Unit 9 Carbohydrate Fermentation Durham Tubes

Summary

The video explains the process of testing carbohydrate fermentation in microorganisms using Durham tubes. These tubes contain phenol red as an indicator, which turns yellow when acid is produced during fermentation, signaling the presence of specific enzymes. The inverted glass tube inside the Durham tube is used to detect gas production. The video demonstrates how different colors indicate whether an organism can ferment sugars like lactose or sucrose, and how this test can be used alongside others like TSI to identify an organism's metabolic capabilities.

Takeaways

• 🔬 The video discusses the fermentation of simple sugars using Durham tubes, a method to test an organism's ability to ferment specific sugars.
• 🌡️ Durham tubes contain an inverted glass tube to capture air bubbles, indicating gas production during fermentation.
• 🍬 The presence of different sugars in separate tubes allows for testing an organism's ability to ferment various simple sugars.
• 🧬 An organism's ability to ferment a sugar suggests it possesses the necessary enzymes, such as lactase for lactose or sucrase for sucrose.
• 🌈 Phenol red is used as an indicator in the broth; it turns yellow if the pH drops due to acid production from fermentation.
• 🟡 A yellow color in the Durham tube indicates a positive result, showing that the organism can ferment the sugar and produce acid.
• 🔴 A red or orange color suggests a negative result, meaning the organism lacks the enzyme to ferment the specific sugar.
• 💨 The clearing of the inverted glass tube indicates the production of CO2, which is associated with acid production and fermentation.
• 🔍 Observing air bubbles in the inverted tube is crucial, as a significant amount of clearing (at least a third of the tube) is needed to confirm gas production.
• 📚 Using Durham tubes in conjunction with other tests like TSI can provide comprehensive information about an organism's carbohydrate fermentation capabilities.

Q & A

What is the purpose of the Durham tube in microbiology?

The Durham tube is used to test the fermentation of simple sugars by microorganisms. It contains an inverted glass tube to catch air bubbles, indicating gas production during fermentation.

How does the inverted glass tube inside the Durham tube function?

The inverted glass tube is used to capture air bubbles produced during fermentation. If the tube is cleared by at least a third, it indicates that the organism can produce CO2 as a byproduct of fermentation.

What role does phenol red play in the Durham tube?

Phenol red is an indicator in the Durham tube that changes color based on pH. It starts red and turns yellow if the pH drops due to acid production, indicating fermentation.

What color change in phenol red indicates acid production during fermentation?

A color change from red to yellow in phenol red indicates acid production, suggesting that the organism can ferment the sugar and produce an acidic byproduct.

What color of phenol red suggests that the organism does not ferment a particular sugar?

If phenol red remains orange or red, it indicates that the organism does not have the enzyme necessary to ferment the sugar, and no acid production has occurred.

How can you determine if an organism has the enzyme to ferment lactose based on the Durham tube test?

If the phenol red in the lactose tube turns yellow and the inverted tube is cleared, it indicates that the organism has the enzyme lactase to ferment lactose.

What does the absence of air bubbles in the inverted tube signify?

The absence of air bubbles in the inverted tube suggests that the organism does not produce CO2 during fermentation of the sugar being tested.

Can the Durham tube test be used with a variety of simple sugars?

Yes, the Durham tube can be used with different simple sugars to determine which ones an organism can ferment, as indicated by color change and gas production.

What is the significance of using the Durham tube in conjunction with a TSI tube?

Using the Durham tube with a TSI tube can provide additional supporting information about which sugars are fermented by an organism, as TSI contains multiple sugars.

What does a cleared inverted tube in a sucrose Durham tube indicate?

A cleared inverted tube in a sucrose Durham tube indicates that the organism has fermented sucrose, producing acid and CO2, and possesses the sucrase enzyme.

How can you interpret a red result in a Durham tube test for a simple sugar?

A red result in a Durham tube test for a simple sugar indicates a negative test, meaning the organism did not ferment the sugar and no acid production occurred.