Cytotoxicity Testing Vs. Microbial Aerosol Challenge Testing
What is cytotoxicity?
The “cyto” in cytotoxicity stands for cell. The “toxic” component of cytotoxicity refers to something poisonous. Thus, cytotoxicity refers to molecules and compounds that are poisonous to living cells. Cytotoxins are often chemical but can also be from natural or biological sources. Cell cytotoxicity tests are in vitro cytotoxicity test methods that identify the presence of cytotoxins. Cytotoxicity test protocols vary depending upon the cytotoxicity test for biocompatibility that best fits your medical device or product. This article covers cytotoxicity testing along with microbial challenge testing.
What is a microbial challenge?
The “microbial” in microbial challenge testing refers to microorganisms. The “challenge” component of microbial challenge testing relates to exposure. In a physical challenge, you are exposing your body to physical challenges. In a microbial challenge, the sterile barrier system (packaging) of a product is exposed to (challenged by) microbes.
What are the differences between microbial challenge and cytotoxicity?
A microbial challenge is a “worst-case scenario” test that adds a microbe at a high concentration to a product, package, device, etc. For microbial aerosol challenge testing, the microorganism selected is commonly Bacillus atrophaeus.
In contrast, cytotoxicity evaluates the innate toxicity of a material, product, or other substance. Cell cytotoxicity testing doesn’t test for a “worst-case scenario.” A cytotoxicity test for biocompatibility and a microbial challenge test do have one overlapping similarity. Some microbes, such as endotoxins from gram-negative bacteria, are cytotoxic. Thus, the microbial part of a microbial challenge assesses cytotoxicity resistance if bacterial endotoxins are part of the microbial challenge. However, there is no parallel between cytotoxicity and the “challenge” component of the term microbial challenge.
What are the differences between cytotoxicity testing and microbial aerosol testing?
A cytotoxicity test for biocompatibility evaluates the biological reactivity of mammalian cells and tissues to contact with elastomeric plastics and other polymeric materials that will come in direct or indirect patient contact during medical device or product use. Cytotoxicity is significant as it evaluates the biological effects of a sample’s leachable chemicals. The types of cytotoxicity testing to perform for your medical device or product depend upon the final product, the final product’s intended use, and the materials the final product is made of and packaged within. In vitro methods of cytotoxicity testing include direct contact, agar diffusion, and elution testing. In vivo methods of cytotoxicity testing include intracutaneous injection, systemic, and implantation testing. Most medical devices and products will only require in vitro cytotoxicity testing. Reusable devices may require cytotoxicity testing for initial use and device use following recommended reprocessing. Cytotoxicity testing follows the methods outlined in USP 87 for in vitro testing and USP 88 for in vivo testing.
Microbial aerosol challenge testing is used to test vial enclosures to ensure that the vial enclosure does not allow microbes to enter the vials following the entry and exit of syringe needles during dosage draws. For microbial aerosol testing, a prepared Bacillus atrophaeus suspension is loaded to an aerosol chamber’s nebulizers, and the suspension is aerosolized overfilled vial samples and positive control vials. Like microbiology testing, microbial aerosol challenge testing is a quantitative test, and results are given in CFUs. Microbial aerosol challenge testing isn’t governed by any USP guidelines but by ASTM, PDA, and ISO guidelines. For specifics, please see the reference section at the bottom of this article.
Why are cytotoxicity testing and microbial aerosol testing important?
Cytotoxicity testing is especially critical for parenteral products or medical devices that will be inserted into the human body. Cytotoxins (such as leachable chemicals or bacterial endotoxins) within parenteral products or on medical devices can cause fever, organ failure, cancer, and (in severe cases) death for patients. Thus, cytotoxicity testing is a vital quality control step for medical devices or products.
Microbial aerosol challenge tests evaluate if external bacterial contaminants can enter a medical product’s sterile packaging system. Microbial aerosol challenge testing is essential for verifying multi-use vial enclosure systems (such as those used for vaccines and other parenteral products). All microbial aerosol challenge methods are performed in an ISO Class 5 laminar flow hood to maintain sterility during the assessment.
Microbial aerosol challenge testing ensures that the sterile or aseptic vials act as an effective microbial barrier and preserve the product’s sterility even when the outside is exposed to high concentrations of bacteria. Vials with robust microbial barriers will not have bacterial growth within the vial after aerosol challenge testing.
Summary
Overall, both cytotoxicity testing and microbial aerosol challenge testing are imperative for regulatory approval of medical devices or products and their packaging. These tests ensure that medical devices, products, manufacturing environments, and packaging are sterile and free from leachable toxins. Non-toxic and sterile products ensure that patients will not be at risk of illness following device exposure or product use. Make sure you choose a contract manufacturing organization that can support you with appropriate cytotoxicity and microbial aerosol challenge testing for your unique medical device or parenteral product needs.
MycoScience is a contract manufacturing organization specializing in Microbial Aerosol Challenge and Cytotoxicity Testing. Additionally, MycoScience provides sterile syringe and vial filling for parenteral products. MycoScience also offers Bacterial Endotoxin Testing, Preservative Efficacy Testing, Sterilization Validations, Cleaning Validations, Accelerated Aging, Bioburden Testing, Microbiology Testing, EO Residual Testing, Package Integrity Testing & Environmental Monitoring services for medical device companies and allied industries. MycoScience is an ISO 13485 certified facility.
References
United States Pharmacopeial Convention. <61> Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests. Rockville, MD, USA. 2021. (USPC <61>).
United States Pharmacopeial Convention. <62> Microbiological Examination Of Nonsterile Products: Tests For Specified Microorganisms. Rockville, MD, USA. 2021. (USP <62>).
ANSI/AAMI/ISO 11607-1, 2006/A1:2014, Packaging for terminally sterilized medical devices – Part 1: Requirements for materials, sterile barrier systems and packaging, Amendment 1.
ASTM F1608 – 16, Standard Test Method for Microbial Ranking of Porous Packaging Materials (Exposure Chamber Method).
Technical Report No. 27, Pharmaceutical Packaging integrity, 1998, PDA.
Technical Information Bulletin No. 4, Aspects of Container/closure Integrity, PDA.
