M
MICROBIOLOGY & PARASITOLOGY
C3
MIDTERMS PHYSICAL AND CHEMICAL METHODS OF STERILIZATION
CONTROL OF MICROBIAL GROWTH killed
- Reduction in number or activity of the total
microbial flora
o Kill: death; irreversible; permanent
loss of ability to reproduce
o Inhibit
o Remove
- Has 2 methods:
o Physical methods
o Chemical methods
DEFINITION OF TERMS
Sterilization
- the process of killing or removing all microbial
forms, including spores.
- Sterilant: sterilizing agent
Commercial Sterilization
- Sufficient heat treatment to kill endospores of Factors affecting the effectiveness of
Clostridium botulinum in canned food. antimicrobial treatments
- More-resistant endospores of thermophilic 1. The number of microbes. The more
bacteria may survive, but they will not microbes there are to begin with, the longer
germinate and grow under normal storage it takes to eliminate the entire population
conditions. 2. Environmental influences. Most
Disinfection disinfectants work somewhat better in warm
- the process by which most microbial forms on solutions.
inanimate objects are killed without necessarily 3. Time of exposure. Chemical antimicrobials
destroying saprophytes and bacterial often require extended exposure to affect
endospores which leads to a reduction in the more-resistant microbes or endospores. See
number of organisms to a level that they the discussion of equivalent treatments
cannot produce infection. 4. Microbial characteristics. The concluding
Antisepsis section of this chapter discusses how
- use of chemical agents on living tissue (e.g., microbial characteristics affect the choice of
skin) to prevent the spread of microorganisms chemical and physical control methods.
either by inhibiting their growth or destroying
them.
Bactericidal or germicidal agent
- agent, physical or chemical, that kills bacteria.
Bacteriostatic agent
- agent, physical or chemical, capable of
inhibiting the growth - of bacteria without
necessarily killing them.
Sporicidal, fungicidal, viricidal
- agents capable of destroying spores, fungi, and
viruses, respectively.
Degerming
- Removal of microbes from a limited area, such
as the skin around an injection site.
- Mostly a mechanical removal by soap and
water or an alcohol-soaked swab.
Sanitization Treatment
- is intended to lower microbial counts on eating
and drinking utensils to safe public health
levels. Note
- May be done with high-temperature washing or Bacterial populations usually die at a
by dipping into a chemical disinfectant. constant rate when heated or when
treated with antimicrobial chemicals.
Rate of Microbial Death It is necessary to use logarithmic numbers
- When bacterial populations are heated or to graph bacterial populations effectively.
treated with antimicrobial chemicals, they Understanding logarithmic death curves
usually die at a constant rate for microbial populations, including the
Example elements of time and the size of the initial
population of 1 million microbes has been population, is especially useful in food
treated for 1 minute, and 90% of the preservation and in the sterilization of
population has died. We are now left with media or medical supplies.
100,000 microbes. If the population is treated
for another minute, 90% of those microbes die, PHYSICAL METHOD OF STERILIZATION
and we are left with 10,000 survivors. In other Heating
words, for each minute the treatment is - the most common physical method of
applied, 90% of the remaining population is sterilization.
Hannah Adan 1
, M
MICROBIOLOGY & PARASITOLOGY
C3
MIDTERMS PHYSICAL AND CHEMICAL METHODS OF STERILIZATION
- rate of killing is expressed in thermal death milk products as well as
time, i.e., the minimum time required to kill a other beverages.
suspension of an organism at a predetermined - variations of this
temperature and environment. method based on
- The mechanisms of action of heating include: the temperature
o formation of single-strand breaks in the utilized. 1.
bacterial DNA; conventional
o coagulation and denaturation of method where the
proteins milk is heated at
o accumulation of toxic levels of 60°C-65 °C followed
electrolytes by rapid cooling.
- alteration of cell membrane structure. 2. flash method
- factors can affect the process of sterilization involves heating at
through heating: 72°C for 15 seconds
o Nature of the heat- moist heat has followed by quick
greater killing action than dry heat. cooling to 13 °C.
o Temperature and time - as 3. ultra-high
temperature increases, the time taken temperature
to sterilize decreases. In other words, (UHT) method
there is an inverse relationship where heating is
between time and temperature. done at 140°C for a
o Number of microorganisms - the period of 15
more microorganisms there are, the seconds and 149 °C
higher the temperature and the longer for 0.5 seconds.
the duration of the process required to Vaccine Bath - used to destroy
destroy all of them. contaminating bacteria
o Nature of microorganisms - spore- in vaccine preparations.
forming microorganisms are more - The vaccine
difficult to destroy than non-spore- preparation is heated in
forming ones. a water bath at 60°C for
o Type of material - the temperature one hour.
required to sterilize materials depend - This procedure is
on the sensitivity of the material to not sporicidal. Only
heat. Heat-sensitive materials will the vegetative forms
require lower temperature than heat- of the bacteria are
resistant materials. destroyed.
o Presence of organic material - the Serum Bath - used to inactivate
presence of organic materials such as bacteria contaminating
fats, proteins, and sugars may serum preparations
necessitate higher temperatures. - is done by heating at
o Thermal Death Point (TDP) - is the 56°C for several
lowest temperature at which all the successive days.
microorganisms in a particular liquid - Similar to vaccine
suspension will be killed in 10 minutes. bath, only the
o Thermal Death Time (TDT) - the vegetative forms are
destroyed since
minimal length of time for all bacteria
higher temperatures
in a particular liquid culture to be killed
will cause
at a given temperature.
coagulation of
o Decimal Reduction time (DRT) - is a
proteins present in
third concept related to bacterial heat
the serum.
resistance; DRT is the time, in minutes,
Inspissation - used to solidify and
in which 90% of a population of
disinfect egg-containing
bacteria at a given temperature will be
and serum- containing
killed
media.
-
- The culture medium is
Types of heat
placed in the slopes of a
Moist Heat
device called an
- kills microorganisms primarily by coagulating
inspissator and is
proteins (denaturation), which is caused by
heated at 80°C-85 °C
breakage of the hydrogen bonds that hold the
for 30 minutes for three
proteins in their three-dimensional structure.
successive days.
- preferred over dry heat because of its more
- The basis for the
rapid killing action.
method is that on the
Classifications of Moist heat
first day, vegetative
Temperature below 100C
forms will die and the
Pasteurization - method of destroying spores that will
disease-producing germinate the following
organisms in milk and
Hannah Adan 2
MICROBIOLOGY & PARASITOLOGY
C3
MIDTERMS PHYSICAL AND CHEMICAL METHODS OF STERILIZATION
CONTROL OF MICROBIAL GROWTH killed
- Reduction in number or activity of the total
microbial flora
o Kill: death; irreversible; permanent
loss of ability to reproduce
o Inhibit
o Remove
- Has 2 methods:
o Physical methods
o Chemical methods
DEFINITION OF TERMS
Sterilization
- the process of killing or removing all microbial
forms, including spores.
- Sterilant: sterilizing agent
Commercial Sterilization
- Sufficient heat treatment to kill endospores of Factors affecting the effectiveness of
Clostridium botulinum in canned food. antimicrobial treatments
- More-resistant endospores of thermophilic 1. The number of microbes. The more
bacteria may survive, but they will not microbes there are to begin with, the longer
germinate and grow under normal storage it takes to eliminate the entire population
conditions. 2. Environmental influences. Most
Disinfection disinfectants work somewhat better in warm
- the process by which most microbial forms on solutions.
inanimate objects are killed without necessarily 3. Time of exposure. Chemical antimicrobials
destroying saprophytes and bacterial often require extended exposure to affect
endospores which leads to a reduction in the more-resistant microbes or endospores. See
number of organisms to a level that they the discussion of equivalent treatments
cannot produce infection. 4. Microbial characteristics. The concluding
Antisepsis section of this chapter discusses how
- use of chemical agents on living tissue (e.g., microbial characteristics affect the choice of
skin) to prevent the spread of microorganisms chemical and physical control methods.
either by inhibiting their growth or destroying
them.
Bactericidal or germicidal agent
- agent, physical or chemical, that kills bacteria.
Bacteriostatic agent
- agent, physical or chemical, capable of
inhibiting the growth - of bacteria without
necessarily killing them.
Sporicidal, fungicidal, viricidal
- agents capable of destroying spores, fungi, and
viruses, respectively.
Degerming
- Removal of microbes from a limited area, such
as the skin around an injection site.
- Mostly a mechanical removal by soap and
water or an alcohol-soaked swab.
Sanitization Treatment
- is intended to lower microbial counts on eating
and drinking utensils to safe public health
levels. Note
- May be done with high-temperature washing or Bacterial populations usually die at a
by dipping into a chemical disinfectant. constant rate when heated or when
treated with antimicrobial chemicals.
Rate of Microbial Death It is necessary to use logarithmic numbers
- When bacterial populations are heated or to graph bacterial populations effectively.
treated with antimicrobial chemicals, they Understanding logarithmic death curves
usually die at a constant rate for microbial populations, including the
Example elements of time and the size of the initial
population of 1 million microbes has been population, is especially useful in food
treated for 1 minute, and 90% of the preservation and in the sterilization of
population has died. We are now left with media or medical supplies.
100,000 microbes. If the population is treated
for another minute, 90% of those microbes die, PHYSICAL METHOD OF STERILIZATION
and we are left with 10,000 survivors. In other Heating
words, for each minute the treatment is - the most common physical method of
applied, 90% of the remaining population is sterilization.
Hannah Adan 1
, M
MICROBIOLOGY & PARASITOLOGY
C3
MIDTERMS PHYSICAL AND CHEMICAL METHODS OF STERILIZATION
- rate of killing is expressed in thermal death milk products as well as
time, i.e., the minimum time required to kill a other beverages.
suspension of an organism at a predetermined - variations of this
temperature and environment. method based on
- The mechanisms of action of heating include: the temperature
o formation of single-strand breaks in the utilized. 1.
bacterial DNA; conventional
o coagulation and denaturation of method where the
proteins milk is heated at
o accumulation of toxic levels of 60°C-65 °C followed
electrolytes by rapid cooling.
- alteration of cell membrane structure. 2. flash method
- factors can affect the process of sterilization involves heating at
through heating: 72°C for 15 seconds
o Nature of the heat- moist heat has followed by quick
greater killing action than dry heat. cooling to 13 °C.
o Temperature and time - as 3. ultra-high
temperature increases, the time taken temperature
to sterilize decreases. In other words, (UHT) method
there is an inverse relationship where heating is
between time and temperature. done at 140°C for a
o Number of microorganisms - the period of 15
more microorganisms there are, the seconds and 149 °C
higher the temperature and the longer for 0.5 seconds.
the duration of the process required to Vaccine Bath - used to destroy
destroy all of them. contaminating bacteria
o Nature of microorganisms - spore- in vaccine preparations.
forming microorganisms are more - The vaccine
difficult to destroy than non-spore- preparation is heated in
forming ones. a water bath at 60°C for
o Type of material - the temperature one hour.
required to sterilize materials depend - This procedure is
on the sensitivity of the material to not sporicidal. Only
heat. Heat-sensitive materials will the vegetative forms
require lower temperature than heat- of the bacteria are
resistant materials. destroyed.
o Presence of organic material - the Serum Bath - used to inactivate
presence of organic materials such as bacteria contaminating
fats, proteins, and sugars may serum preparations
necessitate higher temperatures. - is done by heating at
o Thermal Death Point (TDP) - is the 56°C for several
lowest temperature at which all the successive days.
microorganisms in a particular liquid - Similar to vaccine
suspension will be killed in 10 minutes. bath, only the
o Thermal Death Time (TDT) - the vegetative forms are
destroyed since
minimal length of time for all bacteria
higher temperatures
in a particular liquid culture to be killed
will cause
at a given temperature.
coagulation of
o Decimal Reduction time (DRT) - is a
proteins present in
third concept related to bacterial heat
the serum.
resistance; DRT is the time, in minutes,
Inspissation - used to solidify and
in which 90% of a population of
disinfect egg-containing
bacteria at a given temperature will be
and serum- containing
killed
media.
-
- The culture medium is
Types of heat
placed in the slopes of a
Moist Heat
device called an
- kills microorganisms primarily by coagulating
inspissator and is
proteins (denaturation), which is caused by
heated at 80°C-85 °C
breakage of the hydrogen bonds that hold the
for 30 minutes for three
proteins in their three-dimensional structure.
successive days.
- preferred over dry heat because of its more
- The basis for the
rapid killing action.
method is that on the
Classifications of Moist heat
first day, vegetative
Temperature below 100C
forms will die and the
Pasteurization - method of destroying spores that will
disease-producing germinate the following
organisms in milk and
Hannah Adan 2
