In food microbiology, various components of microbial cells have been assayed in order to rapidly detect and estimate the microbial biomass. Measurements of the so-called adenosine triphosphate (ATP) content using a firefly bioluminescence system has shown considerable promise as a rapid and reliable estimation system for total counts in foods. The conventional cultural techniques for estimating these organisms in foods can take at least 2 days, whereas the ATP test can give a result in approximately 1 hour or less.
This method is based on the fact that all cells contain ATP and that the quantity detected in a certain specimen is referable to a given number of cells. It is employed a luciferin-luciferase (EC 1.13.12.7) preparation. During the reaction, ATP is transformed into adenosine monophosphate (AMP) and light. The intensity of the light produced is directly proportional to the cell concentration of ATP. The basis of the ATP assay is shown in the figure.
The problems that must be dealt with are that the quantity of ATP varies from different bacterial cells, with the amount ranging from 0.1 to 4.0 fg/cell and that the background ATP from food substances must be excluded from the analysis. By one commercially available system, background ATP can be eliminated and ATP assays can be run in an automated manner.
It generally requires 105-106 cells/g in order to have enough ATP to emit a consistent detectable light.