*CIISA, Faculty of Veterinary Medicine, Rua Prof. Cid dos Santos
The aim of this study was to evaluate the in vitro activity of veterinary fluoroquinolones Enrofloxacin and Marbofloxacin and human fluoroquinolone Ciprofloxacin in clinical strains of Pseudomonas spp isolated from small animal samples, at the Laboratório de Análises Clínicas Prof. Dr. Braço Forte, Faculty of Veterinary Medicine.
36 pathogenic strains of Pseudomonas spp of animal origin were isolated, 75% of them from otitis externa, 19.4% from urinary tract infection, and 5.6% from other infections. Of these, 58.3% were identified as Pseudomonas aeruginosa. Pseudomonas aeruginosa ATCC 27853 strain was used as control. Minimal Inhibitory Concentrations (MIC) were determined by broth microdilution according to NCCLS guidelines. For the veterinary fluoroquinolones, the NCCLS(M31-T,1997) veterinary criteria were applied, for Ciprofloxacin the NCCLS (2000) human breakpoints were used.
Enrofloxacin had a MIC50 of 1 µg/ml and a MIC90 of 32 µg/ml, MIC values ranged from 0.125 to 64 µg/ ml. Marbofloxacin MIC50 and MIC90 were 0.5 and 16 µg/ml, respectively, with values going from 0.0125 to 32 µg/ml. The MIC50 and MIC90 of Ciprofloxacin are lower than the ones for the veterinary fluoroquinolones, respectively 0.125 and 8 µg/ml, raging from 0.0625 to 16 µg/ml. Nevertheless Ciprofloxacin MIC90 is already beyond the defined breakpoint for resistance.
In this study the MIC50 found for Enrofloxacin (1 µg/ml) was above the susceptible NCCLS criteria which probably reflects its indiscriminate use. We also found low level of resistance in veterinary clinical strains to Enrofloxacin's metabolite Ciprofloxacin, which is of concern: Ciprofloxacin had greater efficacy in vitro against clinical veterinary Pseudomonas isolates than the veterinary quinolones, in spite of the detection of four resistant strains (11,4%). This work reports significant resistance of Pseudomonas veterinary isolates and supports the need for a rational antibiotic prescribing policy, in order to prevent the selection of resistant strains.