A phenol red broth is inoculated with a slow-growing fermenter. At 48 hours, there is some turbidity, but it is scored as (-/-). A. Is this an example of a false negative or false positive? B. Is this due to poor sensitivity or poor specificity? 2. A student running a catalase test adds hydrogen peroxide to the culture but is immediately distracted by another student asking for help. After a few minutes, the student returns to the catalase test and notes a negative result. A. Is this result reliable? Why or why not?
Added by Ver-Nica V.
Step 1
A. This is an example of a false negative result because there is some growth, but it is scored as negative. B. This is due to poor sensitivity because the test failed to detect the slow-growing fermenter. Show more…
Show all steps
Your feedback will help us improve your experience
Supreeta N and 70 other Biology educators are ready to help you.
Ask a new question
Labs
Want to see this concept in action?
Explore this concept interactively to see how it behaves as you change inputs.
Key Concepts
Recommended Videos
Lab name: Phenol Red Broth. (please be detailed with. your answer) Early formulations of this medium used a smaller amount of carbohydrate and occasionally produced false alkaline (pink) results after 48 hours. Why do you think this happened? List at least 2 steps, as a microbiologist, you could take to prevent the problem. Suppose you inoculate a PR broth with a slow-growing fermenter. After 48 hours, you see slight turbidity but score (-/-). Is this a false positive or a false negative. Is this failure a result of a lack of specificity or sensitivity of the test system?
Adi S.
1. What would be the expected observed results in a phenol red broth + lactose test for a fecal coliform? 1. Yellow, Gas Produced 2. Yellow, No Gas Produced 3. Pink, Gas Produced 4. Pink, No Gas Produced 5. Red (No Change) 2. PRB can provide false results if not enough carbohydrate was added, or if incubated for too long (more than 48 hours). Once a fermenting organism consumes all the carbohydrates in the tube, it will stop producing acid products. The organism will, however, continue to produce ammonia, increasing the previously acidic pH of the broth to above 7.4 over time. This is called reversion. What would you expect the color of the broth to be if this reversion occurred? Would this be a false negative or a false positive? Would adding insufficient carbohydrates / incubating the test for too long decrease sensitivity or specificity of the test? Expected Color: PINK Would this be a false negative or a false positive? Answer Choose: Yellow; Pink; False Negative; Sensitivity; Specificity; False Positive; Red Would the mistakes decrease sensitivity or specificity? Answer Choose: Yellow; Pink; False Negative; Sensitivity; Specificity; False Positive; Red
Sri K.
Recommended Textbooks
Biology for AP Courses
Objective Biology for NEET
Introduction to General, Organic and Biochemistry
Transcript
Watch the video solution with this free unlock.
EMAIL
PASSWORD