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

1. 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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