Abstract
Exposure to low pH and organic acids in the bovine gastrointestinal tract may result in the induced acid resistance of Escherichia coli O157:H7 and other pathogens that may subsequently contaminate beef carcasses. The effect of acid adaptation of E. coli O157:H7 on the ability of acetic acid spray washing to reduce populations of this organism on beef carcass tissue was examined. Stationary-phase acid resistance and the ability to induce acid tolerance were determined for a collection of E. coli O157:H7 strains by testing the survival of acid-adapted and unadapted cells in HCl-acidified tryptic soy broth (pH 2.5). Three E. coli O157:H7 strains that were categorized as acid resistant (ATCC 43895) or acid sensitive (ATCC 43890) or that demonstrated inducible acid tolerance (ATCC 43889) were used in spray wash studies. Prerigor beef carcass surface tissue was inoculated with bovine feces containing either acid-adapted or unadapted E. coli O157:H7. The beef tissue was subjected to spray washing treatments with water or 2% acetic acid or left untreated. For strains ATCC 43895 and 43889, larger populations of acid-adapted cells than of unadapted cells remained on beef tissue following 2% acetic acid treatments and these differences remained throughout 14 days of 4 degrees C storage. For both strains, numbers of acid-adapted cells remaining on tissue following 2% acetic acid treatments were similar to numbers of both acid-adapted and unadapted cells remaining on tissue following water treatments. For strain ATCC 43890, there was no difference between populations of acid-adapted and unadapted cells remaining on beef tissue immediately following 2% acetic acid treatments. These data indicate that adaptation to acidic conditions by E. coli O157:H7 can negatively influence the effectiveness of 2% acetic acid spray washing in reducing the numbers of this organism on carcasses.
Highlights
The involvement of E. coli O157:H7 in food-borne illness outbreaks associated with the consumption of acidic foods such as apple cider, fermented sausage, yogurt, and mayonnaise [3, 9, 34] has drawn attention to the acid resistance properties of this pathogen, and many subsequent studies have demonstrated that this bacterium can survive in a variety of acidic foods [8, 25, 32, 33, 37, 39]
Because of the potential for acid adaptation in the bovine gastrointestinal tract due to exposure to low pH and organic acids [10, 15, 29], and because bovine feces are a common source of bacterial contamination of carcasses, our objective was to determine if acid adaptation can affect the ability of 2% acetic acid (2% AA) spray washes to reduce populations of E. coli O157:H7 on prerigor beef carcass surface tissue (BCT)
To identify strains for use in spray wash experiments, stationary-phase acid resistance and the ability to adapt to acidic conditions were determined for a selection of E. coli O157:H7 strains utilizing the method described by Buchanan and Edelson [6]
Summary
The involvement of E. coli O157:H7 in food-borne illness outbreaks associated with the consumption of acidic foods such as apple cider, fermented sausage, yogurt, and mayonnaise [3, 9, 34] has drawn attention to the acid resistance properties of this pathogen, and many subsequent studies have demonstrated that this bacterium can survive in a variety of acidic foods [8, 25, 32, 33, 37, 39]. RESULTS AND DISCUSSION To identify strains for use in spray wash experiments, stationary-phase acid resistance and the ability to adapt to acidic conditions were determined for a selection of E. coli O157:H7 strains utilizing the method described by Buchanan and Edelson [6].
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