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Three plates are needed for each dilution series, for statistical reasons an average of at least 3 counts are needed. The surface of the plates need to be sufficiently dry to allow a 20μl drop to be absorbed in 15–20 minutes. Plates are divided into equal sectors (it is possible to use up to 8 per plate).
A prior understanding of the microscopic anatomy of the organism can give a better understanding of how the observed CFU/mL relates to the number of viable cells per milliliter. Alternatively it is possible to decrease the average number of cells per CFU in some cases by vortexing the sample before conducting the dilution. However, many ...
A dilution of the cells to be counted is prepared and mixed with Trypan blue, this is normally the stain of choice because it is taken up by dead cells and actively excluded from live cells. Once the cells have been stained, they are counted using a hemocytometer, then a calculation is carried out to the original concentration of live cells. [1]
For example, if you plate 1x 10 7 cells and count 1000 colonies, the transformation efficiency is: (1000/1x 10 7) x 100 = 0.1% Alternatively, CFUs can be reported per microgram of DNA used for the transformation. This can be calculated by multiplying the number of colonies by the volume of the culture plated and dividing by the amount of DNA used.
The "dilution factor" is an expression which describes the ratio of the aliquot volume to the final volume. Dilution factor is a notation often used in commercial assays. For example, in solution with a 1/5 dilution factor (which may be abbreviated as x5 dilution ), entails combining 1 unit volume of solute (the material to be diluted) with ...
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Conversely, in an indirect dilution assay the dose levels are administered at fixed dose levels, so that the response is a stochastic variable. In some assays, there may be strong reasons for believing that all the constituents of the test preparation except one, are without any effect on the studied response of the subjects.
Because bird flu viruses can mutate and gain the ability to spread more easily between people, California public health officials said they are monitoring animal and human infections carefully.