Download Introduction to Mycology.

Introduction to Mycology.
 Over the course of time, more than 100,000
species of fungi have been recognized and
described. However, fewer than 500 of
these species have been associated with
human disease. The remainders are only
able to produce disease in hosts that are
debilitated or immunocompromised.
 What is mycology?
 Mycology is the study of fungi. The
disease caused by fungi is called
MYCOSES.
 What are fungi?
 Eukaryotic, spore-bearing, heterotrophic
organisms that produce extracellular
enzymes and absorb their nutrition.
General information's about FUNGI:
 Fungi are not plants or animals, they form a
separate group of higher organisms, distinct
from both plants and animals, which differ from
other groups of organisms in several major
respects:
First:
 Fungal cells are encased within a rigid cell wall,
mostly composed of chitin and glucan. These
features contrast with animals, which have no
cell walls, and plants, which have cellulose as
the major cell wall component.
 Second:
 Fungi are heterotrophic. This means that they
are lacking in chlorophyll and cannot make their
organic food as plants can, through
photosynthesis. Fungi live embedded in a food
source or medium, and obtain their nourishment
by secreting enzymes for external digestion and
by absorbing the nutrients that are released from
the medium. Some live on humans e.g. the
cause ringworm infections. Some live on insects,
or plants.
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 Third:
 Fungi are simpler in structure than plants or
animals. There is no division of cells into organs
or tissues.
The basic structure of the fungi:
 The basic structural unit of fungi is either a chain of
tubular, filament-like cells, termed a hypha or hyphae
(plural) or an independent single cell.
 The living body of a fungus is called a mycelium which
is made up of a branching network of filaments known
as hyphae.
 Fungal cell differentiation is no less complicated than
is found in plants or animals, but it is different. Many
fungal pathogens of humans and animals change their
growth form during the process of tissue invasion.
These dimorphic pathogens usually change from a
multicellular hyphal form in the natural environment to
a budding, single-celled form in tissue.
 In most multicellular fungi the vegetative
stage consists of a mass of branching
hyphae, termed a mycelium. Each
individual hypha has a rigid cell wall
 They are filamentous, gram positive and
bear fruiting bodies called spores.
 Can exist as single cells or chains of
cells.
 History of taxonomy
 All organisms were classified to:
– Plants
– Animals
 Fungi were classified with plants:
– Immobility
 Cell wall
 By the Development of the electron microscope
in 1995s, Fundamental differences between the
bacteria and fungus were discovered:
 Although in many ways fungi resemble bacteria
(neither has chlorophyll), they are unlike bacteria
in:
 Composition of the cell walls.
 Reproducing through sporulation or spore formation.
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So it was classified again into 5 Kingdoms:
Bacteria.
Protista .
Animalia
Fungi
Plant
 Importance of the fungi:
 Fungi are abundant in the human environment,
and can found every where.
 Most of them lead a saprophytic life, living on
dead matter (e.g. Mushrooms).
 Fungal infections are assuming a greater
importance, why!!
 This because of their increasing incidence
among:
– Transplant patients
– Immunocompromised
- AIDS
In the last 20 years extraordinary changes in
fungal infection pattern!!
 New pathogens have emerged
 Increasing international travel
 use wrongly of antimicrobial agents
Helpful fungi: In every day life
 The common bread-mould is a fungus.
 Mushrooms (a vegetarian fungal protein)
 Saccharomyces cerevisiae is used to ferment
sugar to produce alcohol
 We also use fungi to produce flavourings and
vitamins.
 Fungi play an essential role in both the Nitrogen
and Carbon cycle by breaking down dead
organic material.
 We get some important drugs from fungi such as
the antibiotic (penicillin and cyclosporine).
Helpful fungi: In Research:
 Scientists use several fungi to investigate
basic functions that occur in all cells
because they are:
 Simple
 Easy to grow
 Some cancer research is done using fungi
Why studying medical mycology is important?
1. In humans, fungi cause skin infections such as
ringworm and athlete's foot.
2. They also cause several deadly diseases which
can be hard to treat.
3. Most patients with deadly fungal diseases do
not have a fully functional immune system.
– Leukaemia
– AIDS
– Drugs to suppress their immune system because of
organ transplantation.
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4- Antifungal drugs are often toxic.
5- There is a desperate need for new and
better anti-fungal agents.
Some basic terms:
 Fungi (fungus)
 Hyphae (hypha) = cellular thread
 Septate = hyphae with cross walls
 non-septate = hyphae without cross walls
 Mycelium = complex of hyphae
 The term mould is generally used to
describe a fungus which produces hyphae.
 The term yeast is generally used to
describe a fungus which reproduces by
budding.
Morphology:
 Filamentous (mould).
 Yeast
 Dimorphic
Reproduction
--Asexual reproduction
 Budding, fission
 Asexual spore - mitosis
 zoospores, sporangiospores.
 oospores, zygospores, chlamydospores
--Sexual reproduction
– sexual spore - meiosis
– ascospore, basidiospore
 Some fungi have no sexual reproduction
(Imperfect fungi).
1- Yeast
 Round, oval or elongated unicellular cells.
 3-15 µm
 Few capsulated
 Reproduction
– Sexual .
– Asexual : by budding (blastoconidia or
blastospores)
– May give arise to pseudohyphae
 Examples of pathogenic yeast:
 Candida albicans
 2- Filamentous fungi:
– Multicellular
– Form branching filamentous called hyphae
– Hyphae form mycelium
– Hyphae may be septate of aseptate
– Reproduction:
– Asexual: by Conidia and spore
– Sexual.
 Examples of pathogenic moulds
 Dermatophytes
 3- Dimorphic fungi:
 Dimorphism this term is used to describe
a fungus which occurs in two different
forms (temperature and place), for
example, some pathogenic fungi are
filamentous in culture and yeast-like in
infected tissues.
 37°C
yeast
 20 – 30° C
moulds.
 Examples:
– Paracoccidioides brasiliensis
 When fungal infections should be
considered?
 Prolong fever not responding to antibiotics.
 Neutropenia
 Diabetes with ketoacidosis
 Bone marrow and solid organs
transplantation
 HIV patients
 Travel or stay in endemic areas.
 Categories
True pathogens – 4 species (dimorphic)
 – Blastomyces dermatitidis
 – Coccidioides immitis
 – Histoplasma capsulatum
 – Paracoccidioides brasiliensis
Opportunistic fungi
 – Not cause diseases in healthy
individuals
 – Invasive medical procedures
 – Surgery, implants
 – Medical therapies
Preexisting condition
 –inherited defects, AIDS, severe burns, etc
Lifestyle factors
 –Poor diet, poor hygiene, IV drug abuse
Mycoses can be classified according to the
site of infection into:
1.
2.
3.
4.
Superficial
Subcutaneous
Deep (systemic).
Other Mycoses
General notes:
 Unlike bacteria colonies, fungal colonies
spread rapidly by the hyphae which
continue to form more and more new
colonies.
 Rate of growth, color, texture and form of
the colony is distinct for each species.
 Is it useful and harmful, some of them may
be harmful or may even be life-threatening
to humans (e.g. mycotic meningitis), but
never cause wide-spread or endemic
disease.
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Cause complex signs
Resistant to antimicrobial agents
Found almost everywhere (spores, fungi)
Inhalation, trauma, or ingestion
Spore formation:
 Most fungi reproduce by forming spores.
When the spores germinate, they send out
tube-like projections, called germ tubes,
which lead to the formation of branching
tube-like structures, called hyphae. . The
spores may be produced in many different
ways and their size, shape, colour, and
manner of production are of value in
identifying individual species.
The principle types of spore are as follow:
1-Chlamydospore: a rest stage, forms when a cell
swells up and develops a thick resistant wall.
2- Arthrospore: a spore forms by septation
followed by fragmentation of hyphae.
3- Blastospore: a single vegetative cell of yeast
which is produced by budding.
4- Conidium: a spore produced externally on
a specialized hypae called conidiophore,
the conidium (plural conidia) becomes
detached when it mature.
5- Sporangiospore: a spore produced within
a swollen spherical cell (sporangium) at
the end of specialized hyphae called a
sporangiophore.