Principles of Bacterial Detection: Biosensors, Recognition Receptors and Microsystems

Abstract

Luminescence-based techniques for the detection of microbial pathogens are extensively employed in industrial setting where the continuous monitoring of bacterial contamination is of great importance. The primary advantage of all luminescence-based assays is their rapidity and sensitivity. Here we describe two different types of luminescence systems that have been adapted for commercial use, bioluminescence (BL) and chemiluminescence (CL). BL is a naturally occurring process by which living organisms convert chemical energy into light. Light-emitting pathways have been identified in bacteria, insects, and other eukaryotic organisms. Bacterial lux systems have been extensively studied and have been engineered for a variety of purposes. In the most common adaptation of the lux genes for the microbial detection, luciferase reporter phages are constructed for the direct and specific identification of many bacterial species including Salmonella spp., Listeria , and E. coli O157:H7. Central to the lux reaction is that bioluminescence is dependent on higher-level energy intermediates, allowing levels of light to be correlated to changes in bacterial metabolism. The firefly LUC luciferase is also widely used in biotechnology. Since all living things possess intracellular pools of ATP, many applications of the LUC system capitalize on the ATP-dependency of this luminescence reaction for the detection of microbial populations in situ. The LUC system is also useful in determining the efficacy of sanitizing agents, as decreases in BL are proportional to the number of active bacteria within a defined matrix. Other eukaryotic luciferases, such as those from marine copepod Gaussia princeps and Jamican click beetle, are currently been explored as alternative means for bacterial detection in extreme environmental conditions, and in situations where the simultaneous detection of multiple bacterial species is desired. CL is generally defined as the production of light by chemicals during an exothermic reaction, and CL differs from BL in that light production is not catalyzed by biological reactions. Although not as widely used in industrial applications, CL is sometimes preferred to BL-based detection systems due to the relative simplicity of the reaction and the elimination of certain steps sometimes required for the optimization of BL. CL has been used mainly for the detection of foodborne pathogens in combination with immunoassays. Using CL-linked antibodies specific for certain bacterial antigens, allows the simultaneous detection of E. coli O157:H7, Yersinia enterocolitica, Salmonella typhimurium , and Listeria monocytogenes . Luminescence-based techniques are proven effective agents in the detection of contaminating microbial populations, and with increases in the sensitivity and simplicity of such techniques, their application in numerous industrial and commercial settings will only grow.