Exam 3 Lecture 25 Flashcards
(28 cards)
Falkow’s Molecular Koch’s Postulates
- phenotype must be associated with pathogenic strain
- specific inactivation should lead to loss in virulence
- replacement of the mutated gene should restore pathogenicity
(this is kind of like find it lose it rescue)
Mechanisms of bacterial pathogenesis:
- production of toxins
- attaching and colonizing a host surface
- invasion of host tissues
- avoiding host defenses
exotoxin
protein toxins
What does a pore-forming toxin do?
Oligomerizes in the host cell membrane and forms a pore that allows cytoplasmic contents to leak out
pore forming toxin mechanism?
First present as inactive monomers in solution. When they bind to protein or lipid receptor, they recruit other monomers and this forms a pore. Or a preformed oligomer can just insert into the membrane.
What is Pore Forming Toxin structure in the membrane?
Forms beta barrel, 7 monomers
What is AB exotoxin?
A is the toxin, B is the binding portion that will bind to receptor
What kind of activity does A have of AB toxin?
ADP ribosyltransferase activity. Depending on the target protein, this transfer can either inactivate or constitutively express
Cholera toxin mechanism
AB toxin binds to receptor, A enters cell and locks G protein in on position, turning on adenylate cyclase, increases cAMP concrentation, causes ion channels to open and release ions out of cell, water follows due to osmosis
How can bacteria adhere to cell surfaces?
Express adhesins, such as pili, cell surface proteins, capsules
True or false: bacteria can adhere to any type of cell to cause infection
False. The adherence is cell type specific and hijack certain hsot receptors. This causes localized infections
impediments to colonization
compete with host microbiome; obtain nutrients; mucosal immunity
____ is the most limiting nutrient during infection
Iron
What proteins do the host make to prevent iron toxicity?
lactoferrin, transferrin, hemoglobin
Siderophores
Small molecules that bind to iron very tightly that can then be used by bacteria
Main antibody present at mucosal surface
Secretory IgA (secreted by plasma cells)
How can bacteria protect against secretory IgA?
capsule, secrete protease to cleave IgA, antigenic variation (changes type of surface protein expressed)
examples of invading host tissue
through damaged skin, maybe even hair follicle, through mucous membrane (entry through damaged epithelium, or forced invasion)
Salmonella invasion mechanism
TYPE 3 Secretion System!!!
Uses injectosome to “inject” effector molecules
What do effector molecules?
cause dramatic rearrangement of host cytoskeleton. this can cause engulfing of the bacteria to force its way in
M cell
samples environment in intestinal lumen, passes on these to macrophages on basolateral side of M cell
How does shigella avoid M cell/macrophage?
It can survive inside a macrophage, then goes back into intestinal cells to protect itself (hides)
Examples of phagocytes
Neutrophils, macrophages, dendritic cells
How can bacteria avoid being killed by phagocytes?
prevent phagocytosis; survive inside phagocytes
