Monocytogenes Populations Research Articles

Effect of Salt Reduction on Growth of Listeria monocytogenes in Meat and Poultry Systems

Reducing sodium in food could have an effect on food safety. The objective was to determine differences in growth of Listeria monocytogenes in meat and poultry systems with salt substitutes. For phase 1, fresh ground beef, pork, and turkey with NaCl, KCl, CaCl(2), MgCl(2), sea salt, or replacement salt added at 2.0% were inoculated with L. monocytogenes to determine growth/survival during 5 d at 4 °C to simulate a pre-blend process. L. monocytogenes populations significantly decreased (0.41 log CFU/g) during the storage time in beef, but no differences (P > 0.05) were observed over time in pork or turkey. Salt type did not affect (P > 0.05) L. monocytogenes populations during pre-blend storage. MgCl(2) and NaCl allowed significant growth of aerobic populations during storage. For phase 2, emulsified beef and pork products were processed with 2% NaCl, KCl, sea salt, or a NaCl/KCl blend and post-process surface-inoculated with L. monocytogenes to determine growth/survival at 4 °C for 28 d. Pork products showed significantly greater L. monocytogenes population growth at all sampling times (0, 7, 14, 21, and 28 d) than beef products, but salt type had no effect on L. monocytogenes populations with sampling times pooled for data analysis. Although salt types had no impact on L. monocytogenes populations in preblend and emulsified meat products, pork and turkey preblends and emulsified pork had greater L. monocytogenes populations compared with beef products. These studies demonstrate that sodium may not affect the safety of preblends and emulsified meat and poultry products.

Effect of native microflora, waiting period, and storage temperature on Listeria monocytogenes serovars transferred from cantaloupe rind to fresh-cut pieces during preparation.

The most recent outbreak of listeriosis linked to consumption of fresh-cut cantaloupes indicates the need to investigate the behavior of Listeria monocytogenes in the presence of native microflora of cantaloupe pieces during storage. Whole cantaloupes were inoculated with L. monocytogenes (10(8)-CFU/ml suspension) for 10 min and air dried in a biosafety cabinet for 1 h and then treated (unwashed, water washed, and 2.5% hydrogen peroxide washed). Fresh-cut pieces (∼3 cm) prepared from these melons were left at 5 and 10°C for 72 h and room temperature (20°C) for 48 h. Some fresh-cut pieces were left at 20°C for 2 and 4 h and then refrigerated at 5°C. Microbial populations of fresh-cut pieces were determined by the plate count method or enrichment method immediately after preparation. Aerobic mesophilic bacteria, yeast and mold of whole melon, and inoculated populations of L. monocytogenes on cantaloupe rind surfaces averaged 6.4, 3.3, and 4.6 log CFU/cm(2), respectively. Only H(2)O(2) (2.5%) treatment reduced the aerobic mesophilic bacteria, yeast and mold, and L. monocytogenes populations to 3.8, 0.9, and 1.8 log CFU/cm(2), respectively. The populations of L. monocytogenes transferred from melon rinds to fresh-cut pieces were below detection but were present by enrichment. Increased storage temperatures enhanced the lag phases and growth of L. monocytogenes. The results of this study confirmed the need to store fresh-cut cantaloupes at 5°C immediately after preparation to enhance the microbial safety of the fruit.

Antagonistic effect of Pseudomonas graminis CPA-7 against foodborne pathogens in fresh-cut apples under simulated commercial conditions

Recently, we reported that the application of the strain CPA-7 of Pseudomonas graminis, previously isolated from apple, could reduce the population of foodborne pathogens on minimally processed (MP) apples and peaches under laboratory conditions. Therefore, the objective of the present work was to find an antioxidant treatment and a packaging atmosphere condition to improve CPA-7 efficacy in reducing a cocktail of four Salmonella and five Listeria monocytogenes strains on MP apples under simulated commercial processing. The effect of CPA-7 application on apple quality and its survival to simulated gastric stress were also evaluated. Ascorbic acid (2%, w/v) and N-acetyl-l-cysteine (1%, w/v) as antioxidant treatments reduced Salmonella, L. monocytogenes and CPA-7 recovery, meanwhile no reduction was observed with NatureSeal® AS1 (NS, 6%, w/v). The antagonistic strain was effective on NS-treated apple wedges stored at 10 °C with or without modified atmosphere packaging (MAP). Then, in a semi-commercial assay, efficacy of CPA-7 inoculated at 105 and 107 cfu mL−1 against Salmonella and L. monocytogenes strains on MP apples with NS and MAP and stored at 5 and 10 °C was evaluated. Although high CPA-7 concentrations/populations avoided Salmonella growth at 10 °C and lowered L. monocytogenes population increases were observed at both temperatures, the effect was not instantaneous. No effect on apple quality was detected and CPA-7 did not survived to simulated gastric stress throughout storage. Therefore, CPA-7 could avoid pathogens growth on MP apples during storage when use as part of a hurdle technology in combination with disinfection techniques, low storage temperature and MAP.

Control of Listeria monocytogenes and spoilage bacteria on smoked salmon during storage at 5 °C after X-ray irradiation

In this study, smoked salmon fillets were artificially inoculated with Listeria monocytogenes (3.7 ± 0.2 log CFU g−1) and treated with X-ray irradiation generated by a RS 2400 X-ray machine (Rad Source Technologies Inc.) using doses of 0.0, 0.1, 0.5, 1.0, and 2.0 kGy. Unirradiated and irradiated samples were then stored at 5 °C for 35 days and tested for L. monocytogenes count after 0, 5, 10, 15, 20, 25, 30, and 35 days. Also, uninoculated-untreated and uninoculated-treated samples with the lowest and highest X-ray doses (0.1 and 2.0 kGy) were stored at 5 °C and examined for psychrotrophs and mesophiles counts after 0, 5, 10, 15, 20, 25, 30, and 35 days. The initial L. monocytogenes population (3.7 log CFU g−1 ) was significantly (p < 0.05) reduced to an undetectable level (<1.0 log CFU g−1) by treatment with 1.0 kGy X-ray. Treatment with 0.1 kGy X-ray significantly reduced the initial psychrotrophs and mesophiles counts from 5.3 and 3.0 to 3.3 and 2.3, respectively. However, L. monocytogenes, psychrotrophs and mesophiles counts were gradually increased during storage. Treatment with 2.0 kGy X-ray kept the L. monocytogenes population under detectable level until 35 days. Treatment with 2.0 kGy X-ray kept the mesophiles and psychrotrophs counts within the acceptable level until 35 days. These results revealed that treatment with X-ray irradiation can significantly reduce the risk of listeriosis and extend the shelf life of smoked salmon during storage at 5 °C.

Viability of Salmonella and Listeria monocytogenes in delicatessen salads and hummus as affected by sodium content and storage temperature.

A study was conducted to determine survival and growth behavior of Salmonella and Listeria monocytogenes in commercially prepared mayonnaise-based potato salad, macaroni salad, and coleslaw and in hummus (initial mean pH values were 4.80 to 4.94, 4.18 to 4.31, 3.87, and 4.50 to 4.52, respectively) as affected by sodium concentration (133 to 364, 190 to 336, 146 to 272, and 264 to 728 mg/100 g, respectively) and storage at 4 or 10°C for up to 27 days. Salmonella did not grow in any of the test products. Initial populations (2.02 to 2.38 log CFU/g) decreased in coleslaw to undetectable levels (<1 CFU/25 g) within 13 days and in most formulations of macaroni salad within 20 to 27 days. Salmonella survived in highest numbers in potato salad and hummus. The presence of added sodium in macaroni salad stored at 4°C and hummus stored at 4 or 10°C appeared to protect Salmonella against inactivation. L. monocytogenes, at an initial population of 1.86 to 2.23 log CFU/g, did not grow in test products, but with the exception of coleslaw containing sodium at a concentration used in the standard (control) recipe, this pathogen was detected by direct plating (≥ 1.0 log CFU/g) in all products stored at 4 or 10°C for 27 days. L. monocytogenes populations were significantly (P < 0.05) lower in potato salad and hummus with no added sodium than in test products with added sodium after storage at 4°C. Sodium concentration did not markedly affect aerobic plate counts over the 27-day storage period. Results confirm that the acidic pH of mayonnaise-based salads and hummus is a major factor preventing growth and influencing rates of inactivation of Salmonella and L. monocytogenes. In the absence of added sodium, death of these bacteria may be more rapid. However, in general decreasing or increasing the sodium concentration in selected delicatessen salad and hummus recipes does not markedly affect the behavior of Salmonella and L. monocytogenes when products are stored at 4 or 10°C for up to 27 days.

Listeria monocytogenesGrowth Dynamics on Produce: A Review of the Available Data for Predictive Modeling

Several listeriosis outbreaks have been linked to the consumption of fresh or processed produce in recent years. One major determinant of the listeriosis risk is the ability of a food to support growth of Listeria monocytogenes during storage. However, data regarding the ability to support growth of L. monocytogenes are scarce or nonexisting for many produce commodities. Here we synthesize the available data regarding growth behavior of L. monocytogenes on produce, compare the growth data with listeriosis outbreak data, and evaluate the adequacy of the data for predictive modeling. Growth rates and maximum L. monocytogenes population densities differed markedly among produce commodities, and post-harvest processing had a considerable effect on growth dynamics for certain commodities such as tomatoes. However, data scarcity prevented reliable estimation of growth rates for many commodities. Produce outbreaks seemed frequently associated with processed produce and often involved storage under suboptimal conditions (e.g., at room temperature for several hours or for several months in the refrigerator) or environmental cross-contamination after processing. However, no clear associations between high growth rates of L. monocytogenes on fresh produce and outbreaks were detected. In conclusion, produce commodities differ in the supported growth rate of L. monocytogenes, the maximum attainable L. monocytogenes population density, and possibly in the impact of post-harvest processing, but data are currently insufficient to predict growth behavior, and the listeriosis risk appears to be also governed by additional factors.

Reduction in Listeria monocytogenes and spoilage bacteria on smoked catfish using X-ray treatments

To determine the efficacy of X-ray processes in inactivating L. monocytogenes levels in smoked catfish during storage at 5°C and to determine the effects of X-ray doses on controlling the growth of spoilage bacteria on smoked catfish during storage at 5°C for up to 5 weeks. Smoked catfish fillets inoculated with L. monocytogenes were treated with 0.0-2.0 kGy X-ray and stored at 5°C for 5 weeks. The negative controls (uninoculated/untreated) and uninoculated samples treated with the lowest (0.1 kGy) and highest (2.0 kGy) doses were stored at 5°C and tested for psychrotrophs count during the 5 weeks of storage. The initial L. monocytogenes population on smoked catfish was significantly (P < 0.05) reduced to undetectable level by a treatment of 1.0 kGy or higher. The initial psychrotrophs count on smoked catfish was significantly reduced from 4.7 CFU g(-1) to below the detectable level by a treatment with 2.0 kGy. Smoked catfish treated with 2.0 kGy X-ray had no detectable L. monocytogenes throughout 35 days of storage at 5°C. A treatment with 2.0 kGy X-ray also kept the levels of psychrotrophs in the smoked catfish within the acceptable level until 35 days. The results of this investigation indicate that X-ray at 2.0 kGy can eliminate L. monocytogenes and extend the shelf life of smoked catfish stored at refrigeration temperature.

Reduction of Listeria monocytogenes in queso fresco cheese by a combination of listericidal and listeriostatic GRAS antimicrobials

Single and combined effects of three GRAS (generally recognized as safe) antimicrobials including, bacteriophage P100 (phage P100), lauric arginate (LAE), and potassium lactate–sodium diacetate mixture (PL–SD) were evaluated against Listeria monocytogenes cold growth in queso fresco cheese (QFC). The fate of phage P100 when exposed to LAE (200ppm) or PL–SD (2.8% PL and 0.2% SD) was determined at 4°C and 30°C in a broth model. Phage P100 was found to be stable in the presence of these antimicrobial agents as plaque forming units (PFU) did not vary between control, LAE or PL–SD treatments. When 9logCFU/ml of stationary phase cells of L. monocytogenes was exposed to these antimicrobials in tryptic soy broth, there was a 3 to 5logCFU/ml reduction with phage P100 and a complete 9logCFU/ml reduction with LAE but no measurable reduction with PL–SD after 24h at 4°C or 30°C. In QFC, the L. monocytogenes populations increased from the initial 3.5logCFU/cm2 to 7.7logCFU/cm2 in 28days at 4°C. Treatment with 7.8logPFU/cm2 of phage P100 or 200ppm of LAE showed strong listericidal effect initially by reducing L. monocytogenes counts by 2 to 3.5–4logCFU/cm2 while there was a subsequent regrowth of L. monocytogenes at 4°C. Treatment with PL–SD showed strong listeriostatic effect without decreasing L. monocytogenes counts but growth was prevented for 28days at 4°C. Only the combined treatment of listericidal phage P100 or LAE with listeriostatic PL–SD reduced the initial L. monocytogenes counts by 2–4logCFU/cm2 and also kept the L. monocytogenes counts at that reduced level in QFC for 28days at 4°C.

Fate of Listeria monocytogenes Inoculated onto Turkey Ham and Treated with Sodium Metasilicate

Sodium Metasilicate (SMS) is a USDA approved antimicrobial and has been shown to be inhibitory towards various foodborne pathogens in refrigerated raw poultry and beef trimmings. The objectives of this study were to determine the antimicrobial effects of SMS against Listeria monocytogenes in ready-to-ea t turkey ham and to ascertain effects of various treatments on pH. Ready-to-eat turkey ham slices were inoculated with L. monocytogenes , treated with either 0% SMS (only sterile de-ionized water) and no inoculum (negative control), 0% SMS (only sterile de-ionized water) and inoculum (positive control) and 6% SMS solution with final concentration of 300 ppm and 600 ppm of SMS in turkey ham samples plus inoculum. In each treatment, the turkey ham samples were vacuum-packaged and stored at 4±1°C. All samples were analyzed on day 0, 7, 14, 21 and 28 of storage for presence of L. monocytogenes and pH. The use of 6% SMS solution at 300 and 600 ppm concentrations was not effective in reducing L. monocytogenes populations (p>0.05) in turkey ham and pH values were similar (p>0.05) for all treatments from d 0 to d 28. The findings from this study suggested that SMS is ineffective in reducing L. monocytogenes in turkey ham, at the currently approved levels and higher concentrations of SMS may be needed to restrict growth of L. monocytogenes in ready-to-eat poultry products.

Bactericidal effects of roselle (Hibiscus sabdariffa) against foodborne pathogens in vitro and on romaine lettuce and alfalfa sprouts

Introduction An increased fresh-produce consumption trend accompanied by increased associated outbreaks suggests a need for better intervention strategies. Limitations of chemical sanitizers have necessitated alternative strategies. Research on antimicrobial properties of roselle against food pathogens is limited. Objectives The study aims to investigate Escherichia coliO157:H7, Salmonella enterica and Listeria monocytogenes survival in roselle calyx aqueous (RCA) or roselle leaf aqueous (RLA) extracts over 72 h at 4, 8 and 25 °C; bactericidal effects of roselle calyx concentrate (RCC) and roselle tea (RT) against E. coliO157:H7 on lettuce and of RCC against Salmonella on alfalfa sprouts. Methods Microbiological analyses and preparation of RCA, RLA, RCC and RT were done according to standard and established methods. Results No E. coliO157:H7 and Salmonella survivors were detected in RCA or RLA at 24 h and all temperatures. L. monocytogenes population was reduced by 5 and 3 logs in RCA and RLA, respectively, at 24 h and all temperatures; by 4–6 logs at 4 °C and 8 °C and to undetectable levels at 25 °C, at 48 h. At 24 h, E. coliO157:H7 and Salmonella were not detected on RCC- or RT-treated lettuce or sprouts. Conclusion These observations suggest the application of roselle extracts as potential antimicrobials in foods.

Probabilistic Models for the Prediction of Target Growth Interfaces of Listeria monocytogenes on Ham and Turkey Breast Products

This study developed growth/no growth models for predicting growth boundaries of Listeria monocytogenes on ready-to-eat cured ham and uncured turkey breast slices as a function of lactic acid concentration (0% to 4%), dipping time (0 to 4 min), and storage temperature (4 to 10 °C). A 10-strain composite of L. monocytogenes was inoculated (2 to 3 log CFU/cm²) on slices, followed by dipping into lactic acid and storage in vacuum packages for up to 30 d. Total bacterial (tryptic soy agar plus 0.6% yeast extract) and L. monocytogenes (PALCAM agar) populations were determined on day 0 and at the endpoint of storage. The combinations of parameters that allowed increases in cell counts of L. monocytogenes of at least l log CFU/cm² were assigned the value of 1, while those limiting growth to <1 log CFU/cm² were given the value of 0. The binary data were used in logistic regression analysis for development of models to predict boundaries between growth and no growth of the pathogen at desired probabilities. Indices of model performance and validation with limited available data indicated that the models developed had acceptable goodness of fit. Thus, the described procedures using bacterial growth data from studies with food products may be appropriate in developing growth/no growth models to predict growth and to select lactic acid concentrations and dipping times for control of L. monocytogenes. The models developed in this study may be useful in selecting lactic acid concentrations and dipping times to control growth of Listeria monocytogenes on cured ham and uncured turkey breast during product storage, and in determining probabilities of growth under selected conditions. The modeling procedures followed may also be used for application in model development for other products, conditions, or pathogens.

Efficacy of freezing, frozen storage and edible antimicrobial coatings used in combination for control of Listeria monocytogenes on roasted turkey stored at chiller temperatures

The presence and growth of Listeria monocytogenes on ready-to-eat (RTE) turkey is an important food safety issue. The antilisterial efficacy of four polysaccharide-based edible coatings (starch, chitosan, alginate and pectin) incorporating sodium lactate (SL) and sodium diacetate (SD) as well as commercial preparations Opti.Form PD4, NovaGARD™ CB1, Protect-M and Guardian™ NR100 were compared against L. monocytogenes on roasted turkey. Pectin coating treatments incorporating SL/SD, Opti.Form PD4 with or without Protect-M, and NovaGARD™ CB1 displayed higher antimicrobial efficacy against.L. monocytogenes than the other antimicrobials and coating materials. In the second phase of the study, it was investigated whether frozen storage could enhance the antilisterial effectiveness of pectin coating treatments on chilled roasted turkey. Inoculated roasted turkey samples coated with pectin-based treatments were frozen for up to 4 weeks and subsequently stored at 4 °C for 8 weeks. Frozen storage significantly enhanced the antilisterial activity of various coating treatments; with selected treatments reducing the L. monocytogenes populations by as much as 1.1 log CFU/cm2 during the subsequent 8-week chilled storage. This study demonstrates that pectin-based antimicrobial edible coatings hold promise in enhancing the safety of RTE poultry products and frozen storage has the potential to enhance their effectiveness.

Effect of osmotic stress and culture density on invasiveness of Listeria monocytogenes strains

The effect of osmotic stress on its capacity to invade the human enterocytic cell line HT-29 was studied in the early log through the stationary phase in 10 L. monocytogenes strains representing three genetically independent lineages. The results demonstrate that the transition of the bacteria from the log to the stationary phase results in a stepwise reduction of invasiveness. This effect was heterogeneous in the studied L. monocytogenes population, as the range of invasiveness reduction between the log and stationary phases varied from 10- to 380-fold depending on the strain. Ten-minute exposure to 0.3M NaCl was sufficient to generate invasiveness alteration. No significant change in invasiveness induction caused by osmotic stress was found between the different points of the log phase (OD600 0.4–1.2), being significantly different in the early log phase (OD600 0.2–0.3) and in the stationary phase after 18h of culture. The level of internalins and opuCA transcripts in response to osmotic stress did not correlate with invasiveness alteration in most L. monocytogenes strains.Prolongation of stress exposure to 1h and an increase in NaCl concentration from 0.3 to 1.8M had no significant effect on a further increase in invasiveness. Short exposure times and low NaCl concentrations were sufficient for the generation of maximal invasiveness response of L. monocytogenes. It appears that although stationary-phase bacteria exhibit lower invasiveness than log-phase bacteria, they have a greater capacity to enhance their pathogenicity in response to stress.

Antimicrobial activity of essential oils of three herbs against Listeria monocytogenes on chicken frankfurters

Listeria monocytogenes is a foodborne pathogen responsible for listeriosis. The inhibitory effect of essential oils (1% v/w) of Thymus daenensis Celak (Lamiaceae), Thymbra spicata L. (Lamiaceae) and Satureja bachtiarica Bunge (Lamiaceae) applied to the surface of chicken frankfurters was determined on L. monocytogenes inoculated at low (103 CFU/g) and high (106 CFU/g) populations and stored for seven and 14 days. The results showed that L. monocytogenes populations increased during seven and 14 days of storage at 4 °C on control frankfurters without essential oil. The application of 1 % essential oil (v/w) of herbs to frankfurter surfaces can significantly reduce (p&lt;0.05) the L. monocytogenes populations as compared to control in two inocula treatments after seven and 14 days of storage at 4 °C.

Effectiveness of barrier film with a cellulose coating that carries nisin blends for the inhibition of listeria monocytogenes

AbstractThe objective of this study was to determine the effectiveness of two nisin blend antimicrobial agents (Guardian NR 250, Novagard CBI) incorporated into a cellulose coating that was applied onto a barrier film against Listeria monocytogenes. The minimum inhibitory concentration (MIC) of the agents in solution against L. monocytogenes was found to be 2.74 mg/ml for the two nisin blends. The concentrations tested for both nisin blend treatments were 5.49, 10.9, 16.4 and 21.9 mg/ml. Guardian NR 250 resulted in wider zones of inhibition compared to the Novagard CBI at all levels tested. The MIC for Guardian NR 250 in the film was 5.49 mg/ml. Films containing Novagard CBI did not show any antimicrobial activity. A food challenge study was conducted using the film containing Guardian NR 250 at levels of 5.49 and 21.9 mg/ml. Inoculated fresh beef cubes were individually packaged with pre‐made barrier film pouches that had an interior cellulose coating containing the antimicrobial agent and stored at 4°C for 36 days. Bacterial colonies were enumerated every 6 days on modified Oxford agar. There was no significant difference in the L. monocytogenes population between two levels of Guardian NR 250 throughout the study. There was statistically significant inhibition of L. monocytogenes for both levels of Guardian NR 250 during 18–30 days of storage compared to a control film without the antimicrobial agent. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Growth control of Listeria monocytogenes in experimental cheese samples by Lactobacillus casei RN 78 and its bacteriocin.

Anti-listerial effect of freeze dried fractions of partially purified bacteriocin (Fd-PPL) and the producer strain Lactobacillus casei RN 78 strain was evaluated in experimental cheese samples during storage at two different temperatures (4 and 35˚C). With the addition of 6400 AU/g of Fd-PPL fractions to the cheese samples of the initial concentration of 4.81 +/- 0.06 log CFU/ml of Listeria monocytogenes was reduced up to 0.91 +/- 0.01 log CFU/ml. Whilst, in the presence of 10 7 CFU/ml live bacterial cells of L. casei RN 78 of the viability of the sensitive cells decreased sharply (0.71 log CFU/ml). The effect was more pronounced after 24 h of incubation and high levels of antibacterial activity (12800 AU/ml) was seen in these samples. An enhanced reduction in the pH was recorded (4.8 - 5.0) in the cheese samples inoculated with live producer cells compared to control samples without any enrichment. A synergistic bactericidal effect of Lactocin RN 78 in combination with 3% Sodium chloride in cheese samples was observed, and L. monocytogenes population were reduced to 0.69 log CFU/ml within 90 days of incubation, at 35˚C. In contrast to the producer strain, the antibacterial effect of Lactocin was more pronounced in cheese samples stored at 4˚C. The texture of the experimental cheese samples including odour, colour and consistency in different batches were also recorded through out the study.

Efficacy of Ultraviolet Light Exposure Against Survival of Listeria monocytogenes on Conveyor Belts

Listeria monocytogenes has been repeatedly isolated from foods and food-processing facilities including food contact surfaces such as conveyor belts (CB). CBs are often difficult to clean and require rigorous sanitation programs for decontamination. Ultraviolet (UV) light has exhibited microbicidal properties on food contact surfaces and this study was conducted to determine the efficacy of UV against L. monocytogenes on CB made of different materials. A four-strain cocktail of L. monocytogenes (serotypes 3A, 4A, 4B, and 4C) was made to give a suspension of approximately 10(7) CFU/mL. CBs made from four different types of materials, (1) Ropanyl DM 8/2 A2 + 04 (belt 1), (2) Volta FRMW-3.0 (belt 2), (3) Volta FRMB-3.0 (belt 3), and (4) Ropanyl DM (belt 4), were inoculated with 1 mL of the four-strain cocktail (approximately 10(7) CFU/mL) of the bacterial suspension. CBs were treated with UV light (254 nm) for 1 and 3 sec at 5.53 and 5.95 mW/cm(2). Three replications of the experiments were conducted. Two-way analysis of variance of survival populations of L. monocytogenes showed that bacterial counts were significantly reduced (p < 0.05) on all belt types irrespective of UV light intensities and times of exposure. L. monocytogenes populations were reduced (p < 0.05) to below detection limits on belts 1, 2, and 3 after exposure to 5.95 mW/cm(2) UV light intensity for 3 sec. L. monocytogenes-inoculated CBs that were exposed to 5.53 mW/cm(2) showed higher (p < 0.05) survival populations of L. monocytogenes compared with 5.95 mW/cm(2) on all the four CBs. Belt 4 showed survival populations of L. monocytogenes ranging from 1.42 to 1.73 log(10) CFU/cm(2) after UV light treatment for 1 and 3 sec. UV light can be effectively used to reduce L. monocytogenes contamination on CBs.

Hot air treatment for surface decontamination of table eggs experimentally infected with Salmonella, Listeria, and Escherichia coli

Hot-air pasteurization was investigated in the EU-funded project "Reducing Egg Susceptibility to Contaminations in Avian Production in Europe (RESCAPE)" as an innovative treatment for surface bacterial decontamination of table eggs. Possible side effects of the treatment on egg quality traits were also studied. The decontamination power of hot air was evaluated over 1 month on shell eggs that were experimentally inoculated with Salmonella enteritidis, Escherichia coli, or Listeria monocytogenes. The S. Enteritidis and L. monocytogenes populations on the surfaces of treated eggs showed a significant reduction compared with untreated eggs. No statistically significant results were obtained comparing E. coli loads on treated and untreated eggs. No detrimental effects on quality traits either immediately after treatment or after 28 days of storage at 20 degrees C were recorded.

Loss of viability of Listeria monocytogenes in contaminated processed cheese during storage at 4, 12 and 22 °C

The behaviour of Listeria monocytogenes in a processed cheese product was evaluated over time by inoculating the product with three different L. monocytogenes strains (Scott A, CA and a strain isolated from processed cheese) at three different inoculation levels (ca. 6 × 10 5, ca. 6 × 10 3 and 10 2 CFU/g of cheese or less) and after storage of the contaminated products at 4, 12 or 22 °C. Growth of L. monocytogenes was not observed in any of the experimental trials (experiments involving different combinations of strain, inoculum level and storage temperature) throughout the storage period. L. monocytogenes populations decreased over time with a rate that was strain- and storage temperature-dependent. Nonetheless, for cheeses that had been inoculated with the higher inoculum and stored at 4 °C viable populations of L. monocytogenes could be detected for up to nine months post-inoculation. The L. monocytogenes survival curves obtained from the different trials were characterised by a post-inoculation phase during which the populations remained essentially unchanged (lag phase) followed by a phase of logarithmic decline. The duration of the lag phase and the rate of inactivation of L. monocytogenes in the different trials were estimated based on data from the linear descending portions of the survival curves. In addition, a non-linear Weibull-type equation was fitted to the data from each survival curve with satisfactory results. The results of the present study emphasize that, according to the definition laid down in the European Union Regulation 1441/2007, the processed cheese product tested in this work should be considered and classified as one that does not support the growth of L. monocytogenes under reasonable foreseeable conditions of distribution and storage. However, post-processing contamination of the product should be austerely avoided as the pathogen can survive in the product for extended periods of time, particularly under refrigerated storage (4 °C).

Antimicrobial activity of essential oils of three herbs against Listeria monocytogenes on chicken frankfurters

Listeria monocytogenes is a foodborne pathogen responsible for listeriosis. The inhibitory effect of essential oils (1% v/w) of Thymus daenensis Celak (Lamiaceae), Thymbra spicata L. (Lamiaceae) and Satureja bachtiarica Bunge (Lamiaceae) applied to the surface of chicken frankfurters was determined on L. monocytogenes inoculated at low (10 3 CFU/g) and high (10 6 CFU/g) populations and stored for seven and 14 days. The results showed that L. monocytogenes populations increased during seven and 14 days of storage at 4 °C on control frankfurters without essential oil. The application of 1 % essential oil (v/w) of herbs to frankfurter surfaces can significantly reduce (p<0.05) the L. monocytogenes populations as compared to control in two inocula treatments after seven and 14 days of storage at 4 °C.