Underlined bases denote SphI and XhoI restriction sites, respectively. Backbone pBR Δbla::cml, without the tet tetracycline resistance gene, was amplified from pBR Δbla::cml using BRCf (5′-ATGCGCATGCATGGAAGCCGGCGGCACCTC-3′) and BRCr (5′-ATGCCTCGAGTTGAAGACGAAAGGGCCTCG-3′) primers.