Antibiotic uptake by bacteria as measured by partition in polymer aqueous phase systems

Polyethyleneglycol/dextran and polyethyleneglycol/salt two-phase systems are used to measure the entry of antibiotics into Escherichia coli and Staphylococcus aureus cells. Aminoglycosides, macrolides, a quinolone, and a cycline were assayed. The method is simple and rapid and eliminates the problems encountered with filters, especially nonspecific binding; it allows rapid uptake kinetics to be measured.