mimicking WT and CIP resistant J774 cells, by fluorescence polarization spectroscopy. In this respect, we observed a decrease in the melting temperature in vesicles mimicking the membrane composition of CIP resistant cells, indicating that changes in the fluidity of these membranes may be due to the decrease of SM. Studies are currently performed to investigate potential changes in other components of rafts like glucosylceramides. These data might have important relevance to relate the interaction of fluoroquinolones with lipids and change in the processes involved in cellular accumulation of fluoroquinolones.