Unformatted text preview: Important Point: Methods are employed to destroy, remove,
and/or inhibit the growth of microorganisms.
This is either on inanimate objects or on body
Most of these approaches are non-selective
meaning that they can negatively impact a
diversity of microbial (and non-microbial) life
We can distinguish these microbial control
methods into Physical and Chemical methods.
“…simple hand washing with plain soap and
water is considered the simple most important
step in preventing the spread of many infectious
diseases. Plain soap itself generally does not
destroy many organisms; it simply aids in the
mechanical removal of transient microbes,
including most pathogens...” Important Terms I’m not sure why
these Ss are
missing! Important Terms Nosocomial Infections Control of Microbial Growth Chapter 5:
Microbial Growth “Minimizing the numbers of microorganisms in a
hospital is particularly important because of the danger
of hospital-acquired, or nosocomial, infections.
Hospitalized patients are often more susceptible to
infectious agents because of their weakened condition.
In addition, patients may be subject to invasive
procedures such as surgery, which breaches the intact
skin that would otherwise help prevent infection.
Finally, pathogens are more likely to be found in
hospitals because of the high concentration of patients
with infectious disease. These patients may shed
pathogens in their feces, urine, respiratory droplets, or
other body secretions. Thus, hospitals must be
scrupulous in their control of microorganisms. Nowhere
is this more important than in the operating room,
where instruments used in invasive procedures must
be sterile to avoid introducing even normally benign
microbes into deep body tissue where they could easily
establish infection.” 1 “Although all microbiology laboratory personnel
must use these prudent measures, those who
work with known disease-causing microbes must
be even more diligent.” “It takes
more time to
kill a large
it does to kill
a fraction of
die during a
interval. Killing-Resistant Microorganisms “The use of specific methods to exclude
contaminating microorganisms from an
environment is called aseptic technique.” More Terms & Concepts “All materials used to grow microorganisms must
again be treated before disposal to avoid
contamination of workers and the environment.” Using Heat to Control Microbes Aseptic Technique
Using Heat to Control Microbes “To work with pure cultures, all media and
instruments that contact the culture must first be
rendered sterile to avoid contaminating the
culture with environmental bacteria.” Endospore formers (endospores): Bacillus
spp. & Clostridium spp. are highly heatand chemical-treatment resistant.
Mycobacterium spp. are highly chemicaltreatment resistant.
Certain Pseudomonas spp. can actually
grow in certain disinfectants (i.e., in quats
Naked viruses (i.e., those lacking lipid
envelopes) often are resistant to chemical
disinfection. Decimal Reduction Time (D value) = the time it
takes to kill 90% of a bacterial population (1 log
reduction) under specific conditions.
Note importance of temperature: higher
temperatures can result in dramatically faster
Dirt and organic compounds can interfere with
disinfection—if possible it consequently is important
to clean items well before disinfecting or sterilizing
(which also will reduced organism number).
Obviously the above is not practical if one is
disinfecting in order to avoid contacting an item.
Critical Items penetrate into body tissues.
Semicritical Items come into contact with but don’t
penetrate mucous membranes.
Non-Critical Items come into contact only with
unbroken skin. 10 min
sea level). 121°C for 15 min to kill endospores
(but must be penetrating, moist
heat, and 15 min at 121°C) 2 Categories of Germicides Categories of Germicides “To perform properly, germicides must be used
strictly according to the manufacturer’s directions,
especially as they relate to dilution, temperature,
and the amount of time they must be in contact with
the object being treated.”
“It is extremely important that the object be
thoroughly cleaned and free of organic material
before the germicidal procedure is begun.” Categories of Germicides Categories of Germicides
Today iodine is more often
used as an iodophore which
is a less-irritating, slowrelease form of iodine. Note that temperature can
affect rate of water
purification (i.e., cold water
purifies slowly). Iodine typically is used
as a tincture (i.e.,
dissolved in alcohol). Watch out because
Pseudomonas spp. can live
and grow in some iodophores! “Formulae: Fresh juice of Organic
Habanero peppers, New Mexico
Jalapeno, African Bird peppers and
Hatch Chili peppers. Tincture Iodine & Iodophores But don’t use scented
chlorine bleach to
purify water! Dosage: Five to thirty drops, three
times daily. CAUTION ~
Therapeutic Action: Cayenne is
the greatest herbal aid to circulation
and should be used on a regular
basis. The extract is very
concentrated and gets into the
bloodstream quickly and makes it a
perfect first aid remedy for heart
attacks, stroke, fainting, shock,
dizziness, hemorrhage, internal and
external bleeding. Use a few drops
to 10 droppers full. It has saved
many lives. 3 Categories of Germicides Categories of Germicides Membrane Filtration of Liquids Irradiation: UV and Gamma HEPA Filtration of Air Quats However, HOOH is still useful for supplying oxygen
to otherwise anaerobic environments. Bacteria removal
is not quite
sterilization. Bacteria removal
is easier than
viruses. Gamma radiation is penetrating and effective but
not always practical (or legal) to use.
UV radiation is not terribly penetrating but
generally is safe (and legal) to employ.
UV disinfection generally is limited to surfaces
and shallow (and UV transparent) aqueous
solutions (e.g., water).
Neither is terribly effective against bacterial
Contact with either is hazardous to human
tissues. 4 Food Preservation Chemical preservatives.
Low-temperature storage (freezing works better than
above freezing). Hands Spread Disease Removing water by submerging in highly osmotic
solutions (usually high salt or high sugar).
Dessication = drying.
Lyophilization = freeze drying.
All of above generally are better at preventing microbial
growth than they are at outright killing microbes, so
some care must be taken upon reversal of these foodpreservation conditions.
One also must consider that removing microorganisms
from foods can make food more susceptible to
subsequent microbial contamination.
An important example of the latter is staphylococcal
food poisoning which can result when Staphylococcus
aureus is allowed to incubate in only moderately saltpreserved foods such as potato salad. Link to Next Presentation 5 Using Heat to Control Microbes 5 Categories of Germicides 5 Categories of Germicides 5 ...
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This note was uploaded on 06/03/2011 for the course MCB 205 taught by Professor Abedon during the Spring '11 term at Ohio State.
- Spring '11