title: Cell membrane integrity and lysis in Lactococcus lactis: the detection of a population of permeable cells in post-logarithmic phase cultures.
abstract: A method was developed that enabled an analysis of the proportion of permeable cells in a culture of Lactococcus lactis. This used the fluorescence of propidium iodide (PI) when in contact with DNA and the impermeability of the intact cell membrane to this compound. A permeability index was suggested that expresses the PI-induced fluorescence of a cell suspension as a percentage of the value obtained from wholly permeabilized cells after treatment with cetyltrimethylammonium bromide. This method was applied to the determination of cell permeability in death phase cultures. A large proportion of unlysed cells was freely permeable to PI, a finding that may have some significance for the investigation of the role of cell lysis in cheese maturation. This method is suggested as a useful addition to the techniques available for the study of cell damage in a variety of fields, and for the screening of cheese starter bacteria.
authors.affiliation: Institute of Food Research, Reading Laboratory, Earley Gate, Reading, Berks, UK.
authors.forename: G W
authors.initials: GW
authors.lastname: Niven
authors.forename: F
authors.initials: F
authors.lastname: Mulholland
mesh_terms: D001433:Bacteriolysis; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D002611:Cheese / Q000382:microbiology*; D005285:Fermentation; D005516:Food Microbiology; D013294:Lactococcus lactis / Q000201:enzymology / Q000648:ultrastructure*; D013050:Spectrometry, Fluorescence