Conjugative Transfer of bla NDM Plasmid

The transfer of the bla_NDM-harboring plasmid (donor) to sodium azide-resistant E. coli J53 (recipient) was performed in a solid-state mating assay using a medium supplemented with MEM (2 mg/L) and sodium azide (100 mg/L). For some isolates, conjugation was not successful. Hence, purified plasmid DNA was electrotransformed using electrocompetent E. coli DH10B cells (Invitrogen, CA, USA) in a Gene Pulser II (Bio-Rad Laboratories, Hercules, CA, USA). Transformants (TFs) were screened in the presence of MEM (2 mg/L). The presence of bla_NDM was confirmed, along with other β-lactamase genes, via PCR in transconjugants (TCs) and TFs (32 (link)). The MIC for MEM was determined for the TCs and TFs via MBD assay (43 (link)).