Levofloxacin disk potency and tentative interpretive criteria for susceptibility tests

Levofloxacin disk susceptibility test criteria were evaluated by testing 350 bacterial isolates. Either 5- or 10-micrograms disks could be used satisfactorily. A 5-micrograms levofloxacin disk with zone size breakpoints of < or = 12 mm for resistance (MIC, > or = 8.0 micrograms/ml) and > or = 16 mm for susceptibility (MIC, < or = 2.0 micrograms/ml) is recommended.