Oxygen sensitivity of heated cells of Escherichia coli O157:H7.

Following defined heat treatments (55 degrees C for 100 min, 50 degrees C for 5 min, 61 degrees C for l min), a 6 decimal (6-D) reduction was obtained when cells of Escherichia coli O157:H7 were enumerated in aerobic growth medium. Part of this reduction (3-D) was due to thermal inactivation (as determined when cells were enumerated in anaerobic growth 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 oxygen. When held anaerobically, the injured cells regained their ability to grow in the presence of oxygen. Following heating at 59 degrees C for 5 min, repair took 4 h at 30 degrees C, 48 h at 20 degrees C, 95 h at 10 degrees C, but did not occur in 816 at 5 degrees C. Recovery from sub-lethal heat injury was not influenced by heat shock. These findings are relevant to the safety of minimally-heated foods.