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Applied and Environmental Microbiology, August 2009, p. 5315-5320, Vol. 75, No. 16
0099-2240/09/$08.00+0     doi:10.1128/AEM.00458-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Role of Growth Temperature in Freeze-Thaw Tolerance of Listeria spp. {triangledown}

Reha O. Azizoglu,1 J. Osborne,2 S. Wilson,3 and S. Kathariou1*

Department of Food, Bioprocessing, and Nutrition Sciences,1 Department of Statistics, North Carolina State University, Raleigh, North Carolina,2 Department of Biology, St. Augustine's College, Raleigh, North Carolina3

Received 24 February 2009/ Accepted 12 June 2009

The food-borne pathogen Listeria monocytogenes can grow in a wide range of temperatures, and several key virulence determinants of the organism are expressed at 37°C but are strongly repressed below 30°C. However, the impact of growth temperature on the ability of the bacteria to tolerate environmental stresses remains poorly understood. In other microorganisms, cold acclimation resulted in enhanced tolerance against freezing and thawing (cryotolerance). In this study, we investigated the impact of growth temperature (4, 25, and 37°C) on the cryotolerance of 14 strains of L. monocytogenes from outbreaks and from food processing plant environments and four strains of nonpathogenic Listeria spp. (L. welshimeri and L. innocua). After growth at different temperatures, cells were frozen at –20°C, and repeated freeze-thaw cycles were applied every 24 h. Pronounced cryotolerance was exhibited by cells grown at 37°C, with a <1-log decrease after 18 cycles of freezing and thawing. In contrast, freeze-thaw tolerance was significantly reduced (P < 0.05) when bacteria were grown at either 4 or 25°C, with log decreases after 18 freeze-thaw cycles ranging from 2 to >4, depending on the strain. These findings suggest that growth at 37°C, a temperature required for expression of virulence determinants of L. monocytogenes, is also required for protection against freeze-thaw stress. The negative impact of growth at low temperature on freeze-thaw stress was unexpected and has not been reported before with this or other psychrotrophic microorganisms.

* Corresponding author. Mailing address: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Schaub Hall Rm. 339, Raleigh, NC 27695-7624. Phone: (919) 513-2075. Fax: (919) 513-0014. E-mail: skathar{at}unity.ncsu.edu

{triangledown} Published ahead of print on 19 June 2009.

Applied and Environmental Microbiology, August 2009, p. 5315-5320, Vol. 75, No. 16
0099-2240/09/$08.00+0     doi:10.1128/AEM.00458-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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