Advanced Techniques in Diagnostic Microbiology

58 Y. F. Wang
the reliability of these assays, when used under real-time clinical conditions, has
not been well studied. The decision to switch will be made on the basis of adequate
quality through validation of assays and cost. As methods change, the new
automated assays must be validated against the existing ones for better sensitivity,
specificity, predictive values, and clinical utility.
Most chemiluminescent reactions can be adapted to this assay format by labeling
either with a chemiluminescent compound or with an enzyme and using
a chemiluminescent substrate. Most commercially developed immunoassays are
of this type (Table 4.2). For example, Lumi-Phos 530 of Luminol CLIA is used
as the detection reagent in the Access immunoassay analyzer (Beckman Coulter
Inc., Fullerton, CA, USA). Lumigen PPD and enhancer are incorporated in the
chemiluminescent detection reagent used in the Immulite Immunoassay Analyzer
from Diagnostic Products Corporation (DPC). The AxSYM immunoassay system
(Abbott) is based on the microparticle enzyme immunoassay technology (Fiore
et al., 1988; Hennig et al., 2000, Lazzarotto et al., 2001). The DPC Immulite (Diagnostic
Products Corporation) is a benchtop immunoassay analyzer with continuous
random-access capabilities that uses enzyme-amplified chemiluminescence
chemistry for antibody or antigen detection (Schaap et al., 1987).
As shown in Table 4.2, several high-throughput systems that can provide streamlined
operations to reduce total processing time are available in the market. Many
types of immunoassays can be developed on the automated system for hepatitis
virus A, B, and C, cytomegalovirus, and HIV assays.
Summary
Over the past 20 years, immunodiagnostic technologies have been developed to
identify infectious agents with better sensitivity and specificity to ensure that every
true-positive case is diagnosed. Antibody-based methods used to be the tool for
the detection and epidemiological analysis of slow-growing, difficult-to-culture,
uncultivatable, or emerging infectious agents.
Conventional ELISA has been the predominant technology used for such assays,
with CLIA, ECL, and TRF detection formats becoming more promising technologies
for automated antibody detection. Handheld assay and multiplexed flow cytometry
methods are also emerging as the next generation of rapid laboratory-based
technologies.
Acknowledgement
Proof-reading by Yona Pogue is appreciated.
References
Aggerbeck, H., Norgaard-Pedersen, B., & Heron, I. (1996). Simultaneous quantitation of
diphtheria and tetanus antibodies by double antigen, time-resolved fluorescence immunoassay.
J Immunol Methods, 190, 171–183.