5.0 Basics Flashcards
gram + will stain what colour? why?
purple - gram stain adheres to thick peptidoglycan outer layer
gram - will stain what colour? why?
pink - relatively thin peptidoglycan layer is covered by an outer membrane, so stain does not stick well
why is it important to know if a bacteria is gram + or -?
The spectrum of antibiotics which work for Gram-positives or for Gram-negatives is not the same
What do bacteria need to cause disease? (4 things)
- Interact with host surfaces: adherence, biofilms, invasion
- Avoid clearance by the host: capsule, survival in phagocytic cells
- Acquire nutrients to grow: iron acquisition
- Once established, bacteria can cause damage which contributes to the clinical manifestations of disease: toxins
what is bacterial adherence and what is its purpose? How does it work?
- Ability to associate with host surfaces
- Allows bacteria to resist mechanical clearance
- Adhesins: ligand protein
- Adhesins have cognate receptors
– Lipids, carbohydrates, proteins
– Tissue tropism
> > allow for bacterial colonization of host tissues
A vaccine designed against bacterial pili would inhibit:
a) Bacterial iron acquisition
b) Attachment of bacteria to host cells
c) Peptidoglycan production
d) Penetration of bacteria through human tissues
e) Capsular polysaccharide production
b) Attachment of bacteria to host cells
what is a biofilm? whaat does it help bacteria to do?
strategy for bacterial colonization
-Communities of microorganisms encased within an extracellular polymeric matrix and living on a surface
>biofilm confers protection against antibiotics and immune system
-Structurally complex in terms of composition (extracellular polymeric matrix) and microorganisms inhabiting them
RATIONALE: Bacteria on periphery killed, cells in the middle are protected
what is the purpose of bacterial invasion? what routes are there and how do they work?
- Allows bacteria to cross physical barriers, hide from the immune system, disseminate from the site of infection
- Paracellular route: by passage through intercellular spaces (do not invade host cells)
- Intracellular route: invade host cells
General strategy: rearrangement of actin cytoskeleton
> zipper mechanism
>trigger mechanism
what is the purpose of bacterial invasion? what routes are there and how do they work?
- Allows bacteria to cross physical barriers, hide from the immune system, disseminate from the site of infection
- Paracellular route: by passage through intercellular spaces (do not invade host cells)
- Intracellular route: invade host cells
General strategy: rearrangement of actin cytoskeleton
> zipper mechanism
>trigger mechanism
what is the zipper mechanism of bacterial invasion? how does it work?
-bacteria has adhesins along surface that connect sequentially to host receptors
-bacteria is engulfed by host membrane (actin re-arrangement)
-bacteria secrete invasins to escape the lysozome
what is the trigger mechanism of bacterial invasion of host cells? how does it work?
- Requires injection of bacterial proteins into the cytoplasm of host cell
- Type Three Secretion System (TTSS) “needles”
what are 3 strategies bacteria use to avoid clearance by the host?
-capsule
-phase variation
-survival inside phagocytes
what is the purpose of a bacterial capsule?
> Avoid clearance by the host/evasion
– Antiphagocytic
– Prevents opsonization( binding of complement and antibody to the bacterial surface)
– Many are hydrophilic (protects against desiccation)
– Composed of polysaccharides (resist desiccation)
what is the purpose of bacterial phase variation?
> Avoid clearance by the host/evasion
- Ability to switch on or off the expression of a gene product (phenotypic changes)
- Why? To save metabolic energy and reduce the risk of the host to develop immunity to a certain virulence factor
why is iron an important nutrient for many bacteria? why can this be a problem for them?
-Co-factor for many enzymes
* The problem with iron: the body is an extremely iron limiting environment. Competition with host and other bacteria
