Fatty Acid Profiles (Fatty Acid Methyl Esters [FAMEs])
Type of Technology: Cell-component-based.
Premise of Technology:
Fatty acids are present in microorganisms. The fatty acid composition typically is homogeneous within different taxonomic
groups. Isolates are grown on standard media and selected for testing. The testing procedure includes saponification of fatty
acids, methylation, and extraction, to produce fatty acid methyl esters (FAMEs). The FAMEs are measured using gas chromatography,
and the measurements are compared to a library of known organisms.7
Commercial Systems Available:
Sherlock Microbial Identification System (MIDI).
Other:
The methods used for growth of microorganisms (media and incubation) should be standardized. Gas chromotographs should
be calibrated frequently.
Fluorescent Detection of Carbon Dioxide
Type of Technology: Growth-based.
Premise of Technology: This technology allows continuous monitoring for contamination using a fluorescent carbon dioxide system. A pH-sensitive,
fluorescent CO2 sensor is poured into the bottom of each container. A series of computer algorithms assess an increased rate of change and
a sustained increase in CO2 production.12
Commercial Systems Available:
Bactec (Becton Dickinson and Company).
Other: Commercial formulations of all microbial growth media may not be available.
Flow Cytometry (Fluorescence)
Type of Technology:
Viability-based.
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 individually through a laser excitation beam for detection.
The staining and detection mechanisms are similar to solid-phase cytometry. Flow cytometry detects organisms in solution and
not in the solid phase, allowing for non-filterable solutions to be tested. Typically, results are obtained within 1.5 to
2 hours, although the limit of detection is approximately 100 cfu per mL.
Commercial Systems Available:
D-Count (AES Chemunex) and RBD3000 (AATI).
Other:
Systems developed for the pharmaceutical sector range from simple manual systems with single-test capability to highly
automated units with high test throughput potential.
Fluorescent Probe Detection
Type of Technology:
Combination, cell-component-based, nucleic-acid-based.
Premise of Technology:
Nucleic acid probes are designed to bind to specific target sites on or in cells. The probes contain a molecule that
is capable of fluorescing when stimulated by an energy source such as a laser. (See Nucleic Acid Probes)
Commercial Systems Available: RBD3000 (AATI).
Other: Some systems have restrictions on the sample size allowed.
Fourier Transform Infrared Spectroscopy (FTIR)
Type of Technology:
Cell-component-based.
Premise of Technology:
Fourier transform infrared spectroscopy can be used to generate an infrared spectrum of microorganisms. The patterns
generated are stable across taxonomic groups. The patterns are compared to a database of spectra of known microorganisms.
Commercial Systems Available: A variety of systems is commercially available.
Other: Standardization is a critical performance aspect, e.g., using isolates grown on standard media using standard incubation conditions.
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