Control of Microorganism lecture 03......pdf

This pdf contains all information about how to control microorganisms by chemical and physical methods.

1. Control of Microorganisms
Unite 02
By : Hafiz Ahmad Lubab ktk
Institute of Nursing Sciences,
Khyber Medical University , Peshawar

2. Leaning Goals
By the completion of this unit learners will be able to:
Introduction to microbial control
General terminologies regarding to microbial control
Methods of microbial control
Physical Methods
Chemical Methods
Mechanical Methods
Anti-microbial agents

3. INTRODUCTION
Control of microbial growth means to inhibit or prevent growth of
microorganisms. Control of microbial growth usually involves the use of
physical or chemical agents which either kill or prevent the growth of
microorganisms.
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.
It Aims to reduce or destroy undesirable microbes in a given area.

4. REASONS FOR CONTROLLING
MICROORGANISMS
Reasons for Controlling Microorganisms.
Prevent contamination.
Prevent transmission of pathogen
To prevent decomposition & spoilage of products
To prevent contamination in aseptic areas, processes like production of
pharmaceuticals by fermentation
To maintain aseptic condition in operation theaters, filling area of non
sterile pharmaceuticals.

5. ACTION OF MICROBIAL AGENTS

Primary targets of microbial agents are to prevent microorganisms that can
cause infection or spoilage of food that are constantly present in the
external environment.
Modes of action fall into two basic categories.
–Alteration of cell walls or cytoplasmic membranes
–Interference with protein and nucleic acid structure

6. ALTERATION OF CELL WALL AND
MEMBRANES
Cell wall maintains integrity of cell.
When disrupted, cannot prevent cell from bursting due to osmotic effects.
Cytoplasmic membrane contains cytoplasm and controls passage of
chemicals into and out of cell.
When damaged, cellular contents leak out.
Viral envelope responsible for attachment of virus to target cell.
Damage to envelope interrupts viral replication.

7. INTERFERENCE WITH PROTEIN
AND NUCLEIC ACIDS
Protein function depends on 3-D shape.
Extreme heat or certain chemicals denature proteins.
Break Hydrogen and covalent bonds in proteins.
Chemicals, radiation, and heat can alter or destroy nucleic acids.
Interfere with DNA,RNA, protein synthesis.
Can halt protein synthesis through action on RNA.

8. RESISTANCE OF MICROBES

Highest Resistance:
Bacterial endospore and prions.
Moderate Resistance:
Pseudomonas sp.
Mycobacterium tuberculosis.
Staphylococcus aureus.
Protozoan cysts.
Least Resistance:
Most vegetative cells/Fungal spores
Yeast / protozoan trophozoites.

9. EFFECTIVENESS OF ANTIMICROBIAL
TREATMENT DEPENDS ON:

Number of microbes.
Nature of microbes in the population ( microbial characteristics e.g. cell
wall, resistance).
Environment (temperature, PH).
Concentration or dosage of agents.
Mode of action of the agent.
Time of exposure ( time to kill in proportion to the population size).

10. DEFINITION OF FREQUENTLY
USED TERMS
Sterilization: (Latin sterilis means unable to produce offspring)
Sterilization is the process of destroying all living organisms and viruses. A
sterile object is one free of all life forms, including bacterial endospores, as
well as viruses. Sterilization is the removing of all microorganism in a
material or on the surface of an object(an extreme level of cleanliness).
Disinfection:
Disinfection is the elimination of microorganisms, but not necessarily
endospores, from inanimate (non-living) objects or surfaces. Disinfection is
reducing the number of bacteria to a level low enough that disease is
unlikely to occur. For example, disinfection of the water supply is achieved
by treatment with chlorine.

11. GENERAL TERMS

12. GENERAL TERMS
Decontamination:
De-contamination is the treatment of an object or inanimate surface to
make it safe to handle. Physical removal of contaminant means pre-
sterilization cleaning. e.g. hypochlorite solution.
Disinfectant:
A disinfectant is an agent used to disinfect inanimate objects but generally
is toxic to use on human tissues.e.g iodine solution, Ozone, Chlorine gas.
Antiseptic:
An antiseptic is an agent that kills or inhibits growth of microbes but is safe
to use on human tissue. Antiseptic are generally less toxic than disinfectant
because they must not cause to much damage to the host living tissue.
e.g. Isopropyl alcohol, Hydrogen peroxide.

13. GENERAL TERMS
Sanitization:
Cleansing technique that mechanically remove microbes to a safe level.
Sanitization is the cleaning of pathogenic microorganism from public
eating utensils and object such as that done by the kitchen of a restaurant.
Subject to a high temperature washing (Dishwashers).
Sanitization any cleansing technique that mechanically remove microbes.
A sanitizer is an agent that reduces microbial numbers to a safe level.
Practical examples of sanitizing include:
–Mopping the floor with water and a chemical sanitizer
–Sanitizing dishes in a dishwasher.

14. GENERAL TERMS
Degerming: (Swab the skin)
Removing microorganism from an objects surface.
Degermation mechanically remove microbes from surface (skin) such as
surgical hand scrubbing, or wiping skin with alcohol prior to venipuncture.

15. GENERAL TERMS
Antisepsis:
Removal of pathogen from living tissue (Disinfection of Living tissue).
Sepsis:
The presence of Bacterial Contamination. Sepsis is usually caused by
bacterial infections but may be the result of other infections such as viruses,
parasite or fungi.
oSepsis is a serious complication of an infection. Without quick treatment,
sepsis can lead to multiple organ failure and death.
oSepsis can be triggered by an infection in any part of the body.
oSepsis is your body extreme reaction to an infection.

16. GENERAL TERMS
Asepsis:
The absence of Bacteria, viruses, and other microorganisms.
oAsepsis is a condition in which no living disease causing microorganisms
are present. Asepsis covers all those procedures designed to reduce the risk
of bacterial, fungal or viral contamination.
oThe exclusion of microorganism, typically during surgery
Aseptic Technique:
Used to prevent microbial contamination of any clinical procedure and
products of pharmaceutical and food industry to keep standards.
oAseptic technique is a collection of medical practices and procedure that
helps protect patient from dangerous germs.

17. GENERAL TERMS

18. 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 .
Static:
An agent that is static in action; will inhibit the growth of microorganisms.

19. GENERAL TERMS
Bacteriostatic Agent: 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.
e.g. formaldehyde.
Virucide: An agent that inactivates/ kill viruses. E.g. Ethyl alcohol.
Fungicide: An agent that kills fungi. e.g. Ethanol.
Sporicide: An agent that kills bacterial endospores and fungal spores e.g.
Sodium hypochlorite (NaClO).

20. GENERAL TERMS

21. METHODS OF MICROBIAL
CONTROL

22. PHYSICAL METHODS

23. 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

24. 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.

25. PHYSICAL METHODS
Heat: Kills microorganisms by denaturing their enzymes and other proteins.
Heat resistance varies widely among microbes.
A. Thermal death point (TDP)
Lowest temperature at which all of the microbes in a liquid suspension will
be killed in ten minutes.
This aspect of thermal death is useful in purifying water via boiling.
Kills many vegetative cells, Fungi, protozoa trophozoites, and inactivate
viruses within 10 minutes,
(30 minutes to be safe but no effect on spore).

26. PHYSICAL METHODS
B. Thermal death time (TDT)
Shortest length of time required to kill all microbes at a specific
temperature.
It was developed for good canning and has found application in cosmetics
and pharmaceuticals.
C. Decimal reduction time (DRT)
The time required to kill 90% of the bacteria in a liquid culture at a given
temperature.
Reduce the number of organism to 1/10 the initial level.
used in commercial sterilization

27. PHYSICAL METHODS
A: High temperature:
Vegetative 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.

28. PHYSICAL METHODS
B. 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 shape).
It also may melt lipids in cytoplasmic membranes.
Boiling water
Autoclaving
Pasteurization

29. PHYSICAL METHODS
1. 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 to 100°C or more. It kill vegetative form of bacterial pathogen,
almost all viruses, and fungi and their spores within 10 minutes or less.
Endospores and some viruses are not destroyed quickly.
 Hepatitis virus: Can survive up to 30 minutes of boiling. However brief
boiling will kill most pathogens.

30. PYHYSICAL METHODS
2. Autoclaving:
Autoclaving employs steam under pressure.
Reliable sterilization with moist heat requires temperature above that of
boiling water.
Example of moist heat is autoclave, a chamber which is filled with hot
steam under pressure .this is preferred method of sterilization for non-heat
sensitive materials in which temperature of steam reaches 121°C at 15 psi
pressure.(pound per square inch).
Autoclaving is cidal for both vegetative organisms and endospores, and is
the most common method of sterilization for materials not damaged by
heat.
All organisms and endospores are killed within 15 minutes.

31. PYHYSICAL METHODS



AUTOCLAVE:

32. PHYSICAL METHODS
3. Pasteurization: (Not sterilization heat loving microbes survive):
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.
This is sufficient to kill the vegetative cells of the milk-borne pathogens
(e.g. mycobacterium, salmonella, streptococcus),but not to sterilize the milk.
Pasteurization extends the shelf life of products and reduce the level of
pathogens in the products.

33. PHYSICAL METHODS
Classic method of Pasteurization:
Milk is heated to 62°C for 30 minutes.
High Temperature short time pasteurization:
Milk is exposed to 72°C for 15 seconds.
Ultra high temperature pasteurization:
Milk is treated at 140°C for 3 seconds and then cooled very quickly in
a vacuum chamber.
Advantages: Milk can be stored at room temperature for several months.

34. PHYSICAL METHODS




c. Pasteurization:

35. PHYSICAL METHODS
b.Dry Heat:
Used for materials that cannot be sterilized with damaged by moist heat.
Denature protein and oxidizes metabolic and structural chemicals.
Examples of dry heat include:
Direct Flaming
Hot air Sterilization
Incineration

36. PHYSICAL METHODS
Direct Flaming:
Bunsen burner.
Dehydrates cells and remove water.
Used to sterilize inoculating loops and needles. Heat metal until it has a red
glow.

37. PHYSICAL METHODS
Hot air Sterilization:
Microbiological ovens employ very high dry temperatures: 171°C for 1
hour; 160°C for 2 hours or longer.
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.

38. PHYSICAL METHODS


Hot air Sterilization:

39. PHYSICAL METHODS
Incineration:
The process of burning waste material at temperature high to destroy
contaminants.
Three types of waste to which incineration is applied extensively are
municipal solid waste, hazardous waste, medical waste.
Incinerators are used to destroy disposable materials by burning.
Incineration is a method of treating waste which involves the combustion
of the organic substances found in waste materials.

40. PHYSICAL METHODS



Incineration:

41. PHYSICAL METHODS
ii. Low Temperature:
Low temperature inhibits microbial growth by slowing down microbial
metabolism. Examples include: refrigeration and freezing.
Refrigeration at 0°C to 7°C slows the growth of microorganisms
and keeps food fresh for a few days. Bacteriostatic effect.
Freezing items are protected by stopping the growth of microbes at
temperature below 0°C , and keeps food fresh for several months.

42. PHYSICAL METHODS
ii. Refrigeration and freezing:
Refrigeration is a great short term solution, it decreases microbial
metabolism, growth and reproduction.
Chemical reaction occur slower at low temperature.
Refrigeration halts growth of most pathogens.
Lower temperature result in greater long term storage (-20c).

43. PHYSICAL METHODS
2. Desiccation:
It is the gradual removal of water from cells ( Dehydration).
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.
Viruses and Endospore can resist Desiccation.

44. PHYSICAL METHODS
3. Radiation: ( Radiation damage DNA)
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.
Ions disrupt hydrogen bonding, oxidize double covalent bonds, and create
hydroxide ions, hydroxide ions denature other molecule ( DNA).
Cause mutations in DNA .
Used to sterilize pharmaceuticals and disposable medical supplies.
Food industry is interested in using ionizing radiation.
Food irradiation is a process whereby the food is exposed to high levels of
radiation in order to kill insect, bacteria and make the food last longer on
the store shelves.
Disadvantages:
 Penetrates human tissues. May cause genetic mutations in humans.

45. PHYSICAL METHODS
4. Ultraviolet light (Nonionizing Radiation):
Wavelength is longer than 1 nanometer Damages DNA by producing
thymine dimers.
The greatest antimicrobial activity of UV light occurs at 250 to 260 nm,
which is the wavelength region of maximum absorption by the purine and
pyrimidine bases of DNA.
DNA replication is inhibited and the organism can not grow.
Used to disinfect operating rooms, nurseries.
Disadvantages: Damages skin and eyes.

46. CHEMICAL METHODS
1: Phenol (carbolic acid):
was first used by Lister(1860) as a disinfectant.
Phenol are effective antibacterial agents, and they are also effective against
fungi and many viruses but not effect on spore.
Destroys plasma membrane and denatures proteins.
Effective against gram-positive staphylococci and streptococci.
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.
Disadvantages :Excessive use in infants may cause neurological damage.

47. CHEMICAL METHODS
2: Halogens:
Effective alone or in compounds. They damage enzyme.
A. Iodine:
Tincture of iodine (2% solution of iodine and potassium iodide in ethanol)
denatures proteins.
It Stains skin and clothes.
Used as skin antiseptic in surgery.
Not effective against bacterial endospores.
Iodine is normally considered to be the least toxic
of the disinfectant.

48. CHEMICAL METHODS
B. Chlorine:( purified drinking water)
Used to disinfect drinking water, pools, and sewage.
Denaturation of protein by disrupting disulfide bonds.
Chlorine compound are good disinfectant on clean surface, but are quickly
inactivated by dirt.
Acts as a disinfectant in gaseous form or in solution as calcium hypochlorite
Sodium hypochlorite is active ingredient of bleach.
Chlorine can be irritating to skin .can be sporocidal.
When mixed in water, forms hypochlorous acid:
Cl
2 + H
2O ------> H+ + Cl- + HOCl

49. CHEMICAL METHODS
3: Alcohols:
 Kill most bacteria, fungi, but not endospores.
Act by denaturing proteins and disrupting cell membranes.
Used to mechanically wipe microbes off skin before injections or blood
drawing.
Not good for open wounds, because cause proteins to coagulate.
They are bactericidal, and fungicidal
but not sporicidal.

50. CHEMICAL METHODS
4: Heavy Metals:
Heavy metals and their compounds are microbicidal.
Include copper, selenium, mercury, silver, and zinc.
Denature protein by breaking disulfide bonds.
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 .
B. Copper:
Copper sulfate is used to kill algae in pools and fish tanks.

51. CHEMICAL METHODS

52. 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.

53. CHEMICAL METHODS
5: Oxidizing Agents:
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.

54. CHEMICAL METHODS
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.

55. CHEMICAL METHODS

56. CHEMICAL METHODS
6. Peracetic Acid :
 One of the most effective liquid sporicides available.
Sterilant : - Kills bacteria and fungi in less than 5 minutes.
Kills endospores and viruses within 30 minutes.
Used widely in disinfection of food and medical instruments because it
does not leave toxic residues.

57. CHEMICAL METHODS
6. Aldehydes:
 Highly effective molecule that combine with nucleic acids and protein and
inactivate them.
They are sporicidal and can be used as chemical sterilant.
Formaldehyde ,which is available as a 37% solution in
water(formalin),denature proteins and nucleic acids.
Glutaraldehyde is used to disinfect hospital ,laboratory equipment,
respiratory therapy equipment.

58. 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.
Used to sterilize heat sensitive material like vaccine injectable drugs etc.
Also used in hospital isolation units and industrial clean rooms.
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.

59. HEPA & ULPA FILTER

60. 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.
Cells in a hypertonic solution of salt or sugar lose water causes
plasmolysis.i.e. shrinkage of cytoplasm ( water in cell is drawn out by
osmosis, cell desiccates.
Note: Staphylococci spp, Yeast are resistant to high osmotic pressures.

61. 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.
Ensures the provision of safe drinking water to public.
Improves and ensures the safety of agricultural products.