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By Anne Dantz In choosing a disinfectant, cleaning managers first
need to know what microorganisms they must reduce or eliminate. Disinfecting chemicals
generally are used to reduce a specific microbial population, which may or may not result
in sterilization.
Disinfectants are classified by the specific action
they perform on different forms of microorganisms. Bactericides kill vegetative
microorganisms, sporocides destroy spores, viricides kill viruses and fungicides eliminate
fungi.
An antiseptic chemical can be safely used to
disinfect skin and mucous membrane surfaces. A bacteriostatic substance prevents the
reproduction or multiplication of bacteria without actually killing them.
Chemical agents can affect cells in a variety of
ways:
* Protein coagulation. Most of the proteins in a
cell are enzymatic, and exist in a finely dispersed state within the cell. Disinfecting
chemicals that cause these proteins to precipitate and coagulate make the cell
non-functional and it dies.
* Disruption of cell membrane. The cell membrane
acts as a selective barrier, allowing some solutions to pass through and other to be
adsorbed onto the cell wall. Substances that concentrate at the cell membrane may alter
the physical and chemical properties of the membrane, preventing its normal function. This
may result in inhibition or death of the cell.
* Removal of free sulphydryl groups. Many of the
enzyme proteins in a cell contain cysteine (an amino acid) and have side chains
terminating in sulphydryl groups. These enzymes cannot function unless the sulphydryl
groups remain free and reduced. If the sulphydryl groups are tied down -- for example, by
an oxidizing agent such as chlorine - widespread damage to the cell occurs, and death may
result.
* Chemical antagonism. Enzymes perform their
catalytic function through their affinity for specific chemical compounds normally found
within cells, referred to as their "natural substrates." If a disinfecting
compound structurally resembles a substrate in its essential aspects, the enzyme will have
an affinity for that compound.
If this affinity is strong enough, the compound
will take the place of the normal substrate of the enzyme and prevent the proper reaction
from occurring -- thereby inhibiting the reproduction of the cell.
Ethyl alcohol (ethanol) and isopropyl alcohol are
frequently used for chemical disinfection. They are mainly used as skin antiseptics and
act by "denaturing" or altering the molecular structure of bacterial proteins,
destroying the cell. Alcohols kill vegetative forms of bacteria but have no action on
spores or viruses.
Aldehydes -- such as formaldehyde-- are active
against amino organic compounds in protein molecules and are bactericidal and sporicidal,
also exerting a lethal effect on the influenza and poliomyelitis viruses.
All metallic salts in solution are germicidal to a
certain extent, depending on the concentration. In general the salts of heavy metals are
more toxic than those of lighter metals.
The salts mainly used as disinfectants are derived
from mercury, copper and silver. When used at high concentrations they function as protein
coagulants. At lower concentrations -- as they are generally used -- metallic salts belong
to the group of chemical disinfectants that combine with the free sulphydryl groups of
cell enzymes.
Chlorine has been used for many years as a
disinfectant and has generally been associated with treatment of swimming pool water and
water supplies. Chlorine gas reacts with water to form hypochlorous acid (HOCl).
Hypochlorites are salts of this acid and represent the form in which chlorine is most
commonly used. Chlorine and hypochlorites are bactericidal and act by oxidizing the cell
membrane.
Iodine is most often used as a skin disinfectant.
It combines with cell protein and is an active germicidal agent with a moderate activity
against spores. It is effective against the tubercle bacillus and many other viruses.
Phenol (an acidic compound) was the forerunner of a
wide range of phenolic compounds developed as disinfectants. The activity of phenolic
compounds against microorganisms depends upon the type of compound used. Organic matter
tends to absorb phenol and lowers the concentration available to kill microorganisms.
Phenol, a corrosive substance, is toxic to living
tissues and act on the bacterial cell by denaturing and coagulating the protein within the
cell. In low concentrations, phenol disrupts the cell wall, allowing leakage of cellular
constituents.
Exerpted from: Sterilization: Methods and Control,
Butterworth & Co. (Publishers) Ltd., New York.
Copyright National Trade Publications, Inc.
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