Antimicrobial activity of enrofloxacin against Staphylococcus intermedius strains isolated from canine pyodermas

This study examined and compared the minimal inhibition concentrations (MIC s) of enrofloxacin against 393 Staphylococcus intermedius strains isolated in France from canine pyodermas during three different years, 1995 (174 iso lates), 1997 (101 isolates) and 1999 (118 isolates). The MICs of enrofloxac in against these strains ranged from 0.063 to 64 mg L-1, with MIC50 and MIC 90 equal to 0.125 and 0.25 mg L-1, respectively. Two resistant strains were found, but only among isolates collected in 1999. The data show that resis tance to enrofloxacin among S. intermedius strains is still rare in dogs, b ut the selection in vitro of variants in which the MICs were increased 4-16 -fold after 10 serial passages in subinhibitory concentrations of enrofloxa cin suggests that inappropriate use might favour the development of resista nt strains in vivo.