ATP Bioluminescence Moves Mainstream

According to Dr. Easter, ATP’s widespread adoption resulted from three major advances. First, the instrumentation decreased in size and increased in performance, utility, and price, like the calculator or mobile phone. Second, the chemistry improved from an initial freeze-dried environment, with 25 tests per bottle and a four-day shelf life after it was regenerated, to its current use of a synthetic enzyme that is more robust and temperature tolerant and can last 12 months. And, finally, the liquid is now stable and is built into the pen-like swab in which reagent mixtures can be snapped and squeezed, then put into a luminometer for readings. Hygiena makes both the Ultrasnap or Aquasnap swabs and SystemSURE Plus palm-sized readers.

Importantly, the technology is much easier to use than it was 20 years ago. “My young son, who is eight years old, tested the counter in the house,” Dr. Easter said. “The technology is more affordable and has been deskilled.”

ATP bioluminescence methods involve the interaction between ATP and the enzyme luciferase. ATP transfers its energy to luciferin to form luciferyl adenylate, which is then oxidized by the luciferase in a reaction that emits light. The light reading intensity is directly proportional to the amount of ATP present: The higher the reading, the more ATP there is. The luminometer detects ATP on a swab using one of two systems: a photomultiplier glass vacuum tube that electronically amplifies the light signal or a photodiode using solid-state semiconductor devices.

Dr. Easter and others emphasize that it is important to use more specific tests with ATP to assure sterile surfaces. “The inside of a tomato is sterile and doesn’t contain bacteria, yet there is a huge amount of ATP,” Dr. Easter explained. “So you can have a huge amount of ATP and no bacteria.” Likewise, it is possible to have bacteria and still get a pass from an ATP system. The test is an indicator of surface hygiene and the potential risk of contamination, but it is not an absolute measure of surface contamination. Bacteria can be present but not show up on the test.

“ATP is not a linear correlation between an RLU and bacteria, so we don’t measure bacteria. We are measuring soil and adenosine triphosphate levels,” said Virginia Deibel, PhD, CEO of TRAC Microbiology Inc. in Monona, Wis., a testing, research, auditing, and consulting company. “You need to set a food safety program in conjunction with ATP. It is one tool in the toolbox.” The United States Department of Agriculture (USDA) and the Food and Drug Administration (FDA) do not require ATP testing because it is so broad, but Dr. Deibel said the FDA likes to see ATP testing during pre-operation inspections after sanitation. “ATP’s greatest strength is it allows the sanitation group to improve their work right away.”

click for large version

ATP bioluminescent instruments have evolved over the years, as shown in this timeline of one company’s products, from suitcase-sized luminometers that had to be plugged into a direct power source to battery powered devices that weighed about four pounds. The technology has now evolved into rapid-response handheld readers weighing about a pound.

Longer Shelf Lives

One of the first applications of ATP bioluminescence, according to Dr. Easter, was to long-life sterile products like milk. “So instead of milk lasting two to three weeks in the fridge, it could last 12 months in an ambient stable market,” he said. Longer shelf life is a recent trend in a broad array of liquid products, including soup broths that are boxed rather than canned. This makes ATP bioluminescence an important tool in finished product testing, which Celsis in Chicago does exclusively with its CellScan Innovate system for the dairy and beverage markets.