Important words and
concepts from Chapter 12, Black, 1999 (3/28/2003):
by Stephen T. Abedon (abedon.1@osu.edu)
for Micro 509
at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to access
text’s website Vocabulary
words
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(1) Chapter title: Sterilization and Disinfection
(a)
Some
general external links: [sterilization and disinfection
(Google Search)] [the control of microbial
growth] [the control of microbial
growth] [sterilization and disinfection
(CDC hospital infections program)] [index]
ELIMINATING MICROBES
(a)
A
disinfectant is a chemical or physical agent that is applied to inanimate
objects to kill microbes
(b)
[disinfectants (Google Search)] [index]
(a)
Typically
an antiseptic is a chemical agent that is applied to living tissue to kill
microbes
(b)
Note
that not all disinfectants are antiseptics because an
antiseptic additionally must not be so harsh that it damages living tissue
(c)
With
this constraint imposed on antiseptics, in general antiseptics are either not
as cheap or not as effective at killing microbes as disinfectants
(d)
[antiseptics (Google Search)] [antiseptic] [index]
(a)
Sterilization
is the killing of all microorganisms in a material or on the surface of an
object
(b)
A
surface or an object is either sterile or it is not sterile, there are no
gradations in sterility
(c)
Typically
the last things to die when one attempts sterilization is the highly heat- (and
chemical-, etc.) resistant endospores
(d)
[sterilization and microbiology
(Google Search)]
[index]
(a)
Disinfection
means reducing the number of viable microorganisms present in a sample
(b)
Not
all disinfectants are capable of sterilizing, but,
of course, all disinfectants are employed with the hope of disinfecting
(c)
[disinfection (Google Search)] [aircraft disinfection requirements] [child-care cleaning and disinfection] [Kleen® Pen pen and pencil disinfecting system] [index]
(a)
Sanitization
is the cleaning of pathogenic microorganisms from public eating utensils and
objects such as that done by the kitchen of a restaurant
(b)
[sanitization (Google Search)] [index]
KILLING MICROBES
(a)
The
killing of microorganisms occurs exponentially where some fraction of the
living population dies per unit time
(b)
"A definite proportion of the organisms die
in a given time interval."
(c)
"Soon
the probability of finding even a single live organism becomes very small. Most
laboratories say a sample is sterile if the probability is no greater than one
chance in a million of finding a live organism."
(d)
[exponential death (Google Search)] [index]
(a)
"The fewer organisms present, the shorter the
time needed to achieve sterility. Thoroughly cleaning objects before
attempting to sterilize them is a practical application of this principle.
Clearing objects of tissue debris and blood is also important because such
organic matter impairs the effectiveness of many chemical agents."
(b)
[cleanliness and disinfection
(Google Search)]
[index]
(a)
"Microorganisms differ in their
susceptibility to antimicrobial agents."
(b)
Often
what fails to be killed by a disinfectant are endospores though
certain viruses and some vegetative bacteria are also highly resistant to
disinfection
(c)
Also,
the same organism may differ in susceptibility depending on growth phase with
actively growing organisms typically more susceptible to disinfection than
not-growing cultures
(a)
Increasing
temperatures increases the efficacy of most chemical antimicrobials
(b)
The
converse of this statement is that relatively cold temperatures result in
relatively poor disinfection
(c)
[disinfection and temperature
(Google Search)]
[index]
(a)
Generally,
the use of more disinfectant provides better killing than the
use of less disinfectant
(a)
An
antimicrobial that kills a microorganism (or,
more specifically, a bacterium) is said to be bactericidal
(b)
[bactericidal (Google Search)] [index]
(a)
Some
antimicrobials are only bacteriostatic,
including some bactericidal agents used at too-low
concentrations
(b)
Bacteriostatic
means that the antimicrobial
inhibits bacterial growth but does not kill the bacteria; consequently, removal
or dilution of the antimicrobial can result in a resurgence of bacterial growth
(c)
Note
that sufficient, prolonged application of even bacteriostatic agents can often
result in bacterial death, a consequence, for example, of extended dormancy in
which cellular repair is inhibited
(d)
[bacteriostatic (Google Search)] [index]
(a)
As
quoted from your text: "An ideal disinfectant should
(i)
Be
fast acting even in the presence of organic substances, such as those in body
fluid; [resistant to inactivation]
(ii)
Be
effective against all types of infectious agents without destroying tissues or
acting as a poison if ingested; [broadly active]
(iii)
Easily
penetrate material to be disinfected without damaging or discoloring the
material; [not poisonous or otherwise harmful]
(iv)
Be
easy to prepare and stable even when exposed to light, heat, or other
environmental factors; [penetrating; not damaging to non-living materials]
(v)
Be
inexpensive and easy to obtain and use; [stable; easily prepared]
(vi)
Not
have an unpleasant odor. [not unpleasant to work with]"
(b)
Note
that different disinfectants typically have different strengths and weaknesses,
and often what disinfectant one uses depends on circumstances
(c)
Remember,
the best thing one can do if unsure or ignorant of disinfectant abilities is to
read the label
(d)
[ideal disinfectant (Google Search)] [phenol factsheet] [index]
SPECIFIC CHEMICAL ANTIMICROBIALS
(15) Mechanisms of action of chemical agents
(a)
Different
disinfectants have different mechanisms of action
(b)
All
disinfectants act by harming microorganisms in some manner
(c)
Mechanisms
of harm include
(i)
Protein
denaturation
(ii)
Membrane
disruption
(iii)
Nucleic
acid damage
(iv)
Inhibition
of metabolism
(16) Specific antimicrobial agents
(a)
A
variety of chemical antimicrobials exist including
(i)
Surfactants
(ii)
Various
organic acids and bases
(iii)
Heavy
metals
(iv)
Halogen-containing
compounds
(v)
Alcohols
(vi)
Phenol and phenol derivatives
(vii)
Oxidizing
agents
(viii)
Alkylating agents
(ix)
Certain
dyes
(x)
Other
agents
(b)
A
variety of physical antimicrobials exist including
(i)
Heat
(the most economical and widely employed antimicrobial)
(iii)
Ionizing radiation
(iv)
Strong visible light
(v)
Ultrasonic
waves
(vi)
Filtration
(vii)
Osmotic
pressure
(c)
We
additionally will consider freezing as a means of microbe preservation
(a)
Surfactants
are substances that are soluble in water but are able to dissolve lipids
(b)
In
that way they are able to increase the solubility of lipids in water solutions
(c)
Surfactants
additionally increase the ability to water solutions to wet, i.e., move along
or penetrate, lipid surfaces
(d)
Examples
of surfactants are soaps and detergents
(e)
[surfactants and disinfection
(Google Search)]
[index]
(a)
Soaps
are sodium or potassium salts of fatty acids
(b)
Consequently,
soaps are alkaline (pH greater than 7)
(c)
Soaps
exert their antimicrobial effects in two ways
(i)
By
harming bacteria that are sensitive to high pH's
(ii)
By
removing pathogens from surfaces by cleaning the surface (a.k.a., degerming)
(d)
See Figure 12.3, The action
of a surfactant [which shows, particularly, soaps in action]
(e)
[soap and disinfection
(Google Search)]
[index]
(a)
Detergents
are synthetic surfactants
(b)
There
are a variety of structural types of detergents
(c)
A
detergent may be cationic (positively charged) or anionic (negatively charged)
(d)
Cationic detergents are better at killing
bacteria than anionic detergents
(e)
[detergents and disinfection
(Google Search)]
[index]
(20) Quaternary ammonium compounds (quats)
(a)
One
type of commonly employed cationic detergent disinfectants are
quaternary ammonium compounds (quats)
(b)
Problems
with the use of quats as disinfectants include
(i)
Their
inactivation by soaps
(ii)
Their
inhibition by divalent cations (calcium and magnesium ions)
(iii)
Their
inhibition by cotton and other porous organic substances
(iv)
Their
inability to kill certain species of Pseudomonas
(c)
"Quats
are now often mixed with another agent to overcome some of these problems and
to increase their effectiveness."
(d)
["quarternary
ammonium" and disinfection, quats and disinfection
(Google Search)] [adding ammonia to their
chlorine disinfection systems] [index]
(a)
Various
organic acids are employed especially as inhibitors of fungi and molds in foods
(b)
For
example, benzoate of soda is a sodium salt of benzoic acid, an organic acid
(c)
[antimicrobial and
"organic acids" (Google Search)] [index]
(a)
Various
metals and metal salts are commonly employed to prevent microbial growth or
kill microbes
(b)
For
example, silver nitrate has been and increasingly is again used to treat the
eyes of newborns to kill any Neisseria gonorrhea that may have been
acquired during passage down the birth canal
(c)
A
common example in Ohio is the treatment of ponds with copper sulfate (which is
blue in water solution) as an anti-algal; note that though effective at
inhibiting algal growth in ponds, it may be similarly disruptive of algal
growth in down-stream ecosystems
(d)
Selenium
compounds are effective antifungals
(e)
["silver nitrate" and
antimicrobial (Google Search)] [index]
(a)
Halogens
are the seventh (VII) column of the periodic table of elements
(b)
Two
halogens are regularly employed as antimicrobials: iodine
and chloride
(c)
[halogens and disinfection
(Google Search)]
[index]
(24) Chlorine and Hypochlorite ion
(a)
Drinking
water is commonly disinfected using hypochlorite
(b)
Hypochlorite
may either be added directly (i.e., in the form of bleach) or created within
water by bubbling chlorine gas through the water
(c)
Note
that chlorine is less effective in the presence of significant organic
compounds (basically because the hypochlorite ion interacts
with--oxidizes--organic compounds indiscriminately and thus is used up in the
presence off excess organic compounds)
(d)
(bromine
sometimes is employed as a substitute for chlorine)
(e)
[chlorine and disinfection,
hypochlorite and disinfection
(Google Search)]
[index]
(a)
Iodine
is often employed as a tincture or as an iodophor
(b)
A
tincture is an alcohol solution of a substance, in this case iodine
(c)
Iodine
tinctures may be employed as antiseptics
(d)
[iodine and disinfection
(Google Search)]
[index]
(a)
Iodophors
are organic compounds that slow the release of iodine
(b)
The
iodophors additionally serve as surfactants, thus increasing penetration
while simultaneously steadily supplying iodine over long periods
(c)
Betadine
and Isodine are examples of iodophors
(d)
[iodophor and disinfection,
betadine and disinfection,
isodine and disinfection
(Google Search)]
[index]
(a)
Alcohols
work best as 70 to 99% mixtures with water
(b)
Alcohol-water
mixtures are additionally more penetrating than pure alcohols
(c)
Either
ethanol or isopropyl (rubbing) alcohol may be employed for disinfecting
(d)
Alcohols
are especially appropriate for application to sites in which their propensity
to evaporate away is convenient (e.g., to disinfect skin prior to injection)
(e)
The
down side of alcohols is that they are not terribly penetrating nor capable of
killing endospores or other
resistant cells
(f)
Alcohols
should not be applied to wounds since they can cause tissue damage
(g)
[alcohol and disinfection
(Google Search)]
[index]
(28) Phenol and phenol derivatives (phenolics)
(a)
Phenol
and their derivatives (called phenolics) are especially useful when
disinfecting materials contaminated with organic materials
(b)
Lysol®
employs phenolics
(c)
Some
phenolics are mild enough for use as antiseptics while
others are too harsh or otherwise dangerous to be employed on living tissue
(d)
[phenol and disinfection
(Google Search)]
[index]
(29) Oxidizing agents (hydrogen peroxide)
(a)
Hydrogen
peroxide (HOOH) is a typical oxidizing agent
(b)
Note
that hydrogen peroxide is actually not a terribly effective antiseptic
or disinfectant
(c)
This
is because bacteria and body tissues contain enzymes (catalase) that inactivate
hydrogen peroxide
(d)
On
the other hand, the oxygen released upon inactivation can help oxygenate deep
wounds and thus kill strict-anaerobe contaminants
(e)
[peroxide and disinfection
(Google Search)]
[index]
(30) Alkylating agents (formaldehyde, glutaraldehyde,
ethylene oxide)
(a)
Formaldehyde,
glutaraldehyde, and ethylene oxides are alkylating agents—they add
carbon-containing functional groups to biological molecules
(b)
Formaldehyde
is employed to inactivate viruses and toxins to produce whole-killed vaccines
and toxoid vaccines [whole-killed vaccines]
(c)
Glutaraldehyde
is capable of sterilizing equipment, though to effect
sterilization often requires many hours of exposure
(d)
Ethylene
oxide is a gaseous chemosterilizer that is especially useful due to its
extraordinary penetrating power; this allows it to penetrate all sorts of nooks
and crannies
(e)
Ethylene
oxide is employed to sterilize prepackaged laboratory equipment that is
otherwise destroyed by heat (e.g., plastic petri dishes)
(f)
[ethylene and disinfection
(Google Search)]
[ethyleneoxide second edition]
[ethylene oxide laboratory
safety] [ethylene oxide UATW]
[index]
(g)
[formaldehyde and disinfection,
glutaraldehyde and
disinfection (Google Search)] [index]
SPECIFIC PHYSICAL ANTIMICROBIALS
(a)
Heat
is a highly efficient means of sterilization so long as the material to
be sterilized is resistant to heat
(b)
Different
types of heat application include
(i)
Dry
heat
(ii)
Moist
heat
(iii)
Pasteurization
(c)
[heat and disinfection
(lots of stuff on disinfecting contact lenses), heat and disinfection -contact,
heat and sterilization
(Google Search)]
[index]
(a)
To
effect sterilization dry heat typically requires higher temperatures
than moist heat
(b)
It
also is less penetrating and requires longer exposure
(c)
Nevertheless,
application of dry heat is cheap and easy
(d)
Typically
one bakes materials in an oven at
(i)
171ºC
for at least one hour
(ii)
160ºC
for at least two hours
(iii)
121ºC
for at least 16 hours
(e)
Note
that the length of exposure necessary is inversely proportional to the
temperature (lower temps require longer exposures)
(f)
Note
additionally that the times given are for once the indicated temperature has
been achieved; this is true for all methods of disinfection and sterilization:
the clock does not begin until the material has been exposed to the antimicrobial
(g)
Incineration
is another common method of dry heat sterilization, e.g., such as the flame
incineration of an inoculating loop
(h)
[disinfection and "dry
heat" (Google Search)]
[index]
(a)
Moist
heat is more effective than dry heat at a given temperature or length
of exposure
(b)
Moist
heat is also more penetrating than dry heat
(c)
However,
to achieve sterilization employing moist heat requires
rather elaborate equipment, i.e., the employment of an autoclave
(d)
Just
as with dry heat, temperature and length of exposure are inversely related and
penetration is absolutely critical
(e)
With
moist heat, penetration is even more of a problem since penetration of heat
without associated penetration of moisture is simply dry heat and dry
heat is less effective as an antimicrobial than
moist heat; consequently, things that block moisture penetration can inhibit
sterilizing efficacy
(f)
Boiling
water is the most common form of application of moist heat but is not capable
of killing endospores or
killing all viruses
(g)
[disinfection and "moist
heat" (Google Search)]
[index]
(a)
An
autoclave is a high pressure device used to allow the application of moist
heat above the normal-atmosphere boiling point of water
(b)
Exposure
to 121ºC for 15+ minutes is typically sufficient to sterilize
(c)
Again,
the material must be 121ºC before the clock starts
(d)
Large
items, large volumes, and items that are poorly penetrated by steam may take
much longer than 15 minutes to sterilize
(e)
See Figure 12.10, The
autoclave
(f)
[autoclave (Google Search)] [index]
(a)
Pasteurization
is the application of moist heat of less-than boiling temperatures to
foods to prevent the growth of food-spoiling organisms as well as various
heat-labile pathogens
(b)
[pasteurization (Google Search)] [index]
(a)
Microbial
preservation includes methods of avoiding all of the above as well as the
ravages of exponential decline associated with the standard bacterial growth curve
(b)
Methods
of microbial preservation include:
(i)
Refrigeration
(ii)
Freezing
(iii)
Desiccation
(iv)
Freeze
drying (lyophilization)
(c)
[microbe preservation
(Google Search)]
[index]
(a)
Refrigeration
is a great short term solution, but it merely slows the decline of organisms
rather than preventing it
(b)
Of
course, for psychrophiles the refrigerator could
represent a fairly good growth environment
(c)
[refrigeration and microbiology
(Google Search)]
[index]
(a)
Freezing
is employed to more completely stave off organismal deterioration
(b)
For
organisms that survive the freezing process, freezing constitutes a reasonably
good long-term preservation method with prevention of deterioration increasing
as temperatures are lowered
(c)
Prevention
of damage during freezing is accomplished by mixing cultures with glycerol
(d)
Lower
temperatures result in greater long-term storage:
(i)
-20ºC
is the temperature of a standard freezer
(ii)
-80ºC
is a good temperature for long-term storage of microorganisms
(iii)
-180ºC
is the temperature of liquid nitrogen, a common medium for long-term storage of
microorganisms
(e)
[freezer and microbiology,
freezing and microbiology
(Google Search)]
[index]
(a)
Desiccation
means drying, i.e., removal of water
(b)
Desiccation
prevents organism metabolism, and is a good means of preventing organism growth
(c)
Desiccation
is an effective means of organism storage for those organisms capable of
remaining viable upon desiccation
(d)
[desiccation and bacteria
(Google Search)]
[index]
(40) Freeze drying (lyophilization)
(a)
Freeze-drying
involves freezing something and then evacuating air so that boiling occurs at
low temperatures; this desiccates material thereby preventing deterioration and
spoilage
(b)
Lyophilization
is the word used for the freeze-drying preservation of microorganisms; it is
widely effective but has been to a large extent supplanted by the use of
ultra-low temperature freezers (e.g., -80ºC)
(c)
[lyophilization, preservation and bacteria and
"freeze dry" (Google Search)] [index]
(41) Ultraviolet (UV) radiation
(a)
UV
light is not terribly penetrating but is good for disinfecting
surfaces and air
(b)
This
is accomplished by a long-term exposure to UV light
(c)
On
the down side, UV light is damaging to human tissue as well as to many plastics
(d)
[ultraviolet and disinfection
(Google Search)]
[UV waterworks: reliable,
inexpensive water disinfection for the world] [safe sun?] [index]
(a)
Ionizing
radiation is radiation that ionizes water; this temporarily turns water into an
oxidizing agent
(b)
Different
types of ionizing radiation display different degrees of penetration
(c)
One
potential application of ionizing radiation is as an antimicrobial is in
food preservation
(d)
[disinfection and
"ionizing radiation" (Google Search)] [index]
(a)
Strong
visible light can negatively affect bacterial viability so excessive exposure
to strong visible light should be avoided when one's goal is culture
preservation
(b)
Practical
application of strong visible light to disinfection involves the use of sun
light to dry laundry (i.e., that “old-fashioned” alternative to a cloths dryer)
(c)
[bacteria and "strong
visible light" (Google Search)] [solar disinfection studies:
drinking water] [water disinfection by solar radiation] [index]
(44) Filtration (HEPA filters)
(a)
Filtration
is a common means of antimicrobial
treatment used when materials are heat labile
(b)
Filtration
does not necessarily sterilize unless very small filter pores are employed (and
the speed and ease with which one may filter something is indirectly
proportional to pore size with large pores much quicker and easier than small
pores)
(c)
High-efficiency
particulate air (HEPA) filters are used to filter the air flowing into aseptic
environments and out of potentially contaminated ones (e.g., containment
facilities)
(d)
[filtration and microbiology,
"hepa filter"
-vacuum (Google Search)]
[minimize microbial growth]
[index]
ASSESSING ANTIMICROBIAL EFFICACY
(a)
Lister's
disinfectant, phenol, is considered the disinfectant standard against which all
other disinfectants are compared
(b)
These
comparisons give rise to the phenol coefficient where a disinfectant that
(i)
is
more efficacious than phenol is given a phenol coefficient that is greater than
1
(ii)
one
less efficacious than phenol is given a coefficient of less than 1
(iii)
one
of equal efficacy to phenol is given a phenol coefficient of 1 (i.e., efficacy
of disinfectant divided by efficacy of phenol)
(c)
Two
organisms, Salmonella typhi and Staphylococcus aureus are commonly used to
determine phenol coefficients
(d)
Note
that phenol coefficients are determined under an "ideal" condition
and therefore may not be indicative of disinfectant performance under other
conditions
(e)
See Table 12.2, Phenol
coefficients of various chemical agents [to get a feel for relative efficacies as well as how phenol
coefficients may be employed]
(f)
[phenol coefficient (Google Search)] [phenol factsheet] [index]
(a)
A
method that requires less manipulation to judge the efficacy of disinfectants is the filter paper method
(b)
Here
filter paper is soaked with disinfectant and then simply placed on the agar
surface of a petri dish that has been inoculated with a lawn of test organism
(c)
The
clear area around the disk following incubation is used as an indication of
disinfectant efficacy
(d)
Figure 12.1, The filter
paper method of evaluating disinfectants and antiseptics
(e)
[disinfection and "filter
paper" (Google Search)] [index]
(a)
A
third method of determining disinfectant efficacy, and one that is
especially useful for determining the ability of disinfectants to kill
microorganisms dried onto a typical clinical surface (stainless steel) is the
use-dilution test
(b)
Organism
is air dried onto a stainless-steel surface and then exposed to disinfectant;
following sterile-water rinsing the entire surface is then placed in broth;
successful disinfection results in no bacterial growth in the broth
(c)
Disinfectants
that completely kill (or otherwise remove) microbes at the lowest dilutions (of
the disinfectant) are considered the most efficacious
(d)
[use-dilution test (Google Search)] [index]
(48) Vocabulary [index]
(a)
Alcohols
(c)
Antiseptic
(d)
Autoclave
(g)
Chlorine
(j)
Desiccation
(k)
Detergent
(l)
Disinfectant
(m)
Disinfection
(n)
Dry heat
(o)
Ethylene
oxide
(r)
Filtration
(s)
Formaldehyde
(t)
Freeze
drying
(u)
Freezing
(v)
Glutaraldehyde
(x)
Heat
(y)
Heavy metals
(z)
HEPA
filters
(aa)
Hydrogen peroxide
(bb)
Hypochlorite
ion
(dd)
Iodine
(ee)
Iodophors
(ff)
Ionizing radiation
(gg)
Lyophilization
(hh)
Mechanisms of action
of chemical agents
(jj)
Moist heat
(kk)
Organic acids
(nn)
Pasteurization
(oo)
Phenol and
phenol derivatives
(pp)
Phenol coefficient
(qq)
Phenolics
(rr)
Refrigeration
(ss)
Quaternary
ammonium compounds
(tt)
Quats
(uu)
Sanitization
(vv)
Soap
(ww)
Specific
antimicrobial agents
(xx)
Sterilization
(yy)
Strong visible light
(zz)
Surfactants
(aaa)
Temperature effects
(bbb)
Ultraviolet (UV)
radiation
(ccc)
Use-dilution test