Download Document

TORTORA • FUNKE
• CASE
Microbiology
AN INTRODUCTION
EIGHTH EDITION
B.E Pruitt & Jane J. Stein
Chapter 13, part A
Viruses, Viroids, and Prions
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Viruses
• Viruses contain DNA or RNA
• And a protein coat
• Some are enclosed by an envelope
• Some viruses have spikes
• Most viruses infect only specific types of cells
in one host
• Host range is determined by specific host
attachment sites and cellular factors
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Viruses versus cellular organisms
Viruses
Cellular Organisms
• simple organization
• complex organization
• DNA or RNA but not
both (one exception)
• both DNA and RNA
• unable to reproduce
outside of living cells
• some are obligate
intracellular parasites
• obligate intracellular
parasites
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
• carry out cell division
Viruses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.1
Helical Viruses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.4a, b
Polyhedral Viruses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.2a, b
Complex Viruses
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.5a
Viral Taxonomy
• Family names end in -viridae
• Genus names end in -virus
• Viral species: A group of viruses sharing the same
genetic information and ecological niche (host).
Common names are used for species
• Subspecies are designated by a number
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Viral Taxonomy
• Herpesviridae
• Retroviridae
• Herpesvirus
• Lentivirus
• Human herpes
virus 1, HHV 2,
HHV 3
• Human
Immunodeficiency Virus
1, HIV 2
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Growing Viruses
• Viruses must be
grown in living
cells.
• Bacteriophages
form plaques on
a lawn of
bacteria.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.6
The Cultivation of Viruses
• requires inoculation of appropriate living host
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Hosts for animal viruses
• suitable animals
• embryonated eggs
• tissue (cell) cultures
• monolayers of animal cells
• plaques
• localized area of cellular destruction and lysis
• cytopathic effects
• microscopic or macroscopic degenerative changes or
abnormalities in host cells and tissues
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Growing Viruses
• Animal viruses
may be grown in
living animals or
in embryonated
eggs.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.7
Growing Viruses
• Animal and plants viruses may be grown in cell
culture.
• Continuous cell lines may be maintained
indefinitely.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.8
Virus Identification
• Cytopathic effects
• Serological tests
• Detect antibodies against viruses in a patient
• Use antibodies to identify viruses in neutralization
tests, viral hemagglutination, and Western blot
• Nucleic acids
• RFLPs
• PCR
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Hosts for bacteriophages
• usually cultivated in broth or agar cultures of
suitable, young, actively growing bacteria
• broth cultures lose turbidity as viruses
reproduce
• plaques observed on agar cultures
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Multiplication of Bacteriophages (Lytic Cycle)
• Attachment
Phage attaches by tail fibers to
host cell
• Penetration
Phage lysozyme opens cell wall,
tail sheath contracts to force tail
core and DNA into cell
• Biosynthesis
Production of phage DNA
and proteins
• Maturation
Assembly of phage particles
• Release
Phage lysozyme breaks cell wall
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Bacterial
cell wall
Bacterial
chromosome
Capsid
DNA
Capsid
Sheath
Tail fiber
1 Attachment:
Phage attaches
to host cell.
Base plate
Pin
Cell wall
Tail
Plasma membrane
2 Penetration:
Phage penetrates
host cell and
injects its DNA.
Sheath contracted
Tail core
3 Biosynthesis:
DNA and Protein
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.10.1
Tail
DNA
4 Maturation:
Viral components
are assembled into
virions.
Capsid
5 Release:
Host cell lyses and
new virions are
released.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Tail fibers
Figure 13.10.2
One-step Growth Curve
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.11
• Lytic cycle
Phage causes lysis and death of
host cell
• Lysogenic cycle
Prophage DNA incorporated in
host DNA
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
The Lysogenic Cycle
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.12
Specialized Transduction
Prophage
gal gene
Bacterial DNA
1 Prophage exists in galactose-using host
(containing the gal gene).
Galactose-positive
donor cell
gal gene
2 Phage genome excises, carrying
with it the adjacent gal gene from
the host.
gal gene
3 Phage matures and cell lyses, releasing
phage carrying gal gene.
4 Phage infects a cell that cannot utilize
galactose (lacking gal gene).
Galactose-negative
recipient cell
5 Along with the prophage, the bacterial gal
gene becomes integrated into the new
host’s DNA.
6 Lysogenic cell can now metabolize
galactose.
Galactose-positive recombinant cell
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 13.13
Multiplication of Animal viruses
• Attachment
Viruses attaches to cell membrane
• Penetration
By endocytosis or fusion
• Uncoating
By viral or host enzymes
• Biosynthesis
Production of nucleic acid and proteins
• Maturation
Nucleic acid and capsid proteins
assemble
• Release
By budding (enveloped viruses) or
rupture
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Virus Purification and Assays
• development of virology closely linked to
development of these methods
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Virus Purification
• four commonly used methods
• differential centrifugation and density gradient
centrifugation
• precipitation of viruses
• denaturation of contaminants
• enzymatic digestion of cell constituents
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Differential centrifugation
• separates based
on size
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Density gradient centrifugation
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Measuring concentration of infectious units
• plaque assays
• dilutions of virus preparation made and plated
on lawn of host cells
• number of plaques counted
• results expressed as plaque-forming units
(PFU)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Measuring concentration of infectious units…
• infectious dose and lethal dose assays
• determine smallest amount of virus needed to
cause infection or death of 50% of exposed
host cells or organisms
• results expressed as ID50 or LD50
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Graph
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings