During microbiological testing, negative controls are always used. Negative controls are used to verify the testing environment, analyst handling, sterile glasswares, sterile items etc. which were used during the testing. According to pharmacopoeia if there is any product failure no repeat testing is allowed unless otherwise it has been confirmed during investigation that test is invalid. Negative control must be included during every testing like product testing, water testing, environmental monitoring etc. This is the pharmacopoeial requirement. On the basis of negative control one can differentiate between product failure or invalid test by observing negative control. No growth should be there in negative control. If growth found in the negative control then that test would be considered invalid and one can repeat the test after proper investigation. So, negative control is used to check whether the environment was proper during the testing or not, is there any mishandling done by the analyst during testing or is there any problem in the sterilized glasswares or any sterilized item. That's why negative controls are very important and should be used during every testing. Negative control should be incubated till the completion of the incubation of particular test.
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