Salmonellae are mammalian pathogens that are transmitted mainly through foodstuffs and their handlers. Rapid detection requires both specificity and sensitivity in samples containing other bacteria. A solution to this problem is the use of the great specificity conferred by bacteriophages. After implanting reporter genes in a phage genome, the reporter gene products can be measured with great sensitivity when a bacterial host is present. Bacteriophage Felix 01 infects almost all Salmonella strains and has been manipulated to contain the lux genes specifying bacterial luciferase, an enzyme that converts chemical energy to visible light. A widely applicable methodology for preventing the escape of such recombinant phage has also been developed.