Antilisterial Activity Research Articles

Antilisterial Activity of Polypropylene Film Coated with Chitosan with Propolis and/or Bee Pollen in Food Models.

The aim of the study was to evaluate the effect of propylene film coated with solution of chitosan (CH), ethanolic extracts of propolis (EEP), and bee pollen (EEBP) and its combination on L. monocytogenes number in wrapped salmon, salami, and cheese. Sterile fragments of propylene film were coated with solution containing CH, CH+EEP, CH+EEBP, and CH+EEP+EEBP. The coated film was applied directly after preparation (AP) after 10 days of storage from preparation (AS). L. monocytogenes strains isolated from cheese, salmon, and salami were transferred on adequate food type. ATCC 19111 reference strain was placed on all examined slices. Contaminated slices were wrapped in the coated film. The film adhered strictly to the slices surface and was left for 0, 1, 6, 12, and 24 hours. Antilisterial activity of AP film was additionally assessed during 15-day storage of products wrapped in the coated film. In conclusion, the chitosan-coated film exhibited antibacterial activity. Incorporation of EPP and EEBP enhanced this activity. The antilisterial activity depended on the type and concentration of solutions, the types of food, and the origin of strains. This study proved that the time that passed since the use of coated film for packing food was of great importance.

Bacteriocin production and adhesion properties as mechanisms for the anti-listerial activity of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA

Probiotics play an important role in maintaining a healthy and stable intestinal microbiota, primarily by preventing infection. Probiotic lactic acid bacteria (LAB) are known to be inhibitory to many bacterial enteric pathogens, including antibiotic-resistant strains. Whilst the positive role that probiotics have on human physiology, specifically in the treatment or prevention of specific infectious diseases of the gastro-intestinal tract (GIT) is known, the precise mechanistic basis of these effects remains a major research goal. In this study, molecular evidence to underpin the protective and anti-listerial effect of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA against orally administered Listeria monocytogenes EGDe in the GIT of mice is provided. Bacteriocins plantaricin 423 and mundticin ST4SA, produced by L. plantarum 423 and E. mundtii ST4SA, respectively, inhibited the growth of L. monocytogenes in vitro and in vivo. Bacteriocin-negative mutants of L. plantarum 423 and E. mundtii ST4SA failed to exclude L. monocytogenes EGDe from the gastrointestinal tract (GIT) of mice. Furthermore, L. plantarum 423 and E. mundtii ST4SA failed to inhibit recombinant strains of L. monocytogenes EGDe in vivo that expressed the immunity proteins of the two bacteriocins. These results confirmed that bacteriocins plantaricin 423 and mundticin ST4SA acted as anti-infective mediators in vivo. Compared to wild type strains, mutants of L. plantarum 423 and E. mundtii ST4SA, in which the adhesion genes were knocked out, were less effective in the exclusion of L. monocytogenes EGDe from the GIT of mice. This work demonstrates the importance of bacteriocin and adhesion genes as probiotic anti-infective mechanisms.

Controlled release of nisin from Neusilin particles to enhance food safety of sour curd cheese.

Nisin is frequently added as food additive to soft cheese to increase food safety against foodborne pathogens like Listeria monocytogenes. The goal of this study was the extension of the antimicrobial activity of nisin in sour curd cheese (SCC) by self-releasing adsorbed nisin from Neusilin UFL2 over production-based pH shift. First, the antimicrobial activity of nisin adsorbed to Neusilin UFL2 (UFL2-N) and free nisin was investigated in BHI broth at a pH range from 7.5 to 4.5 for each of six L. monocytogenes field isolates. UFL2-N showed similar minimal inhibition concentration to L. monocytogenes over time as free nisin. Distribution of nebulized, fluorescence-labelled UFL2 was homogenous on SCC surface. Thereafter, SCC surface was inoculated with L. monocytogenes and 0.004, 0.013, 0.026, and 0.132mgmL-1 UFL2-N or free nisin. In SCC, L. monocytogenes was below quantification limit at 0.132mgmL-1 UFL2-N or free nisin after 2days of ripening. Collectively, UFL2-N enabled a slow release and antilisterial activity in vitro as well as in cheese manufacturing.

Antilisterial efficacy of Lactobacillus brevis MF179529 from cow: an in vivo evidence

BackgroundListeria monocytogenes is an opportunistic foodborne pathogen that causes human Listeriosis and high mortality particularly in immunocompromised individuals. Pregnant women are more prone to L. monocytogenes infection resulting in abortions.In the present study, antilisterial activity of Lactobacillus brevis (LB) MF179529, a probiotic bacterial strain, was investigated in a murine model.MethodsInitially a pilot study was conducted to determine the dose of L. monocytogenes required to cause symptomatic listeriosis. In the main trial, mice were divided into 4 groups. Group I was kept as negative control, group II was exposed to L. monocytogenes and maintained as positive control. Group III was fed with L. brevis only, while group IV received L. brevis for 3 days prior to L. monocytogenes infection. A volume of 200 μl of L. monocytogenes ATCC 19115 and L. brevis MF179529 bacterial suspension corresponding to cell density of 109CFU/ml were given to respective groups by intragastric route. Progress of infection was monitored for 7 days including general health scoring, listeria dispersion in organs, bacterial load in intestine and blood biochemistry were recorded on 3rd, 5th and 7th days post infection (dpi).ResultsClinical listeriosis was induced by 109CFU/ml of L. monocytogenes ATCC 19115 in mice.Animals of group IV displayed minor signs of infection. L. brevis supplementation resulted in significant reduction in dispersion and propagation of L. monocytogenes in liver, spleen and intestine. L. brevis MF179529 consumption led to a significant elevation of number of lactic acid bacteria and reduction of total plate count, anaerobic count and coliform population in intestine. Moreover, total leukocyte and neutrophil counts of treated animals were similar to the negative control while positive control group displayed higher number. Safety evaluation of L. brevis was performed by monitoring general health, hematological and serological parameters of L. brevis fed and negative control group (group III and I). No significant difference in feed intake, body temperature, body weight and blood picture could be detected in L. brevis supplemented and control groups.ConclusionOur results indicate ameliorative role of L. brevis in L. monocytogenes infection and suggest that L. brevis could be used for prophylactic measure.

Antilisterial Activity of Lactose Fatty Acid Esters in Milk

Carbohydrate fatty acid esters have been shown to inhibit the growth of bacteria in growth media. In this study, the antilisterial activities of the carbohydrate esters lactose monodecanoate (LMD) and lactose monolaurate (LML) were tested in milk samples with variable fat content (up to 10%) and at different temperatures (37°C, 24°C and 5°C) after inoculation with a 5-strain Listeria monocytogenes cocktail. Both LMD and LML demonstrated antilisterial properties against L. monocytogenes in milk, with the observed log reductions in the LMD milk samples being higher than those in the LML samples at all tested temperatures. LMD in 1% and 2% fat milk was found to be bactericidal with no Listeria growth by day 6. LMD showed significant antilisterial activity in milk samples containing up to 9% fat at 37° and in samples with up to 3.5% fat at 24°C and in milk samples with up to 2% fat at 5°C. LML showed significant Listeria log reductions at 37°C with milk containing up to 9% fat but showed no microbial inhibition in milk in any samples at 24°C and 5°C. Although carbohydrate fatty acid esters have proven microbial bactericidal/bacteriostatic properties in growth media, their antimicrobial properties are reduced in a food system containing fat and at temperatures lower than 37°C. The significance of this research is identifying food constituents and storage temperatures that limit the microbial inhibitory properties of lactose esters to ensure appropriate use as potential food grade antilisterial agents.

Bioactivity of Juniperus communis essential oil and post-distillation waste: Assessment of selective toxicity against food contaminants

Previously chemically characterized Juniperus communis essential oil (EO) and post-distillation waste (PDW) were tested for cytotoxicity and antimicrobial activity against food contaminants. Microdilution assay showed that PDW induced moderate antifungal (minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values, ranging between 0.118-0.900 mg mL-1), and an antibacterial effect against Listeria monocytogenes (MIC and minimum bactericidal concentration (MBC) were 0.39 and 0.74 mg mL-1, respectively). Combinations of EO/PDW with selected antibiotics induced synergistic antilisterial activity in the checkerboard assay. The MTT assay determined that cytotoxicity against colon cancer cells was high for the EO but negligible for PDW (IC50 values were 0.087-0.106 and 1.450-6.840 mg mL-1, respectively). The selectivity indices indicated high selectivity of PDW against tested fungi and L. monocytogenes. In the adhesion-inhibition assay, PDW reduced in vitro adhesion of L. monocytogenes to colon cells (29-62% of inhibition). In conclusion, PDW exhibited an antimicrobial effect against important food spoilage and poisoning fungi and L. monocytogenes, and also reduced in vitro adhesion of L. monocytogenes to colon cells. The results indicate that J. communis PDW could be considered as natural preservative against food spoilage and poisonous fungi, and as an adjuvant to conventional therapy of listeriosis.

Development of Hydrogels to Improve the Safety of Yukhoe (Korean Beef Tartare) by Reducing Psychrotrophic Listeria monocytogenes Cell Counts on Raw Beef Surface.

This study developed an antimicrobial hydrogel to control Listeria monocytogenes in Yukhoe (Korean beef tartare). Four hydrogels (hydrogel 1: 5% alginate+1% chitosan+0.2% CaCl2, hydrogel 2: 1% κ-carrageenan+1% chitosan, hydrogel 3: 2% κ-carrageenan+1% CaCl2, and hydrogel 4: 2% κ-carrageenan+3% CaCl2) were prepared. The hydrogels then absorbed 0.1% grapefruit seed extract (GSE) and 0.1% citrus extract (CE) for 30, 60, 120, and 240 min to be antimicrobial hydrogels. To select the most effective antimicrobial hydrogel, their swelling ratio (SR) and antilisterial activities were determined. The selected hydrogel (2×2 cm) was then placed on surface of beef (round; 3×3 cm), where L. monocytogenes (ca. 106 CFU/g) were inoculated, and the cell counts were enumerated on PALCAM agar. Among the hydrogels, the SR of hydrogel 1 increased with absorbing time, but other hydrogels showed no significant changes. Antimicrobial hydrogel 1 showed higher (p<0.05) antilisterial activity than other antimicrobial hydrogels, especially for the one absorbed the antimicrobial for 120 min. Thus, the antimicrobial hydrogel 1 absorbed antimicrobials for 120 min was applied on raw beef at 4℃, and reduced (p<0.05) more than 90% of L. monocytogenes on raw beef. These results indicate that antimicrobial hydrogel 1 formulated with 0.1% GSE or 0.1% CE is appropriate to improve the safety of Yukhoe by reducing psychrotrophic L. monocytogenes cell counts on raw beef.

Antilisterial and antistaphylococcal activity of a Lactococcus lactis strain isolated from Brazilian fresh Minas cheese

Abstract Lactococcus lactis QMF 11, isolated from Brazilian fresh cheese, produces bacteriocin like inhibitory substances (bac+). To evaluate L. lactis QMF11 possible application on biopreservation systems of dairy food, co‐inoculation studies were performed in pasteurized milk (8 °C, 10 days) targeting the inhibition of Listeria monocytogenes ATCC 7644 or Staphylococcus aureus ATCC 25923. Lactobacillus sakei ATCC 15521 was used as a negative control for bacteriocin production (bac−). L. monocytogenes and S. aureus reached 8 log CFU ml−1 and 5.4 log CFU ml−1 in monoculture, respectively, compared to &lt;2.3 log CFU ml−1 and 4.7 log CFU ml−1 in co‐culture with L. lactis QMF 11. Instead, in the presence of the bac−, L. monocytogenes population reached 7.3 log CFU ml−1 and S. aureus populations 5.5 log CFU ml−1. These results indicate that L. lactis QMF11 may have potential for be use as biopreservative culture in dairy products, mainly because of its antilisterial activity.Practical applicationsThere is a renewed interest in the use protective bacterial cultures or their metabolites to guarantee the microbiological safety and to extend the shelf life of dairy products, in a process called biopreservation. The research in this area has been leveraged by consumers demand for naturally preserved foods. Dairy products are natural niches for Lactococcus lactis strains, and these bacteria have been associated with food production and preservation since ancient times. As a dominant species in dairy ecosystems, L. lactis strains are very interesting because they are not likely to require regulatory approval for practical application as bioprotective cultures.

Inhibition of Listeria monocytogenes using biofilms of non-pathogenic soil bacteria (Streptomyces spp.) on stainless steel under desiccated condition

Of the 1648 microbial isolates from 133 soil samples collected from 30 diverse locations in the Republic of Korea, two isolates exhibited strong antilisterial activity and ability to grow to high populations (>8.0 log CFU/ml) in Bennett's broth. Isolates were identified as Streptomyces lactacystinicus (strain Samnamu 5–15) and Streptomyces purpureus (strain Chamnamu-sup 4–15). Both isolates formed biofilms on the surface of stainless steel coupons (SSCs) immersed in Bennett's broth within 24 h at 25 °C. Cells retained antilisterial activity after biofilm formation and showed significantly (P ≤ 0.05) enhanced resistance against dry conditions (43% relative humidity [RH]) compared to the cells not in biofilm. An initial population (ca. 3.2 log CFU/cm2) of Listeria monocytogenes inoculated on SSCs lacking Streptomyces biofilm decreased to 1.4 log CFU/cm2 within 48 h at 25 °C and 43% RH. In contrast, L. monocytogenes (3.3 log CFU/cm2) inoculated on SSCs containing Streptomyces biofilm decreased to populations below the theoretical detection limit (0.5 log CFU/cm2) within 24 h. The results indicate that biofilms formed by the Streptomyces spp. inhibitory to L. monocytogenes showed enhanced resistance to desiccation condition (43% RH) and effectively inhibited the growth of L. monocytogenes on the surfaces of SSCs. Antilisterial biofilms developed in this study may be applicable on desiccated environmental surfaces in food related environments such as food storage, handling, and processing facilities to enhance the microbiological safety of foods.

Antilisterial and Antibiofilm Activities of Pediocin and LAP Functionalized Gold Nanoparticles

In this study, we synthesized and assessed the antilisterial and antibiofilm properties of a novel gold nanocomposite, functionalized with antimicrobial peptide, Pediocin AcH and Listeria adhesion protein (LAP) for targeted inactivation of L. monocytogenes. The gold nanoparticle (GNP) and the gold nanocomposites (GNP-Pediocin-LAP) were characterized using spectroscopic and transmission electron microscopy (TEM) and their effect on human enterocyte-like Caco-2 cells were assessed by lactate dehydrogenase (LDH)-based cytotoxicity and inhibition of Listeria adhesion assay. The antilisterial and antibiofilm activities of nanocomposites on L. monocytogenes were determined by a plating method. TEM image analysis indicated that the size of GNP and the gold nanoconjugates to be about 20 nm and 40 nm, respectively; and spectroscopy indicated the successful loading of proteins onto citrate-stabilized GNPs. Gold nanocomposites were non-toxic and significantly reduced L. monocytogenes adhesion to Caco-2 cells. Relative to the GNP-Pediocin conjugate, the GNP-Pediocin-LAP conjugate showed 11.1% higher zone of inhibition in agar diffusion assay, and higher reduction (1.5 log10 CFU/mL) in L. monocytogenes counts. Same preparation also showed 24% and 31% more reduction in Listeria counts in biofilms after 24 h and 48 h of incubation, respectively. Nanocomposites were also highly effective in decontamination of L. monocytogenes on a miniature industrial conveyor system. Altogether, co-action of Pediocin and the LAP functionalized on GNP (GNP-Pediocin-LAP), demonstrated higher antilisterial and antibiofilm activities compared to the Pediocin functionalized GNP or Pediocin alone suggesting GNP can provide a platform to load multiple proteins for surface decontamination of L. monocytogenes in industrial settings.

A comparison of dynamic tertiary and competition models for describing the fate of Listeria monocytogenes in Minas fresh cheese during refrigerated storage

This study compares dynamic tertiary and competition models for L. monocytogenes growth as a function of intrinsic properties of a traditional Brazilian soft cheese and the inhibitory effect of lactic acid bacteria (LAB) during refrigerated storage. Cheeses were prepared from raw or pasteurized milk with or without the addition of selected LAB with known anti-listerial activity. Cheeses were analyzed for LAB and L. monocytogenes counts, pH and water activity (aw) throughout cold storage. Two approaches were used to describe the effect of LAB on L. monocytogenes: a Huang-Cardinal model that considers the effect of pH and aw variation in a dynamic kinetic analysis framework; and microbial competition models, including Lotka-Volterra and Jameson-effect variants, describing the simultaneous growth of L. monocytogenes and LAB. The Jameson-effect with γ and the Lotka-Volterra models produced models with statistically significant coefficients that characterized the inhibitory effect of selected LAB on L. monocytogenes in Minas fresh cheese. The Huang-Cardinal model [pH] outperformed both competition models. Taking aw change into account did not improve the fit quality of the Huang-Cardinal [pH] model. These models for Minas soft cheese should be valuable for future microbial risk assessments for this culturally important traditional cheese.

Antioxidant and antimicrobial activity and potential of heather (Erica spp.) extracts in the control of Listeria monocytogenes

SummaryIn this work, heather and its flowers were studied regarding their antioxidant and antimicrobial activities. Plants were subjected to ultrasound‐assisted methanolic extraction followed by fractionation. A phytochemical characterisation of extracts content in total phenols and flavonoids, and their antioxidant activity was performed. The antimicrobial activity was evaluated through the determination of minimum inhibitory concentration and by bioautography. Following, studies on the antilisterial potential were carried out by: time‐kill curves, inhibition of biofilm formation and tolerance of Listeria monocytogenes to adverse conditions. The results evidenced the antioxidant activity in both extracts, as well as, the antimicrobial activity against Gram‐positive bacteria. Concerning the evaluation of the antilisterial potential, a bacteriostatic behaviour and inhibition of biofilms formation ability were observed. Listeria monocytogenes showed an increased susceptibility to adverse conditions when preincubated with extracts. Thus, heather and its flowers may be a source of new compounds with antilisterial activity potential.

Nanoencapsulation of a Bacteriocin from Pediococcus acidilactici ITV26 by Microfluidization

The bacteriocin (pediocin) produced by Pediococcus acidilactici ITV26 is a bioconservative with antilisterial activity that can be inactivated when added in free form into foods. Proteolytic enzymes or interaction/binding with some food components are among the factors that can affect its antimicrobial activity. Hence, there is a need to protect these peptides by encapsulation into liposomes as well as to control their release. The aim of this research was to establish conditions to obtain stable liposomes with pediocin, to keep their activity and to control the release of the encapsulated bacteriocin. Pediocin was purified by adsorption-desorption and liposomes were prepared by using different phosphatidylcholine concentrations (1, 3, and 5% w/v) and different operating conditions in the microfluidizer (500–1000 bar and 1–2 cycles). The liposomes obtained were characterized by using dynamic light scattering, backscattering light, and cryo transmission electron microscopy. In addition, the effect of pH on the kinetics of pediocin release was studied, and its antimicrobial activity was tested by following the growth kinetics of Listeria innocua AST-062 under different treatments with pediocin-encapsulated liposomes.

Isolation and Characterization of an Anti-listerial Bacteriocin from Leuconostoc lactis SD501.

Although bacteriocins with anti-listerial activity have been isolated from a wide variety of lactic acid bacteria, little is known about those from Leuconostoc lactis, a heterofermentative bacterium that produces diacetyl and exopolysaccharides in dairy foods. In this study, an anti-listerial bacteriocin was isolated from Leuc. lactis SD501 and characterized. It was particularly potent against Listeria monocytogenes and also inhibited Enterococcus faecalis. Anti-listerial activity reached a maximum during the early stationary phase and then decreased gradually. The anti-listerial substance was sensitive to proteinase K and ɑ-chymotrypsin, confirming its proteinaceous nature. Its activity remained stable at pH values ranging from 1 to 10. In addition, it was strongly resistant to high temperatures, retaining its activity even after incubation for 15 min at 121℃. The apparent molecular mass of the partially purified anti-listerial bacteriocin was approximately 7 kDa. The characteristics of the SD501 bacteriocin, including its small molecular size (<10 kDa), strong anti-listerial activity, wide pH stability and good thermostability, indicate its classification as a Class IIa bacteriocin.

Genetic diversity and antimicrobial activity of lactic acid bacteria in the preparation of traditional fermented potato product 'tunta'.

Fermentation microorganisms, lactic acid bacteria (LAB) and yeast from 12 samples of tunta production chain were quantified, from the native potatoes used by the process fermentation of potatoes in the river up to the final product. During fermentation, the LAB population steadily increased from 3 to 4 to 8 log CFU/g during the first 8days in the river and the yeast population increased from 2 to 3 to 3-4 log CFU/g. Overall, 115 LAB strains were isolated using a culture-dependent method. Molecular techniques and 16S rRNA gene sequencing enabled the identification of native species. In LAB isolates, members of the Lactobacillaceae (64%), Leuconostocaceae (9%) and Enterococcaceae (2%) families were identified. The most prevalent LAB species in the tunta production chain was Lactobacillus curvatus, followed by Leuconostoc mesenteroides and Lactobacillus sakei, Lactobacillus brevis and Enterococcus mundtii were also present. Only 13 LAB strains showed anti-listerial activity, and one of them, identified as En. mundtii DSM 4838T [MG031213], produced antimicrobial compounds that were determined to be proteins after treatment with proteolytic enzymes. Based on these results, we suggest that traditional fermented product-derived LAB strains from specific environments could be selected and used for technological application to control pathogenic bacteria and naturally protect food from post-harvest deleterious microbiota.

Effect of Bacillus cereus peptide conjugated with nanoporous silica on inactivation of Listeria monocytogenes in apple juice, as an ecofriendly preservative.

Bacteriocins are ribosomally synthesized antimicrobial proteins/peptides. They are of great interest in the food processing industries as potential natural preservative agent to control food-borne pathogens. Bacillus spp. are one among the potential probiotics receiving more attention since they produce a broad spectrum of antimicrobial bioactive peptides. In this study, a small-scale medium composition and bioprocessing parameters were statistically optimized to increase the yield of bacteriocin namely cerein from Bacillus cereus NS02 showing antagonism against a wide range of food-borne pathogens. The cerein was partially purified, characterized, and evaluated for their optimal reaction condition. It was subjected to surface adsorption onto food-grade silica to evaluate its maximal adsorption, reached at 4h, 40°C, pH 6-7, and at the initial concentration of 200AUmL-1. The effectiveness of silica-adsorbed and silica-free cerein was checked in Listeria monocytogenes inoculated fresh apple juice and demonstrated biopreservative activity. In juice treated with silica-cerein, the colony forming unit (CFU) was found to be less in count on the 15th day of storage at 4°C whereas, free-cerein was found to contain 3.8logCFUmL-1. While, on the same day of storage, the control juice contained the strength of 14.6logCFUmL-1. Based on the above, this study concludes that the identified heat stable low molecular weight peptide cerein from B. cereus NS02 could serve as a potential biopreservative with effective antilisterial activity in the food system. However, a more detailed study is required to determine if their quality change especially the effect of cerein in organoleptic and nutritional properties of food beyond their addition is necessary, before it is to be exploited as an ecofriendly biopreservative.

Enhancement of the antibacterial activity of an E. faecalis strain by the heterologous expression of enterocin A

The genus Enterococcus occurs as native microbiota of fermented products due to its broad environmental distribution and its resistance to salt concentrations. Enterococcus faecalis F, a non-pathogenic strain isolated from a ripened cheese, has demonstrated useful enzymatic capabilities, a probiotic behavior and antibacterial activity against some food-borne pathogens, mainly due to peptidoglycan hydrolase activity. Its use as a natural pathogen-control agent could be further enhanced through the production of a bacteriocin, e.g. Enterocin A, because of its remarkable antilisterial activity. In this work, a markerless allelic insertion method was used to obtain an enterococcal strain capable of producing a functional enterocin. Agar diffusion tests showed that the recombinant strain was active against Staphylococcus aureus, Listeria monocytogenes and the pathogenic strain E. faecalis V583. When grown in liquid culture together with L. monocytogenes, it attained a two-log reduction of the pathogen counts in lesser time relative to the native strain. Because the DNA construction is integrated into the chromosome, the improved strain avoids the use of antibiotics as selective pressure; besides, it does not require an inductor because of the inclusion of a constitutive promoter in the construction. Its technological and antibacterial capabilities make the improved E. faecalis strain a potential culture for use in the food industry.

Detection of Antilisterial Activity of 3-Phenyllactic Acid Using Listeria innocua as a Model.

The 3-Phenyllactic acid (PLA) produced by various lactic acid bacteria (LAB) possesses a broad spectrum of antimicrobial activity. In this study, the effect of PLA against Listeria innocua was studied with the aim to obtain additional information about its mechanism of action. The effect of pH on the antilisterial activity of PLA was investigated and a pH-dependent behavior, typical of weak acid, was detected. The antilisterial effect of PLA was firstly compared to that produced by lactic acid (LA) and than to that expressed by phenolic acids (gallic, caffeic, and ferulic acids) evaluating minimum inhibitory concentration (MIC), MBC, and survival kinetic parameters. PLA showed MIC values and death kinetic parameters significantly different from those exhibited by LA and by tested phenolic acids. In particular, the MIC value observed for PLA vs L. innocua resulted lower than that of the other preservative compounds studied herein, and consistent with the quantity generally produced by LAB. Moreover, the effect of PLA and phenolic acids on bacterial surface charge and loss of cellular content resulted different. The overall results highlighted strong differences in the antilisterial mechanism of action among PLA and other compounds such as LA and phenols. Specifically, it is possible to hypothesize that the antilisterial mechanism of action due to PLA is associated with the affinity to cell surface, which contributes to the cellular damage.

Triticale flour films added with bacteriocin-like substance (BLIS) for active food packaging applications

Abstract Active triticale flour films were obtained by adding bacteriocin-like substances (BLIS) produced by Enterococcus faecium ES216 with antimicrobial activity against Listeria innocua ATCC33090. Active and control films were characterized. The incorporation of the active fractions did not significantly affect the density, moisture content, water vapor permeability and puncture strength of films. Solubility, color and opacity were dependent on the fraction incorporated into the films. Activated films maintain the antilisterial activity until 45 days of evaluation. Also, active and control triticale films were used to obtain heat-sealed pouches to package inoculated cheese slices under controlled conditions. Active triticale packaging could reduce the counts of Listeria in 3 log comparing to control after 15 days of storage. These results suggest that triticale flour films activated with this BLIS could provide an alternative strategy for active food packaging applications.

Antilisterial effects of hop alpha and beta acids in turkey slurry at 7 and 37°C.

Chemical components of hop resins effectively inhibit the growth of L. monocytogenes in microbiological culture media. This study was conducted to investigate antilisterial activities of hop α- and β-acid in turkey slurry. Turkey slurries were inoculated with L. monocytogenes, formulated with hop α- or β-acid from 0 to 1,000ppm, and incubated at 37°C for 24h or at 7°C for 12 days. During storage at 37°C for 24h, L. monocytogenes populations were reduced from 2.40 log CFU/g to non-detectable (<1 log CFU/g) in α-acid at ≥750ppm and β-acid at 1,000ppm, whereas the control (0ppm) allowed the pathogen to grow to 8.0 log CFU/g. During storage at 7°C for 12 d, the slurry treated with α-acid at ≥100ppm and β-acid at ≥500ppm showed listeristatic effects, while listericidal effects were observed in the slurries at 1,000ppm, regardless of hop acid type. Hop α-acid ≤ 50ppm and β-acid ≤ 100ppm failed to inhibit L. monocytogenes, and the pattern of bacterial growth was similar to that of control with no significant difference (P >0.05). Based on these results, the concentration of α-acid >100ppm or β-acid >500ppm is minimally required to inhibit L. monocytogenes when turkey batters are formulated with hop acids as a single antilisterial agent prior to cooking and storage at 7°C.