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

This study examined and compared the minimal inhibition concentrations (MICs) of enrofloxacin against 393 Staphylococcus intermedius strains isolated in France from canine pyodermas during three different years, 1995 (174 isolates), 1997 (101 isolates) and 1999 (118 isolates). The MICs of enrofloxacin against these strains ranged from 0.063 to 64 mg L-1, with MIC50 and MIC90 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 resistance to enrofloxacin among S. intermedius strains is still rare in dogs, but the selection in vitro of variants in which the MICs were increased 4-16-fold after 10 serial passages in subinhibitory concentrations of enrofloxacin suggests that inappropriate use might favour the development of resistant strains in vivo.