ATP is the primary energy transfer molecule present in all living biological cells on Earth. ATP cannot be produced or maintained by anything but a living organism, and as such, its measurement is a direct indication of biological activity. For hygiene testing the total ATP content of the sample is determined.
The purpose of ATP testing is to achieve and defensibly document effective cleaning by following the principle that if biomass is not present on critical surfaces after cleanup there is not enough medium for microbiological proliferation. Simply stated: no biological contamination, no microbial growth.
The main advantage of ATP as a biological indicator is the speed of the analysis. Unlike quantitative microbiological monitoring that requires at least several hours, quantitative biological monitoring takes only minutes from collecting the samples to obtaining the results. Results are given in real time.
Here is how it works: ATP is rapidly detected by light emission through the combined use of luciferase and a luminometer. An ATP free swab is moistened with an ATP free buffer, water or extractant. The use of the extractant helps releasing ATP from the surface being sampled. Using a portable luminometer, testing the swab is usually done immediately. There are some systems where the swabs are stable for a number of hours; thereby allowing the user to complete the analysis at a workstation or other location.
Note: Although studies show there is often a correlation between ATP measurements and presence of live bacteria, ATP testing is not a substitute for plate counts and pathogen testing in healthcare environments, even though the temptation is there to use it as such in this age of expediency.
Interpretation of Results
There is a grave misunderstanding in our industry that the ATP monitoring system is a 'bug test' when it really is a 'dirt test.' I would be remiss if I did not advise you about some of the nuances of data interpretation. The test readout is in relative light units (RLUs), which mean the systems measure luminescent units, not cells. Remember, the luminometer detects bioluminescence from ATP, a cell constituent.