp.

Filamentous Fungi

AspergillusAspergillus

PenicilliumPenicillium

Rhizopus

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