2. Introduction to fungi

3. objectives
Discuss the structure of fungi. How are fungi different from bacteria and viruses?
Discuss the basis of classification of fungi
Discuss the predisposing factors for fungal infections

4. Structure of fungus
Hyphae: Tubular, branching filaments , hyphae anchor the colony and absorb nutrients.
Mycelium: Mass or mat of hyphae, mold colony
Pseudohyphae: Chains of elongated buds or blastoconidia
Yeasts: Unicellular, spherical to ellipsoid (3–15 µm) fungal cells that usually reproduce by budding
Imperfect fungi: Fungi that lack sexual reproduction; . They are identified on the basis of asexual reproductive structures
Perfect fungi: Fungi that are capable of sexual reproduction, which is the teleomorph.

5. Conidia: Asexual reproductive structures produced from the transformation of a vegetative yeast or hyphal cell. Conidia may be formed on specialized hyphae, termed conidiophores.
Microconidia: are small, and macroconidia are large or multicellular.
Chlamydospores (chlamydoconidia): Large, thick-walled, usually spherical conidia produced from terminal or intercalary hyphal cells (Candida albicans,
Phialoconidia: Conidia that are produced by a "vase-shaped" conidiogenous cell termed a phialide (eg, Aspergillus fumigatus
Dematiaceous fungi: Fungi whose cell walls contain melanin, which imparts a brown to black pigment).

6. Mycology: study of fungus
Most species of fungi are beneficial to humankind.
They reside in nature.
Some fungi greatly enhance our quality of life by contributing to
the production of food and spirits, including cheese, bread, and beer.
fungi have served medicine by providing useful bioactive secondary metabolites such as antibiotics (eg, penicillin) and immunosuppressive drugs (eg, cyclosporine)
All fungi are eukaryotic organisms,
Each fungal cell has at least one nucleus and nuclear membrane, endoplasmic reticulum, mitochondria, and secretory apparatus.
Most fungi are obligate or facultative aerobes.
They are chemotrophic, secreting enzymes that degrade a wide variety of organic substrates into soluble nutrients which are then passively absorbed or taken into the cell by active transport

7. Mycoses may be classified as superficial, cutaneous, subcutaneous, systemic, and opportunistic
Grouping mycoses in these categories reflects their usual portal of entry and initial site of involvement

8. Difference between fungi, bacteria and viruses
Features
Viruses
Bacteria
Fungi
Size µ
0.3-2µ
3-10µ
Cell Type
Acellular
Prokaryote
Eukaryote
DNA/ RNA
Either
Both
Nucleic acid replication
Host cell
Continuous
G & S phase
Replication
Complex
Binary fission
Mitosis/ Meiosis
Organelle
Uses host
Not membrane bound
Membrane bound
Ribosomes
None
70S(30S+50S)
80S(40S+60S)
Cell memb
Env/Non env
No sterol #Mycoplasma
Ergosterol
Cell wall
Peptidoglycan
Chitin, Glucan

9. Classification of fungus
A: morphological classification:
Yeasts: round, oval or elongated unicellular fungi. Reproduce by budding. on culture form smooth creamy colonies .example: Cryptococcus neoformans
Yeast like fungi: grow partly as yeast and partly as elongated cells like hyphae. Example: Candida albicans
Molds or filamentous fungi: form true mycelium and reproduce by formation of different types of spores. Example: dermatophytes, Aspergillus
Dimorphic fungi: yeast form in host tissue and in vitro at 37°C on enriched media and hyphal form in vitro at 25°C, example: Histoplasma,, sporothrix, Blastomyces, Paracoccidiodes, Penicillium

10. B. Systemic classification: on the basis of formation of sexual spores
Zygomycetes: lower fungi with nonseptate hyphae and form asexual spores called sporangiospoes contained within oospores. Examples: Rhizopus
Ascomycetes: form sexual spores(ascospores) within a sac:example: yeasts and filamentous fungi
Basidiomycetes: form sexual spores (basidiospores) on a basidium or base. Example: mushrooms, cryptococcus
Deuteromycetes ( Fungi imperfecti) : lack a known sexual state. Most fungi of medical importance are in this group

11. Factors predisposing to fungal infections
Transplantation
Diabetes mellitus
Malignancies
Myeloma
Immunosuppression
Corticosteroid therapy
Antineoplastic therapy
Advancing age