Effects of organic acids on thermal inactivation of acid and cold stressed Enterococcus faecium

In this study the adaptative response to heat (70 °C) of Enterococcus faecium using fresh and refrigerated (at 4 °C for up to 1 month) stationary phase cells grown in Brain Heart Infusion (BHI) buffered at pH 7.4 (non-acid-adapted cells) and acidified BHI at pH values of 6.4 and 5.4 with acetic, ascorbic, citric, lactic, malic and hydrochloric acids (acid-adapted cells) was evaluated. In all cases, the survival curves obtained were concave upward. A mathematical model based on the Weibull distribution accurately described the inactivation kinetic. The results indicate that previous adaptation to a low pH increased the bacterial heat resistance, whereas the subsequent cold storage of cells reduced E. faecium thermal tolerance. Fresh acid-adapted cells showed t_2.5-values (time needed to obtain an inactivation level of 2.5 log₁₀ cycles) ranging from 2.57 to 9.51 min, while non-acid-adapted cells showed t_2.5-values of 1.92 min. The extent of increased heat tolerance varied with the acid examined, resulting in the following order: citric ≥ acetic > malic ≥ lactic > hydrochloric ≥ ascorbic. In contrast, cold storage progressively decreased E. faecium thermal resistance. The t_2.5 values found at the end of the period studied were about 2–3-fold lower than those corresponding to non-refrigerated cells, although this decrease was more marked (about 5-fold) when cells were grown in buffered BHI and BHI acidified at pH 5.4 with hydrochloric acid. These findings highlight the need for a better understanding of microbial response to various preservation stresses in order to increase the efficiency of thermal processes and to indicate the convenience of counterbalancing the benefits of the hurdle concept.     

Sensitivity of Bacillus weihenstephanensis to acidic changes of the medium is not dependant on physiological state

This study aims to quantify the effect of salt and acid preliminary exposure on acid resistance of vegetative cells of Bacillus weihenstephanensis. The psychrotolerant strain KBAB4 was cultured until the mid-exponentially phase (i) in BHI, (ii) in BHI supplemented with 2.5% salt or (iii) in BHI acidified at pH 5.5 with HCl. The growing cells were subsequently inactivated in lethal acid conditions ranging from 4.45 to 4.70. Based on statistical criteria, a primary mixed-Weibull model was used to fit the acid inactivation kinetics. The acid resistance was enhanced for acid-adapted cells and decreased for salt-adapted cells. The secondary modelling of the bacterial resistance allowed the quantification of the change in pH leading to a ten folds variation of the bacterial resistance, i.e. cells sensitivity (z_pH). This sensitivity was not significantly affected whatever the preliminary mild exposure and the presence of sub-populations with different acid resistances. These results highlighted that pre-incubation conditions influence bacterial acid resistance without affecting the sensitivity to acidic modifications, with a 10 fold reduction of Bacillus acid resistance observed for a reduction of 0.37 pH unit. Quantification of such adaptive stress response might be instrumental in quantitative risk assessment more particularly in food formulation, particularly for low-acid minimally processed foods.     

Relationship between membrane fatty acid composition and heat resistance of acid and cold stressed Salmonella senftenberg CECT 4384

This study evaluates the adaptative response to heat (63 °C) and the modifications in membrane fatty acid composition of Salmonella senftenberg after its growth in an acidified medium and after its exposure to combinations of acid and cold stresses. Cells were grown in Brain Heart Infusion (BHI) buffered at pH 7.0 and acidified up to pH 4.5 (fresh cultures) and kept at refrigeration temperature (4 °C) for 7 days (refrigerated cultures). The results indicate that previous adaptation to a low pH increased the bacterial heat resistance, but combinations of sublethal stresses reduced S. senftenberg heat tolerance, specially when the growth medium pH was decreased. Acid-adapted cells showed D₆₃-values ranging from 3.10 to 6.27 min, while non-acid-adapted cells showed D₆₃-values of 1.07 min. As pH decreased, over the pH range studied (7.4–4.5), D₆₃-values of the resulting cells increased. However, refrigerated acid-adapted cells showed lower D₆₃-values, which ranged from 0.95 to 0.49 min. A linear relationship between the thermotolerance of S. senftenberg cells and the previous growth medium pH was found in both fresh and refrigerated cultures, which allowed us to predict changes in heat resistance of S. senftenberg that occur at any pH value within the range used in the present study in which most foodstuffs are included.     

Acid tolerance in Salmonella typhimurium induced by culturing in the presence of organic acids at different growth temperatures

The influence of growth temperature and acidification of the culture medium up to pH 4.25 with acetic, citric, lactic and hydrochloric acids on the growth and subsequent acid resistance at pH 3.0 of Salmonella typhimurium CECT 443 was studied. The minimum pH value which allowed for S. typhimurium growth within the temperature range of 25–37 °C was 4.5 when the pH was reduced using citric and hydrochloric acids, and 5.4 and 6.4 when lactic acid and acetic acid were used, respectively. At high (45 °C) or low (10 °C) temperatures, the growth pH boundary was increased about 1 pH unit. The growth temperature markedly modified the acid resistance of the resulting cells. In all cases, D-values were lower for cells grown at 10 °C and significantly increased with increasing growth temperature up to 37 °C, at which D-values obtained were up to 10 times higher. Cells grown at 45 °C showed D-values similar to those found for cells grown at 25 °C. The growth of cells in acidified media, regardless of the pH value, caused an increase in their acid resistance at the four incubation temperatures, although the magnitude of the Acid Tolerance Response (ATR) observed depended on the growth temperature. Acid adapted cultures at 10 °C showed D-values ranging from 5.75 to 6.91 min, which turned out to be about 2 times higher than those corresponding to non-acid adapted cultures, while higher temperatures induced an increase in D-values of at least 3.5 times. Another finding was that, while at 10 and 45 °C no significant differences among the effect of the different acids tested in inducing an ATR were observed, when cells were grown at 25 and 37 °C citric acid generally turned out to be the acid which induced the strongest ATR. Results obtained in this study show that growth temperature is an important factor affecting S. typhimurium acid resistance and could contribute to find new strategies based on intelligent combinations of hurdles, which could prevent the development or survival of Salmonella spp. in foods. The fact that moderately low temperatures (10 °C) markedly decrease the acid resistance and increase the growth pH boundary of S. typhimurium suggests the convenience to control the temperature during food processing as a strategy to prevent the growth and survival of this pathogenic microorganism.     

Growth of Listeria monocytogenes on a RTE-meat matrix enhances cell invasiveness to mouse J774A.1 macrophages

It remains unclear whether the growth of Listeria monocytogenes on a ready-to-eat (RTE) meat matrix has an impact on the bacterium's pathogenic abilities. In this study, we investigated the impact of environments on virulence by growing L. monocytogenes (F2365 strain) on brain heart infusion agar (BHI), tryptic soy agar (TSA), and RTE turkey meat matrices. Bacteria cultured from these media were harvested and used to infect mouse macrophage cell line J774A.1 with different MOIs to examine their invasion ability. At MOI = 10 and 50, the numbers of bacteria recovered from cells infected with turkey-meat-grown Listeria were significantly higher than those from the two nutrient-rich growth media. Additionally, MOI played a role in determining L. monocytogenes recovery rates, since significant differences were found amongst all three groups at low MOI, while no significant differences were found between BHI and TSA groups at high MOI. These results indicate that environmental changes affect the ability of L. monocytogenes to invade and survive intracellularly while grown on RTE-meat matrix.     

Effects of cold storage and heat–acid shocks on growth and verotoxin 2 production ofEscherichia coliO157:H7

Escherichia coliO157:H7 was cold-stored (4°C) either in nutritious menstruum [buffered Brain Heart Infusion (BHI) broth] or with starvation (buffered saline) at pH 7.0 or 5.5. Cultures grown in BHI broth at 37°C for 24h served as non-cold-stored controls. After 4-weeks cold storage, bacterial cells were shocked by heat (45°C for 5min) and acid (pH 2.5 for 30min at 37°C) and subsequently moved to optimal conditions (BHI broth of pH 7.4 incubated at 37°C). The results showed: (a) both lag-phase duration and growth rate of this pathogen at 37°C significantly increased after cold-storage with starvation, but not after cold storage in the nutritious menstruum; (b) combined heat–acid shocks increased growth rates at 37°C of both previously cold-stored and non-cold-stored bacterial cells; (c) final concentrations of verotoxin produced by bacterial cells at 37°C were not affected by previous cold storage in the nutritious menstruum; (d) verotoxin production by bacterial cells at 37°C increased after cold storage with starvation, and heat–acid shocks further enhanced that production. Further research is needed to evaluate the food safety implications of these results, i.e. whether cells ofE. coliO157:H7 originating from nutrient-poor/lower-pH environments may be more harmful to humans than those from nutrient-rich/higher-pH foods.     

Application of Central Composite Design to evaluate the antilisterial activity of hydro-alcohol berry extract of Myrtus communis L.

The antimicrobial activity of the hydro-alcohol extract of Myrtus communis L. (ME) berries was investigated against six Listeria monocytogenes strains (2 type strains and 4 isolates). Sub-lethal ME concentrations reduced L. monocytogenes counts by at least 2 log cycles. A Central Composite Design was used to investigate the combined effects of sub-lethal concentrations of ME (0.039–0.195 mL/100 mL), NaCl (0–2.0 g/100 mL) and pH (5.0–7.0) on strains growth. ME affected growth parameters, generally extending lag phase length and reducing maximum growth, sometimes with interactive effects with pH. The highest ME concentrations (0.117–0.195 mL/100 mL) combined with the lowest pH values (5.0–6.0) strongly reduced or even inhibited strains growth.     

Evaluating the use of fatty acid profiles to identify deep-sea Vibrio isolates

Capillary gas chromatography with flame ionisation detection (GC-FID) was used to determine the cellular fatty acid (CFA) profiles of a number of Vibrio strains obtained from ATCC and grown on various media. This initial determination for optimal growth conditions, including type of medium and incubation temperature, for these various ATCC Vibrio species, was important for use in the subsequent evaluation of deep-sea Vibrio strains. The deep-sea Vibrios were obtained from Harbor Branch Oceanographic Institution (Fort Pierce, FL), and GC-FID analysis was used to determine whole cell fatty acid methyl esters (FAMEs) from the cells. The Vibrio strains were cultured for 24 h on a specific medium which included brain heart infusion (BHI) agar, trypticase soy agar (TSA), trypticase soy broth agar (TSBA), and Luria–Bertani (LB) agar. The temperature of incubation was 28 °C for cells grown on TSA, TSBA, and LB and 35 °C for BHI. A data set for each Vibrio species was prepared, using fatty acid profiles for a specific medium. Major fatty acids of the Vibrio strains evaluated in this study were straight-chain C_12:0, C_14:0, C_16:0, and unsaturated summed C_16:1 ω7c/C_16:1 ω6c, C_18:1 ω7c, and summed C_14:0 3-OH/iso-C_16:1. Most of the deep-sea Vibrio isolates were identified as Vibrio parahaemolyticus and Vibrio harveyi. Analysis of FAMEs from Vibro strains grown on a specific medium by this rapid GC-FID method can provide a sensitive procedure for the identification of these organisms, and the differentiation between Vibrio species.     

Antimicrobial activity of lactic acid and copper on growth of Salmonella and Escherichia coli O157:H7 in laboratory medium and carrot juice

Outbreaks of food-borne pathogens, such as Escherichia coli O157:H7 and Salmonella, continue to draw public attention to food safety. Several reports have demonstrated the efficacy of using natural ingredients to control the growth of food-borne pathogens. The objective of this study was to investigate antimicrobial effects of lactic acid and copper, alone and in combination, on the survival and growth of Salmonella spp. and E. coli O157:H7 in laboratory medium and carrot juice. Survival and growth of 38 Salmonella spp. and six E. coli O157:H7 strains were compared when grown in brain heart infusion (BHI) broth and carrot juice under conditions including either lactic acid (0.2%) alone, copper sulfate (50 ppm) alone or the combination of the two. The growth inhibition was negligible when copper sulfate was added to BHI broth and carrot juice. Lactic acid (0.2%) retarded the growth of bacterial strains. However, the growth of bacterial strains was significantly inhibited when both lactic acid and copper were in BHI broth and carrot juice within the time frame of this study. These findings indicated that lactic acid, in combination with copper sulfate, could be used to inhibit the growth of pathogens. Natural ingredients, such as lactic acid and low dose of copper ions, can be used to improve the safety of food products.     

Amino acids improve acid tolerance and internal pH maintenance in Bacillus cereus ATCC14579 strain

This study investigated the involvement of glutamate-, arginine- and lysine-dependent systems in the Acid Tolerance Response (ATR) of Bacillus cereus ATCC14579 strain. Cells were grown in a chemostat at external pH (pH_e) 7.0 and 5.5. Population reduction after acid shock at pH 4.0 was strongly limited in cells grown at pH 5.5 (acid-adapted) compared with cells grown at pH 7.0 (unadapted), indicating that B. cereus cells grown at low pH_e were able to induce a marked ATR. Glutamate, arginine and lysine enhanced the resistance of unadapted cells to pH 4.0 acid shock of 1-log or 2-log populations, respectively. Amino acids had no detectable effect on acid resistance in acid-adapted cells. An acid shock at pH 4.0 resulted in a marked drop in internal pH (pH_i) in unadapted cells compared with acid-adapted cells. When acid shock was achieved in the presence of glutamate, arginine or lysine, pH_i was maintained at higher values (6.31, 6.69 or 6.99, respectively) compared with pH_i in the absence of amino acids (4.88). Acid-adapted cells maintained their pH_i at around 6.4 whatever the condition. Agmatine (a competitive inhibitor of arginine decarboxylase) had a negative effect on the ability of B. cereus cells to survive and maintain their pH_i during acid shock. Our data demonstrate that B. cereus is able to induce an ATR during growth at low pH. This adaptation depends on pH_i homeostasis and is enhanced in the presence of glutamate, arginine and lysine. Hence evaluations of the pathogenicity of B. cereus must take into account its ability to adapt to acid stress.     

Mixed species biofilms of Listeria monocytogenes and Lactobacillus plantarum show enhanced resistance to benzalkonium chloride and peracetic acid

We investigated the formation of single and mixed species biofilms of Listeria monocytogenes strains EGD-e and LR-991, with Lactobacillus plantarum WCFS1 as secondary species, and their resistance to the disinfectants benzalkonium chloride and peracetic acid. Modulation of growth, biofilm formation, and biofilm composition was achieved by addition of manganese sulfate and/or glucose to the BHI medium. Composition analyses of the mixed species biofilms using plate counts and fluorescence microscopy with dual fluorophores showed that mixed species biofilms were formed in BHI (total count, 8-9 log₁₀ cfu/well) and that they contained 1-2 log₁₀ cfu/well more L. monocytogenes than L. plantarum cells. Addition of manganese sulfate resulted in equal numbers of both species (total count, 8 log₁₀ cfu/well) in the mixed species biofilm, while manganese sulfate in combination with glucose, resulted in 1-2 log₁₀ more L. plantarum than L. monocytogenes cells (total count, 9 log₁₀ cfu/well). Corresponding single species biofilms of L. monocytogenes and L. plantarum contained up to 9 log₁₀ cfu/well. Subsequent disinfection treatments showed mixed species biofilms to be more resistant to treatments with the selected disinfectants. In BHI with additional manganese sulfate, both L. monocytogenes strains and L. plantarum grown in the mixed species biofilm showed less than 2 log₁₀ cfu/well inactivation after exposure for 15 min to 100 μg/ml benzalkonium chloride, while single species biofilms of both L. monocytogenes strains showed 4.5 log₁₀ cfu/well inactivation and single species biofilms of L. plantarum showed 3.3 log₁₀ cfu/well inactivation. Our results indicate that L. monocytogenes and L. plantarum mixed species biofilms can be more resistant to disinfection treatments than single species biofilms.     

Effect of pH-dependent,stationary phase acid resistance on the thermal tolerance of Escherichia coli O157:H7

The ability of pH-dependent, stationary phase acid resistance to cross-protect Escherichia coli O157:H7 against a subsequent lethal thermal stress was evaluated using microbiological media and three liquid foods. Three strains were grown for 18 h at 37°C in acidogenic (TSB+G, final pH 4·6–4·7) and non-acidogenic (TSB-G, final pH 7·0–7·2) media to provide stationary phase cells with and without induction of pH-dependent acid resistance. The cells were then heated in BHI broth (pH 6·0) at 58°C, using a submerged coil apparatus. The TSB+G grown strains had greatly increased heat resistance, with the heating time needed to achieve a five-log inactivation, being increased two- to four-fold. The z -values of TSB+G and TSB-G grown cells were 4·7°C and 4·3°C, respectively. Increases in heat resistance with TSB+G-grown E. coli O157:H7 were also observed using milk and chicken broth, but not with apple juice. However, cross-protection was restored if the pH of the apple juice was increased from 3·5 to 4·5. The data indicate that pH-dependent acid resistance provides E. coli O157:H7 with cross-protection against heat treatments, and that this factor must be considered to estimate this pathogen's thermal tolerance accurately.     

Resistance of Listeria monocytogenes F2365 cells to synthetic gastric fluid is greater following growth on ready-to-eat deli turkey meat than in brain heart infusion broth

Ready-to-eat (RTE) deli meats have been categorized as high-risk foods for contraction of foodborne listeriosis. Several recent listeriosis outbreaks have been associated with the consumption of RTE deli turkey meat. In this study, we examined whether the growth of Listeria monocytogenes F2365 on commercially prepared RTE deli turkey meat causes listerial cells to become more resistant to inactivation by synthetic gastric fluid (SGF). Listerial cells grown on turkey meat to late logarithmic-early stationary phase were significantly more resistant to SGF at pH 7.0, 5.0, or 3.5 than listerial cells grown in brain heart infusion (BHI) broth. The pH was lower in the fluid in packages of turkey meat than in BHI broth (6.5 versus 7.5). However, listerial cells grown in BHI broth adjusted to a lower pH (6.0) did not exhibit enhanced resistance to SGF. The lesser resistance to SGF of listerial cells grown in BHI broth may be due, in part, to the presence of glucose (0.2%). This study indicates the environment presented by the growth of L. monocytogenes on deli turkey meat affects its ability to survive conditions it encounters in the gastrointestinal tract.     

Comparison of Yersinia pestis to other closely related Yersinia species using fatty acid profiles

Capillary gas chromatography with flame ionisation detection (GC–FID) was used to determine the cellular fatty acid (CFA) profiles of six Yersinia pestis strains. The profiles were then compared with the CFA profiles of other closely related Yersinia species including: Y. pseudotuberculosis, Y. enterocolitica, Y. intermedii, Y. kristensenii and Y. frederiksenii. For GC–FID analysis, whole cell fatty acid methyl esters (FAMEs) from cells cultured on brain–heart infusion (BHI) agar at 35 °C for 24 h were obtained by saponification, methylation and extraction into hexane/methyl tert-butyl ether. A data set for each Yersinia species was prepared using fatty acid profiles from five replicates prepared on different days. Major fatty acids of the 26 Yersinia strains evaluated in this study were straight-chain 12:0, 14:0, 15:0, 16:0 and unsaturated summed 16:1 ω7c/16:1 ω6c, 18:1 ω7c, and summed 14:0 3OH/16:1 iso, and 17:0 ω cyclo 7–8. The CFA profiles for Y. pestis and Y. pseudotuberculosis are similar, but there are several fatty acids, 16:1 ω5c, 16:0, 17:1 ω7c, 17:0 ω cyclo 7–8, 19:0 and summed 18:2 ω6c, 9c/18:0 ante, that differ significantly between these two species. Analysis of FAMEs from Yersinia strains grown on BHI agar by a rapid GC–FID method can provide a sensitive procedure for the identification of these organisms, and this analytical method provides a procedure for the differentiation of Y. pestis strains from closely related Yersinia species.     

Growth of Salmonella enterica Serovar Enteritidis PT4 in media containing glucose results in enhanced RpoS-independent heat and acid tolerance but does not affect the ability to survive air-drying on surfaces

The heat and acid tolerance of isolates of Salmonella enterica serovar Enteritidis PT4 was markedly higher if cells were grown to stationary phase in either commercially produced Tryptone Soya (TSBG) or brain–heart infusion (BHI) broth containing glucose than when cells were grown in either nutrient or Tryptone Soya broth without glucose. Differences between the populations were found to be related to the production of acid in either TSBG or BHI which caused the culture media pH values to fall to pH 5·8–4·7 during overnight incubation. This led to habituation, which increased both heat- and acid-tolerance, although there was no effect on the abilities of cells to survive air-drying on surfaces. The acid tolerance mechanisms, induced by fermentative growth in complex media, responsible for survival at pH 2·8, were RpoS-independent. In addition, although growth rates as measured by cfu were essentially the same in all media, optical density measurements were very different, with those of cells in media containing glucose being much higher. This was found to be due to the formation of larger cells by the Salmonella in these media.     

Improving the storage stability of Bifidobacterium breve in low pH fruit juice

Bifidobacterial food applications are limited since bifidobacteria are sensitive to e.g. acidic conditions prevalent in many food matrices. The aim of the present study was to investigate whether a low pH selection step alone or combined to UV mutagenesis could improve the viability of an acid sensitive Bifidobacterium strain, B. breve 99, in low pH food matrices. Furthermore, the potential of carriers and an oat fibre preparation to further improve the stability was studied. The best performing low pH tolerant variants in the present study were generated by UV-mutagenesis with 70-700 μJ/cm² followed by incubation in growth medium at pH 4.5. The most promising variants regarding the low pH tolerance showed, in repeated tests with cells grown without pH control, about one Log-value better survival in pH 3.8 fruit juice after one week storage at 4 °C compared to wild-type B. breve 99. Cells grown with pH control, PDX formulated and then frozen showed poorer viability in low pH fruit juice than cells grown with no pH control. For frozen concentrates pH 3.8 was too stressful and no or small differences between the variants and the wild-type strain were seen. The differences detected at pH 3.8 with the cells grown without pH control were also seen with the frozen concentrates at pH 4.5. Some improvement in the stability could be achieved by using a combination of trehalose, vitamin C and PDX as a freezing carrier material, whereas a significant improvement in the stability was seen when oat fibre was added into the fruit juice together with the frozen cells. Due to the initial very poor fruit juice tolerance of B. breve 99 the obtained improvement in the stability was not enough for commercial applications. However, the same methods could be applied to initially better performing strains to further improve their stability in the fruit juice.     

Habituation to organic acid anions induces resistance to acid and bile in Listeria monocytogenes

We evaluated the intrinsic and inducible resistance of four human pathogenic strains of Listeria monocytogenes to acid and bile, factors associated with virulence. Cells were grown in media at pH 7.4, or in media at pH 6.0 containing 0 (HCl control) or 4.75 mM of different organic acids, harvested at stationary or mid log phase, and challenged for 1 h in acid or bile. Stationary phase cells were intrinsically more resistant to either challenge than log phase cells, and large differences between strains were evident among the latter. Compared to the HCl control, habituation to log phase with organic acids induced significant (p < 0.05) and meaningful (≥ 1 log) increases in acid resistance of three of four strains tested, and in bile resistance of two strains suggesting that exposure to organic acid anions may enhance virulence in L. monocytogenes.     

Evaluation of multiple strains of Enterobacter sakazakii using fatty acid profiles

Fatty acid profiles are useful for identifying Gram-negative Enterobacter sakazakii strains within the family Enterobacteriaceae. The majority of cases of E. sakazakii infection have involved sepsis, meningitis, or enteritis, especially in neonates and infants. Gas chromatography with flame ionization detection (GC-FID) was utilized for the analysis of cellular fatty acid methyl esters (FAMEs). Thirty E. sakazakii strains isolated from food and environmental sources were cultured for 24 h on brain heart infusion (BHI) agar on three different days at 37 °C. Whole cell FAMEs were obtained by saponification, methylation and extraction into hexane:methyl tert-butyl ether. The day to day variations for the 30 E. sakazakii strains for each fatty acid were determined. Gram-negative bacteria commonly contain combinations of straight-chain, unsaturated, hydroxyl, and cyclo fatty acids. Major fatty acids of E. sakazakii strains evaluated in this study were straight chain 12:0, 14:0, 16:0 and unsaturated 16:1, 18:1, and 17:0 ω cyclo 7–8. Analysis of FAMEs from E. sakazakii strains grown on BHI agar by this rapid GC-FID method is highly reproducible and provides a sensitive procedure for identification of this organism. The fatty acid profile assay could be used to rapidly screen infant formula samples for E. sakazakii and reduce the time required for the current assay by up to 5 days.     

Antibacterial effects of American cranberry (Vaccinium macrocarpon) concentrate on foodborne pathogens

Antibacterial effects of American cranberry (Vaccinium macrocarpon) concentrate on foodborne pathogens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, and Staphylococcus aureus in vitro were investigated. Cranberry concentrate at various concentrations was prepared in distilled water (DW) or Brain Heart Infusion (BHI) broth. Pathogens were inoculated in each sample and incubated at 21 and 4 °C for 0, 1, 5, 7, and 24 h (DW samples) and 0, 1, 3, and 5 days (BHI samples). Transmission electron microscopy (TEM) was used to study the effects of cranberry concentrate on cellular structure of pathogens. DW results showed that S. Typhimurium and L. monocytogenes were reduced to non-detectable levels at 5 h in 100 μl/ml treatment at 21 and 4 °C. At 24 h, no target pathogens were detected from the 100 μl/ml treatment. BHI data indicated that the 100 μl/ml treatment reduced the four pathogens by 3-8 log CFU/ml compared with the control on Day 5 at 21 and 4 °C. TEM revealed damage to the bacterial cell walls and membranes. Cranberry concentrate has antibacterial effects on the four foodborne pathogens. Based on potential health benefits and proven antimicrobial effects, American cranberry concentrate may have dual applications as a food preservative.