Effects of growth temperature and strictly anaerobic recovery on the survival of Listeria monocytogenes during pasteurization

Abstract

Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-.6% yeast extract (TSBYE) or sterile, whole milk and heated at 62.8°C in sealed thermal death time tubes. Severely heat-injured cells were recovered in TSBYE within sealed thermal death time tubes because of the formation of reduced conditions in the depths of the TSBYE. Also, the use of strictly anaerobic Hungate techniques significantly increased recovery in TSBYE containing 1.5% agar compared with aerobically incubated controls. The exogenous addition of catalase, but not superoxide dismutase, slightly increased the recovery of heat-injured cells in TSBYE containing 1.5% agar incubated aerobically. Growth of cells at 43°C caused a greater increase in heat resistance as compared with cells heat shocked at 43°C or cells grown at lower temperatures. Growth of L. monocytogenes at 43°C and enumeration by the use of strictly anaerobic Hungate techniques resulted in D62.8°C values that were at least sixfold greater than those previously obtained by using cells grown at 37°C and aerobic plating. Results indicate that, under the conditions of the present study, high levels of L. monocytogenes would survive the minimum low-temperature, long-time treatment required by the U.S. Food and Drug Administration for pasteurizing milk. The possible survival of low levels of L. monocytogenes during high-temperature, short-time pasteurization and enumeration of injured cells by recovery on selective media under strictly anaerobic conditions are discussed.

Heat inactivation data for Mycobacterium avium subsp. paratuberculosis: implications for interpretation

“…If stress occurs during growth, such as low pH, starvation, low water activity or high temperature, vegetative cells or their spores can become more, or less, heat resistant. This has been shown for a number of bacteria, such as Listeria monocytogenes (Bunning et al 1982;Knabel et al 1990;Farber et al 1992), Salmonella (Garibaldi et al 1969;Mackey and Derrick 1986), Escherichia coli (Yamamori and Yura 1982) and Bacillus subsp. (Harnulv and Snygg 1972;Wilkinson and Davies 1973;Palop et al 1996;Periago et al 1998;Palop et al 1999).…”

Effect of oxygen concentration and redox potential on recovery of sublethally heat-damaged cells of Escherichia coli O157:H7, Salmonella enteritidis and Listeria monocytogenes

“…An important recent finding has been the enhanced recovery of sublethally heatdamaged cells of facultatively anaerobic organisms in anaerobic conditions. Studies with Escherichia coli O157:H7 (Mur-ano andPierson 1992, 1993), E. coli (Gadzella and Ingham 1994), Salmonella enteritidis (Xavier and Ingham 1993), Listeria monocytogenes (Knabel et al 1990;Linton et al 1992;Mendonca and Knabel 1994;Knabel and Thielen 1995;Patel et al 1995) and Staphylococcus aureus (Ugborogho and Ingham 1994), have all shown a significantly greater recovery in anaerobic than in aerobic conditions. The method of producing anaerobic conditions in these studies varied and included anaerobic overlays, addition of oxygen scavengers, incubation of plates in anaerobic jars, and preparation of media using strictly anaerobic techniques.…”

“…The increased heat resistance of cells of L. monocytogenes under anaerobic conditions may explain why a minimal heat treatment had only a marginal effect on L. monocytogenes inoculated into chicken gravy (Huang et al 1992) and sous-vide chicken breast (Shamsuzzaman et al 1992). Listeria monocytogenes also appeared to survive pasteurization at 62·8°C for 15 min when recovered anaerobically (Knabel et al 1990).…”

Impact of different pasteurization temperatures on the survival of microbial contaminants isolated from pasteurized milk

“…L. monocytogenes (1273) has been found to survive LTLT pasteurization and even HTST pasteurization (Knabel et al 1990;Bunning et al 1992;Doyle et al 1997). In this study the L. monocytogenes (1273) strain did not survive pasteurization at 63°C for 30 min and could not be detected after 15 min at the 1 × 10 4 cfu mL −1 inoculum and after 20 min at the 1 × 10 6 cfu mL −1 inoculum level (Tables 3 and 4).…”