Mastering the masters
Know, how your disinfectants work against the smart microbes
_____________________________________________________________________________________________
Microorganisms occur everywhere on the surface of the earth. They are able to grow and survive
under wide range of environmental conditions. Man has always been searching for toxic
chemicals, which kill or inhibit the growth of microorganism mainly to prevent their infective or
destructive actions. The search for such chemicals goes on continually in an effort to find those
having highest toxicity for microorganisms with lowest possible effect on man, animals and
plants .The chemical substances used for this purpose are many and are divided into three main
groups –
1.Antiseptics and disinfectants-Show very little specificity, eg. acid and alkali, soap, halogens,
phenols and heavy metals, are able to kill many types of organisms.
2.Antimetabolites-These are structural analogues of the intermediates in the metabolism of the
cell. A false molecule is built up which is functionally inactive.
3.Antibiotics-These are substances formed by one organism and are toxic to another. They are
highly specific in action.
These chemicals act at different levels and their mode of action can be classified asDisinfection- Microorganisms can be killed, removed or inhibited by various chemical agents
called disinfectants. It kills vegetative cell but not heat resistant spores .It is normally applied to
inanimate objects such as floors, utensils, equipment, laundry etc.
Sterilization –Process of destroying all forms of life by physical and chemical agent. It implies
the complete absence or destruction of microorganisms including spores. An object or substance
is sterile or nonsterile but never semi or almost sterile.
Antiseptic – Any substance that would prevent sepsis either by killing microorganisms or by
inhibiting their growth and activity. An antiseptic can be applied to body tissues whereas
disinfectants are too destructive on tissues.
Sanitizer-It is an agent that reduces microbial population to a safe level. Applied only to
inanimate objects like toilets and bathroom.
Germicide- Kills vegetative spores but not resistant spores
Factors influencing antimicrobial activity –
Anything, which can interfere with molecular complexity of a cell, can kill it. Factors related to a
killing agent are 1) Concentration 2) Time 3) Temperature
Factors related to a killing agent
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1) Intensity/concentration-The term intensity is applied to physical factors e.g. temperature and
concentration. Higher the temperature more effective is the agent.
Concentration-It refers to the strength of the chemical agents. There is an optimal concentration
of chemical agent beyond which it accomplishes increasingly less and is wasteful.
2-Time-No agent acts instantaneously. Sufficient time for contact must be allowed.
3-Temperature-Heat is inversely related to time. Higher the temperature shorter is the time
required. An increase in temperature when used with another agent such as a chemical hastens
the destruction of organism. Thus a small amount of chemical at an elevated temperature gives
the same result as a larger amount of same substance at a lower temperature
Factors related to the microorganisms to be killed1) Number of organisms 2) kind of organism 3) physiological state
1. Number of Organisms-Greater the number of organisms longer it will take to kill them
and greater is the chance of having some with higher heat resistance.
Always keep the number of microorganisms (called load) as low as possible
2. Kind of organism-Microorganisms differ in their susceptibility to chemical and physical
agents. Growing vegetative cells are more susceptible where as spores are extremely
resistant.
3. Physiological state – Age of culture influences the susceptibility. Young cells are more
easily destroyed than old non dividing cells .In old cells the metabolic activity is slowed
down, thickening of cell wall and encapsulation of cell may increase the resistance of
cells.
Nature of environment
There must be interaction between the organism and the agent and the environment may prevent
or enhance the interaction with a particular disinfectant.
The chemical composition of the medium or substance carrying the organism influences the rate
as well as the efficiency of microbial destruction. The action of both physical and chemical agent
is increased by increase in concentration of H+or OH- ions. Heat tends to increase acid effect and
causes coagulation and denaturation. The consistency of the material influences the penetration
of antimicrobial agent.
The presence of extraneous organic matter such as blood, serum, animal tissues, mucus, faeces
can significantly reduce the efficacy of anti microbial agent because of the following reasons An antimicrobial agent may combine with the organic matter to form a product which is
not microbicidal i.e. the agent is inactivated.
 The agent may combine to form a precipitate The interaction between the agent and the
organism is prevented .
 Accumulation on organic matter may provide coating which may prevent interaction.
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Mechanism of cell injury
Microorganisms’ posses a well-defined cell wall and a cell membrane, both of which protect the
cell, their damage may bring death of the cell.
1.Damage to cell wall - Lowering of surface tension of a medium in which microorganisms are
suspended, often injures the cell wall. Substances, which reduce surface tension, are called
Surfactants. e.g. soap, bile salts, hexyl resorcinol and detergents dissolve the damaged part of
the cell and cause emulsifying effect.
2.Damage to cytoplasmic membrane –Surfactants which dissolve lipids disrupt the cytoplasmic
membrane. This destroys the selective permeability causing disruption of normal metabolite
processes leading to inhibition of growth or death of cell.
3.Denaturation and coagulation of protein –Native configuration of protein molecule is essential
for normal metabolic activity of the cell .A condition or substance, which alters this native state
i.e., which denatures or coagulates the protein may damage or kill the cell. High temperatures,
alcohol, formaldehyde etc, are important coagulants or denaturants.
Oxidising agents stronger than molecular oxygen are often microbicidal. Such agents include
halogens, hydrogen peroxide, sodium per borate, potassium permanganate etc. A sulphydryl
group is an important constituent of many enzymes. An alteration of this group by an oxidizing
agent inactivates enzymes.
Enzymes-(SH)2 +1\2 O2  enzymes-SS + H2O
One of the commonly used disnfectant is Sodium hypochlorite. Its properties are a result of the
equilibrium reaction between elemental chlorine and caustic soda. The presence of caustic soda
is necessary to keep the pH at high values, thus avoiding the release of free chlorine (very toxic
gas). Usually it is supplied as an aqueous solution.
Chlorineis slowly liberated .It is very effective in its germicidal action .The action is due to the
formation of hypochlorous acid when free chlorine reacts with water.
Cl2 +H2O →
HCl +HClO ( hypochlorous acid)
The hypoclorous acid formed is further decomposed :2HClO→2HCl+O2
The oxygen released in this reaction (nascent oxygen ) brings about microbial destruction by
oxidation .Combination of chlorine with proteins of the cell membrane and enzymes is also
responsible for the death of organisms.
It is a very powerful oxidizing, bleaching and disinfecting agentDisinfection: Sodium hypochlorite is one of the most effective disinfecting agents. Its ability to
pass through the cell membranes joined to its high chemical potential, permits the product to kill
practically every kind of microorganism, even at low temperature and low concentration. Due to
that, sodium hypochlorite is widely used in industrial and household applications for fast and
ensured disinfecting action. It is also widely used in the sterilization of potable water.
Oxidation: Sodium hypochlorite shows a very high chemical potential. This property is exploited
in a wide range of chemical reactions. It is highly effective in removing a wide range of stains
and soils not totally removed by laundry detergents alone, e.g. blood, coffee, grass, mustard, red
wine, etc. It provides a significant boost to the whitening and cleaning power of laundry
detergents even in cold or hard water and its unique disinfecting properties assures sanitization,
which is of particular importance in hospital linens for example, to reduce the possible
transmission of disease.
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Sodium hypochlorite is a very effective bactericide. The product is diluted to varying degrees to
suit specific applications. Sodium hypochlorite has several major uses, some of its uses in the
hospital are:

General-purpose domestic bleach and disinfectant.

As a sterilizer in food processing and medical applications.

Effluent control including purification of sewage and decomposition of cyanide waste.
Sodium Hypochlorite (NaOCl) is a pale greenish liquid also known as soda bleach or liquid
bleach. It is prepared by reacting dilute caustic soda solution with liquid or gaseous chlorine
accompanied by cooling.
Chemical Reactions:
Cl2 + 2NaOH  NaOCl + NaCl + H2O + Heat
Properties/Specifications
pH
Solubility
12
Soluble in cold water, decomposes in hot water
Common uses of Sodium Hypochlorite
Common Actions
Used in places
Bleaching
Disinfection
Odor Control
Chlorination of drinking and process
water
Elimination of slime and algae
Laundry and home
Hospitals
Toilets
Property
responsible
Oxidation
Coagulation
Precipitation
Water tanks
Septication
Swimming pool and boiler water
pH Adjustment
Hazard Identification
Depending on the concentration involved, hypochlorite solutions can be classified as either
irritant or corrosive and appropriate precautions should be taken. Particular attention must be
paid to avoid mixing with other products, such as toilet bowl cleaners, rust removers, ammonia
or acids. Hypochlorite should not be applied to metals which it corrode or to cloth, which it may
damage.
Although skin and mucous membrane irritation can occur when the exposure concentration is
greater than 5%, these effects are reversible. It is documented that sodium hypochlorite is not a
mutagen, carcinogen, teratogen or skin sensitizer.
Under normal household use, sodium hypochlorite is broken down in the environment into table
salt, oxygen and water. Other substances may be formed, to a small extent. These by-products
are most often referred to as AOX (adsorbable organic halides). A great many studies have been
made to provide a risk assessment of household bleach in terms of its formation of AOX, and the
conclusions drawn were:

the amount of AOX is very small both in absolute terms and relative to other human
activities and natural sources,
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
the majority of these AOX are easily degradable,

the AOXs formed are primarily water soluble and not bio-accumulative.

highly chlorinated species, such as dioxins, are not formed.
Emergency Overview
Harmful if swallowed or inhaled. Causes irritation to eyes and respiratory tract. Causes
substantial but temporary eye injury.
Potential Health Effects
Inhalation: May cause irritation to the respiratory tract, (nose and throat); symptoms
may include coughing and sore throat.
Ingestion: May cause nausea, vomiting.
Skin Contact: May irritate skin.
Eye Contact: Contact may cause severe irritation and damage, especially at higher
concentration.
Chronic Exposure: A constant irritant to the eyes and throat. Low potential for
sensitization after exaggerated exposure to damaged skin.
Aggravation of Pre-existing Conditions: Persons with impaired respiratory function, or
heart disorders (or disease) may be more susceptible to the effects of the substance.
First Aid Measures
Inhalation: Remove to fresh air. If not breathing, give artificial respiration. If breathing is
difficult, give oxygen. Get medical attention immediately.
Ingestion: If swallowed, do not induce vomiting. Give large quantities of water. Never give
anything by mouth to an unconscious person. Get medical attention immediately.
Skin Contact: Immediately flush skin with plenty of water for at least 15 minutes while
removing contaminated clothing and shoes. Get medical attention immediately. Wash clothing
before reuse. Thoroughly clean shoes before reuse.
Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes, lifting lower
and upper eyelids occasionally. Get medical attention immediately.
Note to Physician: Consider oral administration of sodium thiosulfate solutions if sodium
hypochlorite is ingested. Do not administer neutralizing substances since the resultant
exothermic reaction could further damage tissue.
MISCELLANEOUS DISINFECTANTS
Phenols-Phenol [carbolic acid] is powerfully microbicidal and cheaper phenolic disinfectants
derived from coal tar are widely used for decontamination of infective discharges, bathrooms and
hospital floors. They are too toxic and irritant to be left on object that will come in contact with
the skin. Lysol and other crysol fluids [black fluid and white fluid ] are active against a wide
range of organisms .
Phenol is bactericidal at a concentration of 1%, but its activity is reduced by dilution It is
virtually inactive at 0.1%Phenol and coal tar derivatives are toxic to man Sudol is less toxic than
Lysol it contains xylenol and phenols .
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Aniline acridine dyes are active against Gram-positive organisms but less active against Gramnegative organisms.
Proflavine and acriflavine in aqueous solution are slowly bactericidal and effective in presence
of organic matter .
The oxidizing agents, hydrogen peroxide and potassium permanganate have been used as
antiseptics in the past. They are readily inactivated by organic matter and hence are discarded.
Boric acid is used as a bacteriostat in preserving samples of urine prior to examination for viable
counts in the laboratory.
Sodium azide is sometimes used in preservative in biological preparations .
Gaseous Disinfectants:
Formaldehyde Gas: The gas is liberated by spraying formalin or by heating solid Para
formaldehyde .The atmosphere must have high relative humidity and a temperature of at least
18○C The materials must be arranged to allow access of the gas to all infected surfaces, since its
penetration into porous fabrics is slow. Small articles such as shoes hair-brushes, are disinfected
by exposure for at least 3 hours formaldehyde gas.
Ethylene Oxide –This gaseous disinfectant is also highly lethal to all kinds of microbes and
spores but is capable of much more rapid diffusion into dry porous material .It is of value for
sterilizing articles liable to be damaged by heat .A non explosive mixture of 10%ethylene oxide
in carbon dioxide or a halogenated hydrocarbon may be employed for sterlization. The
sterlization time depends among other factors eg.temperature and humidity.
Use and abuse of disinfectants
A wide range of disinfectant is used and some are unsuitable for the purpose for which they are
employed. In dispensing the solution of household disinfections, the members of the staff
apparently rely upon measures such as, ‘a table spoon of bucket’ or ‘until it looks enough’ and
depending on the smell. The important principle of ‘strong enough for long enough’ is generally
overlooked.
Floor cleaning mops are frequently found to be contaminated with potentially pathogenic Gramnegative bacteria. Holders for disposable bedpans are contaminated with faecal organisms. These
observations provide a timely reminder that antimicrobial chemicals must be properly applied if
they are to be of service to medicine. Their abuse gives a false sense of security. Each hospital
should adopt a properly planned policy on the kind and concentration of disinfectants to be used
for particular purpose .A system of in use- test should be made by a bacteriologist on samples of
disinfectant dilutions actually used in different parts of hospital areas.
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Table showing the properties of some disinfectantsa
Active against
Fun
-gi
Bacteria
Gram+ve -ve
Myco
Bacteria
Spores
Lipid
Viruses
Non
Lipid
Viruses
Inactivated by
Protien
Natural
Materia
l
Phenolic
Compounds
+++
+++
+++
++
-
+
V
+
HypoChlorities
+
+++
+++
++
++
+
+
Alcohols
-
+++
+++
+++
-
+
Formaldehyde
+++
+++
+++
+++
+++b
Glutaral
+++
+++
+++
+++
Idophors
+++
+++
+++
+++
Toxicity
Skin
Syntheti
c
material
s
Hard
water
Detergent
++
++
+
C
+
+++
+
+
+
C
+
V
+
+
+
+
-
-
+
+
+
+
+
+
-
+
+++c
+
+
NA
+
+
+
-
+
+
+
+
+++
+
+
+
A
+
a
+++, good; ++, fair; +, slight; -,nil; V, depends on virus; C, cationic; A, anionic; NA, not
applicable
b
above40 C
c
above 20 C
Source:
USE AND ABUSE OF DISINFECTANTS –
A wide range of disinfectant is used and some are unsuitable sometimes for the purpose for
which they where employed .In dispensing the solution of household disinfections, the members
of the staff apparently rely upon measures such as ,a table spoon of bucket, or until it looks
enough ,and depending on the smell. The important principle of strong enough for long enough
is generally over looked.
Floor cleaning mops were frequently found to be contaminated with potentially pathogenic
Gram-negative bacteria. Holders for disposable bed pans are contaminated with faecal
organisms. These observations provide a timely reminder that antimicrobial chemicals must be
properly applied if they are to be of service to medicine. There abuse provides a dangerously
false sense of security Each hospital should adopt a properly planned policy on the kind and
concentration of disinfectants to be used for particular purpose .A system of in use- test should
be made by a bacteriologist on samples of disinfectant dilutions actually used in different parts of
hospital areas.
PHENOLS-Phenol [carbolic acid] is powerfully microbicidal and cheaper phenolic disinfectants
derived from coal tar are widely used for decontamination of infective discharges, bathrooms and
hospital floors. They are too toxic and irritant to be left on object that will come in contact with
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the skin. Lysol and other crysol fluids [black fluid and white fluid ] are active against a wide
range of organisms .
Phenol is bactericidal at a concentration of 1%, but its activity is reduced by dilution It is
virtually inactive at 0.1%Phenol and coal tar derivatives are toxic to man Sudol is less toxic than
Lysol it contains xylenol and phenols .
MISCELLANEOUS DISINFECTANTS
The aniline acridine dyes active against Gram-positive organisms but less active against Gramnegative organisms. Proflavine and acriflavine in aqueous solution are slowly bactericidal and
effective in presence of organic matter .The oxidizing agents, hydrogen peroxide and potassium
permanganate have been used as antiseptics in the past. They are readily inactivated by organic
matter and hence are discarded. Boric acid is used as a bacteriostat in preserving samples of
urine prior to examination for viable counts in the laboratory .Sodium azide is sometimes used in
preservative in biological preparations .
Gaseous Disinfectants
Disinfection by formaldehyde gas .The gas is liberated by spraying formalin or by heating solid
Para formaldehyde .The atmosphere must have high relative humidity and a temperature of at
least 18 deg Celsius The materials must be arranged to allow access of the gas to all infected
surfaces, since its penetration into porous fabrics is slow .
Small articles such as shoes hair-brushes, are disinfected by exposure for at least 3 hours
formaldehyde gas .
ETHYLENE OXIDE –This gaseous disinfectant is also highly lethal to all kinds of microbes
and spores but is capable of much more rapid diffusion into dry porous material .It is of value for
sterilizing articles liable to be damaged by heat .A non explosive mixture of 10%ethylene oxide
in carbon dioxide or a halogenated hydrocarbon may be employed for sterlization.The
sterlization time depends among other factors eg.temperature and humidity.
Human error and poor technique can compromise the best of safe guards and equipment
provided specifically to protect the laboratory worker .Thus a safety conscious staff , well
informed about the recognition and control of hazards is a key element in prevention of lab
accidents and acquired infections . For this reason continous I n service training in safety
measures is essential
Disinfectants and chemicals There should be a written policy stating which disinfectant. are to
be used for what purpose and the manufacturers recommended dilutions for each .Sodium
hypoclorite and phenolic compounds are the disinfectants recommended for
general
laboratory use .For ` special purposes various surface active or lipid destroying agents, including
alcohols ,iodines iodophores and and other oxidizing agents as well as a very high or low pH
can be effective provided that it has been established that the agent to be destroyed is not
resistant to the procedure.
Selection of a disinfectant –Successful disinfection depends on1] the selection of a disinfectant
capable of performing the required task and 2] its careful use under appropriate conditions of
concentration, duration of exposure, temperature, pH and absence of neutralizing substances.
The three main purposes for which disinfectants should be used correctly are
1)Decontamination of objects before disposal or reuse
When there is heavy soiling with organic matter ,phenolic disinfectants of black fluid,
white fluid and Lysol are mostly used .Because they are cheap and have a wide spectrum of
activity and not very liable to become inactive in the presence of organic matter,these phenolic
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derivatives are the most commonly used general disinfectants. In the absence of heavy soiling
with organic matter ,hypochlorite solution ,which is much less toxic and more easily washed
away after disinfection is recommended.Care must be taken to ensure that only fresh ,active
solutionis used .
2) Reduction of microbial contamination of inanimate environment.
In hospitals ,pathogenic staphylococci,streptococci ,enterobacteria,and pseudomonads may be
present on the floors,wall and furnitures of wards ,surgical theatres ,wash basins etc.The risk of
crossinfection is probably reduced if the amount of this environmental contamination is
lessened.Hypochlorite is preferred as a surface disinfectant because it leaves no objectionable
residues.
3)Disinfection of skin of hands and operation sites
Transient organisms that are picked up by contact with outside sources and are lying on the
surface of the skin till they are cleaned or disinfected.Staphylococcus aureus grow in
the depth of the skin ,hence these are impossible to be eliminated completely.
Comparitive test of disinfectants
The efficacy of a new disinfectant or antiseptic may be measured by comparision with that of
phenol under given condition.The ‘phenol coeffici ent’is determined in parallel tests that
compare killing times observed with suspension of the typhoid bacillus exposed to known
concentration of the test substance and killing times observed with the suspension exposed to
known concentration of phenol (Rideal-Walker test).The efficiency of new disinfectant is judged
in terms of ability to inactivate a known number of a standard strain of a pathogenic
staphylococcus on a given surface within a certain time.
Dos
Measure the disinfectant correctly
Put right amount of water
Use clean dry pot or bucket
Wash away dirt if possible
Throw away the solution after use
Remember if disinfectant is used carelessly
it may grow microbes and spread infections
DON’Ts
Use disinfectant for sterlization
Store instruments in disinfectant
Use yesterdays disinfectant solution
Use two disinfectants together
Add your detergent to a disinfectant
Expect any disinfectant to make your dirt safe
When a disinfectant is used the following factors have to be considered
 It should have wide range of microbial activity .
 Surface disinfection should be rapid .
 It should not be neutralized by soaps ,hard water ,organic matter and plastics.
 Control of substances hazardous to health regulations needs to be considered .
 It should not be irritant to skin.
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DISINFECTANT
FECTANT
STRENGTH
Sodium
Granules
Dichloroisocyanuraterate
10000ppm
rate(hypoclorite)
1000ppm
140ppm
Phenolic
2%
Chlorhexidine
0.5% in70%alcohol
4% in 70% alcohol
0,5% in 70% alcohol
0.5% in 70% alcohol
Chlorhexidine
And cetrimide
0.015%to 0.15%
Providone-iodine
Dry powder spray
Surgical scrub
10% solution
70%
2%
alcohols
gluteraldehyde
RECOMMENDED USAGE
Blood spillage only
Spillage of body substances
Baths, bed pans of infected persons
Babies feeding bottle
Spillage of body substances on carpet,soft furnishing etc.
Preoperative and pre procedural skin preparation
Hand washing prior to clinical or surgical procedures
Disinfection of clean hands dressing ,nursing proceduresetc
Cleaning of infected wounds and genitalia prior to urinary catheter
isation
Cleaning of dirty traumatic wounds, theatre and accident and emergency, preoperative skin preparations for sensitive areas e.g face
scrotum,obstetric examination.
Care of skeletal pinsites ,infected pressure sores,ulcers etc
Handwashing
Preoperative and pre procedural skin preparations
Skin preparations prior to injection cleaning of thermometers
Sterlisation of non autoclavable instrument e.g endoscopes
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