Conditions for Conducting a Sterility Test
A sterility test is done under aseptic conditions. Clean rooms that have met
the pharmacopeia specifications are used. Although aseptic conditions can be
created outside a clean room, their efficiency is low. Additionally, the
operator must observe hygiene and disinfection protocols.
Procedure
1. Sampling
A given percentage of products or devices are selected from a given batch.
2. Methodology
The pharmacopeia specifies the method to be used. The specifications give
directions on how to introduce samples into the nutrient media.
Membrane Filtration
Generally, the preferred method is membrane filtration. A membrane filter is
used for the filtration of the product. After that, it is washed and
transferred to the nutrient media.
Direct Transfer
In direct transfer, the whole product is introduced into the nutrient media. The media is then incubated. It is commonly used for medical devices.
Product Flush
A product is flushed with a special sterile fluid, fluid D. The eluate is
filtered by a membrane filter and transferred to a suitable growth media.
3. Incubation
The media is incubated for 14 days after the introduction of the test sample.
The pharmacopeia specifies the conditions of incubation.
4. Results Interpretation
The primary indicator of growth after incubation is turbidity. Any samples that
show turbidity are further examined for possible contamination.
Types of Culture Media Used
The nutrient media chosen should allow the growth of both bacterial and fungi.
Thus, a growth promotion test is done before sterility testing. A validation
test may be done to determine the inhibitory potential of a given media. Fluid
Thioglycolate media and Tryptic Soy Broth are commonly used.
In the case of fastidious microorganisms, alternative media may be used. The
media to be used in sterility testing must be free from microbial
contamination. Thus, eliminating false positives.
A sterility test is a microbiological test. It tests for the presence of
microorganisms in products sampled from a sterilized batch. The absence of
viable microorganisms denotes a state of sterility.
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