Bacterial Cell Structure/Function Flashcards
List two functions of a capsule
- ) Adherence
- ) Immune System Avoidance
Note: Capsule is made up of DNA, protein, and polysaccharides
Explain the role of a biofilm layer
Biofilms form when the bacteria sense a correct density of their cohort, signaled by pheromones. Without the biofilm, bacteria attach poorly to surfaces and are at a greater danger of being exposed to host defenses.
List some characteristics of biofilm.
- ) Adherence
- ) Controlled release of bacteria from the biofilm
- ) Immune system avoidance
- ) Alteration of bacterial growth kinetics
- )Activation of bacterial stress and defense responses
- ) Alteration of drug pharmacokinetics (ex. Less susceptible to antibiotics)
Note: Biofilm could explain why drug therapy fails/disease recurs in some situations
Discuss how biofilm plays a role in trying to remove a bacterial infection
First treat biofilm, then treat the bacterium
Ex: Apply a drug that blocks pheromone communication among bacteria in the biofilm. This blocks cell-cell communication, and no biofilm is formed.
What is one main possible mechanism that explains the varying levels of biofilm levels in the GI tract?
What other mechanisms could be possible?
Biofilms are more prominent in the proximal colon and appendix, and levels decline moving towards the distal colon. Potentially, the interactions between biofilm and IgA differ in the colon (i.e. perhaps IgA binds biofilm better in the distal colon, so more is removed there)
Other mechanisms: enzymes are present that degrade biofilms, other causes of inflammatory response, production of toxic molecules by the host, other features of the immune system that decrease the microbial burden
What are the three types of flagellar organization? What is the clinical relevance of the flagellum?
Peritrichous (star-like)
Monotrichous (one tail)
Flphotrichous (multiple tails)
Clinical relevance:
- ) Swimming required for disease
- ) The immunological response to flagella can be a diagnostic tool (serotyping)
- ) Flagella can be organelles of attachment
What is the cap at the tip of a flagellum used for?
Adherence (via adhesin, which replaces the normal cap in some cases)
How do pili help with attachment?
They have adhesive molecules at their tips which can be switched to facilitate adherence to diverse host tissues
List the components of gram negative cell envelopes
Inner membrane, peptidoglycan, outer membrane, LPS (lipopolysaccharides)
List the components of gram positive cell envelopes
Inner membrane, peptidoglycan, teichoic acid and lipteichoic acid
Peptidoglycan layer is much thick in gram positive than gram negative
Describe the structure/components of the inner membrane of a cellular envelope
In both +/-. Molecules with very specific functions, can be peripheral, can be integral w/o spanning the membrane, or integral spanning the membrane. The inner membrane is a separate cellular compartment, containing many biochemical and transport functions, including major proteins of oxidative metabolism.
Describe the components of the peptidoglycan layer and its usefulness in treating an infection.
Strands of sugar molecules with special cross links to make a sheet. Peptidoglycan is essential for integrity of the bacterium—if lysed, the bacterium is unlikely to survive. Can be lysed by lysozyme.
Clinically, human cells do not have peptidoglycan. Drugs can be used to target that layer without incurring any harm to the host.
Describe the structure of the LPS layer in gram negative envelopes.
Lipid belayer with lipopolysaccharide embedded, very impermeable except for porins.
Porins are usual composed of 3 OmpF monomers.
Which component of the LPS is useful for diagnosis: Lipid A Toxic, Core, or O-specific side chain (variable)?
O-specific side chain
Describe the steps of the multi drug efflux system. How could this system cause adverse effects?
Drugs come in through the outer and inner member. The multidrug efflux system (a trans-envelope channel, not a porin) pumps the drugs back out of the cell.
If we are trying to kill a cell with a certain drug, this could inhibit uptake and prevent any effect from being seen in the target cells.
Additionally, clinically significant multidrug resistance is usually associated with a relatively impermeable outer membrane.