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 the 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 (NaDCC), 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 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 healthcare 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 on 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

Various germicidal agents are used as antiseptics and disinfectants in healthcare 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 increasingly used, and perhaps overused, in the home. Their overuse is a factor in the development of antibiotic-resistant pathogens.

Bibliography

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Sanford, Jay P., et al. The Sanford Guide to Antimicrobial Therapy. 52nd ed., Antimicrobial Therapy, 2022.

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, vol. 38, no. 5, Suppl 1, 2010, pp. S25–33, doi.org/10.1016/j.ajic.2010.04.196. Accessed 20 Oct. 2024.

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