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3. Plate count data are used to calculate microbial population density as colony forming units (CFUs) per milliliter of culture. Culture density (CFU/mL) = number of colonies / (dilution factor) x (volume plated, in mL) Use the data below to calculate the CFU/mL in this sample of bacteria after 1 hr of growth. Important to know for these types of questions – only use colony counts that are between 10 and 300. TNTC = too numerous to count, so many colonies that you can’t distinguish them to count. Use the plates with numbers of colonies that can be counted, calculate the CFU on each one, and then the average between all of them. Looking for more assistance? Read section 6.4 in the textbook. Time | Dilution (before plating) | Volume spread on plate | Number of colonies observed (replicate plates) 1 h | none | 0.1 mL | TNTC | TNTC | 1:10 (1 x 10^-1) | 0.1 mL | 499 | 518 | 1:100 (1 x 10^-2) | 0.1 mL | 83 | 87 | 1:1,000 (1 x 10^-3) | 0.1 mL | 10 | 8 TNTC indicates too numerous to count. * Cell density could not be calculated accurately because plates contained too many colonies to be counted, too many colonies to be counted accurately (>300), or too few colonies to be meaningful (<10)

          3. Plate count data are used to calculate microbial population density as colony forming units (CFUs) per milliliter of culture.

Culture density (CFU/mL) = number of colonies / (dilution factor) x (volume plated, in mL)

Use the data below to calculate the CFU/mL in this sample of bacteria after 1 hr of growth. Important to know for these types of questions – only use colony counts that are between 10 and 300. TNTC = too numerous to count, so many colonies that you can’t distinguish them to count. Use the plates with numbers of colonies that can be counted, calculate the CFU on each one, and then the average between all of them. Looking for more assistance? Read section 6.4 in the textbook.

Time | Dilution (before plating) | Volume spread on plate | Number of colonies observed (replicate plates)
1 h | none | 0.1 mL | TNTC | TNTC
| 1:10 (1 x 10^-1) | 0.1 mL | 499 | 518
| 1:100 (1 x 10^-2) | 0.1 mL | 83 | 87
| 1:1,000 (1 x 10^-3) | 0.1 mL | 10 | 8

TNTC indicates too numerous to count.
* Cell density could not be calculated accurately because plates contained too many colonies to be counted, too many colonies to be counted accurately (>300), or too few colonies to be meaningful (<10)

3. Plate count data are used to calculate microbial population density as colony forming units (CFUs) per milliliter of culture.

Culture density (CFU/mL) = number of colonies / (dilution factor) x (volume plated, in mL)

Use the data below to calculate the CFU/mL in this sample of bacteria after 1 hr of growth. Important to know for these types of questions – only use colony counts that are between 10 and 300. TNTC = too numerous to count, so many colonies that you can’t distinguish them to count. Use the plates with numbers of colonies that can be counted, calculate the CFU on each one, and then the average between all of them. Looking for more assistance? Read section 6.4 in the textbook.

Time | Dilution (before plating) | Volume spread on plate | Number of colonies observed (replicate plates)
1 h | none | 0.1 mL | TNTC | TNTC
| 1:10 (1 x 10^-1) | 0.1 mL | 499 | 518
| 1:100 (1 x 10^-2) | 0.1 mL | 83 | 87
| 1:1,000 (1 x 10^-3) | 0.1 mL | 10 | 8

TNTC indicates too numerous to count.
* Cell density could not be calculated accurately because plates contained too many colonies to be counted, too many colonies to be counted accurately (>300), or too few colonies to be meaningful (<10)

Added by Alexander W.

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