The document discusses various methods for sterilizing and controlling microorganisms, including physical methods like heat, radiation, and filtration as well as chemical methods. It provides details on sterilization techniques like autoclaving, pasteurization, and fractional sterilization. Specific temperatures, exposure times, and processes are outlined for killing different microbes using methods like moist heat, dry heat, UV light, and chemicals.

1. • sterilization
• Sterlization is the destruction or removal of all
living microbes,spores, and viruses on an
object or in an area.
• Agents that kill microbes are microbicidal
• (-cide = “kill”) or more simply called
“germicides

2. • If the agent specifically kills bacteria, it is
bactericidal;if it kills fungi, it is fungicidal.
Many physical methods and chemical agents
are capableof destroying microbes on
nonliving materials or on the skin surface.
• Sanitization involves those procedures
reducing the numbers of pathogenic microbes
or discouraging (inhibiting) their growth.

3. • Many chemical agents are microbiostatic
• (-static = “remain in place”); they reduce
microbialnumbers or inhibit their growth.
Again, agents can be bacteriostatic or
fungistatic.
• Contaminated:
• In microbiology, a once sterile object that is
again harboring microorganisms and/or
viruses.

4. • Aseptic : Free of, or using methods to keep
free of, microorganisms.
• Aseptic processing: The act of handling
materials in a controlled environment, in
which the air supply, materials, equipment,
and personnel are regulated to control
microbial and particulate contamination
within acceptable levels.

5. • The killing rate of heat may be expressed as a
• function of time and temperature. For example,
• bacilli of Mycobacterium tuberculosis are destroyed
• in 30 minutes at 58°C, but in only 2 minutes at
• 65°C, and in a few seconds at 72°C. Each microbial
• species has a thermal death time, the time
• necessary for killing the population at a given
temperature.
• Each species also has a thermal death
• point, the minimal temperature at which it dies
• in a given time.

6. • decimal reduction time (DRT) or D
• value, which is the time required at a
• specific temperature to kill 90% of the
• viable organisms. These are the values
• typically used in the canning industry.
• D values are usually identified by the
• temperature used for killing.

7. Incineration
• Using a direct flame can incinerate
• microbes very rapidly. For example, the flame
• of the Bunsen burner is employed for a few
seconds to sterilize the bacteriological loop
before removing a sample from a culture
tube. In past centuries, the bodies of disease
• victims were burned to prevent spread of the
• plague.

8. hot-air oven
• Dry Heat. The hot-air oven uses radiating dry
• heat for sterilization. This type of energy does not
• penetrate materials easily, and therefore, long periods
• of exposure to high temperatures are necessary.
• For example, at a temperature of 160°C (320°F), a
• period of two hours is required for the destruction
• of bacterial spores.
• . The hot-air method is useful for sterilizing dry powders and
• water-free oily substances, as well as for many types
• of glassware, such as pipettes, flasks, and syringes.
• Dry heat does not corrode sharp instruments as
• steam often does, nor does it erode the ground
• glass surfaces of non disposable syringes

9. hot-air oven

10. • Environmental conditions also influence
• the sterilization time. Microbes
• in acidic or alkaline materials decrease
• sterilization times while microbes in fats
• and oils, which slow heat penetration,
• increase sterilization times.

11. Moist Heat as Boiling Water
• Boiling water is an example of moist heat that
penetrates materials much more rapidly than dry heat
because water molecules conduct heat better than air.
Moist heat kills microorganisms by denaturing
• their proteins. Denaturation is a change in
• the chemical or physical property of a protein.
• It includes structural alterations due to destruction
• of the chemical bonds holding proteins in
• a three-dimensional form

12. • Boiling water is not considered a sterilizing
• agent because the destruction of bacterial spores and
the inactivation of viruses cannot always be assured.
• most species of microorganisms
• can be killed within 10 minutes. Indeed, the
• process may require only a few seconds.
• However, fungal spores, protozoal cysts, and large
concentrations of hepatitis A viruses require up to 30
minutes’ exposure. Bacterial spores often require two
• hours or more.
• Because inadequate information
• exists on the heat tolerance of many species of
• microorganisms, boiling water is not reliable for
• sterilization purposes

13. • Spores killed in 2 hours in hot-air oven
• or 1 hour in hot oil
• Pathogenic bacteria killed in 3 seconds in
• ultra high temperature method
• Most bacterial species killed in 15 minutes and
• spores killed in 30 minutes in autoclave
• Spores killed in 2 hours in boiling water or
• 30 minutes/day for 3 days in fractional
sterilization

14. • Pathogenic bacteria killed in 15 seconds in
flash pasteurization (71.6°C)
• Pathogenic bacteria killed in 30 minutes in
• holding method pasteurization (62.9°C)
• 37°C Human body temperature
• 5°C Refrigerator temperature
• -10°C Home freezer temperature

15. Sterilization with Pressurized Steam.
• Moist heat in the form of pressurized steam is
regarded as the most dependable method for
sterilization, including
• the destruction of bacterial spores. This
method is incorporated into a device called
the autoclave.

16. autoclave

17. • Autoclaves contain a sterilizing chamber into
• which articles are placed, and a steam jacket where
• steam is maintained . As steam flows
• from the steam jacket into the sterilizing chamber,
• cool air is forced out and a special valve increases
• the pressure to 15 pounds/square inch (lb/in2)
• above normal atmospheric pressure.
• The temperature rises to 121.5°C, and the superheated
steam
• rapidly conducts heat into microorganisms. The
• time for destruction of the most resistant bacterial
• species is about 15 minutes. For denser objects or
• larger volumes, more than 30 minutes of exposure
• may be required

18. • The autoclave is used to control microorganisms
• in both hospitals and laboratories. It is
• employed for blankets, bedding, utensils, instruments,
• intravenous solutions, and a broad variety
• of other objects. The laboratory technician uses
• it to sterilize bacteriological media and destroy
• pathogenic cultures. The autoclave is equally valuable
• for glassware and metalware, and is among
• the first instruments ordered

19. Sterilization without Pressurized
Steam.
• In the years before the development of
• the autoclave, liquids and other objects were sterilized
• by exposure to free-flowing steam at 100°C
• for 30 minutes on each of three successive days,
• with incubation periods at room temperature
• between the steaming. The method was called
• fractional sterilization because a fraction of the
• sterilization was accomplished on each day. It was
• also called tyndallization after its developer, John
• Tyndall.

20. • During the first day’s exposure, steam kills virtually all
• organisms except bacterial spores. During overnight
• incubation, the spores germinate and the
• viable cells multiply only to be killed on the second
• day’s 100ºC exposure.
• Again, the material is cooled and any remaining spores
may germinate, the resulting cells only to be killed on
the third day. Although the method usually results in
• sterilization, occasions arise when several spores
• fail to germinate.

21. Pasteurization.
• The final example of moist
• heat involves the process of pasteurization,
which reduces the bacterial population of a
liquid such as milk and destroys organisms
that may cause spoilage and human disease ( .
Spores are not affected by pasteurization.

22. • One method for milk pasteurization, called
• the holding (or batch) method, involves heating at
63°C for 30 minutes. Although any thermophilic
• bacteria would thrive at this temperature, they are
• of little consequence because they cannot grow at
• body temperature. For decades, pasteurization has
• been aimed at destroying Mycobacterium tuberculosis,
• long considered the most heat-resistant bacterial
• species. More recently, however, attention has
• shifted to destruction of Coxiella burnetii, the agent
• of Q fever

23. • bacteria would thrive at this temperature, they are
• of little consequence because they cannot grow at
• body temperature. For decades, pasteurization has
• been aimed at destroying Mycobacterium tuberculosis,
• long considered the most heat-resistant bacterial
• species. More recently, however, attention has
• shifted to destruction of Coxiella burnetii, the agent
• of Q feve

24. • Pasteurization also is
• used to eliminate the Salmonella and Escherichia
• coli that can contaminate fruit juices. Two other
• methods are the flash pasteurization method at
• 71.6°C for 15 seconds and the ultra high temperature
• (UHT) method at 140°C for 3 seconds.
• The UHT method is the only method that sterilizes
• the liquid (MICROFOCUS 7.2). These methods are
• discussed

25. Filtration
• Among the early pioneers of filter
• technology was Charles Chamberland, an
associate of Pasteur. His porcelain filter was
important to early virus research. Another
pioneer was Julius Petri (inventor of the Petri
dish), who developed a sand
• filter to separate bacterial cells from the air.

26. Filtration
• Filtration is a mechanical method that can
• be used to remove microorganisms from a
solution or gas. Several types of filters are
used in the microbiology laboratory. The most
common is the membrane filter,
• which consists of a pad of cellulose acetate
• or polycarbonate mounted in a holding device

27. • The most common is the membrane filter,
• which consists of a pad of cellulose acetate
• or polycarbonate mounted in a holding device.
The membrane filter is particularly valuable
• because bacterial cells trapped on the filter
multiply and form colonies on the filter pad when
• the pad is placed on a plate of culture medium.
• Microbiologists then can count the colonies to
• determine the number of bacteria originally
present

28. Filtration

29. • Membrane filters are used
• to purify such heat-sensitive liquids as
beverages,some bacteriological media,
toxoids, many pharmaceuticals,
• and blood solutions

30. high-efficiency
particulate air (HEPA) filter,
• Air also can be filtered to remove microorganisms.
• The filter generally used is a high-efficiency
• particulate air (HEPA) filter, which consists of
• a mat of randomly arranged fibers that trap particles,
• microorganisms, and spores. As part of a
• biological safety cabinet, HEPA filters can trap
• over 99% of all particles, including microorganisms
• and spores with a diameter larger than 0.3 μm

31. A Biological Safety Cabinet

32. • A Biological Safety Cabinet. The cabinet
• shown has a metal grid at the top that covers a
HEPA filter through which air enters the cabinet.
• As the filtered air,
• free of contaminants and microbes, moves into
and across the workspace, it exits out the bottom
front and rear.
• A UV light is also positioned at the top rear to
decontaminate the metal surfaces maintaining a
contaminant-free workspace when the cabinet is
not in use.

33. Ultraviolet Light
• Visible light is a type of radiant energy
detected by the light-sensitive cells of the eye.
The wavelength of this energy is between 400
and 800 nanometers (nm). Other types of
radiation have wavelengths longer or shorter
than that of visible light, and therefore cannot
be detected by the human eye.

34. • One type of radiant energy, ultraviolet (UV)
• light, is useful for controlling microorganisms.
• Ultraviolet light has a wavelength between
100 to 400 nm, with the energy at about 265
nm most destructive to bacterial cells.
Ultraviolet light effectively reduces the
microbial population where direct exposure
takes place.
• It is used to limit airborne or surface
contamination in a hospital room, morgue,
pharmacy, toilet facility, or food ser vice
operation

35. • When microorganisms are subjected to UV
light,
• cellular DNA absorbs the energy, and adjacent
thymine
• molecules (in the same strand) link together,
• linking the double helix and disrupting DNA
replication
• . The damaged organism can
• no longer produce critical proteins or
reproduce,
• and it quickly dies

36. • Ultraviolet light effectively reduces the microbial
population where direct exposure takes place. It
is used to limit airborne or surface contamination
in a hospital room, morgue, pharmacy, toilet
facility, or food ser vice operation.
• UV light from the sun may be an important
• factor in controlling microorganisms in the air and
• upper layers of the soil, but it may not be
effective against all bacterial spores. Ultraviolet
light does not penetrate liquids or solids, and it
can lead to human skin cancer.

37. X rays and gamma rays
• X rays and gamma rays both have
wavelengths shorter than the wavelength of
• UV light. As X rays and gamma rays pass
through microbial molecules, they force
electrons out of their shells, thereby creating
ions. For this reason,the radiations are called
ionizing radiations.

38. • The ions quickly combine, mainly with cellular
water,
• and the free radicals generated affect cell
metabolism
• and physiology. Ionizing radiations currently
• are used to sterilize such heat-sensitive
pharmaceuticals
• as vitamins, hormones, and antibiotics
• as well as certain plastics and suture materials.

39. • Irradiation now is used as a preservative in more than
40 countries for over 100 food items, including
potatoes, onions, cereals, flour, fresh fruit, and poultry.
• The U.S. Food and Drug Administration (FDA) approved
cobalt-60 and cesium-137 irradiation to preserve or
extend the shelf life of several foods.
• This includes irradiating poultry and red meats such as
beef, lamb, and pork.In 2008, the FDA approved the
irradiation of fresh and bagged spinach, and iceberg
lettuce, to reduce potential foodborne illness.
Irradiation has been used to prepare many meals for
the U.S. military and the American astronauts

40. • a pasteurizing dose is used on meats, poultry,
• and other foods. Such levels are not intended
to eliminate all microbes in the food, but, like
pasteurization of milk, to eliminate the
pathogens.The foods are not necessarily
sterile.

41. Preservation Methods Retard Spoilage
by Microorganisms in Foods
• Dehydration and cold temperatures slow
microbial growth.
• Drying is useful in the preservation of various
• meats, fish, cereals, and other foods. Because
• water is necessary for life, it follows that where
there is no water, there is virtually no life. Many
• nonperishable foods (such as cereals, rice, and
• sugar) in the kitchen pantry represent such
shelfstable products

42. • Preservation by salting is based upon the principle
• of osmotic pressure. When food is salted
• (usually sodium chloride), water diffuses out of
• microorganisms toward the higher salt concentration
• and lower water concentration in the surrounding
• environment.
• This flow of water, called
• osmosis, leaves the microorganisms dehydrated,
• and they die. The same phenomenon occurs in
• highly sugared foods (usually sucrose) such as
• syrups, jams, and jellies. However, fungal contamination
• (molds and yeasts) and growth at the surface may occur
because they can tolerate low water and high sugar
concentrations.

43. • Low temperatures found in the refrigerator
• and freezer retard spoilage by lowering the
metabolic rate of microorganisms and thereby
reducing Spoilage is not totally eliminated in
cold foods, however, and many psychrotrophs
remain alive, even at freezer temperatures.
These organisms multiply rapidly
• when food thaws, which is why prompt
cooking is recommended

44. • The preservation methods are described as
• Bacteriostatic because they prevent the
further multiplication of food-borne
pathogens such as Salmonella and Clostridium

45. Chemical Control Methods
• As early as 1830, the United States
Pharmacopoeia listed tincture of iodine as a
valuable antiseptic, and soldiers in the Civil
War used it in plentiful amounts. Joseph Lister
established the principles of aseptic surgery
using carbolic acid (phenol) for treating
wounds.

46. • the physical agents for controlling
microorganisms generally are intended
• to achieve sterilization. Chemical agents, by
contrast, rarely achieve sterilization. Instead,
they are expected only to destroy the
pathogenic organisms on or in an object or
area. The process of destroying pathogens is
called disinfection and the object is said to be
disinfected

47. • If the object treated is lifeless, such as a tabletop,
the chemical agent used is called a disinfectant.
However, if the object treated is living, such as a
tissue of the human body, the chemical agent
used is an antiseptic It is important to note that
• even though a particular chemical may be used as
• a disinfectant as well as an antiseptic (e.g.,
iodine).

48. • Antiseptics and disinfectants are usually
• microbicidal; they inactivate the major
enzymes of an organism and interfere with its
metabolism so that it dies. A chemical also
may be microbiostatic,disrupting minor
chemical reactions and slowing the
metabolism, which results in a longer time
between cell divisions

49. • The word sepsis (seps = “putrid”) refers to a
• condition in which microbes or their toxins are
• present in tissues or the blood; thus, we have
• septicemia, meaning “microbial infection of the
blood,” and antiseptic, “against infection.” It
• is the origin of the term asepsis, meaning “free
• of disease-causing microbes.”

50. • To sanitize an object is to reduce the
• microbial population to a safe level as determined
• by public health standards. For example, in dairy
• and food-processing plants, the equipment usually
• is sanitized through the process of sanitization.
• Commercial establishments, such as restaurants,
• depend on disinfectants to maintain a sanitary
• kitchen and work establishment.
•
• To degerm an object is merely to remove organisms from
its surface. Washing with soap and water degerms the
• skin surface but has little effect on microorganisms
• deep in the skin pores.

51. • To be useful as an antiseptic or disinfectant,
• a chemical agent must have a number of properties.
• The agent should be:
• • Able to kill or slow the growth of microorganisms.
• • Nontoxic to animals or humans, especially
• if it is used as an antiseptic.
• • Soluble in water and have a substantial
• shelf life during which its activity is
• retained.
• • Useful in much diluted form and able to
• perform its job in a relatively short time.

52. • Other characteristics also will contribute to
• the value of a chemical agent: It should not
separate on standing, it should penetrate well,
and it should not corrode instruments

53. • Because disinfection is essentially a chemical
• process, several chemical parameters should be
• considered when selecting an antiseptic or disinfectant.
• • Temperature. It is important to know at
• what temperature the disinfection is to
• take place because a chemical reaction
• occurring at 37°C (body temperature) may
• not occur at 25°C (room temperature).
• • pH. A particular chemical may be effective
• at a certain pH but not another.
• • Stability. The chemical reaction may be
• very rapid with one agent and slower
• with another. Thus, if long-term disinfection
• is desired, the second agent may be
• preferable.

54. Antiseptics and Disinfectants
Can Be Evaluated for Effectiveness
• Standards have been established to know the
relative effectiveness of a chemical agent.
• One measure of effectiveness for chemical
• agents is the phenol coefficient (PC). This
• is a number indicating the disinfecting ability
• of an antiseptic or disinfectant in comparison
• to phenol under identical conditions

55. • A phenol coefficient (PC) higher than 1 indicates the
• chemical is more effective than phenol; a number less
than 1 indicates poorer disinfecting ability than phenol.
• The phenol coefficient is determined by a laboratory
• procedure in which dilutions of phenol
• and the test chemical are mixed with standardized
• bacterial species, such as Staphylococcus aureus,
• Salmonella typhi, or other species. The laboratory
• technician then determines which dilutions have
• killed the organisms after a 10-minute exposure
• but not after a 5-minute exposure.

56. • more practical way of determining the value
• of a chemical agent is by an in-use test. For
example,
• swab samples from a floor are taken before
• and after the application of a disinfectant to
determine
• the level of disinfection.
• Another method is to dry standardized cultures of
a bacterial species on small stainless steel
cylinders and then expose the cylinders to the
test chemical. After an established period of time,
the organism is tested for
• survival rates.

57. Halogens
• The halogens are a group of highly reactive
elements
• whose atoms have seven electrons in the
• outer shell Two halogens, chlorine
• and iodine, are commonly used for disinfection.
• In microorganisms, halogens are believed
• to cause the release of atomic oxygen, which
then combines with and inactivates certain
cytoplasmic

58. • proteins, such as enzymes. Killing almost
always occurs within 30 minutes after
application.
• Chlorine (Cl) is effective against a broad
• variety of organisms, including most gram
positive and gram-negative bacteria, and
many viruses, fungi, and protozoa. However, it
is not sporicidal Chlorine is available in a
gaseous form and as both organic and
inorganic compounds

59. • It is widely used in municipal water
• supplies and swimming pools, where it keeps
• microbial populations at low levels

60. • It is widely used in municipal water
• supplies and swimming pools, where it keeps
• microbial populations at low levels. Chlorine
• combines readily with numerous ions in water;
• therefore, enough chlorine must be added to
• ensure a residue remains for antimicrobial
activity.
• In municipal water, the residue of chlorine is
• usually about 0.2 to 1.0 parts per million (ppm)
• of free chlorine. One ppm is equivalent to 0.0001
• percent, an extremely small amount.

61. • Hypochlorite compounds cause cellular proteins
• to clump together, destroying their function. To
• disinfect clear water for drinking, the Centers
• for Disease Control and Prevention (CDC)
recommends
• a half-teaspoon of household chlorine
• bleach in two gallons of water, with 30 minutes of
• contact time before consumption. Hypochlorites
• also are useful in very dilute solutions for
sanitizing
• commercial and factory equipment.

62. • The chloramines, such as chloramine-T, are
• organic compounds used as bactericides and
for the disinfection of drinking water.

63. • The iodine atom (I) is slightly larger than the
• chlorine atom and is more reactive and more
germicidal.
• A tincture of iodine, a commonly used
• antiseptic for wounds, consists of 2% iodine. For
• the disinfection of clear water, the CDC
recommends
• five drops of an iodine tincture in one quart
• of water, with 30 minutes of contact time before
• consumption. Iodine compounds in different
• forms are also valuable sanitizers for restaurant
• equipment and eating utensils.

64. • Iodophors are iodine linked to a solubilizing
• agent, such as a detergent or nondetergent carrier.
• These water-soluble complexes release iodine over
• a long period of time and have the added advantage
• of not staining tissues or fabrics.
• The solubilizing agent loosens the organisms from the surface
• and diatomic iodine (I2) irreversibly damages the
• microbe by reacting with enzymes and with proteins in the cell
membrane and cell wall.
• Some examples of iodophors are Wescodyne, used in preoperative
• skin preparations; and Betadine, for local wounds.
• Iodophors also may be combined with nondetergent
• carrier molecules. The best known carrier is
• povidone, which stabilizes the iodine and releases
• it slowly.

65. Phenol and Phenolic Compounds
• Phenol (carbolic acid) and phenolic compounds have
played a key role in disinfection practices since Joseph
Lister used them in the 1860s. Pheno remains the
standard against which other antiseptics
• and disinfectants are evaluated using the
• phenol coefficient test. It is active against gram
• Positive bacteria, but its activity is reduced in the
• presence of organic matter. Phenol and its derivatives
• act by denaturing proteins, especially in the
• cell membrane.

66. • Phenol is expensive, has a pungent odor, and is
• caustic to the skin; therefore, the role of phenol as an
• antiseptic has diminished However,
• phenol derivatives have greater germicidal activity
• and lower toxicity than the parent compound.
• Hexylresorcinol is used in some mouthwashes,
• topical antiseptics, and throat lozenges. It has
• the added advantage of reducing surface tension,
• thereby loosening bacterial cells from tissue and
• allowing greater penetration of the germicidal
• agent

67. • Combinations of two phenol molecules called
• bisphenols are prominent in modern disinfection and antisepsis.
Orthophenylphenol, for example,
• is used in Lysol and Amphyl. Another bisphenol,
• hexachlorophene, was used extensively during
• the 1950s and 1960s in toothpastes, underarm
• deodorants, and bath soaps.
• One product,pHisoHex, combined hexachlorophene with a
• pH-balanced detergent cream. Pediatricians recommended
• it to retard staphylococcal infections
• of the scalp and umbilical stump and for general
• cleansing of the newborn.
• However, studies indicate that excessive amounts can be absorbed
• through the skin and cause neurological damage,
• so hexachlorophene has been removed from overthe-
• counter products. The product pHisoHex is
• still available, but only by prescription

68. • An important bisphenol relative is chlorhexidine.
• This compound is used as a surgical scrub,
• hand wash, and superficial skin wound cleanser.
• A 4% chlorhexidine solution in isopropyl alcohol
• is commercially available as Hibiclens. Another
• bisphenol in widespread use is triclosan, a broadspectrum
• antimicrobial agent that destroys bacterial
• cells by disrupting cell membranes (and
• possibly cell walls) by blocking the synthesis of
• lipids. Triclosan is fairly mild and nontoxic, and
• it is effective against pathogenic bacteria (but only
• partially against viruses and fungi).
• The chemical is included in antibacterial soaps, lotions,
mouthwashes,
• toothpastes, toys, food trays, underwear,
• kitchen sponges, utensils, and cutting boards

69. Heavy
metals
• Mercury, silver, and copper are called heavy
• metals because of their large atomic weights and
complex electron configurations. They are very reactive
with proteins, particularly at the protein’s sulfhydryl
groups (–SH), and they are believed to bind protein
molecules together by forming. bridges between the
groups. Because many of the
• proteins involved are enzymes, cellular metabolism
• is disrupted, and the microorganism dies.
• However, heavy metals are not sporicidal.

70. Mercury (Hg)
• Mercury (Hg) is very toxic to the host and the
• antimicrobial activity of mercury is reduced
when other organic matter is present.
mercury is combined with carrier
• compounds and is less toxic when applied to
the skin, especially after surgical incisions.
• Hg is used as skin antiseptic and
disinfectant.Their compounds are mercuric
chloride ,merthiolate and merbromin.

71. • Copper (Cu) is active against chlorophyll
containing organisms and is a potent inhibitor
of algae. As copper sulfate (CuSO4), it is
incorporated into algicides and is used in
swimming pools and municipal water supplies.

72. Silver (Ag)
• Silver (Ag) in the form of silver nitrate
• (AgNO3) is useful as an antiseptic and disinfectant.
• For example, one drop of a 1% silver nitrate
• solution used to be placed in the eyes of newborns
• to protect against infection by Neisseria
• gonorrhoeae. This gram-negative diplococcus can
• cause blindness if contracted by a newborn during
• passage through an infected mother’s birth
• canal

73. Alcohols
• For practical use, the preferred alcohol is ethyl
• alcohol (ethanol), which is active against
vegetative bacterial cells, including the
tubercle bacillus,but it has no effect on spores.
It denatures proteins and dissolves lipids, an
action leading to cell membrane
disintegration. Ethyl alcohol also
• is a strong dehydrating agent.

74. • Because ethyl alcohol reacts readily with
• organic matter, medical instruments and
thermometers must be thoroughly cleaned
before exposure. Usually, a 10-minute
immersion in 50% to 80% alcohol solution is
recommended to disinfect because water
prevents rapid evaporation. Ethyl
• alcohol is used in many popular hand
sanitizers.

75. • Alcohol is used to treat skin before a injection.
It mechanically removes bacterial cells from
the skin and dissolves lipids. Isopropyl
• alcohol, or rubbing alcohol, has high
bactericidal activity in concentrations as high
as 99%.

76. Soaps and Detergents
• Soaps are chemical compounds of fatty acids
combined with potassium or sodium
hydroxide. The pH of the compounds is usually
about 8.0, and some microbial destruction is
due to the alkaline conditions they establish
on the skin. the major activity of soaps is as
degerming agents for the mechanical removal
of microorganisms from the skin surface

77. • Soaps, therefore, are surface-active agents
• called surfactants; that is, they emulsify and
solubilize particles clinging to a surface and
reduce the surface tension. Soaps also remove
skin oils, further reducing the surface tension
and increasing the cleaning action.

78. Detergents
• Detergents are synthetic chemicals acting
• as strong surfactants. Because they are actively
• attracted to the phosphate groups of cellular
membranes,
• they also alter the membranes and encourage
• leakage from the cytoplasm. When used to
• clean cutting boards, for example, they can
reduce the possibility of transmitting
contaminants.

79. • The most useful detergents to control
microorganisms are cationic (positively
charged) derivatives of ammonium chloride.
In these detergents, four organic radicals
replace the four hydrogens. and at least one
radical is a long hydrocarbon chain Such
compounds often are called quaternary
ammonium compounds or, simply, quats.
They react with cell membranes and can
• destroy some bacterial species and enveloped
• viruses.

80. Quats
• Quats have rather long, complex names,
• such as benzalkonium chloride in Zephiran and
• cetylpyridinium chloride in Ceepryn. Quats are
• bacteriostatic, especially on gram-positive bacteria,
• and are relatively stable, with little odor.
• They are used as sanitizing agents for industrial
• equipment and food utensils; as skin antiseptics;
• as disinfectants in mouthwashes and contact lens
• cleaners; and as disinfectants for use on hospital
• walls and floors.
• Their use as disinfectants for food-preparation surfaces can help
reduce contamination incidents.

81. Peroxides
• Peroxides are compounds containing oxygen-
oxygen single bonds. Hydrogen peroxide (H2O2)
• has been used as a rinse in wounds, scrapes, and
• abrasions. However, H2O2 applied to such areas.
• foams and effervesces, as catalase in the tissue
• breaks down hydrogen peroxide to oxygen and
• water. Therefore, it is not recommended as an
• antiseptic for open wounds

82. • Hydrogen peroxide decomposition
• also results in a reactive form of oxygen—
• the superoxide radical—which is highly toxic to
microorganisms.
• New forms of H2O2 are more stable than
traditional forms, do not decompose
spontaneously, and therefore can be used
topically. Such materials as soft contact lenses,
utensils, heat sensitive
• plastics, and food-processing equipment
• can be disinfected within 30 minutes.

83. • Benzoyl perioxide is another peroxide
chemical.At low concentrations (2.5%), it is
used to treat acne and is an active ingredient
in teeth whitening products.

84. • Aldehydes. Aldehydes are agents that react
• with amino and hydroxyl groups of nucleic
acids and proteins. The resulting cross linking
inactivates the proteins and nucleic acids.

85. • Formaldehyde is a gas at high temperatures
• and a solid at room temperature. As a 37% solution
• it is called formalin. For over a century, formalin
• was used in embalming fluid for anatomical
• specimens (though rarely used anymore) and by
• morticians for disinfecting purposes.
• In microbiology, formalin is used for inactivating
viruses in certain vaccines and producing toxoids from
• toxins (

86. • Instruments can be sterilized by placing them
• in a 20% solution of formaldehyde in 70%
alcohol for 18 hours.
• Formaldehyde, however, leaves a
• residue, and instruments must be rinsed
before use. Many allergic individuals develop
a contact dermatitis to this compound

87. • Glutaraldehyde is a small, organic molecule
• that destroys bacterial cells within 10 to 30
minutes
• and spores in 10 hours. As a 2% solution,
• glutaraldehyde can be used for sterilization
purposes.
• Materials have to be precleaned, then
• immersed for 10 hours, rinsed thoroughly with
sterile water, dried in a special cabinet with
sterile air, and stored in a sterile container to
ensure that the material remains sterile. If any of
these parameters are altered, the materials may
be disinfected but may not be considered sterile

88. • Glutaraldehyde does not damage delicate
• objects, so it can be used to disinfect or
sterilize optical equipment, such as the fiber-
optic endoscopes used for arthroscopic
surgery. It gives off irritating fumes, however,
and instruments must be rinsed thoroughly in
sterile water.

89. Sterilizing Gases
• . In the 1950s, research scientists discovered
• the antimicrobial abilities of ethylene oxide,
• which essentially made the plastic Petri dish
and plastic syringe possible.

90. • Ethylene oxide is a small molecule with
excellent penetration capacity, and is
microbicidal as well as sporicidal by combining
with cell proteins. However, it is carcinogenic
and highly explosive. Its explosiveness is
reduced by mixing it with Freon

91. • gas or carbon dioxide gas, but its toxicity
remains a problem for those who work with it.
• The gas is released into a tightly sealed
chamber where it circulates for up to four
hours with carefully controlled humidity.
• The chamber then must be flushed with inert
gas for 8 to 12 hours to ensure that all traces
of ethylene oxide are removed; otherwise the
chemical will cause “cold burns” on contact
with the skin.

92. • Ethylene oxide is used to sterilize paper,
• leather, wood, metal, and rubber products as
• well as plastics. In medicine, it is used to
sterilize catheters, artificial heart valves,
heart-lung machine components, and optical
equipment

93. • Chlorine dioxide has properties very similar
• to chloride gas and sodium hypochlorite but,
• unlike ethylene oxide, it produces nontoxic byproducts
• and is not a carcinogen.
• Chlorine dioxide
• can be used as a gas or liquid. In a gaseous form,
• with proper containment and humidity, a 15-hour
• fumigation can be used to sanitize air ducts, food
• and meat processing plants, and hospital areas.
• It was the gas used to decontaminate the 2001
• anthrax-contaminated mail and office buildings