Investigations on the synergic effects of aminoglycosides, polymyxins and fluoroquinolones combinations against Pseudomonas aeruginosa isolated from dog.

Many times, the treatment of severe bacterial infections determined by multiresistant microorganisms need a combination of antibiotics. This paper present the activity of some antibiotics, used alone and in combination, on Pseudomonas aeruginosa strains isolated from dogs having chronic otitis. In order to demonstrate the efficacy of these antibiotics on the isolated strains, the dilution method was used and minimum inhibitory concentration was determined for each antibiotic and for the combinations. The results were interpreted by the National Committee for Clinical Laboratory Standards. Antibiotics from the groups of fluoroquinolones, aminogycosides and polymyxins, and combination between enrofloxacin-gentamicin, enrofloxacin-amikacin, enrofloxacincolistin were tested on 7 bacterial strains. The fractional inhibitory concentration index was calculated and showed that the phenomenon of synergism appeared for all strains when enrofloxacin-gentamicin and enrofloxacin-amikacin combinations were used. The enrofloxacin-colistin combination showed synergism only in 57.14 % of cases, in 42.86 % of strains being observed the additive phenomenon. Based on these results comes the recommendation of using combination of antibiotics when necessary, because of the higher efficacy together, much more than alone, in the therapy.