Cell membrane integrity and lysis in Lactococcus lactis: the detection of a population of permeable cells in post-logarithmic phase cultures |
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Authors: | Niven G W Mulholland F |
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Institution: | Institute of Food Research, Reading Laboratory, Earley Gate, Reading, Berks, UK. |
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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. |
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