A survey of literature would reveal that there exists quite a few well recognized
‘chemical entities’
which are being used in the management and control for the usual growth of microorganisms
specifically on both
living tissue and inanimate* objects. However, a relatively much smaller segment of
chemical agents can actually accomplish complete sterility effectively. Interestingly, a large segment of
such substances only succeed either in lowering the so called
‘microbial populations’ to a much safer
levels or getting rid of the vegetative forms of the
pathogens** from the infected objects.
As we have observed under the
‘physical methods’ that there exists not even a single appropriate
method
for the effective and meaningful microbial control which may be successfully used in
every situation.
Exactly, on the same lines there occurs no one typical disinfectant which would be
perfectly suitable for most of the prevailing circumstances.
In order to have a better understanding of the various aspects of the
‘chemical methods of
microbial control’
, we may extensively categorize them under the following three heads :
(
a) Effective Disinfection — Fundamentals,
(
b) Disinfectant — Critical Evaluation, and
(
c) Variants — In Disinfectants.
The aforesaid
three classes shall now be discussed explicity in the sections that follows :
Effective Disinfection—Fundamentals
In order to critically select a
disinfectant*** which must serve as an effective agent for complete
sterilization one should bear in mind the following
cardinal factors, namely :
(1) The concentration of a
distinfectant actually determines its action (which is usually stated onthe ‘label’ clearly).
(2)
Disinfectant should be diluted strictly according to the directives given on the ‘label’ by its
manufacturer.
(3) Diluted solutions (very weak) may serve as a
bacteriostatic rather than a bactericidal.
(4) Nature of the material to be disinfected must be taken into account.
Examples :
A few typical examples are :
(
a) Organic Substances — may directly or indirectly interfere with the specific characteristic
action of the disinfectant.
(
b) pH — of the medium frequently exerts a considerable effect upon the disinfectant’s
inherent activity profile.
(5)
Accessibility to Microbes. The ease and convenience with which the disinfectant is capable
of gaining an access to the prevailing microbes poses a vital consideration. Thus, an area
to be treated may require to be
scrubbed, and rinsed subsequently just prior to the actual
application of the
disinfectant. If need be, the disinfectant must be left in contact with the
‘affected surface’
for many hours.
(6)
Temperature. Higher the temperature used for the actual application of the ‘disinfectant’,
the higher would be its effectiveness or versatility.
Disinfectant—Critical Evaluation
The critical evaluation of the
disinfectants may be accomplished adopting any one of the following
two
techniques, namely :
(
a) Use-Dilution Tests, and
(
b) Filter-Paper Method.
Use-Dilution Tests
It is, however, pertinent to state here that there is an absolute necessity to cause an effective
evaluation of the various
disinfectants and antiseptics commonly used.
Phenol-Coefficient Test :
It has been duly employed as the ‘standard test’, that particularly
compared the activity of a
‘given disinfectant’ with that of ‘phenol’ (as a standard).
AOAC* Method :
The AOAC dilution method is the standard currently being employed for
the evaluation of
disinfectants. Methodology — Three strains of microorganisms are usually employed
in the
AOAC-method, such as : Salmonella choleraesuis, Staphylococcus aureus, and Pseudomonas
aeruginosa.
The various steps involved are as follows :
(1) To carry out a
use-dilution test, the metal-carrier rings are duly dipped into the standard
cultures
of the test organism adequately grown in a liquid media—removed carefully–
dried at 37°C for a short duration.
(2) Resulting
‘dried cultures’ are subsequently placed in contact with a solution of the disinfectant
at a concentration specified by its manufacturer, and left there for a duration of 10
minutes at 20°C.
(3) Consequently, the carrier rings are duly transferred to a medium which would allow the
growth of any surviving microorganisms.
(4)
Result — The actual effectiveness of the disinfectant may be estimated by the residual
number of cultures.
Filter Paper Method
The
filter paper method is commonly used in the efficacious evaluation of a ‘chemical agent’
as a
disinfectant in teaching practice in laboratories. A small disk of filter paper (preferably ‘Whatman’
Grade) is duly soaked in a solution of the
‘chemical agent’, and placed aseptically on the surface of an
agar-plate
which has been previously inoculated and incubated duly with a pure test organism. The
effectiveness of the
‘chemical agent’ under investigation will be exhibited by a clear zone (known as
the
zone of inhibition) designating precisely the inhibition of growth just around the disk.
Disinfectant Variants
A good number of the
disinfectant variants are being used extensively based on their individual
merits and superb characteristic features, such as :
(
i) Alcohols (ii) Aldehydes,
(
iii) Chlorohexidine, (iv) Gaseous chemosterilizers,
(
v) Heavy Metals and Derivatives, (vi) Halogens,
(
vii) Organic Acid and Derivatives, (viii) Oxidizing Agents,
(
ix) Phenol and Phenolics (x) Quaternary Ammonium Compounds (QUATS), and
(
xi) Surface-Active Agents.
The aforesaid
disinfectant variants shall now be treated individually with appropriate typical
examples in the sections that follows :
Alcohols
It has been duly observed and established that
alcohols specifically exert a bactricidal and fungicidal
action quite effectively. However, they fail to cause any noticeable action upon the
endospores
and the
nonenveloped viruses.
Mechanisms of action :
Alcohols invariably display their activity as a disinfectant due to the
protein denaturation
of the bacteria. Besides, they may also cause disinfectant action based on the
following
two mechanisms, namely :
(
a) disruption of tissue membranes, and
(
b) dissolution of several lipids* (fats).
Advantages :
There are as stated under :
(
i) They usually exert their action upon the microbes due to protein denaturation—evaporating
readily—and leaving virtually no residue at all.
(
ii) Degermination (or swabbing) of the skin-surface before an injection (IM or IV), the major
component of the
microbial control activity is simply provided by wiping out the microorganismsalong with the possible presence of the dirt.
Demerit :
The main demerit of alcohols as ‘antiseptics’ when applied to the exposed wounds
being their ability to cause immediate coagulation of a layer of protein beneath which the
organisms do have a tendency to grow and multiply.
Examples :
The Two most frequently employed alcohols are, namely :
(1)
Ethanol [H5C2–OH]. The usual recommended optimal strength (concentration) of ethanol
is
70% (v/v) ; however, varying concentrations between 60–95% (v/v) appear to cause bactericidal/
fungicidal effect quite rapidly. Interestingly,
pure ethanol [> 98% (v/v)] is found
to be amazingly less effective in comparison to the corresponding aqueous ethanolic solutions
by virtue of the fact that the phenomenon of denaturation essentially requires water.
(2)
Isopropanol [(H3C)2CHOH] [Syn. : Rubbing Alcohol] — is observed to be definitely
superior to ethanol
as an antiseptic as well as disinfectant. Besides, it is available more
conveniently, less volatile in nature (than ethanol), and less expensive.
Common Feature :
Both ethanol and isopropanol are remarkably and distinctly employed to
augment (or potentiate) the overall effectiveness of certain other
chemical substances.
Examples :
Following are two typical examples, namely :(a) Aqueous Solution of ZephiranTM — is found to kill almost 40% of the prevailing population
(
b) Tincture of ZephiranTM — is observed to kill nearly 85% of the test organism in just two
minutes.
Aldehydes
In general, the
aldehydes are found to be the most effective antimicrobial agents (disinfectants).
There are
two most glaring examples, such as :
(
a) Formaldehyde — It invariably causes inactivation of the proteins by forming
the
most critical covalent cross-linkages together with a plethora of ‘organic functional moieties’ on
the proteins
viz., —NH2, —OH, —COOH, and —SH.
Important Points — Formaldehyde gas
is found :
(
i) to exert an excellent disinfectant action.
(
ii) Formalin (i.e., a 37% aqueous solution of ‘formaldehyde gas’) was previously employed to
embalm dead bodies, to preserve biological specimens, and also to cause inactivation of
microbes andviruses in vaccines.
(
b) Tincture of ZephiranTM — is observed to kill nearly 85% of the test organism in just two
minutes.
Aldehydes
In general, the
aldehydes are found to be the most effective antimicrobial agents (disinfectants).
There are
two most glaring examples, such as :
(
a) Formaldehyde — It invariably causes inactivation of the proteins by forming
the
most critical covalent cross-linkages together with a plethora of ‘organic functional moieties’ on
the proteins
viz., —NH2, —OH, —COOH, and —SH.
Important Points — Formaldehyde gas
is found :
(
i) to exert an excellent disinfectant action.
(
ii) Formalin (i.e., a 37% aqueous solution of ‘formaldehyde gas’) was previously employed to
embalm dead bodies, to preserve biological specimens, and also to cause inactivation of
microbes andviruses in vaccines.
(
b) Glutaraldehyde [H⎯C⎯CH ⎯CH ⎯CH ⎯ ⎯ ] 2 2 2 C H
O O
[
Syn. : Cidex ; Glutarol, Sonacide ;
Verutal ;]
— It represents a chemical entity relative to formaldehyde which being less irritating and
definitely has an edge over the latter (formaldehyde).
Advantages :
These are as given under :
(
i) In the sterilization of various hospital equipments, instruments, including the respiratorytherapy
assembly.
(
ii) As CidexTM — i.e., a 2% (w/v) aqueous solution is usually employed as a bactericidal,
virucidal,
and tuberculocidal in about 10 minutes ; whereas as a sporocidal within a range of 3–10 hours.
(
iii) Glutaraldehyde enjoys the wide-spread recognition and reputation of being the only liquidchemical disinfectant which may be regarded as a possible sterilant (or sterilizing agent).Chlorohexidine
Obviously,
chlorohexidine is not a phenol but its chemical structure
and uses are very much identical to those of
hexachlorophene.
It is abundantly used for the disinfection of mucous membranes
as well as skin surfaces.
Merits :
(
i) An admixture with either alcohol (H5C2–OH) or detergent (surface-active agent) its usage
has been justifiably extended to
surgical hand scrubs and in such patients requiring pre-operative
skin preparations.
Mechanism :
The probable mechanism of action of chlorhexidine are as follows :
(
a) due to its distinctly strong affinity for getting adequately bound either to the skin or mucous
membranes,
thereby producing its low toxicity.
(
b) its cidal effect (i.e., killing effect) is virtually related to the actual damage it renders to the
plasma membrane.
Advantages
—Chlorhexidine is found to be advantageous in two particular instances, namely :
(
i) Effective against most vegetative microorganisms, but certainly is not sporicidal in nature,
and
(
ii) Certain enveloped (i.e., lipophilic) types of viruses are affected exclusively.
Gaseous Chemosterilizers
Gaseous chemosterilizers
may be defined as—‘chemicals that specificallysterilize in a closed environment.’*
Example :
The typical example being Ethylene oxide.
Mechanism :
The most probable mechanism of action of ethylene oxide solely depends upon its
inherent ability to cause
‘denaturation of proteins’. In fact, the labile H-atoms strategically attached
to the proteins
viz., —OH, —SH, or —COOH are critically replaced by the available alkyl moieties
(alkylation),
for instance : —H2C—CH2—OH.
Advantages—
These are as stated below :
(1)
Ethylene oxide practically kills all microorganisms besides the endospores ; however, it
may require a perceptionally lengthy exposure ranging between 4–18 hours.*
(2) It has an extremely high degree of penetrating power to such an extent that it was specifically
selected for the complete
sterilization of spacecraft despached to land on the Moon plus
certain other
planets.
Heavy Metals and Derivatives
A plethora of
heavy metals and their corresponding derivatives viz., Hg, HgCl2, Cu, CuSO4,
Ag, AgNO
3, Zn, ZnCl2 find extensive usages as germicidal and antiseptic agents.
Mechanism
— Oligodynamic action refers to the precise ability of relatively smaller quantum
of heavy metals
viz., Ag and Cu, to predominantly exert antimicrobial activity. In reality, the respective
metal ions (
e.g., Ag+ and Cu2+) categorically combine with the specific—SH moieties critically located
on the
‘cellular proteins’ thereby causing denaturation ultimately.
Examples :
A few typical examples are cited below :
(
a) Ag in AgNO3 1% (w/v) Solution : It was a mandatory practice earlier to treat the eyes of the
newborns with a few drops of silver nitrate solution to prevent and protect against any possible
infection of the eyes usually termed as
gonorrheal ophthalmia neonatorum.**
(
b) HgCl2 : It perhaps enjoy the longest historical usage as an effective disinfectant. It indeed
possessed a rather broad-spectrum of activity together with its
prime bacteriostatic activity.
The usage of the
‘mercurochrome antiseptic’ (i.e., an organic mercury compound) is
still prevalent in the domain of
domestic chests.
(
c) CuSO4 : It finds its abundant utility for the critical destruction of green algae (an algicide)
which grow profusely in
fish-aquariums, swimming pools, and reservoirs.
(
d) ZnCl2 : It is mostly an essential ingredient in mouth washes like ‘Listerine’ etc. It also
serves as a potential
antifungal agent in acrylic-based paints.
Halogens
The
two most important halogens that are effectively employed as the antimicrobial agents are
iodine (I
2) and chlorine (Cl2) frequently in solution ; besides, being used as the integral constituents ofboth organic or inorganic compounds.
(
a) Iodine (I2) : The most commonly used Iodine Solution was the Iodine Tincture*, which
has become more or less obsolete nowadays ; and has been duly replaced by
Iodophor.
An
iodophor may be defined as — ‘an unique combination of iodine and an organic
molecule, from which iodine gets released gradually’.
Mechanism :
The most probable and proposed mechanism for the activity of iodine being
that it particularly and critically gets combined with
tyrosine–an amino acid which essentially
represents an integral common constituent of :
•
several enzymes, and
•
many cellular proteins,as depicted
Advantages of an Iodophor :
It essentially possesses three major advantages, namely :
Possesses the same activity as that of iodine as an antimicrobial agent,
Does not stain either the skin surface or clothes, and
It is much less irritating in nature (contrary to the iodine tincture).
Example :
The most typical example is that of :
Povidone Iodines [
Syn. : Betadine(R) ; Isodine(R)] which essentially improves the wetting
action
due to the fact that povidone is a surface-active iodophor.
Uses :
Iodines are used exclusively for the treatment of infected wounds and skin infections.
Note : However, the
Pseudomonas may adequately survive for comparatively longer
durations in iodophores.
(
b) Chlorine (Cl2) : As to date chlorine (Cl2) finds its abundant use as a disinfectant in the form
of a
‘gas’ or in combination with certain other chemical substances.
Mechanism :
The probable mechanism whereby chlorine exerts its germicidal action is on
account of the production of
hypochlorous acid (HOCl) which forms specifically on the
incorporation of
chlorine to water. The various chemical reactions which take place may beexpressed
Hypochlorous Acid.
The precise and exact mechanism whereby hypochlorous acid causes the
‘cidal effect’
(i.e., killing power) is not yet known fully. Neverthless, it is indeed a strong oxidizing
agent
which eventually blocks and prevents a major segment of the vital cellular enzyme system to
function in a
normal manner.
Advantages :
There are two main advantageous functionalities of hypochlorous acid, namely :
(
a) It represents the most effective form of chlorine (Cl2) by virtue of it being absolutely neutral
with respect to its electrical charge ; and, therefore, undergoes diffusion as quickly as possible
via
the cell wall.
(
b) The hypochlorite ion [OCl–] [see Eqn. (ii)] bears a distinct negative charge which critically
renders its free entry and access into the body of the
infected cell.
Liquid Chlorine Gas :
The usage of pure liquid form of compressed chlorine (Cl2) gas is invariably
done for carrying out the effective disinfection of
municipal supply of potable (drinking) water,
swimming-pool water,
and sometimes even the municipal sewage-drain outlets.
Compounds of Chlorine :
A good number of compounds of chlorine viz., calcium hypochlorite
[Ca(OCl)
2], and sodium hypochlorite [NaOCl] are largely employed as effective disinfectants.
Ca(OCl)
2 is used to disinfect both the ‘dairy-equipments’ and ‘cooking/eating utencils’ in
eateries (restaurants).
Clorox
(R). It is a frequently used household disinfectant and a bleach that finds its extensive
applications in various industrial and hospital environments, such as :
Dairy-Processing Organisations
— industry ;
Food-Processing Establishments
— industry ; and
Haemodialysis Systems
— hospital.
Organic Acids and Derivatives
A large number of
organic acids are employed both extensively and profusely as potential preservatives
to control the growth of
mold.
Examples :
There are several typical examples, such as :
(
a) Benzoic Acid [or salt derivative Sodium Benzoate] is duly recognized
as a vital
antifungal agent which is observed to be extremely
effective at relatively lower pH values.
Uses : Benzoic acid/Sodium benzoate
are employed extensively in
a broad range of
acidic food products viz., pickles, lime juices ; beverages
viz.,
soft drinks, lime cordials, fruit squashes, canned fruit-juices ; and processed
food products
viz., fruit jams, cheese, neat products, vegetables/fruits (canned), tomatopastes,tomato-sauces, and the like.
(
b) Sorbic Acid [or salt derivative Potassium Sorbate] is
invariably employed to prevent and inhibit the
mold growth
in
acidic foods particularly viz., cheese.
(
c) Parabens — e.g., methylparaben and propylparaben find their abundant applications
to control and inhibit
mold growth in galenicals, liquid cosmetics, foods, shampoos,
and
beverages.
HO
OCH
3
O
Methylparaben
HO
OC
3H7
O
Propylparaben
[Note : Parabens are nothing but derivatives of ‘benzoic acid’ that essentially work at
a neutral pH (
viz., 7).]
(
d) Calcium Propionate— is an inhibitor of moulds and other microorganisms
invariably found in a wide-spectrum of products, such as :
foods, tobacco, pharmaceuticals, butyl-rubber to improve the
processability, and scorching resistance.
Mechanism :
The precise mechanism of activity of these aforesaid organic acid and their
respective derivatives is not exclusively associated to their inherent
acidity but realistically
to the following
two cardinal aspects, namely :
(
i) inhibition of enzymatic activity, and
(
ii) inhibition of metabolic activity.
In a rather broader perspective the human body is capable of
metabolizing these organic acids
quite rapidly thereby rendering their usage
in vivo quite safe in all respects.
Oxidizing Agents
It has been observed that the oxidizing agents usually display and exert their
‘antimicrobial
activity’
by specifically oxidizing the cellular components of the treated microorganisms.
A few typical examples are discussed briefly as under :
(
a) Ozone [O3]. It is an extremely reactive state of oxygen (O2) that may be generated by passing
oxygen
via a high-voltage electrical discharge system. In fact, one may critically observe
the presence of
ozone in the following particular instances :
•
presence of air’s fresh odour immediately after a lightning storm,
•
nearest place to a reasonably large electric spark, and
•
in the vicinity of an UV light (or lamp).
Important Points :
There are two vital points to note :
(
i) Though ozone [O3] exerts a more effective, marked and pronounced cidal effect
(or
killing effect), yet its overall residual activity is practically difficult to maintain
in water, and
(ii) Ozone is definitely more expensive than chlorine as an antimicrobial agent.
(
b) Hydrogen Peroxide [H2O2] : Hydrogen peroxide finds a pivotal place in several hospital
supply facilities as well as household medicine cabinets.
Mechanism : Ozone
gets rapidly cleaved into water and nescent gaseous oxygen due to the
critical action of the enzyme
catalase usually found in human cells, as illustrated under :
Catalase
H
2O2 ⎯⎯⎯⎯→ H2O + (O)
Hydrogen Water Nescent
peroxide oxygen
Perhaps it could be the valid supportive evidence and proof that
ozone fails to serve as a
‘good antiseptic’
particularly for the open wounds.
Uses :
These are as follows :
(1) It effectively disinfects the
inanimate (i.e., showning no sign of being alive) objects.
(2) It proves to be
sporocidal in nature, specifically at elevated temperature(s).
(3) Presence of usual
protective enzymes belonging to the aerobic microorganims, and
the
facultative anaerobes in the non-living surface zones, are found to be largely
overwhelmed by the
critical high concentrations of hydrogen peroxide actually employed.
Based on these
stark realities and superb functionalities the hydrogen peroxide is frequently
used in :
food industry for ‘aspectic packaging’,* and
users of ‘contact lenses’ (i.e., a pharmaceutical aid) usually disinfect them (lenses) with
H
2O2. After carrying out the said disinfection procedure, a Pt-catalyst invariably present in
the
lens-disinfecting kit helps to cause destruction of the residual H2O2 ; and, therefore, it
no more persists on the
contact lens, where it could serve as an irritant.
(
c) Benzoyl Peroxide [Syns. : Debroxide ; Lucidol ; Nericur ;
Sanoxit ; Theraderm ; Xerac BP ;]
— Benzoyl peroxide is an
useful
oxidizing agent for treating such wounds that are usually
infected by the
anaerobic pathogens. However, it is found to be
the major component in most of the over-the-counter (OTC) medicaments
meant for curing
acne** that is generally caused by a
specific kind of
anaerobic bacterium infecting the hair-follicles.
Phenol and Phenolics
Phenol [
Syn. : Carbolic acid ; Phenic acid ;] happens to be the first and foremost chemical
substance that was duly used by the famous British Physician Joseph Lister for sterilization of his
‘operation
theater’.
However, it has become quite obsolete as an antiseptic or disinfectant due to two
major drawbacks, namely :
irritating action on skin, and highly inherent sharp disagreable odour.
Phenolics
i.e., derivatives of phenol, which essentially contain a phenolic moiety that has been
meticulously and chemically modified to accomplish the following
two important objectives :
(
a) in minimizing phenol’s most irritating qualities, and
(
b) in enhancing phenol’s antimicrobial activity in combination with either a detergent or a soap.
Mechanism — Phenolics
predominantly exert its antibacterial activity by injuring the plasma
membranes
particularly ; besides, denaturation of proteins, and inactivation of enzymes.
Uses :
The various uses of phenolics are as stated under :
(1) As disinfectants due to the fact that they usually remain active even in the presence of
organic compounds.
(2)
Phenolics are found to be fairly stable in nature.
(3)
Phenolics do persist for a relatively longer duration of action after their adequate treatment.
(4)
Phenolics find their abundant usage as the most sort after and adequately suitable antimicrobial
agents particularly for the disinfection of
saliva, pus, and faeces.
Examples :
There are two most important and typical examples of phenolics, such as :
(
a) o-Phenylphenol [Syn. : Orthoxenol ; Dowicide ;] : It is an extremely
important
cresol originally derived from a group of coal-tar chemicals.
In fact,
o-phenylphenol constitute as the major ingredient in
most formulations of
Lysol(R). Generally, the cresol do serve as very
good surface disinfectants.
(
b) Hexachlorophene [Syn. : Bilevon ; Dermadex ; Exofene ;
Hexosan ; pHisohex ; Surgi-Cen ; Surofene ;] :
Hexachlorophene
was initially used abundantly as a vital
constituent in a host of antiseptic, cosmetic, and allied formulations,
such as : surgical scrubs, cosmetic soaps, deodorants,
feminine hygiene sprays, toothpastes, and hospital bacterial
control procedures.
It is found to be effective as a
bacteriostatic agent, and specifically effective against two Grampositive
organisms
viz., Staphylococci and Streptococci which usually cause dermatological infections.
Note : US-FDA, in 1972, has regulated the use of hexachlorophene because of its potential neurotoxicity
in humans.
Uses :
(1)
Hexachlorophene is chiefly used in the manufacture of the germicidal soaps.
(2) It is a potential antiseptic and disinfectant.
Quaternary Ammonium Compounds [QUATS]
It has been established beyond any reasonable doubt that the most profusely employed
surfaceactive
agents
are essentially the cationic detergents, and particularly the quaternary ammonium
compounds
[QUATS]. Importantly, the highly effective and the most potential cleansing ability solelyresides to the positively charged segment—the cation of the molecular entity.
Nevertheless, the
quaternary ammonium compounds are observed to be strongly bactericidal
against the
Gram-positive microorganisms, and apparently reduced activity profile against
the
Gram-negative microorganisms.
•
QUATS—are found to be amoebicidal, fungicidal, and virucidal against the enveloped
viruses particularly.
•
QUATS—fail to exert cidal effect on the endospores or tuberculosis organism i.e.,
Mycobacterium tuberculosis
.
Mechanism
—The exact chemical mode of action of QUATS are not known explicitely ;
however, they most probably do affect the plasma membrane particularly. Noticeable change in the
cell’s permeation ability may be seen thereby resulting into the appreciable quantum loss of the most
vital
‘cytoplasmic components’ e.g., potassium.
Examples :
There are two quite common and widely popular QUATS, such as :
(
a) Benzalkonium chloride—[i.e., ZephiranTM—the brand name],
(
b) Cetylpyridinium chloride—[i.e., Cepacol(R)—the brand name].
The following Figure : 7.8 clearly depicts the
ammonium ion vis-a-vis quaternary ammoniumcompounds viz., Benzalkonium chloride [ZephiranTM], and Cetylpyridinium chloride [Cepacol(R)].
Interestingly, both the above cited
QUATS are found to be absolutely colourless, odourless,
tasteless, fairly stable, easily diluted, nontoxic in nature, possess strongly antibacterial activities—except
at relatively high concentrations.
Salient Features
—The salient features of these QUATS are as stated under :
(1) Presence of
‘organic matter’ squarely interferes with the activities of QUATS.
(2) They are neutralized almost instantly on coming in contact with either the
anionic detergents
or the
soaps.
(3)
Pseudomonas do survive in the presence of QUATS, and subsequently grow in them.(4) Broadly recognized as pharmaceutic aid (preservative).
Surface-Active Agents [or Surfactants]
Surface-active
agents may be defined as—‘substances that specifically lower, the surface
tension prevailing amongst the molecules of a liquid.
Such agents essentially include oil, soaps, and
various types of
detergents.
Soap
—The soap is made by the saponification of vegetable oils with the removal of glycerine as
a by-product. Though it possesses rather little value as an antiseptic/disinfectant as such, but it does
exert an extremely important function in the mechanical removal of microorganisms by means of gentle
scrubbing*.
In actual practice, the soap actually aids in the careful cleavage of the thin-oily film (present on
the skin-surface)
via a superb phenomenon invariably termed as emulsification, whereby the mixture of
water/soap meticulously abstracts the emulsified oil together with the
debris of dead cells, dirt particulate
matters,
and microorganisms, and float them away swiftly when the latter thus produced is flushed out
with water.
Uses :
(1) In general, soaps do serve as reasonably good and efficacious
degerming agents.
(2)
Deodorant soap essentially containing typical chemical entities e.g., triclocarban, predominantlyinhibit the Gram-positive microorganisms.
Triclocarban
finds its abundant usage as a bacteriostat and antiseptic in soaps (medicated) and
other cleansing compositions.
Acid-Anionic Surface-Active Sanitizers :
They usually designate an extremely vital and important
group of chemical substances that are being used extensively in the cleaning of dairy utensils
and equipments. It has been duly observed that their
‘sanitizing ability’ is duly confined to the strategic
negatively charged segment (anion)
of the molecule, that eventually interacts critically with the respective
plasma membrane. Besides, such type of sanitizers invariably exert their action upon a broad
spectrum of the microorganisms, even including certain most fussy and troublesome
thermoduric microbes.
In reality, these sanitizers are found to be absolutely nontoxic, fast-acting, and above all
noncorrosive in nature.