Preparation and Quality Control of Media used for Medical Device Sterilization Validation. Blog post by Justin Kamal

August 25, 2023

In the microbiology world, culture media serves as the base of all research and discovery. These bacteria-loving recipes create the perfect environment for surviving microorganisms to grow by providing the necessary nutrients in their composition. The ingredients vary depending on the microorganism being studied but creating culture media is straightforward. However, the quality control measures associated with it are often neglected, although it is fundamental to accurate and reproducible results as per ISO 17025 accreditation requirements.

Why is quality control so important when it comes to culture media? In every sterilization validation, there are two main components which include the bacteria and the culture media. Improper media preparation can cause unsatisfactory conditions for the growth of surviving microorganisms and can lead to unreliable results.

High-quality media is required to have confidence in the accuracy and validity of a sterilization validation study and its results. There are quality control tests that must be routinely performed on all prepared media to ensure that each batch of media satisfies the requirements for a supply of high-quality in-house prepared media.

After the culture media is prepared it is essential that it is sterilized to eliminate any existing and unwanted microorganisms. This can be achieved through autoclaving at a validated cycle using heat and pressure to kill any microbial life. Along with sterilization, there are key quality control steps that can be taken by conducting the following:

Growth Promotion test which tests the medium’s ability to support the growth of the bacteria needed for the validation of the specified sterilization modality. This is done by inoculating a population of less than 100 viable organisms onto the media and monitoring for growth. The productivity ratio for a non-selective medium is at least 70% for positive strains when compared to the reference medium indicating a successful growth promotion test.

pH test is another crucial test that can be conducted, as different microorganisms thrive under different conditions. Each type of media has a different acceptable pH range that it must fall within in order to support the growth of the specific microorganism.

Visual Inspection confirms the quality of the medium as it should be clear and free from deformation, turbidity, or discoloration. Any of these irregularities can indicate contamination or poor-quality media.

Another way to ensure media is prepared to the highest quality is that when handling with microorganisms and culture media it is of the utmost importance to practice aseptic techniques – conditions and procedures used to minimize the risk of the introduction of microbial contamination. Not only is this important for controlling contamination but also for biosafety.

As the foundation of microbiological testing, maintenance, and storage under validated conditions is critical to keep its quality preserved. For agar plate storage, it is good practice to place them in a sealed package to reduce moisture loss. It should never be frozen as this can cause damage to the gel structure. All prepared culture media should be labeled with the media name, batch number, preparation, and expiration date as well as the name, or initials, of the person who prepared it prior to being placed in validated storage conditions.

As long as these steps are taken into consideration during media preparation and storage, a consistent supply of media optimum for recovery of microorganisms during sterilization cycle validation can be attained.