In-vitro susceptibility of Streptococcus pneumoniae to the d- and l-isomers of ofloxacin: Interpretive criteria and quality control limits

The 1-isomer of ofloxacin (levofloxacin) was twice as active as ofloxacin and the d-isomer was inactive against 654 Streptococcus pneumoniae isolates. For disc susceptibility tests of pneumococci, 5 mu g levofloxacin discs can be used with interpretive criteria of less than or equal to 12 mm for resistant (MIC greater than or equal to 8.0 mg/L) and greater than or equal to 16 mm for susceptible (MIC less than or equal to 2.0 mg/L). For quality control of levofloxacin tests, S. pneumoniae ATCC 49619 should give zones 20-25 mm in diameter and MICs 0.5-2.0 mg/L.