Page 10 - Quality control of pharmaceuticals (07-PA 704) practical

-As the concentration of the antimicrobial agent increases, the inhibition zone diameter increases.

Inhibition zone (Definition):
It is the area around the drop of the bacteriostatic agent, where the growth of the organism is
inhibited i.e. it is the clear area around the cup, whereas there is growth in the rest of the plate.
☺Advantage of cup-plate technique:
Any contaminant (different colonies) can be easily detected on agar media.
Disadvantages of cup-plate technique:
It cannot be used for non-diffusible substances as phenol.
It cannot be used for substances which precipitate proteins (since nutrient agar contains peptone).
It cannot be used for solutions of very high or very low pH (since extreme pH affects agar).
Preparation of seeded agar:
Seeded agar is nutrient agar containing 1% of the test organism i.e. 1 mL organism/ 100 mL.
The nutrient agar is autoclaved at 121°C for 15 minutes, left to cool to 45-50°C, then put the
organism and mix by rolling the test tube & pour into sterile Petri- dish.
Leave the plate to solidify.
Make 4 cups by a sterile cork borer and remove the agar discs using a sterile loop.

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