Control of Microbial Growth

1
Control of Microbial Growth

• We will talk about antifungals, antibiotics,
  antivirals, etc. when we begin to talk about
  specific diseases.

2
Definitions

• Sterilization destruction of all forms of
  microbial life (including endospores).
• Disinfectant destruction of vegetative
  pathogens (does not include endospores).
• Antiseptic destruction of vegetative pathogens
  on living tissue (not endospores).
• -cide this suffix means, kills
• Ie. Germicide kills germs
• biocide kills life

3

• -stasis or static inhibits bacterial growth.
• Ie. Bacteriostatic inhibits growth of bacteria.
• Main targets that are used to control microbial
  growth are bacterial cell wall, plasma membrane,
  DNA, RNA, and protein synthesis.

4
Methods of Sterilization

• Osmotic Pressure beef jerky (addition of salt
  or sugar).
• Radiation (UV light) UV light causes lethal
  mutations in DNA when exposed for long periods of
  time. It is frequently used in virology labs to
  sterilize rooms where viruses are transferred
  from old media to fresh media. It is also used
  to sterilize equipment such as goggles.
• Filtration air filters are used in hospitals to
  keep patients from contracting disease while
  there. This is especially important in the burn
  unit where patients are extremely susceptible to
  infection. Death among burn patients is usually
  due to infection.
• Some liquids are heat sensitive and can be
  damaged if exposed to the temperatures needed to
  sterilize it. Filters are used to sterilize
  those too.

5

• Dry heat means using an open flame to kill
  organisms, for example.
• In lab flaming loops with the bunsen burner is an
  example of dry heat.
• Incineration (or burning) of carcasses is also an
  example of dry heat.
• Moist heat The best example of moist heat is an
  autoclave. An autoclave is a machine that uses
  water and heat. It creates hot steam by
  increasing the pressure inside of it. As the
  pressure increases, the temperature increases.
  It is able to reach very hot temperatures and is
  very effective in killing many organisms and
  endospores.
• Autoclaves are found in many places. They are
  used to sterilize surgical equipment, gowns,
  towels, media, test tubes, etc.

6

• Some Chemicals Formaldehyde, glutaraldehyde
• Most chemicals are not considered sterilizing
  agents.
• Formaldehyde and glutaraldehyde are so effective
  in killing organisms that they are included as
  sterilizing agents.
• They work by inhibiting enzyme function.
• Generally these chemicals are used to disinfect
  instruments or materials that may be damaged by
  heat. They are also used to preserve tissue so
  that it can be studied.

7
Types of Disinfectants and Antiseptics

• Most chemicals have a particular concentration
  and length of exposure to microbes, to be most
  effective.
• For example, isopropyl alcohol is frequently used
  in the clinic when administering injections or
  drawing blood. It is most effective when the
  solution is 65-75 alcohol. Some stores sell 95
  alcohol and consumers buy it because they think
  that the greater the concentration, the better.
• The other challenge with alcohol is that it
  evaporates very quickly. So as an antiseptic, it
  is not very effective because it evaporates off
  the skin so quickly and there is not in contact
  with the bacteria long enough to kill it.
• The other challenge with alcohol is that it
  denatures (or inactivates) protein but does not
  remove it very well. So if a surface is
  particularly dirty the alcohol just denatures the
  protein and leaves it on the surface.

8

• Triclosan common antibacterial agent added to
  soaps, cutting boards and other products.
• Triclosan is a pretty effective antibacterial
  agent (antiseptic) but it is being overused. A
  decreased sensitivity is being seen in several
  microorganisms including Staphylococcus.
• Triclosan is what is added to antibacterial hand
  soaps. It kills the organisms but the soap
  leaves a residue of triclosan in the sink. As
  the organisms are continually exposed to the
  triclosan it gives them opportunities to develop
  resistance.
• In addition, there is no need, particularly in a
  home, to use antibacterial soap. Ordinary hand
  soap removes the organisms just as effectively
  and does not needlessly use an extra chemical to
  which microbes are now growing resistant.

9

• Chlorhexadine used for surgical hand scrubs and
  pre-operative skin preparation as well as other
  uses.
• This chemical damages the plasma membrane and
  causes protein denaturation.
• In medium to high concentrations it is very
  effective against vegetative pathogens but not
  against endospores.
• An advantage to using chlorhexadine is that it
  has a very low toxicity. That means that it can
  be used in large or amounts as an antiseptic
  without being toxic.
• Halogens iodine, chlorine
• Effective against all kinds of bacteria and
  endospores, various fungi, and viruses.
• This group interferes with protein synthesis and
  folding.

10

• Chlorine can be used as an antiseptic or a
  disinfectant depending upon the form in which it
  is used.
• It is used to treat drinking water and swimming
  pools for example.
• In higher concentrations it is used to disinfect
  equipment, bedding, etc.
• Iodine is used as a disinfectant to sterilize
  cutting blades, plastic, and rubber items.
  (Its exact method of killing microorganisms is
  not really understood yet.)
• It is also used as an antiseptic for wound care.
• Tincture of iodine combination of iodine and
  alcohol
• An iodophore is a combination of iodine and an
  organic molecule that allows iodine to be
  released slowly.
• The best example I can think of is those tablets
  they sell in the pet stores for feeding fish
  while your on vacation. The longer the tablet
  sits in the water, the more the outer coating is
  exposed to the water and wears it away. As it is
  worn away, the food is gradually released.
• Betadine, and Isodine are examples of iodophores.

11

• Hydrogen Peroxide decomposes in the presence of
  light, metals, or catalase into water and oxygen
  gas.
• That is why it is stored in dark bottles, to
  prevent its decomposition.
• It is more stable now than used to be.
• It is highly toxic to cells that dont have the
  enzyme, catalase.
• Bactericidal, virucidal, fungicidal, and can be
  sporicidal

12

• Surface-active agents (surfactants) soaps and
  detergents
• Surfactants disrupt cell membranes, more useful
  in killing microbes.
• Not an antiseptic but does bind to org. to remove
  from skin.