Activity of difloxacin against bacteria isolated from canine otitis

Abstract

OBJECTIVES: Difloxacin is a difluorinated quinolone approved only for veterinary use. It has a wide spectrum of activity being active against a wide range of Gram negative and Gram positive veterinary pathogens. Difloxacin is indicated for the management of canine bacterial infections in the urinary tract, the respiratory tract and the skin. The aim of this study was to investigate the in vitro antibacterial activity of difloxacin against bacteria isolated from canine otitis. MATERIALS: Otitis samples were obtained from different clinics of Gran Canaria. Samples were cultured onto Agar McConkey, Blood Agar and Agar Sabouraud. Gram negative, oxidase negative strains were identified by API 20E system; Gram negative, oxidase positive strains were identified by API 20NE system. Catalase and coagulase tests were used to identify Gram positive bacteria. Minimal Inhibitory Concentrations (MICs) were calculated by twofold dilution method on Isosensitest Agar using a Steer's replicator. Concentrations of antibiotic range from 128 mg/L to 0.06 mg/L. RESULTS: MIC50 values of difloxacin were 0.125 mg/L for E. coli, 0.5 mg/l for Proteus mirabilis, 1 mg/L for Pseudomonas and 0.25 mg/L for Staphylococcus intermedius. MIC90 values were 128 mg/L for E. coli, 1 mg/L for P. mirabilis, 16 mg/L for Pseudomonas and 2 mg/L for Staphylococcus intermedius. Ranges of CMIs obtained were from 0.06 to >128 mg/L for E. coli; from 0.06 to 1 mg/L for P. mirabilis; from 0.06 to 32 mg/L for Pseudomonas and from 0.25 to 4 mg/L for Staphylococcus intermedius. MIC50 and MIC90 values are defined as concentrations at which 50% and 90% of the isolates are inhibited respectively. Pseudomonas showed the higher percentage of resistant strains (35%, n = 54). Similar percentages of resistant strains were found for E. coli (13%, n = 15) and Staphylococcus intermedius (12.5%, n = 48). All the strains of Proteus mirabilis (n = 21) tested were susceptible to difloxacin. CONCLUSION: Difloxacin showed a broad spectrum of activity against bacteria isolated from canine otitis. This fluoroquinolone could be useful for the treatment of canine otitis caused by Enterobacteriaceae or Staphylococcus intermedius but not for otitis due to Pseudomonas infection.