Sodium hypochlorite is a very powerful oxidizing ...



[pic]

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 as-

Disinfection- 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

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 killed-

1) 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.

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 agent-

Disinfection: 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.

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 |12 |

|Solubility |Soluble in cold water, decomposes in hot water |

  Common uses of Sodium Hypochlorite

|Common Actions |Used in places |Property responsible |

|Bleaching |Laundry and home |Oxidation |

|Disinfection |Hospitals |Coagulation |

|Odor Control |Toilets |Precipitation |

|Chlorination of drinking and process water |Water tanks |Septication |

|Elimination of slime and algae |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,

• 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 .

Aniline acridine dyes are active against Gram-positive organisms but less active against Gram-negative 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 Gram-negative 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.

Table showing the properties of some disinfectantsa

|Active against |Inactivated by |Toxicity |

| |Fun-gi |Bacteria |Myco |Spores |Lipid |Non Lipid |Protien |Natural |Synthetic |Hard water |Deter-gent |Skin |Eyes |Lungs |

| | |Gram- |Bact-eria | |Virus-es |Viruses | |Material |materials | | | | | |

| | |+ve -ve | | | | | | | | | | | | |

|Phenolic |+++ |+++ |+++ |++ |- |+ |V |+ |++ |++ |+ |C |+ |+ |- |

|Compounds | | | | | | | | | | | | | | | |

|Hypo- |+ |+++ |+++ |++ |++ |+ |+ |+++ |+ |+ |+ |C |+ |+ |+ |

|Chlorities | | | | | | | | | | | | | | | |

|Alcohols |- |+++ |+++ |+++ |- |+ |V |+ |+ |+ |+ |- |- |+ |- |

|Formal-dehyde |+++ |+++ |+++ |+++ |+++b |+ |+ |+ |+ |+ |+ |- |+ |+ |+ |

|Glutaral |+++ |+++ |+++ |+++ |+++c |+ |+ |NA |+ |+ |+ |- |+ |+ |+ |

|Idophors |+++ |+++ |+++ |+++ |+ |+ |+ |+++ |+ |+ |+ |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 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 Gram-negative 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 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 |DON’Ts |

|Measure the disinfectant correctly |Use disinfectant for sterlization |

|Put right amount of water |Store instruments in disinfectant |

|Use clean dry pot or bucket |Use yesterdays disinfectant solution |

|Wash away dirt if possible |Use two disinfectants together |

|Throw away the solution after use |Add your detergent to a disinfectant |

|Remember if disinfectant is used carelessly |Expect any disinfectant to make your dirt safe |

|it may grow microbes and spread infections | |

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.

|DISINFECTANT |STRENGTH | RECOMMENDED USAGE |

|FECTANT | | |

| | | |

|Sodium |Granules |Blood spillage only |

|Dichloroisocyanuraterate |10000ppm |Spillage of body substances |

|rate(hypoclorite) |1000ppm |Baths, bed pans of infected persons |

| |140ppm |Babies feeding bottle |

|Phenolic |2% |Spillage of body substances on carpet,soft furnishing etc. |

|Chlorhexidine |0.5% in70%alcohol |Preoperative and pre procedural skin preparation |

| |4% in 70% alcohol |Hand washing prior to clinical or surgical procedures |

| |0,5% in 70% alcohol |Disinfection of clean hands dressing ,nursing proceduresetc |

| |0.5% in 70% alcohol |Cleaning of infected wounds and genitalia prior to urinary catheteri |

| | |isation |

|Chlorhexidine |0.015%to 0.15% |Cleaning of dirty traumatic wounds, theatre and accident and eme- |

|And cetrimide | |rgency, preoperative skin preparations for sensitive areas e.g face |

| | |scrotum,obstetric examination. |

|Providone-iodine |Dry powder spray |Care of skeletal pinsites ,infected pressure sores,ulcers etc |

| |Surgical scrub |Handwashing |

| |10% solution |Preoperative and pre procedural skin preparations |

|alcohols |70% |Skin preparations prior to injection cleaning of thermometers |

|gluteraldehyde |2% |Sterlisation of non autoclavable instrument e.g endoscopes |

| | | |

| | | |

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download