Dear Forum Members
USP in Biological Tests and Assays (Chapter 81, page 2513, Year 2006) suggests to do Bioassay by Cylinder plate assay. For assay plates I am using 20 X 100 mm petri plates. The assay cylinders are of SS and of the same dimension as described in USP.
I face the problem of not getting any zone of Inhibition around the cylinder. Only the zone of inhibition was within the cylinder.
I tried with Agar Cup method, by using 8 mm SS cork borer with Internal Diameter 6 mm, punching the agar surface making a well. This method yields good results by showing proper zone of inhibition. The antibiotics tested was Nystatin.
All the standards solutions, Media and Cultures used in both techniques were same. Both techniques carried out at same time. Please advice me on following.
1. Precautions to be taken for Cylinder Plate Method so as to get proper zone of Inhibition.
2. Can I carry out USP Bioassay of Antibiotics by using Agar Cup Method instead of Cylinder Plate Method ?
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