TEMPERATURE SHIFT EFFECTS ON INJURY AND DEATH IN LISTERIA MONOCYTOGENES SCOTT A

Abstract

Exposure of Listeria monocytogenes Scott A grown at 37°C to a 1 h heat treatment at 52°C resulted in little death of the cells (< 0.5 log). However, as the temperature of growth decreased, there was an increase in the extent of death (> 4 logs at 10°C growth temperature). Heat induced injury, however, decreased as the growth temperature decreased. Shifting L. monocytogenes grown at 10, 19, or 28°C to 37°C for periods up to 5 h led to cells with increased heat tolerance. However, there was little effect on injury by the shift‐up procedure. Presence of chloramphenicol during the shift‐up period inhibited the gain in heat tolerance. L. monocytogenes grown at low temperatures (< 28°C), were more susceptible to killing by heat, but this susceptibility could be lost if cells grown at low temperatures are given a short incubation at 37°C. The data obtained here suggest that if foods containing L. monocytogenes are temperature‐abused for even short periods, the organisms will acquire an increased heat tolerance and will require higher inactivation temperatures or longer processing times.

Effects of several factors on the heat-shock-induced thermotolerance of Listeria monocytogenes

“…This suggests that, although the development of a higher D t value and of a shoulder in the profile of survival curves are both induced by heat shock, they respond to different mechanisms. The role of HSP in bacterial heat damage repair seems to be well established (21,23,32,37). Perhaps the shoulder and also the increase in D t are due to the capacity of cells to repair heat damage through a mechanism involving some HSP, as discussed below.…”

“…Despite the work carried out by many authors on the relationship between heat shock and the increase in thermotolerance and the production of HSP by L. monocytogenes, some aspects are still not clear. Whereas most authors have reported an increase in thermotolerance as a result of heat shock (9,13,18,20,22,23,34,37,43), Bunning et al (2), after a detailed study on the effect of heat shocks of different durations at four different temperatures, were unable to detect any increase in thermotolerance and suggested that the effect reported by some authors (13) was most probably due to methodological problems.…”

Effects of Above-Optimum Growth Temperature and Cell Morphology on Thermotolerance of Listeria monocytogenes Cells Suspended in Bovine Milk

“…Both cell forms were recovered after a longer duration of heating when enumerated on TSYEA immediately after heat- ing and after a 2-day enrichment period (Table 3). Other researchers also reported inferior recovery of heat-injured L. monocytogenes as a result of enumeration on selective plating media (31,34,35,47,48). Despite their enhanced thermotolerance, atypical cell forms of L. monocytogenes were unable to survive the LTLT pasteurization process (Table 3).…”

Investigating the control of Listeria monocytogenes on uncured, no-nitrate-or-nitrite-added meat products

“…monocytogenes may be able to withstand thermal processing treatments. This phenomenon has been found to occur at sublethal temperatures ranging from 43 to 52°C (Farber and Brown 1990;Smith and Marmer 1990). This suggests that if foods containing L. monocytogenes are temperature-abused for even short periods, the organisms will acquire an increased heat tolerance and will require higher inactivation temperatures or longer processing times (Smith and Marmer 1990).…”