OXYGEN SENSITIVITY OF HEATED CELLS OF ESCHERICHIA-COLI O157-H7

Following defined heat treatments (55 degrees C for 100 min, 59 degree s C for 5 min, 61 degrees C for 1 min), a 6 decimal (6-D) reduction wa s obtained when cells of Escherichia coli O157:H7 were enumerated in a erobic growth medium. Part of this reduction (3-D) was due to thermal inactivation (as determined when cells were enumerated in anaerobic gr owth medium), and part (3-D) was due to the inability of sub-lethally heat-injured cells of E. coli O157:H7 to grow in the presence of oxyge n. When held anaerobically, the injured cells regained their ability t o grow in the presence of oxygen. Following heating at 59 degrees C fo r 5 min, repair took 4 h at 30 degrees C, 48 h at 20 degrees C, 95 h a t 10 degrees C, but did not occur in 816 h at 5 degrees C. Recovery fr om sub-lethal heat injury was not influenced by heat shock. These find ings are relevant to the safety of minimally-heated foods.