Microbiology 3.4 Flashcards
What technique is used to differentiate between two bacteria?
Gram staining.
What two bacteria does gram staining show?
Gram positive and gram negative.
What are the differences between gram positive and gram negative?
Gram negative- Outer membrane, lipoproteins, thin layer of peptidoglycan.
What are the similarities between gram positive and negative?
They both have periplasmic space and cytoplasmic membrane.
What dyes are used in gram staining?
Safranin- stains cells red
Crystal violet- stains cells purple
What is the procedure of gram staining?
Fixation
Crystal violet
Iodine treatment
Decolourisation
Counter stain safranin
What colour are gram negative bacteria?
Red.
What colour are gram positive bacteria?
Purple.
What shape is cocci?
Sphere.
What is an example of cocci?
Staphylococci aureus.
What shape is bacilli?
Rod.
What is an example of bacilli?
Salmonella typhi.
What happens in the lag phase?
Bacteria has to climatize to the conditions so there aren’t many live cells.
What happens in the log/ exponential phase?
There are many live cells as cells divide by binary fission and double which creates the exponential growth.
What happens during the stationary phase?
The bacteria population size mainly stays constant. This is because cells stay metabolically active and waste products begin to accumulate.
What happens during the death phase?
Living cells stop metabolic functions and begin to die leaving only few cells viable. This is because waste products grow at a maximum.
What does total count mean?
Cells that are alive and dead.
What does viable count mean?
Only cells that are living or actively growing.
What are three condition that are needed for bacteria to grow on an agar plate?
pH of 6-8, oxygen and water.
How are penicillin more effective again gram-positive bacteria than gram negative?
Gram negative bacteria has an outer membrane (lipoproteins), and gram-positive bacteria does not. This leads to the peptidoglycan in the gram-positive bacteria to weaken. This makes them less susceptible to attack by lysozyme and the lipids act as an endotoxin.
What are bacterial cell walls made up of?
A three-dimensional mesh of peptidoglycan, a polymer of amino acids and sugars.
Define gram positive bacteria.
Bacteria that have a thick peptidoglycan wall.
Why are gram positive bacteria purple?
The thick peptidoglycan wall retains crystal violet when rinsed with alcohol.
Define gram negative bacteria.
Bacteria that has a thin peptidoglycan wall with an outer lipopolysaccharide membrane.
Why are gram negative bacteria red?
When it is treated with alcohol it looses its lipopolysaccharide layer and the crystal violet washes away. The counterstain safranin stains the thin peptidoglycan layer red.
What is an obligate aerobe?
An organism that requires oxygen for metabolism.
What is an obligate anaerobe?
An organism that can only survive in environments which lack oxygen.
What is an obligate anaerobe?
An organism that can only survive in environments which lack oxygen.
What is a facultative anaerobe?
An organisms that normally respired aerobically and it is capable of switching to anaerobic respiration in the absence of oxygen.
What are aseptic techniques?
A range of techniques used to culture microorganisms under sterile conditions in order to minimise contamination.
Basic aseptic techniques:
Wipe surface with antibacterial cleaner, set up Bunsen burner nearby, flame inoculating loop and neck of bottles before use, minimise time that vessels containing bacteria are open, sterilize equipment and wear protective clothing.
What is the difference between total cell count and viable cell counts?
In a given area or volume, total cell count is the total number of cells (both living and dead) whereas a viable cell count is the total number of living cells.
What is assumed when conduction a viable cell count?
It is assumed that one cell gives rise to a single colony.
What is wrong with the one cell one colony assumption?
It does not account for clumping of cells which may result in lower estimate of number of cells.
