The key difference between the traditional culture method and Growth DirectTM is the camera's ability to detect colonies rather than the human eye.
This difference can be easily validated by taking the CFU count on the cassette generated by the system and comparing it to the count on the same cassette by the analyst. It is important to use multiple analysts to generate the standard count as there is an operator to operator difference, as seen on the chart.
The validation of the system in terms of PQ would require a study of accuracy and precision with known organisms from the USP/EP and in house organisms.
*Precision from reps of 6-10 from a range of sample types and CFU levels are shown below
Accuracy is shown by inoculating known numbers of organisms (typically <100) to the sample type and comparing the count recovered to the control sample. An example of recovery of organisms inoculated to water is shown below.