Microbiological Test Required to product for sterilization

 

Sterility test: As per USP 71 Sterility testing required for pharmaceutical products, medical devices, Cosmetics, and food items including liquids and water samples. Sterility testing is required during the sterilization validation process as well as for routine release testing.

 

Types of USP Sterility Methods

There are three USP Sterility Methods:

·        Membrane Filtration

·        Direct Transfer (Product Immersion)

·        Product Flush/Extract/Rinsing

Membrane Filtration Method for Sterility Testing

The Membrane Filtration Sterility Test is the method of choice for many medical devices, food, cosmetics and pharmaceutical products. An appropriate use of this test is for devices that contain a preservative and are bacteriostatic and/or fungistatic under the direct transfer method. With membrane filtration, the concept is that the microorganisms will collect onto the surface of a 0.45-micron pore size filter. This filter is segmented and transferred to appropriate media. The test media are fluid thioglycolate medium (FTM) and Tryptone soy broth (TSB). FTM is selected based upon its ability to support the growth of aerobic and anaerobic microorganisms. TSB is selected based upon its ability to support a wide range of aerobic bacteria and fungi (i.e. yeasts and molds). Incubation time is 14 days.

Direct Transfer Sterility Testing

This method is the method of choice for small size and easily cut medical devices keep that save product from contaminant exposure because the device is in direct contact with test media throughout the incubation period. Viable microorganisms that may remain in or on a product after sterilization have a chance and an ideal environment within which to grow and flourish. This is true with treated microorganisms where the damage is due to a sub-lethal sterilization process. All microorganisms have biological regeneration mechanisms/strategy that can take advantage of environmental conditions supportive to growth. The direct transfer method is beneficial to these treated microorganisms. The complete product or cut into pieces immersed in test media. With large devices preferably cut the device otherwise, patient contact areas must be exposed to both growth media. Large catheters can cut into pieces or be syringe filled with test media prior to immersion keep in view aseptic condition. It is necessary to modify test method up to the appropriate modifications level due to the size and shape of test samples. The method requires that the product be transferred to separate containers of both testing media (FTM and TSB). The product is aseptically cut, or transferred whole, into the media containers. After immersion, the sample should be incubated for 14 days.

Product Flush Sterility Testing

The product flush sterility test is reserved for products that have hollow tubes such as transfusion and infusion assemblies where immersion is impractical and where the fluid pathway is labeled as sterile. This method is easy to perform and requires a modification of the FTM media for small lumen devices. The products are flushed with fluid and the eluate is directly poured into FTM and TSB.

Interpretation of Sterility Test Results

During the incubation period the media is viewed for growth. The media should be generally clear and transparent against a light source. Turbid (cloudy) areas in the media are indicative of microbial growth. Once growth is detected, the suspect vessel is tested to confirm that the turbidity present is due to microorganisms and not due to disintegration of the sample; sometimes samples produce turbidity because of particulate shedding or chemical reactions with the media. Once a suspect container has been tested, it should be returned to the incubator for the remainder of the incubation period. Samples that render the media turbid are transferred on Day 14 of the test and incubated for 14 days. Growth positive samples require further processing such as identification and storage.