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Applied and Environmental Microbiology, April 2004, p. 2289-2295, Vol. 70, No. 4
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.4.2289-2295.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Pulsed Electric Field Alters Molecular Chaperone Expression and Sensitizes Listeria monocytogenes to Heat

Beatrice H. Lado,1 Joshua A. Bomser,1 C. Patrick Dunne,2 and Ahmed E. Yousef1*

Department of Food Science and Technology, The Ohio State University, Columbus, Ohio 43210,1 U.S. Army Natick Soldier Center, Natick, Massachusetts 01760-50182

Received 8 September 2003/ Accepted 12 January 2004

Pulsed electric field (PEF)-resistant and PEF-sensitive Listeria monocytogenes strains were sublethally treated with electric pulses at 15 kV/cm for 29 µs and held at 25°C for 5 to 30 min prior to protein extraction. The levels of the molecular chaperones GroEL, GroES, and DnaJ were determined by immunoblotting. After 10 to 20 min after sublethal PEF treatment, a transient decrease in molecular chaperone expression was observed in the PEF-sensitive strain (Scott A). The levels of GroEL and DnaJ increased back to the basal expression level within 30 min. A substantial decrease in GroES expression persisted for at least 30 min after PEF treatment. Chaperone expression was suppressed after PEF treatment to a smaller extent in the PEF-resistant (OSY-8578) than in the PEF-sensitive strain, and no clear expression pattern was identified in OSY-8578. Inactivation of Scott A and OSY-8578 in phosphate buffer was compared when lethal PEF (27.5 kV/cm, 144 µs) and heat (55°C, 10 min) were applied in sequence. When PEF and heat treatments were applied separately, the populations of L. monocytogenes Scott A and OSY-8578 decreased 0.5 to 0.6 log CFU/ml. Cells treated first with PEF and incubated at 25°C for 10 min showed substantial sensitivity to subsequent heat treatment; the decrease in counts for Scott A and OSY-8578 was 6.1 and 2.8 log CFU/ml, respectively. The sequence and time lapse between the two treatments were crucial for achieving high inactivation rates. It is concluded that PEF sensitized L. monocytogenes to heat and that maximum heat sensitization occurred when chaperone expression was at a minimum level.

* Corresponding author. Mailing address: Department of Food Science and Technology, The Ohio State University, 2015 Fyffe Rd., Parker Food Science and Technology Building, Columbus, OH 43210. Phone: (614) 292-7814. Fax: (614) 292-0218. E-mail: yousef.1{at}osu.edu.

Applied and Environmental Microbiology, April 2004, p. 2289-2295, Vol. 70, No. 4
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.4.2289-2295.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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