1.4 Bacteria In The Body Flashcards
What are the “bacterial strategies” for causing infections?
Gain entry
Replicate/Disseminate
Cause damage to the host
Spread to a new victim
What are the five virulence factors required to cause disease?
Adhesin Invasin Impedin Aggressin Modulin
Adhesin
Coordinates binding of the organism to a host tissue
Invasin
Enable the organism to invade a host cell
Impedin
Enables the organism to avoid one ore more of the hosts defence mechanisms
Aggressin
Causes damage to the host
Modulin
Induces damage in the host indirectly
What types of host molecules act as receptors for bacterial adhesions?
Glycolipids Phospholipids Glycolipids Receptors (for cytokines, hormones, Ig, ECM molecules) Transmembrane proteins ECM molecules
What types of surfaces can bacteria bind to?
Mucous or other host secretions Cells and or specific receptors on cells Components of the ECM (collagen, fibronectin, laminin, heparin) Other bacteria (e.g. biofilm) Teeth Surgical implants
What bacterial factors are involved in adhesion?
Polysaccharide (capsule of +/-) Lipopolysaccharide (-ve) Lipotechoic Acid (+ve) Cell wall / peptidoglycan (+ve) Outer membrane proteins Enzymes Fimbriae/Pili Surface-layers Flagella
What are Fimbriae/Pili
Strands of protein that are use for binding to host cell. Recently discovered to be used for motility
What are bacterial surface layers?
Crystalline protein structures that are displayed on top of the peptidoglycan layer in gram + bacteria or on top of the outer membrane in gram negative bacteria.
Are bacteria able to switch their surface layer?
Yes. Body mounts an immune response to the original layer, then the bacterium switches to new layer.
What are flagella?
A long tail like structure with a motor that rotates the structure around and is used for motility. Can have one or many flagella.
How does helicobacter pylori utilise its flagella.
Can detect presence of bicarbonate (through chemotaxis) in gastric juices (more neutral pH) and will use it’s flagella to move there (more suitable environment)
What is a biofilm?
A biofilm is any group of microorganisms in which cells stick to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS).
What are the steps in biofilm development?
Early colonisers, through the use of adhesins, bind to a host surface.
Can then become associated with proteins/molcules in the vicinity
This allows for binding of other bacteria to form the film.
The bacteria in the film can then use each other for resources and can communicate with each other.
What are some consequences of host-microbe contact?
No apparent effect Invasion Induction of fluid loss Alteration of morphology Up-regulation of intercellular adhesion molecules Induction of cytokine release Apoptosis Cell death Decreased mucin synthesis Induction of matrilysin release
What two regions can bacteria replicate in?
Intracellular (invade host cells)
Extracellular (independent)
What are obligate intracellular pathogens?
Pathogens that cannot survive outside a host cell and require host products for growth.
What are facultative or optional intracellular bacteria?
Bacteria that benefit from an intracellular environment but is not required
What two invasion mechanisms are there for intracellular bacteria?
Forcibly enter
Induce changes in cell’s cytoskeleton (Shigella flexneri)
What are the consequences for the bacteria after invasion?
Adaptation to the new environment
Replication in a supportive and protected environment
Intra or intercellular spread
Through what mechanisms can bacteria disseminate?
Physical (such as trauma or abscesses)
Intra and extracellular spread
Infection of macrophages (then travel through lymphatics)
Haemotogenous spread (blood, lymphatics or needles)
Local and systemic dissemination of bacterial toxins
Give an example of intra/intercellular spread
Salmonella breaches the endothelial barrier, through M cells in peyer’s patches in the small bowel.
Then taken up by macrophages (which are unable to kill the salmonella) and then hitch a ride in the macrophages through the lymphatics.
Can also induce apoptosis in the macrophage and then enter the endothelial cell through the basolateral membrane and spread to neighboring cells that way
Define: Exotoxins
Proteins that are released in to the extracellular environment
What is a spore?
Differentiated, metabolically inert form developed from a vegetative cell (active form of the bacteria)
Describe the formation of endospores
Starts with division of the bacterial cell that splits off in to a single cell.
The cell membrane collapses at both ends and a spore septum is formed.
The mother cell then engulfs the fore-spore and the forespore is then enclosed in the mother cell in its own membrane.
A cortex develops around the forespore and is then coated in proteins and is then released from the mother cell in to the external environment.
What triggers endospore formation?
Depleted nutrients
Exposure of anaerobes to oxygen
Generally an unfavourable environment
What is germination?
The process of an endospore becoming a vegetative cell again
What are the three stages of germination?
Activation (needs an appropriate trigger)
Germination (exposure to increased nutrients)
Outgrowth (cell swelling and emergence, leaving the cortex behind)
What are the advantages of endospore formation (for the bacteria)?
Increased resistance to drying, radiation and chemicals such as acids and disinfectants
Increased heat resistance
Antibiotics are useless because they are inert
