Bacteria & Viruses

Question 1

(Describe the structure and function of bacteria.) - Outline the types of cell walls possessed by bacteria.

Answer 1

Gram+; 90% of cell wall is comprised of peptidoglycan making it rigid and stains purple due to peptidoglycan binding.
Gram-; 10% of cell wall is comprised of peptidoglycan making it elastic and stains pink due to peptidoglycan binding. Has an LPS layer (endotoxin)!!!
Acid Fast; Mycobacterium TB, stained by Ziehl-neelson method.

Question 2

(Understand how bacteria are classified.) - Outline general bacteria classification & morphology with examples.

Answer 2

Gram+; Strep. Pyogenes & S. aureus
Gram-; Neisseria gonorrhoea & meningitis
Spirals; leptospira

Question 3

What are the factors that affect bacterial growth?

Question 4

What is a virus? And describe its morphology.

Answer 4

Viruses are genetic elements that contain either RNA or DNA (Nucleic acids) that replicates in cells–(intracellular), but has an extracellular state.

Morphology:
Nucleic acid & capsid with or without envelope.
Capsid – the protein coat surrounding the nucleic acid core, functionality includes protection of nucleic acid from inactivation and aids in introduction of viral genome into the host cell.
Capsomers - the repeating protein subunits that make up the capsid
Protomers – the polypeptide chains which make up the capsomers

Question 5

Describe a viruses life cycle and how they might replicate.

Answer 5

Every virus has 2 stages in the general cycle:

-Metabolically inactive; Particulate, transmissible virion stage consisting of nucleic acid, capsid, envelope. Entirely dependent on external physical factors for chance movement and spread to infect other susceptible cells/hosts.
-An active, intracellular stage called the infectious stage.Viruses can be isolated from all kinds of living things: animal, plants, fungi and bacteria.

How does it enter into the host cell?
-Surface Fusion, Fusion in Endosome, or Lysis of Endosome.

Attachment - penetration - uncoating - biosynthesis - maturations and assembly - release.

Question 6

Outline how viruses are classified.

Answer 6

Schemes have been based on the consideration of five major properties of viruses:
1. The type of viral nucleic acid which is found (RNA or DNA).
2. The symmetry and shape of the capsid.
3. The presence or absence of an envelope

Question 7

Describe/Explain the Baltimore Classification criteria.

Answer 7

By convention the top strand of coding DNA written in the 5’ - 3’ direction is + sense. The mRNA sequence is also + sense. Viruses can be classified into seven (arbitrary) groups:
I: Double-stranded DNA eg.Adenoviruses; Herpesviruses; Poxviruses
II: Single-stranded (+)sense DNA (Parvoviruses)
III: Double-stranded RNA (Reoviruses; Birnaviruses) segmented genomes.
IV: Single-stranded (+)sense RNA (Picornaviruses; Togaviruses, etc)
V: Single-stranded (-)sense RNA(Orthomyxoviruses, Rhabdoviruses,)
VI: Single-stranded (+)sense RNA with DNA intermediate (Retroviruses)
VII: Double-stranded DNA with RNA intermediate (Hepadnaviruses)
Subviral agents: Satellites, Viroids,and Prions

Question 8

What is a bacteriophage? Describe its life cycle (+ how that might affect virulence). *Draw the cycle + example?

Answer 8

Bacteriophages(or phages) are viruses that infect and replicate in bacteria. They can be lytic or lysogenic(temperate).

-Typical cycle follows: Absorption, penetration, biological synthesis, maturenation, and release.
-Lysogenic life cycle: After infecting a cell, they can undergo a typical lytic replicative cycle or they become dormant in a lysogenic cycle. The phage is still present in the cell as a prophage and under certain conditions it becomes active and resumes a lytic growth cycle.

Question 9

What is the difference between endogenous and exogenous bacterial infections?

Question 10

List or tabulate examples of organisms, their gram result, causes, and manifestations.

Question 11

Outline Koch’s 4 Postulates.

Answer 11

1. The microorganism (pathogen) must be present in all cases of the disease
2. The pathogen can be isolated from the diseased host and grown in pure culture
3. The pathogen from the pure culture must cause the same disease when inoculated into a healthy, susceptible laboratory animal
4. The pathogen must be re-isolated from the new host and shown to be the same as the originally inoculated pathogen

Question 12

List examples of bacterial virulence factors and elaborate on toxins specifically and in detail (with examples if possible).

Answer 12

1. Adherence; (Colonization) specific recognition of receptor sites on target cells enhances pathogenic advantage.
2. Invasion
3. Degradative Enzymes
4. Exo and Endotoxins;
   -Endotoxins- Gram negatives usually. Part of LPS. (e.g. E. coli, Shigella, etc). Causes fever leukopenia, metabolic effects, lymphocyte factors, cellular death.
   -Exotoxin-secreted by bacteria into surroundings(e.g. Corynebacterium diphtheria [Diphtheria toxin] - ADP-ribosylation inhibits cell protein, Botulinum neurotoxin - binding domain binds to neuroreceptor gangliosides, inhibits release of acetylcholine resulting in fatal paralysis)
5. Immune Evasion/Resistance to Antibiotics; Encapsulation, Antigenic Mimicry, Masking, Shift, phagocytic Inhibition, etc…
   -One way in which an infectious agent can evade immune surveillance is by altering its antigens; this is particularly important for extracellular pathogens, against which the principal defense is the production of antibodies against their surface structures.