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This method is used to detect bio­chemical mutants for the determination of the spectra of antibiotic sensitivity and for the classification of fer­mentation reactions. The principle used here is, threads of velvet or chamois leather are utilised( acting as inoculating needles) the mutants can be replicated and isolated.

The replica plating procedure is very simple. 1. Place a piece of sterile velvet on a cylindrical metallic block . 2. Mount the block with velvet facing upwards. 3. Invert the petri dish that includes the lawn of bac­terial cells and press against the velvet. The projection fibres of the velvet act as inoculating needles and samples every single clone of the cells in the lawn. Next remove the petri dish and press dual phage coated agar against the vel­vet and save the original master plate. 5. This is followed by incubating the subsequent phage coated plates. 6. Colonies that appear on the phage coated plates represents mu­tant that arose during the occurrence of the cell divisions. 7. Mark the position and pick up the colony from the same location from the master plate. 9. Put this to a tube of broth and incu­bate them to increase the total cell number and spread the sample over a fresh agar plate.

Keerthi, Zeba has explained the procedure. But if you want to know more about this technique watch https://www.youtube.com/watch?v=exWgCRn0d84, https://www.youtube.com/watch?v=uYb-_hYSVYw.

Thank you so much for the explanation and the links guys.