Micro Exam 1 Flashcards
Classification
Based on taxonomic groups- morphological, biochemical, physiologic or genetic properties
Nomenclature
Naming the organism based on it’s characteristics
Identification
Use of classification scheme to isolate and identify organisms
2 most common shapes
Cocci- round
Bacillus- rod shaped
4 other common shapes
Coccobacillus- in between cocci and rod
Vibrio- comma
Spirochete- flexible corkscrew
Spirillum- rigid corkscrew
Groupings on a single division plane
Diplo- pair
Strepto- chain
Groupings on 2 or more planes
Staphylo- grapelike cluster
Tetras- packets of 4 cells
Sarcina- packets of 8 cells
What bacteria have sterols and why don’t more?
Most bacteria do not contain sterols because the pathway that creates sterols requires O2- only some aerobic bacteria produce it.
Cell membrane functions
- transport
- secretion
- house receptors and other proteins for chemotaxis and sensory transduction
Cell wall description and functions (4 functions)
Semi-rigid structure outside the cell membrane
- maintain cell shape
- prevent osmotic lysis
- environmental protection
- anchor for external structures
What is peptidoglyclan? What cell walls have it?
Peptidoglycan is found in virtually all cell walls.
-Repeating disaccharide (NAGs and NAMs) with tetrapeptides crosslinking the NAMs.
What can interfere with the structure or synthesis of peptidoglycan?
- antimicrobial compounds
- lysozyme
Describe how antimicrobial compounds damage cell walls?
Multiple different targets, but require actively growing cells that are synthesizing peptidoglycan
How does lysozyme damage cell walls?
Weakens the integrity of the cell wall by degrading the glycan backbone of peptidoglycan
Describe the cell wall of gram-negative bacteria.
Thin peptidoglycan layer- <10-15 sheets
Describe the cell wall of gram-positive bacteria
Thick peptidoglycan layer- >20 sheets
From outside in, the order of the layers in a gram-negative cell wall.
- Lipopolysaccharide- attached to the outer membrane
- outer membrane (with porins in the membrane, and lipoproteins into the periplasmic space)
- periplasmic space with the cell wall
- inner membrane
What are the three components of the LPS layer?
- O antigen
- Core polysaccharide
- Lipid A
What is the O antigen?
- outer portion of LPS
- linear repeating units of carbohydrates
- attachment site
- highly variable and immunogenic
What is the core polysaccharide?
- branched polysaccharide
- connects lipid A to O antigen
What is lipid A?
- lipid embedded in outer membrane
- has toxin activity
- responsible for bacterial sepsis
How does LPS cause septic shock?
- LPS can activate complement through the alternative pathway
- binds receptors causing cytokines and pro-inflammatory mediators
- leading to septic shock
Describe the outer membrane of Gram negative cell wall.
Has porins and lipoproteins
What are porins?
trimeric non-specific protein channels that controls transport substances in/out.
What are lipoproteins?
Most abundant protein of gram neg cells, stabilize and anchor the outer membrane to the peptidoglycan layer.
Describe the periplasmic space.
Space between the outer and the cell membrane, houses the thin peptidoglycan layer, transport proteins, and hydrolytic enzymes.
Gram positive cell wall description.
Thick peptidoglycan layer with one or both wall teichoic acids and lipoteichoic acids, which provide elasticity and stability.
What are WTA and LTA anchored to?
WTA: peptidoglycan
LTA: cell membrane
