End-User or Third-Party Resistance Verification

Introduction

Users of biological indicators (BIs) need to have an appropriate level of knowledge of the product and its intended use prior to purchase. Once achieved, users also need to have confidence in the quality of the product received prior to placing it into use. There are two general methods for gaining confidence in product quality, 1) performing a quality audit(s) of the manufacturer to verify compliance to relevant standards/regulations, and 2) performing quality testing on each incoming BI lot. There are several important BI qualities that can be evaluated by second/third parties including, BI spore count (population), BI resistance to the process (D-value and Survival/Kill), and identity/purity of the test organism.     

This edition of Spore News will cover the various aspects of resistance verification and the options for the end-user to consider. There are several methods noted in the standards to assess the resistance of BIs, all of which require the use of a resistometer (specialized equipment not widely available to organizations other than BI manufacturers or third-party labs). The method used to evaluate a BI lot and resulting data can be verified during an audit. Once the manufacturer has received a successful audit, it is not recommended to perform second/third party resistance verification.    

Standards & References

ISO 11138-7:2019 Sterilization of health care products – 
Biological indicators – Part 7: Guidance for the selection, use and interpretation of results 

 6.1.4 When the user has established a high level of confidence in the supplier (see 6.1.3), the testing performed by the user can be minimal. At a minimum, the user should have a mechanism to ensure that a shipment of biological indicators contains all agreed-upon documentation, such as appropriate label information, packet inserts, storage and handling instructions, etc. There should be a mechanism to ensure that the BI supplier continues to maintain the expected quality standards, such as a BI supplier or BI manufacturer’s declaration of conformity to standards. If the user has not established the supplier relationship required to be ensured of consistent biological indicator performance, additional testing could be necessary until an appropriate assurance can be established that the biological indicators meet the BI manufacturer’s label claim and/or user requirements. 

6.1.5 Testing by the user, if deemed necessary, can consist of population assays and defined resistance tests such as D value or survival-kill time on samples from each new batch of  biological indicators received (see also 8.6 and Clause 11). Testing should be conducted under exact conditions specified by the manufacturer. Provided that the biological indicator manufacturer produces the based upon detailed standard specifications, i.e., the ISO 11138 series, and the user uses the biological indicator as intended by the biological indicator manufacturer, testing of the resistance characteristics by the user is considered unnecessary. 

 11.3.1 If the user chooses to verify the label claims or determine the D value of the biological indicator in or on the item to be sterilized, then they should employ the same conditions as the manufacturer. This includes employing the specific parameters for the relevant resistometer. 

 5.1.4 . . . The strain, the production method, the suspension fluid, the carrier and packaging materials and the testing conditions all affect the resistance characteristics of the finished product (see ISO 11138-1). 

 ISO 11138-1:2017 Sterilization of health care products – Biological indicators – Part 1: General  Requirements 

 6.4.3 The D value shall be within ±20% of the manufacturer’s stated value when determined by the manufacturer during the stated shelf life using the method specified by the manufacturer. Confirmation test results of the D value determined by end users or manufacturers during stated shelf life may meet the ±20% requirement, but could fall below the minimum D value specification as defined in the document. In these cases, the original D value is considered to be verified if the confirmation test results are within the ±20% range. 

United States Pharmacopoeia 2022
GENERAL CHAPTER <1229.5> BIOLOGICAL INDICATORS FOR STERILIZATION
BI Manufacturer’s Responsibility
…The BI manufacturer should include survival and kill times for the BI in their documentation and this should be verified by the end user. When a BI is used in accordance with the BI manufacturer's directions, the resistance of the BI need not be reconfirmed.

CHAPTER <55> BIOLOGICAL INDICATORS-RESISTANCE PERFORMANCE TESTS 
Survival Time and Kill Time 
…The Survival Time and Kill Time should be provided by the BI manufacture and verified by the end user. 

 Mesa Labs’ Recommendations 

1. Perform a quality audit(s) of the manufacturer to verify compliance to relevant standards/regulations. 
2. Conduct second- or third-party D-value verification studies only if a quality audit has not been conducted or if the intended use of the BI is outside of the manufacturer’s label claims. 
3. Perform resistance verification study according to the manufacturer's instructions. 
4. Utilize the Contract Studies Lab at Mesa Labs for all third-party testing.  Mesa Labs Contract Studies Lab provides a variety of testing services including biological indicator population verification and resistance (D-value, z-value, and Survival/Kill times) verification.  Since many variables make it difficult to guarantee the ability to reproduce this testing, Mesa Labs, an experienced biological indicator manufacturer, offers these services to customers to support their compliance with standard requirements. The Contract Studies Lab is ISO 13485 certified for these services and functions as an independent lab because its reporting authority is separate from Mesa’s biological indicator manufacturing. 

Additional Resources 

1. Spore News SN014 Impact of Culture Media on Biological Indicator Spore Recovery 
2. Spore News SN019 Verification Testing with Different Media is a Waste of Time 
3. Spore News SN020 Spores Do Not Have an Intrinsic D-value 
4. Spore News SN036 BI Label Claim Verification Testing Part I 
5. Spore News SN039 4 BI Label Claim Verification Testing Part II
6. ISO 18472:2018 Sterilization of health care products – Biological and chemical indicators –Test equipment 
7. Position Statement - TS-504 Separation of Authority for Reporting of Results in Contract Studies 

SN076-V1