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Chapter 5: Control of Microbial Growth


Chapter 5: Control of Microbial Growth Important Point: Control of Microbial Growth Important Terms Important Terms Nosocomial Infections Aseptic Technique Killing ... – PowerPoint PPT presentation

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Title: Chapter 5: Control of Microbial Growth

Chapter 5Control ofMicrobial Growth
Important Point
If you are having trouble understanding lecture
material Try reading your text before
attending lectures. And take the time to read it
Control of Microbial Growth
  • 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
Important Terms
Im not sure why these Ss are missing!
Nosocomial Infections
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.
Aseptic Technique
  • 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.
  • All materials used to grow microorganisms must
    again be treated before disposal to avoid
    contamination of workers and the environment.
  • The use of specific methods to exclude
    contaminating microorganisms from an environment
    is called aseptic technique.
  • Although all microbiology laboratory personnel
    must use these prudent measures, those who work
    with known disease-causing microbes must be even
    more diligent.

Killing-Resistant Microorganisms
  • Endospore formers (endospores) Bacillus spp.
    Clostridium spp. are highly heat- and
    chemical-treatment resistant.
  • Mycobacterium spp. are highly chemical-treatment
  • Certain Pseudomonas spp. can actually grow in
    certain disinfectants (i.e., in quats and
  • Naked viruses (i.e., those lacking lipid
    envelopes) often are resistant to chemical

Exponential Death
It takes more time to kill a large population of
bacteria than it does to kill a small population,
because only a fraction of organisms die during a
given time interval.
More Terms Concepts
  • 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
    disinfectionif possible it consequently is
    important to clean items well before disinfecting
    or sterilizing (which also will reduced organism
  • Obviously the above is not practical if one is
    disinfecting in order to avoid contacting an
  • Critical Items penetrate into body tissues.
  • Semicritical Items come into contact with but
    dont penetrate mucous membranes.
  • Non-Critical Items come into contact only with
    unbroken skin.

Using Heat to Control Microbes
Using Heat to Control Microbes
10 min boiling (at sea level).
121C for 15 min to kill endospores (but must be
penetrating, moist heat, and 15 min at 121C)
Categories of Germicides
  • To perform properly, germicides must be used
    strictly according to the manufacturers
    directions, especially as they relate to
    dilution, temperature, and the amount of time
    they must be in contact with the object being
  • 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
But dont use scented chlorine bleach to purify
Note that temperature can affect rate of water
purification (i.e., cold water purifies slowly).
Categories of Germicides
Today iodine is more often used as an iodophore
which is a less-irritating, slow-release form of
Iodine typically is used as a tincture (i.e.,
dissolved in alcohol).
Watch out because Pseudomonas spp. can live and
grow in some iodophores!
Iodine Iodophores
  • Formulae Fresh juice of Organic Habanero
    peppers, New Mexico Jalapeno, African Bird
    peppers and Hatch Chili peppers.
  • Dosage Five to thirty drops, three times daily. 
  • 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.

Categories of Germicides
Categories of Germicides
However, HOOH is still useful for supplying
oxygen to otherwise anaerobic environments.
Membrane Filtration of Liquids
Bacteria removal is not quite equivalent to
Bacteria removal is easier than removal of
HEPA Filtration of Air
Irradiation UV and Gamma
  • 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.

Food Preservation
  • Chemical preservatives.
  • Low-temperature storage (freezing works better
    than above freezing).
  • Removing water by submerging in highly osmotic
    solutions (usually high salt or high sugar).
  • Desiccation 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 food-preservation conditions.
  • One also must consider that removing
    microorganisms from foods can make food more
    susceptible to subsequent microbial
  • An important example of the latter is
    staphylococcal food poisoning which can result
    when Staphylococcus aureus is allowed to incubate
    in only moderately salt-preserved foods such as
    potato salad.

Hands Spread Disease
WASH 'EM !!!
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