Download Oct17 microbialcontrolHO

Control of Microbial Growth
A few terms
•  Bacteriostatic: inhibits bacterial growth
•  Bactericidal: something capable of killing
bacteria
•  Antiseptic: an agent that is used to inhibit/kill
bacterial growth on skin and mucus membranes
•  Disinfectant: an agent that is used to inhibit/kill
bacterial growth on inanimate objects
History behind microbial control
•  Joseph Lister was the first
to introduce the use of
carbolic acid to reduce
bacterial infections in
hospitals (1860s)
•  Ignatz Semmelweis
regarded as the “Father of
Infection Control”,
physicians used
chlorinated lime to cleanse
hands (1850s)
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What factors influence the
success of microbial control?
•  What type of organism are you targeting?
•  What type of environment are you treating?
Are all microbes equally sensitive?
What parts of a bacterial cell are
sensitive to physical treatments
and chemicals?
•  Plasma membrane
•  DNA and proteins
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Physical Methods
Physical Methods
•  Heat
–  Dry: kills by oxidation, ex: incineration
–  Moist: promotes coagulation of proteins
•  Boiling (100oC)
•  Autoclave(121oC, 15lbs/sq inch)
•  Pasteurization
–  Classic-63oC for 30 minutes
–  HTST-72oC for 15 seconds
–  UHT-140oC for 3 seconds
Autoclave
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Autoclaves work due to steam
under pressure
Indicators used in autoclaving
What if the substance is heat
sensitive?
•  Filtration is the best
choice
•  Pore sizes can be
either .45um or .22um
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Physical Methods
•  Low temperature: freezing does not kill
bacteria, most cultures are stored at -80oC
•  Dessication: remove the water and bacteria
can remain viable
Physical Methods
•  Radiation
– Ionizing radiation (gamma rays, x-rays)
– Non-ionizing radiation (uv rays)
– Microwaves
Electromagnetic Spectrum
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Chemical Methods
•  Most are only able to reduce the numbers of
organisms, not achieve sterility
•  Types of chemicals
–  Phenol and phenolics
–  Halogens
–  Alcohols
–  Heavy metals
–  Soaps
–  Quaternary Ammonium compounds
–  Biguanides
Evaluation of chemicals: disc
diffusion method
Chemical Control
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Chemical structure of phenols/
phenolics
Chemical Control
•  Phenols and phenolics
–  Destroy cytoplasmic membranes and denature
proteins
–  Kill most vegetative bacteria and in higher
concentrations kill Mycobacterium tuberculosis
–  Reasonable cost to use, effective in presence of
organics
Chemical control
•  Halogens
1. Iodine (binds to tyrosine, alters cell membranes)
•  Tincture
•  Iodophore
Target: all bacteria, fungi, most endospores, and some viruses
-Are all organisms killed by iodine???
2. Chlorine (strong oxidizing agent)
Target: all types of microbes and viruses
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Chemical Control
•  Alcohols
–  Mechanism of action is protein denaturation,
can also dissolve lipids
–  Most common are ethanol and isopropanol
Target: kill vegetative cells and fungi, do not kill
endospores and some naked viruses
Chemical control
•  Heavy metals exert
oligodynamic action
•  Silver, copper and
mercury Chemical control
•  Surfactants (soaps)
–  Little value as an antiseptic
–  Acid-anionic surface-active sanitizers are
important in cleaning of dairy equipment and
utensils
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Chemical control
•  Quaternary Ammonium Compounds (Quats)
–  Group of positively charged detergents
Action: react with the cell membrane
Target: kill many vegetative bacteria and enveloped
viruses, do NOT kill endospores, Mycobacteria, or
naked viruses
Chemical control
–  Biguanides (chlorhexidine)
•  Used in antiseptic products
•  Adheres to skin and mucus membranes, low toxicity
•  Action: membrane disruption
•  Target: wide range of bacteria, fungi, and some
enveloped viruses
Which antiseptic works the best?
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