The use of enterocin CCM 4231 in soy milk to control the growth of Listeria monocytogenes and Staphylococcus aureus

The inhibitory effect of enterocin CCM 4231 (concentration 3200 AU ml-1) was used to control the growth of Listeria monocytogenes Ohio and Staphylococcus aureus in soy milk. The growth and bacteriocin (enterocin) production of producer strain CCM 4231 in soy milk was also checked. Bacteriocin production by CCM 4231 strain in soy milk was first detected after 2 h from the beginning of cultivation (100 AU ml-1). The stationary phase for CCM 4231 was reached after 6 h reaching 10.38 cfu ml-1 (log10) with a slight increase up to 24 h (10.43 cfu ml-1, log10), and the maximum bacteriocin production in soy milk (200 AU ml-1) was noted after 8 h of the beginning of cultivation with stability up to 24 h. The addition of enterocin CCM 4231 at 3200 AU ml-1 to a growing indicator strain, L. monocytogenes Ohio, in soy milk resulted in inhibition for 24 h. The high inhibitory effect of enterocin was found after 1 h and 2 h of its addition (in 5 h-6 h of cultivation), the difference between the experimental and the control samples (ES, CS) being 4.96 log cycles at 5 h and 5.15 log cycles at 6 h. Staphylococcus aureus was not fully inhibited, although a difference of 3.55 log cycles was found when ES and CS were compared at the end of cultivation (24 h). The pH was not influenced by enterocin addition. The inhibitory effect of enterocin CCM 4231 against L. monocytogenes Ohio in soy milk was probably bacteriocidal; while Staph. aureus was influenced bacteriostatically. In general, the observed inhibitory activity confirmed the possibility for further application of bacteriocins in food environments as the protective agents. Of course, legislation problems must be solved.     

Response surface methodology, an approach to predict the effects of a lactoperoxidase system, Nisin, alone or in combination, on Listeria monocytogenes in skim milk

Experimental designs using Response Surface Methodology (RSM) were used to determine effects and interactions of Nisin (0-200 i.u. ml-1), pH values (5.4-6.6), incubation time (0-36 h or 0-144 h) and the lactoperoxidase-thiocyanate-hydrogen peroxide system (LPS) on Listeria monocytogenes CIP 82110 in skim milk, at 25 degrees C. The LPS varied from level 0-2; LPS at level 1 consisted of lactoperoxidase (35 mg l-1), thiocyanate (25 mg l-1) and H2O2, which was supplied exogenously by glucose-oxidase (1 mg l-1) and glucose (0.2 g l-1); LPS activity was dependent on LPS level and incubation time. In the presence of LPS at level 1, a bacteriostatic phase was followed by growth, whereas at a higher level, a bactericidic phase was observed. Nisin response was time- and pH-dependent. Nisin was bactericidic at acidic pH values and for a short incubation time (12 h) only; then, a re-growth phase was observed. Nisin and LPS in combination gave an original response which lacked the transitory bactericidal effect of Nisin and had a continuously bactericidal affect, leading to 10 cfu ml-1 of L. monocytogenes at 144 h; the response was greatly affected by incubation time. Predicted values were in good agreement with experimental values. Response Surface Methodology is a useful experimental approach for rapid testing of the effects of inhibitors.     

Purification and characterization of curvaticin L442, a bacteriocin produced by Lactobacillus curvatus L442

Lactobacillus curvatus L442, isolated from Greek traditional fermented sausage prepared without the addition of starters, produces a bacteriocin, curvaticin L442, which is active against the pathogen Listeria monocytogenes. The bacteriocin was purified by 50% ammonium sulphate precipitation, cation exchange, reverse phase and gel filtration chromatography. Partial N-terminal sequence analysis using Edman degradation revealed 30 amino acid residues, revealing high homology with the amino acid sequence of sakacin P. Curvaticin L442 is active at pH values between 4.0 and 9.0 and it retains activity even after incubation for 5 min at 121 °C with 1 atm of overpressure. Proteolytic enzymes and α-amylase inactivated this curvaticin, while the effect of lipase was not severe.     

Purification and partial amino acid sequence of curvaticin FS47, a heat-stable bacteriocin produced by Lactobacillus curvatus FS47.

Curvaticin FS47, a bacteriocin produced by Lactobacillus curvatus FS47, is inhibitory to Listeria monocytogenes, as well as Lactobacillus, Pediococcus, Enterococcus, and Bacillus spp. The bacteriocin was purified by 40% ammonium sulfate precipitation, solid-phase extraction, and reversed-phase high-pressure liquid chromatography. Purified curvaticin FS47 was determined to be 4.07 kDa by mass spectrometry and was partially sequenced. Thirty-one N-terminal amino acids were identified; the curvaticin FS47 protein sequence did not show homology to the pediocin-like group of bacteriocins.     

Growth condition-related response of Listeria monocytogenes 412 to bacteriocin inactivation

Bacteriocin inactivation of Listeria monocytogenes 412 was studied as a function of growth phase. Cells were treated with nisin (300 IU ml-1) or pediocin (320 or 2560 AU ml-1) for 20 min at 30 degrees C. Inactivation with nisin or the low concentration of pediocin was growth phase dependent, with exponentially growing cells being more susceptible than stationary cells. No effect of growth phase was observed for the high pediocin concentration. Pediocin inactivation (320 AU ml-1) of L. monocytogenes 412 exposed to osmotic (6.5% NaCl) or low-temperature (5 degrees C) stress was investigated. Pediocin failed to inactivate osmotically stressed cultures and was unable to inhibit cold-stressed cells to the same degree as unstressed cells.     

Treatment of sanitary-important bacteria by bacteriocin substance V24 in cattle dung water

Quantification of sanitary-important bacteria (e.g. Enterobacteriaceae), as well as indicators of environmental contamination, was assessed in samples of cattle dung from 25 cattle farms in 15 north-eastern Slovakia districts. The inhibitory effect of crude bacteriocin extract CBE V24 from Enterococcus faecalis V24 against Listeria monocytogenes Ohio and Yersinia enterocolitica YE85 was examined in cattle dung water with the aim of finding a new way of eliminating the health risk of the animal slurry. The following bacterial groups were quantified: Salmonella spp., Shigella-like spp. , Proteus spp., Enterobacter spp., Citrobacter spp., Pseudomonas spp. , Escherichia coli, Listeria spp., staphylococci, streptococci and enterococci (the average count ranged from 102 up to 104 cfu ml-1). Antagonistic effect of the crude bacteriocin from Enterococcus faecalis V24 in the range of 100-600 Arbitrary units per ml (AU ml-1) was shown against the following bacteria: Enterobacter cloacae, Ent. asburiae, Proteus spp., Salmonella spp., Acinetobacter lwoffi, L. monocytogenes as well as Y. enterocolitica YE85. During tests performed to study the inhibitory effect of the crude bacteriocin CBE V24 (concentration 800, 1600 AU ml-1) against L. monocytogenes Ohio and Y. enterocolitica YE85 in experimentally contaminated cattle dung, a reduction of 2.03 and 1.44 log cfu ml-1, respectively, was already noted after 1 h after crude bacteriocin CBE V24 addition.     

Effect of NaCl and KCl on fate and growth/no growth interfaces of Listeria monocytogenes Scott A at different pH and nisin concentrations

AIMS: The fate of Listeria monocytogenes Scott A, was studied in broth, at different a(w)s (by adding NaCl or KCl from 0.0 to 1.4 mol l(-1)), pHs (from 4.0 to 7.3 by adding lactic acid), and nisin concentrations (from 0 to 100 IU ml(-1)). METHODS AND RESULTS: Increasing salt and nisin concentrations and decreasing pH resulted in lower growth rates and extended lag phases. At pH 4.5 no growth was observed while in presence of nisin and/or 1 mol l(-1) salts of both kinds, L. monocytogenes Scott A was inactivated. Equal-molar concentrations of NaCl or KCl (similar a(w)), exerted similar effects against L. monocytogenes in terms of lag phase duration, growth or death rate. The growth boundaries of L. monocytogenes Scott A at 5 degrees C were also estimated by growth/no growth turbidity data, modeled by logistic polynomial regression. The concordance of logistic models, were 99.6 and 99.8% for NaCl and KCl, respectively. CONCLUSIONS: The growth interfaces derived by both NaCl and KCl models were almost identical. Hence, NaCl can be replaced by KCl without risking the microbiological safety of the product. Increasing nisin concentrations markedly affected the interface resulting in a more inhibitory environment for L. monocytogenes Scott A. Low to medium salt concentrations (0.3-0.7 mol l(-1) of either NaCl or KCl) provided a protective effect against inhibition of L. monocytogenes Scott A by nisin. SIGNIFICANCE AND IMPACT OF THE STUDY: Modelling the growth boundaries not only contributes to the development of safer food by providing useful data, but can also be used to study interactions between factors affecting initiation of growth of pathogenic micro-organisms.     

Inhibition of Bacillus licheniformis spore growth in milk by nisin, monolaurin, and pH combinations

The effects of nisin and monolaurin, alone and in combination, were investigated on Bacillus licheniformis spores in milk at 37 degrees C. In the absence of inhibitors, germinated spores developed into growing vegetative cells and started sporulation at the end of the exponential phase. In the presence of nisin (25 IU ml-1), spore outgrowth was inhibited (4 log10 reduction at 10 h). Regrowth appeared between 10 and 24 h and reached a high population level (1.25 x 10(8) cfu ml-1) after 7 d. Monolaurin (250 micrograms ml-1) had a bacteriostatic effect during the first 10 h but thereafter, regrowth occurred slowly with a population level after 7 d (4 x 10(5) cfu ml-1) lower than that of nisin. Different combined effects of nisin (between 0 and 42 IU ml-1), monolaurin (ranging from 0 to 300 micrograms ml-1), pH values (between 5.0 and 7.0) and spore loads (10(3), 10(4), 10(5) spores ml-1) were investigated using a Doehlert matrix in order to study the main effects of these factors and the different interactions. Results were analysed using the Response Surface Methodology (RSM) and indicated that nisin and monolaurin had no action on spores before germination; only pH values had a significant effect (P < or = 0.001), i.e. spore count decreased as the pH value increased in relation to germination. Sublethal concentrations of nisin (30 IU ml-1) and monolaurin (100 micrograms ml-1) in combination acted synergistically on outgrown spores and vegetative cells, showing total inhibition at pH 6.0, without regrowth, within 7 d at 37 degrees C.     

Effects of divercin V41 combined to NaCl content, phenol (liquid smoke) concentration and pH on Listeria monocytogenes ScottA growth in BHI broth by an experimental design approach

AIMS: To investigate the main effects and interactions of different factors : divercin V41 (0-4 ng ml(-1)), NaCl content (0.5-5.5% w v(-1)), phenol (liquid smoke) concentration (0-8 ppm), and pH (5.5-7.5) on Listeria monocytogenes ScottA growth. METHODS AND RESULTS: Experiments were carried out in BHI broth using a central composite design. Divercin V41 (div41), NaCl content and pH were found to be the most influential factors whereas phenol concentration in liquid smoke had no effect on L. monocytogenes ScottA growth in our experimental domain. The combined effects of div41, NaCl content and pH decreased L. monocytogenes ScottA maximum specific growth rate (mu(max)) from 0.34 to 0.01 h(-1) and led to a significant increase in lag time (t(lag)) from 5.5 to 25 h. CONCLUSION: In this study, NaCl, pH and phenol conditions were similar to those currently observed in smoked salmon production. This shows that L. monocytogenes ScottA growth could be efficiently delayed by the use of div41 in addition to the usual technological hurdles. SIGNIFICANCE AND IMPACT OF THE STUDY: In conclusion, the technological hurdles of cold smoked salmon production could be further optimized and combined with the use of div41 or the div41 producer strain to improve the food safety of the product.     

In vitro study on bacteriocin production of Enterococci associated with chickens

In recent years, the approach of using innovative strategies such as probiotics or bacteriocins for the prevention or treatment of bacterial infections has come into focus. The present study was undertaken to check in vitro ability of Enterococci-isolated from the gastrointestinal tract of chickens-to produce a bacteriocin-like substance and to describe some further probiotic properties in five selected Enterococcus faecium strains. All strains (n=17) were found to produce bacteriocin-like substances against 14 out of 20 indicator bacteria of animal, food or environmental origin. Selected E. faecium strains expressed sufficient survival by pH 3.0 after 3h, in the presence of 1% bile after 24h and they were sensitive to most of antimicrobials tested. All tested strains adhere to the human, canine and porcine intestinal mucus (between 1.5% and 9.2%). However, better adhesion ability was observed for the canine mucus. PCR detection of enterocin structural genes determined presence of enterocins A and P genes in all selected strains. Characterization of bacteriocin substance in detail was performed in E. faecium EF55. The EF55 strain produced a bacteriocin-like substance (during the late logarithmic and early stationary growth phase) with inhibitory activity mostly against Gram-positive bacteria (100-51,200 AU/mL) including Listeria monocytogenes. Proteinaceous character of the bacteriocin substance was confirmed (its inhibitory activity was lost after its treatment with proteases), it was found to be stable after heating (100 degrees C 10 min) and during 12 months storage at -20 degrees C. The highest inhibitory activity of bacteriocin produced by EF55 strain (growing in MRS) broth was achieved between pH 7.0 and 9.0.     

Inhibition of Listeria monocytogenes by piscicolin 126 in milk and Camembert cheese manufactured with a thermophilic starter

The effect of bacteriocin, piscicolin 126, on the growth of Listeria monocytogenes and cheese starter bacteria was investigated in milk and in Camembert cheese manufactured from milk challenged with 10(2) cfu ml(-1) L. monocytogenes. In milk incubated at 30 degrees C, piscicolin 126 added in the range of 512-2,048 AU ml(-1) effectively inhibited growth of L. monocytogenes for more than 20 d when challenged with approximately 10(2) cfu ml(-1) L. monocytogenes. At higher challenge levels (10(4) and 10(6) cfu ml(-1)), piscicolin 126 reduced the viable count of L. monocytogenes by 4-5 log units immediately after addition of the bacteriocin; however, growth of Listeria occurred within 24 h. The minimum inhibitory concentration (MIC) of piscicolin 126 against lactic acid cheese starter bacteria was generally greater than 204,800 AU ml(-1) , and the viable count and acid production of these starter cultures in milk were not affected by the addition of 2,048 AU ml(-1) piscicolin 126. Camembert cheeses made from milk challenged with L. monocytogenes and with added piscicolin 126 showed a viable count of L. monocytogenes 3-4 log units lower than those without piscicolin 126. Inactivation of piscicolin 126 by proteolytic enzymes from cheese starter bacteria and mould together with the emergence of piscicolin 126-resistant isolates was responsible for the recovery of L. monocytogenes in the cheeses during ripening.     

Efficacy of lactic acid against Listeria monocytogenes attached to poultry skin during refrigerated storage

AIMS: The aim of this study was to evaluate the effect of lactic acid washing on the growth of Listeria monocytogenes on poultry legs stored at 4 degrees C for 7 days. METHODS AND RESULTS: Fresh inoculated chicken legs were dipped into either a 0.11, 0.22 mol l(-1) or 0.55 mol l(-1) lactic acid solution for 5 min or distilled water (control). Surface pH values, sensorial characteristics and L. monocytogenes, mesophiles and pychrotrophs counts were evaluated after treatment (day 0) and after 1, 3, 5 and 7 days of storage at 4 degrees C. Legs washed with 0.55 mol l(-1) lactic acid for 5 min showed a significant (P < 0.05) inhibitory effect on L. monocytogenes compared with control legs, being about 1.74 log units lower in the first ones than in control legs after 7 days of storage. Sensory quality was not adversely affected by lactic acid, with the exception of colour. CONCLUSIONS: Treatments with 0.55 mol l(-1) lactic acid reduced bacterial growth and preserved reasonable sensorial quality after storage at 4 degrees C for 7 days. However, it was observed a reduction in the colour score within 1 day post-treatment with 0.55 mol l(-1) lactic. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates that, while lactic acid did reduce populations of L. monocytogenes on poultry, it did not completely inactivate the pathogen. The application of lactic acid may be used as an additional hurdle contributing to extend the shelf-life of raw poultry.     

Investigation of the effect of combined variations in temperature, pH, and NaCl concentration on nisin inhibition of Listeria monocytogenes and Staphylococcus aureus.

Gradient plates were used to investigate the effects of varying temperature, pH, and sodium chloride (NaCl) concentration on nisin inhibition of Staphylococcus aureus and Listeria monocytogenes, Nisin was incorporated into the plates of 0, 50, 100, 250, and 500 IU ml -1. Gradients of pH (3.7 to 7.92) at right angles to NaCl concentration (2.1 to 7% [wt/vol]) were used for the plates, which were incubated at 20, 25, 30 and 35 degrees C. Growth on the plates were recorded by eye and by image analysis. The presence of viable but nongrowing cells was revealed by transfer to nongradient plates. Lower temperatures and greater NaCl concentrations increased the nisin inhibition of S. aureus synergistically. Increasing the NaCl concentration potentiated the nisin action against L. monocytogenes; the effect of temperature difference was not so apparent. Between pH 7.92 and ca. pH 5, a fall pH appeared to increase nisin's effectiveness against both organisms. At more acid pH values (ca. pH 4.5 to 5), the organisms showed resistance to both nisin and NaCl at 20 and 25 degrees C. Similar results were obtained with one-dimensional liquid cultures.     

Growth, morphology and surface properties of Listeria monocytogenes Scott A and LO28 under saline and acid environments

AIMS: The effect of salt and acid on the growth and surface properties of two strains of Listeria monocytogenes was investigated. METHODS AND RESULTS: Medium acidification and NaCl supplementation induced a marked increase in the lag and growth times (up to fivefold higher) and a decrease in the maximal optical density. Due to a strong synergic effect of pH and NaCl, growth was only detected after 280 h incubation for Scott A and not detected after 600 h for LO28 at pH 5.0 and 10% NaCl. Furthermore, the addition of NaCl in acidic conditions gave rise to cell filamentation and cell surfaces became strongly hydrophilic. CONCLUSIONS: Some L. monocytogenes strains subjected to high NaCl concentrations in acidic conditions are able to grow but may present altered adhesion properties due to modification of their surface properties. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlighted that L. monocytogenes do represent a hazard in acid and salted foods, such as soft cheese.     

Enhanced thermal destruction of Listeria monocytogenes and Staphylococcus aureus by the lactoperoxidase system

The lactoperoxidase system (LPS) enhanced thermal destruction of Listeria monocytogenes and Staphylococcus aureus. After LPS activation, biphasic survival curves were observed for L. monocytogenes at 57.8 degrees C and for S. aureus at 55.2 degrees C. The data were consistent with a model that assumed two bacterial populations differing in heat sensitivity. The more heat-sensitive fractions (93% of the L. monocytogenes, 92% of the S. aureus) were killed almost instantly. For these biphasic survival curves, D values were based on the much smaller, less-heat-sensitive fractions. For L. monocytogenes, the D52.2 degrees C values were 30.2 min (untreated milk) and 10.7 min (LPS activated); corresponding D55.2 degrees C values were 8.2 and 1.6 min; corresponding D57.8 degrees C values were 2.3 and 0.5 min. For S. aureus, the D52.2 degrees C values were 33.3 min (untreated milk) and 2.2 min (LPS activated), and the corresponding D55.2 degrees C values were 7.6 and 1.1 min, respectively. The most rapid killing of L. monocytogenes occurred when samples were heated soon after activation of the LPS. Activation of the LPS followed by heating can increase the margin of safety with respect to milkborne pathogens.     

Enhanced thermal destruction of Listeria monocytogenes and Staphylococcus aureus by the lactoperoxidase system.

The lactoperoxidase system (LPS) enhanced thermal destruction of Listeria monocytogenes and Staphylococcus aureus. After LPS activation, biphasic survival curves were observed for L. monocytogenes at 57.8 degrees C and for S. aureus at 55.2 degrees C. The data were consistent with a model that assumed two bacterial populations differing in heat sensitivity. The more heat-sensitive fractions (93% of the L. monocytogenes, 92% of the S. aureus) were killed almost instantly. For these biphasic survival curves, D values were based on the much smaller, less-heat-sensitive fractions. For L. monocytogenes, the D52.2 degrees C values were 30.2 min (untreated milk) and 10.7 min (LPS activated); corresponding D55.2 degrees C values were 8.2 and 1.6 min; corresponding D57.8 degrees C values were 2.3 and 0.5 min. For S. aureus, the D52.2 degrees C values were 33.3 min (untreated milk) and 2.2 min (LPS activated), and the corresponding D55.2 degrees C values were 7.6 and 1.1 min, respectively. The most rapid killing of L. monocytogenes occurred when samples were heated soon after activation of the LPS. Activation of the LPS followed by heating can increase the margin of safety with respect to milkborne pathogens.     

High nisin Z production by Lactococcus lactis UL719 in whey permeate with aeration

The influence of controlled pH (5.0–6.5) and initial dissolved oxygen level (0–90% air saturation) on nisin Z production in a yeast extract/Tween 80-supplemented whey permeate (SWP) was examined during batch fermentations with citrate positive Lactococcus lactis subsp. lactis UL719. The total activity corresponding to the sum of soluble and cell-bound activities, as measured by a critical dilution method, was more than 50% lower at pH 5.0 than in the range 5.5–6.5, although the specific production decreased as pH increased. A maximum nisin Z activity of 8200 AU/ml (4100IU/ml) was observed in the supernatant after 8h of culture for pH ranging from 5.5 to 6.5. Prolonging the culture beyond 12h decreased this activity at pH 6.0 and 6.5 but not at pH 5.5 or 5.0. A corresponding increase in cell-bound activity was probably due to adsorption of soluble bacteriocin to the cell wall. Aeration increased cell-bound and total activity to maximum values of 32800 and 41000 AU/ml (16400 and 20500IU/ml), respectively, with an initial level of 60% air saturation after 24h of incubation at pH 6.0. The specific production at 60% or 90% initial air saturation was eight-fold higher than at 0%.     

Solubility and antimicrobial efficacy of protamine on Listeria monocytogenes and Escherichia coli as influenced by pH

The antimicrobial efficacy of protamine on Listeria monocytogenes and Escherichia coli was evaluated at concentrations from 50 to 10 000 microgram ml-1 and pH levels from 5.5 to 8.0. The minimum inhibitory concentrations decreased with increasing pH. Protamine inhibited E. coli at all pH values while L. monocytogenes was inhibited at pH 6.5 and above. The antimicrobial efficacy of protamine decreased in the presence of negatively charged gelatine B but remained almost unchanged with addition of the positively charged gelatine A. Binding studies showed that the amount of protamine adsorbed to culture media components in tryptic soy broth and bacterial cells increased with increasing pH values. The increased efficacy of protamine at alkaline pH may be explained on the basis of an increase in electrostatic affinity for the cell surface of target cells. E. coli produced a protamine-degrading enzyme, however, was still susceptible to protamine.     

Effect of the lactoperoxidase system on Listeria monocytogenes behavior in raw milk at refrigeration temperatures.

Activity of raw milk lactoperoxidase-thiocyanate-hydrogen peroxide (LP) system on four Listeria monocytogenes strains at refrigeration temperatures after addition of 0.25 mM sodium thiocyanate and 0.25 mM hydrogen peroxide was studied. The LP system exhibited a bactericidal activity against L. monocytogenes at 4 and 8 degrees C; the activity was dependent on temperature, length of incubation, and strain of L. monocytogenes tested. D values in activated-LP system milk for the four strains tested ranged from 4.1 to 11.2 days at 4 degrees C and from 4.4 to 9.7 days at 8 degrees C. The lactoperoxidase level in raw milk declined during a 7-day incubation, the decrease being more pronounced at 8 degrees C than at 4 degrees C and in control milk than in activated-LP system milk. The thiocyanate concentration decreased considerably in activated-LP system milk at both temperatures during the first 8 h of incubation. LP system activation was shown to be a feasible procedure for controlling development of L. monocytogenes in raw milk at refrigeration temperatures.     

Cold shock induction of thermal sensitivity in Listeria monocytogenes

Cold shock at 0 to 15 degrees C for 1 to 3 h increased the thermal sensitivity of Listeria monocytogenes. In a model broth system, thermal death time at 60 degrees C was reduced by up to 45% after L. monocytogenes Scott A was cold shocked for 3 h. The duration of the cold shock affected thermal tolerance more than did the magnitude of the temperature downshift. The Z values were 8.8 degrees C for controls and 7.7 degrees C for cold-shocked cells. The D values of cold-shocked cells did not return to control levels after incubation for 3 h at 28 degrees C followed by heating at 60 degrees C. Nine L. monocytogenes strains that were cold shocked for 3 h exhibited D(60) values that were reduced by 13 to 37%. The D-value reduction was greatest in cold-shocked stationary-phase cells compared to cells from cultures in either the lag or exponential phases of growth. In addition, cold-shocked cells were more likely to be inactivated by a given heat treatment than nonshocked cells, which were more likely to experience sublethal injury. The D values of chloramphenicol-treated control cells and chloramphenicol-treated cold-shocked cells were no different from those of untreated cold-shocked cells, suggesting that cold shock suppresses synthesis of proteins responsible for heat protection. In related experiments, the D values of L. monocytogenes Scott A were decreased 25% on frankfurter skins and 15% in ultra-high temperature milk if the inoculated products were first cold shocked. Induction of increased thermal sensitivity in L. monocytogenes by thermal flux shows potential to become a practical and efficacious preventative control method.