Lecture 21
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
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
Streptococcus pyogenes
Membrane-disrupting. Erythrogenic Diseases Caused by Exotoxins
Entry into host: - different portals
Mucous membranes Respiratory tract Gastrointestinal tract Genitourinary tract - Conjunctiva Skin Parenteral Route
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
IgA proteases
- some pathogens produce proteases that can destroy these antibodies
Vibrio cholerae
A-B toxin. Enterotoxin Diseases Caused by Exotoxins
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")
an example of Antigenic variation
As each clone of Trypanosome is removed by the immune system a new clone takes its place
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
cause clotting of fibrin in blood
Coagulases
Virulence
The extent of pathogenicity
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
Collagenase:-
breaks down collagen in connective tissue and muscle - helps spread of bacteria Siderophores:- help scavenge iron from
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
Coagulases
cause clotting of fibrin in blood - clot may prevent phagocytosis e.g. in boils caused by Staphylococcus
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.
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"
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
What is the portion of the polysachharide in endotoxins?
Lipid portion called Lipid A
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
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
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
Staphylococcus aureus
Superantigen. Enterotoxin Diseases Caused by Exotoxins
Pathogenicity
The ability to cause disease
ID50
infectious dose for 50% of inoculated hosts
LD50
lethal dose for 50% of inoculated hosts
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)
Toxemia
toxins in the blood
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
