Spectrofluorimetric assessment of bacterial cell membrane damage by pulsed electric field

摘要

A rapid fluorescence staining technique was used to assess cell membrane damage and ensuing injury and death caused by pulsed electric field (PEF) treatment. Cell suspensions of Lactobacillus leichmannii ATCC 4797. Listeria monocytogenes Scott A andExcherichia coli O157:H7 ATCC 35150 were subjected to PEF for 145.6 mu s at field strengths of 5-20 kV/cm. Immediately after PEF treatment, cells were stained with propidium iodide (PI), and changes in fluorescence intensity were measured with a spectrofluorimeter. Increase in field strength decreased the count of survivors and proportionally increased the fluorescence intensity, confirming that cell inactivation by PEF is caused by membrane damage. Cells of E. coli O157:H7 were incubated with or without EDTA before exposure to PEF. but similar inactivation was observed, regardless of the EDTA pre-treatment. Increase in the fluorescence intensity, however, was appreciable in the EDTA-PEF-treated cells. The fluorescence staining technique, therefore, revealed membrane-related injury when EDTA pre-treated cells were PEF-treatcd. In conclusion, the fluorescence staining technique can be used to assess membrane damage associated with PEF treatments and is potentially useful in determining the relative sensitivity of microorganisms to PEF or monitoring the efficacy of such treatments.