1. An Introduction to the Viruses
Microbiology: A Systems Approach
An Introduction to the Viruses
Chapter 6 Part 3
Copyright © The McGraw-Hill Companies, Inc) Permission required for reproduction or display.
Chapter 6, pages 139 to 167

2. Damage to the Host Cell and Persistent Infections
Cytopathic effects- virus-induced damage to the cell that alters its microscopic appearance
Inclusion bodies- compacted masses of viruses or damaged cell organelles
Synctia- fusion of cells
Latent infections
Tranformation – oncogenic, cancer causing (oncoviruses)

3. Cytopathic Effects

4. Results of Viral Infections- Examples
Death of host cell = Most viruses
Proliferation of cells = Papillomavirus
Fusion of host cells = Respiratory syncytial virus
Transformation of cells = Adenovirus
No obvious changes = Rubella

6. Viruses that Infect Bacteria
Bacteriophage
Most contain dsDNA
Often make the bacteria they infect more pathogenic for humans
Some are named “T-even phages”, such as T2 and T4
Attach, but do not enter host bacterial cell

7. T-even Bacteriophages
Icosahedral capsid head containing DNA
Central tube surrounded by a sheath
Collar
Base plate
Tail pins and fibers
Inject nucleic acid into bacterial cell

8. Bacteriophages
Entry of the nucleic acid causes the cessation of host cell DNA replication and protein synthesis
The host cell machinery is then used for viral replication and synthesis of viral proteins
As the host cell produces new parts, they spontaneously assemble
Eventually host cell lyses

9. Lysogeny: The Silent Virus Infection
Temperate phages- special DNA phages that undergo adsorption and penetration but are not replicated or released immediately
Instead the viral DNA enters an inactive prophage stage
Lysogeny: the cell’s progeny will also have the temperate phage DNA
Lysogenic conversion: when a bacterium acquires a new trait from its temperate phage

10. Lytic and Lysogenic Cycles

11. Bacteriophage vs. Animal Virus Multiplication

12. An Introduction to the Viruses
Concept Check
Microbiology: A Systems Approach
Corynebacterium diphtheriae becomes more pathogenic when a bacteriophage called beta is incorporated into its genome. What is this process called? A. Transposition B. Transformation C. Lysogenic conversion D. Lytic cycle
Correct answer is C; the bacterium has been converted to a more toxic form by the incorporated viral genes
UNDERSTANDING (Bloom’s taxonomy) – must use the provided vocabulary terms in a new and specific setting
Chapter 6, pages 139 to 167

13. An Introduction to the Viruses
Concept Check
Microbiology: A Systems Approach
How are the infectious cycles of viruses different in bacterial and eukaryotic host cells?
The virus genome does not enter a eukaryote.
The virus genome does not enter a bacterium.
The capsid does not enter a eukaryote.
The capsid does not enter a bacterium.
Correct answer is D; The genome is injected into the bacterial cell by the capsid; it remains outside
KNOWLEDGE (Bloom’s taxonomy): Simple recall of material from the previous slides.
Chapter 6, pages 139 to 167

14. 6.6 Techniques in Cultivating and Identifying Animal Viruses
Primary purposes of viral cultivation
To isolate and identify viruses in clinical specimens
To prepare viruses for vaccines
To do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells
Using Live Animal Inoculation
Specially bred strains of white mice, rats, hamsters, guinea pigs, and rabbits
Occasionally invertebrates or nonhuman primates are used
Animal is exposed to the virus by injection

15. Viral Culture Using Bird Embryos
Enclosed in an egg- nearly perfect conditions for viral propagation
Chicken, duck, and turkey are most common
Egg is injected through the shell using sterile techniques

16. Using Cell (Tissue) Culture Techniques
Most viruses are propagated in some sort of cell culture
The cultures must be developed and maintained
Animal cell cultures are grown in sterile chambers with special media
Cultured cells grow in the form of a monolayer
Primary or continuous

17. Detecting Viruses in the Lab
Plaque assays (used to visualize the presence of virus)
Bacteria cultures used for bacteriophage
Tissue culture used for eukaryotes

18. 6.7 Medical Importance of Viruses
Infectious diseases
Chronic affliction association
Type I diabetes, multiple sclerosis
Cancer

19. 6.8 Noncellular Infectious Agents
Viroids
Plant pathogens
Naked RNA, Single-stranded, Circles, Very small (100 to 300 nucleotides)
Prions
Animal pathogens, “Slow viruses”
Spongiform encephalopathy
Mad Cow Disease, Creutzfeld-Jakob Disease
Defectively folded host protein