Technology Types

GROWTH-BASED

• Adenosine Tri-Phosphate (ATP) Bioluminescence Premise of Technology: Adenosine triphosphate (ATP) is present in all living cells. In the presence of the substrate D-luciferin, oxygen and magnesium ions, the enzyme Luciferase will utilize the energy from ATP to oxidize D-luciferin and produce light.
• Adenylate Kinase Premise of Technology: Adenylate kinase is a cellular component that allows for microbial detection. The adenylate kinase released from cells is reacted with ADP to form ATP. The ATP is detected using an ATP bioluminescence method.⁷
• Changes in Head-space Pressure Premise of Technology: Electronic transducers are used to measure positive or negative pressure changes in the head-space of each culture bottle. Changes are caused by microbial growth. If the growth produces significant production and/or consumption of gas, the samples are flagged as positive.
• Colorimetric Detection of Carbon Dioxide Production Premise of Technology: As microorganisms grow, they produce carbon dioxide. Test samples are placed in culture bottles and are incubated, agitated, and monitored for the presence of microorganisms. These systems use colorimetric detection of CO₂ production from the growth of organisms.
• Conductivity Premise of Technology: Works like impedance methods, the measurement taken in conductance.
• Conventional Methods with Computer-Assisted Imaging Premise of Technology: Images are collected using a charge coupled device camera; the collected images are digitized on a computer utilizing image processing software that has programming capabilities (alternatively, some systems collect the data directly with a digital camera). The digitized picture is processed to detect colonies present, and separated colonies are counted.
• Fluorescent Detection of Carbon Dioxide Premise of Technology: This technology allows for continuous monitoring for contamination using a fluorescent carbon dioxide system.
• Impedance (also known as an Electrochemical Method) Premise of Technology: Microbial detection systems based on impedance technology are classified as either direct or indirect impedance systems. Direct impedance systems work by detecting changes in electrical conductivity of growth media when an AC current is passed across two electrodes. Indirect impedance systems detect carbon dioxide produced by metabolizing organisms. As the carbon dioxide is ionized, changes in impedance occur.
• Turbidimetry Premise of Technology: As microorganisms grow, one can detect changes in the capacity of the growth medium. Optical density measurements detect the differences in opacity at specified wavelengths using a spectrophotometer. Another version of this methodology uses microtitre plate readers with continuous detectors, to detect organism growth earlier.⁶ A common usage for this type of test us to determine microbiological suspension or inoculum sizes.