Excercise #22B (Antibiotics)

Question 1

Kirby-Bauer disk diffusion technique

o What is it?
o Be able to interpret sensitivity or resistance, using the diameter of zone of inhibition and an interpretive chart.

Answer 1

A petri plate containing Muller-Hinton Agar is inoculated with the organism then paper filters are disks impregnated with known antibiotics
Those that are sensitive to the drug are the ones that would want to be used against the organism

Question 2

What is an antibiotic? Where do they come from?

Answer 2

agent of biological origin that is used to control bacterial only
sources include: bacteria, fungi, trees, frogs

Question 3

How do they work?
o Distinguish between bacteriostatic & bactericidal antibiotics
o What parts/pathways of the bacterial cell do antibiotics target?

Answer 3

INHIBITION OF CELL WALL SYNTHESIS (Penicillin, Bacitracin)
antibiotic that prevents the bacterium from building its’s cell wall. Penicillin binds to enzymes that are used in the synthesis of peptidoglycan which is what a bacterium make their cell wall out of. If bacterium can’t make a cell wall and protect against osmosis therefore water is always rushing into the cell and without a cell wall to resist the pressure then the cell will lyse because of osmotic pressure

Question 4

How do you choose which one to use?

Answer 4

those antibiotics that have sensitivity

Question 5

What do “broad spectrum” and “narrow spectrum” mean?

Answer 5

broad spectrum: controls many different species of bacteria

narrow spectrum: controls one or a few species of bacteria

narrow is better because don’t want to kill normal flora & you know exactly the pathogen to target but it takes a long time. Also with broad spectrum it creates potential antibiotic resistance

Question 6

THE END