Modelling the influence of temperature on the recovery of Listeria monocytogenes from heat injury

The ability of Listeria monocytogenes Scott A to recover from heat injury, as monitored by repair of salt-tolerance, was modelled as a function of temperature and extent of cell injury. A modification to the equation of Hills and Mackey ((1995) Food Microbiology, 12, 333-346), which included parameters for the maximum rate of recovery (R-r), and the decreasing rate of recovery (a(r)), and eliminated the parameter describing the increasing rate of recovery (b(r)), was used to model the recovery from injury. Lag phase duration (LPD) and R-r were well predicted 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 cells had recovered salt-tolerance at the end of the lag phase (i.e. proportion 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 account for the contribution of sub-populations of cells to growth after repair of heat injury. (C) 1997 Academic Press Limited.