Fungi

FUNGI
Muhammed Mahfuzur Rahman
Lecturer
Department of Pharmacy

Introduction
 Fungi is the plural of fungus.
 A member of a large group of eukaryotic organisms.
 Familiar as mushrooms.
 These organisms are classified as a kingdom, Fungi, which is separate from
plants, animals, protists and bacteria.
 One major difference is that fungal cells have cell walls that contain chitin, unlike
the cell walls of plants and some protists, which contain cellulose, and unlike the
cell walls of bacteria.
 The study of fungi is known as MYCOLOGY. Mycology has often been regarded
as a branch of botany, even though it is a separate kingdom in biological
taxonomy.
 Genetic studies have shown that fungi are more closely related to animals than
to plants.

Intro... Contd.
 However, little is known of the true biodiversity of Kingdom Fungi, which has been
estimated at 1.5 million to 5 million species, with about 5% of these having been
formally classified.
 Ever since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus,
Christian Hendrik Persoon, and Elias Magnus Fries, fungi have been classified
according to their morphology or physiology.
Mold growth covering a decaying peach. The frames were taken approximately 12 hours
apart over a period of six days.

Morphological Characteristics of Fungi
 Non-motile eukaryotic organisms which exists as saprophytes, parasites.
 Posses differentiated nuclei surrounded by a nuclear membrane.
 Reproduce either by budding or by forming spores.
 Nonphotosynthetic (heterotrophic).
 Morphologically may be either simple oval cells or long tubular septate hyphae showing true
lateral branching.
 Most fungi grow as thread-like filamentous microscopic structures called hyphae (which are
microscopic filaments between 2–10 μm in diameter and up to several centimeters in length)
and which collectively form the mycelium (aggregates of hyphae).
 Hyphae can be septate, i.e., divided into compartments separated by a septum, each
compartment containing one or more nuclei, or can be coenocytic, i.e., lacking hyphal
compartmentalization.
 May be unicellular or multicellular.
 Most are microscopic molds or yeasts.

Difference between Fungi and Bacteria
Characteristics Fungi Bacteria
Cell type Eucaryotic Procaryotic
Optimum pH 4-6 6.5-7.5
Optimum temperature 25-30oC (saprophytes)
32-37oC (parasites)
32-37oC
Cell membrane Sterols present Sterols absent except
mycoplasm
O2 requirement Strictly aerobic (moulds)
Facultative anaerobic(Some
yeasts)
Aerobic to anaerobic
Light requirement None Some photosynthetic gr.
Carbon source Organic Organic/ Inorganic
Conc. of sugar in media 4-5% 0.5-1%
Cell wall components Chitin, cellulose or hemicellulose Peptidoglycan
Susceptibility to
antibiotics
Sensitive to griseofulvin,
Resistant to penicillinis,
chloramphenicol etc.
Sensitive to penicillinis,
Resistant to griseofulvin,
tetracyclines etc.

Classification of fungi
 Depending on cell morphology, fungi can be divided into 4 classes:
I. Moulds
II. Yeasts
III. Yeast like fungi and
IV. Dimorphic fungi
 Based on their sexual spore formation fungi are divided into 4 classes:
I. Phycomycetes
II. Ascomycetes
III. Basidiomycetes
IV. Fungi imperfecti

1. Moulds
 Fungi which form mycelia are called moulds or
filamentous fungi.
 Filaments of fungi are called hyphae.
 Diameter is 2-10μm .
 The cell walls contain chitin.
 Some hyphae may divided by cross sections called septa
 Two types of hyphae: Septate and Non-septate
I. Septate: septa divide the hyphae into distinct,
uninucleate or mulitnucleate cell-like units.
II. Nonseptate/coenocytic: does not contain septa
and appear as long, continuous cells with many
nuclei.
 Example: Aspergillus fumigatus, Aspergillus niger,
Penicillium notatum
Septated
Nonseptated -coenocytic

2. Yeasts
 Round, oval or elongated, unicellular
fungi
 Reproduce by an asexual process
called budding in which the cell
develops a protuberance which
enlarges and eventually separates
from the parent cell
 On culture they form smooth, creamy
colonies
 Example: Saccharomyces cerevisae,
Cryptococcus neoformans

3. Yeast like fungi
 The bud remains attached to the mother cell and
elongates, followed by repeated budding, forming
chains of elongated chains known as
pseudohyphae.
 Example: Candida albicans
4. Dimorphic fungi
 Mainly pathogenic species exhibit dimorphism i.e. 2 forms of growth
 Fungi can grow either as a mould or as a yeast
 Mouldlike forms produce vegetative and aerial mycellium and Yeast like forms
reproduce by budding
 Dimorphism is temperature and CO2 dependant.
 At 37oC, the fungus grows yeastlike and at 25oC it shows mouldlike growth
 Example: Mucor rouxii, Histoplasma capsulatum

1. Phycomycetes
 Fungi having non-septate hyphae, forms endogenous asexual spores
(sporangiospores) contained within a sac like structures called sporangia.
 Also produce sexual spores known as oospores and zygospores.
 Example: Mucor, Rhizopus.
2. Ascomycetes
 Form sexual spores within a sac and are called ascospores.
 The sac is called as ascus.
 They form septate hyphae.
 Include both yeasts and filamentous fungi e.g. Histoplasm, Candida etc.

3. Basidiomycetes
 Reproduce sexually and form septate hyphae.
 These basidiospores are borne at the tip of the basidium
 Example: Cryptococcus neoformans
4. Fungi imperfecti
 Also called as Deuteromycetes or Hyphomycetes.
 Consist of group of fungi whose sexual phases have not been
identified and they form septate hyphae and asexual conidia.
 Majority of the pathogenic moulds, yeasts, yeasts like fungi and
dimorphic fungi.
 Example: Trichophyton, Epidermophyton

Reproduction
 Most fungi reproduce both sexually and asexually.
 When environmental conditions are favorable, asexual reproduction occurs
rapidly.
 When unfavorable conditions stress the organism, sexual reproduction
occurs and the offspring have an increased likehood that they will be better
suited for the environment.

Asexual Reproduction
 Production of various types of spores
 Sporangiophores
 Upright stalk with an enclosed sac (bread mold)
 Conidia
 Upright stalk with no enclosed sac (penicillin)
 Fragmentation
 Hyphae dry out and shatter releasing individual cells that
act like spores (athlete’s foot)
 Budding
 Small offspring

Sexual Reproduction
 “Plus and minus” mating types
 Hyphae of different mating
types fuse and give rise to a
specialized structure that
produces spores (diploid)
 Most fungi are haploid
throughout most of their life
cycle

Classification of Fungal Infections
 When fungi do pass the resistance barriers of the human body
and establish infections, the infections are classified according
to the tissue levels initially colonized.
 Systemic mycoses
 Opportunistic mycoses
 Superficial mycoses
 Cutaneous mycoses
 Sub-cutaneous mycoses

Systemic Mycoses
 Fungal infections that enter into the body and invade internal
organs are called systemic mycoses.
 Infection can arise from inhalation of fungal spores, although
such cases are not usually life threatening.
 Most people that suffer from a systemic fungal infection are
usually sick already.
 The fungus is said to be ‘opportunistic’ because if the person
was healthy the fungus would not usually cause any serious
harm.
 If someone is sick the body is less able to defend itself against
pathogenic organisms, they therefore have an increased risk of
susceptibility to infectious fungi.

Mycoses by Aspergillus
 Bronchopulmonary aspergillosis, the fungus grows within the
lumen of the bronchiloes.
 Colonising aspergillosis developes in pre-existing pulmonary
cavities such as TB or cystic disease.
 If they remains in these cavities it grows into a huge mass of
mycelium in the form of fungus ball, may be needed to removed
surgically.
 Treatment
 Amphotericin B
 Importance
 Used in industries for the production of citric acid and
gluconic acid

Superficial mycoses
 Infections limited to the outermost layers of the skin and hair.
Disease Etiological Agent Symptoms
Pityriasis versicolor Malassezia furfur
hypopigmented macules
(lesions in skin rashes)
Tinea nigra Exophiala werneckii black macules
Black piedra Piedraia hortai black nodule on hair shaft
White piedra Trichosporum beigelii
cream-coloured nodules on
hair shaft

Cutaneous mycoses
 Cutaneous mycoses - infections that extend deeper into the
epidermis, as well as invasive hair and nail diseases.
 These diseases are restricted to the keratinized layers of the
skin, hair and nails.
 Unlike the superficial mycoses, various cellular immune
responses may be evoked, causing pathologic changes in the
host that may be expressed in the deeper layers of the skin.
 The agents causing these diseases are termed dermatophytes.
The diseases are referred to as ringworm or tinea.
 All of the dermatophytic diseases are caused by members of
three genera: Microsporum, Trichophyton and Epidermophyton.

Sub-cutaneous mycoses
 Subcutaneous mycoses include a heterogeneous group of
fungal infections that develop at the site of transcutaneous
trauma.
 Infection slowly evolves as the etiologic agent survives and
adapts to the adverse host tissue environment.
 The main subcutaneous fungal infections include
sporotrichosis, chromoblastomycosis, mycetoma, lobomycosis,
rhinosporidiosis, subcutaneous zygomycosis, and
subcutaneous phaeohyphomycosis.

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