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Applied and Environmental Microbiology, April 2003, p. 2223-2229, Vol. 69, No. 4
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.4.2223-2229.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Selection and Identification of a Listeria monocytogenes Target Strain for Pulsed Electric Field Process Optimization

Department of Food Science and Technology, The Ohio State University, Columbus, Ohio 43210

Received 27 August 2002/ Accepted 19 January 2003

Nine Listeria monocytogenes strains were treated individually with a continuous pulsed electric field (PEF) apparatus, and their sensitivities to the treatment were compared at 25 kV/cm. When cell suspensions of these strains in 0.1% NaCl (pH 7.0) were treated at 23°C for 144 µs, inactivation ranged from 0.7 to 3.7 log₁₀ CFU/ml. Inactivation by 72-µs PEF treatments at 37°C ranged from 0.3 to 2.5 log₁₀ CFU/ml. L. monocytogenes OSY-8578 was substantially more resistant than other strains when cells were PEF treated in 0.1% NaCl, whereas Scott A was one of the most sensitive strains. The superiority of OSY-8578's resistance to that of Scott A was confirmed in 50% diluted acid whey (pH 4.2). Changes in sensitivity to PEF during phases of growth were minimal in OSY-8578 and substantial in Scott A. Use of L. monocytogenes OSY-8578, therefore, is recommended in studies to optimize PEF processes that target L. monocytogenes. The nine L. monocytogenes strains were genotyped with pulsed-field gel electrophoresis (PFGE) and arbitrarily primed PCR (AP-PCR) techniques. These strains were better differentiated with PFGE than with AP-PCR. The target strain (OSY-8578) was characterized by both molecular typing techniques, but resistance to PEF, in general, was not associated with a particular genotype group.

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