*Constança Pomba-Féria, Marta Costa, Mónica Ferreira, José Duarte Correia, Manuela Caniça
*CIISA, Faculty of Veterinary Medicine, Rua Prof. Cid dos Santos
To evaluate in vitro efficacy of enrofloxacin, marbofloxacin and ciprofloxacin against Escherichia coli strains isolated from dogs with urinary tract infection.
A total of 75 E. coli strains were isolated from urine specimens collected from dogs with urinary tract infection. Significant bacteriuria criteria used in this study were as follows: for cystocentesis samples - >102 CFU/ml; for catheter samples - >103 or 104 CFU/ml; for midstream urine - >105 CFU/ml. Clinical manifestations and pyuria quantitation (>5 leucocytes/400 power field) were also taken in consideration in the above criteria. Strains were biotyped using the API 20E system. Minimal Inhibitory Concentrations (MIC) were done by broth microdilution with enrofloxacin (ENR), marbofloxacin (MAR) and ciprofloxacin (CIP), according to NCCLS guidelines.
Cumulative MIC values analysis demonstrated that MIC50 values were 0,031 ug/ml for CIP and 0,062 ug/ml for both MAR and ENR. However, MAR and CIP resistance was detected in 9 out of 75 strains (12%), and ENR resistance occurred in 10 out of 75 strains (13,3%). The level of resistance detected implied MIC90 values of 16 ug/ml for the three fluoroquinolones studied. Since resistance breakpoint established for these three quinolones is > or equal than 2 ug/ml, MIC90 values of CIP, MAR and ENR showed a relevant level of resistance against uropathogenic E. coli strains.
We found an emerging level of resistance towards fluoroquinolones in canine E. coli strains isolated from urinary tract infection. This work shows the importance of antibiotic pressure in therapy and the need for antimicrobial resistance surveillance in veterinary medicine.