Sodium chloride enhances recovery and growth of acid-stressed E. coli O157:H7.
OBJECTIVE
Combinations of sodium chloride and acid are frequently used to inhibit growth of spoilage and pathogenic bacteria in food. The influence of differing sodium chloride, lactate and pH values on the growth of stressed and unstressed cells of a non-toxigenic strain of Escherichia coli O157:H7 was studied.


RESULTS
At pH 5.5 or 6.0, there was little or no effect on the growth rate in the presence of lactate and/or sodium chloride, but the lag times were longer as the lactate concentration increased. At pH 5.0, in the absence of sodium chloride, increasing the lactate concentration increased the growth rate and the lag time; no growth occurred in the presence of 1.5 g 100 g(-1) lactate. In the presence of 4-6 g 100 g(-1) sodium chloride, growth occurred at 1.5 g 100 g(-1) lactate. The growth rate was similar at all lactate concentrations.


CONCLUSIONS
The results demonstrate that the presence of sodium chloride promoted growth of E. coli O157:H7, especially under stressful conditions of low pH.


CONCLUSIONS
These findings could have implications for the use of acid and sodium chloride as a preservation treatment for the inhibition of E. coli O157:H7 in food.
Jordan
K N
KN
Unilever Research Laboratory, Bedford, UK. kjordan@moorepark.teagasc.ie
Davies
K W
KW
D015169:Colony Count, Microbial / Q000379:methods; D003470:Culture Media; D003611:Dairy Products / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D005516:Food Microbiology; D005520:Food Preservatives; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid; D012965:Sodium Chloride / Q000494:pharmacology*
D003470:Culture Media; D005520:Food Preservatives; D019344:Lactic Acid; D012965:Sodium Chloride