Fungal Classification

1. S. T. V. Raghavamma,
Assoc.Prof. CIPS

2. Features of Fungi and its value in 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 of immunocompromised patients.

3. Fungal Taxonomy:
Kingdom Fungi (Myceteae)
5 main classes of medically important fungi.
1. Zygo - mycetes,
2. Asco - mycetes,
3. Archiasco - mycetes,
4. Basidio - mycetes
5. Deutero - mycetes

4. Fungal Morphology and Structure
Eukaryotic organisms, distinguished by a rigid cell wall
composed of chitin and glucan, and a cell membrane in
which ergosterol is substituted for cholesterol as the major
sterol component.
Fungal taxonomy relies heavily on morphology and mode of
spore production
Fungi may be unicellular or multicellular.
The simplest grouping based on morphology divides fungi
into either yeast or mold forms.

5. 1- Yeast can be defined morphologically as a cell that
reproduces by budding or by fission. Daughter cells may
elongate to form sausage-like pseudohyphae.

6. 2- Moulds are multicellular organisms consisting of threadlike
tubular structures called Hyphae that elongate by apical
extension.
Hyphae are either:
Coenocytic: hollow and multinucleate
Septate: divided by partitions or cross-walls
Hyphae form together to produce a mat-like structure
called a Mycelium.
Vegetative hyphae, grow on or under surface of culture
medium,
Aerial Hyphae: project above surface of medium
Aerial H. produce Conidia (asexual reproductive elements)
Conidia can easily airborne and disseminate the fungus.
Many medical fungi are termed dimorphic because they exist in
yeast and mould forms.

8. Asexual spores consist of two general types:
1) sporangiospores and 2) conidia.
Sporangiospores are asexual spores produced in a containing
structure or sporangium ( in class Zygomycetes: as Rhizopus
and Mucor spp.)
Conidia are asexual spores that are borne naked on
specialized structures (Aspergillus, Penicillium, and the
dermatophytes).

9. Aspergillus niger conidiophore
and conidia
Dermatophyte conidia
Penicillium conidia

10. Sporangiospores of Mucor

11. Physiology
Most fungi are Aerobic, some are facultative anaerobic, or strict
anerobic.
Fungi are heterotrophic and biochemically versatile:
Primary metabolites: citric acid, ethanol, glycerol
Secondary : antibiotics [as penicillin], and aflatoxins.
Fungi are slow growing with cell-doubling times in hours.
Fungi reproduce by formation of spores, which may be sexual
(teleomorph), or asexual (anamorph):
Fungi in class: Zygomycetes, Ascomycetes, Archiascomycetes, and
Basidiomycetes produce both sexual and asexual spores.
Histoplasma capsulatum (anamorph) and Ajellomyces capsulatum
(teleomorph) are two forms of same fungus !!

12. The 5 Medical Fungal Classes
1) ZYGOMYCETES:
 Moulds with broad, sparsely septate, coenocytic hyphae.
 Zygomycetes produce sexual zygospores following the fusion of
two compatible mating types.
 The asexual spores of the order Mucor are contained within a
sporangium (sporangiospores, see figure.. )
 The sporangia are borne at the tips of stalk-like sporangiophores
that terminate in a bulbous swelling called the columella
 The presence of root-like structures, called Rhizoids, is helpful in
identifying specific genera within the Mucorales. (see next figure )

14. Zygomycetes: medical
significance
 This group, having a worldwide
distribution, may be found in soil or
decaying vegetable matter.
 They may also be found on stored
grain, fruits and vegetables,
compost, and air.
 They are generally associated with
warmer climates.
They may be allergenic and are
known to cause opportunistic
infections in immunocompromised
individuals.
 This group includes : Absidia ,
Rhizopus and Mucor.
Mucor

15. Absidia
 A Zygomycete, it has been reported to be allergenic.
 It may cause zygomycosis (an opportunistic fungal infection)
and mycotic keratitis (an opportunistic fungal infection of
the cornea).
 Absidia can cause serious
infections in individuals who are
malnourished, in diabetic
acidosis, or immunocompromised.

16. 2) ASCOMYCETES
 Ascomycetes include yeasts and moulds.
 The hyphae are septate
 Asexual spores conidiophores.
 Sexual spore of called “ascospore”, found within a sac or
ascus.

17. Fluffy,
filamentous
growth of a
saprophytic
mucor on a
peach.
Yeast colonies on
agar

18. 3) ARCHIASCOMYCETES
 Archiascomycetes is a new class that was recently described
to include an organism, Pneumocystis carinii, that had
formerly been considered a protozoan.
 The organism exists in a vegetative, trophic form that
reproduces asexually by binary fission.
 Fusion of compatible mating types results in a spherical cyst
or spore case, which on maturity contains eight spores.

19. Pneumocystis carinii cysts

20. 4) BASIDIOMYCETES
 Basidiomycetes are rarely encountered clinically.
 The only human pathogen is Cryptococcus neoformans.
 The sexual spore is called basidiospore, characterized by
the extension from a club-shaped structure, the basidium
(see figure above).

21.  Have both yeasts and mould forms.
 No sexual phase.
 Many of pathogenic fungi are included in this class.
 They have septate hyphae and produce conidia from
conidiophores and conidiogenous cells.
 The yeasts reproduce by budding, and the moulds produce
conidia by either a blastic (budding) process or a thallic
process, in which hyphal segments fragment into individual
cells or arthroconidia.
5) DEUTEROMYCETES

22. Macroconidia of dermatophyte
(Microsporum canis)

23. Arthroconidia