Tài liệu Nature and Properties of Micro-organisms doc

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

encephalopathy:
transmissible, familial

Transmission: oral,
operative (neural
tissue, dura,
corneas), ??? blood

Resistance to
disinfectants

Formaldehyde
increases infectivity

Viruses

DNA or RNA

Shell of protein (capsid) surrounding nucleic
acid

Classification on basis of nucleic acid

DNA viruses: eg Herpes simplex virus
(HSV)

RNA viruses: eg influenza virus

DNA viruses: herpes simplex virus (HSV)

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


Transformation: malignancy (parvoviruses)

Latent infection - no sign of infection until
reactivation

‘cold sores’ (HSV)

chickenpox  shingles (VZV)

CMV hepatitis
owl eye effect inclusion body

Varicella zoster virus (VZV)

VZV: Chickenpox

VZV: Shingles

Re-activation of
latent infection

Suppression of
cell mediated
immunity

Bacteria

Unicellular, prokaryotes

DNA and RNA


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

Wound swab: S. aureus