Chapter 5: Control of Microbial Growth

1
Chapter 5Control ofMicrobial Growth
2
Important Point
If you are having trouble understanding lecture
material Try reading your text before
attending lectures. And take the time to read it
well!
3
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
  surfaces.
• Most of these approaches are non-selective
  meaning that they can negatively impact a
  diversity of microbial (and non-microbial) life
  forms.
• 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...

4
Important Terms
5
Important Terms
Im not sure why these Ss are missing!
6
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.
7
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.

8
Killing-Resistant Microorganisms

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

9
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.
10
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
  disinfection.
• 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
  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
  dont penetrate mucous membranes.
• Non-Critical Items come into contact only with
  unbroken skin.

11
Using Heat to Control Microbes
12
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)
13
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
  treated.
• It is extremely important that the object be
  thoroughly cleaned and free of organic material
  before the germicidal procedure is begun.

14
Categories of Germicides
15
Categories of Germicides
But dont use scented chlorine bleach to purify
water!
Note that temperature can affect rate of water
purification (i.e., cold water purifies slowly).
16
Categories of Germicides
Today iodine is more often used as an iodophore
which is a less-irritating, slow-release form of
iodine.
Iodine typically is used as a tincture (i.e.,
dissolved in alcohol).
Watch out because Pseudomonas spp. can live and
grow in some iodophores!
17
Iodine Iodophores
18
Tincture

• 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. 
  CAUTION EXTREMELY HOT!!
• 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.

19
Categories of Germicides
20
Categories of Germicides
However, HOOH is still useful for supplying
oxygen to otherwise anaerobic environments.
21
Quats
22
Membrane Filtration of Liquids
Bacteria removal is not quite equivalent to
sterilization.
Bacteria removal is easier than removal of
viruses.
23
HEPA Filtration of Air
24
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
  endospores.
• Contact with either is hazardous to human tissues.

25
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
  contamination.
• 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.

26
Hands Spread Disease
WASH 'EM !!!
27
Link to Next Presentation