FIG. 3.

L. monocytogenes LO28 colonies following transformation with the pMADΔclpB plasmid. Cells were cultivated at 30°C for 6 h, followed by incubation at 39°C for 3 h; dilutions were plated on TSA X-Gal plates in the absence of antibiotics. White colonies have undergone the excision and loss of the plasmid vector, whereas blue colonies retain a copy of the plasmid integrated in the chromosome.