The effect of biofilm production on the antimicrobial susceptibility of pseudomonas aeruginosa strains isolated from dogs

The aim of this study was to evaluate the in vitro activity of marbofloxacin, gentamicin, colistin and combinations. The authors compared the sensitivity of planktonic cells with bacteria in bioflims. The susceptibility of the planktonic cells was determined to marbofloxacin, marbofloxacin-gentamicin and marbofloxacin-colistin combination with the microdilution method by determining MIC values according to CLSI (Clinical Laboratory Standards Institute) guidelines. In the second part of the study the bacterial strains were incubated without antimicrobials in microplate wells for 12 hours to form bioflims. To determine the sensitivity of bioflim-grown cells a photometric utilizing MTS-formazan formation was performed. Among the examined planktonic P. aeruginosa strains 91.7% was sensitive to marbofloxacin and all of the strains were susceptible to the 1:1 combination of the antimicrobials. In case of marbofloxacin, MICs ranged from 0.25 to 4 mu g/ml, in case of the marbofloxacin-gentamicin and marbofloxacin-colistin combinations these were between 0.0625 and 1 mu g/ml. The MIC and MIC, values of marbofloxacin were 1 mu g/ml and 2 mu g/ml, respectively. These values for the marbofloxacin:gentamicin combination were 0.5 mu g/ml and 1 mu g/ml, respectively, while for the marbofloxacin:colistin combination 0.0625 mu g/ml and 0.5 mu g/ml, respectively. To examine the susceptibility of bioflim-grown strains EC (effective concentration 50%) was used. Concerning marbofloxacin these values ranged from 64 to 4096 mu g/ml. In case marbofloxacin-gentamicin combination the EC50 was found between 8-2048 mu g/ml, while the 1:1 combination of marbofloxacin-colistin showed EC50 values between 8-128 mu g/ml. Based on the results, the susceptibility of the examined strains was significantly decreased in bioflim compared to planktonic cells, and the antimicrobial combinations increased the sensitivity of these strains.