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Updated: Aug 4, 2026

Using the Overlay Assay to Qualitatively Measure Bacterial Production of and Sensitivity to Pneumococcal Bacteriocins
Published on: September 30, 2014
An overlay gel method for identification and isolation of bacterial beta-lactamases
Fereshteh Eftekhar1, Roya Rafiee
1Department of Biology, Faculty of Sciences, Shahid Beheshti University, Evin, Tehran, Iran. f-eftekhar@cc.sbu.ac.ir
Abstract:
A modification of the iodometric technique using an overlay gel was employed for fast identification and isolation of beta-lactamase types TEM, SHV and AmpC from non-denaturing gels. Osmotic shock preparations of the three beta-lactamases were run on polyacrylamide gels without SDS and ampicillin containing overlay gels were flooded with the iodine solution before being placed on polyacrylamide gel strips. Distinct clear bands appeared in dark blue backgrounds indicating beta-lactamase activity.
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