CELL-MEMBRANE INTEGRITY AND LYSIS IN LACTOCOCCUS-LACTIS - THE DETECTION OF A POPULATION OF PERMEABLE CELLS IN POST-LOGARITHMIC PHASE CULTURES

A method was developed that enabled an analysis of the proportion of p ermeable cells in a culture of Lactococcus lactis, This used the fluor escence of propidium iodide (PI) when in contact with DNA and the impe rmeability of the intact cell membrane to this compound, A permeabilit y index was suggested that expresses the PI-induced fluorescence of a cell suspension as a percentage of the value obtained from wholly perm eabilized cells after treatment with cetyltrimethylammonium bromide. T his method was applied to the determination of cell permeability in de ath phase cultures, A large proportion of unlysed cells was freely per meable to PI, a finding that may have some significance for the invest igation of the role of cell lysis in cheese maturation. This method is suggested as a useful addition to the techniques available for the st ud! of cell damage in a variety of fields, and for the screening of ch eese starter bacteria.