Abstract
The activity of ten 4-quinolone drugs was tested against fiveEscherichia coli mutants. Mutational resistance was found to reduce the activity of all ten drugs, indicating that they display biochemical cross-resistance with each other. However, ciprofloxacin and, to a lesser extent, ofloxacin and norfloxacin were so highly active that the most resistance exhibited by any mutant fell well within the serum drug concentration ranges attainable in humans. Hence, clinical cross-resistance inEscherichia coli at least, need not necessarily apply to such highly active 4-quinolone antibacterial agents.