Ampicillin sodium a -lactam antibiotic inhibits bacterial cell wall synthesis through interference with transpeptidase enzymes during cell division exerting activity against various Gram-positive and Gram-negative bacteria This sterile-filtered ampicillin sodium aqueous solution (100 mg/ml 1000X) is routinely employed in molecular biology for selective propagation of bacteria harboring plasmids carrying an ampicillin-resistance gene Typical usage involves addition into liquid or agar bacterial media at a final concentration of 100 g/ml for efficient selection It effectively maintains plasmid stability and prevents contamination in bacterial transformation or cloning experiments Compatible bacterial hosts often include competent E coli strains (e g DH5 genotypically characterized as recA1 endA1 lacZ M15) which feature suitable genetic backgrounds facilitating high plasmid retention and transformation efficiencies typically 1 10 8 cfu/ g DNA