- Direct Epi-fluorescent Filter Technique (DEFT) Premise of Technology: Samples are filtered and stained using a fluorescent viability indicator. Sensitivity of technique depends on the volume
filtered and the number of fields viewed under the microscope. The robustness of the test can be affected by the distribution
of the microorganisms on the membrane. This methodology is best suited for low viscosity fluids, although it may be possible
to use pre-filtration to allow testing of other solutions.10
Flow Cytometry (fluorescence)
Premise of Technology: Using flow cytometry, microorganisms are labeled in solution with a non-fluorescent marker. The marker is taken up into
the cell and cleaved by intracellular enzymatic activity to produce a fluorescing substrate. The labeled sample is automatically
injected into a quartz flow cell, which passes each microorganism past a laser excitation beam for detection.
Premise of Technology: The process of microbial catabolism results in heat that can be measured by microcalorimetry. A calorimeter can be used to
establish growth curves. When high levels of contamination are present, one may need to use flow calorimetry.6 This technology cannot be used to determine if a single contaminant is present or used on samples with mixed contaminants.
Solid Phase Cytometry
Premise of Technology: Solid phase cytometry uses membrane filtration to separate potential microbial contaminants from filterable samples prior
to labeling of the captured cells with a universal viability substrate. Solid phase cytometry eliminates the need for cell
multiplication. Solid phase cytometry has been accepted for pharmaceutical water testing by FDA in February 2004 and also
has been accepted by the United Kingdom in 2000.
Concentric Arcs of Photovoltaic Detectors with Laser Scanning
Premise of Technology: The system is comprised of five concentric arcs of photovoltaic detectors, almost in an orb-like platform. The sample being
evaluated is suspended in a liquid or gas inside a collection device, placed near the center of the orb. A laser beam of
red, solid state composition is passed through the sample. Identification occurs within a few milliseconds after the particle
passes through the beam.10
Fluorescent Probe Detection
Premise of Technology: Nucleic acid probes are designed to bind to specific target sites on or in cells. Probes contain a molecule that is capable
of fluorescing when stimulated by an energy source. Some of these systems have restrictions on the sample size allowed.
Lab-on-a-Chip (LOC), Arrays, Microarrays, and Microchips
Premise of Technology: The use of an array of data to perform tests has been used in many microbiology applications. Each microchip is like a miniature
laboratory and often referred to as a "lab on a chip" device. Typical microbiological reagents include oligonucleotides, proteins,
DNA, etc.7 One application of this technology is the antibody dot or microspot assay. A small amount of antibody is placed on the bottom
surface of a plastic well. This antibody dot is used as the capture antibody in a microimmunoassay.
Arrays, Microarrays, Microchips
Biosensors and Immunosensors
Premise of Technology: Immunological reagents are combined with sensor detection systems to produce an immunosensor. These types of systems are
used for pathogens (including bioterrorism organisms).7
When evaluating a system for use, consider a variety of factors:
- Type of technology considered versus the type of microbiological test being performed
- Initial system cost
- Cost per test on an on-going basis
- Can the system handle the type of products manufactured, filterability, sample size, detection limits appropriate for the
- System through-put
- Level of automation required and available