Description about General mycology

1. By
HAFIZ ULLAH KHAN
B.Sc (Hons) MLT
BMC & BCMT’s Bannu
INTRODUCTION TO MYCOLOGY

2. INTRODUCTION
Fungi are a diverse group of parasitic eukaryotic
organisms
Kingdom: Mycota
Of 100,000 fungal species only 100 have pathogenic
potential for humans, only a few account for clinically
important infections
Mycoses : Human Fungal Diseases
Fungal spores may be important as human allergenic
agents

3. Mycology: Study of fungi
Mycoses: fungal infections
Mytoxicosis: intoxication of fungi
MYCOSES
CUTANEOUS: limited to the dermis
SUBCUTANEOUS : when infection penetrates
significantly beneath the skin
SYSTEMIC : when the infection is deep within the body or
disseminated to internal organs

4. Difference between fungi, bacteria and viruses
Features Viruses Bacteria Fungi
Size 0.02-0.3 µ 0.3-2µ 3-10µ may be large i-e
mashroom
Cell Type Acellular Prokaryote Eukaryote
DNA/ RNA Either Both 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 None Peptidoglycan Chitin, Glucan

5. Structure of fungi
 The main body of most fungi is made up of fine, branching, usually colourless threads
called hyphae. Each fungus will have vast numbers of these hyphae, all intertwining to
make up a tangled web called the mycelium.The mycelium is generally too fine to be seen
by the naked eye, except where the hyphae are very closely packed together.
 Fruiting bodies (such as mushrooms) are made up of thick collections of hyphae. They vary in size from
small and insignificant, to large eye-catching structures.

7. Structural components of fungi
 Thallus
 Vegetative body of a fungus
 Septum
 cell wall division between hyphae of a fungus
 Hyphae
 a long, branching, filamentous structure of a fungus that is the main mode of vegetative growth
 Mycelium
 the vegetative part of any fungus, consisting of a mass of branching, threadlike hyphae, often underground
 Ergosterol
 the functional equivalent of cholesterol found in cell membranes of fungi.
 Glucan
 any polysaccharide that is a polymer of glucose
 Chitin
 a complex polysaccharide, a polymer of N-acetylglucosamine, found in the exoskeletons of arthropods and in the
cell walls of fungi; thought to be responsible for some forms of asthma in humans

8. Cell Wall and Membrane
Composed mainly of chitin (Chitin is a long-chain polymer of an
N-acetylglucosamine, a derivative of glucose,) rather than
peptidoglycan (bacteria)-so unaffected by antibiotics
Chitin: consists of a polymer of N-acetylglucosamine
Fungal Membrane contains ergosterol rather than cholesterol
found in mammalian cells, use in antifungal agents such as
amphotericin which binds to ergosterol⇒pores that disrupts
membrane function ⇒cell death

9. HABITAT
All fungi are heterotrophs ( their require some form of
organic carbon for growth)
They depend on transport of soluble nutrients across
their cell membrane
To do this they secrete degradative enzymes ( proteases
etc) into their immediate environment, therefore they
live on dead organic material
So Natural Habitat : is soil or water containing decaying
organic matter

10. MODES OF FUNGAL GROWTH
FILAMENTOUS
MOLDS
UNICELLULAR
YEASTS
However there are some dimorphic fungi ( they switch between these
Two forms depending on their environment)

11. Filamentous (mold-like) Fungi
Thallus (vegetitive body) –mass
of threads with many branches
resembling cotton ball
Mass: mycelium
Threads: hyphae, tubular cells
that in some fungi are divided
into segments –septate whereas
in other fungi the hyphae are
uninterrupted by crosswalls-
nonseptate
Grow by branching and tip
elongation

12. YEAST like FUNGI
These fungi exist as populations
of single , unconnected ,
spheroid cells, not unlike many
bacteria, although they are
sometimes 10 times larger than a
typical bacterial cell
Yeasts reproduce by budding
Some fungal species particularly
those that cause systemic
infection exist as dimorphic fungi

13. REPRODUCTION
Fungi can reproduce asexually by fragmentation, budding, or
producing spores, or sexually with homothallic or
heterothallic mycelia.

14. Reproductive components of fungal cell
spore
a reproductive particle, usually a single cell, released by a fungus.
Gametangium
an organ or cell in which gametes are produced that is found in fungi
Homothallic
male and female reproductive structures are present in the same plant or fungal mycelium
Karyogamy
the fusion of two nuclei within a cell
Plasmogamy
stage of sexual reproduction joining the cytoplasm of two parent mycelia without the fusion
of nuclei
Sporangium
a case, capsule, or container in which spores are produced by an organism

16. Asexual Reproduction
Fungi reproduce asexually by fragmentation, budding, or producing spores.
Fragments of hyphae can grow new colonies.
Mycelial fragmentation occurs when a fungal mycelium separates into pieces
with each component growing into a separate mycelium.
Somatic cells in yeast form buds. During budding (a type of cytokinesis), a
bulge forms on the side of the cell, the nucleus divides mitotically, and the bud
ultimately detaches itself from the mother cell.

17. ASEXUAL SPORULATION
Colour of a particular fungus seen on bread, culture plate is due to the
Conidia, easly airborne and disseminated

18. Sexual Reproduction
When both mating types are present in the same mycelium,
it is called homothallic, or self-fertile. Heterothallic mycelia
require two different, but compatible, mycelia to reproduce
sexually.

19. SEXUAL SPORULATION
Relatively rare compared to asexual sporulation, and spore shape often
Used as a method of identification

20. Generalised life cycle of fungi
SexualSexual
AsexualAsexual

21. Laboratory Identification
Standard media –Sabouraud`s agar, potato dextrose
agar, low ph 5.0 , inhibits bacterial growth but allows
fungal colonies to form
Cultures can be started from spores or hyphae fragments
Specimens: blood, pus, CSF, sputum, tissue biopsies,
skin scrapings , nail clippings
Identification by the morphology of conidia structures
and carbonhydrate assimiliation tests

22. Laboratory Diagnosis Of Fungal
Infection
Specimens
Depends on site of infection
Systemic: -Blood culture( really only useful for yeast-
low sensitivity) or
- antigen testing e.g.crytococcal
and histoplamsosis antigen
Pneumonia: Bronchoscopy washings or brushings
for staining and fungal culture or bronchial biopsy

23. laboratory diagnosis of fungal
infections
Meningitis: Cerebrospinal fluid for methylene blue
staining and indian ink and crytococcal antigen and fungal
culture
If Skin infection require skin scrapings
If nail infection require nail clippings
Galactomannan antigen testing for aspergillus infection

24. Laboratory Diagnosis Fungal Infections
Types of tests carried out
Fungal Staining – methylene blue staining or wet
prep using KOH to dissolve tissue material
Fungal culture on media that encourages fungal
growth e.g. PDA
Antigen Testing i.e. to test for antigen present in the
wall of fungus
PCR: but not used on a routine basis on samples