ATP testing is a quick method for the detection of bacteria activity on a surface, or liquid samples by measuring the light produced by the reaction between ATP and the luciferin/luciferase complex.
What is ATP?
ATP stands for Adenosine Triphosphate and it is known as the universal unit of energy in all living organisms. The ATP molecule consists of three parts. The core is represented by the sugar ribose attached on one side to a string of three phosphates and on the other side the nucleobase adenine, a nitrogenous base also found in DNA.
When catalyzed by an enzyme, ATP loses the endmost phosphate group releasing energy which is used for many metabolic processes. The reaction leaves ADP (Adenosine diphosphate) that through a series of biochemical reactions regain the lost phosphate to become energetically active again.
What are luciferin and luciferase?
Both compounds, luciferin and luciferase, are essential for bioluminescence which is the biochemical emission of light by living organisms, primarily fireflies and deep-sea fishes. Luciferin is a light-producing compound while luciferase is the enzyme that catalyzes the reaction. During the reaction luciferase allows oxygen (or other substances like ATP) to combine with the luciferin; this reaction produces photons of light at different wavelengths that could potentially be measured. The terms luciferin and luciferase are generic terms used to defined the role rather than a chemical structure. Lots of substances can act as luciferins and luciferases depending on the organism and the biochemical pathway used for the production of light.
How does the reaction occur in ATP testing?
The reaction basically happens as explained before. By many cleaning and extraction steps the ATP from bacterial cells is released and bound to the complex of luciferin/luciferase, when oxygen interacts too, light is released and quantified in a photometer. If there is no ATP (no cell activity) the compounds remain inactive and no light is produced.
How is light measured?
Light from bioluminescence is mostly measured in RLU (Relative Light Units). The relation of ATP from a sample is linear to the RLU reading; which means that high RLU concentration is the result of high concentration of ATP being measured. Depending on the manufacturer of an ATP measuring kit, there are several methods or formulas that could be used for transforming RLU in bacterial units, for example CFU, ME, among others. However, it is not a 100% percent accurate given that some ATP can be from contaminants or residual from other chemical reactions. The accuracy also depends on the manufacturer and how the kit is actually used.