The great majority of all medical device sterility testing is accomplished by the direct transfer method of full product immersion. Following ISO standards, this is the test Microtest usually recommends.
Each sample product is completely immersed in a container of bacteriological growth medium. If the sample product is too large to fit into the media container, it is first aseptically cut into pieces, and then fully immersed. This gives any viable organisms that may be present on or in the product following a faulty sterilization cycle — even organisms simply damaged by a sub-lethal process — an optimal environment in which to grow and proliferate.
After a 14-day incubation period, a fully-trained and validated microbiologist tests each sample to determine the presence of any bacteria, and supply a count.