1. Sterilization - the destruction of all microorganisms, including endospores, on an object or in a material. 2. Disinfection - the destruction of pathogens, but not endospores, on an object or in a material. The number of pathogens is reduced or growth is inhibited to a level that does not produce disease. 3. Antisepsis - chemical disinfection of the skin, mucosal membranes, or other living tissues. 4. Germicide ("cide" = kill) - a chemical agent that rapidly kills microorganisms. Specific germicides include: (I) Sporicide - kills spores (II) Bactericide - kills bacteria (III) Viricide - kills viruses (IV) Fungicide - kills fungi

1. CONTROL OF MICRORGANISMS
BY,
N.MUTHUGANESAN
B.TECH FOOD TECHNOLOGY, PROJECT ASSISSTANT,
CENTRAL FOOD TECHNOLOGICAL RESEARCH INSTITUTE, MYSORE-INDIA

2. Terms Related to Destruction of Microorganisms
1. Sterilization - the destruction of all microorganisms, including
endospores, on an object or in a material.
2. Disinfection - the destruction of pathogens, but not endospores, on
an object or in a material. The number of pathogens is reduced or growth
is inhibited to a level that does not produce disease.
3. Antisepsis - chemical disinfection of the skin, mucosal membranes, or
other living tissues.
4. Germicide ("cide" = kill) - a chemical agent that rapidly kills
microorganisms.
Specific germicides include:
(I) Sporicide - kills spores
(II) Bactericide - kills bacteria
(III) Viricide - kills viruses
(IV) Fungicide - kills fungi

3. METHODS
PHYSICAL CHEMICAL

4. PHYSICAL METHODS
THERMAL
 HEAT
 BOILING
 STERILIZATION
 HOT AIR OVEN
 PASTEURIZATION
 REFRIGERETOR
 FREEZING
 COLD STORAGE
NON THERMAL
 IRRADITION
 PULSED ELECTRIC FIELD

5. Heat
Heat is the most common, inexpensive, simplest,
and effective method used to destroy microorganisms. Heat
denatures the proteins and enzymes of the microorganisms.
Most pathogens will be destroyed at temperatures
between 50° and 70°C for a duration of 10 minutes, except
endospores which may survive 1 to 2 hours at 100°C.

6. Boiling
 Bacteria, fungi, and many viruses are
destroyed by boiling at 100°C for I0 to
30 minutes. Some viruses and
endospores may require boiling for up
to 20 hours. Sterilization is
accomplished by denaturing the
proteins and enzymes of the
microorganisms.

7. STERILIZATION
 destruction of all microorganisms, including endospores
 Water is heated under pressure which raises the
temperature above 100°C which denatures proteins and
amino acids. The most common device used is an
autoclave for sterilizing surgical bandages, instruments,
media, and contaminated material.
 At a pressure of 15 pounds/square inch and a temperature
of 121°C for 15 to 20 minutes it will destroy
microorganisms and endospores.

8. Thermal Death Measurements
 Thermal death time (TDT)
shortest length of time required to kill all
microbes at a specified temperature
 Thermal death point (TDP)
lowest temperature required to kill all
microbes in a sample in 10 minutes

9. PASTEURIZATION
 Heat treatment
 Three methods : LTLT , HTST, UHST
 It is mainly used in the food and dairy industries and it involves
raising the temperature high enough to destroy pathogens or inhibit
their growth without affecting the quality of the product.
Primary pathogen targets of pasteurization: ______________,
Listeria, Mycobacterium, Campylobacter, Brucella
 Does not kill endospores or thermoduric microbes

10.  (1). incineration - The burning of disposable substances
in a chamber.
 (2). direct flaming - Sterilization of inoculating loops,
needles, and rims of test tubes with a Bunsen burner. Wire
heated to a red glow is 100% effective.

11. Hot-air oven
 Sterilization of glassware, test tubes, petri dishes,
instruments, syringes, and needles requires higher
temperatures for a longer period of time than other
methods.
 Most endospores will be destroyed at 160-165"C for
a period of 2 hours.

13. Psychrophilic
(cold-loving) can grow at 0oC, and some even as low as -10oC; their
upper limit is often about 25oC.
Mesophilic
grow in the moderate temperature range, from about 20oC (or
lower) to 45oC.
Thermophiles
are heat-loving, with an optimum growth temperature of 50o or
a maximum of up to 70oC or more, and a minimum of about 20oC.
Hyperthermophiles
have an optimum above 75oC and thus can grow at the highest
temperatures tolerated by any organism. An extreme example is the
genusPyrodictium, found on geothermally heated areas of the seabed. It
has a temperature minimum of 82o, optimum of 105o and growth
maximum of 110oC.

14. Physical Methods of Microbial
Control:
Filtration: Removal of microbes by passage of a liquid
or gas through a screen like material with small
pores. Used to sterilize heat sensitive materials like
vaccines, enzymes, antibiotics, and some culture
media.
 High Efficiency Particulate Air Filters (HEPA): Used in
operating rooms and burn units to remove bacteria from air.
 Membrane Filters: Uniform pore size. Used in industry and
research. Different sizes:
 0.22 and 0.45um Pores: Used to filter most bacteria. Don’t retain
spirochetes, mycoplasmas and viruses.
 0.01 um Pores: Retain all viruses and some large proteins.

15. Non ionizing Radiation: Ultraviolet Rays
 Wavelength approximately 100 nm to 400 nm
 Germicidal lamp: 254 nm
 Not as penetrating as ionizing radiation
 Powerful tool for destroying fungal cells and spores, bacterial vegetative cells,
protozoa, and viruses
Ultra-violet radiation and ionizing radiation (x -rays and gamma rays)
 Both types of radiation damage the DNA of microorganisms and denatures their
proteins. U-V radiation cannot penetrate materials such as glass, clothing, dirt, paper,
or pus and is used to kill microorganisms on surfaces. Germicidal lamps in operating
rooms, nurseries, and communicable disease wards reduce the number of bacteria in
the air, but they do not sterilize.

16. Chemical Agents: Alcohols
 Ethanol; isopropanol; used at concentrations between 70
– 95%
 Denature proteins; disrupt membranes
 Kills vegetative cells of bacteria & fungi but not spores
 Used in disinfecting surfaces; thermometers; “ethanol-
flaming” technique used to sterilize glass plate spreaders
or dissecting instruments at the lab bench

17. Alcohols:
Kill bacteria, fungi, but not endospores or naked viruses.
 Act by denaturing proteins and disrupting cell membranes.
 Evaporate, leaving no residue.
 Used to mechanically wipe microbes off skin before injections or
blood drawing.
 Not good for open wounds, because cause proteins to
coagulate.
 Ethanol: Drinking alcohol. Optimum concentration is 70%.
 Isopropanol: Rubbing alcohol. Better disinfectant than ethanol. Also
cheaper and less volatile.

18. Phenol and phenol derivatives
 Phenol (5-10%) was the first disinfectant commonly used.
 These include orthophenylphenol, hexachlorophene, triclosan,
hexylresorcinol, and chlorhexidine. Orthophenylphenol
 Triclosan is a chlorine-containing phenolic antiseptic very common in
antimicrobial soaps and other products
 A 4% solution of chlorhexidine in isopropyl alcohol and combined with
detergent (Hibiclens® and Hibitane®) is a common hand washing agent
and surgical hand scrub.
 These agents kill most bacteria, most fungi, and some viruses, but are
usually ineffective against endospores. They alter membrane
permeability and denature proteins.

19. Soaps and detergents
 Some cosmetic soaps contain added antiseptics to increase antimicrobial activity.
 Detergents may be anionic or cationic. Anionic (negatively charged) detergents, such as
laundry powders, mechanically remove microorganisms and other materials but are not
very microbicidal. Cationic (positively charged) detergents alter membrane permeability
and denature proteins.
 They are effective against many vegetative bacteria, some fungi, and some viruses.
However, bacterial endospores and certain bacteria such as Mycobacterium tuberculosis
and Pseudomonas species are usually resistant. They are also inactivated by soaps and
organic materials like excreta.
 Cationic detergents include the quaternary ammonium compounds such as
benzalkonium chloride, zephiran, diaprene, roccal, ceepryn, and phemerol.

20. Chlorhexidine
 Chlorhexidine is used as an antiseptic on skin and mucosal membranes
and functions in disruption of the plasma membrane of gram-positive and
gram-negative bacteria resulting in lysis.

21.  Halogens
The major halogens are iodine and chlorine. Iodine is an effective antiseptic for the skin and
superficial wounds. It destroys many kinds of bacteria, some endospores, fungi, and some viruses.
Iodine inhibits protein function in the micro -organism. Chlorine is used as a disinfectant and it is a
strong oxidizing agent which affects functions of the Microorganisms enzymes.
 Ions of heavy metals
The major metal ions are mercury and silver, and they function in denaturing proteins and
enzymes. Both are used in combination with other substances as antiseptics.

23. Heavy Metals:
Oligo dynamic action: Very tiny amounts are effective.
A. Silver:
 1% silver nitrate used to protect infants against gonorrheal eye
infections until recently.
B. Mercury
 Organic mercury compounds like merthiolate and
mercurochrome are used to disinfect skin wounds.
C. Copper
 Copper sulfate is used to kill algae in pools and fish tanks.

24. Aldehydes:
B. Glutaraldehyde:
 Less irritating and more effective than formaldehyde.
 One of the few chemical disinfectants that is a sterilizing agent.
 A 2% solution of glutaraldehyde (Cidex) is:
 Bactericidal, tuberculocidal, and viricidal in 10 minutes.
 Sporicidal in 3 to 10 hours.
 Commonly used to disinfect hospital instruments.
 Also used in mortuaries for embalming.
Ethylene Oxide:
 Kills all microbes and endospores, but requires exposure of 4 to 18 hours.
 Toxic and explosive in pure form.
 Highly penetrating.
 Most hospitals have ethylene oxide chambers to sterilize mattresses and large
equipment.

25. D. Selenium
 Kills fungi and their spores. Used for fungal infections.
 Also used in dandruff shampoos.
E. Zinc
 Zinc chloride is used in mouthwashes.
 Zinc oxide is used as antifungal agent in paints.