Antibiotic-resistance marker genes

• Antibiotic-resistance marker genes use a technique called replica plating. This process involves the other antibiotic-resistance gene in the plasmid (i.e. the gene that was cut to in order to incorporate the required gene, meaning it will no longer produce the enzyme that breaks down the other antibiotic (tetracycline)).
• During replica plating, the bacteria have already lost their resistance to tetracycline (because this resistance gene was cut earlier), meaning that we can identify these bacteria by growing them on a culture that contains tetracycline.
• The major issue with antibiotic-resistance marker genes is that treatment with tetracycline will destroy the cells that contain the required gene. However, by using replica plating, it is possible to identify living colonies of bacteria containing the required gene.