Introduction to fungi
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
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 ( ecudorper yllausu taht sllec lagnuf )mµ15 –3
gniddub yb
 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 .
 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: dna ,llams era macroconidia .ralullecitlum ro egral era
 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 ,ge( Aspergillus fumigatus
 Dematiaceous fungi: Fungi whose cell walls contain melanin, which imparts a brown to black
pigment.)

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
o
the production of food and spirits, including cheese, bread, and
beer.
o
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

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
Difference between fungi, bacteria and viruses
Features
Viruses
Bacteria
Fungi
Size
0.02-0.3 µ
0.3-2µ
3-10µ
Cell Type
Acellular
Prokaryote
Eukaryote
DNA/ RNA
Either
Both
Both
Nucleic acid Host cell
replication
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
None
Peptidoglycan
Chitin, Glucan
CLASSIFICATION OF FUNGUS
A: morphological classification:
I.
Yeasts: round, oval or elongated unicellular fungi.
Reproduce by budding. on culture form smooth creamy
colonies .example: Cryptococcus neoformans
II.
Yeast like fungi: grow partly as yeast and partly as
elongated cells like hyphae. Example: Candida albicans
III.
Molds or filamentous fungi: form true mycelium and
reproduce by formation of different types of spores.
Example: dermatophytes, Aspergillus
IV.
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
B. Systemic classification: on the basis of formation of sexual
spores
I.
Zygomycetes: lower fungi with nonseptate hyphae and
form asexual spores called sporangiospoes contained
within oospores. Examples: Rhizopus
II.
Ascomycetes: form sexual spores(ascospores) within a
sac:example: yeasts and filamentous fungi
III.
Basidiomycetes: form sexual spores (basidiospores) on
a basidium or base. Example: mushrooms,
cryptococcus
IV.
Deuteromycetes ( Fungi imperfecti) : lack a known
sexual state. Most fungi of medical importance are in
this group
FACTORS PREDISPOSING TO FUNGAL INFECTIONS
1.
Transplantation
2.
Diabetes mellitus
3.
Malignancies
4.
Myeloma
5.
Immunosuppression
6.
Corticosteroid therapy
7.
Antineoplastic therapy
8.
Advancing age