ABSTRACT
The specificity of the interaction of a virus with its host cell immediately lends itself to methods for the identification of bacteria, in particular the pathogens. While many other procedures based upon antibodies (ELISA) or nucleic acid amplification (PCR) have been artificially developed to allow differentiation of bacterial cell structures, here we have a naturally evolved system in which the bacteriophage specifically recognizes and binds only to its own host cells. This interaction has been exploited in a number of different methods for the specific detection and differentiation of the individual host bacteria. One of the first uses of phage was in typing schemes, where a panel of phages with different lytic spectra is used to discriminate between different isolates of a bacterial species or genus, according to their ability to infect the isolate and form plaques. Differences in infectivity reflect differences in a number of cellular characteristics, such as cell surface receptors, the presence of restriction modification systems and related prophage, plasmid carriage, etc. When using an identical set of phages, typing results are highly reproducible between different laboratories, although
it is important that the phages used are propagated under specified conditions. The ease of use and inexpensiveness of phage typing also contribute to the fact that it is still among the most widely used methods for strain identification of many bacteriain particular, Salmonella, Listeria, and Staphylococcus.
