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Appl. Environ. Microbiol., Mar 1997, 945-950, Vol 63, No. 3
KJ Hauben, DH Bartlett, CC Soontjens, K Cornelis, EY Wuytack and CW Michiels
Alternating cycles of exposure to high pressure and outgrowth of surviving
populations were used to select for highly pressure-resistant mutants of
Escherichia coli MG1655. Three barotolerant mutants (LMM1010, LMM1020, and
LMM1030) were isolated independently by using outgrowth temperatures of 30,
37, and 42 degrees C, respectively. Survival of these mutants after
pressure treatment for 15 min at ambient temperature was 40 to 85% at 220
MPa and 0.5 to 1.5% at 800 MPa, while survival of the parent strain,
MG1655, decreased from 15% at 220 MPa to 2 x 10(-8)% at 700 MPa. Heat
resistance of mutants LMM1020 and LMM1030 was also altered, as evident by
higher D values at 58 and 60 degrees C and reduced z values compared to
those for the parent strain. D and z values for mutant LMM1010 were not
significantly different from those for the parent strain. Pressure
sensitivity of the mutants increased from 10 to 50 degrees C, as opposed to
the parent strain, which showed a minimum around 40 degrees C. The ability
of the mutants to grow at moderately elevated pressure (50 MPa) was reduced
at temperatures above 37 degrees C, indicating that resistance to pressure
inactivation is unrelated to barotolerant growth. The development of high
levels of barotolerance as demonstrated in this work should cause concern
about the safety of high-pressure food processing.
Copyright © 1997, American Society for Microbiology
Escherichia coli mutants resistant to inactivation by high hydrostatic pressure
Laboratory of Food Microbiology, Katholieke Universiteit Leuven, Belgium.
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