Bacteriophage: Powerful Tools for the Detection of Bacterial Pathogens

Abstract

Methods for detection of bacterial pathogens have to be rapid, sensitive, specific, inexpensive, easy to perform, and robust. Traditional culture-based plating techniques are hampered by time-consuming enrichment steps. This and other problems are tackled by culture-independent detection methods. The use of bacteriophage or parts thereof for bacterial detection attracts increasing attention, as reflected by a multitude of different phage-based techniques recently reported. Bacterial viruses have been optimized by evolution to specifically target their host organisms and are therefore ideal tools for detection of these microbes. For this purpose, every stage in the replication cycle of phages, from adsorption to host cell lysis, has been exploited. Phage amplification assays are among the easiest methods to harness the host specificity of phages; the use unmodified phage particles to infect target organisms, followed by amplification of the infection as a signal by addition of helper cells. The capacity of phages to infect and lyse their host cells is utilized in assays which detect the release of cytoplasmic molecules. Cell wall recognition, phage adsorption, and injection of phage DNA into the host bacterium have also been exploited by detection methods, including capture of cells by immobilized phages and labeling of target organisms by fluorescently tagged phage particles. Phage encoded high affinity molecules such as tail fiber proteins or cell wall binding domains of phage endolysins have proven to be suitable for this purpose, especially when coupled with magnetic separation of captured bacteria. For bacterial detection, genetically modified reporter phages introduce reporter genes into their hosts. Upon infection, these gene products are produced in the target cells and can be detected with high sensitivity. Other detection methods employ phages without making use of their own host specificity. Phage display is a popular technique that can be used for production of non-phage derived high affinity molecules for recognition of pathogenic bacteria. Filamentous phages present entire libraries of randomized peptides on their surfaces, and the most suitable ones can be selected by repeated rounds of screening. In conclusion, the use of phages for detection of pathogenic bacteria offers interesting alternatives and advantages compared to traditional analytical methods.