Disinfectant efficacy testing must reflect actual use conditions—including dilution, contact time, and temperature—and should incorporate site-specific environmental isolates to ensure relevance and regulatory compliance.
Surface material coupons used in testing must be representative of cleanroom surfaces, free from rust or pitting and compatible with sterilization methods; improper coupon condition or processing can compromise test validity.
Microbial suspensions must be freshly prepared and appropriately concentrated, with special handling for fungi (e.g., filtration of conidial suspensions) to ensure accurate log₁₀ reduction assessments per USP <1072> standards.
Neutralization validation is essential to confirm that disinfectant activity is halted at the defined wet contact time, using methods outlined in USP <1227>, USP <61>, and EN 13697, with appropriate neutralizers selected based on active ingredients.
Immersion recovery is the preferred method for microbial recovery from coupons, and the recovery method must be validated for the specific surface and organism to ensure accurate efficacy results.
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Technical Tip
Best Practices for Disinfectant Validation in Cleanrooms
Find out best practices for test coupons, environmental monitoring and more.
2019-02-08
Disinfectants used in cleanrooms in the pharmaceutical, biotechnology, and medical device industry must be validated for intended use. This is a regulatory expectation to ensure the appropriate disinfectant is employed and microbial control is maintained in the environment. Disinfectant efficacy testing is one component of the validation, where the disinfectant is challenged for antimicrobial effectiveness in the laboratory. The following Technical Tip provides best practice recommendations for the laboratory disinfectant efficacy testing.
General Expectations
The use dilution, contact time, and exposure temperature of the disinfectant being evaluated in the study should match the actual, intended conditions of use of the disinfectant in the classified area.
It is critical, from a regulatory perspective, to evaluate site isolates from Environmental Monitoring (EM). Select isolates to use in the disinfectant efficacy testing after baseline EM conditions have been established.
These should be based on:
Frequency of occurrence
Anticipated and/or demonstrated difficulty to disinfect (e.g. Bacillus cereus)
Occurred in high numbers, when recovered
Testing Coupons
Work with manufacturers of cleanroom surfaces to procure representative classified area surface material coupons. Surfaces with well-defined specifications (e.g. 304 SS, 316L SS) may be procured from general sourcing options.
Coupon condition can have a significant impact on disinfectant efficacy testing. Coupons should:
Not have rust or pitting that is not representative of classified area surfaces
Be flat
Not be on a backing that is absorbent, shedding, or linting
Evaluate surface material coupons for heat tolerance, if processing in a moist heat sterilizer. Chemical decontamination with a sporicide, such as Spor-Klenz™ RTU Sterilant, may also be used. Improper coupon processing can negatively impact testing.
Microorganisms
Increase probability of viable vegetative bacterial cultures, by:
Incubating cultures for 18-24 hours, for most vegetative bacteria
Use suspensions within 2 hours, if stored at room temperature or within 24 hours, if stored in refrigeration
Use a spectrophotometer curve to estimate suspension Colony Forming Unit (CFU) levels, rather than to await population results
Ensure that concentration of the inoculum suspension is sufficient to demonstrate the required log10 reduction. Consider the detection limit of the recovery method and potential loss of viable cells, due to desiccation mortality. Preliminary drying studies of problematic species, such as Pseudomonas aeruginosa and Candida albicans, may prevent the need for low recovery related repeat testing.
If working with a fungal spore (conidial) suspension, filtration of the spore suspension to remove mycelial fragments, is necessary. Filtration can be achieved by using a variety of filtration materials, such sterile glass wool or a fritted filter. The presence of mycelial fragments or hyphae may shield the fungal spores from contact with the disinfectant or sporicide.
Ensure that appropriate log10 reduction acceptance criteria are used to evaluate the efficacy of disinfectants. USP <1072> Disinfectants and Antiseptics calls for:
3 log10 reduction of vegetative bacteria
2 log10 reduction of bacterial spores
These are the appropriate acceptance criteria for disinfectant efficacy testing for an aseptic manufacturing environment.
Laboratory Procedure
If storing a use dilution of a concentrated disinfectant (e.g. in a holding tank or spray bottle), it is a regulatory expectation to have data to support the internally set expiry date of the use dilution.
Take extreme caution to avoid depositing organisms outside of the intended test product exposure area. As little as 0.01 µL of inoculum not being exposed to test product can lead to a test failure.
A neutralization validation must be conducted to qualify a discrete wet contact time. USP <1227> Validation of Microbial Recovery from Pharmacopeial Items, USP <61> Microbial Examination of Nonsterile Products: Microbial Enumeration Tests, and EN 13697 Chemical Disinfectants and Antiseptics, provide potential study designs for neutralization validation. Below is a list of common chemical neutralizers for specific active ingredients.
TABLE 1. Chemical Neutralizers of Common Disinfectant Active
Chemical Neutralizer
Active Ingredient
Polysorbate (Tween)
Lecithin
Catalase
Sodium Thiosulfate
Phenolics, Quaternary Ammonium Compounds
Phenolics, Quaternary Ammonium Compounds
Hydrogen Peroxide
Sodium Hypochlorite
Evaluate appropriate culture media and incubation conditions for each organism prior to study initiation.
Recovery by immersion of the coupons is typically the most efficient recovery method. ASTM E2197 Standard Quantitative Disk Carrier Test Method and EN 13697 Chemical Disinfectants and Antiseptics provide potential immersion recovery methods. Surface coupon size can have a significant impact upon recovery method. The appropriateness of recovery methods should be evaluated with specific study surface coupons.
Additional Resources:
USP <1072> Disinfectants and Antiseptics
PDA TR 70 Fundamentals of Cleaning and Disinfection Programs for Aseptic Manufacturing Facilities
EN 13697 Chemical Disinfectants and Antiseptics
ASTM E2197 Standard Quantitative Disk Carrier Test Method
ASTM E2614 Standard Guide for Evaluation of Cleanroom Disinfectants
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Regulatory guidance and standards, such as the European Good Manufacturing Practice (EU GMP) Annex 1, are created to provide standards for requirements. While this can be helpful to strive toward best-practice, it is also important to remember that procedures need to be tailored to their facilities and processes.
There are many potential sources of residue in aseptic areas, from people to processing equipment. In most situations, residue on floors and walls pose limited risk, hence visually clean is generally the recognized target for a residue management program.
Regulatory guidance and standards, such as the European Good Manufacturing Practice (EU GMP) Annex 1, are created to provide standards for requirements. While this can be helpful to strive toward best-practice, it is also important to remember that procedures need to be tailored to their facilities and processes.
There are many potential sources of residue in aseptic areas, from people to processing equipment. In most situations, residue on floors and walls pose limited risk, hence visually clean is generally the recognized target for a residue management program.
