Class Of Disinfectants That Tolerates The Presence Of Some Organic Matter Is

Fungi Viruses

Category of Germicide




All Nonlipid Lipid





yes yes yes

High Level




yes yes yes

Intermediate Level




yes varies yes

Low Level




varies no varies

only weakly germicidal, but have a bacteriostatic action, can be used as preservatives.

Potency of Germicidal Chemical Formulations

Numerous different germicidal chemicals are marketed for medical and industrial use under a variety of trade names. Frequently, they contain more than one antimicrobial chemical as well as other chemicals such as buffers that can influence their antimicrobial activity. In the United States, the Food and Drug Administration (FDA) has the responsibility for regulating chemicals that can be used to process medical devices in order to ensure they perform as claimed. Most chemical disinfectants are considered pesticides and, as such, are regulated by the Environmental Protection Agency (EPA). To be registered with either the FDA or EPA, manufacturers of germicidal chemicals must document the potency of their products using testing procedures originally defined by the EPA. Germicides are grouped according to their potency (table 5.3):

■ Sterilants can destroy all microorganisms, including their endospores, and viruses. Destruction of endospores usually requires a 6- to 10-hour treatment. These can be used to treat heat-sensitive critical items such as scalpels.

■ High-level disinfectants destroy all viruses and vegetative microorganisms, but they do not reliably kill endospores. Most high-level disinfectants are simply sterilants used for time periods as short as 30 minutes, a time period not long enough to ensure endospore destruction. These can be used to treat semicritical items such as gastrointestinal endoscopes.

■ Intermediate-level disinfectants destroy all vegetative bacteria including mycobacteria, fungi, and most, but not all, viruses. They do not kill endospores even with prolonged exposure. They can be used to disinfect non-critical instruments such as stethoscopes.

■ Low-level disinfectants destroy fungi, vegetative bacteria except mycobacteria, and enveloped viruses. They do not kill endospores, nor do they reliably destroy naked viruses. Intermediate-level and low-level disinfectants are also called general-purpose disinfectants.

To perform properly, germicides must be used strictly according to the manufacturer's directions, especially as they relate to dilution, temperature, and the amount of time they must be in contact with the object being treated. It is extremely important that the object be thoroughly cleaned and free of organic material before the germicidal procedure is begun.

Selecting the Appropriate Germicidal Chemical

Selecting the appropriate germicide is a complex decision. Some points to consider include:

■ Toxicity. By nature, germicides are at least somewhat toxic to humans and the environment. Therefore, the benefit of disinfecting or sterilizing an item or surface must be weighed against the risks associated with using the germicidal procedure. For example, the risk of being exposed to a pathogenic microorganism in a hospital environment warrants using the most effective chemical germicides, even considering the potential risks of their use. The microbiological risks associated with typical household and office situations, however, may not justify the use of many of those same germicides.

■ Activity in the presence of organic matter. Many germicidal chemicals, such as hypochlorite, are readily inactivated by organic matter and would not be appropriate to use in situations where organic material is present. Chemicals such as phenolics, however, tolerate the presence of some organic matter.

■ Compatibility with the material being treated. Items such as electrical equipment often cannot tolerate liquid chemical germicides, and so gaseous alternatives, which will be discussed shortly, must be employed. Likewise, corrosive germicides such as hypochlorite often damage some metals and rubber.

■ Residue. Many chemical germicides leave a residue that is toxic or corrosive. If a germicide that leaves a residue is used to sterilize or disinfect an item, the item must be thoroughly rinsed to entirely remove the residue. Obviously, sterile items must be rinsed with sterile water.

■ Cost and availability. Some germicides are less expensive and more readily available than others. For

118 Chapter 5 Control of Microbial Growth example, hypochlorite can easily be purchased in the form of household bleach. On the other hand, ethylene oxide gas is not only more expensive, but it must be used in a special chamber, which influences the cost and practicality of the procedure.

■ Storage and stability. Germicides such as phenolics and iodophores are available in concentrated stock solutions, decreasing the required storage space. The stock solutions are simply diluted according to the manufacturer's instructions before use. Germicides such as glutaraldehyde and chlorine dioxide come in two-component systems that, once mixed, have a limited shelf life.

■ Environmental risk. Germicides that retain their antimicrobial activity after use can interfere with sewage treatment systems that utilize bacteria to degrade sewage. The activity of those germicides must be neutralized before disposal.

Classes of Germicidal Chemicals

Germicides are represented in a number of chemical families. Each type has characteristics that make it more or less appropriate for specific uses (table 5.4).

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