Page 9 - Quality control of pharmaceuticals (07-PA 704) practical
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IV. MICROBIOLOGICAL ASSAY OF ANTIBIOTICS BY CUP PLATE
METHODS
Aim: To carryout microbiological assay of antibiotics by cup-plate methods
The microbiological assay is based upon a comparison of the inhibition of growth of
microorganism by measured concentration of the standard preparation of the anti-biotics to be
examined with that produced by known concentration of a standard preparation of the antibiotic
having a known activity.
1. Cup plate method or cylinder plate
2. Turbidimetric or tube assay method
Cup plate method
Principle: (Agar diffusion)
When a hole is made in a seeded agar plate by a cork borer (8 mm in diameter) and the agar disc
is removed by means of a sterile loop, and the cup is filled with an antimicrobial agent, the agent
diffuses in all directions from the cup to a certain extent and inhibits the growth of the organism.
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