There are several ways to sterilize a product. The following information is specific to radiation sterilization. By definition a product that is sterile contains zero viable microorganisms. The sterilization process must be validated and audited to insure that each product labeled as sterile is truly free of all contaminating microorganisms that may have been present on the un-sterilized product. Sterile products are used for many product types including Medical Devices, Pharmaceuticals, and Life Science Research products. A manufacturer that chooses to make and sell sterile products must do sterility testing. There are two major governing bodies that the FDA recognizes for having developed valid guidelines for Sterility testing.
Devices such as medical devices and those used for research such as plastic consumables (pipets, pipet tips, tubes etc.) are generally tested using guidelines for Radiation Sterilization Validation set by The Association for the Advancement of Medical Instrumentation (AAMI). The purpose of these validation guidelines is to provide testing that shows a process will consistently produce sterile devices. AAMI Method 1 guidelines are based on statistics. A manufacturer can determine what statistically relevant Sterility Assurance Level (SAL) is appropriate for a product. We strongly encourage all customers interested in this type of testing to review the AAMI guidelines we reference below to verify that this validation procedure is appropriate for your product.
MO BIO Laboratories uses AAMI Method 1 (ANSI/AAMI/ISO 11137) to validate and audit the gamma radiation sterilization process for medical devices and laboratory products labeled as sterile. AAMI Method 1 is the method most commonly utilized to calculate and validate the radiation dose required to sterilize a medical device.
Drugs and pharmaceuticals, as well as raw materials can be tested using guidelines set by the United States Pharmacopeia (USP). MO BIO Laboratories, Inc. also performs USP Sterility Testing.
A validation protocol is required for the initial sterilization validation process of a particular product. The validation protocol is an outline of the requirements of the proposed validation process. This protocol includes:
Specific test procedures can be included in this protocol upon request by the customer. The sterilization validation protocol will be based on the needs of the customer as well as the particular needs of the product to be effectively sterilized. Generally, once the initial validation is successfully completed, no additional validation protocols are required for subsequent quarterly dose audits.
A sample item portion is a specialty prepared portion of the product that is used in the AAMI dose setting procedures and sterility assurance programs. Occasionally large and/or complex products cannot be tested in their entirety. Using non sterile, finished product samples, a defined portion of the device is aseptically removed and packaged for testing in the bioburden and verification dose studies. Upon evaluation, MO BIO will indicate whether or not a particular product needs a SIP procedure. For some particularly complex products, it may be necessary to disassemble or cut apart sections of the product in order to fit it into rinse fluid and media containers used in the validation test. The disassembly or cutting will be done aseptically to retain the natural bioburden.
Extraction Efficiency Test
An Extraction Efficiency test will provide a validated Bioburden recovery test method for a particular product. This is necessary to determine accurate product bioburden levels. It will show the efficiency of recovering microorganisms that are present on the product. The data collected by performing this Extraction Efficiency test is used to determine if a recovery factor needs to be applied to the results of the Bioburden portion of the validation. Insufficient recovery during bioburden tests would result in an underestimation of the true bioburden of the product and an inadequate sterilization dose could be applied to the product. If any changes are made to the product, such as the method of production or the raw materials used, then the bioburden method must be re-validated. The two most commonly used Extraction Efficiency methods to validate the Bioburden test method are Repetitive (Exhaustive) Recovery and Product Inoculation.
Repetitive (Exhaustive) Recovery MethodThe idea behind this method is that the extraction procedure on a single sample product is to be repeated until there is no significant increase in the number of recovered microorganisms. The goal is to recover all viable microorganisms by washing the sample product repeatedly. Using this method determines the efficiency of recovering the naturally occurring bioburden from a product. The counts in colony forming units (CFU) that are recovered from the first extraction are compared to the total counts recovered from all the washes to calculate a percent recovery when doing just one extraction. The percent recovery is used to calculate a correction factor which is then applied to the Bioburden test numbers for the product. In this way routine bioburden tests only require one extraction. The CFU recovered from one extraction are then simply multiplied by the correction factor to determine the total bioburden of a product. This represents the true bioburden value which is what is used to determine the needed gamma radiation sterilization dose for the particular product. These doses are determined by following the information in Table B.1 of the ANSI/AAMI/ISO 11137 guidelines.Product Inoculation MethodIn this method the product is inoculated with a known number of microorganisms in order to create an artificial bioburden and thus establish recovery efficiencies and a correction factor. The product is inoculated and then the inoculum is allowed to dry. Once the inoculum has dried, the chosen method for removing microorganisms from the particular product is applied. A ratio of the recovered titer to initial inoculum count establishes the recovery efficiency and correction factor for the product. We do not recommend The Product Inoculation Method because in many cases it is impossible to guarantee the viability of the organisms during the drying process.
This test is performed in order to verify that the irradiation dose as determined by the Bioburden portion of the Validation is effective in killing the microbial load and sterilizing the product. One hundred units of product are irradiated at a Sterility Assurance Level (SAL) of 10-2 dose, usually given in units of kGy. A SAL of 10-2 means that there is a 1 in 100 chance that a product will not be sterilized based on the microbial load of the product. This dose is determined by applying the results of the Bioburden test to the AAMI guidelines Table B.1. This table specifies which radiation dose is appropriate for the desired SAL. Once the dose is derived from the AAMI guidelines table, 100 units of the product are sent to the contract sterilizer and dosed at the specified SAL 10-2 dose. The 100 units of product are then returned to MO BIO Laboratories, Inc. for the Dose Verification Sterility Test. Each of the 100 units of product are individually placed in sterile media bottles and incubated for 14 days. At day 3, day 7 and day 14 the 100 bottles of media and product are observed for growth. Any bottle of media and product that is not sterile will show growth. These would be considered failures. Based on statistical error, no more than 2 of the 100 units tested can fail. If there are no more then 2 failures, the Bioburden and Sterility Tests are considered valid.
The Bacteriostasis / Fungistasis test is used to validate the Sterility Test (Dose Verification) procedure chosen for the product by showing that nothing in or on the product inhibits growth of microorganisms. Anything that inhibits growth can cause false negative results. The Bacteriostasis/ Fungistasis test demonstrates whether or not microorganisms present on the product will be detected by the dose verification method chosen. Using the same type and volume of media that is used for the Sterility Test, the product is inoculated with known numbers of a bacteria culture and a fungi culture. Inoculated products are then incubated. Any product that shows no growth or slowed growth is considered bacteriostatic or fungistatic. This test is necessary because some products contain bacteriostatic and/or fungistatic substances that can inhibit the growth of microorganisms. The inhibition of microorganism growth can cause a misinterpretation of the Sterility Test, which causes the product to be substantiated for an inappropriate dose setting. When inhibition is observed, additional testing is required in order to determine what method modifications are needed to overcome the inhibition. This test is performed on sterilized product before the end of the Sterility Test.
It should be understood that the final product that is sold to your customer generally receives a radiation sterilization dose that is higher than SAL 10-2. In many cases a dose of SAL 10-6 is common for final product dosing. Final product doses are based on the sterility assurance level that you determine to be appropriate for your particular product.
Once the Radiation Sterilization Validation is completed for a product, Quarterly Dose Audits are required every three months in order to ensure that the dose being used for the product continues to efficiently sterilize the product. MO BIO Laboratories, Inc. will send you a reminder notice whenever a product is due for a Quarterly Dose Audit. Upon receipt of the notice, send at least 110 units of non-sterilized product from the same lot to MO BIO Laboratories, Inc.. Ten units of the product are required for the Bioburden Test and 100 units are required for the 100 unit sterility test. The 100 units of non-sterilized product are sent to the sterilizer and dosed at the setting determined by the original Radiation Sterilization Validation and then returned for the sterility test. If no more than 2 failures occur, the product passes the Quarterly Dose Audit.
This checklist indicates the general process that a manufacturer must follow for each product they specify to require a sterility assurance program. Depending on the type and characteristics of a particular product, the steps on this list may or may not apply and other steps may be needed. Please consult your Quality Assurance Officer when creating a sterility assurance program for a particular product.
|Test||Product Units Required||Non-Sterile||Sterilized at SAL 10-2|
|Extraction Efficiency Test|
separate production lots)
|Sterility Dose Verification|
|Quarterly Dose Audit|
Download an Excel file to submit your samples for testing by MO BIO.