MODELING THE INFLUENCE OF TEMPERATURE ON THE RECOVERY OF LISTERIA-MONOCYTOGENES FROM HEAT INJURY

The ability of Listeria monocytogenes Scott A to recover from heat inj ury, as monitored by repair of salt-tolerance, was modelled as a funct ion of temperature and extent of cell injury. A modification to the eq uation of Hills and Mackey ((1995) Food Microbiology, 12, 333-346), wh ich included parameters for the maximum rate of recovery (R-r), and th e decreasing rate of recovery (a(r)), and eliminated the parameter des cribing the increasing rate of recovery (b(r)), was used to model the recovery from injury. Lag phase duration (LPD) and R-r were well predi cted by models including both temperature and extent of injury (R-2=0. 99 and 0.92 for LPD and R-r respectively), while the growth rate (R-g) was influenced by temperature alone (R-2=0.96). The degree to which c ells had recovered salt-tolerance at the end of the lag phase (i.e. pr oportion of cells capable of growth on agar containing 5% ((w/v) NaCl) was found to be related to the initial extent of injury. The results suggest that loss of salt-tolerance may not be the most important site of injury, and that alternative models are needed to adequately accou nt for the contribution of sub-populations of cells to growth after re pair of heat injury. (C) 1997 Academic Press Limited.