Salmonella detection in eggs using Lux(+) bacteriophages

Recombinant bacteriophages specific for Salmonella spp. and containing bacterial luciferase genes were constructed. The phage caused the host cells to luminesce when mixed with Salmonella spp. and the luminescence could be detected using a photon-counting charge-coupled device (CCD) camera, a luminometer, or X-ray film. The initial assay system was capable of detecting Salmonella isolates from group B and group D. Certain isolates from group C could also be detected, With 6 h of preincubation, as few as 10 CFU of Salmonella cells per mi in the original sample could be detected. The minimum time required for the detection of 10(8) CFU/ml was 1 to 3 h with no preincubation, depending on bacteriophage adsorption temperatures. The phage-based assay could be carried out on Petrifilm E. coli Count Plates and the light emission detected within 24 h. The system allowed Salmonella cells to be detected in whole eggs by direct addition of recombinant bacteriophages into the eggs followed by visualization of the luminescent Salmonella cells inside the eggs.