Use of the lambda Red recombinase system to produce recombinant prophages carrying antibiotic resistance genes

Seven phages carrying two different antibiotic resistance genes were derived from phages that are directly involved in the pathogenesis of Shiga toxin-producing strains, using this modified protocol.This approach facilitates exploration of the transduction processes and is a valuable tool for studying phage-mediated horizontal gene transfer.The analysis of microbial sequences has revealed that a substantial fraction of the genome of some bacteria corresponds to prophage DNA [1,2]. Such prophage DNA is inserted into the bacterial chromosome after infection by free phage particles. Bacteiophages have recently regained part of their former importance, but now with a medical and ecological focus.Phage λ DNA integrates into host DNA at one preferential site in Escherichia coli. This integration occurs through homologous recombination, mediated by the action of site-specific recombinases [3]. Bacteriophage can be released from cells containing an intact prophage through a process called induction. In this process, the prophage genes required for lytic growth are turned on, and progeny virions are produced and released from the cell. Cells carrying a prophage are called 'lysogens' because of their potential to be induced and to lyse [2,4]. Most phage genes, including those required for lytic growth and virion production, are turned off in integrated prophages. However, prophages express regulatory proteins involved in the maintenance of the lysogenic state and 'lysogenic conversion' genes which alter the properties of the host bacterium. The products of these genes may have strong effects on the host bacterium, which can have its phenotype modified by expression of genes encoded by the prophage. These changes range from protection against further phage infection to increasing the virulence of a pathogenic host.The presence or absence of prophages can account for much of the variation among individuals within a bacterial species. In addition, phages are likely to be importa