Nature and Properties
of Micro-organisms
Laura JV Piddock

Smallest to largest…..

Prions

Viruses

Bacteria

Fungi

Prions

Infectious protein

No DNA or RNA

Normal cellular form of protein vs.
pathological form
Pathological form
found in neural
tissue and tonsils
PrP-C & PrP-Sc

Pathology

Spongiform

RNA viruses: Influenza

Viruses

Obligate intracellular parasites

Use host cell for nucleic acid and
protein synthesis

Cell attachment: target for blocking
antibody vaccines

Intracellular replication: target for
antiviral drugs

n.b. retroviruses (RNA) e.g. HIV
RNA

DNA

Viral effects on host cells

Degeneration (cytopathic effect): CMV

Cell lysis

Cell fusion, syncytia formation: RSV

Cell proliferation



Binary fission

No mitochondria

Rigid cell wall containing
peptidoglycan

Eubacteria

Classified according to:

size & shape

cell wall (Gram stain)

aerotolerance

Gram stain reaction

positive - purple

negative - pink

Shape

coccus - round (chains?
clusters?)

bacillus - rod