Transcript Control of Microorganisms

Control of Microorganisms
Control of Microbial Growth
Effected in two basic ways:
1. By Killing Microorganisms
2. By inhibiting the Growth of Microorganisms
Usually involves the use of:
1. Physical Agents
2. Chemical Agents
Principles of Microbial Control
(Definitions)
• Prevention / Control of Growth to Prevent Infection
and Spoilage
Principles of Microbial Control
(Definitions)
• Sterilization / Complete Destruction
- No degrees of sterilization (All or Nothing)
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Principles of Microbial Control
• Disinfection / Reducing Growth Nonliving
Surfaces
Principles of Microbial Control
• Antisepsis / Reducing Growth on Living
Tissue
Principles of Microbial Control
• Antisepsis / Reducing Growth on Living
Tissue
• Antiseptics are generally less toxic than
disinfectants because they must not cause too
much damage to the host living tissue.
Examples of antiseptics include iodine, 70%
ethanol and 3% hydrogen peroxide.
Principles of
Microbial
Control
• Sanitize
Subject to High
Temperature
Washing
(Dishwashers)
Principles of Microbial Control
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Cide – Suffix Meaning to Kill
Stat – Suffix Meaning to Inhibit
Sepsis – Bacterial Contamination
Asepsis – Lack of Bacterial Contamination
Time to Kill in Proportion to the
Population Size
• Large Numbers Require Greater Time
• Small Numbers Require Less Time
Susceptibilities Vary
• Endospores are Difficult to Kill
• Organic Matter May Interfere with Heat
Treatments and Chemical Control Agents
Control Agents Act By
• Alteration of Membrane Permeability
- Susceptibility of membrane is due to its
lipid and protein composition
- Control Agents can alter permeability
• Damage to Proteins and Nucleic Acids
- Break hydrogen and covalent bonds in proteins
- Interfere with DNA, RNA, Protein
Synthesis
Types of methods
• Physical
• Chemical
Physical Methods of Microbial
Control
Physical
Methods
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Heat
Filtration
Low Temperatures
Desiccation
Osmotic Pressure
Radiation
Heat
• Most Frequent and Widely Used.
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1. Type of Heat
– Moist
– Dry
2. Time of Application
3. Temperature
• Thermal Death Point (TDP) / Lowest
Temp to Kill All the Bacteria in a Broth in
10 Minutes
• Thermal Death Time (TDT) / Time Span
Required to Kill All the Bacteria in a Broth
at a Given Temperature
• Decimal Reduction Time (DRT) / Length
of Time in Which 90% of a Bacterial
Population will be Killed at a given
Temperature
• Boiling / Kills Many Vegetative Cells and
Inactivates Viruses Within 10 Minutes
Moist Heat Sterilization
• Boiling
• Autoclaving
Boiling
• 100° C for 30 Minutes
• Kills Everything Except Some Endospores
Autoclaving
• Steam Under
Pressure
• 121° C for 15
Minutes at
15 lb/in2
• Heat-labile
Substances will
be Denatured
• Steam Must
Contact the
Material
Dry Heat Sterilization
• Direct Flaming
• Incineration
• Hot-Air Sterilization (Oven)
Flaming the Loop
 Flaming the loop
helps to prevent
contamination of
the bacteria.
 When flaming the
loop, make sure
that all of the wire
has been heated to
redness.
Incineration
• Burns and Physically Destroys Organisms
• Used for
a. Needles
b. Inoculating Wires
Dry Heat (Hot Air Oven)
• 160° C for 2 Hours or 170° C for 1 hour
• Used for
a. Glassware
b. Metal
c. Objects That Won’t Melt
Pasteurization
• A High Temperature
Is Used For a Short
Time
• Batch Method
– 63°C for 30 Minutes
– 71 for 15 seconds
• (UHT) sterilization
140°C for 3 seconds.
– 2 months with only
minimal changes in
flavor.
Filtration
• The passage of a liquid or gas through a filter with
pores small enough to retain microbes.
• Especially important to sterilize solutions which
would be denatured by heat (antibiotics, injectable
drugs, amino acids, vitamins.)
HEPA Filters
• HEPA filters are High-Efficiency Particulate Air
filters designed for the filtration of small particles.
Certified HEPA filters must capture a minimum of
99.97% of 0.3 microns contaminants.
Low Temperatures
• Decreasing Temperature
Decreases Chemical Activity
• Low Temps are Not Bactericidal
Desiccation
• Disrupts Microbial Metabolism
• Stops Growth / Microbes Are Still Viable
• Freeze-drying / Dehydration
• Viruses and Endospores
Can Resist Desiccation
Osmotic Pressure
• Plasmolysis
• Sugar Curing / Salting
• May Still Get Some Mold or Yeast Growth
Radiation
• Ionizing Radiation
• NonIonizing Radiation
1. High Degree of
1. Low Degree of Penetration
Penetration
2. Harmful / Skin / Eyes
2. Examples
3. Cell Damage / Thymine
- Gamma Rays
4. Germicidal / 260 nm
- X-rays
5. Example: Ultraviolet
- High Energy
Electron Beams
Ionizing Radiation
• Ionizing radiation (gamma radiation) can
penetrate deeper into objects, and is used to
sterilize food, drugs, and medical supplies
Chemical Control Methods
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Phenols and Phenolics
Halogens
Alcohols
Heavy Metals and Their Compounds
Surface-Active Agents
Quaternary Ammonium Compounds
Chemical Food Preservatives
Aldehydes
Types of Disinfectants
• Phenol and Phenolics
- Exert Influence By
1. Injuring Plasma membranes (lipids)
2. Inactivating Enzymes
3. Denaturing Proteins
Not effective against spores
Types of
Disinfectants
• Halogens
- Can be Used Alone or in Solution
- Chlorine -- Purifies Drinking Water
a. Forms an Acid Which is Bactericidal
b. Disinfectant in Gaseous Form or in
Solution as Calcium Hypochlorite
Types of Disinfectants
• Halogens
- Iodine – combines with Amino Acids
a. Inactivates Enzymes
b. Tincture / Alcohol
Types of
Disinfectants
• Alcohols
- Denature Proteins
- Dissolve Lipids
- Tinctures
- Wet Disinfectants
a. Aqueous Ethanol (60% - 95%)
b. Isopropal Alcohol
Types of Disinfectants
• Heavy Metals and Their Compounds
- Used for Burn Treatment
- Prevents Neonatal Gonorrheal Opthalmia
- Denature Proteins
- Example / Silvadene Ointment / Silver
Types of Disinfectants
• Surface-Active Agents
- Decrease Molecular Surface Tension
- Include Soaps and Detergents
- Soaps Have Limited Germicidal Action but
Assist in the Removal of Organisms by
Scrubbing
- Acid-Anionic Detergents / Dairy
Types of
Disinfectants
• Quaternary Ammonium
Compounds (QUATS)
- Cationic Detergents
Attached to NH4+1
- Disrupt Plasma
Membranes
- Most Effective on
Gram-Positive Bacteria
- Mouthwashes and Sore
Throat Remedies
Types of
Disinfectants
• Chemical Food Preservatives
- Sorbic Acid
- Benzoic Acid
InhibitFungus
- Propionic Acid
- Nitrate and Nitrite Salts / Meats /
To Prevent Germination of Clostridium
botulinum endospores
Types of
Disinfectants
• Aldehydes
- Formaldehyde
- Glutaraldehyde
- Inactivate proteins by cross-linking
with functional groups (–NH2, –OH, –
COOH, —SH)
Antibiotics
• Cell wall antibiotics
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Bactracin
Cycloserine
Vancomycin
Penicillin and beta lactam antibiotics Cell menbrane
antibiotics
DNA Synthesis Inhibitors
RNA Synthesis Inhibitors
Protein Synthesis Inhibitors
Metabolism