Enumeration and Detection
Enumeration and Detection Worksheet
FDST 7060E – Harrison
Assignment 2 – Enumeration and Detection
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1. What modifications of the standard aerobic plate count method would be needed/appropriate if you were trying to enumerate the following groups? (20 words or less for each part) a. Anaerobes Click here to enter text. b. Psychrotrophs Click here to enter text. c. Xerophilic molds Click here to enter text. d. Generic E. coli Click here to enter text.
2. One ml of a 24-h broth culture was mixed in a 99 ml dilution blank. Dilutions of 1:10, 1:100, 1:1000, and 1:10000 were made from the initial dilution, and 0.1 ml was plated in duplicate from the last dilution. After an incubation period, the duplicate plates were observed and 139 and 141 colonies were counted on the two plates. What was the population per ml of sample? Click here to enter text.
3. Twenty-five g of raw lettuce was added to a 225 ml dilution blank. After mixing, dilutions of 1:10, 1:100, and 1:1000 were made from the initial dilution. From the last dilution, 1 ml was placed into a petri plate and plate count agar was added to the plate. After incubation, 88 colony forming units were counted on the plate. What was the population per g of lettuce? Click here to enter text. FDST 7060E – Harrison
4. The following colony forming units were enumerated from duplicate petri plates with the dilution factors noted. What would the reported count be for this sample? Dilution factor 10-3 10-4 104 20 111 17 Click here to enter text.
5. The following colony forming units were enumerated from duplicate petri plates with the dilution factors noted. What would the reported count be for this sample? Dilution factor 10-4 10-5 285 34 275 32 Click here to enter text.
6. What is the purpose of selective enrichment? (25 words or less) Click here to enter text.
7. What is the principle behind the PCR method? (25 words or less) Click here to enter text.
8. What is the principle behind the ELISA method? (25 words or less) Click here to enter text.
9. What is the principle behind using biochemical testing for foodborne pathogen detection? (25 words or less) FDST 7060E – Harrison Click here to enter text.
10. Define the following as they apply to microbial enumeration and detection: (20 words or less for each part) a. Sublethal injury Click here to enter text. b. Selective agent Click here to enter text. c. Differential agent Click here to enter text. d. CFU Click here to enter text.
11. Using the FDA-BAM, summarize in outline form the steps used to test black pepper to determine if it contains Salmonella (through confirmation of typical colonies). Include time or time range required for each step and give a total time for complete the test. Click here to enter text.
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