Micro lab exercise 21

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Micro lab exercise 21
2011-07-24 15:33:35
micro lab

TSI media and OF media
Show Answers:

  1. What are the key ingedients in TSI media that produce the various reactions? Why is one sugar lower in % concentration than the other sugars?
    • Ingredients: Dextrose, lactose, sucrose, sodium, thiosulfate, ferric ammonia citrate
    • To detect bacteria that ferments only dextrose the concentration is 1/10 of the concentration of the sugars. Small acid produced in the slant oxidizes quickly through revert back to alkaline pH or red color.
    • Low oxygen tension in the butt of the tube keeps an acid pH yellow color
    • If hydrogensulfide from thiosulfate it reacts with ferrious citrate to form a black precipitant
  2. Describe the reactions and the processes involved to produce the reactions in the following TSI tube. 1.) A/A gas 2.) Alk/A H2S 3.) Alk/Alk
    • 1.) A/A gas- glucose and/or sucrose and/or lactose is formented producing gas produced cause bubbles splitting of agar and/or displacement of agar in tube
    • 2.) Glucose only is fermented producing a red slant in a yellow butt H2S production is indicated by a black color precipitant that spreads throughout the butt.
    • 3.) None of the sugars are fermented, no change in color or pH and/or red slant and red butt
  3. What is the purpose of the OF procedure? List and explain the three reactions that can occur?
    • Determination of oxidative and fermenation metabolism of carbohydrates or sugars by gram negative bacilli.
    • Oxidation- air tube is yellow and oil tube is green, bacteria can only utilize the presents of oxygen. So air tube turns yellow to do the acid by products of oxidation and the oil tube without oxygen cannot utilize the sugar so it remains green.
    • Fermentation- both tube are yellow, bacteria doesn't need oxygen to utilize the sugar. So both tubes turn yellow by acid by products. Non utilization air and oil tubes are green bacteria doesn't utilize the sugars
  4. BONUS: Describe how to perform the OF procedure. List materials needed.
    • Materials: 2 OF tubes, needles, stock cultures, mineral oil
    • Procedure: Using needles innoculate both OF tubes with a stock culture by stabbing each tube 4 or 5 times but not all the way to the botton.
    • Overlay one tube with mineral oil, leave both caps loose, incubate overnight
  5. Why should a control tube with no sugars be used?
    • Some bacteria utilize other substances besides sugar producing acid by products and producing yellow color or a false positive.
    • A conttrol tube doesn't contain any sugars