Download Microbiology bio 123

Module C-6
Physical Control Methods in Microorganisms
Sterilization – killing all of the organism, including spores, nothing will be living.
Disinfectant and germicide – kills vegetative cells but not necessarily spores. Are normally used on inanimate
objects (lab counters, S-steal)
Spore – a very thick wall around the nucleic acid, typically a state that the cell uses in unfavorable conditions.
They are resistant to heat and chemicals, and can remain viable for 60-80 years. Once in a favorable conditions,
they will germinate and turn into a vegetative state.
Antiseptic – must inhibit the growth of vegetative bacteria. They are used on living tissue.
Sanitizer – reduces microorganisms to safe levels by killing microorganisms to the 99.99% levels
-cide – means to kill.
Bacteriostasic – inhibition, but not death of the bacteria.
Anti-microbial agent – anything that interferes with the growth of microbes.
Typically these agent work better at higher temperatures.
The lower the pH the better.
If urine or feces are present, bacteria are harder to kill.
Time – ingeneral, the longer that you expose them to an agent the better.
Concentration – the higher the concentration the better.
Young actively working cells are more susceptible to anti-microbial agent. Cells that are metabolizing are
susceptible to these because most anti-microbial agent effect a metabolic pathway.
How do these agents work,
1. By causing damage to the cell wall,
1. This causes lysis of the cell,
2. Some naturally occurring enzymes work this way, found in the mucus of most humans,
3. Penicillin,
1. they prevent the synthesis of the gram positive cell wall,
2. By changing the permeability of the cell wall,
1. Either causes the increase in the permeability, or decrease of it.
3. Alteration of the synthesis of the cells proteins or nucleic acid,
4. Attack the enzymes that are responsible for producing energy in the bacteria's cell,
1. Cyanide, inhibits cytochrome isonase,
2. Fluoride, inhibits glycolosis,
3. Trivalent arsinic compounds, interfer with the tca cycle,
Some agents that are used as anti-microbial agents,
1. Chemical agents,
1. Halogens,
1. Chlorine,
2.
3.
4.
5.
6.
7.
1. Disinfectant, works by oxidizing proteins (removes oxygen from proteins),
2. is an irritant on the skin and eyes,
3. inactivates tyrosine units in enzymes,
2. Iodine,
1. used in surgery,
2. can be used on living tissue,
3. can be used to purify water,
Alcohols,
1. antiseptics,
2. work by denaturing proteins,
3. they are dehydrating agents, they dissolve lipids,
4. The more carbons in the alcohol the better,
1. CH3OH, methanol, very weak alcohol,
2. C2H5OH, ethanol, better,
3. C3H7OH, isopropanol, best,
5. 70% isopropanol is better than 95% because the 30% water dissociates and binds the free H+ to
the protein which can then be denatured by the alcohol,
Peroxides,
1. Short lived,
Detergents,
1. In general, don't have anti-microbial activity,
2. They work by physically eliminating oils, lipids, and other organic material and therefore removes
the bacteria that they contain
Heavy metals,
1. Mercury,
2. Silver,
1. Oligodynamic effect – an all purpose effect, they work by denaturing proteins, proteins in
general are attracted to the metal ion,
2. Drops of AgNO3, (silver nitrate) used in babies eyes to protect against gonorrhea,
3. Some have started putting erythromicin in the eyes instead of AgNO3 because it is effective
against other bacteria,
4. Silvadine, AG and sulfonamide,
Alkylating agents,
1. Aldehydes,
1. formaldehyde,
2. gutteraldehyde,
1. work by denaturing proteins,
2. work well against all bacteria, but do not kill spores,
3. common way to inactivate viruses for vaccine,
4. Common used to clean tubing, ventilator and respirators, endoscopes, etc.
5. They are not very stable, must be made fresh,
6. Very toxic to humans,
Gaseous chemosterilizers,
1. Ethylene oxide,
1. Must have an airtight chamber,
2. Can't let the gas escape,
3. Normally used on objects that can't be exposed to moisture, heat, etc.
4. Kills all life forms,
8. Phenols,
1. The first disinfectant developed,
2. Hexachlorophene,
3. Not used much because they tend to be caustic and
4. Used as a guide of how effective a disinfectant is,
5. This is measured as a number and is called the phenol coefficient,
1. phenol coefficient is = to (dilution of brand x that kills in ten minutes, but not in 5 min.) /
(dilution of phenol that kills in 10 min, but not 5 min.)
2. Must be done:
1. At 20 degrees Celsius,
2. With the same organisms,
1. S. aureus, Gram positive,
2. S. typhi, Gram negative
3. Time intervals,
1. 5, 10, 15, 20,
2. preferred at 10,
4. Must be the same dilution,
1. 1:2, 1:5, 1:10, 1:20, 1:100,
Disinfectants,
1. Qualities that we would like in disinfectants,
1. Broad spectrum of activity,
1. Bacteria,
2. molds,
3. yeasts,
4. protozoa,
2. Soluble in water,
1. Cheapest form of solute,
2. not flammable,
3. Stability,
1. A reasonable shelf life,
4. Non-toxic to animals,
1. includes humans,
5. homogeneity,
1. generally have to be diluted,
2. Dilutes to the same concentration throughout the mixture,
6. Does not combine with extraneous organic material,
1. organic material material will absorb the disinfectant,
7. Toxic at room or body temperatures,
1. the temperatures at which we live,
8. Penetrating power,
1. many surfaces are somewhat porous,
2. must penetrate the pores of the surface,
9. Non-corroding/Non-staining,
10. Deodorizing,
11. Detergent capacity,
1. Able to cut through lipids,
12. Availability and price,
1. Is it hard to get,
2. Is it pricey,
Physical Control Methods to control microorganisms,
1. Heat,
1. One of the oldest methods,
2. There are two forms of heat,
1. Moist heat,
1. Works by denaturing proteins,
2. More efficient, to test, you have to use the most resistant heat bacteria and use both dry and
moist heat, dry heat kills C. botulinium in 4 hrs @ 121°C., Moist heat kills
3. Clostridium botulinium is the most resistant bacteria, especially in the spore form,
4. The autoclave is a steam heater, it uses pressurized steam to kill bacteria, pressure is normally
15 lbs, temp. 121°C, for fifteen minutes. This will kill most bacteria and the liquid is then
considered sterile.
5. You cannot use this to sterilize oils or powders, and is not recommended for empty glass
containers.
6. Boiling water does not sterilize, boiling water only disinfects. It does not kill spores.
7. Pasteurization,
1. Temperature is slowly brought up to the death point of the most heat resistant organism.
This is done without boiling the liquid. Does not kill all bacteria or spores. Does not
disinfect the liquid either, but does inhibit the growth of bacteria.
2. There are several different methods of pasteurization.
2. Dry heat,
1. Oxidizing cell parts(structures),
2. Sterilizing with dry heat
1. Necessitates 160°C for 2 hrs.
2. Can be used with powders, oils, and glassware,
3. Incineration,
1. Limited applications,
2. Is used for some medical wastes,
3. Used for dead animals,
3. Cold,
1. Microbistatic,
2. As the temperature decreased, metabolism of the bacteria decreases,
4. Desiccation,
1. Drying,
2. Some are very susceptible, others are very resistant,
3. Most of the ones that are susceptible are GU organisms,
4. The most resistant is probably the TB organism,
5. Radiation,
1. Gamma Radiation,
1. Does not penetrate the surface, is used to sterilize surfaces,
2. inhibits bacteria by making free radicals,
2. Ultraviolet radiation,
1. Can penetrate surfaces,
2. Disrupts the DNA, Produces thymine dimers,
3. causes the Thymine in the DNA sequence to bind to another Thymine,
3. Filtration,
1. Used with fluids that cannot handle heat,
2. Uses special filters,
3. Filters and made of glass, porcelain, cellulose, or asbestos,
4. Uses the very small pours in these materials,
5. Filters have an opposite charge of the fluids,
6. Some of the newer filters can even filter out viruses,
7. Used in the brewery industry to filter beer,
4. Osmotic pressure,
1. usually Bacteriostasic,
2. Uses salt or sugar to create a hypertonic solution,
3. jams and jellies, syrups, pickling, and many other manifestations,
Gonococcus – The gonnococcal organism,