4.2.4 Transfection of bacteria.
FAM-labeled S1 was used for the preparation of fluorescently labeled Td.
Bacteria (1×106 CFU/mL) were incubated with 0.1, 0.5,
or 1 μM FAM-Td in PBS and then
treated with 500 U/mL DNase for 15 min. FAM-S1 was used as a control. To
optimize the transfection conditions,
LP2000 was mixed with Td at ratios
of 0.0025, 0.0125, 0.025, and 0.125 μL/μg before incubating with
bacteria, and the optimum ratio (0.125 μL/μg) was used in subsequent
experiments.