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31 terms

Lecture 21

STUDY
PLAY
Pathogenicity
The ability to cause disease
Virulence
The extent of pathogenicity
Entry into host: - different portals
Mucous membranes
Respiratory tract
Gastrointestinal tract
Genitourinary tract -
Conjunctiva
Skin
Parenteral Route
LD50
lethal dose for 50% of inoculated hosts
ID50
infectious dose for 50% of inoculated hosts
Using examples, explain how microbes adhere to host cells
Capsules - prevent phagocytosis
Cell Wall Components - help adherence
Enzymes - destroy blood cells, other functions
Cytoskeleton - invasins - 'basket around bacteria"
Explain how capsules and cell wall components contribute to pathogenicity.
Capsules - can prevent phagocytosis

When the body produces antibodies against the capsule then phagocytosis is efficient
Antigenic variation
Some pathogens alter their surface antigens - alternative genes for surface proteins - so they change by the time the host mounts a full response
Coagulases
cause clotting of fibrin in
blood - clot may prevent phagocytosis
e.g. in boils caused by Staphylococcus
Kinases
break down fibrin - dissolve
clots that are used to prevent spread
of the pathogen
- Staphylokinase has been used
therapeutically to dissolve clots
causing heart attacks
cause clotting of fibrin in
blood
Coagulases
Hylauronidase:-
breaks down hyaluronic acid - a polysaccharide that bonds cells in connective tissue - helps bacteria to spread
- causes blackening of infected area
Used with drugs to help their dispersal throughout the body
Collagenase:-
breaks down collagen in connective tissue and muscle - helps spread of bacteria
Siderophores:- help scavenge iron from
IgA proteases
- some pathogens produce proteases that can destroy these antibodies
Some pathogens alter their surface antigens - alternative genes for surface proteins - so they change by the time the host mounts a full response
Antigenic variation
an example of Antigenic variation
As each clone of Trypanosome is removed by the immune system a new clone takes its place
Describe how bacteria use the host cell's cytoskeleton to enter the cell.
use actin to move to the host cell then they Penetration into the Host Cell Cytoskeleton Invasins
Provide an example of direct damage, and compare this to toxin production.
Many bacteria cause direct cytopathic effects on host cells by growing inside cells and rupturing them. Some cause damage as they "pass through" host cells.
Most damage however is caused by toxins -poisonous substances produced by certain m/o's
Toxemia
toxins in the blood
Contrast the nature and effects of exotoxins and endotoxins
proteins produced inside bacteria and released into medium
Endotoxins derived from an outer portion of the cell wall in Gram -ve bacteria (outer membrane)
What is the portion of the polysachharide in endotoxins?
Lipid portion called Lipid A
Toxoids
(inactive toxin) injected to boost immune system
Diphtheria toxin
2 polypeptides A (Active) and B (Binding)
work together. B binds surface and promotes transport of entire protein into cell
A inhibits protein synthesis
Streptococcus pyogenes
Membrane-disrupting. Erythrogenic
Diseases Caused by Exotoxins
Clostridium botulinum
Diseases Caused by Exotoxins ..A-B toxin. Neurotoxin
Toxin produced during sporulation released late in growth
toxin binds in nerve/muscle junction and prevents transmission of impulses
C. tetani
A-B toxin. Neurotoxin
Diseases Caused by Exotoxins
binds to nerve cells in central nervous system (CNS) that normally terminate contractions
uncontrollable contractions ("lockjaw")
Vibrio cholerae
A-B toxin. Enterotoxin
Diseases Caused by Exotoxins
Staphylococcus aureus
Superantigen. Enterotoxin
Diseases Caused by Exotoxins
Using examples, describe the roles of plasmids and lysogeny in pathogenicity.
R (resistance plasmids) can carry genetic information that allow bacteria to degrade antibiotics.
In addition plasmids may encode instructions to make toxins

Lysogenic Conversion
When a virus enters the lysogenic cycle (integrates in host DNA) then it may carry extra genes that alter the host
what is a virus?
Pathogenic properties depend on access and damage to host during replication

Grow inside cells - avoid immune response - AIDS virus enters cells of the immune system
List nine cytopathic effects of viral infections.
1: Inhibition of macromolecular synthesis

2: Release of lysosome contents

3: Inclusion bodies (site of viral synthesis/assembly)

4: Formation of fused cells (Syncytium)

5: Change in cell function - e.g. when measles virus attaches to CD46 cells they reduce IL-12 production
6: Some viral infected cells produce interferon

7: Viral infections can induce antigenic changes on host cell surface

8: Changes to host chromosomes, oncogenes may be added

9: Cancer causing viruses inhibit "contact inhibition" between host cells thus promoting cancer.