Fungi are eukaryotic organisms that exist as single cells (yeasts) or filamentous cells (hyphae) and are relatively nonpathogenic to humans. They reproduce through sexual and asexual spores, and their classification depends on cell morphology and spore formation. Fungal diseases include allergies, mycotoxicoses, and infections, with diagnosis involving clinical examination and laboratory testing, while control measures are primarily antifungal treatments.

1. Lecturer: Mr. Osman H. Ali

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Fungi as Infectious Agents
• Fungi are non-motile eukaryote, widely
distributed in air, dust, fomites and normal flora.
• They have a cell wall composed of complex
carbohydrates such as chitin with glucans and
mannose-proteins.
• Ergosterol is the dominant fungal membrane
sterol.
• Grow as single cells (yeasts) or multi-septate,
branching filamentous cells (hyphae).
• Fungi are relatively nonpathogenic and humans
are relatively resistant.

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5. Structure
1. Hyphae : filamentous cells
of molds
•
•
•
Septae
Nonseptate or aseptate
Dematiaceous (dark
or hyaline
colored)
(colorless).
Mycelia
•
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6. 2. Yeasts
• These are single-celled fungi,
generally round to oval shaped.
• They reproduce by budding
(blastoconidia).
3. Pseudohyphae :
• Hyphae with sausagelike
constrictions at septations.
• Formed by some yeasts when
they elongate but remain attached
to each other (Candida albicans). 6

7. 4. Thermally dimorphic fungi:
• These are fungi exist in the
from a yeast or yeast-like in
human and filamentous form
in environment (temperature,
nutrient)
• They include the major
pathogens: Blastomyces,
Coccidioides,
Histoplasma,
Sporothrix and
Paracoccidioides.
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9. Fungal reproduction
• They reproduce by sexual or asexual
spores.
• Spores morphology may be used in
identification.
❑Asexual reproduction
• Conidia are asexual spores of filamentous
fungi (molds)
Blastoconidia are the new yeast ‘‘buds’’
•
• Arthroconidia are conidia formed by
laying down joints in hyphae followed by
fragmentation of the hyphal strand
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10. • Chlamydoconidium is a thick-
walled
rounding
spore formed by
and enlargement
within a hyphal segment
• Sporangiospore formed within a
sporangium, or sac, at the end
of an aerial hypha called a
sporangiophore.
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11. ❑Sexual reproduction.
mating types come
• In this process, opposite
together
and fuse.
• A visible fruiting body often
results and it is the location of
the haploid spores.
• The most recognized fruiting
body from which spores are
produced is the mushroom.
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13. Classification
 Depending on cell morphology
1. Yeasts
2. Yeast like fungi
3. Molds
4. Dimorphic fungi

14.  Unicellular fungi which
reproduce by budding
 On culture - produce smooth,
creamy colonies
e. g Cryptococcus neoformans
(capsulated yeast)

15. 2. Yeast like fungi
 Grow partly as yeasts and partly as elongated
cells resembling hyphae which are called
pseudohyphae.
e.g. Candida albicans

16. 3. Molds/ Filamentous fungi
 Form true mycelia &
reproduce by formation of
different types of spores.
 Vegetative/ aerial
hyphae
e.g. Rhizopus, mucor

17. 4. Dimorphic fungi
 Occur in 2 forms
Molds (Filaments) – 25 0 C (soil)
Yeasts – 370C (in host tissue)
Most fungi causing systemic infections are
dimorphic:
 Histoplasma capsulatum
 Blastomyces dermatidis
 Paracoccidioides brasiliensis
 Coccidioides immitis
 Penicillium marneffei
 Sporothrix schenkii

18. Systematic classification
 Based on sexual spore formation: 4 classes
1. Zygomycetes
2. Ascomycetes
3. Basidiomycetes
4. Deuteromycetes (fungi imperfectii)
reproduce sexually

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Fungal nutrition
• Fungi usually grow better in an environment with a
pH5.
• Almost all molds are aerobic. Most yeasts are
facultative anaerobes.
• Most fungi are more resistant to osmotic pressure than
bacteria.
• Fungi can grow on substances with a very low
moisture content, generally too low to support the
growth of bacteria.

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• Fungi require preformed organic compounds derived
from their environment.
1. Saprobes: live on dead organic material. Some are
opportunistic.
2. Commensal colonizers: generally live in harmony on
humans, deriving their nutrition from compounds on
body surfaces. Some are opportunistic.
3. Pathogens: infect the healthy but cause more severe
disease in the compromised hosts. The damage to living
cells provides nutrition. Most of these are also
environmental saprobes.

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Fungal disease
1. Fungal allergies : due to spores and volatile fungal
metabolites (sick building syndrome and farmer’s
lung).
2. Mycotoxicoses : ingestion of fungal-contaminated
bread or aflatoxin
foods (e.g., ergot-contaminated
contaminated peanuts).
3. Fungal infections (mycoses)
– True pathogens: Systemic, Subcutaneous, Cutaneous, and
Superficial Mycoses
– Opportunistic mycoses: Increasing prevalence due to
increased use of antibiotics, corticosteroids, and cytotoxic
drugs.

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Pathogenesis of the Fungi
• Portal of entry
– Cutaneous and superficial – contamination of skin
surface
– Subcutaneous - inoculated skin; trauma
– Systemic mycoses – respiratory portal; inhaled
spores
• Virulence factors – thermal dimorphism, toxin
production, capsules and adhesion factors,
hydrolytic enzymes, inflammatory stimulants

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Diagnosis of Mycotic Infections
1. Clinical manifestations
2. Microscopic examination
3. Histologic staining
4. Serologic testing
5. Cultures for fungi
6. Fungal antigen detection
7. DNA probes

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Control of Mycotic Infections
• Immunization is not usually effective.
• Control involves intravenous, oral and
topical antifungal.
• In some cases surgical removal of damaged
tissues
• Prevention limited to masks and protective
clothing to reduce contact with spores

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