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.