6. Please read the following case study, and answer the questions that follow. C
ID: 198637 • Letter: 6
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6. Please read the following case study, and answer the questions that follow. CASE STUDY: DETERMINING THE EFFECTIVENESS OF A FOOD PRESERVATIVE Background To determine whether a newly synthesized chemical might be a useful food preservative, the chemical was tested for its ability to inhibit bacterial growth. Control 500 ml of cottage cheese was inoculated with 2 ml of a 24-hr culture of Pseudomonas aeruginosa and incubated at 25°C. Five hours after inoculation, a standard plate count showed there were 200 bacterial cells/ml in the cottage cheese. After 29 hours at 25°C, there were 61,000,000 cells/ml in the cottage cheese. Experiment 500 ml of cottage cheese containing the preservative was inoculated with 2 ml of a 24-hr culture of P. aeruginosa. After 6 hours of incubation at 25°C, a standard plate count was performed. There were 700 bacterial cells/ml in the cottage cheese. After 18 hours, there were 1,000,000 bacterial cells/ml in the cottage cheese. Leg 0.00 0.30 0.70 0.78 1.38 1.51 2.30 2.85 6.00 6.79 7.79 Number 24 32 200 700 1.00 x 10 6.10 x 10* 6.10 x 10 Questions 1. How did the control cottage cheese and the experiment cottage cheese differ? Was this experimental design valid? (2 points)Explanation / Answer
Ans 1) The control and experimental cottage cheese differed because in the former the preservative was not added and in the later preservative was added. The number of bacterial cells that grew in the control was comparatively less as compared to the experimental design. It was found that same treatment was given to both but the one that is expected to be a preservative actually led to more bacterial colony or cell growth.
Ans 2) The food preservative that was used in the experimental cottage cheese is not a preservative. The preservative is a substance which is meant to control the growth of the bacteria which means after standard plating the colony formation or cell formation must be inhibited. It did not inhibit the growth of the bacteria and instead led to more growth as compared to the control.
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