Various tests are available that can be used to assess the presence of biological analytes in a sample (e.g. surface, water, air, etc). Such tests include those based on the detection of ATP using the firefly luciferase reaction, tests based on the detection of protein using colorimetry, tests based on the detection of microorganisms using microbiological culture techniques, and tests based on detection of microorganisms using immunochemical techniques. Surfaces can be sampled using either a swab device or by direct contact with a culture device such as an agar plate. The sample can be analyzed for the presence of live cells and, in particular, live microorganisms.
Results from these tests are often used to make decisions about the cleanliness of a surface. For example, the test may be used to decide whether food-processing equipment has been cleaned well enough to use for production. Although the above tests are useful in the detection of a contaminated surface, they can require numerous steps to perform the test, they may not be able to distinguish quickly and/or easily the presence of live cells from dead cells and, in some cases, they can require long periods of time (e.g., hours or days) before the results can be determined.
The tests may be used to indicate the presence of live microorganisms. For such tests, a cell extractant is often used to release a biological analyte (e.g., ATP) associated with living cells. The presence of extracellular material (e.g., non-cellular ATP released into the environment from dead or stressed animal cells, plant cells, and/or microorganisms) can create a high “background” level of ATP that can complicate the detection of live cells.
In spite of the availability of a number of methods and devices to detect live cells, there remains a need for a simple, reliable test for detecting live cells and, in particular, live microbial cells.