Studies of multidrug efflux pump activity in Lactococcus lactis using ethidium cations

Abstract

Multidrug resistance (MDR) efflux pump is the main reason of bacteria resistance to antibiotics. Lactococcus lactis is very important bacterium in food industry. We used spectrofluorimetric measurments to assay the activity of MDR pumps and to investigate the response of the pumps to cell growth conditions. We used ethidium (Et) as as indicatory compound, which increases its fluorescence because of the binding to DNA. We also used another MDR pump substrate tetraphenylphosphonium (TPP+ ) as a competitive compound and antibiotic gramicidin D as the cell permeabilizer. In this study we demonstrated that the differences in MDR efflux pump activity depend on the growth conditions (with or without heme source) and the energetic state of cells.