Antimicrobial strategies in cleanroom environments
W. Curtis White, Director of Research and Development and Tracey Whitehouse, Editor, ÆGIS Environments
“Clean, clean, clean... Disinfect, disinfect, disinfect!” The mantra for microbial control in cleanroom environments may not be the only solution for controlling problem-causing microorganisms. Understanding microbial sources, life habits, routes of transmission, and antimicrobial technologies can help direct new and effective strategies for control.
The cleanroom and cleanroom-garment industries are challenged by the presence of microorganisms and the negative effects they cause. Deterioration, defacement and odors are dramatic effects that can occur as a result of the microbial contamination of woven, nonwoven, composite fabrics, and building surfaces. These cleanroom elements act as “harbors” and transfer routes, offering ideal environments for medically significant microorganisms and those that cause problems in process equipment and products. The ability to make textiles and environmental surfaces resistant to microbial contamination has advantages in many applications and market segments.
Cleanroom managers must possess a reaction plan for avoidance and control of airborne, human, and surface-sourced microbial contaminants. Strategies for control of microbes must include garments, beddings, linens, wipes, surgical fabrics, and other textiles used in cleanroom operations, construction materials and operating systems.
The term antimicrobial refers to a broad range of technologies that provide products and buildings with varying degrees of protection against microorganisms. This control reduces or eliminates the problems that microbes can cause, such as deterioration, staining, odor, product cross-contamination, and health concerns. Antimicrobials are very different in their chemical nature, mode of action, impact on people and the environment, in-plant-handling characteristics, durability on various substrates, costs, and how they interact with good and bad microorganisms. Antimicrobial strategies for bad organisms must include ensuring that nontarget organisms are not affected or that adaptation of microorganisms is not encouraged.
Antimicrobials primarily function in two ways. The conventional leaching type of antimicrobial leaves the treated surface and chemically enters or reacts with the microorganism, acting as a poison. The unconventional bound antimicrobial stays affixed to the treated surface and, on a molecular scale, physically stabs and electrocutes the microorganism on contact to kill it. Like an arrow shot from a bow or bullet shot from a gun, leaching antimicrobials are often effective, but are depleted in the process of working, wasted in random misses, or are compromised by other chemicals. Some companies incorporate leaching technologies into fibers and slow the release rate in order to extend the useful life of the antimicrobial, even adding antimicrobials to chemical binders and claiming they are “bound.” Whether leaching antimicrobials are extruded into the fiber, placed in a binder, or simply added as a finish to fabrics or finished goods, they all function in the same way. In all cases, leaching antimicrobial technologies provide a killing field or “zone of inhibition.” The zone of inhibition is the area around the treated substrate into which the antimicrobial chemistry leaches or moves, killing or inhibiting microorganisms. The killing or inhibiting action of a leaching antimicrobial is witnessed when a zone of inhibition test, such as AATCC 147, is conducted. These tests are used to measure the zone of inhibition created by a leaching antimicrobial and to clearly define the area where the antimicrobial came off the substrate and killed the microorganisms in the agar.
Figure 1. A graphical representation of the zone of inhibition test method.
As substrates treated with unconventional leaching antimicrobial are washed, treatments are easily removed. Figure 1 graphically presents a typical zone of inhibition test method. The blue area represents a textile material treated with a leaching antimicrobial. The clear zone surrounding the substrate represents the zone of inhibition and the sublethal zone is shown in gray. The area at which the zones merge is presented as the zone of adaptation. Figure 2 shows actual results of the difference between the leaching and the nonleaching antimicrobial treatments on textiles, both as first treated and then after five household launderings.
Figure 2. The difference between leaching and nonleaching antimicrobial treatments on garments.
Microbes are living organisms and, like any living organism, will take extreme measures to survive. Microorganisms can be genetically mutated and develop into “superstrains” if exposed to sublethal doses of an antimicrobial agent. Sublethal levels of antibiotics are generated in patients who discontinue taking antibiotics once their symptoms subside instead of continuing through to the end of the prescribed period. This is of serious concern to the medical community and should be a serious consideration for the textile and building products industries since they choose the antimicrobials to which they will expose their employees and the public.
As with any chemistry that migrates from the surface, a leaching antimicrobial is strongest in the reservoir, or at the source, and weakest the farther it travels from the reservoir. The outermost edge of the zone of inhibition is where the sublethal dose can be found-this is known as the zone of adaptation. This is where resistant microbes that have been produced by leaching antimicrobials are found. The ongoing challenge for leaching technologies is controlling the leach rate from the reservoir such that a lethal dose is available at the time that it is needed.
A significantly different and much more unique antimicrobial technology used in the fabrics and building construction industries does not leach but instead remains permanently affixed to the surface on which it is applied. Applied in a single stage of the wet-finish process or in water sprayed onto building surfaces, this technology encourages attachment to surfaces in two ways. First and most important is a very rapid process that coats the substrate (fabric, fiber, etc.) with the cationic species (physisorption) one molecule deep. This is an ion-exchange process by which the cation of the silane quaternary ammonium compound replaces protons from water or chemicals on the surface. The second mechanism is unique to materials such as silane quaternary ammonium compounds. In this case, the silanol allows covalent bonding to receptive surfaces to occur (chemisorption). This bonding to the substrate is then made even more durable by the silanol functionality, which enables the compounds to homopolymerize. After they have coated the surface in this manner, they become virtually irremovable, even on surfaces with which they cannot react covalently (see Fig. 3).
Figure 3. Silanol allows covalent bonding to receptive surfaces to occur.
Once polymerized, the treatment does not migrate or create a zone of inhibition, thus does not allow organisms to adapt. Because this technology stays on the substrate, it does not cross the skin barrier, does not affect normal skin bacteria, and does not cause skin irritation. It does not poison the microorganism: When a microbe contacts the organofunctional silane-treated surface of the fabric, the cell is physically ruptured by a sword-like action and then electrocuted by a positively charged nitrogen molecule. This antimicrobial technology has been verified by its use in consumer and medical goods including socks, surgical drapes, and carpets in the U.S., Asia, and other areas in the world. Buildings such as homes, hospitals, hotels, restaurants, office buildings, and schools worldwide have been treated successfully with this technology for more than twenty-five years.
Antimicrobial treatments for bacterial, fungal and mite control are proving to be popular among consumers, manufacturers and building operators. These treatments not only provide protection from microorganisms, they also add aesthetic and emotive values to a full range of products. Deterioration, defacement, odors, and “harboring” of medically significant microorganisms can occur in buildings and products where microbial contamination is present. The ability to make surfaces and nonwoven, woven, and composite fabrics resistant to microbial contamination has advantages and value in the cleanroom industry.
The garment/skin interface (see Figs. 4 and 5.) is a perfect incubator and amplification site for microorganisms. All of the key life-sustaining factors are present and optimal for growth of microorganisms. Growth in the fabric provides a ready source for microorganisms moving to the workspace.
Figure 4. Untreated fabric allows bodyborne contaminants to enter the work environment.
The cut and sew garment industry has an almost unending array of fibers, fabrics, and performance- and comfort-enhancing finishes to choose from as increasingly sophisticated garments are designed. The choice of woven, nonwoven, coated, or composite/laminate materials provides the ability to customize garments for any definable end-use, including single-use, multiple-use, and life-of-the-goods garments.
Figure 5. Fabric treated with antimicrobials can help protect the work environment from bodyborne contaminants.
When considering the world of biocontamination, garments can be part of the problem, yet could provide a useful matrix for being part of the solution. This is especially true when considering skin-sourced microorganisms or the garment as a “home” and amplification site for microorganisms.
Complementing the basic composition of garment fabrics are a variety of functional and comfort-enhancing finishes: Flame retardant, stain resistant and/or release, wicking, thermo (hot and cold) enhancing, softening, draping, alcohol resistant, autoclavable, barrier, and antimicrobial are some of the existing and growing finishes available for garments. For example, a typical garment for cleanroom use would include barrier properties to protect the work environment from bodyborne contaminants (skin scales, hair, microbes, etc.) and to protect the wearer from workspace pollutants. This same garment would also include vapor transmission properties, alcohol resistance, cleanability, meet wearer comfort and safety requirements, control electro-inductive migration, be launderable and sterilizable, and provide for bioburden/biopermeation control.
Table 1: Biocontamination control garments, matching fabric design and desirable antimicrobial technology properties1
The level of sophistication and specialization offered by a variety of quality suppliers is very high. One company, for example, provides data that lists some of the desirable and attainable properties for biocontamination-control garments (see Table 1). The addition of antimicrobial protection to the fabric further enhances the sophistication and utility of the garment, unlike conventional cleanroom fabric-thus making it a high-performance fabric.
A multifaceted approach is paramount for cleanroom biocontaminant environmental control. Not only is it essential to protect the hard surfaces within the cleanroom, but minimizing the influx of microbes through worker protection is also necessary: Garments in all kinds of manufacturing and service environments are the first line of defense between skin-sourced microorganisms and the workplace and work products. Antimicrobial treatments, chosen and used responsibly, offer the ability to extend the microbial barrier properties of garments, furnishings, equipment and building surfaces to active antimicrobial surfaces. The ability to reduce the flow-through potential and reservoir potential of microorganisms with antimicrobial-treated garments and cleanroom structural surfaces offers a new measure of protection for wearers and the products they produce. Treated building surfaces offer a powerful tool for control of microbes in active service areas and out-of-sight and out-of-mind places in cleanroom facilities.
W. Curtis White is the director of research and development for ÆGIS Environments.
Tracey Whitehouse is the editor for ÆGIS Environments.
References for Table 1
- Edwards, Daniel and Gunther Voegeli, Precision Fabrics Group, Inc. “Business Briefing,” Pharmagenerics, 2003.
- INTERGRITY 1800®, Precision Fabrics Group, Inc.
- Porometer Method
- ASTM D 96, Method B @ 50%
- AATCC Method 20
- ASTM E2140-1 (Escherichia coli)
Building component treatment after flood
The safety profile, broad-spectrum antimicrobial activity, and durable micropolymer of the silane quaternary antimicrobial allows for its use in treating environmental surfaces in buildings. The following case study has important biocontaminant-control implications for the cleanroom industry.
The Arthur G. James Cancer Center Hospital and Research Institute
The study building is a 12-story comprehensive cancer center and research institute located in Columbus, Ohio. Just prior to its opening in January 1990, a ruptured water pipe on the twelfth floor flooded the building with an estimated 500,000 gallons of water. Ceilings, walls, carpeted floors and upholstered furnishings were either wet or exposed to high humidity.
After ensuring that the building’s structural integrity had not been compromised, attention focused on restoring the microbiological quality of the building to levels consistent with its intended use, particularly in Bone Marrow Transplant and other areas where immunosuppressed patients would be housed.
Despite high-efficiency air filtration and widespread use of a chlorine-based disinfectant fog throughout the building and its ventilation system, large numbers of fungi and bacteria were retrieved from the air in all areas of the hospital. Large numbers of water-associated bacteria, such as Acinetobacter sp., as well as fungi, were retrieved from carpeting.
Prior to the flood, hospital and university researchers had designed a study protocol to investigate the effect of surface modification with silane antimicrobials on infection rates within Bone Marrow Transplant, Hematology and Oncology areas in the hospital. The flood and subsequent microbial contamination pre-empted the study. But, investigation of various antimicrobial systems for achieving sustained microbial control during the study provided an important tool for use in remediation and beyond.
All accessible interior surfaces (including carpeting, ceilings, walls, above-ceiling space, furnishings, elevator shafts, mechanical and electrical chases) were treated with the organosilicon antimicrobial 3-trimethoxysilylpropyldimethyloctadecyl ammonium chloride (ÆGIS Antimicrobial) in water in accordance with the manufacturer’s application specifications. The applications were randomly tested for uniformity and penetration throughout the treatment process.
- Pretreatment retrievals were in a range of 721-2,800 CFU/m3. Of the 209 sample sites, 122 sites (58 percent) produced 2,800 CFU/m3, the upper detection limit of the sampler.
- Post-treatment sampling during the seven months following restoration of the building produced an average of 4.1 CFU/m3 at 643 sites. Retrievals were in a range of 0-25 CFU/m3. Of the sample sites, 289 sites (45 percent) produced 0 CFU/m3; an additional 231 sites (36 percent) produced retrievals in a range of 1-5 CFU/m3.
- The second post-treatment samplings were performed in 1991 at 82 sites randomly selected by floor. The samplings produced retrievals in a range of 0-9 CFU/m3, with an average retrieval of 0.8 CFU/m3. Forty sites (48 percent) produced 0 CFU/m3.
- The final post-treatment samplings were performed in 1992 at 86 sites randomly selected by floor. The samplings produced retrievals in a range of 0-4.7 CFUs/m3, with an average retrieval of 0.4 CFU/m3. Fifty-six sites (65 percent) produced 0 CFU/m3.
- Each of the 24 Bone Marrow Transplant patient rooms was negative for microorganisms during all of the post-treatment samplings.
The facility is presently free of odor and has a new appearance unaffected by the extensive application of a surface antimicrobial. No fungal nosocomial infections were recorded in this facility over the thirty months or in a post-study check after five years. All renovations or reconstruction in the facility were strictly controlled and all newly added or modified surfaces were treated with an unconventional, bound antimicrobial for five years after the initial treatment.