Control and destruction of Microbes
methods of control a) Principles and methods of microbial
and destruction of control
microbes -Sterilization
-Disinfection the CSSD
-Chemotherapy and antibiotics
-Pasteurization
b) Medical and surgical asepsis
c) Bio-safety and waste management
Definitions
(1) Sterile:-Free from micro-organism of any kind.
(2) Sterilization:-The process of killing or removing microbes including pathogenic, non-pathogenic, spores.
(3) Disinfection:-The process of removing or killing pathogenic organisms, not necessarily including non-pathogenic organisms.
(4) Disinfectant:- An agent that is infection free. It has bactericidal action.
(5) Sepsis:- Growth of pathogenic organisms in living tissues is called sepsis.
Asepsis:- Absence or prevention of growth of pathogenic organisms in living tissues is called asepsis.
Antiseptic:-A chemical substance used to prevent infection by inhibiting the growth of harmful micro-organisms.
Fumigation:- The destruction of organisms through a gaseous agent is known as fumigation.
Principles & Method of microbial control Microbes
Microbes are almost everywhere. But we are not aware of them. Their presence is more in hospitals where patients release large numbers through their urine, stool, sputum, secretion.
Apart from this, microbes are also present in blood, food, water, sewage, air and soil etc.
Since they are found in many ways, different methods have been developed to destroy them.
Which include physical and chemical methods, which are used according to the knowledge and requirement of the operator.
The personal comfort of a person also depends on his knowledge of this matter and the way to control microbes.
Such as, Environment, Equipments, Cleanings, Food & kitchen, Body care etc. The main three reasons for destroying or inhibiting micro-organisms are
(1) To prevent infection and transmission of disease.
(2) To prevent decomposition and spoilage of food.
(3) To prevent contamination of material used in culture.
Physical agents
(1) Heat
(2) Sunlight
(3) Cold (law temp.)
(4) Drying or Dessication
(5) Radiation
(6) Filtration
(7) Sound waves and Ultrasonic vibration.
Chemical agents
(1) Phenol and cresol compounds
(2) Alcohol
(3) Halogens (Iodine and chlorine compound)
(4) Dyes
(5) Aldehydes
(6) Acids
(7) Alkalies
8) Gases
9) Metallic salts
(10) Oxidizing agents
(11) Surface active agents.
Physical Agents
Heat :- Heat is a trusted most effective economic and wildly used agent.
The effect of heat on microbes depends on four factors.
1.Type of Heat (Dry or Moist Heat)
2.Characteristics of Germs
3.Environment Factors
4.How long is the organism exposed to heat?
Dry Heat
(i)Direct flaming :-
Platinum, copper and other metals are used to sterilize wires, points of forceps, needles etc.
In this method the object is kept in the flame till it becomes red hot
If there is protein material or fat on the tip of forceps or on the object then it should be dipped in a chemical disinfectant first
This method is also used for glass slides. Glass articles are passed through the flame quickly but are not kept till they become red.
(ii) Burning or Incineration
Infected laboratory materials, contaminated swabs, paper sputum cups, dressings, books, magazines, clothes, mattresses, etc. are used for hospital waste disposal.
It is a safe, easy, cheap and excellent method. Incinerators are made in hospitals for this purpose.
Conti……………
In this method, an oven is used to sterilize various items.
Such as instruments, glass-wares, bandages, cotton swabs, dusting powder, solutions with low water content.
It cannot be used for alcohol or other solutions.
The oven is a double coated chamber. It is operated by electric or gas heat.
The temperature is controlled by a thermostat mechanism.
The material is kept at 180° C for 30 minutes, 160° C – 60 min and 140 ° C – 90 min without pressure.
The oven door should be kept closed during heating (to maintain temp.) and should not be opened for 2 hours after heating, because there is a possibility of glass ware cracking due to sudden cooling.
(B) Moist heat
For different objects, below 100° C & 100° C and above 100 C temperature are used.
Temperature below 100* C
(i) Pasteurization of milk
Discovered by Pasteur in 1860.
It was earlier used in wine beer.
But now it is used for milk.
In pasteurization, either 62° C for 30 minutes (holder method) or 121° C for 15 10 20 seconds (flush method), a high temperature is immediately followed by a cooling effect at 13 or less.
Pasteurization kills all pathogenic bacteria such as mycobacterium tuberculosis, salmonella typhi bracella, etc.
So that milk can be made safe for drinking, it is not a method of sterilization, but the organism that remains after pasteurization. It is harmless.
Temp < 100° C is also used for many other objects. So that they can be disinfected. Such as eating utensils, nursing equipments are cleaned with hot water.
80 C for 15 minutes, Destroys the vegetative forms of all bacteria.
Temperature at 100′ c (i) Boiling (100° C) :
Boiling is a very simple method of disinfection.
It kills most of the vegetative forms of bacteria within 10 min, but spores survive.
Boiling is a suitable method for sterilizing syringes, glassware, and clothes of infectious patients and articles that cannot be damaged by boiling.
It is not recommended for instruments used in operations because it only disinfects, not sterilizes
Different types of boilers are available in the market for boiling which can be used for different purposes. Any household utensil that can be covered can also be used as a sterilizer.
(ii) Fractional sterilization (Intermittent sterilization )
Since it was developed by British scientist John Tyndall, it is also called Tyndallization.
In this process, 100* C temp. is required for 20 min.
And this is done for 110 4 days.
In other words, repeated heating at intervals of days (12 to 24 hrs) kills vegetative forms of bacteria and spores.
In the third heating, almost all remaining organisms are killed, except in the preparation of culture media. This method is not used except in the preparation of culture media.
Arnold, a German bacteriologist, developed a special apparatus called the Arnold steam sterilizer, in which steam is used without pressure.
Temperature above 100° C (Steam under pressure) Autoclaving
Heat under pressure is a practical and useful agent in sterilization.
In this method, 15 lbs pressure and 121° C temp. are required for 30 minutes for sterilization.
Pressure does not kill organisms, but steam under pressure can do the job.
The time depends on how bulky the material is to be sterilized. This is considered one of the best methods of sterilization. Which destroys all bacteria and spores.
The equipment used for this process is called an autoclave machine, which is like a pressure cooker at home.
AUTOCLEAVE MACHINE
An autoclave is a double-walled metal device.
It has an airtight chamber. It usually has 2 gauges (meter gauges).
It reads the steam pressure of the outer inner chamber.
To prevent explosion due to high pressure, it has a safety valve, which releases steam when the pressure increases as necessary.
There is also an exhaust valve to remove the steam from the inner chamber.
There is also a valve to send steam from the outer chamber to the inner chamber.
In some autoclaves, a thermometer is also fitted inside the chamber.
After placing the object on the plate inside the inner chamber, the heating is started after closing the lids tightly.
15 lbs/inch, 120° C 30 minutes The advantages of autoclave are that it can kill organisms including spores.
And the specified temperature and pressure of steam can be maintained. This method can sterilize culture media, rubber goods, linens, dressing, syringes and… It can be used in the sterilization of instruments and many other important consumables. It is one of the best, most practicable, dependable methods of sterilization.
(2) Sunlight
This natural method is used in water tanks, rivers, lacks etc. for sterilization.
This is the best method to disinfect clothes among the methods used at home. (Mattresses, clothes etc.)
Many types of bacterial spores and microbes can be removed by direct exposure to sunlight.
Tuberculosis germ can be killed by a few hours of sunlight exposure.
The germicidal action of sunlight is due to the ultra violet and infrared rays present in sunlight.
The germicidal action of sunlight is due to the ultra violet and infrared rays present in sunlight.
(3) Cold (low temperature)
Micro-organisms of diseases like meningitis and gonorrhoea can be killed by cold.
But not all bacteria can be killed by low temperature, e.g. typhoid bacilli cannot be killed even in frozen state.
Cold generally prevents the multiplication of ordinary bacteria.
Hence it is used for food preservation.
Microbial activities can be delayed by cold. It is not a reliable or reliable method for disinfection or sterilization.
4) Drying or Dessication
Unreliable method. Spores can remain alive for months or years in dried objects.
Germs of cholera, pneumonia, diphtheria, whooping cough which have been found sensitive to cold.
While drying does not affect yeasts, moulds and most bacteria and they can survive for months.
(4) Radiation
The effect of radiation energy on microbial cells is the death of microbes. Two types of radiation are used.
(1) Non-ionising agents include infrared, ultraviolet radiation and
(2) Ionising agents include x-rays, gamma rays, cathode rays etc.
Infrared radiation is used at 190°C temp. for 10 minutes.
The heat produced by it is sufficient for killing micro – organisms.
Ultraviolet radiation is useful in disinfection of O.T., hospital wards, swimming pools, rooms etc.
Apart from the energy law present in these rays, the penetration power is also poor.
It can be easily produced artificially. It can be produced by passing electric current through a special type of tube or germicidal lamp.
Ionising radiation is produced using high voltage generators. This method is expensive,
Filtration
Used for materials that can be damaged by heat.
Mostly used in pharmaceutical fluids and bacteriological laboratories.
It is a mechanical method of removing micro-organisms without changing the chemical properties of the substance.
Different types of remove filters are used in the laboratory. In which materials like candles, cellulose membrane, porcelain etc. are used.
Viruses cannot be removed by it.
(7) Sound and Ultrasonic vibrations
Bacteria can also be killed through rapid vibration. Which are sound waves. Many apparatuses are available in the market that can provide sufficient sound waves intensity – sufficient time.
These waves break down cells and cell walls. This method is practical for sterilization or disinfection.
CHEMICAL STERILIZATION
Many chemical agents available in the market have antiseptic and disinfectant properties.
Which exhibit antimicrobial activities.
But their mode of action is different. Many cell proteins and many enzymes are destroyed through oxidation and radiation.
There is no single chemical available that is completely effective against all types of microbes.
Many chemical agents are used in hospitals, homes and industries.
a) Phenol and cresol compound
These are Coaltar derivatives, used in hospitals for a hundred and one years.
Phenol (carbolic acid) was first used in 1865 by Lister. (The father of antiseptic surgery) Phenol is not used in pure form as it is very expensive and not effective.
It is usually used in the form of a 3% solution.
Used to disinfect instruments, furniture, floors, walls etc.
There are many derivatives of phenol such as cresol, tricresol, Lysol, dettol, chlorophenols, chloroxyphenols, hexachlorophene, chlorohexidine etc. which are useful against gm+ve and gm-ve bacteria.
(b) Alcohols
Many alcohols have disincentive properties.
But ethyl alcohol and isopropyl alcohol are commonly used
They are used at a concentration of 70%. They kill bacteria by destroying the protein of the bacterial cell.
They are not effective against spores and viruses.
Methyl alcohol has less bacteriocidal action but is effective against fungal spores.
Although it is highly toxic and inflammable,
It is commonly used to disinfect incubators in laboratories.
(c) Halogens (Iodine and chloride compounds)
Iodine is one of the oldest and most effective germicidal agents
It has been in use for more than a hundred years.
It is commonly used for skin preparation.
Iodine is not used in concentrated forms (as a disinfectant) because it burns tissue and causes blisters.
Its wet form is used to treat infected wounds and inflamed mucous surfaces, especially throat, skin, diseases and before operations.
The most common available chlorine compounds are bleaching powder (chlorinated lime), chloramines and hypochlorite.
It is available in powder and liquid forms with different concentrations.
Bleaching powder is used for disinfection in drinking water, swimming baths, foods & dairy industries.
Bleaching powder is used for disinfection in drinking water, swimming baths, foods & dairy industries.
(d) Dyes
Dye is extensively used in skin and wound infections and laboratories due to its antimicrobial activities
It is bacteriocidal and sporocidal.
A 40% formaldehyde solution in water is known as formalin,
It is used for fumigation of rooms, wards and laboratories.
10% formalin is used for specimen preservation. It can be used under very carefully controlled conditions.
It is also necessary for disinfection of Asputum, faeces, instruments, clothes, bedding, books, furniture etc.
As formaldehydes irritate the skin, eyes, nose, throat, and mucous membranes, control of the environment is necessary.
It is toxic by inhalation and loses its effect if exposed to ambient air.
Acids
Acetic acid has been used for years in the prevention of Pseudomonas infection that occurs in food.
Boric acid, although weak antiseptic, is used for wound infection and inflammation of mucous surfaces.
(f) Alkalies
Sodium hydroxide and lime have powerful germicidal action.
Formaldehyde is used for the preservation of specimens.
Gases
(Many things are sterilized with the help of chemical agents like gases.
A gas is released in a specific area. Many biological materials (test tubes, petridishes, laboratory equipments, machines, clothes, plastics, soil etc.) are sterilized by gas.
Formaldehyde is used to disinfect rooms with potassium permanganate.
Ethylene oxide is also used as a gas. It can kill all types of micro-organisms including spores.
Used with Co2 or N2 at a concentration of 3%. Used for metal glass, paper and plastic materials. Ethylene oxide is explosive and toxic, so precautions must be taken.
h) Metallic salts
( (Inorganic or Organic)Metal compounds such as mercury, silver, copper, arsenic and zinc are used in very limited amounts.
Metal combination with proteins of the organism causes cell death. Not widely used
Oxidising Agents
( KMn04, H2O2Potassium permanganate is used as an antiseptic in skin infection. H2O2 is not a good disinfectant but is useful for wound treatment.
Surface active agents
A substance which reduces surface tension is called a surface active agent.
It usually mechanically removes micro-organisms.
Soap is a very good surface active agent which is used for skin cleaning.
CHEMOTHERAPY AND ANTIBIOTICS
Chemotherapeutic drugs are used in chemotherapy for the prevention and treatment of infection.
There are many chemotherapeutics, among which sulphonamides are the most commonly used drugs Examples of such potentiated sulfonamide preparations include( trimethoprim-sulfadiazine (cotrimazine), trimethoprim-sulfamethoxazole (cotrimoxazole), trimethoprim-sulfadoxine (co- trimoxine), and ormetoprim-sulfadimethoxine). Antibiotics are obtained from living organisms.
These drugs have bacteriostatic and bacteriocidal action.
Bacteriostatics only inhibit bacterial growth. While bacteriocidals kill bacteria.
Source and action of antibiotics
Antibiotics are obtained from living organisms.
They are produced by bacteria, fungi, actinomycetes, streptomycetes or plants.
Some organisms produce more than one antibiotic.
Sometimes more than one type of organism produces antibiotics.
These antibiotics have bacteriocidal (e.g, penicillin) or bacteriostatic (e.g. chloromphericol) action
Antibiotics are produced during the growth of microbes in the culture media during the culture process. Later, the culture is filtered to obtain antibiotics.
The differences in antibiotics are usually due to their route of administration. Many are used in the form of ointments, many in oral form and others in injection (i.v. /i.m. /sc /) form.
Many antibiotics are effective against gm+ve bacteria and many against gm-ve bacteria.
There are also antibiotics that prove useful against both gm+ve and gm-ve types of bacteria. Antibiotics that provide a wide range of activities are called broad spectrum antibiotics.
Mycostatin, Actidione antibiotics have antifungal action. Hence they are used in laboratories to protect cultures from fungi. Penicillin, streptomycin, terramycin, aureomycin, chloromycetin, erythrocin are examples of antibiotics.
These are known as miracle drugs. Their disadvantages and hypersensitivity are also seen, in which allergic reactions like Skin rashes, joint pains, enlargement of lymph nodes, a fall in W.B.C. counts, haemorrhages etc. are seen.
Almost every antibiotic causes a decrease in normal flora and this leads to deficiency of Vit.B.
Sometimes changes are seen in the mucous membrane. It is necessary to check the sensitivity of the organism before using antibiotics.
PASTEURIZATION
Pasteurization is a method of sterilizing milk. In which only harmful bacteria are destroyed. But lactic acid and necessary organisms are not destroyed. Due to this, some changes occur in the protein and sugar present in the milk. Three methods of pasteurization are in use.
(1) Holder or Wet method
In this, milk is heated at 62 c for 30 min. After that it is cooled very quickly to a temperature less than 5‘c.
For T.B. and Typhoid organisms at 121’c for 15 to 20 seconds It is heated. It is called flash method.
(2) H.T.S.T. (“Temp, ↓ Time)
Milk is heated rapidly to 72 c and cooled to a temperature of less than 5 c.
(3) UHT method (Ultra high temp.)
Milk is heated to a high temp. of 121’c to 150’c and then cooled very quickly. Phosphatic method is used to check the pasteurization of milk. Raw milk contains phosphate. Which is destroyed during pasteurization.