9 Flashcards
sterilization
In its strictest sense, sterilization refers to the removal or
destruction of all microbes, including viruses and bacterial endospores,
in or on an object. (The term does not apply to prions,
which are infectious proteins, because standard sterilizing techniques
do not destroy them.)
- In practical terms, sterilization indicates only the eradication
of harmful microorganisms and viruses; some innocuous
microbes may still be present and viable in an environment
that is considered sterile.
aseptic
describes an environment or procedure
that is free of contamination by pathogens
disinfection
refers to the use of physical or chemical
agents known as disinfectants, including ultraviolet light, heat, alcohol, and bleach, to inhibit or destroy microorganisms,
especially pathogens. Unlike sterilization, disinfection does
not guarantee that all pathogens are eliminated; indeed, disinfectants
alone cannot inhibit endospores or some viruses. Further,
the term disinfection is used only in reference to treatment
of inanimate objects.
antisepsis
When a chemical is used on skin or other
tissue, the process is called antisepsis3 (an@te@sep´sis), and the
chemical is called an antiseptic. Antiseptics and disinfectants
often have the same components, but disinfectants are more
concentrated or can be left on a surface for longer periods of
time
degerming
the removal of microbes from a surface by
scrubbing, such as when you wash your hands or a nurse prepares
an area of skin for an injection. Though chemicals such
as soap or alcohol are commonly used during degerming, the
action of thoroughly scrubbing the surface may be more important
than the chemical in removing microbes.
sanitization
the process of disinfecting places and utensils
used by the public to reduce the number of pathogenic microbes
to meet accepted public health standards. Thus, the difference between disinfecting dishes at
home and sanitizing dishes in a restaurant is the arena—private
versus public—in which the activity takes place.
pasteurization
the use of heat to kill pathogens and
reduce the number of spoilage microorganisms in food and
beverages.
two major types of microbial
control
sterilization, which is the elimination of all
microbes, and antisepsis or disinfection, which each denote the
destruction of vegetative (nonspore) cells and many viruses.
Modifications of disinfection include degerming, sanitization,
and pasteurization
-stasis/-static
indicate that a chemical or physical
agent inhibits microbial metabolism and growth but does not
necessarily kill microbes.
-cide/-cidal
refer to agents that destroy
or permanently inactivate a particular type of microbe
microbial death
the permanent loss of
reproductive ability under ideal environmental conditions.
microbial death rate
One technique for evaluating the efficacy of an antimicrobial
agent is to calculate the microbial death rate, which is usually
found to be constant over time for any particular microorganism
under a particular set of conditions
There are many types of chemical and physical microbial controls,
but their modes of action fall into two basic categories:
those that disrupt the integrity of cells by adversely altering
their cell walls or cytoplasmic membranes and those that interrupt
cellular metabolism and reproduction by interfering with
the structures of proteins and nucleic acids.
hypotonic
surroundings < cell. water go in
virus covering
In enveloped viruses, the envelope is a membrane composed
of proteins and phospholipids that is responsible for the
attachment of the virus to its target cell. Damage to the envelope
by physical or chemical agents fatally interrupts viral replication.
The lack of an envelope in nonenveloped viruses accounts
for their greater tolerance of harsh environmental conditions,
including antimicrobial agents.
As we have seen, a protein’s function
depends on an exact three-dimensional shape, which is
maintained by
hydrogen and disulfide bonds between amino
acids.
ribozyme
that portion of a
ribosome that actually catalyzes the synthesis of proteins is a
ribozyme—that is, an enzymatic RNA molecule. For this reason,
physical or chemical agents that interfere with nucleic
acids also stop protein synthesis.
Ideally, agents used for the control of microbes should be
inexpensive,
fast acting, and stable during storage.
most resistant microbes
- bacterial endoposres (bacillus, clostiridum) – most resilient forms of life
- mycobacterium (tb)
- protoozoa cysts
y mycobacterium resilient
contain a large
amount of a waxy lipid. The wax allows these bacteria to
survive drying and protects them from most water-based
chemicals
y cysts resilient
A protozoan cyst’s wall prevents entry
of most disinfectants, protects against drying, and shields
against radiation and heat.
high level germicides
kill all pathogens, including
bacterial endospores. Health care professionals use them
to sterilize invasive instruments such as catheters, implants, and
parts of heart-lung machines.
intermediat elevel germicides
kill fungal
spores, protozoan cysts, viruses, and pathogenic bacteria but
not bacterial endospores. They are used to disinfect instruments
that come in contact with mucous membranes but are noninvasive,
such as respiratory equipment and endoscopes.
low level germicides
Low-level
germicides eliminate vegetative bacteria, fungi, protozoa, and some
viruses; they are used to disinfect items that contact only the skin
of patients, such as furniture and electrodes
Temperature and pH affect microbial death rates and the efficacy
of antimicrobial methods.
Warm disinfectants, for example,
generally work better than cool ones because chemicals
react faster at higher temperatures (Figure 9.3). Acidic conditions
enhance the antimicrobial effect of heat.
bsl 1
suitable for handling microbes,
such as E. coli, not known to cause disease in healthy humans.
Precautions in BSL-1 are minimal and include hand washing
with antibacterial soap and washing surfaces with disinfectants
bsl 2
- for handling moderately hazardous agents, such as hepatitis
and influenza viruses and methicillin-resistant Staphylococcus
aureus - Access to BSL-2 labs
is limited when work is being conducted, extreme precautions
are taken with contaminated sharp objects, and procedures that
might produce aerosols are conducted within safety cabinets
bsl 3
- requiring that all manipulations be done
within safety cabinets containing high-efficiency particulate
air (HEPA) filter - special design features: entry through double sets of
doors and ventilation such that air moves into the room only
through an open door. Air leaving the room is HEPA-filtered
before being discharged outside the room. - designed for
experimentation on microbes such as tuberculosis and anthrax
bacteria and viruses of yellow fever and Rocky Mountain spotted
fever.
bsl 4
designated
for working with dangerous or exotic microbes that cause severe
or fatal diseases in humans, such as Ebola, smallpox, and
Lassa fever viruses. BSL-4 labs are either separate buildings or
completely isolated from all other areas of their buildings. Entry
and exit are strictly controlled through electronically sealed
airlocks with multiple showers, a vacuum room, an ultraviolet
light room, and other safety precautions designed to destroy all
traces of the biohazard. All air and water entering and leaving
the facility are filtered to prevent accidental release. Personnel
wear “space suits” supplied with air hoses (Figure 9.4). Suits
and the laboratory itself are pressurized such that microbes are
swept away from workers.
thermal death pt
the
lowest temperature that kills all cells in a broth in 10 minutes
thermal death time
the time it takes to completely sterilize
a particular volume of liquid at a set temperature
deciaml reduction time (D)
When measuring the effectiveness of heat sterilization, researchers
calculate the decimal reduction time (D), which is the time
required to destroy 90% of the microbes in a sample (Figure 9.5).
This concept is especially useful to food processors because
they must heat foods to eliminate all the endospores of anaerobic
Clostridium botulinum, which could germinate inside sealed cans
boiling time
It
is impossible to boil something more quickly simply by applying
more heat; the added heat is carried away by the escaping
steam. Boiling time is the critical factor. Further, it is important
to realize that at higher elevations water boils at lower temperatures
because atmospheric pressure is lower; thus, a longer boiling
time is required in Denver than in Los Angeles to get the
same antimicrobial effect.
pressure fo rsterilization
Practically speaking, true sterilization using heat
requires higher temperatures than that of boiling water. To
achieve the required temperature, pressure is applied to boiling
water to prevent the escape of heat in steam. The reason
that applying pressure succeeds in achieving sterilization is that
the temperature at which water boils (and steam is formed) increases
as pressure increases
