Introduction to Medical Mycology
Session 31: Introduction to Medical Mycology
Total Session Time: 120 minutes
Pre-requisites
Students Learning Tasks
By the end of this session students are expected to be able to:
basidiomycotina, deuteromycota)
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |5 minutes |Presentation |Introduction, Learning Tasks |
|2 |20 minutes |Presentation |Common Terminologies used in |
| | | |Mycology |
|3 |10 minutes |Presentation |Occurrence and Distribution of |
| | | |Fungi |
|4 |15 minutes |Buzzing/ |Characteristics of Fungi |
| | |Presentation | |
|5 |25 minutes |Presentation |Fungal Growth and Reproduction |
|6 |25 minutes |Presentation |Structure of Fungal Cells |
|7 |10 minutes |Presentation |Classification of Fungi |
|8 |5 minutes |Presentation |Key Points |
|9 |5 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
ASK students if they have any questions before continuing
STEP 2: Common Terminologies Used in Mycology (20 minutes)
o Mycology is the study of fungi
o Mycosis is a term referring to infections caused by fungi
o Hyphal or mycelial colony or form of growth
o Mass or mat of hyphae, mould colony
o Unicellular, spherical to ellipsoid fungal cells that usually
reproduce by budding
o A common mode of asexual reproduction, typical of yeasts
o During mitosis, the parent cell wall protrudes outwardly and enlarges
to form a nascent bud that contains the progeny nucleus
o A fungal cell may produce single or multiple buds
o A specialized propagule with enhanced survival value, such as
resistance to adverse conditions or structural features that promote
dispersion. Spores may result from asexual (e.g. conidia,
sporangiospores) or sexual reproduction
o Fungi whose cell walls contain melanin, which imparts a brown to black
pigment
o Fungi that have two growth forms, such as a mold and a yeast, which
develop under different growth conditions (e.g. Blastomyces
dermatitidis forms hyphae in vitro and yeasts in tissue) They are the
cause of most fungal infection
o Tubular, branching filaments of fungal cells, the mould form of
growth.
Septate hyphae are separated by porous cross-walls (or septa) and
aseptate hyphae are continuous and also known as coenocitic hyphae.
o
o Vegetative or substrate hyphae anchor the colony and absorb nutrients
o Aerial hyphae project above the colony and bear the reproductive
structures
o Chains of elongated buds or blastoconidia; the septations between
cells are constricted
STEP 3: Occurrence and Distribution of Fungi (10 minutes)
play major roles in ecosystem processes
of great environmental and medical importance
symbiotic relationships with plants or animals
of vegetative growth and nutrient intake
of the organisms (mycelia) and they digest organic matter externally
before absorbing it into their mycelia
freshwater or marine environments
do not tolerate high degrees of salinity
thrive in highly polluted streams
large number of species; only a small number of species are found in
drier areas or in habitats with little or no organic matter
where there is sufficient moisture to enable them to grow
although they are rare and are more often found living in symbiosis
with algae in the form of lichens
STEP 4: Characteristics of Fungi (15 minutes)
|Activity: Buzzing (5 minutes) |
| |
|ASK students to pair up and buzz on the following exercise for 2 |
|minutes |
| |
|List the characteristics of fungi? |
| |
|ALLOW few pairs to respond and let other pairs to add on points not |
|mentioned |
| |
|WRITE their response on the flip chart/board |
| |
|CLARIFY and SUMMARIZE by using the content below |
o Chitin is a polysaccharide composed of long chain of N-
acetyleglucasamine.
o Also the fungal cell wall contains other polysaccharide, β-glucan
STEP 5: Growth and Reproduction in Fungi (25 minutes)
Fungal Growth
enclosed by a rigid cell wall made up a rigid polymer, chitin
a complicated, radially expanding network called the mycelium, which
makes up the thallus, or undifferentiated body, of the typical fungus
upon reaching a certain stage of maturity, forms—either directly or in
special fruiting bodies—reproductive cells called spores
active mechanisms; upon reaching a suitable substrate, the spores
germinate and develop hyphae that grow, branch repeatedly, and become
the mycelium of the new individual
fungal structures are therefore made up of hyphae or portions of
hyphae
cells that multiply by budding or, in certain species, by fission
grow at the hyphal tips as long as conditions remain favourable
Reproduction in Fungi
o This is somatic reproduction and is very common in fungi and occurs by
variety of mechanisms
o Fragmentation
similar fragments
o Budding
necessary structures and separated to grow into new individuals
ultimately become new individuals
o Fission
each of which develop into a new individual
o Asexual reproduction takes place by means of spores
o The spores develop into new individuals
o The spores may be produced asexually or sexually
o Sexual reproduction produces sexual spores
o Asexual reproduction produces asexual spores
o Types of asexual spores produced in different groups of fungi:
o Sexual reproduction involves union of two nuclei or gametes of
opposite sex a gamete is unisexual. i.e. haploid.
o Sexual reproduction in fungi consists of three distinct phases
same of common cell
plasmogamy, Karyogamy immediately follows plasmogamy
reduces the number of chromosomes to haploid.
differentiated sex cells gametes or may contain one or more gamete
nuclei
[pic] Refer students to Handout 35.1: Reproduction in Fungi
STEP 6: Structure of Fungal Cell (25 minutes)
o The structure and composition of the fungal cell wall have unique
characteristics
o The cell wall is made up of rigid polymer called Chitin (β (1,4) N-
acetil-glucose-amine)
o he organization of the fungal cell membrane is the same as the general
eukaryotic cell membrane
o But in fungal cells, there is a special fungal sterol that affects
membrane fluidity of the fungi
o The special membrane components have great importance in antifungal
therapy
the ergosterols and disintegrate the membrane,
synthesis pathway of ergosterols
o Fungi possess microtubules composed of the protein tubulin
o These structures are involved in the movement of organelles,
chromosomes, nuclei, and Golgi vesicles containing cell wall
precursors.
o Microtubules are the principal components of the spindle fibers, which
assist in the movement of chromosomes during mitosis and meiosis
with microtubule-associated proteins involved in the assembly of the
tubulin dimers. By interfering with tubulin polymerization,
griseofulvin stops mitosis at metaphase
o The fungal nucleus is bounded by a double nuclear envelope and
contains chromatin and a nucleolus
o Fungal nuclei are variable in size, shape, and number
o Are as in eukaryotic cells
STEP 7: Classification of Fungi (10 minutes)
o Reproduction in a sack called an ascus with the production of
ascopspores
o Sexual reproduction in a sack called a basidium with the production of
basidiospores
o Sexual reproduction by gametes and asexual reproduction with the
formation of zygospores
o No recognizable form of sexual reproduction
o Includes most pathogenic fungi
STEP 8: Key Points (5 minutes)
basidiomycoa, zygomycota and deuteromycota
STEP 9: Evaluation (5 minutes)
References
Hugo and Russell (2011), Pharmaceutical Microbiology 8th Edition, Willey-
Blackwel publications
Karen C. Carroll et al (2013); Jawetz, Melnick and Adelberg’s Medical
Microbiology 26th Ed. McGraw Hill Co. Inc.
Greenwood et al (2012); Medical Microbiology, 18th edition Churchill
Livingstone
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