Classes of disinfectants and their MOA
Classes of disinfectants and their MOA
Intended learning objectives
At the end of this lecture, the student will be able to:
• Classify the different types of disinfectants with examples
• Explain the mechanism of the different classes of disinfectants
• List the applications of various disinfectants
Classes of disinfectants
• Phenols and phenolics
• Bisphenols
• Biguanides
• Halogens
• Alcohols
• Heavy Metals and Their Compounds
• Surface-Active Agents
– Soaps and Detergents
– Acid-Anionic Sanitizers
• Quaternary Ammonium Compounds
Phenols and phenolics
• Lister was the first to use phenol (carbolic acid) to control surgical infections in the operating room
• Rarely used as an antiseptic or disinfectant because it irritates the skin and has a disagreeable odour
Phenolics:
• A molecule of phenol that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combination with a soap or detergent
• Mechanism of action: Injuring lipid-containing plasma membranes, which results in leakage of cellular contents.
• Phenolics remain active in the presence of organic compounds, are stable, and persist for long periods after application.
Bisphenol
• Derivatives of phenol that contain two phenolic groups connected by a bridge
Examples:
Hexachlorophene and triclosan
Dettol
The active germ-killing ingredient in Dettol is in fact 4-chloro-3,5-dimethylphenol, also known by its non-systematic name para-chloro-meta-xylenol or PCMX,
Biguanides
• Broad spectrum of activity
• Mode of action: primarily affecting bacterial cell membranes
• Examples:
chlorhexidine – frequently used for microbial control on skin and mucous membranes
• Alexidine is a similar biguanide and is more rapid in its action
Halogens
- Iodine
• Iodine is active against all kinds of bacteria, many endospores, various fungi, and some viruses
• Iodine impairs protein synthesis and alters cell membranes
• Iodine is available as a tincture
• An iodophor is a combination of iodine and an organic molecule, from which the iodine is released slowly.
Eg. Betadine (povidone iodine)
2. Chlorine
• Used as a gas or in combination with other chemicals
• Its germicidal action is caused by the hypochlorous acid (HOCl) that forms when chlorine is added to water
Chlorine compounds used as disinfectants:
• Calcium hypochlorite (bleaching powder)
• Sodium hypochlorite
• Chloramines - combinations of chlorine and ammonia
Alcohols
• Effectively kill bacteria and fungi but not endospores and nonenveloped viruses
The mechanism of action:
• Protein denaturation
• Disrupt membranes and dissolve many lipids, including the lipid component of enveloped viruses
Ethanol
• Recommended optimum concentration of ethanol is 70%
• Pure ethanol is less effective
• Isopropanol (rubbing alcohol)
Heavy Metals and their compounds
• Heavy metals like silver, mercury, and copper can be biocidal or antiseptic
• Oligodynamic action: ability of very small amounts of heavy metals, especially silver and copper, to exert antimicrobial activity
Mechanism of action: When the metal ions combine with the sulfhydryl groups on cellular proteins, denaturation results
• Silver-impregnated dressings that slowly release silver ions have proven especially useful against antibiotic - resistant bacteria
• A combination of silver and the drug sulfadiazine, Silver sulfadiazine is used as a topical cream in the treatment of burns
• Surfacrine (silver iodide) new antimicrobial for application to surfaces, either animate or inanimate
Mercury
• Mercuric chloride: has broad spectrum of activity
• Primarily bacteriostatic
Copper in the form of copper sulfate used chiefly to destroy green algae
Zinc In the form of zinc chloride is a common ingredient in mouthwashes, and Zinc pyrithione is an ingredient in anti-dandruff shampoos
Surface-Active Agents
Soaps and Detergents
• Help in mechanical removal of microbes through scrubbing
Acid-Anionic Sanitizers
• Negatively charged portion (anion) of the molecule, reacts with the plasma membrane of microbes
• Nontoxic, non-corrosive, and fast acting
Quaternary Ammonium Compounds (Quats)
• Cationic surface active agents are most commonly used
• Their antimicrobial action is due to the cation
• Strongly bactericidal against gram positive, fungicidal, amoebicidal, and virucidal against enveloped viruses
• Mechanism of action: They probably affect the plasma membrane
• Two popular quats are benzalkonium chloride and cetylpyridinium chloride
• Strongly antimicrobial, colorless, odorless, tasteless, stable, easily diluted and nontoxic
• Organic matter interferes with their activity, and they are rapidly neutralized by soaps and anionic detergents
Summary
| Phenol and Phenolics | • Disruption of plasma membrane • Denaturation of enzymes |
| Biguanides (Chlorhexidine) | • Skin disinfection especially for surgical scrubs |
| Alcohols | • Protein denaturation and lipid dissolution |
| Halogens | • Iodine inhibits protein function and is a strong oxidizing agent • Chlorine forms the strong oxidizing agent hypochlorous acid, which alters cellular components |
| Heavy Metals and Their Compounds | • Denaturation of enzymes and other essential proteins |
| Surface· Active Agents | • Mechanic al removal of microbes through scrubbing • Enzyme inhibition • Protein denaturation • Disruption of plasma membranes |
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