Medical Microbiology

GeneralCharacteristicsofFungi 349

Thetaxonomyofthefungiisessentiallybasedontheirmorphology.In

medicalmycology,fungiareclassifiedaccordingtopracticalaspectsasder-

matophytes,yeasts,molds,anddimorphicfungi.Moldsgrowinfilamentous

structures,yeastsassinglecellsanddermatophytescauseinfectionsofthe

keratinizedtissues(skin,hair,nails,etc.).Dimorphicfungicanappearin

bothofthetwoforms,asyeastcellsorasmycelia(seethefollowingpages).

Fungiarecarbonheterotrophs.Thesaprobicorsaprophyticfungitakecar-

boncompoundsfromdeadorganicmaterialwhereasbiotrophicfungi(para-

sitesorsymbionts)requirelivinghostorganisms.Somefungicanexistinboth

saprophyticandbiotrophicforms.

Morphology

Twomorphologicalformsoffungiareobserved(Fig.5. 1 ):

&Hypha:thisisthebasicelementoffilamentousfungiwithabranched,

tubularstructure, 2 – 10 lminwidth.

Table5. 1 SomeDifferencesbetweenFungiandBacteria

Properties Fungi Bacteria

Nucleus Eukaryotic;nuclear

membrane;morethanone

chromosome;mitosis

Prokaryotic;nomembrane;

nucleoid;onlyone“chromo-

some”

Cytoplasm Mitochondria;endoplasmic

reticulum;80Sribosomes

Nomitochondria;

noendoplasmicreticulum;

70Sribosomes

Cytoplasmic

membrane

Sterols(ergosterol) Nosterols

Cellwall Glucans,mannans,chitin,

chitosan

Murein,teichoicacids

(Gram-positive),proteins

Metabolism Heterotrophic;

mostlyaerobes;

nophotosynthesis

Heterotrophic;obligate

aerobesandanaerobes,

facultativeanaerobes

Size,meandiameter Yeastcells: 3 – 5–1 0 lm.

Molds:indefinable

1 – 5 lm

Dimorphism Insomespecies None

5

Kayser, Medical Microbiology © 2005 Thieme