This document provides an overview of methods for controlling microorganisms. It discusses physical methods like temperature, radiation, and filtration which use heat, cold, or removal to control microbes. Chemical methods like disinfectants, antibiotics, and heavy metals are also covered. The document defines key terms and explains sterilization, disinfection, and how techniques like boiling, autoclaving, and pasteurization work. It emphasizes the importance of microbial control for preventing disease transmission and food spoilage.

1. Microbiology
BSN Semester:I
Unit:2
IFTIKHAR UL HAQ
DEMONSTRATOR
INS-KMU, PESHAWAR
Control of Microorganisms

2. Lecture Overview
Introduction to microbial control
General terminologies regarding microbial control
Methods of microbial control
Physical Methods
Chemical Methods
Mechanical Methods
Anti-microbial agents
Difference between broad spectrum and narrow spectrum antibiotics

3. INTRODUCTION
• Control of microorganisms is essential in order to prevent the transmission of
diseases and infection, stop decomposition and spoilage, and prevent unwanted
microbial contamination.
• Microorganisms are controlled by means of physical agents and chemical agents.
• Physical agents include such methods of control as high or low temperature,
desiccation, radiation, and filtration.
• Control by chemical agents refers to the use of disinfectants, antiseptics and
antibiotics.

4. GENERAL TERMS
• Sterilization:
Sterilization is the process of destroying all living organisms and viruses.Asterile object is
one free of all life forms, including bacterial endospores, as well as viruses.
• Disinfection:
Disinfection is the elimination of microorganisms, but not necessarily endospores, from
inanimate (non-living) objects or surfaces.
• Decontamination:
De-contamination is the treatment of an object or inanimate surface to make it safe to
handle.

5. GENERAL TERMS

6. GENERAL TERMS
• Disinfectant:
Adisinfectant is an agent used to disinfect inanimate objects but generally is toxic to use on
human tissues.
• Antiseptic:
An antiseptic is an agent that kills or inhibits growth of microbes but is safe to use on
human tissue.
• Sanitizer:
Asanitizer is an agent that reduces microbial numbers to a safe level.

7. GENERAL TERMS

8. GENERAL TERMS
• Antibiotic:
Antibiotic is a substance derived from microorganisms or produced synthetically to kill or
inhibit the growth of other microorganisms i.e. bacteria.
• Chemotherapeutic synthetic drugs:
Synthetic chemicals that can be used therapeutically.
• Cidal:
An agent that is cidal in action; will kill microorganisms and viruses.
• Static:
An agent that is static in action; will inhibit the growth of microorganisms.

9. GENERAL TERMS
• BacteriostaticAgent: An agent that inhibits the growth of bacteria e.g.
tetracycline, macrolides, clindamycin etc.
• Bactericidal agent: An agent that kills bacteria e.g. Aminoglycoside, betalactum,
Fluorquinolones etc.
• Germicide:An agent that kills certain microorganism/ germs
• Virucide:An agent that inactivates/ kill viruses.
• Fungicide: An agent that kills fungi.
• Sporicide:An agent that kills bacterial endospores and fungal spores e.g.
Sodium hypochlorite (NaClO)

10. GENERAL TERMS

11. METHODS OF MICROBIAL CONTROL

12. Physical Methods

13. Physical Methods
Physical methods:
The methods which are used to destroy or remove microorganisms by means of physical
things are known as physical methods.
Examples:
• Temperature
• Radiation
• Refrigeration
• Desiccation

14. Physical Methods
1: Temperature:
• Microorganisms have a minimum, an optimum, and a maximum temperature for growth.
• Temperatures below the minimum usually have a static action on microorganisms. They
inhibit microbial growth by slowing down metabolism but do not necessarily kill the
organism.
• Temperatures above the maximum usually have a cidal action, since they denature
microbial enzymes and other proteins. Temperature is a very common and effective way of
controlling microorganisms.

15. Physical Methods
A. Thermal death point (TDP)
The lowest temperature at which all bacteria in a liquid culture are killed within 10 minutes.
B. Thermal death time (TDT)
The time required to kill all bacteria in a liquid culture at a given temperature.
C. Decimal reduction time (DRT)
The time required to kill 90% of the bacteria in a liquid culture at a given temperature.

16. Physical Methods
i. High temperature:
• V
egetative microorganisms can generally be killed at temperatures from 50°C to 70°C
with moist heat.
• Bacterial endospores, however, are very resistant to heat and extended exposure to much
higher temperature is necessary for their destruction.
• High temperature may be applied as either moist heat or dry heat.

17. Physical Methods
a. Moist heat:
Moist heat is generally more effective than dry heat for killing microorganisms because of
its ability to penetrate microbial cells.
Moist heat kills microorganisms by denaturing their proteins (causes proteins and enzymes
to lose their three-dimensional functional shape).
It also may melt lipids in cytoplasmic membranes.
• Boiling water
• Autoclaving

18. Physical Methods
Boiling water:
• Boiling is the process of turning a liquid into a vapor and for a certain atmospheric
pressure, the boiling happens at a specific temperature.
• Boiling happens because molecules of water (or any liquid really) gain enough kinetic
energy to lose the intermolecular forces that exist in liquids.
• Boiling water (100°C) will generally kill vegetative cells after about 10 minutes of
exposure. However, certain viruses, such as the hepatitis viruses, may survive exposure to
boiling water for up to 30 minutes, and endospores of certain Clostridium and Bacillus
species may survive even hours of boiling.

19. Physical Methods
Autoclaving:
• Autoclaving employs steam under pressure. Water normally boils at 100°C;
however, when put under pressure, water boils at a higher temperature.
During autoclaving, the materials to be sterilized are placed under 15 pounds
per square inch of pressure in a pressure-cooker type of apparatus. When
placed under 15 pounds of pressure, the boiling point of water is raised to
121°C, a temperature sufficient to kill bacterial endospores.
• Autoclaving is cidal for both vegetative organisms and endospores, and is the
most common method of sterilization for materials not damaged by heat.

20. Physical Methods
b. Dry Heat:
Dry heat kills microorganisms through a process of protein oxidation rather than protein
coagulation. Examples of dry heat include:
• Hot air Sterilization
• Incineration

21. Physical Methods
Hot air Sterilization:
Microbiological ovens employ very high dry temperatures:
171°C for 1 hour; 160°C for 2 hours or longer; or 121°C for 16
hours or longer depending on the volume. They are generally
used only for sterilizing glassware, metal instruments, and
other inert materials like oils and powders that are not
damaged by excessive temperature.

22. Physical Methods
Incineration:
• Incinerators are used to destroy disposable or expendable
materials by burning.
• Incineration is a method of treating waste which involves
the combustion of the organic substances found in waste
materials.

23. Physical Methods
c. Pasteurization:
Pasteurization is the mild heating of milk and other
materials to kill particular spoilage organisms or
pathogens. It does not, however, kill all organisms.
Milk is usually pasteurized by heating to 71.6°C for
at least 15 seconds in the flash method or 62.9°C for
30 minutes in the holding method.

24. Physical Methods
ii. Low Temperature:
Low temperature inhibits microbial growth by slowing down
microbial metabolism. Examples include: refrigeration and freezing.
• Refrigeration at 5°C slows the growth of microorganisms and
keeps food fresh for a few days.
• Freezing at -10°C stops microbial growth, but generally does not
kill microorganisms, and keeps food fresh for several months.

25. Physical Methods
2. Desiccation:
It is the process of removal of water. In the absence of water, microbes cannot
grow or reproduce, but some may remain viable for years. After water
becomes available, they start growing again.

26. Physical Methods
3. Radiation:
Two types of radiation kill microbes:
1.Ionizing Radiation: Gamma rays, X rays, electron
beams, or higher energy rays. Have short wavelengths
(less than 1 nanometer).
• Dislodge electrons from atoms and form ions.
• Cause mutations in DNA and produce peroxides.
• Used to sterilize pharmaceuticals and disposable
medical supplies. Food industry is interested in using
ionizing radiation.
Disadvantages: Penetrates human tissues. May cause
genetic mutations in humans.

27. Physical Methods
2. Ultraviolet light (Nonionizing Radiation):
• Wavelength is longer than 1 nanometer. Damages
DNAby producing thymine dimers.
• Used to disinfect operating rooms, nurseries,
cafeterias.
Disadvantages: Damages skin, eyes. Doesn’t
penetrate glass, and cloth.

28. Chemical Methods
1: Phenol (carbolic acid):
• 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, and remain active in the presence of
organic compounds.

29. Chemical methods
2: Halogens:
Effective alone or in compounds.
A. Iodine:
• Tincture of iodine denatures proteins.
• It Stains skin and clothes.
B. Chlorine:
• Used to disinfect drinking water, pools, and sewage.
• Chlorine is easily inactivated by organic materials.
• When mixed in water, forms hypochlorous acid:
• Cl2 + H2O ------> H+ + Cl- + HOCl

30. Chemical methods
3:Alcohols:
• Kill most bacteria, fungi, but not endospores.
• Act by denaturing proteins and disrupting
membranes.
cell
• Used to mechanically wipe microbes off skin before
injections or blood drawing.
• Not good for open wounds, because cause proteins to
coagulate.

31. Chemical methods
4: Heavy Metals:
• Heavy metals and
microbicidal.
their compounds are
• Include copper, selenium, mercury, silver, and
zinc.
• The property of heavy metal to exert biocidal
effect is called Oligodynamic action.
A. Silver:
1% silver nitrate used to protect infants against
gonorrheal eye infections until recently.
B. Copper
Copper sulfate is used to kill algae in pools and
fish tanks.

32. Chemical methods
C. Selenium
• Kills fungi and their spores. Used for fungal
infections.
• Also used in dandruff shampoos.
D. Zinc
• Zinc chloride is used in mouthwashes.
• Zinc oxide is used as antifungal agent in paints.

33. Chemical Method
5: OxidizingAgents:
A. Ozone:
• It is Used to disinfect water.
• Helps neutralize unpleasant tastes and odors.
• More effective killing agent than chlorine, but
less stable and more expensive.

34. Chemical method
B. Hydrogen Peroxide:
• Used as an antiseptic.
• Not good for open wounds because quickly broken
down by catalase enzyme present in human cells.
• Effective in disinfection of inanimate objects.
• Sporicidal at higher temperatures.
• Used by food industry and to disinfect contact lenses.
C. Benzoyl Peroxide:
• Used in acne medications.

35. Mechanical Methods
1. Filtration:
• Mechanical means of removing microorganisms. The liquid or gas is passed through a filter
with pores small enough to prevent passage of microbes. This method can be used for
substances that are sensitive to heat.
• HEPA filters: removes at least 99.97% of airborne particles 0.3 micrometers (µm) in
diameter.
• ULPA filter: remove from the air at least 99.999% of dust, pollen, mold, bacteria and any
airborne particles with a size of 120 nanometers or larger.

36. HEPA & ULPA Filter

37. Mechanical Methods
2. Osmotic pressure:
• The use of high concentrations of salts and
sugars in foods is used to increase
the osmotic pressure and create a
hypertonic environment.
• The addition of salt to meat creates a
solute-rich environment where osmotic
pressure draws water out of
microorganisms, thereby retarding their
growth.

38. Importance of control of microbial growth
• Control of microbial growth means to kill or inhibit the growth
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 situations, and
significant advances in medicine, agriculture, and food science have been
made through the study of microbiology.

39. Importance of control of microbial growth
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
• *Improves and ensures the safety of agricultural products
• *Ensures the provision of safe drinking water to public

40. THE LAST TWOOBJECTIVES WILLBE COVERED IN
SECONDPARTOFTHIS UNIT