Effects of pH, dissolved oxygen, and ionic strength on the survival of Escherichia coli O157:H7 in organic acid solutions.
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 dissolved oxygen conditions (< or = 0.05 and 5 mg/liter) and a range of ionic strengths (0.086 to 1.14). All solutions contained 20 mM gluconic acid, which was used as a noninhibitory 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/liter dissolved oxygen (present in tap water) over a range of ionic strengths at pH 3.2 exhibited a decrease in survival over 6 h at 30 degrees C as the ionic strength was increased. Cells challenged in 40 mM protonated L-lactic and acetic acid solutions with ionic strength of 0.684 achieved a > 4.7-log CFU/ml reduction at pH 3.2. However, under oxygen-limiting conditions in an anaerobic chamber, with < or = 0.05-mg/ liter oxygen, E. coli O157:H7 cells showed < or = 1.55-log CFU/ml reduction regardless of pH, acid type, concentration, or ionic strength. 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.
Kreske
Audrey C
AC
Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA.
Bjornsdottir
Kristin
K
Breidt
Fred
F
Hassan
Hosni
H
D000143:Acids / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D018553:Cucumis sativus / Q000382:microbiology*; D004305:Dose-Response Relationship, Drug; D019453:Escherichia coli O157 / Q000187:drug effects / Q000254:growth & development*; D005506:Food Contamination / Q000032:analysis*; D005519:Food Preservation / Q000379:methods*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D010100:Oxygen / Q000494:pharmacology*
D000143:Acids; D010100:Oxygen