Effects of Organic Acids and Atmosphere on the Survival of Escherichia coli O157:H7 Under Conditions Similar to Acidified Foods

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dc.contributor.advisor Fred Breidt, Committee Chair en_US
dc.contributor.advisor Roger McFeeters, Committee Member en_US
dc.contributor.advisor Todd Klaenhammer, Committee Member en_US
dc.contributor.advisor Hosni Hassan, Committee Member en_US
dc.contributor.author Kreske, Audrey Christina en_US
dc.date.accessioned 2010-04-02T18:36:39Z
dc.date.available 2010-04-02T18:36:39Z
dc.date.issued 2009-12-03 en_US
dc.identifier.other etd-10302009-180736 en_US
dc.identifier.uri http://www.lib.ncsu.edu/resolver/1840.16/3793
dc.description.abstract The ability of Escherichia coli O157:H7 to survive in acidified vegetable products is of concern because of previously documented outbreaks associated with fruit juices. A study was conducted to determine the survival of E. coli O157:H7 in organic acids at pH values typical of acidified vegetable products (pH 3.2 and 3.7), under different atmospheres, and a range of ionic strengths (0.086 to 1.14). Determination of internal pH and catalase activity in acid solutions can explain how dissolved oxygen or D- versus L-lactic acid reduces the survival of Escherichia coli O157:H7 when the organism is exposed to low pH (3.2) values typical of fermented and acidified foods. All solutions contained 20 mM gluconic acid, which was used as a non-inhibitory low pH buffer to compare the individual acid effect to that of pH alone on the survival of E. coli O157:H7. E. coli O157:H7 cells challenged in buffered solution with ca. 5 mg/L dissolved oxygen (present in tap water) over a range of ionic strengths at pH 3.2 exhibited a decrease in survival as the ionic strength was increased over 6 h. Overall, under oxygen limiting conditions in an anaerobic chamber, there is no significant difference in the loss of viability of E. coli O157:H7 cells regardless of pH, acid type, concentration, or ionic strength. For lactate concentrations up to 40 mM, there was no significant difference in internal pH values when cells were incubated in D- versus L-lactic acid solutions. Unexpectedly, cells incubated under aerobic conditions maintained a significantly higher internal pH (ca. 5.8) than cells incubated under anaerobic conditions (ca. 5.4), regardless of the isomer of lactic acid used. Overall, catalase activity was higher when cells were in the presence of L-lactic acid versus D-lactic acid however there is a decrease in survival when cells are incubated in L-lactic acid. Under the conditions tested, differences in survival of E. coli O157:H7 between isomers of lactic acid and atmospheres is not a result of internal pH or catalase activity. However, the lower internal pH maintained by cells incubated anaerobically (5 mM lactic acid) results in a smaller pH gradient and decreases the accumulation of acid anions inside the cell, which may contribute to increased survival under anaerobic conditions. Many acid and acidified foods are sold in hermetically sealed containers with oxygen limiting conditions. Our results demonstrate that E. coli O157:H7 may survive better than previously expected from studies with acid solutions containing dissolved oxygen. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject E. coli O157:H7 en_US
dc.subject organic acids en_US
dc.subject anaerobic en_US
dc.subject oxygen en_US
dc.subject ionic strength en_US
dc.subject gluconic acid en_US
dc.title Effects of Organic Acids and Atmosphere on the Survival of Escherichia coli O157:H7 Under Conditions Similar to Acidified Foods en_US
dc.degree.name PhD en_US
dc.degree.level dissertation en_US
dc.degree.discipline Food Science en_US

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