3 Bacteriology Flashcards
What are the characteristics of bacteria?
- Microscopic organisms
- PROkaryotes
- Lack a true nucleus
- Generally have one chromosome
- DO NOT all look the same
How can bacteria appear?
Cocci (spherical shaped)
Rods (elongated and cylindrical)- straight, curved and spiral
Filamentous
What are the dimensions of bacteria?
Vary by species- generally about 2-3um long and 1.0 um in diameter
How can bacteria be visualised?
Colony form however it is necessary to use microscopy (light microscope or electron microscope)
Benefits of using light microscopy.
Easy to use and provided in most labs
What does oil immersion do?
Allows for a sharp image at the high magnification of x1000
What does the use of dyes to view bacteria rely on?
Cationic organic compounds combining with the negatively charged cell envelope
What steps are involved in the Gram staining process?
Bacteria is stained with Crystal Violet, then iodine (at this point Gram negative becomes decolourised), then counterstain with Safranin
How do you tell the difference between Gram-positive and Gram-negative?
Gram-positive is purple
Gram-negative is pink
What else can Gram staining be used for?
Can be used as a rough approach to check for contamination of bacterial cultures
Are bacteria unicellular or multicellular?
Unicellular
Why do bacteria have cell walls?
Solutes dissolved in the cytoplasm generate osmotic pressure, this pressure would be enough to rupture the cells
What do the bacterial cells walls do?
Gives the cell strength and rigidity and influences the cells shape
What is another name for peptidoglycan?
Murein
What is peptidoglycan composed of?
Two glucose derivatives (NAG and NAM/NAMA) and amino acids (normally 4 but ranges from 3-5
What does NAG stand for? And what is its formula?
N-acetylglucosamine
C8H15NO6
What does NAM or NAMA stand for? And what is its formula?
N-acetylmuramic acid
C11H19NO8
Name some amino acids that compose peptidoglycan.
L- and D- Alanine, D-glutamic acid, Diaminopimelic acid (DAP)/lysine
What do the components of peptidoglycan exist as? And what are they called?
A repeating structure
Glycan tetrapeptides
What is the difference between the thickness of Gram-positive and Gram-negative walls?
Gram positive ~ 20-80nm thick
Gram negative ~ 7-8nm thick
What is the composition of the Gram-positive cells wall?
~90% peptidoglycan
This includes techoic acids
What is the composition of the Gram-negative cell wall?
~5-20% peptidoglycan
LACK techoic acids
There is an additional membrane layer present
What is the additional layer present in a Gram-negative cell?
Lipopolysaccharide layer - exists as a lipid bilayer
Surrounds the peptidoglycan and cytoplasmic membrane
What does the Lipopolysaccharide layer contain?
Proteins, many of which are transmembrane
