Thermotolerance of Escherichia coli O157:H7 ATCC 43894, Escherichia coli B, and an rpoS-deficient mutant of Escherichia coli O157:H7 ATCC 43895 following exposure to 1.5% acetic acid

• Published in: Journal of food protection Vol. 61; no. 9; pp. 1184 - 1186
• Main Authors: Williams, N.C, Ingham, S.C
• Format: Journal Article
• Language: English
• Published: Des Moines, IA International Association of Milk, Food and Environmental Sanitarians 01.09.1998
• Subjects: acetic acid; Biological and medical sciences; cell growth; enumeration; Escherichia coli; Food industries; Fundamental and applied biological sciences. Psychology; heat tolerance; Meat and meat product industries; mortality; mutants; Escherichia coli; Strain; Thermal resistance; Pathogenic; Microorganism culture; Initiation factor σ; Bacteria; Mutation; Pretreatment; Beef; Biological contamination; Acid medium; Comparative study; Enterobacteriaceae
• ISSN: 0362-028X; 1944-9097

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 degrees 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 degrees 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 degrees C), in prewarmed ground beef slurry (GBS; 58 degrees C), or in TSB and GBS inoculated at 5 degrees C and heated to 58 degrees C. The acid stress tested does not enhance subsequent heat resistance of E. coli.