UNIT 2 : CONTROL OF MICROORGANISMS
Sr.no Contents
01 Explain importance of the control of microbial growth.
02 Describe some physical and chemical methods to
control microbial growth
03 Define the terms i.e. Sterilization, Antiseptic, Asepsis,
Aseptic, Macrobiotic, Microbiacidal, Antibiotic etc.
04 Differentiate Between Broad Spectrum And Narrow
Spectrum Antibiotics.
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Control of Microbial Growth
IMPORTANCE OF CONTROL OF MICROBIAL GROWTH
Control of microbial growth means to kill or inhibit the growth of microorganisms Control of
growth usually involves the use of physical or chemical agents which either kill or prevent
the growth of microorganisms The control of microbial growth is necessary in many
practical situation and significant advances in medicine, agriculture, and food science have
been made through the study of microbiology.
Microbial control is very important in the following different aspects
Controls infectious diseases
Minimizes cross and nosocomial infections .
Prevents surgical complications
Decreases morbidity and mortality
Prevents food from spoilage
Food can be preserved for months
What is Sterilization?
Sterilization refers to any process that removes, kills, or deactivates all forms of life.
(particular referring to microorganisms such as fungi, bacteria, viruses, spores.)
Sterilization is define as the complete removal of microorganisms from an object or
surfaces.
METHODS OF STERILIZATION
1.Physical method
Dry heat sterilization: Eg: Incineration, Direct flame, Red heat, Hot air.
Moist heat sterilization: Eg: Pasteurization, Tyndallisation, Autoclave.
Sterilization by radiation: Eg: Use of Ultra-violet rays: UV light(Non-ionising), Ionising
radiations: X-rays Gamma rays, beta rays.
Mechanical sterilization : Filtration
2.Chemical method
Gaseous sterilization Eg:Alcohol Ethylene oxide gas, Formaldehyde, Sterilization by
disinfectant Eg: Alcohols and Aldehydes, Phenols, Oxidizing agents and Saltsetc
PHYSICAL METHODS OF MICROBIAL CONTROL
Involves processes by the use of physical means Utilisation of heat in the presence or in the
absence of heat, moisture, radiation or membrane filtration methods.
A) Dry Heat:
1.Flaming is a type of dry sterilization that involves exposure of metallic objects to
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flame for some time where the flame burns microbes.
Ex :tubes, glass slides, scalpels, needles,cover slips, etc.
2. Incineration: Incineration is a waste treatment process that involves the combustion of
organic substances contained in waste materials.
Ex :Pathological material, contaminated cloth,carcasses
3.Hot Air Oven : Hot air ovens are electrical devices which use dry heat to sterilize.
Temperatures: 170 degrees Celsius for 30 minutes, 160 degrees Celsius for 60 minutes
Ex: glasswares, powders , metallic
B)Moist Heat
1.Autoclave
An autoclave is a machine that uses steam under pressure to kill harmful
bacteria, viruses, fungi, and spores on items
Temperature: 121°C for 15 minutes 15 lb pressure
Ex: surgical equipment, laboratory instruments, pharmaceutical items, and
others material
2.Pasteurization:
Pasteurization or pasteurisation is a process in which packaged and non packaged foods
(such as milk and fruit juices) are treated with mild heat, usually to less than 100 °C (212 °F),
to eliminate pathogens and extend shelf life
Ex: beer, milk, wine, juices, etc.
Classic Method of Pasteurization:
Milk is heated to 62°C for 30 minutes.
High Temperature Short Time Pasteurization (HTST): Milk is exposed to 72°C for 15
seconds.
Ultra High Temperature Pasteurization (UHT): Milk is treated at 140°C for 3 seconds
and thencool quick in a vacuum chamber.
Advantage Milk can be stored at room temperature for several months.
3.Tyndallisation
Tyndallization is a sterilization method that involves heating the material at 100 °C for 20
minutes on 3 consecutive days intermittent with incubation at 37 °C Used for egg, serum
and sugar containing media.
C) Radiations
Radiation kills germs that can cause disease and neutralizes other harmful organisms.
Ionizing radiation :It is the use of short wavelength, high-intensity radiation destroy
microorganisms.
Ex: gamma or X-rays
Non-ionizing radiation :It uses longer wavelength and lower energy. Low penetrating power
used for sterilizing surfaces.
Ex: UV rays
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D)Filtration
Filtration is an interesting sterilization method in laboratories. It's the only method that
uses force to separate rather than to kill. When you filter a liquid or gas, it passes through a
pore, which stops, or filters out, the passage of larger particles.
Chemical sterilization involves the utilization of certain chemicals so as to cause
microbial killing.
Properties of ideal chemical
• Wide spectrum of activity
• Speedy action
• High penetrating power
• Not cause irritation
• Cheap and easily available
• Safe and easy to use
• Not be toxic if absorbed into circulation
• Not interfere with healing
Chemicals used for sterilization
1.Alcohol.
Alcohols are not recommended for sterilizing medical and surgical materials principally
because they lack sporicidal action. Work by denaturing the protein in the cell.
2.Formaldehyde
Formaldehyde another important highly reactive gas which is used for sterilization.
This gas btained by heating formalin (37%w/v) to a temperature of 70-80°C
It poses broad-spectrum biocidal activity and has found application in the sterilization of
reusable surgical instruments, specific medical, diagnostic and electrical equipment, and
the surface , sterilization of powder
3.Ozone
Ozone is a highly reactive industrial gas that is commonly used to sterilize air and water
and as adisinfectant for surfaces.
Ozone has a oxidizing property that is capable of destroying a wide range of organisms.
4.Phenol (carbolic acid):
Phenol was first used by Lister as a disinfectant
Destroys plasma membrane and denatures proteins. Rarely used today because it is a
skin irritant and has strong odor.
Advantages: Stable, persist for long times after applied,
5.Hydrogen peroxide
Hydrogen peroxide is a liquid chemical sterilizing agent which can destroy a wide range
of microorganisms.
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It is useful in the sterilization of heat or temperature-sensitive equipment like
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endoscopes. In medical applications, a higher concentration (35-90%) is used
Not effective for open wound can be breakdown by catalase enzyme ( present in human
body)
6.Hypochlorite solution,
which is also called liquid bleach.
hypochlorite can be used for the disinfection of workstations and even surfaces to clean
blood spills and other liquids.
Terms
Antiseptics : Chemicals that applied on living tissues.
Disinfectants : Chemicals that applied on non living objects
Asepsis : Absence of Microorganisms or uncontaminated object
Sterilization :The destruction of all form of microbial life by physical and chemical
methods
Disinfection :Reducing the numbers of pathogenic microbes
Antimicrobial drugs : These are the chemical substances (natural or synthetic) that
suppress the growth or destroy Microorganism including bacteria,virus ,fungi and
protozoa.
• Antiviral
• Antifungal
• Antibacterial /Antibiotics
• Antiprotozoal
Antibiotics
A medicine that inhibits the growth Or destroy microorganisms
Classification of Antibiotics
1.On the basis of spectrum
• Broad spectrum : That is against or kills wide range of microorganisms
• Narrow spectrum: That is agaisnt or kills narrow range of microorgainsms
2.On the basis of action
• Bacteriostatics hat stop or slows down the growth of bacteria
• Bactericidal That kills the bacteria
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