Microbial Control by Chemical Methods

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Chapter: Pharmaceutical Microbiology : Microbial Control by Physical and Chemical Methods

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.


CHEMICAL METHODS

 

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 appropri-ate 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 :

 

1. 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 on the ‘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 character-istic 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 capa-ble 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.

 

2. Disinfectant—Critical Evaluation

 

The critical evaluation of the disinfectants may be accomplished adopting any one of the fol-lowing two techniques, namely :

 

(a) Use-Dilution Tests, and

 

(b) Filter-Paper Method.

 

(a). 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 disin-fectant 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.

 

(b). 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.

 

3. 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 :

 

i. Alcohols

 

It has been duly observed and established that alcohols specifically exert a bactricidal and fun-gicidal 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 :

(a) They usually exert their action upon the microbes due to protein denaturation—evaporating readily—and leaving virtually no residue at all.

(2) 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 micro-organisms along 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 bac-tericidal/fungicidal effect quite rapidly. Interestingly, pure ethanol [> 98% (v/v)] is found to be amazingly less effective in comparison to the corresponding aqueous ethanolic solu-tions 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 popula-tion of a ‘test microbe’ in less than two minutes.


 

(b) Tincture of ZephiranTM is observed to kill nearly 85% of the test organism in just two minutes.

 

ii. Aldehydes

 

In general, the aldehydes are found to be the most effective antimicrobial agents (disinfect- ants).

 

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 and viruses in vaccines.

 

(b) Glutaraldehyde  [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 respiratory-therapy 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 liquid chemical disinfectant which may be regarded as a possible sterilant (or sterilizing agent).

 

iii. Chlorohexidine

 


Obviously, chlorohexidine is not a phenol but its chemical struc ture 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 :

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.

 

AdvantagesChlorhexidine 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.

 

iv. Gaseous Chemosterilizers

 

Gaseous chemosterilizers may be defined as—‘chemicals that specifi cally sterilize 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.

 

5. Heavy Metals and Derivatives

 

A plethora of heavy metals and their corresponding derivatives viz., Hg, HgCl2, Cu, CuSO4, Ag, AgNO3, 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 possi-ble 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 activ-ity. 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.

 

vi. Halogens

The two most important halogens that are effectively employed as the antimicrobial agents are iodine (I2) and chlorine (Cl2) frequently in solution ; besides, being used as the integral constituents of both 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 essen tially represents an integral common constituent of :

·        several enzymes, and

·        many cellular proteins,

as depicted in Figure 7.7.


 

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 infec-tions.

 

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 be expressed as under :


 

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 invari-ably 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.

 

vii. Organic Acids and Derivatives

 

A large number of organic acids are employed both extensively and profusely as potential pre-servatives to control the growth of mold.

 

Examples : There are several typical examples, such as :

 

(a) Benzoic Acid [or salt derivative Sodium Benzoate] is duly recog nized 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 ; bev erages 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) Parabense.g., methylparaben and propylparaben find their abundant applications to control and inhibit mold growth in galenicals, liquid cosmetics, foods, shampoos, and beverages.


[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 microor ganisms 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.

 

viii. 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 pass-ing 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 main-tain 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 :


 

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 em-ployed.

 

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 H2O2. 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) medi-caments meant for curing acne** that is generally caused by a specific kind of anaerobic bacterium infecting the hair-follicles.


 

ix. 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 ‘op-eration 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 :

 

(a) 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 treat-ment.

 

(4) Phenolics find their abundant usage as the most sort after and adequately suitable anti-microbial 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 chemi-cals. 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 for mulations, such as : surgical scrubs, cosmetic soaps, deodor ants, feminine hygiene sprays, toothpastes, and hospital bac terial control procedures.


It is found to be effective as a bacteriostatic agent, and specifically effective against two Gram-positive organisms viz., Staphylococci and Streptococci which usually cause dermatological infec-tions.

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.

 

x. Quaternary Ammonium Compounds [QUATS]

 

It has been established beyond any reasonable doubt that the most profusely employed surface-active agents are essentially the cationic detergents, and particularly the quaternary ammonium compounds [QUATS]. Importantly, the highly effective and the most potential cleansing ability solely resides to the positively charged segment—the cation of the molecular entity.

 

Nevertheless, the quaternary ammonium compounds are observed to be strongly bacte-ricidal 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 ammonium compounds viz., Benzalkonium chloride [ZephiranTM], and Cetylpyridinium chloride [Cepacol(R)].


 

From Fig. 7.8 one may evidently observe the manner whereby the other moieties strategically replace the hydrogen atoms of the ammonium ion.

 

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—ex-cept 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 deter-gents or the soaps.

 

(3) Pseudomonas do survive in the presence of QUATS, and subsequently grow in them.

 

(4) Broadly recognized as pharmaceutic aid (preservative).

 

xi. 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, predomi-nantly inhibit the Gram-positive microorganisms.

 

Triclocarban [Syn : Cutisan ; Nobacter ; Solubacter ;] :


 

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 im-portant 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 re-spective 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 mi-crobes. In reality, these sanitizers are found to be absolutely nontoxic, fast-acting, and above all noncorrosive in nature.

 

Table : 7.4 records a summarized details of the various chemical agents, as described from Sec-tions 7.3.3.1 to 7.3.3.11, that efficiently controls the microbial growth in general.



 

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