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On a beef carcass, Escherichia coli may sequentially encounter acid-and heat-intervention steps. This study tested whether acid stress (1.5% [vol/vol] acetic acid, pH 4.0, 37°C, 15 min) would enhance subsequent heat resistance of E. coli. Initially, cells (E. coli
O157:H7 ATCC 43894, nonpathogenic E. coli B[strain FRIK-124], and rpoS-deficient mutant 813-6 [derived from E. coli O157:H7 ATCC 43895]) were acid stressed and transferred to 54°C trypticase soy broth (TSB), and survivors were immediately enumerated after at least
three intervals of 12, 2, and 6 min, respectively, by plating. The ATCC 43894 and 813-6 strains survived the acid stress but strain FRIK-124 did not. Acid-stressed ATCC 43894 had significantly lower D values than the non-acid-stressed controls. Strain 813-6 had significantly lower D values
than strain ATCC 43894, with no significant difference between acid-stressed and non-acid-stressed cells. In a second experiment, cooling of cells prior to plating resulted in an increased D value for acid-stressed ATCC 43894 cells, such that it was not significantly different from the D value
for non-acid-stressed controls. Using this protocol, there was no significant difference in D values between acid-stressed and non-acid-stressed ATCC 43894 cells in prewarmed TSB (54,58, and 62°C), in prewarmed ground beef slurry (GBS; 58°C), or in TSB and GBS inoculated at 5°C
and heated to 58°C. The acid stress tested does not enhance subsequent heat resistance of E. coli.
Document Type: Research Article
Department of Food Science, University of Wisconsin-Madison, 1605 Linden Drive, Madison, Wisconsin 53706-1565, USA
Publication date: September 1, 1998
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