A very short introduction to mycology for medical students just starting clinical training.

1. INTRODUCTORY
MYCOLOGY
OLOWOOKERE A.K
AL-HIKMAH UNIVERSITY

2. What is a Fungus ?
MYKES- MUSHROOM
 Eukaryotic Protista – a true nucleus with paired chromosomes
 Do not contain chlorophyll
 Have cell walls containing chitin, mannan and polysacs
 Produce filamentous structures
 Produce spores
 Cytoplasm containing ergosterol. Stores food as glycogen (like mammals)
 Could be unicellular or monocellular
 Reproduction could be Sexually, Asexually or both
 Species of Fungi
 • 100,000 – 200,000 species
 • About 300 pathogenic for man
MYCOSES; diseases caused by fungus

3. FUNGUS EVERYWHERE
How the fungus are nourished
 All are chemo heterotrophs
 Absorption of nutrients: powerful
 Exoenzyme
 Grow at lower pH-5 than bacteria
 Grow in high salt and sugar
 Metabolize complex CH2O like lignin in
 wood-wood rot

4. Features of Fungi and how it impacts our life
 The fungi are a ubiquitous and diverse organisms, that degrade organic matter.
 Fungi have heterotrophic life; they could survive in nature as:
 Saprophytic: live on dead or decaying matter
 Symbiotic: live together and have mutual advantage
 Commensal: one benefits and other neither benefits nor harmed.
 Parasitic: live on or within a host, they get benefit and harm the other.
 Fungi mainly infect immunocompromised or hospitalized patients with serious
underlying diseases.
 The incidence of specific invasive mycoses continues to increase with time
 The list of opportunistic fungal pathogens likewise increases each year “It seems
there are no non-pathogenic fungi anymore ! “
 This increase in fungal infections can be attributed to the ever-growing number
immunocompromised patients.

5. Characteristics of fungi
 A. eukaryotic, non- vascular organisms
 B. reproduce by means of spores, usually wind-disseminated
 C. both sexual (meiotic) and asexual (mitotic) spores may be produced,
depending on the species and conditions
 D. typically not motile, although a few (e.g. Chytrids) have a motile phase.
 E. like plants, fungi have an alternation of generations

6. Fungal Pathogenicity (virulence factors):
 Ability to adhere to host cells by way of cell wall glycoproteins
 Production capsules allowing them to resist phagocytosis
 Production of a cytokine called GM-CSF by Candida albicans that suppress the
production of complement.
 Ability to acquire iron from red blood cells as in Candida albicans
 Ability to damage host by secreting enzymes such as keratinase, elastase,
collagenase
 Ability to resist killing by phagocytes as in dimorphic fungi
 Ability to secrete mycotoxins
 Having a unique enzymatic capacity
 Exhibiting thermal dimorphism
 Ability to block the cell-mediated immune defences of the host.
 Surface hydrophobicity

7. Host defence factors:
 Physical barriers, such as skin and mucus membranes
 The fatty acid content of the skin
 The pH of the skin, mucosal surfaces and body fluids
 Epithelial cell turnover
 Normal flora
 Chemical barriers, such as secretions, serum factors
 Most fungi are mesophilic and cannot grow at 37oC.
 Natural Effector Cells (polymorphonuclear leucocytes) and the Professional
Phagocytes (monocytes and Macrophages)

8. Factors predisposing to fungal infection
 Prolonged antibiotic therapy
 Underlying disease (HIV infection, cancer, diabetes,)
 Age
 Surgical procedures
 Immunosuppressive drugs
 Irradiation therapy
 Indwelling catheters
 Obesity
 Drug addiction
 Transplants
 Occupation

9. classification
 They are classified by several methods:
 1- Morphological classification
 2- Clinical classification
 3- sexual reproduction classification

10. Depending on morphology
 Moulds (Molds): Filamentous fungi, form true mycelia, vegetative hyphae Eg:
Aspergillus sps, Trichophyton rubrum
 Yeasts: unicellular fungi that reproduce by budding Eg: Cryptococcus neoformans,
Saccharomyces cerviciae
 Yeast like: Grow partly as yeasts and partly as elongated cells resembling hyphae
which are called pseudo hyphae. e.g. Candida albicans
 Dimorphic: Occurs in two morphological forms at two different environmental
conditions. They exist as yeasts in tissue and in vitro at 37oC and as moulds in their
natural habitat and in vitro at room temperature. Can also occur with changes in
CO2. Most fungi causing systemic infections are dimorphic Eg: Histoplasma
capsulatum, Blastomyces dermatidis, Paracoccidiodes brasiliensis, Coccidioides
immitis

11. Depending on mode of reproduction
 Zygomycetes: which produce through production of zygospores.
 Ascomycetes: which produce endogenous spores called ascospores in cells called
asci.
 Basidiomycetes: which produce exogenous spores called basidiospores in cells
called basidia.
 Deuteromycetes (Fungi imperfecti): fungi that are not known to produce any
sexual spores. This is a heterogeneous group of fungi where no sexual reproduction
has yet been demonstrated.

12. Reproduction in fungi
 • Sexual - formation of Zygospore, ascospores or basidiospores
 • Asexual reproduction – budding or fission
 • Asexual spores are formed on or in specialized structures.
 • Vary in size, shape & colour but these characteristics are constant for a
species.

13. Clinical classification of
mycoses Remember; Mycoses is referred to as disease caused by
fungus
 Cutaneous- Skin, hair and nails. Rarely invade deeper
tissue. Dermatophytes
 Subcutaneous - Confined to subcutaneous tissue and
rarely spread systemically. The causative agents are soil
organisms introduced into the extremities by trauma
 Systemic - Involve skin and deep viscera. May become
widely disseminated predilection for specific organs
 Opportunistic -Ubiquitous saprophytes and
occasional pathogens that invade the tissues of those
patients who have:
• Predisposing diseases: Diabetes, cancer,
leukemia, etc.
• Predisposing conditions:
Agammaglobulinemia, steroid or antibiotic therapy.
EXAMPLES PLS

14. Harmful effect
 1. Destruction of food, lumber, paper, and cloth.
 2. Animal and human diseases, including allergies.
 3. Toxins produced by poisonous mushrooms and within food (Mycetism and
Mycotoxicosis).
 4. Plant diseases.
 5. Spoilage of agriculture produce such as vegetables and cereals in the godown.
 6. Damage the products such as magnetic tapes and disks, glass lenses, marble
statues, bones and wax.

15. Beneficial effect
 1. Decomposition - nutrient and carbon recycling.
 2. Biosynthetic factories. The fermentation property is used for the industrial production
of alcohols, fats, citric, oxalic and gluconic acids.
 3. Important sources of antibiotics, such as Penicillin.
 4. Model organisms for biochemical and genetic studies. Eg: Neurospora crassa
 5. Saccharomyces cerviciae is extensively used in recombinant DNA technology, which
includes the Hepatitis B Vaccine.
 6. Some fungi are edible (mushrooms).
 7. Yeasts provide nutritional supplements such as vitamins and cofactors.
 8. Penicillium is used to flavour Roquefort and Camembert cheeses.
 9. Ergot produced by Claviceps purpurea contains medically important alkaloids that
help in inducing uterine contractions, controlling bleeding and treating migraine.
 10. Fungi (Leptolegnia caudate and Aphanomyces laevis) are used to trap mosquito
larvae in paddy fields and thus help in malaria control.

16. Laboratory diagnosis
Direct microscopic examination
 KOH mount
 Calcofluor white
 India ink
Culture
 SDA,PDA, Corn Starch, malt extract agar etc
 The tease mount
 Scotch tape preparation
 The microslide culture technique( slide culture)
Serology
 Most serological test for fungi measures antibody, newer tests are just being developed for
antigens and they includes Cryptococcosis, Histoplasmosis and Aspergillosis
Biopsy and histopathology
 For inflammatory reaction
DNA Probes
 Rapid (1-2 Hours). Species specific. Expensive