Deciding what type of disinfectant will provide the greatest efficacy for your application requires a back-to-basics approach.
By Lisa Strickland, Contec, Inc.
It might not be too dramatic to state that bacteria, viruses, fungi, and spores represent a unique, insidious, and dangerous class of contaminants: unique in that under the right conditions the contaminant population can multiply over time; insidious in that these organisms can penetrate into small openings and crevices that can persist for long periods of time; and dangerous in that they can affect human health. So these contaminants must be destroyed and/or removed to achieve the desired cleanliness and aseptic condition. That’s the role of disinfectants.
If there were only one chemical agent–i.e., one disinfectant–available to accomplish our objective, life would be simple. Unfortunately, there are many products to select from. So how do we choose? Do we base our decision on chemical structure? Personnel protection issues? Type of organisms to be destroyed? In this article, we’ll focus our attention on these questions and others.
Chemical agents that destroy microorganisms can be termed “biocides”; it is useful to categorize them in terms of potency. Sanitizers, such as alcohols, can reduce microbial contamination by as much as 99.999 percent (known as a 5-log reduction) but are ineffective against spores. Disinfectants, such as phenolics and quaternary ammonium compounds, provide 100 percent kill of vegetative bacteria, some fungi, and viruses but are also ineffective against spores. To destroy spores and achieve 100 percent kill of all microorganisms requires sterilants–aldehydes or strong oxidants such as bleach or hydrogen peroxide.*
Finding the optimal chemistry for each environment is critical to removing these complex microorganisms.
The great bug hunt
Every facility must determine the resident micro flora unique to each environment. The United States Pharmacopeia (USP) provides guidance on microbial control and testing. Specifically, USP <1072>,“Disinfectants and Antiseptics”1, and USP <797>, “Pharmaceutical Compounding–Sterile Preparations,”2 provide guidance on identifying key organisms in critical areas. Testing to determine the organisms down to the genus and species level is crucial. Identifying the type of microorganisms and the number will provide the framework on which to build a microbial control program.
Now what?
Once the microorganisms have been identified, the cleanroom operator can select the proper biocide solution for the environmental isolates and surface materials. Things to consider:
- Spores and surface sterilization. Did you discover any spores in your testing? If so, it is critical that a surface sterilant be employed.
- Personnel safety. Many biocides are eye and skin irritants, unpleasant to use, and toxic. It is very important when choosing the application mode (fogging, spraying, wiping, mopping, or immersion) to be aware that these applications can create situations that are hazardous to personnel.
- Surface contact time and material compatibility. Dwell times can vary significantly depending on the particular biocide and the specific isolate to be destroyed. The effective contact time can be determined by following the biocide’s label recommended claims or performing an in situ sanitization validation.
- Chemical disinfectant media. Several formats of chemical disinfectants are available for convenience: ready to use, concentrates, and pre-saturated wipers. Sterile solutions of biocides are commercially available as well. These solutions are aseptically sterile-filtered and/or gamma-irradiated to provide the requisite Sterility Assurance Level (SAL).
There are three important components to chemical selection: chemical effectiveness, compatibility with substrates, and safety to personnel. There are numerous biocides available that can offer a broad spectrum of activity to kill susceptible pathogenic species. Arranged alphabetically, and described more fully below, are some of the most commonly used biocides found in critical environments.3,4
Alcohols are sanitizers commonly used as a skin antiseptic. Of the available alcohols, isopropyl alcohol (IPA) is most often employed. Typical IPA concentrations vary between 60 and 85 percent. Most commonly used is 70 percent IPA, because there is enough water in the solution to allow it to effectively penetrate the pathogenic cell. A minimum contact time of 10 minutes is recommended when using IPA. The quick evaporation of IPA is a major disadvantage as a biocide, because the concentration diminishes before the recommended dwell time can be met. Conversely, because of the volatility, IPA is an excellent option to clean and dry equipment without leaving a residue.5,6
Aldehydes are powerful and aggressive disinfectants that can be used effectively as a sterilant. In concentration aldehydes are highly toxic to personnel and require long contact times for sporicidal claims. A typical aldehyde, gluteraldehyde, can require up to 10 hours of exposure at a concentration of 2 percent to kill Bacillus subtilis. Aldehydes are ideal for use on equipment that can be submerged for a period of time, under conditions that can keep irritating vapors at a minimum. Some countries have banned or restricted the use of aldehydes because of their safety profile as carcinogens.5,6
Inorganic chlorine and chlorine compounds solutions are broad-spectrum biocides that can be used as a disinfectant or a sterilant. Chlorine chemistries are inexpensive, readily available, and relatively fast acting. However, these chlorine solutions are corrosive, unstable over time, and rapidly lose activity in the presence of heavy metals found in the environment. Chlorine solutions have a high toxicity profile and must be used in well ventilated areas. Sodium hypochlorite (NaOCl), the most commonly available chlorine solution, can be found in a range of concentrations from 1 to 35 percent. Typically concentrations for sodium hypochlorite are 1 to 5 percent. A 1 percent solution provides approximately 10,000 ppm of free chlorine. As little as 5 ppm will kill vegetative bacteria. Unfortunately, to kill spores the concentration must be 10 to 1,000 times greater.5
Hydrogen peroxide is a potent biocide that is environmentally friendly because it degrades to water and oxygen. Peroxides are rendered ineffective in the presence of organic and inorganic soils, so pre-cleaning is required to achieve the desired reduction in the microbial population. Disinfection can also be achieved with lower concentrations of peroxides.6 In concentrations as low as 0.5 percent, hydrogen peroxide can be combined with other ingredients to dramatically increase its germicidal potency and cleaning performance. These chemistries are effective with short contact times and offer an excellent health and safety profile.7 Sterilization can be achieved with hydrogen peroxide concentrations of 35 to 50 percent. Peroxides used in the vapor form, vaporized hydrogen peroxide (VHP), are very effective in sporicidal cleaning at low concentrations.6
Hydrogen peroxide blended with peracetic acid (PAA) is very effective at low concentrations and degrades to acetic acid and water. It is more effective than peroxide alone because it is not inactivated in the presence of soils. When high concentrations of this biocide are present, adequate ventilation is required. The combination of hydrogen peroxide and peracetic acid is an unstable solution; therefore, concentration testing must be performed prior to application.6
Phenolics are broad range disinfectants that are used on environmental surfaces. Substituted phenolics (e.g., p- t