Topic 11 - Mechanisms of Pathogenicity Flashcards
What are the four hurdles pathogens must over come to cause disease?
- Gain access to host through portals of entry
- Must adhere to host tissues
- Must penetrate or evade host defences
- Must damage host tissues
List the principal portals of entry
Mucous membranes (genitourinary tract, respiratory tract, gastrointestinal tract) Skin Parental route (punctures, bites,cuts etc)
List the requirements for infection
1. Gain access to host 2 Establish and increase in numbers 3.Evade the host immune system 4. Destroy/damage host tissues 5. Exit and survive to infect another host
LOOK AT DIAGRAM LINKING MECHANISMS OF PATHOGENICITY
DO IT SHITHEAD. AND WRITE IT OUT.
A bit about the parental route…?
Bypasses the stomach e.g. if the stomach’s natural acid destroy a drug, it needs to go another way to get into the body e.g. injection, cut, puncture
What is ID50?
Infectious dose for 50% of the test population
What is LD50?
Lethal dose (of a toxin) for 50% of the test population
The lower the LD50, the more…?
virulent the pathogen is
More virulent = low…?
ID50 and LD50
Less virulent = high..?.
ID50 and LD50
All pathogens have a means of attaching to host tissues after gaining entry, which is called…?
adherence
List two Adhesins/ligands. What do they bind to? And what do they form?
- Glycocalyx (helps form capsule)
- Fimbriae (thin filaments)
Bind to receptors on host cells.
Form bioflms.
How does M protein contribute to pathogenicity? (cell wall component)
Mediates attachment of the bacterium to cells of the host and helps bacterium resist phagocytosis by WBC’s
How does Opa protein contribute to pathogenicity? (cell wall component)
Helps bacterium attach to host cells cell
How does Mycolic acid contribute to pathogenicity? (cell wall component)
Resists digestion
How do bacterial capsules contribute to pathogenicity?
Prevent phagocytosis -capsule is slippery and our immune cells cannot catch them.
Bacterial capsules are …… defence
passive
Bacterial enzymes are …. defence
active
How does the bacterial enzyme Coagulase evade host immune system?
Coagulates fibrinogen. (fibrinogen is a proten produced by liver which helps stop bleeding by helping blood clots).
How does the bacterial enzyme Kinase evade host immune system?
Digests fibrin clots
How does the bacterial enzyme Hyaluronidase evade host immune system?
Hydrolyses hyaluronic acid
How does the bacterial enzyme Collagenase evade host immune system?
Hydrolyses collagen
How does the bacterial enzyme IgA protease evade host immune system?
Destroy IgA antibodies
What is antigenic variation?
Some microbes vary expression of surface proteins, thus avoiding the host’s antibodies
How does a bacteria use the host cell’s cytoskeleton to enter the cell?
Invasins - alters host actin and uses it to move from one cell to the next
Give 3 examples of direct damage?
- Disrupt host cell function
- Produce waste products
- Toxins
What is a toxin?
Poisonous substances produced by bacteria
What is toxigenicity?
Ability to produce a toxin
What is toxemia?
Presence of toxin in the host’s blood
What is a toxoid?
Inactivated toxin used in a vaccine
What is an antitoxin?
Antibodies against a specific toxin
What is an exotoxin? A bit about them?
PROTEINS PRODUCED INSIDE PATHOGENIC BACTERIA and released into surrounding medium
Antibodies produced against them are called antitoxins
Specific for a structure or function in host cell
List the different types of exotoxins and what they do
membrane disrupting toxins - Lyse host cells by making channels in plasma membrane (leukocidins, hemolysins, streptolysins)
A-B toxins - Made up of two polpeptides: active enzyme (A) and a binding component (B)
Superantigens - Provoke intense non-specific immune reaction by causing T cells to produce large amounts of cytokines
What is an endotoxin? A bit about them?
LIPID PORTION (LIPID A) OF THE LIPOPOLYSACCHERIDES IN OUTER MEMBRANE OF GRAM -VE CELL WALL BACTERIA
Released when gram -ve bacteria die and cells lyse
Cause:
Fever, inflammation, respiratory distress, decreased cardiac output etc
Compare exotoxins and endotoxins
Source: gram -ve (endo), gram +ve (exo)
Relation to microbe: outer membrane (endo), by-products of growing cell (exo)
Chemistry: Lipid A (endo), Protein (exo)
Fever?: yes (endo), no (exo)
Neutralised by antitoxin?: no (endo), yes (exo)
LD50: large (endo), small (exo)
What is the LAL assay?
Limulus Amoebocyte Lysate assay for detection of endotoxins.
How does the LAl assay work?
Uses WBC’s from horse shoe crab, which differ from human WBC’s so when mixed with endotoxins form a cloudy substance (very turbid).
The degree of turbidity is a measure of endotoxin contamination
List 9 cytopathic effects of viruses
- Halt macromolecular synthesis in host cell
- Cause host cell to release lysosome contents
- Cause inclusion bodies to form in host cell
- Fusion of infected cells to form a syncitium
- Changes in host cell function
- Induce host cells to produce interferons
- Cause antigenic changes on host cell surface
- Induce chromosomal changes in host cell
- Loss of contact inhibition in host cells
What is an interferon?
Proteins made & released by host cells in response to the presence of pathogens e.g. viruses, parasites, bacteria
What are the pathogenic properties of fungi?
- fungal waste products cause symptoms
- Chronic infections provoke allergic response
- Toxin production
- Proteases (candida)
- Capsule prevents phagocytosis
List the portals of exit?
- Respiratory tract
- Gastrointestinal tract
- Genitourinary tract
- Skin
- Blood
