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Applied and Environmental Microbiology, September 2000, p. 3966-3973, Vol. 66, No. 9
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Effects of High Pressure on Survival and Metabolic Activity of Lactobacillus plantarum TMW1.460

Helge M. Ulmer, Michael G. Gänzle,* and Rudi F. Vogel

Technische Universität München, Lehrstuhl für Technische Mikrobiologie, D-85350 Freising, Germany

Received 20 March 2000/Accepted 30 June 2000

The application of high pressure (HP) for food preservation requires insight into mechanisms of HP-mediated cell injury and death. The HP inactivation in model beer of Lactobacillus plantarum TMW1.460, a beer-spoiling organism, was investigated at pressures ranging from 200 to 600 MPa. Surviving cells were characterized by determination of (i) cell viability and sublethal injury, (ii) membrane permeability to the fluorescent dyes propidium iodide (PI) and ethidium bromide (EB), (iii) metabolic activity with tetrazolium salts, and (iv) the activity of HorA, an ATP binding cassette-type multidrug resistance transporter conferring resistance to hop compounds. HP inactivation curves exhibited a shoulder, an exponential inactivation phase, and pronounced tailing caused by a barotolerant fraction of the population, about 1 in 106 cells. During exponential inactivation, more than 99.99% of cells were sublethally injured; however, no sublethal injury was detected in the barotolerant fraction of the culture. Sublethally injured cells were metabolically active, and loss of metabolic activity corresponded to the decrease of cell viability. Membrane damage measured by PI uptake occurred later than cell death, indicating that dye exclusion may be used as a fail-safe method for preliminary characterization of HP inactivation. An increase of membrane permeability to EB and a reduction of HorA activity were observed prior to the loss of cell viability, indicating loss of hop resistance of pressurized cells. Even mild HP treatments thus abolished the ability of cells to survive under adverse conditions.

* Corresponding author. Mailing address: TU München, Lehrstuhl für Technische Mikrobiologie, Weihenstephaner Steig 16, D-85350 Freising, Germany. Phone: 49 (0)8161 71 3959. Fax: 49 (0)8161 71 3327. E-mail: michael.gaenzle{at}blm.tu-muenchen.de.

Applied and Environmental Microbiology, September 2000, p. 3966-3973, Vol. 66, No. 9
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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