PDA Microbiology Conference 2022 Presentation: Answers You Have Been Wanting

The following questions were posed during the 2022 PDA Microbiology Conference related to the presentation called “Pragmatic Approach for Facility Disinfectant Validation – Negotiating the Standards for Biologics, ATMPs, and Small Molecule Manufacturing.” In the Q&A session that followed, due to time constraints, the questions below could not be addressed at the conference.

The views and opinions expressed are solely those of the presenters and not necessarily of their affiliations.

Should a new facility wait a full year to do a new disinfectant efficacy test (DET) using environmental isolates, accounting for seasonal variability? This would replace initial DET using American Type Culture Collection (ATCC) organisms.

Auditors expect to see proof of the effectiveness of your disinfection program, justification of your agents used, and contact time. If you have performed an environmental monitoring performance qualification (EMPQ) for putting your facility into place, this can serve as the opportunity to select initial “isolates” for the study challenge, supplementing any “missing” microorganism types (e.g., a yeast or gram-negative rod) that you have not recovered in EMPQ with the ATCC organisms. The key is to demonstrate and justify that your disinfecting agent, disinfection process (i.e., contact time), and disinfection frequency for surfaces are sufficient to maintain the area(s) in the level of cleanliness and control required for operations. Leveraging equivalent studies already performed within a facility or performing a risk assessment to justify delaying the disinfectant study until environmental isolates are obtained would be options to consider, rather than delaying any study or evaluation for a year during the use of the facility and disinfection procedures.

Why is the DES necessary? Scientifically, shouldn’t the stool be able to stand on two legs? (It was dirty - gets clean - stays clean or does not)

The DES is demonstrating that the disinfectant being used or considered for use by a facility is suitable to reduce the population of the environmental isolate(s) and bioburden present. This is separate from a cleaning validation or cleaning method assessment, showing, through a bioburden recovery study or routine environmental monitoring, that the method and frequency of application of disinfectant maintain control over the microorganisms. If no DES is performed to challenge the agent on the surface with the microorganism being recovered, the microbiologist cannot readily narrow down whether the continued recovery of an organism is due to the cleaning method/frequency, the ineffectiveness of the disinfectant on the microorganism contaminating the surface, or another variable. The DES eliminates the variable of effectiveness, providing data that the target microorganism population can be reduced to desired levels in the presence of the disinfectant agent. The DES, used in conjunction with cleaning validation/cleaning hold studies and environmental monitoring programs, supports that the methods of disinfection, frequency of disinfection, and disinfecting agents are able to maintain required contamination control of the area and surfaces.

For a new facility, at what stage should disinfectant efficacy testing be considered?

A DES needs to be considered as early as possible, even during design and build. Part of the disinfectant efficacy study planning involves identifying surfaces that are disinfected and the agents used on the surfaces. Planning as far in advance and reasonably possible will help ensure the DES execution goes as smoothly as possible. The last part of the planning is determining if environmental isolates will be available or if representative ATCC microorganisms will be utilized. Based on the identified surfaces and any isolates that may be available from EMPQ work or baseline environmental monitoring (EM), a risk assessment can assist in determining when to begin executing the DES using either ATCC organisms or actual recovered EM isolates.

Should we be looking/depending on our EM trends to decide when and if disinfectant rotation is needed?

If EM trends indicate no suitable control of specific microorganisms or microorganism types (e.g., molds), it is prudent to evaluate the types of disinfectants currently used, the frequency of use, and their established effectiveness against the microorganisms being recovered. If spore-forming microorganisms are being recovered, evaluating when a sporicide is being used or rotated into the disinfection routine would be necessary to ensure the disinfectant agent and frequency are sufficient to maintain control of these microorganisms or at what frequency to incorporate a sporicidal disinfectant, if one is not currently used.

Human flora, such as Staphylococcus epidermidis, are the most common facility isolate, but not the most challenging to kill! Is it safe to not include it in disinfectant study?

You can provide references to literature that give data indicating the low resistance of these microbial species along with the report of your laboratory disinfectant efficacy study. Make sure the references state the level of disinfectant and contact time. Otherwise, it is prudent to have representative human flora species (similar to what you recover in your facility) in your disinfectant study. The in-situ data you generate should verify that those types of microorganisms are not routinely recovered because your disinfectant program is effective.

Would you recommend a harmonized surface testing method to be with or without mechanical action or both?

Answer: This depends on what your disinfection program entails. Validation testing without the use of mechanical action would be considered worst-case. Mechanical action is representative of manual cleaning and disinfection applications, either wiping or using a mop. Thus, a harmonized surface testing method could include mechanical action if you are showing efficacy in the specific manner in which disinfectants are applied. The most recent update to European Union GMP Annex 1: Manufacture of Sterile Medicinal Products (2022) states, “The disinfection process should be validated. Validation studies should demonstrate the suitability and effectiveness of disinfectants in the specific manner in which they are used.” 

For those disinfectants applied with manual application techniques, it is acceptable to incorporate mechanical action in your validation studies. Validation methods that incorporate mechanical action can achieve the required log reduction with shorter contact times due to the biocidal effects of the disinfectant in addition to physical removal.

Should a comparability study be an integral part of your DES when using multiple disinfectants?

A wide range of cleanroom biocides on the market have different spectrums of activity or efficacy and different modes of action. Some biocides are bactericidal, yeasticidal, or fungicidal, or they can be all three. Other biocides have sporicidal efficacy as they have the ability to destroy the endospores of spore-forming bacteria.

It is a regulatory expectation to rotate more than one biocidal agent. More than one product should be employed and should include the periodic use of a sporicidal agent at a pre-defined frequency. This is to ensure that the full spectrum of activity is achieved for all organisms likely to be encountered in the cleanroom. The United States Pharmacopeia (USP), chapter <1072> Disinfectant and Antiseptics states the following:

“It is prudent to augment the daily use of a bactericidal disinfectant with weekly (or monthly) use of a sporicidal agent. The daily application of sporicidal agents is not generally favoured because of their tendency to corrode equipment and because of the potential safety issues with chronic operator exposure. Other disinfection rotation schemes may be supported on the basis of a review of the historical environmental monitoring data.”

It is recommended that a matrix approach is taken when designing a DES. When designing the test matrix, the product(s) efficacy and how the product is used within the facility (what surface types it is applied to) should be considered. A well-designed DES will establish the log reduction observed for a known population of microorganisms on a surface for the evaluated contact time. It is important that a surface control is used to evaluate the viable population of microorganisms available to be acted on by the disinfectant at the time of application, rather than relying only on the inoculum concentration added to the coupon surface as microorganism populations will change during the drying/fixing process for the coupons. Comparing multiple disinfectants can be done to determine the one having the most action on an inoculated surface or to assess any visible differences in contact time required to give satisfactory results for the facility. The study design, whether including comparisons or not, is ultimately up to the facility and must be able to be justified.

What is your point of view on wet/dry contact time of disinfectants?

Wet contact time is measurable, and disinfectant efficacy studies are intended to show efficacy with wet surface contact time. Dry surfaces may have disinfectant residue that has some efficacy, but it is more difficult to prove efficacy on a dry surface consistently in an analytical study. The DES outlined in USP <1072> Disinfectant and Antiseptics follows a laboratory study design intended to establish whether a disinfectant would be able to suitably reduce a known microorganism population on a surface. Ensuring continued contact with the disinfectant is done by applying the disinfectant and timing with “wet” contact. Confirming a “dwell” time equivalent to the direct wet contact time used in a DES can be supported by cleaning/bioburden qualification studies in situ using the application method and contact time prescribed in the facility’s written procedure that is further supported by continued acceptable EM data.

Some organisms we see in cleanrooms cannot be killed, even with sporicides at the manufacturer’s recommended contact time. This is a challenge given that the contact time needs to be met. Some organisms cannot be killed at all. What are your thoughts for testing such organisms? 

Recovered microorganisms that seem to be less sensitive to some disinfectants or decontaminating conditions are often protected in their environment by soil or biofilm-type conditions. Determination of the source of these types of microorganisms should be a priority to reduce their entry into your facility. Conditions that warrant a longer contact time with a stronger disinfectant (e.g., sporicide) may be necessary if the origin of the microorganism cannot be mitigated. Ensuring that your contamination control method includes detergent cleaning or other means to periodically remove soils and any disinfectant residues may be necessary. A high starting population of microorganisms on surfaces may require the implementation of processes to reduce the bioburden entering areas to assist in controlling contamination levels. If these types of microorganisms are consistently present or are recovered in high levels that cannot be reduced prior to disinfection, it could indicate the need to evaluate different disinfectant application methods or additional cleaning activities for better contamination control. A risk assessment can be considered to evaluate if recoveries of these organisms are reduced to acceptable levels with a reasonable contact time compatible with operations based on the efficacy data generated from a DES.