Direction: An aliquot of competent E. coli cells were used for determination of cell density by plate count method and another aliquot was used for transformation by plasmid DNA
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E. coli cell culture (1 ml) was diluted 1:1000000 and 200µl of this was used for plating. After 12h incubation of the plate, the number of colony forming units (CFU) was 150. What is the total CFUper ml in original culture ?
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- 7.5 × 108
- 1.5 × 108
- 1.5 × 106
- 3.0 × 106
Correct Option: A
Since, 1 ml = 1000 µl
New volume = 10³ × 106 µl = 109 µl.
Since, only 200 µl is used we have a dilution factor of
| = | = 0.5 × 107 | |
| 200 μl |
Number of colony in original one ml culture would be
= 0.5 × 107 × 150
= 7.5 × 108.
