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
|
|
|
Course-external links are
in brackets Click [index] to access site index Click here to access
text’s website Vocabulary
words
are found below |
|
|
(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]