For each mutant, a colony that generated both flanking-PCR products was selected and plated on MRS with and without 30 μg·ml−1 erythromycin. A single colony for each mutant displaying the anticipated erythromycin-sensitive phenotype was selected and designated NZ3410CM (ΔctsR::cat) and NZ3425CM (ΔhrcA::cat), the latter resulting from the use of plasmid pNZ3425. The L. plantarum WCFS1 ctsR-hrcA mutant was constructed in the NZ3410CM (ΔctsR::cat) background in two steps. First, strain NZ3410 (ΔctsR) was constructed by excision of the lox66-P32-cat-lox71 cassette by expression of the Cre resolvase enzyme from pNZ5348 according to methods described by Lambert et al. (34). Introduction of pNZ3423 and colony confirmation by PCR resulted in strain NZ3423CM (ΔctsR ΔhrcA::cat) (see Table S1 in the supplemental material).