Fate Of Listeria Monocytogenes Research Articles

Monitoring the Bioprotective Potential of Lactiplantibacillus pentosus Culture on Pathogen Survival and the Shelf-Life of Fresh Ready-to-Eat Salads Stored under Modified Atmosphere Packaging.

Globally, fresh vegetables or minimally processed salads have been implicated in several foodborne disease outbreaks. This work studied the effect of Lactiplantibacillus pentosus FMCC-B281 cells (F) and its supernatant (S) on spoilage and on the fate of Listeria monocytogenes and Escherichia coli O157:H7 on fresh-cut ready-to-eat (RTE) salads during storage. Also, Fourier transform infrared (FTIR) and multispectral imaging (MSI) analysis were used as rapid and non-destructive techniques to estimate the microbiological status of the samples. Fresh romaine lettuce, rocket cabbage, and white cabbage were used in the present study and were inoculated with L. pentosus and the two pathogens. The strains were grown at 37 °C for 24 h in MRS and BHI broths, respectively, and then were centrifuged to collect the supernatant and the pellet (cells). Cells (F, ~5 log CFU/g), the supernatant (S), and a control (C, broth) were used to spray the leaves of each fresh vegetable that had been previously contaminated (sprayed) with the pathogen (3 log CFU/g). Subsequently, the salads were packed under modified atmosphere packaging (10%CO2/10%O2/80%N2) and stored at 4 and 10 °C until spoilage. During storage, microbiological counts and pH were monitored in parallel with FTIR and MSI analyses. The results showed that during storage, the population of the pathogens increased for lettuce and rocket independent of the treatment. For cabbage, pathogen populations remained stable throughout storage. Regarding the spoilage microbiota, the Pseudomonas population was lower in the F samples, while no differences in the populations of Enterobacteriaceae and yeasts/molds were observed for the C, F, and S samples stored at 4 °C. According to sensory evaluation, the shelf-life was shorter for the control samples in contrast to the S and F samples, where their shelf-life was elongated by 1-2 days. Initial pH values were ca. 6.0 for the three leafy vegetables. An increase in the pH of ca. 0.5 values was recorded until the end of storage at both temperatures for all cases of leafy vegetables. FTIR and MSI analyses did not satisfactorily lead to the estimation of the microbiological quality of salads. In conclusion, the applied bioprotective strain (L. pentosus) can elongate the shelf-life of the RTE salads without an effect on pathogen growth.

Fate of Listeria monocytogenes, Salmonella spp., and Shiga Toxin-Producing Escherichia coli on Slices of an All-Beef Soppressata during Storage.

Cells of Listeria monocytogenes, Salmonella spp., or Shiga toxin-producing Escherichia coli (STEC) were inoculated (ca. 4.0 log CFU/slice) onto slices (ca. 4 g each slice) of an all-beef soppressata (ca. pH 5.05 and aw 0.85). The storage of vacuum-sealed slices of inoculated soppressata at 4 °C or 20 °C for 90 days resulted in reductions of all three pathogens by ca. 2.2 to 3.1 or ca. ≥3.3 log CFU/slice, respectively. When pathogen levels decreased to below detection (≤1.18 log CFU/slice) by direct plating, it was possible to recover each of the target pathogens by enrichment, albeit more frequently from slices stored at 4 °C (p < 0.05) compared to 20 °C. In summary, the slices of the commercially produced beef soppressata selected for this study did not provide a favorable environment for either survival or outgrowth of surface-inoculated cells of L. monocytogenes, Salmonella spp., or STEC during storage.

Lactic fermentation of cooked, comminuted mussel, Perna canaliculus

The endogenous microflora of mussels, filter feeders, can include pathogens with resulting food safety concerns. The aim was to develop a cook-then-ferment technology to extend shelf life and safety of a ready-to-eat mussels. Only after cooking to destroy the mussel's endogenous microflora could an edible product be made as determined by pH decline after fermentation and the fate of common pathogens. Perna canaliculus was bought live at retail on many dates. Fermentation was with commercial lactic cultures incubated under vacuum at 30 °C for four days. Using one culture containing Pediococcus pentosaceus and Staphylococcus carnosus as a model, pH typically declined to 4.5 to 4.7, and common pathogens, Staphylococcus aureus, Salmonella and Vibrio parahaemolyticus were absent or reduced to acceptable levels. The fate of Listeria monocytogenes was studied with five cultures. These were variably effective at inhibition with one clear success, Chr Hansen's T–SC–150 containing a specific strain of Lactobacillus sakei, and flavour-generating Staphylococcus carnosus. This culture's efficacy was confirmed with sterile extracts of LAB challenging L. monocytogenes in vitro. This culture was also the most rapid fermenter by pH fall. Cook-then-ferment technology may be applied to other novel foods to minimise a disruptive endogenous microflora.

Fate of Listeria monocytogenes and Salmonella Typhimurium in homemade marinade and on marinated chicken drumsticks, wings and breast meat

In recent years, the increase in consumer demands for the products that are processed with natural additives has highlighted the use of natural substances in food processing and safety. For this purpose, the aim of this study is to determine the effect of homemade marinade that are prepared with the natural substances existing in every kitchens and restaurants on Salmonella Typhimurium, Listeria monocytogenes and natural microbiota of chicken wings, drumstick and breast meats. The results of this study revealed that the number of Salmonella Typhimurium decreased about 4.0 log10 in 24 h in marinade sauce, while no significant change was observed in the number of Listeria monocytogenes. The number of Salmonella Typhimurium decreased 0.9 and 1.4 log10 in the marinated chicken wing and breast meat. Marinade has a strong bacteriostatic effect on Listeria monocytogenes, total mesophilic aerobic bacteria and psycrotrophic bacteria in the wing, drumstick and breast meats. The numbers of L. monocytogenes, TMAB and psychrotrophic bacteria in marinated groups were 1.0–3.0 log10 lower than control groups at the end of the storage. The marinades that people can prepare with the natural ingredients existing in their kitchen would enable microbiologically more reliable chicken meats.

Fate of Listeria monocytogenes in the Presence of Resident Cheese Microbiota on Common Packaging Materials.

Literature data regarding the survival of microorganisms on materials used for food package purposes are scarce. The aim of the current study is to assess the survival of Listeria monocytogenes on different packaging materials for dairy products during extended storage at different temperatures. Three packaging materials (5 × 5 cm) were contaminated with a cocktail of five strains of Listeria monocytogenes suspended in a cheese homogenate, including the cheese’s native microbial population. Contaminated samples were incubated at 37°, 12°, and 4°C and periodically analyzed up to 56 days. The evolution of the total viable count and pathogen population was evaluated. At 37°C, the results showed that Listeria monocytogenes was no longer detected on polyethylene-coated nylon (B) by day 4 and on polyethylene-coated parchment (A) and greaseproof paper (C) by day 7. Interestingly, the initial cell population (ranging between 2.5 and 2.7 log CFU/cm2) of Listeria monocytogenes increased to 3 log CFU/cm2 within 4 days of storage at 12°C on A and C. During storage, the number remained fairly constant at 12°C and 4°C on two materials (A–C) and decreased slowly on the third one (B). This study shows that survival of Listeria monocytogenes on packaging materials for dairy products will be higher when stored at 4 or 12°C compared to 37°C. The survival of Listeria monocytogenes on the packaging materials raises concerns of cross-contamination during food handling and preparation at catering and retail premises and within the home, highlighting the importance of treating the packaging materials as a potential source of cross-contamination. These initial findings may aid in quantifying risks associated with contamination of food packaging materials.

Behavior of Listeria monocytogenes in the presence or not of intentionally-added lactic acid bacteria during ripening of artisanal Minas semi-hard cheese

The fate of Listeria monocytogenes during ripening of artisanal Minas semi-hard cheese, as influenced by cheese intrinsic properties and by autochthonous (naturally present) or intentionally-added anti-listerial lactic acid bacteria (LAB) was modeled. Selected LAB strains with anti-listerial capacity were added or not to raw or pasteurized milk to prepare 4 cheese treatments. Counts of LAB and L. monocytogenes, pH, temperature and water activity were determined throughout cheese ripening (22 days, 22±1ᵒC). Different approaches were adopted to model the effect of LAB on L. monocytogenes: an independent approach using the Huang primary model to describe LAB growth and the linear decay model to describe pathogen inactivation; the Huang-Cardinal [pH] model using the effect of pH variation in a dynamic tertiary approach; and the Jameson-effect with Nmax tot model which simultaneously describes L. monocytogenes and LAB fate. L. monocytogenes inactivation occurred in both treatments with added LAB and inactivation was faster in raw milk cheese (−0.0260 h−1) vs. pasteurized milk cheese (−0.0182 h−1), as estimated by the linear decay model. Better goodness-of-fit was achieved for the cheeses without added LAB when the Huang primary model was used. A faster and great pH decline was detected for cheeses with added LAB, and the Huang-Cardinal [pH] model predicted higher pathogen growth rate in cheese produced with raw milk, but greater L. monocytogenes final concentration in pasteurized milk cheese. The Jameson-effect model with Nmax tot predicted that LAB suppressed pathogen growth in all treatments, except in the treatment with pasteurized milk and no LAB addition. The Huang-Cardinal [pH] model was more accurate in modeling L. monocytogenes kinetics as a function of pH changes than was the Jameson-effect model with Nmax tot as a function of LAB inhibitory effect based on the goodness-of-fit measures. The Jameson-effect model may however be a better competition model since it can more easily represent L. monocytogenes growth and death. This study presents crucial kinetic data on L. monocytogenes behavior in the presence of competing microbiota in Minas semi-hard cheese under dynamic conditions.

Fate of Listeria monocytogenes on Broccoli and Cauliflower at Different Storage Temperatures

Understanding a food's ability to support the growth and/or survival of a pathogen throughout the supply chain is essential to minimizing large-scale contamination events. The purpose of this study was to examine the behavior (growth and/or survival) of Listeria monocytogenes on broccoli and cauliflower florets stored at different postharvest temperatures utilized along the supply chain. Broccoli and cauliflower samples were inoculated with L. monocytogenes at approximately 3 log CFU/g and stored at 23 ± 2, 12 ± 2, 4 ± 2, and -18 ± 2°C. Samples were evaluated for L. monocytogenes levels after 0, 0.167 (4 h), 1, 2, 3, and 4 days at 23 ± 2°C; 0, 0.167, 1, 2, 3, 4, 7, 10, and 14 days at 12 ± 2°C; 0, 0.167, 1, 2, 3, 4, 7, 10, 14, 21, and 28 days at 4 ± 2°C; and 0, 1, 7, 28, 56, 84, 112, 140, and 168 days at -18 ± 2°C. L. monocytogenes populations were determined by plating samples onto tryptic soy agar and modified Oxford agar supplemented with nalidixic acid. Broccoli and cauliflower supported the growth of L. monocytogenes at 23, 12, and 4°C, and higher growth rates were observed at higher temperatures. Populations of L. monocytogenes on broccoli and cauliflower samples significantly increased within 1 day at 23°C (by 1.6 and 2.0 log CFU/g, respectively) (P ≤ 0.05). At 12°C, populations of L. monocytogenes on broccoli and cauliflower samples significantly increased over 14 days by 1.4 and 1.9 log CFU/g, respectively (P ≤ 0.05). No significant difference over time was observed in L. monocytogenes populations on broccoli and cauliflower samples held under refrigeration until populations began to grow by day 10 in both commodities (P > 0.05). Under frozen storage (-18°C), populations of L. monocytogenes survived on broccoli and cauliflower at least up to 168 days. Storage of broccoli and cauliflower at lower temperatures can minimize L. monocytogenes growth potential; growth rates were lower at 4°C than at 12 and 23°C.

Fate of Listeria monocytogenes in Ready-to-Eat Refrigerated Dips Treated with High Pressure Processing

Various outbreaks and recalls have been associated with Listeria monocytogenes contamination of ready-to-eat (RTE) food products, including dips. High pressure processing (HPP) is useful for reducing levels of bacteria in many RTE food products, but its efficacy for reduction of pathogens in RTE dips is not well understood. In this study, laboratory-prepared hummus, tahini, baba ghanoush, guacamole, and pesto were initially treated with HPP at 350 MPa for up to 240 s to assess L. monocytogenes inactivation and determine D-values. D350 MPa-values in hummus, guacamole, and baba ghanoush were 105.3, 71.3, and 34.0 s, respectively. No significant reduction in L. monocytogenes levels was observed in tahini or pesto at 350 MPa for 240 s or after additional treatment for up to 600 s at 600 MPa (P > 0.05). Overall, the results of this study highlight the efficacy of HPP for reducing L. monocytogenes levels in certain RTE dips and but not in others.

Fate of Listeria monocytogenes during Ripening of Iranian Traditional Koozeh Cheese Made from Raw Ewe's Milk

Fate of Listeria monocytogenes during Ripening of Iranian Traditional Koozeh Cheese Made from Raw Ewe's Milk

Hygienic Shortcomings of Frozen Dessert Freezing Equipment and Fate of Listeria monocytogenes on Ice Cream–Soiled Stainless Steel

Although frozen dairy desserts have a strong record of safety, recent outbreaks of foodborne disease linked to ice creams have brought new attention to this industry. There is concern that small-scale frozen dessert equipment may not comply with or be reviewed against published comprehensive design and construction sanitation specifications (National Sanitation Foundation or 3-A sanitary standards). Equipment sanitary design issues may result in reduced efficacy of cleaning and sanitation, thus increasing the likelihood of postprocess contamination with pathogenic bacteria. In this context, and given that Listeria monocytogenes outbreaks are of great concern for the frozen dessert industry, a complementary study was conducted to evaluate the fate of L. monocytogenes in ice cream mix on a stainless steel surface. Our results showed that L. monocytogenes survived for up to 6 weeks at room temperature and 9 weeks at 4°C in contaminated ice cream on a stainless steel surface. Furthermore, chlorine- and acid-based surface sanitizers had no detrimental effect on the L. monocytogenes when used at a concentration and contact time (1 min) recommended by the manufacturer; significant reduction in CFU required 5 to 20 min of contact time.

Fate of Listeria monocytogenes on Fresh Apples under Different Storage Temperatures.

Fresh apples are typically stored for up to 1 year commercially; different apple varieties require different storage temperatures to maintain their quality characteristics. There is sparse information available about Listeria monocytogenes survival on fresh apples under various storage temperatures. The objective of this study was to comprehensively evaluate the effect of storage temperature on apple fruit decay and L. monocytogenes survival. Unwaxed apple fruits of selected varieties (Fuji and Granny Smith) were dip inoculated in a three-strain L. monocytogenes cocktail to establish ∼3.5 and 6.0 Log10 CFU/apple. Twenty-four hours post-inoculation, apples were subjected to 1, 4, 10, or 22°C storage for up to 3 months. Apples under the different storage treatments were sampled at 1-, 4-, 7- and 14-day for short-term storage under all four tested temperatures, and 2-, 4-, 8-, and 12-week for long-term storage at 1, 4, and 10°C. A set of uninoculated and unwaxed apples were simultaneously subjected to the previously mentioned storage temperatures and sampled biweekly for their total bacterial count (TPC) and yeasts/molds (Y/M) count. During the 2-week short-term storage, L. monocytogenes population on organic Granny Smith apples stored at 1, 4, or 10°C was reduced by 0.2–0.3 Log. When apples were stored at 22°C, there was a 0.5–1.2 Log10 CFU/apple reduction 14-day post storage dependent on the initial inoculation level. During the 12-week cold storage under 1, 4, and 10°C, L. monocytogenes count on organic Granny Smith apples decreased by 0.5–1.5 Log10 CFU/apple for both inoculation levels. L. monocytogenes had similar survival pattern on conventional Granny Smith and Fuji apples with 0.8–2.0 Log10 CFU/apple reduction over a 3-month cold storage period. Interestingly, both TPC and Y/M count were stable regardless of apple variety or cultivation practice during the 12-week storage at all tested temperatures. In summary, while L. monocytogenes did not proliferate on apple surfaces during 12 weeks of refrigerated storage, only a limited reduction of L. monocytogenes was observed in this study. Therefore, the apple industry cannot rely on cold storage alone to control this pathogen. Additional interventions are needed to eradicate Listeria on fresh apples during long-term cold storage.

Behaviour of Listeria monocytogenes in Lighvan cheese following artificial contamination during making, ripening and storage in different conditions

This study investigated the behaviour and fate of Listeria monocytogenes at different ripening temperatures and NaCl concentrations in traditional Lighvan cheese. L. monocytogenes was added to raw sheep's milk. After producing the cheese, they were stored in 8%, 12% and 15% NaCl at 4, 9 and 14 °C. Sampling was performed for 150 days. Different temperature and NaCl concentrations had a significant effect on the survival of L. monocytogenes (P &lt; 0.001). The lowest growth and survival rates of L. monocytogenes were in 15% NaCl at 14 °C and 12% NaCl at 14 °C, respectively. Also, the highest growth and survival rates of the bacterium were in 8% NaCl at 4 °C.

Investigating the Effect of Different Treatments with Lactic Acid Bacteria on the Fate of Listeria monocytogenes and Staphylococcus aureus Infection in Galleria mellonella Larvae.

The use of Galleria mellonella as a model host to elucidate microbial pathogenesis and search for novel drugs and therapies has been well appreciated over the past years. However, the effect of microorganisms with functional appeal in the specific host remains scarce. The present study investigates the effect of treatment with selected lactic acid bacteria (LAB) with probiotic potential, as potential protective agents by using live or heat-killed cells at 6 and 24 h prior to infection with Listeria monocytogenes and Staphylococcus aureus or as potential therapeutic agents by using cell-free supernatants (CFS) after infection with the same pathogens. The employed LAB strains were Lactobacillus pentosus B281 and Lactobacillus plantarum B282 (isolated from table olive fermentations) along with Lactobacillus rhamnosus GG (inhabitant of human intestinal tract). Kaplan-Meier survival curves were plotted while the pathogen’s persistence in the larval hemolymph was determined by microbiological analysis. It was observed that the time (6 or 24 h) and type (live or heat-killed cells) of challenge period with LAB prior to infection greatly affected the survival of infected larvae. The highest decrease of L. monocytogenes population in the hemolymph was observed in groups challenged for 6 h with heat-killed cells by an average of 1.8 log units compared to non challenged larvae for strains B281 (p 0.0322), B282 (p 0.0325), and LGG (p 0.0356). In the case of S. aureus infection, the population of the pathogen decreased in the hemolymph by 1 log units at 8 h post infection in the groups challenged for 6 h with heat-killed cells of strains B281 (p 0.0161) and B282 (p 0.0096) and by 1.8 log units in groups challenged with heat-killed cells of LGG strain (p 0.0175). Further use of CFS of each LAB strain did not result in any significant prolonged survival but interestingly it resulted in pronounced decrease of L. monocytogenes in the hemolymph at 24 h and 48 h after infection by more than 1 log unit (p < 0.05) depending on the strain. The results of the present work support the broader use of G. mellonella larvae as a low cost in vivo tool for screening for probiotic properties.

Effect of sodium alginate coating incorporated with nisin, Cinnamomum zeylanicum, and rosemary essential oils on microbial quality of chicken meat and fate of Listeria monocytogenes during refrigeration

The present study was conducted to preserve the microbial quality of chicken meat fillets during storage time by using sodium alginate active coating solutions incorporated with different natural antimicrobials including nisin, Cinnamomum zeylanicum (cinnamon), and rosemary essential oils (EOs) which were added individually and in combination. The samples were stored in refrigeration condition for 15days and were analyzed for total viable count, Enterobacteriaceae count, lactic acid bacteria count, Pseudomonas spp. count, psychrotrophic count, and yeast and mold count, as well as fate of inoculated Listeria monocytogenes at 3-day intervals. Results indicated that values of tested microbial indicators in all samples increased during storage. Antimicrobial agents, when used in combination, had stronger effect in preserving the microbial quality of chicken meat samples rather than their individual use and the strongest effect was observed in samples coated with alginate solution containing both cinnamon and rosemary EOs (CEO+REO). However, all treatments significantly inhibited microbial growth when compared to the control (P<0.05). Therefore, based on the results of this study, application of alginate coating solutions containing nisin, cinnamon, and rosemary EOs as natural preservatives is recommended in meat products especially in chicken meats.

Fate of Listeria monocytogenes in Fresh Apples and Caramel Apples

An outbreak of listeriosis in late 2014 and early 2015 associated with caramel apples led to questions about how this product became a vector for Listeria monocytogenes. This investigation aimed to determine information about the survival and growth of L. monocytogenes in both fresh apples and caramel apples, specifically examining the effects of site and level of inoculation, inoculum drying conditions, and storage temperature. At a high inoculation level (7 log CFU per apple), L. monocytogenes inoculated at the stem end proliferated on Gala caramel apples at both 5 and 25°C and on Granny Smith caramel apples at 25°C by as much as 3 to 5 log CFU per apple. Fresh apples and caramel apples inoculated at the equatorial surface supported survival but not growth of the pathogen. Growth rates (μmax) for apples inoculated at the stem end, as determined using the Baranyi and Roberts growth model, were 1.64 ± 0.27 and 1.38 ± 0.20 log CFU per apple per day for Gala and Granny Smith caramel apples, respectively, stored at 25°C. At a low inoculation level (3 log CFU per apple), L. monocytogenes inoculated at the stem end and the equatorial surface survived but did not grow on fresh Gala and Granny Smith apples stored at 25°C for 49 days; however, on caramel apples inoculated at the stem end, L. monocytogenes had significant growth under the same conditions. Although certain conditions did not support growth, the pathogen was always detectable by enrichment culture. The inoculation procedure had a significant effect on results; when the inoculum was allowed to dry for 24 h at 5°C, growth was significantly slowed compared with inoculum allowed to dry for 2 h at 25°C. Variation in stick materials did affect L. monocytogenes survival, but these differences were diminished once sticks were placed into caramel apples.

Microbiological shelf life at different temperatures and fate of Listeria monocytogenes and Escherichia coli inoculated in unflavored and strawberry yogurts

Three different trials were performed on unflavored and strawberry yogurts produced in a small-scale dairy plant. In the first trial, the microbiological shelf life of the products was evaluated at 4, 8, and 20°C. At 4°C the product showed low total viable counts until the end of the trial (d 35=3.0±0.7 and 1.5±0.0 log cfu/g in unflavored and strawberry yogurt, respectively). The loads were lower in strawberry yogurt at 4°C compared with unflavored yogurt because of the antimicrobial activity exerted by potassium sorbate present in the fruit puree added. Yeasts were confirmed to be the specific spoilage agents of this product, reaching rapidly high loads with thermal abuse (5.9–7.4 log cfu/g at d 18). In the second trial, Escherichia coli and especially Listeria monocytogenes added at 2 concentrations (2 and 5 log cfu/g) showed a rapid decrease in both types thanks to the acidic conditions provided by the products, but L. monocytogenes was very resistant; its presence was always detected until the end of the period considered (d 68). In the third trial, no statistically significant differences were detected between wild and acid-adapted strains of L. monocytogenes added to the products, due to the quick adaptation that probably occurred after inoculation.

The fate of Listeria monocytogenes in brine and on Gouda cheese following artificial contamination during brining

The fate of 3 different Listeria monocytogenes strains (Scott A, 2F and 6E) was studied independently in brine and on factory-scale Gouda cheeses that had been submerged in brine that was artificially contaminated with these individual strains. Viable numbers of L. monocytogenes in the brine decreased during brining (0, 1, 2.9 and 8.9 d). L. monocytogenes was enumerated on the surface of Gouda cheese directly after brining and over 26 weeks of ripening at 12.5 °C. Transfer of L. monocytogenes from brine to cheese during brining was limited. L. monocytogenes was detected in the outer layer of Gouda cheese but not in the centre directly after brining or during ripening. Throughout the ripening period, the viable numbers of L. monocytogenes declined significantly. This study adds to the understanding of the fate of L. monocytogenes in brine and on Gouda cheese, and demonstrates that growth of L. monocytogenes on Gouda cheese is not supported following contamination during brining.

Fate of Listeria monocytogenes in Gouda microcheese: No growth, and substantial inactivation after extended ripening times

This challenge study demonstrates that Listeria monocytogenes does not grow in Gouda cheese: during the first 8 weeks of ripening no growth was observed and between 8 and 52 weeks viable numbers declined significantly in a well-established Gouda microcheese system. Cheese milk was artificially contaminated just prior to addition of the starter culture. Three individual L. monocytogenes strains were used, including strains originating from cheese, a cheese plant environment and a reference strain. During curd formation, viable numbers of L. monocytogenes increased by 0.5 log cfu g−1, resulting from entrapment in the curd. No growth was observed during the first 8 weeks of ripening. A significant decline in the viable numbers of L. monocytogenes was observed in Gouda cheese that was ripened for longer than 8 weeks. Two factors that could possibly control the fate of L. monocytogenes in Gouda cheese were lactic acid and water activity.

Modeling growth kinetics of Listeria monocytogenes in pork cuts from packaging to fork under different storage practices

The fate of Listeria monocytogenes in fresh meat products during transport and storage at retail and then at the consumer's house is poorly understood. In this study microbial behavior and concentration of L. monocytogenes in ten lots of naturally contaminated loin chops have been evaluated under four different storage scenarios throughout the product shelf life. Between-and within-lot variability on loin chops, as well as impact of environmental temperatures on pathogen growth were investigated. Secondly, distributions of the microbial concentration in the naturally contaminated lots were fitted using the maximum likelihood estimation (MLE) and variability in growth potential at dynamic storage was assessed by applying a validated predictive model from the literature, together with MonteCarlo simulation techniques. The results show that model estimations are consistent to the observed data even though variability in the growth kinetic parameters impacts the growth of L. monocytogenes in loin chops throughout the product shelf life. Overall, storage at mean refrigerator temperatures did not increase the populations of L. monocytogenes over 2 log colony forming unit per gr (cfu/g). In contrast, final storage at abuse temperatures produced microbial counts greater than 3 log cfu/g for some lots, which would require a more severe heat inactivation treatment before consumption. The results of this study should be used by risk managers to predict the effect of cooking in pathogen inactivation in loin chops, as well as the risk of cross contaminations.

Fate of Listeria monocytogenes and Escherichia coli O157:H7 in the presence of natural background microbiota on conventional and organic lettuce

Foodborne illnesses due to the consumption of contaminated raw vegetables is a continuing food safety concern. The limited efficacy of chlorine products to disinfect in fresh-cut industries, has led to study other methods or strategies to improve the safety of processed fresh-cut products. It has been reported that the presence of competing microorganisms on the surfaces of fresh produce can contribute to the reduction of pathogens. The aim of this study was to evaluate the interactions between the natural background microbiota of shredded conventional and organic lettuce and Listeria monocytogenes and Escherichia coli O157:H7. The effect of different initial load of background microbiota (‘low’, ‘medium’ and ‘high’) was tested for its ability to reduce L. monocytogenes and E. coli O157:H7 populations on shredded lettuce during storage at 10 ± 1 °C for 8 days. After the different pre-conditioning steps in order to obtain different initial loads of microbiota, in general, we observed that varying its size had no effect on L. monocytogenes and E. coli O157:H7 survival/growth during the storage period. Only differences on the survival/growth of L. monocytogenes and E. coli O157:H7 inoculated onto organic and conventional lettuce, respectively at the end of storage period at 10 °C were found. These results highlight the necessity for corrective measures to avoid contamination of fresh-cut vegetables with foodborne pathogens.