mic lecture10.pptx
TRANSCRIPT
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Controlling Microbial Growth inVitro
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Factors that affect microbial growth
Temperature
psychrophiles (cold loving microbes )
range 0 C - 20 C
mesophiles (moderate temp. loving microbes)
range 20 C - 40 C
thermophiles (heat loving microbes) range 40 C - 100 C
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Factors that affect microbial growth
Availability of nutrients:
Many nutrients are energy sources
Nutrients serve as sources of C, O, N, P, &
Sulfur
Source for trace elements as Iron, Iodine, Zinc
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Factors that affect microbial growth
Moisture
All living organisms need water for normal
metabolic processes
Moisture necessary for growing and
reproduction
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pH
Most bacteria grow between pH 6.5 - pH 7.5
Very few can grow at below pH 4.0
Acidophilic microbes:
Alkalophilic microbes:
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Osmotic Pressure
Microbes obtain almost all their nutrients in
solution from surrounding water
Tonicity
isotonic
hypertonic
hypotonic
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Cells
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Barometric pressure
Barophiles: prefer to live in a high
atmospheric pressure like some archeans
Gaseous atmosphere
Some microbes prefer the same human do(e.g O2 21%, N2 78%, other gases 1%)
Other microbes need high concentration of
O2 called Microaerophiles
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Bacterial Growth - increase in the # of
cells
Binary Fission
Generation Time (Doubling Time)
time required for a cell to divide
most about 1 Hr. To 3 Hrs.
E. coli - 20 minutes
Mycobacterium tuberculosis - 24 Hrs.
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Limiting factors in the
environment Lack of food, water or nutrients
space
accumulation of metabolic wastes
lack of oxygen
changes in pH temperature
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Phases of Growth
4 Phases
1. Lag Phase
2. Log Phase
3. Stationary Phase 4. Death Phase
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1. Lag Phase
Bacteria are first introduced into an
environment or media
Bacteria are checking out their
surroundings
cells are very active metabolically
# of cells changes very little
1 hour to several days
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2. Log Phase
Rapid cell growth (exponential growth)
population doubles every generation
microbes are sensitive to adverse conditions
antibiotics
anti-microbial agents
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3. Stationary Phase
Death rate = rate of reproduction
cells begin to encounter environmental
stress
lack of nutrients
lack of water
not enough space
metabolic wastes
oxygen
pH
Endospores would form now
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4. Death Phase
Death rate > rate of reproduction
Due to limiting factors in the environment
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Inhibiting the growth ofmicroorganisms in Vitro
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Methods to Control Microbial
Growth 1. Physical
2. Chemical
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Terms used:
Sterilization vs. Disinfection
Sterilization
destroying all forms of life
Disinfection
destroying pathogens or unwanted organisms
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Disinfectant vs. Antiseptic
Disinfectant
antimicrobial agent used on inanimate objects
Antiseptic
antimicrobial agent used on living tissue
Sanitization: Lowering of microbial counts
to prevent transmission in public setting(e.g., restaurants & public rest rooms)
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cidal vs. static
Bactericidal - kills bacteria
Bacteristatic - inhibits bacterial growth
Fungicidal
Fungistatic
Algacidal
Algastatic
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Factors that effect Antimicrobial
Activity 1. Temp
2. Time
3. Concentration of Antimicrobial agent
4. Type of Microbe
5. Activity of Microbe
6. Presence of organic matter
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Targets of Antimicrobial Agents
1. Cell membrane
2. Enzymes & Proteins
3. DNA & RNA
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Physical Methods of Microbial Control
1. Heat works by denaturing enzymes and proteins
A. Thermal Death Point (TDP)
lowest temp. at which all microorganism in aliquid culture are killed in 10 minutes
B. Thermal Death Time (TDT)
minimum length of time in which allmicroorganisms in a liquid culture are killed at
a given temperature
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Moist Heat
1. Boiling Water
kills vegetative bacterial cells, Fungi and many
viruses not effective for endospores and some viruses
Some spores may survive boiling water for up
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Moist Heat
2. Autoclave (Steam under pressure)
preferred method of sterilization
Water boils at 100 C
Increasing the pressure raises the Temp.
15 lbs./ per sq. inch (psi) ------> 121 C
121 C for 15 min.
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Dry Heat
1. Direct Flaming
Inoculating Loop and Needle 100% effective
2. Incineration
disposable wastes (paper cups, bags, dressings)
3. Hot Air Sterilization
Oven ( 170 C for 2 hours)
used on substances that would be damaged by
moist heat sterilization
gauzes, dressings or powders
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Filtration Removes microorganisms from solutions
that might be damaged by heat
culture media enzymes
vaccines
antibiotics
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Radiation
1. Ionizing Radiation
gamma rays & x-rays
penetrates most substances
Used on substances that could be damaged
by heat
plastic petri dishes plastic syringes
catheters
surgical gloves
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Radiation
2. Non-Ionizing Radiation
UV Light
does not penetrate plastic, glass or proteinaceous
matter
Used to reduce microbial populations hospital rooms
nurseries
operating rooms
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Pasteurization
Disinfection - not sterilization (removes
unwanted organisms)
Mycobacterium tuberculosis
63 C for 30 minutes 72 C for 15 seconds
M h d d l Mi bi l G h
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Methods used to control Microbial Growth 1. Heat
Moist Heat
Boiling Water Steam Heat (Autoclave)
Dry Heat
Direct Flaming
Incineration Hot Air Sterilization (Oven)
2. Filtration
3. Radiation
Ionizing Radiation
Non-Ionizing Radiation
4. Pasteurization (Heat)