Researchers have focused on developing specific assays for conclusively identifying and measuring the levels of bacteria, fungi, protozoa, viruses (microbes), and their associated products (biomarkers) that cause disease in humans and animals (Murray et al., 2003). Traditional methods using microscopy and chemical or immunological stains, test cultures with selective media or target cells, or serological assays have been used effectively to identify infectious agents in biological specimens or environmental samples. However, due to increasing veterinary, medical, and public health concerns, faster and more accurate diagnostic tools have been sought. Multiplex array-based assays allow for a range of biomarkers to be rapidly and simultaneously measured within specimens (Robertson and Nicholson, 2005). Recently, multiplex bead-based flow cytometric immunoassays have been developed and applied that show great promise for improving the study, diagnosis, and therapeutic management of infectious diseases (Alvarez-Barrientos et al., 2000; Jani et al., 2002).

The introduction of flow cytometric bead-based technology has added a new approach for investigators to simultaneously measure multiple analytes in biological and environmental samples. This new technology allows for (1) evaluation of multiple analytes in a single sample; (2) utilization of minimal sample volumes to glean data; (3) reproducibility and results comparative with previous experiments; (4) direct comparison with existing assays; and (5) a more rapid evaluation of multiple samples in a single platform. The cytometric bead array (CBA) system enables simultaneous measurement of multiple analytes in sample volumes too small for traditional immunoassays. Results have been presented for the analysis of a variety of human cytokines. In addition, the technology allows for the design and creation of assays to measure a variety of analytes including inflammatory mediators, chemokines, immunoglobulin isotypes, intracellular signaling molecules, apoptotic mediators, adhesion molecules, and antibodies. New initiatives put forward by the Human Genome Project and the FDA require the development and use of assays for the rapid simultaneous quantitation of multiple analytes. The CBA technology provides the ability to quantify multiple proteins within a given sample, with precision and consistency.