Lecture 1.1: Intro to Infection

Question 1

What is Microbiology?

Answer 1

Study of Microorganisms

Question 2

What is Germ Theory (1861)?

Answer 2

Germ theory states that certain diseases are caused by the invasion of the body by microorganisms, organisms too small to be seen except through a microscope

Question 3

What is Koch’s Postulate (1890)?

Answer 3

A set of criteria that establish whether a particular organism is the cause of a particular disease

Question 4

What are Koch’s 4 Postulates?

Answer 4

• The microorganism must be found in the
diseased animal, and not found in healthy
animals
• The microorganism must be extracted and.
isolated from the diseased animal and
subsequently grown in culture
• The microorganism must cause disease when
introduced to a healthy experimental animal
• The microorganism must be extracted from the
diseased experimental animal and demonstrated
to be the same microorganism that was
originally isolated from the first diseased animal

Question 5

Classification of Microorganisms (5)

Answer 5

• Bacteria (Prokaryotic)
• Archaea (Single Cell Microorganisms)
• Eukaryotic (include fungi, algae and protozoa)
• Multicellular animal parasites (helminths)
• Viruses

Question 6

What are Viruses?

Answer 6

• Submicroscopic spherical, rod-shaped, or filamentous entities consisting of
only one type of nucleic acid (DNA or RNA)
• The nucleic acid is surrounded by a coat consisting of one or more kinds of
protein molecules
• Viruses infect and multiply inside the cells of humans, animals, plants, or
other organisms and usually cause disease

Question 7

What are Viroids?

Answer 7

• Smallest infectious agents that multiply autonomously in plant cells
• Consist only of small, circular RNA molecules
• Infect plant cells and are replicated in their nucleus

Question 8

Prions

Answer 8

• Proposed for the first time in 1972
• Misfolded proteins with the ability to transmit their misfolded shape onto
normal variants of the same protein
• Small protein molecules produced in nerve and other cells of the brain
• When prions are forced by conditions in the brain to change shape, have
adverse effects on the brain and cause disease

Question 9

Gram Positive Bacteria

Answer 9

• Thick peptidoglycan layer
• Contains acidic teichoic acid and lipotechoic acid
• Periplasmic space

Question 10

Gram Negative Bacteria

Answer 10

• Thin peptidoglycan layer
• Outer membrane covers lipoprotein
• Membrane contains lipopolysaccharide and porins
• Periplasmic space

Question 11

Gram Stain: Crystal Violet

Answer 11

Binds to peptidoglycan

Both gram positive and gram-negative cells have peptidoglycan in their cell
walls

So initially, all bacteria stain violet

Question 12

Gram Stain: Gram’s Iodine

Answer 12

Form a crystal violet-iodine complex

Question 13

Gram Stain: 95% Ethyl Alcohol

Answer 13

Alcohol dehydrates the thick cell wall of gram-positive cells

This causes them to shrink thus trapping the stain iodine complex inside

Question 14

Gram Stain: Safranin (Counterstain)

Answer 14

Both gram-positive and gram-negative bacteria pick up the pink stain, but it is not visible over the darker purple of the gram positive bacteria

Question 15

How do Bacteria replicate?

Answer 15

• Bacteria grow by binary fission
• Results in two identical daughter cells

Question 16

4 Phases of Bacterial Growth

Answer 16

• Lag Phase
• Exponential Phase
• Stationary Phase
• Death Phase

Question 17

Stages of Viral Replication (6)

Answer 17

1) Attachment
2) Penetration
3) Un-coating
4) Replication
5) Assembly
6) Virion Release

Question 18

Viral Replication: Attachment

Answer 18

Viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cellular surface

This specificity determines the host range (tropism) of a virus

Question 19

Viral Replication: Penetration

Answer 19

The process of attachment to a specific receptor can induce conformational changes in viral capsid proteins, or the lipid envelope, that results in the fusion of viral and cellular membranes

Some DNA viruses can also enter the host cell through receptor-mediated endocytosis

Question 20

Viral Replication: Un-coating

Answer 20

The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid

Question 21

Viral Replication: Replication

Answer 21

After the viral genome has been uncoated, transcription or translation of the viral genome is initiated

It is this stage of viral replication that differs greatly between DNA and RNA viruses and viruses with opposite nucleic acid polarity

This process culminates in the de novo synthesis of viral proteins and genome

Question 22

Viral Replication: Assembly

Answer 22

After de novo synthesis of viral genome and proteins, which can be post-transrciptionally modified, viral proteins are packaged with newly replicated viral genome into new virions that are ready for release from the host cell

This process can also be referred to as maturation

Question 23

Viral Replication: Virion Release (2 types)

Answer 23

There are two methods of viral release: lysis or budding