Dual-Antibiotic Plasmid Selection: Selecting transformants carrying carbenicillin- and chloramphenicol-resistance plasmids (100 µg/mL carbenicillin disodium, 25 µg/mL chloramphenicol) on LB agar (1.0% tryptone, 0.5% yeast extract, 1.0% NaCl, 1.5% agar).

Clone Screening and Isolation: Picking individual colonies of engineered Escherichia coli for downstream verification of dual-marker constructs.

Co-Transformation and Co-Maintenance: Maintaining strains harboring two plasmids with β-lactamase and chloramphenicol acetyltransferase markers under simultaneous selection.

Library Construction and Screening: Plating combinatorial or genomic libraries where dual selection is required to retain vector and accessory plasmids.

Reporter and Expression Studies: Assessing colony-level reporter activity or expression phenotypes that depend on plasmids selected by carbenicillin and chloramphenicol.

Colony-Forming Unit (CFU) Enumeration: Quantifying transformation efficiencies or viable counts under dual-antibiotic pressure.

Strain Preservation and Streaking: Short-term maintenance and restreaking of dual-resistant Escherichia coli strains to prevent plasmid loss.

Contamination Control: Suppressing growth of non-resistant background flora while enriching for target dual-resistant colonies.

Phage and Recombineering Workflows: Selecting recombinant colonies after phage transduction or recombineering steps that introduce dual-resistance cassettes.

Quality Control of Constructs: Verifying integrity of assembled plasmids via colony PCR and sequencing from selected colonies grown under carbenicillin/chloramphenicol.