Mycology – Study of fungi

WHAT IS MYCOLOGY?

• Study of fungi and related organisms done by

scientists that are called mycologists.

• It is a very wide and diverse field of study.

• Fungi can be beneficial to humans or can harm

humans directly or indirectly.
 WHAT ARE FUNGI (SINGLE: FUNGUS)?
Fungi are:

• Eukaryotic (cells have nuclei enveloped in membrane).

• Heterotrophic (they can't make their own food).

• Osmotrophic (they absorb food, don't ingest food).

• Develop a diffuse, branched, tubular body (radiating hyphae

making up mycelia or colonies).

• Reproduce by means of spores (sexually and asexually

reproduced spores).

• Fungi vary from microscopic organisms to organisms that

produce large fruiting bodies.
http://www.medical-labs.net/fungi-hyphae-1522/
• Many fungi (mostly yeasts) exist as single cells;
reproduce quickly by budding or fission.
• Some fungal species exist either as hyphae or single
cells - dimorphic, e.g. fungi that cause diseases of
humans and other animals.
• Dimorphic fungi grow as hyphae outside their hosts, but
assume a yeast-like appearance inside the host.
FEEDING MODES OF FUNGI

 Saprobes (saprophytic fungi; Gr. sapros = rotten + bios =life).

Obtain their food by digesting dead organic matter.

 Parasites (Gr. parasitos = eating beside another).

Live as parasites on plants, animals and even other fungi.
Two types of parasites occur:

Facultative parasites
Can grow as parasites or as saprophytes. Also called facultative
saprobes – can be grown artificially on synthetic media.

Obligate parasites (biotrophs)

Require living protoplasm for food and are highly specialised as to
the species and the variety of hosts they parasitise. Can only grow
these parasites in association with the host.
Fungal growth on agar plates
Major fungal groups Kingdom Eumycota
Phylum Hyphochytriomycota
Phylum Oomycota

Phylum Chytridiomycota
Phylum Zygomycota
Phylum Ascomycota
Phylum Basidiomycota
Chytridiomycota (chytrids) form flagellated spores.
Zoospore
Zygomycota (zygote fungi) produce asexual sporangiospores and a
zygosporangium (with zygospore) as the sexual stage, e.g. Mucor and
Rhizopus.
Ascomycota (ascomycetes or sac fungi) form the sexual spores
(ascospores) inside sacs (bags) called asci and large numbers of
asexual spores (conidia) are produced, e.g. Aspergillus and Penicillium.
Basidiomycota (basidiomycetes or club fungi) form a variety of elaborate
fruiting bodies with many basidia that produce sexual spores (basidiospores),
e.g. Agaricus and Amanita.
Role of fungi
Decomposers of organic material, also the cellulose and
lignin in plant cell walls.
Form mutualistic relationships with green algae and cyanobacteria -
lichens
Plant roots and mycorrhizae

With mycorrhizae (left)

HUMANS CAN BENEFIT FROM FUNGI,
DIRECTLY OR INDIRECTLY
Fungi used to prepare food or eaten as food
Fungal species such as Saccharomyces, Aspergillus and Penicillium
Antibiotics
Penicillin
A colony of Penicillium chrysogenum,
Fleming's famous contaminant.

Penicillin used against Gram positive

bacteria like Staphylococcus spp. that
causes infection.

 Natural penicillins like penicillin G (benzyl-penicillin). Unstable in acid

solution (such as stomach acid) and must be given by injection.
and penicillin V (phenoxymethyl-penicillin). Not as effective as
Penicillin G, but more acid-stable and can be taken orally.
 Semisynthetic penicillins – variety of side chains added to basic β-
lactam ring core.
 E.g. phenethicillin, methicillin, ampicillin, carbenicillin, amoxicillin.
Antibiotic resistance in bacteria: This is a major problem in
society today and has two major sources of origin namely, the
widespread careless and unnecessary use of antibiotics has
selected for tolerant or resistant individuals in bacterial
populations, and people taking antibiotics frequently and then
fail to complete the treatment.

Bacteria became resistant to (penicillins) by producing

the enzyme, penicillinase or β-lactamase, which made
the penicillin inactive.
Other important drugs used in modern medicine that were originally isolated
from fungi include:

Cephalosporins
• Beta-lactam antimicrobials used against
Gram-positive and Gram-negative bacteria.
• Skin infection, resistant bacteria, meningitis,
and other infections.
• Cephalosporium acremonium.
• Disrupt the synthesis of the peptidoglycan
layer in bacterial cell wall.

Griseofulvin
• Natural organic compound that
contains chlorine
• Penicillium griseofulvum.
• Inhibits the growth of dermatophytic
fungi.
Fusidic acid
• Fusidium coccidium.
• Steroid-like antibiotic often used topically
in creams and eye drops.
• Also given systemically as tablets or
injections.
• Active against Gram-positive bacteria and
Useful against bacterial strains which have
acquired a high resistance to β-lactam
antibiotics.

Fumigallin
• Aspergillus fumigatus
• Originally used against parasite Nosema apis
infections in honey bees.
• Treatment of microsporidiosis [opportunistic
intestinal infection caused by microsporidia
(unicellular fungi) in immunocompromised
individuals].
• Also an amebicide (used against protozoan
infections).
 Cyclosporin A
• Tolypocladium inflatum (now called Tolypocladium
niveum).
• Cyclic peptide used to suppress immunological
rejection of organ transplants by acting as a selective
immunosuppressant.
• Inhibits multiplication of lymphocytes, but not
that of other somatic cells.
• Also effective against rheumatoid arthritis.

Compactin and Lovastatin

• Group of medicines called HMG-CoA reductase
inhibitors, or statins.
• Compactin (Penicillium citrinum) and lovastatin
(Aspergillus terreus).
• Used to treat atherosclerosis; reduces amount of
cholesterol in blood by blocking an enzyme that is
needed by the body to make cholesterol.
• Also used to prevent and treat coronary heart
disease.
FUNGI CAN HAVE A NEGATIVE IMPACT
ON HUMANS, DIRECTLY OR
INDIRECTLY
PLANT PATHOLOGY
FOOD SPOILAGE
MYCOTOXINS Aflatoxins -- Toxins, Mutagens, Carcinogens
Aspergillus flavus
Turkey X disease: Turning point for the use of the term mycotoxin.
In the 1960s, about 100,000 turkey pullets died near London,
England due to peanut meal that was contaminated by Mycotoxins
produced by Aspergillus flavus. Studies showed that the age group
that was most affected was turkeys from two to twenty weeks old.
Ergot Alkaloids Sclerotium

St. Anthony

Claviceps purpurea Salem witch trials

 Convulsive ergotism
(nervous system) – acute
Gangrenous ergotism - chronic poisoning
Medical uses
Ergotamine (tartrate): vaso-
constrictive; control post-partum
bleeding & treat migraine
headaches.
Ergocornine: effective
contraceptive; prevents implant of
fertilised eggs in uterus wall.
Ergonovine: stimulates smooth
muscles; induce and stimulate birth.
Ergotoxin: causes vaso-dilation;
treat high blood pressure & other
circulation problems.
 Human mycoses

1. Cutaneous infections
Involve outer layers of skin and cause an allergic or
inflammatory response.

2. Subcutaneous infections
Involve fungi of low inherent virulence - are
introduced to tissues through a wound of some kind,
remain localised or spread only by direct mycelial
growth.

3. Systemic infections
Caused either by true pathogenic fungi which can
grow in normal hosts, or by opportunistic saprobic
fungi that attack individuals whose immune system is
not working.
 Cutaneous Infections
Tineas
 Tinea or ringworm.

 Fungus stimulates epithelial cells of the host to divide more

often than usual.

 Increases amount of keratin available to the fungus – more

skin flakes with infective mycelium produced.

 Various irritants are produced - enzymes such as proteases,

peptidases and elastases, and other metabolites.

 Actually a form of toxic dermatitis.

 Fungal spores or mycelium is transferred from human to
human, also from pets to humans, from carpets, seats
and hair brushes or combs.

 Certain factors predispose the host to infection:

retention of moisture, over-wearing of shoes (sweating),
frequent wetting of the body part, obesity, moist oily
skin, close-clipping of hair.

 The fungus does not penetrate into living tissue and

symptoms include inflammation, redness, scaling,
brittleness of nails, or hair-loss on the infected part.
Cutaneous Infections Epidermophyton floccosum – athlete’s foot

Trichophyton rubrum
tends to cause chronic
infections of the foot and
toenails.
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Tinea manuum
Trichophyton tonsurans
Tinea capitis, caused by
Trichophyton rubrum

Tinea pedis

Tinea cruris (jock itch)

Epidermophyton floccosum

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Treatment of tineas
Cutaneous Infections
Candida albicans

 Candida albicans (a yeast) - normal part of gut (digestive

system) microbiota.

 Excessive wetness (sweating) or very tight clothing can trigger

rapid overgrowth of skin by this fungus.

 Can cause diaper rash (babies), infection around fingernails, in

armpits and crotch, and under breasts.

 Oral candidiasis (thrush) is common in newborn babies.

 Pregnant women get vaginal candidiasis because of altered

levels of glycogen.
Candidiasis - thrush
Systemic candidiasis
 The fungus is also an opportunistic pathogen.
 Becomes pathogenic in an immuno-compromised individual (e.g.
malnutrition, insanitary conditions, prolonged antibiotic therapy, HIV,
diabetes).
 Infection can become systemic: after Candida cells reach gastro-
intestinal tract it can pass through its surrounding mucosa into the
blood stream, which disseminates the fungus to the kidneys, liver,
spleen, bone, brain, and lungs.
 This systemic infection can be lethal.
 Subcutaneous Infections
Chromoblastomycosis- (Cladosporium carrion)
Entomophthoromycosis (Basidiobolus ranarum)
Mycetoma (Madurella mycetomatis)
Sporotrichosis (Sporothrix schenckii)
• Fungus introduced into body through open wound (e.g. thorn).
• Hyphae grow in body – sometimes change into yeast-like form.
Chromoblastomycosis Entomophthoromycosis
Mycotic mycetoma Sporotrichosis
 Systemic Mycoses
Two very different types:
• Those produced by specialised pathogens, and those caused
by opportunistic saprobes.
• There are four true pathogens, all of which are dimorphic --
this means they have one kind of morphology outside the
host, another inside the host.

Dimorphic Pathogens Opportunistic Pathogens

Histoplasmosis Candidiasis (candidosis)

Coccidioidomycosis Zygomycosis
Paracoccidioidomycosis Cryptococcosis
Blastomycosis Aspergillosis
 Histoplasmosis ('histo’) - caused by Histoplasma
capsulatum anamorph of Ajellomyces capsulatus

 Anamorph (asexual stage) grows well in high-nitrogen substrates

like wild bird droppings, chicken manure and bat guano.
 Conidia of fungus are inhaled and cause primary infections in the
lungs.
 About 95% of all cases heal spontaneously - small calcified
lesion in lung, and resistance to reinfection.
 Inhaled conidia assume yeast-like form, and become parasitic
within histiocytes (phagocytic host cells).
 First 'flu-like, then produce progressive lung disease that mimics
tuberculosis.
 If untreated, develop into generalised, systemic infection that can
be fatal.
 Dimorphic Pathogens
 Histoplasmosis ('histo’) - caused by the Histoplasma
capsulatum anamorph of Ajellomyces capsulatus.
Coccidioidomycosis (valley fever)
 Caused by Coccidioides immitis.
 Fungus grows in dry, saline soils, endemic in desert areas of
southwestern USA and Mexico (absent from deserts of Africa and Asia).
 Very similar to histoplasmosis, but fungus not intracellular.
 Forms spherical structures containing spores.
 Most cases are benign, and healing is spontaneous.
 Few become systemic - fatal if untreated or misdiagnosed.
Paracoccidioidomycosis
 Only in Central and South America; Paracoccidioides brasiliensis.
 Inhalation of conidia causes primary infection in the lungs.
Blastomycosis
 Caused by Blastomyces dermatitidis.

 Infection often seems to be a result of disturbing plant debris.

 Primary infection is in lungs, forming large granulomas that

contain many tiny abscesses.

 Lesions may heal, but organism then emerges in another place –

exposed parts of the face and neck.

 Warty, thickened patches develop - spread widely, cause

extensive scarring and destruction of tissue.

 Bones and brain can later be attacked.

Blastomycosis

Extra-pulmonary
Blastomycosis
 Systemic Mycoses
Opportunistic Pathogens

 None of them can usually cause an infection in a

normal, healthy individual.
 All rely on some breakdown in the mechanisms of
resistance.
 Often a complication of diabetes, AIDS, advanced
cancer, or is a sequel of steroid or antibiotic therapy.
 Opportunistic Pathogens
Zygomycosis
 Opportunistic Mucorales (Zygomycota) - Rhizopus
arrhizus, Rhizopus oryzae, Mucor, Rhizomucor and
Absidia.
 Rhinocerebral, thoracic, gastro-intestinal, and cutaneous.

Rhinocerebral - acidotic diabetics - infection begins in sinuses,

then grows quickly outward to eyes and inward to brain.
Eyes bulge, may become paralysed, eyelids droop, and
facial paralysis. Fatal within 7 days.
 Opportunistic Pathogens
Zygomycosis
Thoracic - leukemia or lymphoma, diabetics, transplant
patients on steroid therapy, or patients on dialysis.
Symptoms like bronchitis and pneumonia, with
complications like thrombosis. Fatal if untreated.

Gastrointestinal - Third-World countries - children already

suffering from Kwashiorkor.
Causal agent, Absidia corymbifera invades walls of stomach
and intestine, blocking the arteries. The resulting necrosis and
perforations are fatal.

Cutaneous - zygomycetous fungi colonise burns.

Infection may spread rapidly and be quickly fatal.
 Opportunistic Pathogens
Cryptococcosis
 Caused by basidiomycetous yeast, Cryptococcus
neoformans var. neoformans.
 Yeast anamorph commonly grows on decaying wood, pigeon
droppings and in soil enriched by pigeon droppings.
 Many people contract sub-clinical or asymptomatic
cryptococcosis which resolves spontaneously.
 Small number develop lung disease which may then
become systemic.
 Involves bones, heart, testicle, prostrate or eye, and is
often fatal.
 Second form of the disease is cryptococcal meningitis.
 Patients complain of increasingly severe headaches,
which eventually escalate into meningitis.
 Untreated cryptococcal meningitis is always fatal.
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 Opportunistic Pathogens
Aspergillosis

1. Bronchopulmonary aspergillosis - caused by Aspergillus

fumigatus - colonises mucus within bronchi - severe
allergic reaction.

2. Aspergilloma - fungus forms mycelial ball in lung cavity

from earlier tuberculosis. Wall of cavity may erode - patient
spit blood – needs surgical intervention.

3. Invasive aspergillosis - only in patients who are severely

debilitated, or immunosuppressed, as in AIDS. Fungus
grows outward from lung, invading blood vessels and
spread to other organs through bloodstream. Usually fatal.
 AIDS and Mycoses
 Many AIDS patients suffer from a variety of mycoses.
 “Diagnostic" mycoses indicating AIDS - aspergillosis, candidiasis,
cryptococcosis, zygomycosis, oesophageal candidiasis.
 Candidiasis of mucous membranes is seen in two-thirds of AIDS
patients.
 Dermatophytes, Trichophyton rubrum and T. interdigitale, also
cause more protracted and more severe infections in AIDS patients.
 Pneumocystis carinii causes the form of pneumonia afflicting most
AIDS patients. Pneumocystis pneumonia controlled by inexpensive
antibiotics such as Bactrim or Septra.
 Immunocompromised or immunosuppressed patients in some
hospitals are apparently threatened by aspergillosis, a lung disease
caused by Aspergillus fumigatus.