What are chemical germicides? |

Definition

Germicides are chemical agents that, as antiseptics, kill microorganisms (bacteria, viruses, and fungi) on the surface of skin or other living tissues and as disinfectants kill microorganisms on nonliving surfaces.

Application

The following is a list of the effectiveness of germicidal chemicals against
pathogens, in descending order: lipid or medium-sized
viruses, vegetative bacteria, fungi, nonlipid or small viruses,
mycobacteria, and bacterial spores. Unlike antibiotics,
chemical germicides typically target multiple sites within the microorganism when
used at sufficiently high concentrations. For that reason, microorganisms tend to
develop tolerance to germicides more slowly than develop resistance to an
antibiotic.

Efficacy

The agent’s effectiveness depends on several factors, including its chemical composition, temperature, the amount of organic matter and microbes on the object that needs to be treated, and the amount of time the germicide is left on the object’s surface. In most cases, higher concentrations increase germicidal activity and rapidity of action, but organic matter (such as blood or fecal material) decreases activity. Germicidal strength is classified as being of high, medium, or low level activity.

Types

Chemicals used as germicides include chlorine compounds, phenolics, alcohols, aldehydes, hydrogen peroxide, iodophors, peracetic acid, and quaternary ammonium compounds. These compounds are not interchangeable because no single germicide is effective against all pathogens and because the agents vary widely according to rapidity of action.

Chlorine compounds. Hypochlorites are oxidizing agents that are widely used to disinfect floors, laundry, and water distribution systems, and to decontaminate small blood spills and medical laboratory waste. They include sodium hypochlorite (bleach), which has broad-spectrum antimicrobial activity but is less effective against fungi. Its advantages are its low cost and rapid action, but it can be corrosive to metal and is inactivated by organic matter. Although relatively nontoxic, mixing sodium hypochlorite with ammonia or acid releases a toxic chlorine or chloramine gas. Other hypochlorites include calcium hypochlorite, sodium dichloroisocyanurate, and chloramine.

Phenolics.
Phenol has been used as a germicide since the nineteenth
century, and numerous derivatives (phenolics) have developed. Phenolics are
medium-to-high level germicides used on environmental surfaces and noncritical
medical devices. Exposure to these compounds can cause hyperbilirubinemia in
infants; therefore, if used on objects such as infant bassinets and incubators,
these surfaces should be rinsed thoroughly with water and dried before use.

Alcohols. Ethyl alcohol (ethanol) and
isopropyl alcohol (isopropanol) are traditional disinfectants that are often
combined or are mixed with formaldehyde or sodium hypochlorite to increase
potency. Alcohols are medium-level germicides that are generally ineffective
against bacterial spores and fungi, and they show variable activity against
nonlipid viruses. Alcohols are used for equipment such as stethoscopes, scissors,
rubber stoppers of medication vials, and the external surfaces of medical
equipment.

Aldehydes. The two most commonly used aldehyde disinfectants are
formaldehyde and glutaraldehyde. Formaldehyde is active against all
organisms at low temperatures; however, it is a potential carcinogen and can
irritate the skin and respiratory system, which limits its use. Glutaraldehyde is
considered a high-level disinfectant with excellent germicidal activity against
all types of microorganisms. Sodium bicarbonate activates glutaraldehyde; it is
not sporicidal when acidic. It is commonly used in health care settings for
medical equipment because it is not corrosive to metal, rubber, or plastic, and it
is not inactivated by organic matter. Ortho-phthalaldehyde has a mechanism of
action similar to that of glutaraldehyde, but is more stable, appears to have
higher germicidal activity, and does not need to be activated with sodium
bicarbonate. However, if not rinsed thoroughly from medical equipment, the residue
can stain unprotected skin and mucous membranes.

Hydrogen peroxide.
Hydrogen
peroxide is a relatively stable and safe compound that exerts
medium-to-high level activity. Its mechanism of action involves the release of
hydroxyl free radicals, which damage microbial cells. In the hospital, hydrogen
peroxide-based products are used to clean equipment and instruments such as
endoscopes and ventilators.

Iodophors. Iodophors are solutions or tinctures of iodine complexed to a solubilizing agent or carrier that gradually releases free iodine. The most commonly used iodophor is povidone-iodine. Iodophors are relatively nontoxic medium-level germicides traditionally used as antiseptics. Unlike other germicides, iodophors are diluted to increase bactericidal action. The iodine rapidly penetrates microorganisms, where they appear to damage proteins and nucleic acids and inhibit their synthesis. They are also used to disinfect various types of medical equipment, but they can damage silicone tubing.

Peracetic acid. Peracetic acid is a fast-acting medium-level germicide that effectively inactivates pathogens, even in the presence of organic material. Because it does not leave a residue, it is useful for disinfecting medical instruments. The combination of peracetic acid and hydrogen peroxide is used to disinfect hemodialyzers for reuse in dialysis centers.

Quaternary ammonium compounds. Quaternary ammonium compounds are low-level disinfectants that appear to exert their effects in microorganisms by denaturing proteins, inactivating energy-producing enzymes, and disrupting the cell membrane. They are not effective against spores and tend not to be active against nonlipid viruses and mycobacteria. Accordingly, these compounds are used to disinfect noncritical surfaces such as floors, furniture, and walls.

Nonchemical germicides. Nonchemical germicides include ozone, a colorless pungent gas that is a powerful oxidizing agent. Because it leaves no residues or toxic compounds, ozone is safe for treating drinking water, food, food containers, and food storage rooms. Certain metals (such as copper, silver, and iron) exert germicidal activity and are therefore incorporated into medical devices and the environments of hospitals and laboratories. Ultraviolet light is also used to inactivate pathogens on surfaces and in the air.

Impact

A variety of germicidal agents are used as antiseptics and disinfectants in
health care settings. Germicides are effective against most emerging pathogens,
including Cryptosporidium parvum, Escherichia
coli O157:H7, avian influenza virus, and
multidrug-resistant bacteria such as vancomycin-resistant
Enterococcus and methicillin-resistant Staphylococcus
aureus. Germicides are also increasing used, and perhaps overused, in
the home. Their overuse does appear to be a factor in the development of
antibiotic-resistant pathogens.

Bibliography

Block, Seymour S., ed. Disinfection, Sterilization, and Preservation. 5th ed. Philadelphia: Lippincott Williams & Wilkins, 2001. Extensively covers the prevention of infection with disinfectants. Includes detailed descriptions of each class of disinfectant, their regulation and testing, and special applications.

Rutala, William A., et al. Centers for Disease Control and Prevention: Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008. Available at http://www.cdc.gov/hicpac/disinfection_sterilization/toc.html. This guideline discusses the use of germicides and similar products in the home, in hospitals, and in other health care settings.

Sanford, Jay P., et al. The Sanford Guide to Antimicrobial Therapy. 18th ed. Sperryville, Va.: Antimicrobial Therapy, 2010. A comprehensive guide to antimicrobial agents.

Weber, David J., et al. “Role of Hospital Surfaces in the Transmission of Emerging Health Care-Associated Pathogens: Norovirus, Clostridium difficile, and Acinetobacter Species.” American Journal of Infection Control 38 (2010): S25-S33. Explores the role of hospitals in the spread of pathogens and discusses current guidelines for surface disinfection and hand hygiene.

Westin, Debbie. Infection Prevention and Control: Theory and Practice for Healthcare Professionals. Hoboken, N.J.: John Wiley & Sons, 2008. Includes background information to support the rationale behind basic principles of infection control and how to apply them using evidence-based recommendations on infection control management.