Inhibition Of Listeria Monocytogenes Research Articles

Nanoemulsions of thymol and eugenol co-emulsified by lauric arginate and lecithin

Lauric arginate (LAE) is a cationic surfactant with excellent antimicrobial activities. To incorporate essential oil components (EOCs) in aqueous systems, properties of EOC nanoemulsions prepared with a LAE and lecithin mixture were studied. The LAE–lecithin mixture resulted in stable translucent nanoemulsions of thymol and eugenol with spherical droplets smaller than 100nm, contrasting with the turbid emulsions prepared with individual emulsifiers. Zeta-potential data suggested the formation of LAE–lecithin complexes probably through hydrophobic interaction. Negligible difference was observed for antimicrobial activities of nanoemulsions and LAE in tryptic soy broth. In 2% reduced fat milk, nanoemulsions showed similar antilisterial activities compared to free LAE in inhibiting Listeria monocytogenes, but was less effective against Escherichia coli O157:H7 than free LAE, which was correlated with the availability of LAE as observed in release kinetics. Therefore, mixing LAE with lecithin improved the physical properties of EOC nanoemulsions but did not improve antimicrobial activities, especially against Gram-negative bacteria.

The potential influence of two Enterococcus faecium on the growth of Listeria monocytogenes

Two strains of Enterococcus faecium isolated from meat products were analyzed for the antimicrobial activity, safety and inhibition of Listeria monocytogenes in co-culture experiments. The production of bacteriocin-like substances and the presence of enterocin A, B, P genes (entA, entB, entP) were confirmed in E. faecium B1 whilst E. faecium B2 harbored neither of these characteristics. None of E. faecium strains harbored the virulent determinants studied (esp, hylEfm, IS 16, VanA and VanB) and were sensitive to most common antibiotics. In the co-culture experiment, both E. faecium B1 and E. faecium B2 had an inhibition effect towards L. monocytogenes. However, E. faecium B1 inhibited the growth of L. monocytogenes in the early stages of co-culture, and then probably reduced the cell counts of L. monocytogenes until an undetectable level after four days. Thus the cell counts of L. monocytogenes stayed at the initial inoculum level during the co-culture with E. faecium B2, suggesting that the bacteriocin-like substance played an important role in the inhibition effect. Meanwhile, the pH in co-culture declined lower than that in mono-culture in the early days, indicating the production of acid might participate in the inhibition process. Also, E. faecium B1 could be considered to be used as an effective potential bio-protective culture, so as to improve the safety of meat products.

Inhibition of Listeria monocytogenes on cooked cured chicken breasts by acidified coating containing allyl isothiocyanate or deodorized Oriental mustard extract

Ready-to-eat meats are considered foods at high risk to cause life-threatening Listeria monocytogenes infections. This study screened 5 L. monocytogenes strains for their ability to hydrolyze sinigrin (a glucosinolate in Oriental mustard), which formed allyl isothiocyanate (AITC) and reduced L. monocytogenes viability on inoculated vacuum-packed, cooked, cured roast chicken slices at 4 °C. Tests involved incorporation of 25–50 μl/g AITC directly or 100–250 mg/g Oriental mustard extract in 0.5% (w/v) κ-carrageenan/2% (w/v) chitosan-based coatings prepared using 1.5% malic or acetic acid. L. monocytogenes strains hydrolyzed 33.6%–48.4% pure sinigrin in MH broth by 21 d at 25 °C. Acidified κ-carrageenan/chitosan coatings containing 25–50 μl/g AITC or 100–250 mg/g mustard reduced the viability of L. monocytogenes and aerobic bacteria on cooked, cured roast chicken slices by 4.1 to >7.0 log10 CFU/g compared to uncoated chicken stored at 4 °C for 70 d. Coatings containing malic acid were significantly more antimicrobial than those with acetic acid. During storage for 70 d, acidified κ-carrageenan/chitosan coatings containing 25–50 μl/g AITC or 250 mg/g mustard extract reduced lactic acid bacteria (LAB) numbers 3.8 to 5.4 log10 CFU/g on chicken slices compared to uncoated samples. Acidified κ-carrageenan/chitosan-based coatings containing either AITC or Oriental mustard extract at the concentrations tested had the ability to control L. monocytogenes viability and delay growth of potential spoilage bacteria on refrigerated, vacuum-packed cured roast chicken.

Starch-halloysite nanocomposites containing nisin: Characterization and inhibition of Listeria monocytogenes in soft cheese

Abstract Starch/halloysite/nisin nanocomposite films were developed as active antimicrobial packaging. Nanocomposites without nisin and control films (containing starch and glycerol only) were also prepared. Scanning electron microscopy revealed that all samples were homogeneous, halloysite nanotubes (HNT) were dispersed in starch matrix, and film surfaces denoted aggregates as higher amount of nisin was added. X-ray diffraction spectra displayed alterations in typical starch peaks after HNT and nisin incorporation, indicating a decrease in polymer crystallization. Mechanical properties were improved when HNT was incorporated, but inferior values of Young modulus and tensile strength were obtained with nisin addition. Thermal stability decreased for bionanocomposites containing nisin, which showed T max values about 20 °C lower than films without nisin. The antimicrobial activity was tested against Listeria monocytogenes, Clostridium perfringens and Staphylococcus aureus in skimmed milk agar and all microorganisms were inhibited by nanocomposites containing nisin. These active films were applied on Minas Frescal cheese surface previously inoculated with L. monocytogenes . After 4 days, antimicrobial nanocomposite films with 2 g/100 g nisin significantly reduced the initial counts of the bacterium and those with 6 g/100 g nisin completely inhibited L. monocytogenes . Results showed that nisin supported in starch/halloysite films can be an active and useful barrier to control food contamination.

Inhibition of Listeria monocytogenes in vitro and in goat milk by liposomal nanovesicles containing bacteriocins produced by Lactobacillus sakei subsp. sakei 2a

Lactobacillus sakei subsp. sakei 2a is a bacteriocinogenic lactic acid bacteria isolated from a Brazilian meat product, capable to inhibit Listeria monocytogenes in vitro and in foods. In this study, bacteriocin produced by this strain were encapsulated in phosphatidylcholine (FC) and 1,2-dioleoyloxy-3-trimethylammonium-propane (DOTAP) liposomes, separately and in combination, were characterized and evaluated for activity against L. monocytogenes in vitro and in experimentally contaminated UHT goat milk, during storage at 7 °C for 14 days and 30 °C for 24 h. The FC and DOTAP/FC (3:1) nanovesicles containing bacteriocins (12.800 AU mL−1) presented zeta potential of −1.54 and + 38.13 mV, Entrapment Efficiency of 80.0% and 94.1%, and diameter of 91.19 and 81.49 nm, respectively. DOTAP/FC nanovesicle presented excellent stability, and maintained the same physicochemical characteristics over 28 days. Both free and encapsulated bacteriocins controlled L. monocytogenes growth in BHI medium and goat milk stored at 30 °C for at least 8 h, in a similar pattern. After 24 h in BHI medium, bacteriocins encapsulated in FC nanovesicles were more effective (p < 0.05) than free bacteriocins. However, in goat milk, no significant differences (p ≥ 0.05) were observed for the two types of nanovesicles. At 7 °C, both free and encapsulated bacteriocins retarded the L. monocytogenes growth, and after 5 days, counts were 5 log lower than in the controls, both in BHI and in goat milk. Encapsulation of bacteriocin in FC and DOTAP/FC nanovesicles did not affect the antimicrobial activity, but the advantages of their application for control of L. monocytogenes in goat milk based dairy products, when compared to free bacteriocins, remain unclear and more studies are needed.

Anti-Listeria Activity of Bioactive Food Packaging on Artificially Contaminated Sliced Cheese

The aims of this study were to (1) study the optimal growth condition for two Lactococcus lactis strains to produce the anti-listeria compounds and (2) evaluate the effect of films activated with a twofold concentrated cell-free supernatant of La. lactis to inhibit Listeria monocytogenes. For the growth conditions, skimmed milk added to either Ml7 or MRS provided the highest levels of anti-listeria activity assayed (800 arbitrary unit per milliliter) for both La. lactis strains. A significant decrease of Li. monocytogenes counts was observed in cheese packed in films treated with an average decrease of 2.12 log colony-forming unit per gram after 15 days of storage. Practical Applications The antimicrobial film for food packaging can be used for the preservation of perishable foods such as the sliced cheese. This film developed in our study inhibits Listeria monocytogenes growth in sliced cheese, and does not have an adverse effect on the lactic microbiota, contributing to the preservation of the quality of the product. Thus, it could be a useful tool for the control of the development of pathogens in foods during storage of dairy products.

Control of Listeria monocytogenes by applying ethanol-based antimicrobial edible films on ham slices and microwave-reheated frankfurters

The objectives of the study were to evaluate: (i) the efficacy of Na-alginate films immersed in 40% v/v distillery ethanol and traditional Greek alcoholic beverages (ABs), namely “tsipouro”, “raki”, and “ouzo” to inhibit Listeria monocytogenes growth on frankfurters and ham slices and (ii) the impact of edible films-ABs on heat sensitivity of the pathogen after microwave (MW) reheating of frankfurters in water during storage at 4 and 10 °C. Samples without edible films (controls) or with edible films but free of distillery ethanol or ABs were also tested. Two pieces of frankfurters were placed between two edible films, while every ham slice was covered by a film from both sides. On ham, all edible films immersed in ABs maintained levels of L. monocytogenes at least 5.0 log CFU/cm2 lower (p < 0.05) than controls after 81 and 52 days at 4 and 10 °C, respectively. Moreover, on frankfurters packaged with edible films–ethanol or -ABs, L. monocytogenes population remained 4.0–4.5 log CFU/cm2 lower (p < 0.05) than controls after 40 days of storage at 4 °C, while growth suppression of 0.8–2.0 log CFU/cm2 was observed after 15 days at 10 °C, at all assays except for samples packaged with raki. However, the results from reheating experiments revealed that subsequent inadequate MW reheating of frankfurters packaged with edible films-ABs would not lead to remarkable inactivation of the pathogen, since cross-protection against thermal stress is been acquired as a result of products' exposure to sub-lethal stresses such as low pH formed by metabolic products, indigenous microbiota, and ethanol exposure (ca. 2.4–2.7% w/w) during cold storage. Our findings suggest that food safety regulations enabling antimicrobial interventions for the safety of ready to eat meat products should ensure both low levels of L. monocytogenes during storage and minimum tolerance to recommended consumer practices, such as MW reheating.

Antimicrobial and antioxidative activities of peptides from goat milk hydrolyzed with various protease

Milk is highly nutritious food containing protein as a good source of bioactive peptide that beneficial for health. This research was aimed to explore potency of bioactive peptide derived from goat milk as an antimicrobial and antioxidant. Milk was hydrolyzed by trypsin, chymotrypsin, pepsin, or protease Bacillus sp. E.13. The peptides obtained were screened for antimicrobial activities through incubation with Staphylococcus aureus, Listeria monocytogenes, Salmonella thyphimurium and Escherichia coli at 10 6 CFU/mL at 37°C for two hours and plated on Mueller Hinton agar. Antimicrobial activities were determined by comparing the total bacterial colonies to that of bacterial control without peptides addition. Oxidative activity was determined by 2.2’-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and 2.2-diphenyl-1-picrylhydrazyl (DPPH) assays. Antimicrobial activities were shown in peptides produced from hydrolysis of goat milk protein by pepsin at 37°C, pH 2 for 90 min and by Bacillus sp. E.13 protease at 55°C, pH 11 for 30 and 60 min but the activities were not detected in peptides from hydrolysis by trypsin and chymotrypsin. Peptide from protein hydrolysis by Bacillus sp. E.13 protease could inhibit Listeria monocytogenes, Salmonella thyphimurium and Escherichia coli up to 5 log cycles. The antimicrobial peptides could scavenge ABTS radical up to 86 % and DPPH radical up to 9 % at 68 μg protein/mL. Results indicated that goat milk protein hydrolyzed by Bacillus sp. E.13 protease is potential as antimicrobes and antioxidant.

Application of a novel antimicrobial coating on roast beef for inactivation and inhibition of Listeria monocytogenes during storage

The antilisterial efficacy of novel coating solutions made with organic acids, lauric arginate ester, and chitosan was evaluated in a three-stage study on inoculated roast beef for the first time. Ready-to-eat roast beef was specially ordered from the manufacturer. The meat surface was inoculated with five-strain Listeria monocytogenes cocktail inoculums at two different levels, ~3 and 6LogCFU/cm2 and treated with the stock solution (HAMS), the 1:5 diluted solution (MAMS), and the 1:10 diluted solution (LAMS) (stage 1). During the 20min contact time, the antimicrobial coatings reduced the Listeria populations by approximately 0.9–0.3LogCFU/cm2. The higher the concentrations of the antimicrobial solution, the better the antilisterial effects were. The treated inoculated beef samples were then stored at 4°C for 30days. During storage, Listeria growth inhibition effects were seen. While no growth was seen from the HAMS-treated samples, a 1.6LogCFU/cm2 increase was seen for MAMS-treated samples, a 4.6LogCFU/cm2 increase was seen for LAMS-treated samples, and a 5.7LogCFU/cm2 increase was seen for NoAMS-treated samples on Day 30 (~3LogCFU/cm2 inoculation level). In the second stage, the impact of the roast beef storage time on solution's antilisterial effect was evaluated. Results showed that the effect of the antimicrobial solution was dependent on both the initial inoculation levels and storage times. In stage 3, the effect of the antimicrobial solution on roast beef quality was studied with both instrument measurement and sensory evaluation. Minor changes in color, pH, and water activity were found. However, only limited sensory differences were seen between the treated and untreated samples. When panels were able to accurately find color differences between samples, they preferred the treated samples. The findings of this research proved the antilisterial efficacy of the novel antimicrobial solution and showed its potential for being used as a roast beef cut surface coating to control Listeria contamination and for color protection.

A Microplate Growth Inhibition Assay for Screening Bacteriocins against Listeria monocytogenes to Differentiate Their Mode-of-Action.

Lactic acid bacteria (LAB) have historically been used in food fermentations to preserve foods and are generally-recognized-as-safe (GRAS) by the FDA for use as food ingredients. In addition to lactic acid; some strains also produce bacteriocins that have been proposed for use as food preservatives. In this study we examined the inhibition of Listeria monocytogenes 39-2 by neutralized and non-neutralized bacteriocin preparations (Bac+ preps) produced by Lactobacillus curvatus FS47; Lb. curvatus Beef3; Pediococcus acidilactici Bac3; Lactococcus lactis FLS1; Enterococcus faecium FS56-1; and Enterococcus thailandicus FS92. Activity differences between non-neutralized and neutralized Bac+ preps in agar spot assays could not readily be attributed to acid because a bacteriocin-negative control strain was not inhibitory to Listeria in these assays. When neutralized and non-neutralized Bac+ preps were used in microplate growth inhibition assays against L. monocytogenes 39-2 we observed some differences attributed to acid inhibition. A microplate growth inhibition assay was used to compare inhibitory reactions of wild-type and bacteriocin-resistant variants of L. monocytogenes to differentiate bacteriocins with different modes-of-action (MOA) whereby curvaticins FS47 and Beef3, and pediocin Bac3 were categorized to be in MOA1; enterocins FS92 and FS56-1 in MOA2; and lacticin FLS1 in MOA3. The microplate bacteriocin MOA assay establishes a platform to evaluate the best combination of bacteriocin preparations for use in food applications as biopreservatives against L. monocytogenes.

Antilisterial effects of different hop acids in combination with potassium acetate and potassium diacetate at 7 and 37 °C

This study was conducted to assess the effect of eight hop acid extracts (α-acid, β-acid, acid-iso, acid-tetra, potassium-iso, potassium-hexa, potassium-tetra, and potassium-rho) with/without potassium acetate/potassium diacetate salts (PAPD) on inhibition of Listeria monocytogenes in trypticase soy broth with yeast extract (TSBYE). Following overnight incubation at 37 °C, 50 ppm α-acid decreased Listeria from 6.0 to <1.0 log CFU/mL, with significant reduction to 3.6–3.8 log CFU/mL using β acid, acid-tetra, K-tetra, or K-hexa.No inhibition was seen for acid-iso, K-iso, K-rho and the control. After incubating Listeria with the five hop acids (α-acid, β-acid, acid-tetra, K-tetra, and K-hexa) at 25 ppm with/without 0.5% PAPD, Listeria population decreased from 5.7 log CFU/mL) to < 1.0 log CFU/mL in PAPD/α-acid, PAPD/β-acid, or PAPD/acid-tetra, with reduction to 1.8–4.2 log CFU/mL for the remaining except the control. When the hop acids at 25 ppm were exposed to 85 °C up to 30 min, α-acid maintained the most effective antilisteiral activity by reducing Listeria from 5.0 to <2.9 CFU/mL, regardless of heat exposure time. The minimal inhibitory concentration was 6.3 ppm for α-acid, β-acid and acid-tetra, with 12.5 ppm seen for K-tetra and K-hexa. During the incubation of hop extracts at 5 ppm/7 °C for 6 days, listeristatic effect was observed in the hop/PAPD mixtures and PAPD at 0.5 and 1%, with no listeristatic effect seen for a single addition of hop acids except β-acid. These findings indicated that the combination of hop/PAPD provided both stable and synergistic effects against Listeria growth compared to any single addition, regardless of incubation temperature and addition amount.

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Comparative Efficacy of Potassium Levulinate with and without Potassium Diacetate and Potassium Propionate versus Potassium Lactate and Sodium Diacetate for Control of Listeria monocytogenes on Commercially Prepared Uncured Turkey Breast

We evaluated the efficacy of potassium levulinate (KLEV; 0.0, 1.0, 1.5, and 2.0%) with and without a blend of potassium propionate (0.1%) and potassium diacetate (0.1%) (KPD) versus a blend of potassium lactate (1.8%) and sodium diacetate (0.125%) (KLD) for inhibiting Listeria monocytogenes on commercially prepared, uncured turkey breast during refrigerated storage. Product formulated with KLD or KLEV (1.5%) was also subsequently surface treated with 44 ppm of a solution of lauric arginate (LAE). Slices (ca. 1.25 cm thick and 100 g) of turkey breast formulated with or without antimicrobials were surface inoculated on both the top and bottom faces to a target level of ca. 3.5 log CFU per slice with a five-strain cocktail of L. monocytogenes, vacuum sealed, and then stored at 4°C for up to 90 days. Without inclusion of antimicrobials in the formulation, pathogen levels increased by ca. 5.2 log CFU per slice, whereas with the inclusion of 1.0 to 2.0% KLEV pathogen levels increased by only ca. 2.9 to 0.8 log CFU per slice after 90 days at 4°C. When 1.0% KLEV and KPD were included as ingredients, pathogen levels increased by ca. 0.8 log CFU per slice after storage at 4°C for 90 days, whereas a decrease of ca. 0.7 log CFU per slice was observed when 1.5 or 2.0% KLEV and KPD were included as ingredients. When used alone, KPD was not effective (≥5.8-log increase). As expected, KLD was effective at suppressing L. monocytogenes in uncured turkey breast. When uncured turkey breast was formulated with KLD or KLEV (1.5%) or without antimicrobials and subsequently surface treated with LAE, pathogen levels decreased by ca. 1.0 log CFU per package within 2 h; no differences (P ≥ 0.01) were observed in pathogen levels for product surface treated with or without LAE and stored for 90 days. Our results validate the use of KLEV to inhibit outgrowth of L. monocytogenes during refrigerated storage of uncured turkey breast. KLEV is at least as effective as KLD as an antilisterial agent.

Listeriaphages and coagulin C23 act synergistically to kill Listeria monocytogenes in milk under refrigeration conditions

Bacteriophages and bacteriocins are promising biocontrol tools in food. In this work, two Listeria bacteriophages, FWLLm1 and FWLLm3, were assessed in combination with the bacteriocin coagulin C23 to inhibit Listeria monocytogenes. Preliminary results under laboratory conditions demonstrated that both antimicrobials act synergistically when they were applied in suboptimal concentrations. The combined approach was further assessed in milk contaminated with 5×104CFU/ml L. monocytogenes 2000/47 and stored at 4°C for 10days. When used alone, phage FWLLm1 added at 5×106PFU/ml, FWLLm3 at 5×105PFU/ml and coagulin C23 at 584AU/ml kept L. monocytogenes 2000/47 counts lower than the untreated control throughout storage. However, when used in combination, inhibition was enhanced and in the presence of FWLLm1 and coagulin C23, L. monocytogenes 2000/47 counts were under the detection limits (less than 10CFU/ml) from day 4 until the end of the experiment. Resistant mutants towards phages and coagulin C23 could be obtained, but cross-resistance was not detected. Mutants resistant to FWLLm3 and coagulin C23 were also recovered from surviving colonies after cold storage in milk which may explain the failure of this combination to inhibit L. monocytogenes. Remarkably, the fraction of resistant mutants isolated from the combined treatment was lower than that from each antimicrobial alone, suggesting that synergy between bacteriocins and phages could be due to a lower rate of resistance development and the absence of cross-resistance.

Evaluation of Novel Micronized Encapsulated Essential Oil–Containing Phosphate and Lactate Blends for Growth Inhibition of Listeria monocytogenes and Salmonella on Poultry Bologna, Pork Ham, and Roast Beef Ready-to-Eat Deli Loaves

Essential oils and their constituents are reported to possess potent antimicrobial activity, but their use in food processing is limited because of low solubility in aqueous systems and volatilization during processing. Two proprietary noncommercial essential oil–containing phosphate blends were evaluated for antimicrobial activity against Salmonella enterica cocktail (SC)– and Listeria monocytogenes (Lm)–inoculated deli meat products made from pork, poultry, or beef. Four treatments were tested on restructured cured pork ham, emulsified chicken bologna, and restructured beef loaf: nonencapsulated essential oil with phosphate version 1 at 0.45% of final batch (EOV145; chicken and pork, or EEOV245 beef), micronized encapsulated essential oil with phosphate version 2 at 0.60% of final batch (EEOV260), a 2.0% potassium lactate (PL) control, and a negative control (CN) with no applied antimicrobial agent. Compared with the CN, none of the antimicrobial agents (EEOV260, EOV145, PL) successfully limited Lm or SC growth to <2.0 log cycles over 49 days or 35 days of refrigerated storage, respectively. The PL and EEOV260-treated ham loaves did show Lm growth limiting ability of up to 1 log cycle by days 35 and 42. On formed roast beef, the EEOV260 was able to extend the lag phase and inhibited the growth of Lm in the same manner as the PL. For SC-treated samples, the following effects were observed: in poultry bologna treated with EEOV260, a lag-phase extension was observed through 35 days of storage compared with the other samples. For pork deli loaves, the EEOV260 inhibited growth of SC at days 21 and 28 to the same level of efficacy as PL (0.5 log cycle). In roast beef samples, on day 35, the SC growth was inhibited ca. 0.5 log CFU/g by EEOV260 when compared with the CN. In conclusion the EEOV260 can function to replace PL to limit Salmonella and Lm growth in ready-to-eat deli products. Further testing is needed to ensure consumer acceptability.

Growth Inhibition of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 by D-Tryptophan as an Incompatible Solute

Under osmotic stress, bacterial cells uptake compatible solutes such as glycine-betaine to maintain homeostasis. It is unknown whether incompatible solutes exist that are similar in structure to compatible solutes but have adverse physiological effects on bacterial physiology. The objective of this study was to evaluate solute incompatibility of various amino acids against bacterial growth. Bacterial growth was evaluated by changes in optical density at 595 nm in peptone-yeast-glucose (PYG) broth. Twenty-three amino acids with l and/or d isomers were examined for the effect of bacterial growth inhibition. Among the various amino acids examined, d-tryptophan (~ 40 mM) in PYG broth supplemented with 0 to 4% (wt/vol) salt inhibited the growth of Listeria monocytogenes, Salmonella enterica, and Escherichia coli O157:H7 at 25°C. d-Tryptophan (30 to 40 mM) completely inhibited the growth of E. coli O157:H7 and Salmonella in the presence of <3% salt, but the growth of L. monocytogenes was not completely inhibited under the same conditions. Low concentrations of salt (0 to 2% NaCl) with d-tryptophan did not significantly inhibit the growth of all bacteria except L. monocytogenes, which was relatively inhibited at 0% NaCl. The effect of d-tryptophan differed depending on the bacterial species, illustrating the difference between gram-positive and gram-negative bacteria. These results indicate that the uptake of d-tryptophan as a compatible solute during osmotic stress may inhibit bacterial growth. The antibacterial effect of d-tryptophan found in this study suggests that d-tryptophan could be used as a novel preservative for controlling bacterial growth in foods.

Effect of chitosan on spoilage bacteria, Escherichia coli and Listeria monocytogenes in cured chicken meat

The effects of essential oil (EO) of oregano and chitosan on the microbial quality and growth inhibition of Listeria monocytogenes and Escherichia coli O157:H7 in the Iranian traditional ready-to-barbecue chicken was evaluated. Thus, three groups of samples were prepared. One of them was considered to evaluate for aerobic plate count (APC), lactic acid bacteria (LAB), psychrophilic and enterobacteriacae counts and the other two groups were inoculated with E. coli O157:H7 and L. monocytogenes 4b to investigate the effect of oregano EO and chitosan on pathogenic bacteria. All groups were stored at 3, 8 and 20°C. Oregano showed antibacterial effects against APC, LAB, psychrophilics, enterobacteriacae and E. coli O157:H7, whereas, such an effect was not observed against L. monocytogenes. Chitosan individually did not show an inhibitory effect on the spoilage-inducing bacteria and E. coli, but was effective against L. monocytogenes. Using chitosan and oregano EO in combination can reduce the number of spoilage and safety indicators and also the two food-borne pathogens in ready-to-barbecue chicken meat.

Functional properties of peanut fractions on the growth of probiotics and foodborne bacterial pathogens.

Various compounds found in peanut (Arachis hypogaea) have been shown to provide multiple benefits to human health and may influence the growth of a broad range of gut bacteria. In this study, we investigated the effects of peanut white kernel and peanut skin on 3 strains of Lactobacillus and 3 major foodborne enteric bacterial pathogens. Significant (P < 0.05) growth stimulation of Lactobacillus casei and Lactobacillus rhamnosus was observed in the presence of 0.5% peanut flour (PF) made from peanut white kernel, whereas 0.5% peanut skin extract (PSE) exerted the inhibitory effect on the growth of these beneficial microbes. We also found that within 72 h, PF inhibited growth of enterohemorrhagic Escherichia coli O157:H7 (EHEC), while PSE significantly (P < 0.05) inhibited Listeria monocytogenes but promoted the growth of both EHEC and Salmonella Typhimurium. The cell adhesion and invasion abilities of 3 pathogens to the host cells were also significantly (P < 0.05) reduced by 0.5% PF and 0.5% PSE. These results suggest that peanut white kernel might assist in improving human gut flora as well as reducing EHEC, whereas the beneficial effects of peanut skins require further research and investigation.

Bacteriocin production and inhibition of Listeria monocytogenes by Lactobacillus sakei subsp. sakei 2a in a potentially synbiotic cheese spread

Survival, bacteriocin(s) production, and antilisterial effect of Lactobacillus sakei subsp. sakei 2a were evaluated in a potentially synbiotic cheese spread, throughout storage at 4 °C and 15 °C for up to 28 days, using culture-dependent (plate count) and culture-independent (qPCR) methods. Bacteriocin(s) production in the food product was monitored by phenotypic and molecular (RT-qPCR) techniques. Three cheese spread trials (T) containing the prebiotic fiber inulin were produced in duplicates and studied: T1 (control – without inoculation of lactic acid bacteria); T2 (inoculated with the non-bacteriocinogenic Lb. sakei ATCC 15521 strain), and T3 (inoculated with the bacteriocinogenic Lb. sakei 2a strain). The cheese spreads were challenged with Listeria monocytogenes serotypes 4b and 1/2a, individually added to the food product. The counts of Lb. sakei 2a in the cheese spread T3 remained high during storage and the growth of L. monocytogenes was inhibited at both temperatures, especially L. monocytogenes 4b in the food product kept at 15 °C due to the production of bacteriocins (up to 6,400 AU/mL). Expression of the genes sakP and sakQ encoding for bacteriocins production during the cheese spread storage was demonstrated. Lb. sakei 2a can be used for production of potentially synbiotic cheese spreads with increased safety.

Lactic acid Bacteria Isolated from Raw Milk Cheeses: Ribotyping,Antimicrobial Activity against Selected Food Pathogens and Resistance to Common Antibiotics

Fermentation with lactic acid bacteria is one of the oldest and effective methods of food preservation that meets the increasing drive of many consumers for foods perceived as minimally processed or free of unwanted chemical preservatives. The isolation and characterization of new wild LAB strains showing potential for application in food preservation may contribute to the processing of food products with good flavor and increasing safety. In the present work ninety-six LAB isolated from raw milk cheeses were subject to a preliminary characterization via identification (ribotyping) and screened for antimicrobial activity against Listeria monocytogenes, Escherichia coli, and Salmonella Newport, while the antibiotic resistance of the isolates against several clinic antibiotics were also studied. Most isolates of interest were identified as Lactobacillus paracasei ss. paracasei, of which, five were shown to completely inhibit Listeria monocytogenes, one inhibited Escherichia coli, five had inhibitory activity against Salmonella Newport, and five were active against both Listeria monocytogenes and Salmonella Newport. The Etest method determined that the isolates were sensitive to β-lactams, including amoxicillin and ampicillin, but were resistant to glycopeptides and aminoglycosides.