The Science Of Disinfectants
Why they work and what you should know to maximize their effectiveness.
We often take for granted the action of disinfectants without fully understanding how they work.
Not only are there differences in the
action of the antimicrobial ingredients, but there are also differences
depending on the concentration of chemical that is used that can impact
the action of a chemical agent or physical process.
In general, disinfectants have three
mechanisms of action or ways that they affect or kill an organism:
Cross-linking, coagulating, clumping; structure and function disruption;
and oxidizing.
Alcohol
Mechanism of action: Cross-linking, coagulating, clumping.
Like many disinfectants, alcohols are
generally considered to be non-specific antimicrobials because of their
many toxic effects.
Alcohols cause cell proteins to clump and lose their function.
Specifically, the cell membranes lose their structure and collapse, thereby killing it.
The alcohol must be diluted with water for the optimum effect, as proteins are not denatured as readily with straight alcohol.
Alcohol is also effective in inhibiting spore germination by affecting the enzymes necessary for germination.
However, once it's removed, spores can recover, so it's not considered a sporicidal.
Chlorine
Mechanism of action: Oxidizing.
Chlorine is a very common disinfectant
used in a wide variety of cleaning solutions and applications — even in
drinking water — because, even in very small amounts, it exhibits fast
bactericidal action.
Chlorine works by oxidizing proteins, lipids and carbohydrates.
Hypochlorous acid, which is a weak acid
that forms when chlorine is dissolved in water, has the most effect on
the bacterial cell, targeting some key metabolic enzymes and destroying
the organism.
Chlorine compounds have also been shown
to affect surface antigen in enveloped viruses and deoxyribonucleic acid
(DNA) as well as structural alterations in non-enveloped viruses.
Very few chemicals are considered
sporicidal; however, chlorine compounds in higher concentrations have
been shown to kill bacterial spores such as Clostridium difficile (C. diff).
Peroxygen Compounds
Mechanism of action: Oxidizing.
Both hydrogen peroxide and peracetic
acid are peroxygen compounds of great importance in infection control
because, unlike like most disinfectants, they are unaffected by the
addition of organic matter and salts.
In addition, the formation of the
hydroxyl radical, a highly reactive ion that occurs as peroxygen
compounds encounter air, is lethal to many species of bacteria because
it is a strong oxidant.
Being highly reactive, the hydroxyl radical attacks essential cell components and cell membranes, causing them to collapse.
Peroxygen compounds also kill spores by removing proteins from the spore coat, exposing its core to the lethal disinfectant.
Phenol
Mechanism of action: Cross-linking, coagulating, clumping.
Phenol and its derivatives exhibit several types of bactericidal action.
At higher concentrations, the compounds penetrate and disrupt the cell wall and make the cell proteins fall out of suspension.
One of the first things to occur is stopping essential enzymes.
The next level in the damage to the
bacteria is the loss in the membrane's ability to act as a barrier to
physical or chemical attack.
Though phenols can act at the
germination — beginning of growth — stage of bacterial spore
development, this effect is reversible, making them unsuitable as
sporicides.
Quaternary Ammonium Compounds
Mechanism of action: Structure and function disruption.
Quaternary ammonium compounds (quats)
are some of the most widely used disinfectants today because of their
broad spectrum effectiveness.
Quaternary ammonium compounds work by
denaturing the proteins of the bacterial or fungal cell, affecting the
metabolic reactions of the cell and causing vital substances to leak out
of the cell, causing death.
Because quats are a charged particle,
something to consider is "quat absorption," which is when quat molecules
are attracted and bound to anionic — negatively charged — fabric
surfaces.
For example, if a pail contains the
correct dilution of a disinfectant with an active ingredient
concentration of 800 parts per million (PPM), that concentration could
be reduced by as much as half after a cotton wipe is placed in the
solution and allowed to soak for 10 minutes.
Some ways to solve quat absorption
include using wipes made from nonreactive textiles and increasing the
solution concentration to compensate for absorption.
The Right Stuff
While each of the chemicals described
above are effective in certain applications, formulations are also made
more or less effective by their other ingredients.
In particular, surfactants are often
important ingredients to disinfectant cleaning solutions because they
achieve uniform wetting of surfaces and frequently help with cleaning.
Something to consider is that some
surfactants contain positively-charged ions, which can inactivate
negatively-charged antimicrobials like quaternary ammonium compounds by
binding with them, making them less effective against a microbe.
In contrast, low surfactant concentrations may improve the microbiocidal effect.
The reason for the improved action is
thought to be an accumulation of the agent within micelles of the
surfactant, which absorb to the microorganism's cell wall.
The active substance thus becomes enriched at the cell wall, which means that a lower dose is required for the desired effect.
While chemistry is important, even the best formulations will not be effective if applied incorrectly or inconsistently.
Other processes and interventions must also be in place to ensure that all areas are cleaned thoroughly each time.
Understanding how different chemistries work can help you evaluate which ones are best suited to your facilities' needs.
Author: Kirsten Thompson, Ecolab Healthcare
Wow. Such a great and easy article. Thanks For sharing. I wanted to know this about quarternary ammonium compounds for such a long time . Thank you again :)
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