mic lecture10.pptx

7/28/2019 Mic Lecture10.pptx

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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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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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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)

mic lecture10.pptx

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