TDK conference 2016

As a result of widespread use of antibiotics, both human and veterinary medicine face the problem of bacterial resistance. Staphylococcus pseudointermedius strains caused otitis externa, pyoderma and other dermatological diseases usually claim for a long term treatment, which leads to the development of antimicrobial resistance in these pathogens. Different antibiotics in combinations can be efficiently used in the field of veterinary medicine to reduce resistance.

The aim of this study was to examine the resistance of the potencial dermatological pathogens mentioned above, in vitro. Bacteria were passaged for 8 days in broths containing subinhibitory concentrations of marbofloxacin and the combination of marbofloxacin:gentamycin 50-50 m/m %. The examined strains were isolated from dogs suffering from otitis externa and pyoderma, including 32 Staphylococcus pseudointermedius strains. Determining the MIC value, the broth microdilution method was performed inaccordance with the Committee of Laboratory Standards Institute (CLSI) guideline. With this method, each bacterium was individually observed each day, and their colonies were passaged each day to another plate. This method mimics the effect of subinhibitory concentrations present in biological systems, and helps understanding and interpreting the risk of drug usage on the development of bacterial resistance. MIC values of marbofloxacin ranged between 0,5 and 8 µg/ml, while the marbofloxacin:gentamicin combination resulted MIC values between 0,125 and 8 µg/ml. Average multiplication of the MICs on Day 8 passaged in marbofloxacin alone and the marbofloxacin:gentamicin (1:1) combination were 11,67 compared to 3.00, respectively. A maximum MIC multiplier of 16 occurred only in one case and the bacterium still remained susceptible according to CLSI breakpoints. In case of marbofloxacin:gentamicin, most of the strains showed a MIC multiplier of two or less, showing an excellent activity of the combination in preventing resistance development.

Considering these results it can be pronounced that the marbofloxacin:gentamicin (1:1) combination can significantly hinder the development of fluoroquinolone resistance in veterinary dermatopathogenic S. pseudintermedius bacteria.