Strain effect on ICE excision. qPCR amplification was performed on total DNA extracted from cells harvested during exponential growth in LM17 medium at OD600 nm = 0.6 (expo0.6) or treated for 2.5 hours by MMC at MIC/2 and harvested at OD600 nm = 0.6 (MMC). ICE and host strains studied are indicated below. ICESt3, in strains CNRZ368 and LMG18311, was tagged with the cat gene, conferring chloramphenicol resistance, for transconjugant selection. To avoid ICE interference, strain CNRZ368 was previously deleted of ICESt1 prior ICESt3cat transfer. Excision percentage is calculated as (attB/fda)×100. Data are presented as average and standard deviation from three independent replicates.