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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Acid Adaptation of Escherichia Coli O157:h7 on Efficacy of Acetic Acid Spray Washes to Decontaminate Beef Carcass Tissue

Authors
item Berry, Elaine
item Cutter, Catherine - PENNSYLVANIA STATE UNIV.

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 7, 2000
Publication Date: April 1, 2000
Citation: Berry, E.D., Cutter, C.N. 2000. Effects of acid adaptation of Escherichia coli O157:H7 on efficacy of acetic acid spray washes to decontaminate beef carcass tissue. Applied and Environmental Microbiology. 66:1493-1498.

Interpretive Summary: Exposure to low pH and acids in the cattle gut may cause adaptation to acidic conditions by Escherichia coli O157:H7 that may later contaminate beef carcasses. Because spray washes with acids such as acetic acid are used to decontaminate fresh beef carcasses, this work examined the effect of acid adaptation of this bacteria on the ability of acetic acid spray washing to reduce E. coli O157:H7 from beef. Three E. coli O157:H7 strains that were shown to be either acid resistant or acid sensitive, or that showed ability to adapt to acid were chosen for spray wash studies. Beef carcass tissue was contaminated with either acid-adapted or unadapted E. coli O157:H7 of each strain. The beef was then spray washed with either water or 2% acetic acid. For both resistant and acid-adaptable E. coli O157:H7 strains, higher numbers of acid-adapted cells remained on beef following acetic acid washing, as compared to remaining numbers of unadapted cells. For the sensitive E. coli O157:H7, there was no difference between the numbers of acid-adapted and unadapted cells remaining on beef following acetic acid treatments. These results indicate that adaptation to acidic conditions by E. coli O157:H7 can negatively affect the ability of 2% acetic acid spray washing to reduce this organism on carcasses. Therefore, it will be important to discover if natural cattle strains of E. coli O157:H7 are adapted to acid conditions.

Technical 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 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 ability to induce acid tolerance were determined for a collection of E. coli O157:H7 strains by testing survival of acid-adapted and unadapted cells at 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. Pre-rigor 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. For ATCC 43895 and 43889, higher populations of acid-adapted cells remained on beef tissue following 2% acetic acid treatments as compared to unadapted cells, and these differences remained throughout 14 days of 4 deg C storage. For both strains remaining populations of acid-adapted cells following 2% acetic acid treatments were similar to those of acid-adapted and unadapted cells on tissue receiving water treatments. For 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 this organism on carcasses.

Last Modified: 12/21/2014
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