In vitro antimicrobial activity of marbofloxacin and enrofloxacin against bacterial strains isolated from companion animals.

Fluoroquinolones were originally developed for the Gram-negative aerobic spectrum, but the newer generation agents are also highly effective against some Gram-positive pathogens and cause few adverse effects. Owing to these characteristics, fluoroquinolones are often used in first line therapy in small animal practice. However, their widespread use has raised concern over emerging bacterial resistance. In this study we evaluated the in vitro efficacy of two fluoroquinolones, marbofloxacin and enrofloxacin, on field strains isolated from clinical infections between 2002 and 2005. Our data show that most of the isolates are still sensitive to both antimicrobials and marbofloxacin was more effective than enrofloxacin, especially against P. aeruginosa and beta-Streptococci (P < 0.01). beta-Streptococci demonstrated the greatest resistance to the two study drugs.