Susceptibility to levofloxacin predicted from in vitro susceptibility testing results obtained with ciprofloxacin and with ofloxacin

A test battery of bacterial strains with a high incidence of resistance to fluoroquinolones was studied to determine the extent to which susceptibility to levofloxacin could be predicted from susceptibility tests performed with ciprofloxacin or ofloxacin as reagents. Isolates susceptible or intermediately susceptible to ofloxacin (MICs, ≤4 μg/ml) may be regarded as susceptible to levofloxacin, with the exception of Enterococcus faecium. Ciprofloxacin-susceptible isolates (MICs, ≤1 μg/ml) were also completely susceptible to levofloxacin. Clinical laboratories could use either of the currently used fluoroquinolones (ciprofloxacin or ofloxacin) to predict levofloxacin activity and spectrum with little risk of false-susceptible errors (0.0 to 1.3%). Results obtained with ofloxacin are superior in maximizing recognition of levofloxacin-susceptible clinical isolates.