A pad assembly for use in a microorganism culture test is provided which comprises, in sterile conditions, a water-absorbing pad which is impregnated with a culture medium for culturing given microorganisms and dried, a filter member bonded to the upper surface of said water absorbing pad and having submicron pores of a size capable of substantially preventing the microorganisms from passing therethrough, and a coating of an antibiotic deactivating agent applied to the upper surface of said filter member or to the common surface between said filter member and said water-absorbing pad, as well as testing apparatus having the pad assembly mounted in a vessel. The invention eliminates the adverse effect of antibiotics in a sample to be tested which will otherwise inhibit the growth of microorganisms in the sample to adversely alter test results.