Microbiological Sterility Testing: Negative Control & Positive Control

Positive control vs Negative control in Microbiology

Negative Control & Positive Control: Both membrane filtration and direct inoculation of the culture media with the product under test can be used to perform the sterility test.

Suitable negative controls & positive controls are involved in either case using preparations known to be sterile.

The positive control and the negative control are the two (2) different types of test controls in microbiology. A positive control experiment entails repeating the test while employing an effective therapy.

It is a duplicate experiment that aids the analyst in verifying the accuracy of the findings of a certain test.


  • For each sterility test, there must be at least one negative control (-ve).
  • Negative control is required to guarantee that any media growth originated from the product itself.
  • Clear media should be used for any negative controls. If any turbidity or growth is visible in the negative control. It demonstrates that the sterility test’s methodologies are not perfect.
  • The environment, the users, or the equipment all have the potential to be contaminated.
  • If a repeat test needs to be run during the working session, the negative control should also be run at the same time.
  • The negative controls don’t show any signs of microbial development.


  • The paper disc used as the negative control in the aforementioned example should be soaked in sterile distilled water. There is no antibacterial substance in sterile distilled water. Bacteria can therefore proliferate unhindered. Inhibition is a sign that the experiment is flawed if it is seen in a negative control.


  • A positive control is an experimental control that produces a successful outcome. It lacks the independent variable under examination by the researcher. However, it demonstrates the desirable outcome that was anticipated given the independent variable.
  • A good indicator of how well the methods, reagents, and equipment are working without any problems is positive control (+ve). Positive control won’t result in the right result if there are experimental flaws.
  • As a result, researchers can find and improve the process without losing their time, energy, or money.
  • For positive control, three (3) sterilized three finished products shall select at random.
  • Spike around 1.0 ml of a suspension of one type of the following organisms:
  • For around two hours, the spiked products were left at room temperature.
  • Apply the sterility test technique to the tampered products as directed.
  • Apply the sterility test technique to the tampered products as directed.
  • All the medium-containing containers should be incubated for no more than 3 days for bacteria and 5 days for fungi at the recommended temperatures (20° to 25° for fungi and 30° to 35° for bacteria).
  • Within the time frame, the inoculate microorganism grows noticeably in all of the inoculate bottles.
  • If the microorganisms grow in a manner that is readily apparent, the media are acceptable.
  • The sterility test should be conducted concurrently with the positive controls test. Positive controls exhibit microbial growth.

What is the main difference between Positive and Negative Control?

Positive ControlNegative Control
DefinitionA positive control is an investigational treatment which is achieved with a known factor to get the chosen effect of the treatment.A negative control is an investigational treatment that does not result in the desired outcome of the experiment.
ImportanceA positive control is an important part of an experiment. As the inoculate microorganism grows noticeably in all of the inoculate bottlesThe negative controls don’t show any signs of microbial development
Reliability of the ExperimentPositive control increases the reliability of the experiment.Negative control also rise the reliability & confidence in the experiment.
positive control vs negative control

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