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14.2: Introduction

  • Page ID
    40240
  • It’s hard to imagine living without oxygen. And it’s hard to imagine that oxygen respiration can result in many toxic products. Animals do require oxygen and have enzymes to break down those toxic products. Bacteria on the other hand are not all the same when it comes to oxygen requirements. There are many categories regarding oxygen utilization in bacteria.

    Aerobes require oxygen, anaerobes cannot survive in the presence of oxygen because they do not have the enzymes to break down toxic by-products and will quickly die in the presence of oxygen. Facultative anaerobes do have the necessary enzymes and can grow with or without oxygen. Two other categories are the microaerophiles, which prefer a reduced oxygen atmosphere, and aerotolerant organisms, which do not use oxygen, but are not killed by it.

    Take a look at the drawing above, which test tube illustrates each of the categories just listed?

    In this lab you will compare two methods for growing and observing oxygen requirements of a few different bacteria. The first is a piece of equipment called a GasPak jar. The other is a medium called Fluid Thioglycollate Medium (FTM). For the GasPak system you will inoculate 2 plates of TSA with the same bacteria and incubate one aerobically in your incubator and one anaerobically in the GasPak jar. You will inoculate tubes of FTM with the given bacteria and incubate them as normal. Then you will compare the growth patterns of the same bacteria in each.

    GasPak System

    Purpose: Permits the growth of anaerobic and facultative bacteria.

    Reagents/Indicators: Oxygen indicator

    Mechanism/reactions: The Gas Generating Sachet reduces oxygen in the container and produces carbon dioxide.

    Directions: Inoculated plates are inserted into the jar. The sachets are opened and packet is removed from the foil. An oxygen indicator is placed in the jar and the jar is immediately closed.

    Interpretation: Growth--Microaerophilic, Facultative anaerobe, Anaerobic

    Fluid Thioglycollate: Oxygen Requirements

    Purpose: The use of thioglycollate broth permits growth of anaerobic bacteria. Growth patterns can help distinguish aerotolerance and oxygen requirements of bacteria.

    Media: Contains glucose, cysteine, and sodium thioglycollate (oxygen reducing agent)

    Reagents/Indicators: Resazurin

    Mechanism/Reactions: This is a nutritive medium with a reducing agent (sodium thioglycollate), which, due to a chemical reaction, removes oxygen from the broth. A chemical indicator is included in the broth- resazurin. The pinkish color indicates the presence of oxygen.

    Directions: Deep stab needle inoculation.

    Interpretation: Aerobic, Microaerophilic, Facultative anaerobe, Anaerobic

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