Paper disk agar plate method

In 1948, Welsh et al. developed a disk plate method using paper disks soaked in milk, which were placed on agar seeded with B. subtilis spores. Whey agar was first seeded with B. subtilis spores, and paper disks (7 mm) were soaked in the milk samples. The impregnated disks were placed on the agar surface, and the plates were incubated at 37°C for 4 h, after which time the zones of inhibition were determined. The sensitivity of this test for benzylpenicillin was found to be 5 xg/l. 

Filter paper disk method Method of evaluating the antimicrobial properties of a chemical agent using filter paper disks placed on an inoculated agar plate. 

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