Mycology
Terminology
• Mykos: Fungus
• Mycoses: A disease caused by
a fungus
• Mycology: Study of fungi
Characteristics of fungi
• Widely distributed in nature (air, water, soil, decaying
organic debris)
• ~400,000 types (Diverse habitats)
• Eukaryotic, highly developed cellular structure
• Facultatively anaerobic/strict aerobic
• Chemotropic, nutrition: by absorption
• Nonphotosynthetic (distinguishes them from plants and
algae)
• Some are aquatic – mainly fresh water, a few marine
• Most are terrestrial – soil or on dead plant material
Characteristics of fungi
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Crucial role in mineralisation of organic carbon
Many are parasites of terrestrial plants
A few are parasitic on animals including humans
Generally less important than bacterial or viral infections
Unicellular (yeasts) or filamentous
(molds).
Rigid cell wall, some are capsulated.
Spore bearing stages in the life cycle
Usually reproduce by sexual and asexual means
Insensitive to antibacterial antibiotics
they have a diploid number of chromosomes
Characteristics of fungi
• Fungi can be beneficial or harmful
• They are especially harmful to people who are
compromised (opportunistic) or are in the hospital for
other infections (nosocomial)
• Fungi are important in the food chain because they
decompose dead plant matter and recycle nutrients
Characteristics of fungi
• Most fungi prefer a moist environment with a
relative humidity of 70% or more.
• Various species can grow at a temperature ranging
from -6 to 50°C with optimaltemperature of 20 to
35°C.
• Most fungi grow well at an acidic pH of 5.0 or
lower and thus they grow well on fruits and many
vegetables that are acidic in nature.
Structure and functions
• A mass of hyphal elements is termed
the mycelium (synonymous with mold).
• Aerial hyphae often produce asexual
reproduction propagules
termed conidia(synonymous with spores).
• Relatively large and complex conidia are
termed macroconidia while the smaller and
more simple conidia are termed microconidia.
• When the conidia are enclosed in a sac (the
sporangium), they are called endospores.
• The presence/absence of conidia and their size,
shape and location are major features used in the
laboratory to identify the species of fungus in
clinical specimens.
Major polysaccharides of
fungal cell wall
POLYMER
Chitin
Chitosan
Cellulose
-Glucan
-Glucan
Mannan
MONOMER
N-acetyl glucosamine
D-Glucosamine
D-Glucose
D-Glucose
D-Glucose
D-Mannose
• The type and amount of the polysaccharide vary
from one fungal species to other.
Differences between Fungi and
Bacteria
Metabolism
• For medical purposes the important aspects of
fungal metabolism are the synthesis of: chitin a
polymer of N-acetyl glucosamine, rather than
peptidoglycan_ a characterestic component of
bacterial cell wall.
• Fungi are there for unaffected by antibiotics (for
example penicillin) that inhibit peptidoglycan
synthesis
ergosterol
for incorporation into the plasma membrane.
This makes the plasma membrane sensitive to
those antimicrobial agents which either
- block the synthesis of ergosterol or
- prevent its incorporation into the membrane
or - bind to it, e.g. amphotericin B
• The synthesis of toxins such as:
a. Ergot alkaloids- these are produced by
Claviceps purpurea
b. Aflatoxins - these are carcinogens produced by
Aspergillus flavus when growing on grain.
When these grains are eaten by humans or when
they are fed to dairy cattle and they get into the
milk supply, they affect humans.
• The synthesis of proteins on ribosomes that are
different from those found in bacteria.
This makes the fungi immune to those
antimicrobial agents that are directed against the
bacterial ribosome, e.g., chloramphenicol.
Penicillium (Source of penicillin)
In Penicillium, phialides may be produced singly, in groups
or from branched metulae, giving a brush-like appearance
known as a penicillus
Morphological structures and types of
conidiophore branching in Penicillium. a. simple;
b. one-stage branched; c. two-stage branched; d.
three-stage branched
Penicillin kills bacteria by interfering with their
ability to synthesize cell wall.
Penicillin quickly became a
primary treatment for pneumonia,
diphtheria, syphilis, gonorrhea,
scarlet fever, and many other
infections. For “the discovery of
penicillin and its curative effect in
various infectious diseases”
Fleming, Chain, and Florey
received the Noble Prize for
Medicine in 1945.
Fungi as human pathogens
• Among the 50 000-250 000 species of fungi
that have been described, fewer than 200
have been associated with human disease
Diseases Caused by Fungi
• Diseases caused by fungal cells are called
(Mycosis).
• Diseases caused by fungal spores are called
(Allergy), either respiratory or skin allergy.
• Diseases caused by fungal byproducts,
mycotoxins, are called (Mycotoxicosis).
Fungi- Morphological
Classification
• Yeast: Unicellular (grows at 37 C)
• Mould: Multicellular (grows
at 25 C)
• Dimorphic: growing in
mould or yeast form
Yeast Budding Mother and Daughter
Cells
Molds are made of hyphae
(cells joined in thread-like strands)
Classification of Hyphae
BASED ON:
A. Existence of septa
Septate
Nonseptate
B. Shape and Morphology
Racquet
Spiral
Nodular
Root-like (rhizoid)
Pectinate
Chandler
Septa
- Regular cross-walls formed in hyphae.
- Hyphae with septa are septate.
- Those lacking septa except to delimit
reproductive structures and aging
hyphae are called aseptate or
coenocytic.
Mono and Di Karyotic
• – Monokaryotic:
single nucleus
each compartment has a
• – Dikaryotic: two distinct nuclei within each
hyphae compartment
Hetero and Homo Karyotic
– Heterokaryotic: dikaryotic or multinucleate
hypha has nuclei from genetically distinct
individuals
– Homokaryotic: hyphae whose nuclei are
genetically similar to one another
DIMORPHIC
• Capable of growing in mould or
yeast form under different
environmental conditions
(temperature, CO2, nutrients)
• Some fungal species, specially
those that cause systemic
mycoses,are dimorphic.
Fungal reproduction
• Anamorph= asexual stage
– Mitospore=spore formed via asexual
reproduction (mitosis), commonly called a
conidium or sporangiospore
• Teleomorph= sexual stage
– Meiospore=spore formed via sexual
reproduction (e.g., resulting from meiosis),
type of spore varies by phylum
Identification of Fungal Species
• The presence/absence of conidia and
their size, shape and location are major
features used in the laboratory to
identify the species of fungus in
clinical specimens.
Asexual fruiting structure of Rhizopus
species
• Asexual fruiting
structure of Rhizopus
species, illustrating
sporangium,
sporangiophore,
sporangiospores,
coenocytic hyphae and
rhizoids.
Asexual fruiting structure of Aspergillus species
• Asexual fruiting
structure of
Aspergillus species,
illustrating septate
hyphae,
conidiophore, vesicle,
phialides and
conidiospores
Asexual fruiting structure of Penicillium species
Asexual fruiting structure of Penicillium species,
illustrating septate hyphae, conidiophore and
conidiospores
Asexual Reproduction by
Budding in Yeast
The cell grows and divides into two daughter cells that each
contain the information and machinery necessary to repeat the
process.
Budding Yeast
ASEXUAL SPORES
1. Arthrospore
2. Blastospore (Budding in Yeast)
3. Chlamydospore
4. Macroconidium (Relatively large)
5. Microconidium (Relatively small)
6. Sporangiospore (Sporangia)
Phylum Zygomycota
e.g. Rhizopus sp. (Black bread Mold)
Zygomycosis
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Caused by:
Rhizopus sp.
Absidia sp.
Mucor sp.
Candidiasis
caused by Candida albicans
• Candidiasis or yeast infection
• Can be thrush (oral) or vulvovaginal
candidiasis
• Found in newborns, AIDS patients, and in
people who have just completed antibiotic
• Is also one cause of diaper rash!
Yeast Infections
Phylum Deuteromycota
Spores produced by the
species in this category are not
quite so easy to categorize by
shape.
Penicillium
Organisms from this phylum are
both beneficial (penicillin from
Penicillium, soy sauce and citric
acid from Aspergillus) and very
harmful (Aspergillus can be toxic
if inhaled).
Aspergillus sp.
Aspergillosis
• Aspergillus causes aspergillosis
Penicillium sp.
Classification of Fungal Infections
In general, humans have a high level of innate immunity
to fungi and most of the infections they cause are mild
and self-limiting.
This resistance is due to:
• Fatty acid content of the skin
• mucosal surfaces
• body fluids
• Epithelial turnover
• Normal flora
• Transferrin
Transferrin is a blood plasma protein binds iron, thus
creating an environment low in free iron, where few
microbes are able to survive – associated with the innate
immune system
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Cilia of respiratory tract
Fungal diseases
• Any fungal infection is a mycosis
• These are long lasting and hard to treat
• Classify these into 4 groups according to degree of
tissue involvement and mode of entry into host:
1- Systemic (endemic)
2- subcutaneous
3- Cutaneous
4- opportunistic
Systemic
• Infections deep in the body
• Can affect a number of tissues and/or organs
• Usually caused by inhalation of spores from fungi
that live in the soil
• Infections that originate primarily in the lung and
may spread to many organ systems.
• Include histoplasmosis and coccidioidomycosis
Systemic mycoses
• (1) Histoplasma
capsulatum (causing
histoplasmosis)
• Dimorphic with mold to
yeast transition when
infecting susceptible
species.
• Yeast cells are relatively
small.
• Saprobic phase shows
tuberculate
macroconidia
Saprobic Phase
Parasitic Phase
Systemic mycoses
• (2) Blastomyces
dermatitidis (causing
blastomycosis)
• Dimorphic with mold to
yeast transition when
infecting susceptible
species.
• Yeast cells are medium
size with thick walls.
Saprobic Phase
Parasitic Phase
Systemic mycoses
(3) Paracoccidioides
brasiliensis (causing
paracoccidiodomycosis)
Dimorphic with mold to
yeast transition when Saprobic Phase
infecting susceptible
species.
Yeast cells have multiple
buds
Parasitic Phase
Systemic mycoses
(4) Coccidioides
immitis (causing
coccidioidomycosis)
Dimorphic with mold
to spherule transition
when infecting
susceptible species.
Spherules are
multinucleate.
Saprobic Phase
Parasitic Phase
Systemic mycoses
(5) Cryptococcus
neoformans (causing a
severe form of
meningitis in people
with HIV infection and
AIDS).
Monomorphic with yeast
phase only.
Saprobic Phase
This is the only pathogenic yeast with a
capsule.
The capsule is extremely large.
Parasitic Phase
subcutaneous
• Infections beneath the skin
• Infections involving the dermis, subcutaneous tissues,
muscle or bone
• It Caused by saprophytic fungi that live in soil or on
vegetation
• Often enter through puncture wound
• Example is sporotrichosis
Subcutaneous mycoses
Disease
Etiological Agent
Symptoms
Identification of Organism
Budding yeast in tissue
exudate that converts to mold
with "rosette pattern" of
conidiation on culture at
25oC.
Sporotrichosis
Sporothrix schenckii
Nodules and ulcers along
lymphatics at site of
inoculation
Chromoblastomycosis
Fonsecaea pedrosoi
Fonsecaea compacta
Wangiella dermatitidis
Warty nodules that
progress to "cauliflowerlike" appearance at site of
inoculation
Copper-colored spherical
yeast called "Medlar bodies"
in tissue
Mycetoma
Pseudallescheria boydii
Madurella grisea
Madurella mycetomatis
Draining sinus tracts at
site of inoculation
White, brown, yellow or black
granules in exudate that are
fungal colonies
Cutaneous
• Fungi that infect only hair, epidermis, and nails are
dermatophytes or cutaneous mycoses
• These produce an enzyme that degrades keratin
(keratinase)
• Can spread by contact (human/human,
animal/human)
• All of the dermatophytic diseases are caused by
members of three genera, Microsporum, Trichophyton
and Epidermophyton, which comprise 41 species.
- There is some specificity, however.
Whereas all three organisms attack the skin,
Microsporum does not infect nails, and
Epidermophyton does not infect hair.
- They do not invade underlying, non
keratinized tissues.
Tinea capitis of the scalp caused
by Microsporum gypseum
Cutaneous mycoses
Disease
Etiological Agent
Symptoms
Indentification of organism
Tinea capitis
Microsporum sp. Trichophyton
sp. Epidermophyton sp.
ringworm lesion of
scalp
presence/absence and shape of micro- and
macroconidia in scrapings from lesion
Tinea corporis
Microsporum sp. Trichophyton
sp. Epidermophyton sp
ringworm lesion of
trunk, arms, legs
presence/absence and shape of micro- and
macroconidia in scrapings from lesion
Tinea manus
Microsporum sp. Trichophyton
sp. Epidermophyton sp
ringworm lesion of
hand
presence/absence and shape of micro- and
macroconidia in scrapings from lesion
Tinea cruris
"jock itch"
Microsporum sp. Trichophyton
sp. Epidermophyton sp
ringworm lesion of
groin
presence/absence and shape of micro- and
macroconidia in scrapings from lesion
Tinea
pedis"athlete's
foot"
Microsporum sp. Trichophyton
sp. Epidermophyton sp
ringworm lesion of
foot
presence/absence and shape of micro- and
macroconidia in scrapings from lesion
Tinea unguium
Microsporum sp. Trichophyton
sp. Epidermophyton sp
infection of nails
presence/absence and shape of micro- and
macroconidia in scrapings from lesion
Ectothrix
Microsporum sp. Trichophyton
sp. Epidermophyton sp
infection of hair shaft
surface
mycelium and spores on hair shaft
Endothrix
Microsporum sp. Trichophyton
sp. Epidermophyton sp
infection of hair shaft
interior
mycelium and spores in hair shaft
Opportunistic mycoses
• Harmless in normal habitat but can become
pathogenic if given the ‘opportunity’
• Infections in patients with immune deficiencies who
would otherwise not be infected
• Opportunistic mycoses are seen in those people with
impaired host defenses such as occurs in:
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AIDS
Alteration of normal flora
Diabetes mellitus
Immunosuppressive therapy
Malignancy
Opportunistic mycoses
Disease
Candidiases
Aspergillosis
Zygomycosis
Etiological Agent
Symptoms
Identification of organism
Candida albicans
Creamy growth
on various areas
of body
Budding yeast, septate hyphae,
pseudohyphae in tissue. Germ
tubeformation in serum
Aspergillus fumigatus
"Fungus ball" in
tissue
Morphology of asexual fruiting
structure
Rhizopus sp. Absidia
sp. Mucor sp.
Various
Morphology of asexual fruiting
structure and mycelium
LABORATORY DIAGNOSIS OF
MYCOSES
• Direct microscopic examination
Gram, potassium hydroxide (KOH),
calcofluor white, India ink
• Culture
Sabouraud dextrose agar
Mycobiotic agar
• Serology
LABORATORY DIAGNOSIS
OF MYCOSES
Visualization of fungi in human tissue preparations
1. Treatment with 10% potassium hydroxide
2. Positive stain with:
a. Lactophenol cotton blue
b. Grocott silver stain
c. Hematoxylin
d. Eosin
3. Negative stain with India ink
Fluorescence of fungi under ultraviolet light
Stained Fungi
Gram Stain of tissue infected with Cryptococcus neoformans
Hematoxylin-eosin-stained
section of cerebral cortex
demonstrating septate hyphal
elements.
India Ink of Cerebro-Spinal Fluid (CSF)
with Cryptococcus neoformans
Clinical Techniques in Mycology
Culture of fungi on
1. Sabouraud's agar (favors fungal growth because of low pH)
2. Mycosel agar (selective for pathogenic fungi because of chloramphenicol
and cycloheximide in medium)
Visualization of cultured fungi (25oC and 37oC)
1. Colony morphology
2. Cellular morphology
a. Hyphal morphology
(1) Aseptate or coenocytic
(2) Septate
(a) Regular connection
(b) Clamp connection