Transduction complicates the detection of conjugative ability in lysogenic salmonella strains

When lysogenic salmonella strains were examined for conjugative ability in tri-parental crosses, false positive results were sometimes obtained because phage carried by the lysogenic strains multiplied on the intermediate salmonella recipient strain and then transduced its streptomycin/sulphonamide resistance plasmid to the final salmonella recipient strain. Back transfer of the plasmid to the lysogenic strains was also detected.