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Pure Culture Techniques Lab Exercise 9

Culturing Microorganisms. Microorganisms are ideal lab subjects- grow rapidly-are small in size-many generations can be observed-results can be applied to other organisms. Pure Culture. Consists of only a single type of organism.Rarely exist in nature. Naturally exist as mixed cultures. Pure cultures must be obtained artificially.

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Pure Culture Techniques Lab Exercise 9

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    1. Pure Culture Techniques (Lab Exercise 9)

    2. Culturing Microorganisms Microorganisms are ideal lab subjects - grow rapidly -are small in size -many generations can be observed -results can be applied to other organisms

    3. Pure Culture Consists of only a single type of organism. Rarely exist in nature. Naturally exist as mixed cultures. Pure cultures must be obtained artificially

    5. Isolation Microorganisms occur in huge numbers. *Isolation of single species (pure culture) is done by : Streak plate method Pour plate method

    6. Streak Plate (Quadrant Streak)

    7. Pour Plate

    8. Growing a Pure Culture To grow microorganisms: nutrients must be supplied in the culture medium (Agar is the solidifying material used in solid media. It is an extract of seaweed that melts at 100o C and solidifies at about 42o C) A suitable environment must be provided

    9. Culture Medium Enriched Media- is formulated with all the necessary ingredients for a wide variety of organisms and grows a multitude of bacterial species (example: Trypticase Soy Agar –TSA) Selective Media- are formulated with ingredients that inhibit the growth of some bacteria, such as an antibiotic, but enhance growth of the target organism (example: Blood Agar –BA) Differential Media- includes ingredients, such as chemical indicators, that produce observable differences between species of bacteria. (example: MacConkeys agar –MAC)

    10. Suitable Environment Temperature pH Oxygen

    11. Temperature Microbes grow over a range of temperatures ( nat. environ) Temperatures maintained in Incubators Waterbaths

    12. pH Optimal pH varies Bacteria? neutral pH 6.5-7.5 Buffers are added to neutralize the by-products of bacteria metabolism

    13. Oxygen microbes respond differently Strict aerobes Strict anaerobes facultative aerobes facultative anaerobes Microaerophiles O2 must be provided , limited or excluded

    16. Enumeration of Bacteria (Lab Exercise 20)

    17. Methods for Determining Bacteria Numbers

    18. Microscopic Counts (Petroff-Hauser slides)

    19. Methods for Determining Bacteria Numbers continued

    20. Chapter 6

    21. Chapter 6

    22. Chapter 6 Determination of Growth by Optical Density Turbidity (cloudiness) Measured by a spectrophotometer at wavelength 686nm Scale %Transmittance (amount of light passing through)(measured) Optical Density or Absorbance(calculated) To convert between the optical density (OD)and transmittance(T) scales, use the equation: OD = 2 – Log (%T)

    23. Chapter 6

    24. Chapter 6

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