Rapidly growing mycobacteria (RGM) and Nocardiae can cause severe or refractory
infections in cats and dogs. Prolonged antibacterial
therapy is required to cure these
infections. As
fluoroquinolones have been used in combination
therapy for treating RGM
infections, isolates from the Mycobacterium smegmatis cluster (n=64), Mycobacterium fortuitum cluster (n=17), and M. mageritense cluster (n=2), collected from feline and canine patients, underwent susceptibility testing to
pradofloxacin. The MIC(50), MIC(90) and tentative epidemiological cut-off (ECOFF) values as determined by microbroth dilution susceptibility testing that inhibited growth of the M. smegmatis and M. fortuitum clusters were 0.063, 0.125 and ≤ 0.25; and 0.125, 0.250 and ≤ 1.0 μg/mL, respectively. E-Test results showed similar trends but MICs were lower than those for microbroth dilution. In summary,
pradofloxacin demonstrated effective in vitro activity against RGM isolates. Additionally, veterinary isolates of Nocardia nova (n=18), Nocardia farcinica (n=3) and Nocardia cyriacigeorgica (n=1) underwent microbroth dilution testing to
ciprofloxacin,
enrofloxacin and
pradofloxacin. The MIC(50) and MIC(90) of
pradofloxacin,
ciprofloxacin and
enrofloxacin that inhibited growth of Nocardia nova isolates were 2 (4), 8 (16), 16 (32) μg/mL, respectively. The tentative ECOFF values for
pradofloxacin and
ciprofloxacin were 32 μg/mL and for
enrofloxacin 64 μg/mL. The MIC or MIC range for the three N. farcinica isolates of
pradofloxacin,
ciprofloxacin and
enrofloxacin were 0.25-0.5, 2 and 2 μg/mL and for the single N. cyriacigeorgica isolate were 1, 4 and 4 μg/mL, respectively. On the basis on these results,
fluoroquinolones appear to have limited therapeutic potential for most
Nocardia infections.