WHAT ARE FUNGI

WHAT ARE FUNGI?

Not plants. They form a separate group of higher organisms distinct from plants and animals. Fungi belong to kingdom mycetea, the study of fungi is called mycology.

General characteristics of fungi.
1. Eukaryotoc
2. Non photosynthetic
3. Have cell wall of chitin or other polysaccharides, animals lack cell wall & plants with cellulose.
4. are heterophilic : digest food first and then absorbed it in to their bodies)they  release digestive enzyme to break down organic material or their host.
5. simpler in structure than animals or plants, have no cell division into organs or tissues →hyphae (are tubular like cells)
6. May be saprophytic (live on other dead organisms) or parasitic.
7. Store food energy as glycogen.
8. Most are multicellular, but some unicellular like yeast.
9. Grow as microscopic tube or filament called hyphae that contain cytoplasm and nuclei. The mass of branching hyphae of the vegetative stage of fungi is called mycelium.
10. Fungi reproduce by means of microscopic propagates called spores. Some fungi reproduce asexually producing spores. Some reproduce sexually , it is either homothallic or heterothallic.
11. Grow best in warm, moist environment and preferring shade.
12. Important decomposers and recyclers of nutrients in the environment.

Dimorphic fungi:

Fungi grow as single called yeast under one set of conditions or as filamentous mold under different circumstance.

Mold:
although patches of mold are visible, the individual cells are microscopic.  Molds are composed of long filament of cells jointed together, end to end. The filament called Hyphae . many molds have cross wall ( septa) in their hypha that divide each hypha into many different cells with individual nuclei. In some classes of fungi the filaments do not contain septa and appear to be one long cell containing many nuclei . this type called Coencytic hypha largest diameter of cells.


Mycelium
Is a mass of branching hyphae of the vegetative stage of fungi .some hyphae are septated and other are not in the primitive fungi → a septate in advanced one → septated.
Yeast:
this form of independent single cells propagate by budding out other cells. The bud may detacheded and forms another bud or still attached .this form of fungi not produces hyphae.

Nutrition in fungi:

Fungi are heterotrophic, and most are saprophytes. They live upon dead or decaying organic matter, grow best at room temperature , many grow at refrigeration and grow well in environment containing large amount of sugar and under acidic conditions , few grow as parasites on human , animals and plants.

Classification of fungi

1. Chytridiomycota: consist of single class with approximately 100 genera , none of which are pathogenic to human.
2. Zygomycota : consist of(175) genera . sexually reproduce by fusion of nuclei from compatible colonies → zygospores.
3. Ascomycota : this consist of (3200) genera . sexually reproduce → ascospores.
4. Basidiomycota: consist of( 22 000) species . sexually reproduce → blasidospores.




Lab diagnosis of fungal infection:

 The diagnosis relies upon combination of clinical observation and lab investigations.
 The successful lab diagnosis of fungal infection depends in major part on the collection of adequate clinical specimens for investigations.
 It is important that clinician indicate the suspect case and provide sufficient background information to the lab. In addition to specify the sources of specimen.

Lab methods based on 3 broad approaches:

 Microscopically detection of the causative agent
 Isolation and identification of the causative agent
 Detection of a serologic response.
 Procedures based on the detection of fungal DNA in clinical materials are presently based nowadays.

Direct microscopic examination of clinical specimens :

• In many cases the definitive diagnosis of fungal infection can be made by the direct microscopic detection.
• Skin scraping reveals → fungi in matter of minutes.
• Keratinized tissues → pre treatment → dissolve the materials → examination.
• Warm 10- 20 % KOH (dekeratiniazation)
• A drop of lactophenol cotton blue is used for diagnosis.
• Calcofluor white stain the fungal cell wall
• Indian ink is negative stain of capsulated fungi.




Histopathological studies.
• It is one of the most reliable methods of establishing the diagnosis of subcutaneous and systemic mycoses.
• Hematoxylin and Eosin (H & E) stains.
• Methamine silver stain, periodic acid shift (PAS).

Culture
 Very important method for the diagnosis of the causative agent, its genus and species.
 Almost are not fastidious
 Sabouraud agar and malt agar are used widely to isolate almost fungi.
 B.H.I.A is used for fastidious forms of fungi →yeast form of H. capsulated.
 CHROM agar → candida species (chromogenic medium).
 Antibacterial agents must add to the medium.
 Optimum growth temperature 28 – 30 Cْ  for 2 – 4 weeks