Negative Control & Positive Control in Microbiological Sterility Testing.


The sterility test may be carried out using the technique of membrane filtration or by direct inoculation of the culture media with the product to be examined.

Appropriate negative controls & positive controls are included in either case using preparations known to be sterile.


Negative control must be at least one for each sterility test. Negative control is necessary to ensure that any growth in the media comes from the product itself.

Media that will be used as negative control should be clear. If any growth or turbidity appears in the negative control. It shows that the techniques of the sterility test are not correct. Contamination might come from environments, the operators, or the apparatus.

Where a repeat test is to be performed during the working session the negative control should be concurrently processed with the repeat test.

Microbial growth is not found in the negative controls.


For positive control, three sterilized three finished products shall select at random.

Spike about 1ml of suspension of one type of the following organisms: Staphylococcus aureus ATCC 6538, Candida albican ATCC 10231 and Clostridium sporengenes into each of the 3 samples.

Left the spiked products at room temperature for about 2 hours.

Carryout sterility test method on the spiked products as per sterility test method.

Incubate all the containers containing medium at prescribed temperatures (20-25° for fungi & 30-35° for bacteria) for not more than 3 days for bacteria and 5 days for fungi.

The conspicuous growth of the inoculate micro-organism occurs in all the inoculate bottles within the period. The media are suitable if a clearly visible growth of the micro-organisms occurs.

The positive controls test should be done at the same time of sterility test.

Microbial growth is found in the positive controls.


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