Lecture 1.1: Intro to Infection Flashcards
What is Microbiology?
Study of Microorganisms
What is Germ Theory (1861)?
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
What is Koch’s Postulate (1890)?
A set of criteria that establish whether a particular organism is the cause of a particular disease
What are Koch’s 4 Postulates?
• 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
Classification of Microorganisms (5)
• Bacteria (Prokaryotic)
• Archaea (Single Cell Microorganisms)
• Eukaryotic (include fungi, algae and protozoa)
• Multicellular animal parasites (helminths)
• Viruses
What are Viruses?
• 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
What are Viroids?
• 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
Prions
• 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
Gram Positive Bacteria
• Thick peptidoglycan layer
• Contains acidic teichoic acid and lipotechoic acid
• Periplasmic space
Gram Negative Bacteria
• Thin peptidoglycan layer
• Outer membrane covers lipoprotein
• Membrane contains lipopolysaccharide and porins
• Periplasmic space
Gram Stain: Crystal Violet
Binds to peptidoglycan
Both gram positive and gram-negative cells have peptidoglycan in their cell
walls
So initially, all bacteria stain violet
Gram Stain: Gram’s Iodine
Form a crystal violet-iodine complex
Gram Stain: 95% Ethyl Alcohol
Alcohol dehydrates the thick cell wall of gram-positive cells
This causes them to shrink thus trapping the stain iodine complex inside
Gram Stain: Safranin (Counterstain)
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
How do Bacteria replicate?
• Bacteria grow by binary fission
• Results in two identical daughter cells
4 Phases of Bacterial Growth
• Lag Phase
• Exponential Phase
• Stationary Phase
• Death Phase
Stages of Viral Replication (6)
1) Attachment
2) Penetration
3) Un-coating
4) Replication
5) Assembly
6) Virion Release
Viral Replication: Attachment
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
Viral Replication: Penetration
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
Viral Replication: Un-coating
The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid
Viral Replication: Replication
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
Viral Replication: Assembly
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
Viral Replication: Virion Release (2 types)
There are two methods of viral release: lysis or budding
