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Title: Survival of Escherichia coli O157:H7 Isolates in Acetic Acid Solutions is Influenced by the Source of Isolation

Author
item OH, DEOG-HWAN - NC STATE UNIVERSITY
item PAN, YOUWEN - NC STATE UNIVERSITY
item Berry, Elaine
item Mandrell, Robert
item Cooley, Michael
item Breidt, Frederick

Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/8/2007
Publication Date: 7/8/2007
Citation: Oh DH, Pan Y, Berry ED, Mandrell RE, Cooley MB, Breidt F. 2007. Survival of Escherichia coli O157:H7 Isolates in Acetic Acid Solutions is Influenced by the Source of Isolation. International Association for Food Protection Proceedings.

Interpretive Summary:

Technical Abstract: Enterohemorrhagic Escherichia coli O157:H7 has been recognized as highly acid resistant in nature because of its low infectious dose and ability to survive in acid foods or to survive in stomach acid. A number of studies on the influence of acid on E. coli O157:H7 have shown considerable strain differences, but limited information has been reported to compare the acid resistance based on the different source of E. coli O157:H7 isolates. Thus, the purpose of this study was to determine the survival of five group mixtures of E. coli O157:H7 strains (5 mixtures of each: food, bovine carcass, bovine feces, water, and human isolates) in acetic acid solutions (400 mM), with ionic strength adjusted to 0.34 (using NaCl) at different pH values (3.3, 3.7, and 4.3) and temperatures (15, 22, and 30 degrees C) for 25 min exposure. Bovine carcass, feces or water isolates survived acetic acid treatment significantly (P is less than or equal to 0.05) better than strain mixtures isolated from acidic foods or human isolates at pH 3.3 and 30 degrees C for 25 min exposures. However, resistance to acetic acid significantly increased as temperature decreased to 15 degrees C for a given pH, with little difference (P is greater than or equal to 0.05) among serotypes. All groups of E. coli O157:H7 strains showed more than 4 to 5 log reduction at pH 3.3 and 30 degrees C. Significantly reduced lethality (less than 2 log reduction) for all E. coli O157:H7 strain mixtures was observed as pH increased to 3.7 or 4.3, with little difference in acetic acid resistance among groups. In the meantime, the addition of glutamate in the acetic acid solution or anaerobic incubation provided the best protection compared to the above condition for all groups of isolates. These results may suggest strategies for improving the safety of acidified foods.