Distribution of microorganisms
Microbes are involved in
nutrient production & energy flow
production of foods, drugs & vaccines
Microorganisms and Human
Beneficial activities: Most microbes are
of benefit to human beings, some are
necessary( nitrogen, carbon cycles, etc)
Harmful activities: A portion of microbes
cause diseases and are poisonous to
human, and these are really that concern
us in the study of medical microbiology,
Impact of pathogens
Nearly 2,000 different microbes cause
10 B infections/year worldwide
13 M deaths from infections/year
Classification of Fungi
Comparison of fungi and bacteria
Sexual and asexual spores for Endospores for survival,
not for reproduction
Require organic carbon; no
May do not require
organic carbon; many
Characteristics of fungi
A. eukaryotic, non- vascular organisms
B. reproduce by means of spores (conidia), usually winddisseminated
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
E. like plants, may have a stable haploid & diploid states
F. vegetative body may be unicellular (yeasts) or multicellular
moulds composed of microscopic threads called hyphae.
G. cell walls composed of mostly of chitin and glucan.
More Characteristics of Fungi
fungi are heterotrophic ( “other feeding,” must feed on
preformed organic material), not autotrophic ( “self feeding,”
make their own food by photosynthesis).
- Unlike animals (also heterotrophic), which ingest then digest,
fungi digest then ingest.
-Fungi produce exoenzymes to accomplish this
I. Most fungi store their food as glycogen (like animals). Plants
store food as starch.
K. Fungal cell membranes have a unique sterol, ergosterol, which
replaces cholesterol found in mammalian cell membranes
L. Tubule protein—production of a different type in microtubules
formed during nuclear division.
Many pathogenic fungi are dimorphic, forming
moulds at ambient temperatures but yeasts at body
Structure of fungi
Hypha: mycelium (vegetative, aerial or
Spores: asexual spore
blastospore, chlamydospore, arthrospore
making up a mycelium
Uni cel l ul ar
Medically important fungi
Includes 4 phyla
Ascomycota Sexual reproduction in a sack called an ascus with
the production of ascopspores.
Basidiomycota Sexual reproduction in a sack called a basidium
with the production of basidiospores.
Zygomycota Sexual reproduction by gametes and asexual
reproduction with the formation of zygospores.
Mitosporic Fungi（Fungi Imperfecti)，No recognizable
form of sexual reproduction. Includes most pathogenic fungi.
Germ theory of disease
Many diseases are caused by the
growth of microbes in the body
experimental steps to
show that a specific
m.o. causes a
Identified cause of
anthrax, TB, & cholera.
The microbe must be found in the body in
all cases of the disease
It must be isolated from a case and grown
in a series of pure culture in vitro
It reproduce the disease on the
inoculation of a late pure culture into a
The microbe must be isolated again into
pure culture from such experimentally
Taxonomy - system for organizing,
classifying & naming living things
Domain - Archaea, Bacteria &
Kingdom - 5
Phylum or Division
Sabouraud culture medium
optimal pH 4-6
optimal temperature 22-28 C some deep
pathogenic fungi need 37 C,
types of colonies– yeast, filamentous
Multiplication:budding, hypha formation,
branching or disruption of hypha, spore
Resistant to dry, sunlight, UV light and many
Sensitive to wet heat
four types of mycotic diseases:
Hypersensitivity - an allergic reaction to molds
Mycotoxicoses - poisoning of man and animals by
feeds and food products contaminated by fungi
which produce toxins from the grain substrate.
Mycotoxin and tumor
Mycetismus - the ingestion of toxin (mushroom
1. Skin scrapings suspected to contain dermatophytes or pus
from a lesion can be mounted in KOH on a slide and
examined directly under the microscope.
2. Skin testing (dermal hypersensitivity) used to be popular as
a diagnostic tool.
3. Serology may be helpful when it is applied to a specific
4. Direct fluorescent microscopy.
5. Biopsy and histopathology.
6. Culture. Pathogenic fungi are usually grown on
Sabouraud dextrose agar . It has a slightly acidic
pH (~5.6); cyclohexamide, penicillin, streptomycin
or other inhibitory antibiotics are often added to
prevent bacterial contamination and overgrowth.