Abstract
The 4-quinolone PD127,391 displays a biphasic effect on Escherichia coli, Staphylococcus aureus and S. epidermidis in nutrient broth. It is as active as ciprofloxacin in terms of its optimum bactericidal concentration against E. coli. However, against staphylococci it is six times as active as ciprofloxacin or any other 4-quinolone previously investigated. Although protein and RNA synthesis are not required for bactericidal activity, cell division is essential.