G 418 sulfate: G 418 is an aminoglycoside antibiotic similar in structure to gentamycin. It exhibits toxicity towards both eukaryotic and prokaryotic cells. The optimal concentration for selection and maintenance must be determined for each cell line. For bacteria and algae, concentrations of 5 µg/ml or less are recommended. Animal cells may require up to 300-500 µg/ml. Typically, resistance is conferred by one of two dominant genes of bacterial origin, which can be expressed in eukaryotic cells. Cells that are multiplying will be affected sooner than those that is not. Cells in log phase may require three to seven days for selection. In general, concentrations of approximately 400 µg/ml for selection and 200 µg/ml for maintenance are required for mammalian cells.