control of microorganisms control of microbial growth effected in two basic ways: 1.by killing...
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Control of MicroorganismsControl of Microorganisms
Control of Microbial GrowthControl 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 Principles of Microbial Control (Definitions)(Definitions)
• Prevention / Control of Growth to Prevent Infection and Spoilage
Principles of Microbial Control Principles of Microbial Control (Definitions)(Definitions)
• Sterilization / Complete Destruction
- No degrees of sterilization (All or Nothing)
-
Principles of Microbial ControlPrinciples of Microbial Control
• Disinfection / Reducing Growth Nonliving Surfaces
Principles of Microbial ControlPrinciples of Microbial Control• Antisepsis / Reducing Growth on Living
Tissue
Principles of Microbial ControlPrinciples 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 Principles of Microbial Microbial ControlControl
• Sanitize
Subject to High Temperature Washing (Dishwashers)
Principles of Microbial ControlPrinciples of Microbial Control
• 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 Time to Kill in Proportion to the Population SizePopulation Size
• Large Numbers Require Greater Time• Small Numbers Require Less Time
Susceptibilities VarySusceptibilities Vary
• Endospores are Difficult to Kill• Organic Matter May Interfere with Heat
Treatments and Chemical Control Agents
Control Agents Act ByControl 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 Physical Methods of Microbial ControlControl
Physical Physical MethodsMethods
• Heat
• Filtration
• Low Temperatures
• Desiccation
• Osmotic Pressure
• Radiation
HeatHeat
• Most Frequent and Widely Used.
• 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 SterilizationMoist Heat Sterilization• Boiling• Autoclaving
BoilingBoiling
• 100° C for 30 Minutes
• Kills Everything Except Some Endospores
AutoclavingAutoclaving• 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 SterilizationDry 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.
IncinerationIncineration
• Burns and Physically Destroys Organisms
• Used for
a. Needles
b. Inoculating Wires
Dry Heat (Hot Air Oven)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
PasteurizationPasteurization• 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.
FiltrationFiltration• 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 FiltersHEPA 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 TemperaturesLow Temperatures
• Decreasing Temperature
Decreases Chemical Activity
• Low Temps are Not Bactericidal
DesiccationDesiccation
• Disrupts Microbial Metabolism• Stops Growth / Microbes Are Still Viable• Freeze-drying / Dehydration
• Viruses and Endospores Can Resist Desiccation
Osmotic PressureOsmotic Pressure
• Plasmolysis
• Sugar Curing / Salting
• May Still Get Some Mold or Yeast Growth
RadiationRadiation
• Ionizing Radiation
1. High Degree of
Penetration
2. Examples
- Gamma Rays
- X-rays
- High Energy
Electron Beams
• NonIonizing Radiation
1. Low Degree of Penetration
2. Harmful / Skin / Eyes
3. Cell Damage / Thymine
4. Germicidal / 260 nm
5. Example: Ultraviolet
Ionizing RadiationIonizing Radiation• Ionizing radiation (gamma radiation) can
penetrate deeper into objects, and is used to sterilize food, drugs, and medical supplies
Chemical Control MethodsChemical Control Methods
• Phenols and Phenolics• Halogens• Alcohols• Heavy Metals and Their Compounds• Surface-Active Agents• Quaternary Ammonium Compounds• Chemical Food Preservatives• Aldehydes
Types of DisinfectantsTypes 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 Types of DisinfectantsDisinfectants
• Halogens- Can be Used Alone or in Solution- Chlorine -- Purifies Drinking Water
a. Forms an Acid Which is Bactericidalb. Disinfectant in Gaseous Form or in Solution as Calcium Hypochlorite
Types of DisinfectantsTypes of Disinfectants
• Halogens- Iodine – combines with Amino Acids
a. Inactivates Enzymesb. Tincture / Alcohol
Types of Types of DisinfectantsDisinfectants
• Alcohols
- Denature Proteins
- Dissolve Lipids
- Tinctures
- Wet Disinfectants
a. Aqueous Ethanol (60% - 95%)
b. Isopropal Alcohol
Types of DisinfectantsTypes of Disinfectants
• Heavy Metals and Their Compounds
- Used for Burn Treatment
- Prevents Neonatal Gonorrheal Opthalmia
- Denature Proteins
- Example / Silvadene Ointment / Silver
Types of DisinfectantsTypes 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 Types of DisinfectantsDisinfectants
• 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 Types of DisinfectantsDisinfectants
• Chemical Food Preservatives
- Sorbic Acid
- Benzoic AcidInhibitFungus
- Propionic Acid
- Nitrate and Nitrite Salts / Meats /
To Prevent Germination of Clostridium botulinum endospores
Types of Types of DisinfectantsDisinfectants
• Aldehydes
- Formaldehyde
- Glutaraldehyde
- Inactivate proteins by cross-linking with functional groups (–NH2, –OH, –COOH, —SH)
Antibiotics• Cell wall antibiotics
• Bactracin
• Cycloserine
• Vancomycin
• Penicillin and beta lactam antibiotics Cell menbrane antibiotics
• DNA Synthesis Inhibitors
• RNA Synthesis Inhibitors
• Protein Synthesis Inhibitors
• Metabolism