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Applied and Environmental Microbiology, October 2000, p. 4351-4355, Vol. 66, No. 10
Eastern Regional Research Center,
Agricultural Research Service, U.S. Department of Agriculture,
Wyndmoor, Pennsylvania 19038
Received 10 March 2000/Accepted 1 August 2000
Differential scanning calorimetry (DSC) and fatty acid analysis
were used to determine how cold shocking reduces the thermal stability
of Listeria monocytogenes. Additionally, antibiotics that
can elicit production of cold or heat shock proteins were used to
determine the effect of translation blockage on ribosome thermal
stability. Fatty acid profiles showed no significant variations as a
result of cold shock, indicating that changes in membrane fatty acids
were not responsible for the cold shock-induced reduction in thermal
tolerance. Following a 3-h cold shock from 37 to 0°C, the maximum
denaturation temperature of the 50S ribosomal subunit and 70S ribosomal
particle peak was reduced from 73.4 ± 0.1°C (mean ± standard deviation) to 72.1 ± 0.5°C (P
0099-2240/00/$04.00+0
Cold Shock and Its Effect on Ribosomes and Thermal
Tolerance in Listeria monocytogenes
0.05), indicating that cold shock induced instability in the associated
ribosome structure. The maximum denaturation temperature of the 30S
ribosomal subunit peak did not show a significant shift in temperature
(from 67.5 ± 0.4°C to 66.8 ± 0.5°C) as a result of cold
shock, suggesting that either 50S subunit or 70S particle sensitivity
was responsible for the intact ribosome fragility. Antibiotics that
elicited changes in maximum denaturation temperature in ribosomal
components also elicited reductions in thermotolerance. Together, these
data suggest that ribosomal changes resulting from cold shock may be
responsible for the decrease in D value observed when
L. monocytogenes is cold shocked.
*
Corresponding author. Mailing address: Eastern Regional
Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA 19038. Phone: (215)
233-6678. Fax: (215) 233-6581. E-mail: dbayles{at}arserrc.gov.
Present address: Center for Food Safety and Applied Nutrition,
U.S. Food and Drug Administration, Washington, DC 20204.
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