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Use of a fluorescent viability stain to assess lethal and sublethal injury in food‐borne bacteria exposed to high‐intensity pulsed electric fields
Author(s) -
Yaqub S.,
Anderson J.G.,
MacGregor S.J.,
Rowan N.J.
Publication year - 2004
Publication title -
letters in applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.698
H-Index - 110
eISSN - 1472-765X
pISSN - 0266-8254
DOI - 10.1111/j.1472-765x.2004.01571.x
Subject(s) - rowan , library science , medicine , biology , computer science , ecology
Aims: To apply scanning electron microscopy, image analysis and a fluorescent viability stain to assess lethal and sublethal in food‐borne bacteria exposed to high‐intensity pulsed electric fields (PEF). Methods and Results: A rapid cellular staining method using the fluorescent redox probes 5‐cyano‐2,3‐ditolyl tetrazolium chloride (CTC) and 4′,6‐diamidino‐2‐phylindole was used for enumerating actively respiring cells of Listeria mononcytogenes , Bacillus cereus and Escherichia coli . This respiratory staining (RS) approach provided good agreement with the conventional plate count agar method for enumerating untreated and high‐intensity PEF‐treated bacteria suspended in 0.1% (w/v) peptone water. However, test organisms subjected to similar levels of lethality by heating at 56°C resulted in ca 3‐log‐unit difference in surviving cell numbers ml −1 when enumerated by these different viability indicators. PEF‐treated bacteria were markedly altered at the cellular level when examined by scanning electron microscopy. Conclusions: While PEF‐treatment did not produce sublethally injured cells ( P < 0.05), substantial subpopulations of test bacteria rendered incapable of forming colonies by heating may remain metabolically active. Significance and Impact of the Study: The fluorescent staining method offers interesting perspectives on assessing established and novel microbial inactivation methods. Use of this approach may also provide a better understanding of the mechanisms involved in microbial inactivation induced by PEF.