Effect of Zataria multiflora Boiss. Essential oil, time, and temperature on the expression of Listeria monocytogenes virulence genes in broth and minced rainbow trout

Inhibitory effect and mechanism of oregano essential oil on Listeria monocytogenes cells, toxins and biofilms

Listeria monocytogenes (L. monocytogenes) is a prevalent foodborne pathogen with a remarkable capacity to form biofilms on utensil surfaces. The Listeriolysin O (LLO) exhibits hemolytic activity, which is responsible for causing human infections. In this study, we investigated the inhibitory effect and mechanism of oregano essential oil (OEO) on L. monocytogenes, evaluated the effects on its biofilm removal and hemolytic activity. The minimum inhibitory concentration (MIC) of OEO against L. monocytogenes was 0.03% (v/v). L. monocytogenes was treated with OEO at 3/2 MIC for 30 min the bacteria was decreased below the detection limit (10 CFU/mL) in PBS and TSB (the initial bacterial load was about 6.5 log CFU/mL). The level of L. monocytogenes in minced pork co-cultured with OEO (15 MIC) about 2.5 log CFU/g lower than that in the untreated group. The inhibitory mechanisms of OEO against planktonic L. monocytogenes encompassed perturbation of cellular morphology, elevation in reactive oxygen species levels, augmentation of lipid oxidation extent, hyperpolarization of membrane potential, and reduction in intracellular ATP concentration. In addition, OEO reduced biofilm coverage on the surface of glass slides by 62.03% compared with the untreated group. Meanwhile, OEO (1/8 MIC) treatment reduced the hemolytic activity of L. monocytogenes to 24.6% compared with the positive control. Molecular docking suggested carvacrol and thymol might reduce the hemolytic activity of L. monocytogenes. The results of this study demonstrate that OEO exhibits inhibitory effects against L. monocytogenes, biofilms and LLO, which had potential as natural antimicrobial for the inhibition of L. monocytogenes.

Concentration of steroid hormones in sediment of surface water resources in China: systematic review and meta-analysis with ecological risk assessment

The risk quotient (RQ) related to Estrone (E1), 17β-E2 (E2), Estriol (E3) and 17α-ethynylestradiol (EE2) in sediment of water resources in China was calculated using Monte Carlo Simulation (MCS) method. Fifty-four papers with 64 data-reports included in our study. The rank order of steroid hormones in sediment based on log-normal distribution in MCS was E1 (3.75 ng/g dw) > E3 (1.53 ng/g dw) > EE2 (1.38 ng/g dw) > E2 (1.17 ng/g dw). According to results, concentration of steroid hormones including E1, E2 and E3 in sediment of Erhai lake, northern Taihu lake and Dianchi river was higher than other locations. The rank order of steroid hormones based on percentage high risk (RQ > 1) was EE2 (87.00%) > E1 (70.00%) > E2 (62.99%) > E3 (11.11%). Hence, contamination control plans for steroid hormones in sediment of water resources in China should be conducted continuously.

Addition of lime juice and NaCl to minced seafood may stimulate the expression of Listeria monocytogenes virulence, adhesion, and stress response genes

Listeria monocytogenes is a ubiquitous opportunistic bacterium responsible for deadly listeriosis outbreaks. This pathogen has been recognized as a significant food-borne pathogen in seafood products. The present study aimed to investigate the transcript levels of virulence, adhesion, and stress response genes of L. monocytogenes upon exposure to sublethal levels of lime juice and NaCl in shrimp matrix. For this purpose, minced and broth shrimp samples (control, 2% NaCl, 5% NaCl, 25 μL/mL lime, and 50 μL/mL lime, as well as 2% NaCl+25 μL/mL lime) were inoculated with approximately 107 CFU/g or ml of L. monocytogenes, and subsequently, the samples were stored at 12°C or 37°C. For the minced samples, the transcription of one stress-related (sigB), two adhesion (imo1634 and imo1847), and four virulence (hly, prf, intA, and plc) genes was assessed by RT-qPCR after different storage times (0 and 48 h). Results showed that the transcript levels of sigB, imo1847, and imo1634 genes increased with increasing storage temperatures of shrimp broth (12°C to 37°C). At the beginning, the transcription of the studied genes decreased in all treatments of minced shrimp; however, after 48 h of storage at 12°C, the transcript levels of hly, prf, imo1847, imo1634, and intA genes were significantly upregulated up to 0.5-9 log2 fold-change in all treatments compared to the control group (p < .05). These results highlight that the survived L. monocytogenes after exposure to moderate salt content or lime juice could represent enhanced virulence and adhesion capabilities, posing a significant public health risk.

Control of Listeria monocytogenes in food industry by a combination treatment of natural aromatic compound with Listeria-specific bacteriophage cocktail

Most Listeria monocytogenes found in the food industry are listeriosis-causing pathogens and possess the ability to form biofilms on food and food contact materials (FCMs). This study aims to evaluate the efficacy of the combination treatment of natural aromatic compounds (thymol, eugenol, carvacrol, and citral) with a Listeria-specific phage cocktail in mitigating the threat posed by L. monocytogenes in the food industry. In vitro combination treatment of 1 minimal inhibitory concentration (MIC) of natural aromatic compound with phage cocktail at multiplicity of infection (MOI) 100 reduced more than 4 log CFU/mL of L. monocytogenes planktonic cells and inhibited biofilm formation. In addition, the expression of virulence-related genes (flaA, motB, hlyA, prfA, and actA) and the stress response (sigB) gene were significantly downregulated. The combination of natural aromatic compound with phage cocktail reduced the biofilm cell population on contaminated celery by more than 2 log CFU/g and by more than 2 log CFU/cm2 on already-formed biofilm on FCMs, but it was less effective on chicken meat, with an approximate reduction of only 1 log CFU/g. The antibiofilm activity toward preformed L. monocytogenes biofilms was also observed using field-emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM). COMSTAT analysis of the structural change of biofilms revealed that major biofilm structure parameters (biovolume, thickness, diffusion distance, and microcolonies at substratum) were reduced after treatment. Our findings suggest that the combination of natural aromatic compounds with a phage cocktail has enormous potential as an antimicrobial and antibiofilm agent for controlling L. monocytogenes in the food industry.

Antimicrobial and Antibiofilm Efficacy and Mechanism of Oregano Essential Oil Against Shigella flexneri

The aim of this study was to assess the antimicrobial activity of oregano essential oil (OEO) against Shigella flexneri and eradication efficacy of OEO on biofilm. The results showed that the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of OEO against S. flexneri were 0.02% (v/v) and 0.04% (v/v), respectively. OEO effectively killed S. flexneri in Luria-Bertani (LB) broth and contaminated minced pork (the initial population of S. flexneri was about 7.0 log CFU/mL or 7.2 log CFU/g), and after treatment with OEO at 2 MIC in LB broth or at 15 MIC in minced pork, the population of S. flexneri decreased to an undetectable level after 2 or 9 h, respectively. OEO increased intracellular reactive oxygen species concentration, destroyed cell membrane, changed cell morphology, decreased intracellular ATP concentration, caused cell membrane depolarization, and destroyed proteins or inhibited proteins synthesis of S. flexneri. In addition, OEO effectively eradicated the biofilm of S. flexneri by effectively inactivating S. flexneri in mature biofilm, destroying the three-dimensional structure, and reducing exopolysaccharide biomass of S. flexneri. In conclusion, OEO exerts its antimicrobial action effectively and also has a valid scavenging effect on the biofilm of S. flexneri. These findings suggest that OEO has the potential to be used as a natural antibacterial and antibiofilm material in the control of S. flexneri in meat product supply chain, thereby preventing meat-associated infections.

Potential of Essential Oils in the Control of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen, the causative agent of listeriosis. Infections typically occur through consumption of foods, such as meats, fisheries, milk, vegetables, and fruits. Today, chemical preservatives are used in foods; however, due to their effects on human health, attention is increasingly turning to natural decontamination practices. One option is the application of essential oils (EOs) with antibacterial features, since EOs are considered by many authorities as being safe. In this review, we aimed to summarize the results of recent research focusing on EOs with antilisterial activity. We review different methods via which the antilisterial effect and the antimicrobial mode of action of EOs or their compounds can be investigated. In the second part of the review, results of those studies from the last 10 years are summarized, in which EOs with antilisterial effects were applied in and on different food matrices. This section only included those studies in which EOs or their pure compounds were tested alone, without combining them with any additional physical or chemical procedure or additive. Tests were performed at different temperatures and, in certain cases, by applying different coating materials. Although certain coatings can enhance the antilisterial effect of an EO, the most effective way is to mix the EO into the food matrix. In conclusion, the application of EOs is justified in the food industry as food preservatives and could help to eliminate this zoonotic bacterium from the food chain.

Novel Antibacterial Metals as Food Contact Materials: A Review

Food contamination caused by microorganisms is a significant issue in the food field that not only affects the shelf life of food, but also threatens human health, causing huge economic losses. Considering that the materials in direct or indirect contact with food are important carriers and vectors of microorganisms, the development of antibacterial food contact materials is an important coping strategy. However, different antibacterial agents, manufacturing methods, and material characteristics have brought great challenges to the antibacterial effectiveness, durability, and component migration associated with the use security of materials. Therefore, this review focused on the most widely used metal-type food contact materials and comprehensively presents the research progress regarding antibacterial food contact materials, hoping to provide references for exploring novel antibacterial food contact materials.

Infection behavior of Listeria monocytogenes on iceberg lettuce (Lactuca sativa var. capitata)

Iceberg lettuce among leafy vegetables is susceptible to contamination with foodborne pathogens, posing a risk of food microbial safety. Listeria monocytogenes (L. monocytogenes) is a highly lethal pathogen that can survive and proliferate on leafy vegetables. In this paper, the contamination stage, attachment site, internalization pathway, proliferation process, extracellular substance secretion and virulence factors expression of L. monocytogenes on iceberg lettuce were researched. Results showed that the contamination stage of L. monocytogenes on iceberg lettuce was 0-20 min, the proliferation stage was after 20 min. The attachment tissues were stomata and winkles. The internalization distance of L. monocytogenes in the midrib was farther than that in the leaf blade. They enhanced the movement ability of cells by up-regulating the expression of flaA and motA genes, and enhanced the adhesion ability of cells by up-regulating the expression of actA and inla genes, which was beneficial to the proliferation. During proliferation, cells gradually secreted extracellular substances to promote the biofilm formation on iceberg lettuce. The formation of biofilms experienced: individual bacteria, cell aggregation and biofilm maturation. Biofilms were more likely to form on the leaf blade of iceberg lettuce.

Effect of sage seed gum film incorporating Zataria multiflora Boiss essential oil on the storage quality and biogenic amine content of refrigerated Otolithes ruber fillets

The effect of an edible film based on sage seed gum (SSG) incorporating 3 % Zataria multiflora Boiss essential oil (ZEO) was investigated on the storage quality and shelf life of tiger-tooth croaker (Otolithes ruber) fillets during storage at 4 ± 1 °C compared to the control film (SSG film without ZEO) and the Cellophane. The SSG-ZEO film significantly decelerated microbial growth (evaluated by total viable count, total psychrotrophic count, pH, TVBN) and lipid oxidation (evaluated by TBARS) compared to the others (P ˂ 0.05). The antimicrobial activity of ZEO was the highest and the lowest on E. aerogenes (MIC: 0.196 μL/mL) and P. mirabilis (MIC: 0.977 μL/mL), respectively. E. aerogenes was identified as an indicator biogenic amine-producer in O. ruber fish at refrigerated temperature. The active film significantly lowered biogenic amine accumulation in the samples inoculated with E. aerogenes. A clear relationship was observed between the release of ZEO's phenolic compounds from the active film to the headspace and the reduction of microbial growth, lipid oxidation, and biogenic amine production in the samples. Consequently, SSG film containing 3 % ZEO is proposed as a biodegradable antimicrobial-antioxidant packaging to extend the shelf life and decrease the biogenic amine production in refrigerated seafood.

Supercritical Fluid Extraction from Zataria multiflora Boiss and Impregnation of Bioactive Compounds in PLA for the Development of Materials with Antibacterial Properties

In this research, the extraction with supercritical carbon dioxide (SC-CO2) and the subsequent impregnation of the extracted bioactive compounds from Zataria multiflora Boiss (Z. multiflora) into polylactic acid (PLA) films was investigated. The effects of temperature (318 and 338 K), pressure (15 and 25 MPa) and cosolvent presence (0 and 3 mol%) on the extraction yield were studied. The SC-CO2 assisted impregnation runs were carried out in a discontinuous mode at different pressure (15 and 25 MPa), temperature (318 and 328 K), and time (2 and 8 h) values, using 0.5 MPa min−1 as a constant value of depressurization rate. ANOVA results confirmed that pressure, temperature, and time influenced the extraction yield. Moreover, antioxidant activities of extracts of Z. multiflora were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. In addition, the antibacterial activities of the extracts were screened against standard strains of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The results of this investigation indicated that extracts obtained from the aerial parts of Z. multiflora possessed antioxidant and antibacterial properties. The impregnated samples presented strong antibacterial activity against the selected microorganisms.

Antimicrobial Activity of Films and Coatings Containing Lactoperoxidase System: A Review

The production of safe and healthy foodstuffs is considered as one of the most important challenges in the food industry, and achieving this important goal is impossible without using various processes and preservatives. However, recently, there has been a growing concern about the use of chemical preservatives and attention has been focused on minimal process and/or free of chemical preservatives in food products. Therefore, researchers and food manufacturers have been induced to utilize natural-based preservatives such as antimicrobial enzymes in their production. Lactoperoxidase, as an example of antimicrobial enzymes, is the second most abundant natural enzyme in the milk and due to its wide range of antibacterial activities, it could be potentially applied as a natural preservative in various food products. On the other hand, due to the diffusion of lactoperoxidase into the whole food matrix and its interaction and/or neutralization with food components, the direct use of lactoperoxidase in food can sometimes be restricted. In this regard, lactoperoxidase can be used as a part of packaging material, especially edible and coating, to keep its antimicrobial properties to extend food shelf-life and food safety maintenance. Therefore, this study aims to review various antimicrobial enzymes and introduce lactoperoxidase as a natural antimicrobial enzyme, its antimicrobial properties, and its functionality in combination with an edible film to extend the shelf-life of food products.

Antibacterial Activity of Pediocin and Pediocin-Producing Bacteria Against Listeria monocytogenes in Meat Products

One of the most important challenges in the food industry is to produce healthy and safe food products, and this could be achieved through various processes as well as the use of different additives, especially chemical preservatives. However, consumer awareness and concern about chemical preservatives have led researchers to focus on the use of natural antimicrobial compounds such as bacteriocins. Pediocins, which belong to subclass IIa of bacteriocin characterized as small unmodified peptides with a low molecular weight (2.7-17 kDa), are produced by some of the Pediococcus bacteria. Pediocin and pediocin-like bacteriocins exert a broad spectrum of antimicrobial activity against Gram-positive bacteria, especially against pathogenic bacteria, such as Listeria monocytogenes through formation of pores in the cytoplasmic membrane and cell membrane dysfunction. Pediocins are sensitive to most protease enzymes such as papain, pepsin, and trypsin; however, they keep their antimicrobial activity during heat treatment, at low temperatures even at -80°C, and after treatment with lipase, lysozyme, phospholipase C, DNase, or RNase. Due to the anti-listeria activity of pediocin on the one hand and the potential health hazards associated with consumption of meat products on the other hand, this review aimed to investigate the possible application of pediocin in preservation of meat and meat products against L. monocytogenes.

Effect of Zataria multiflora essential oil and potassium sorbate on inoculated Listeria monocytogenes, microbial and chemical quality of raw trout fillet during refrigerator storage

Human listeriosis is predominantly associated with contaminated food consumption, including seafood, shrimp, and RTE foods. Listeria monocytogenes is a foodborne pathogen that is mainly found in freshwater, seawater, and fish mucus. Seafood contamination can occur during food processing. L.monocytogenes levels of below 100 cfu/g can be found in seafood samples. The present study was conducted to investigates the effect of Zataria multiflora essential oil (ZEO) and potassium sorbate (PS) on microbial and chemical changes in raw rainbow trout at 4°C to extent shelf life and improve food safety. First, the chemical compositions of ZEO were identified. Then, different percentage of ZEO (1.5, 0.8, and 0.5%) and PS (2%) were inoculated in raw fish fillets and analyzed for TVC, TBA, TVB-N, pH, sensory attributes, Pseudomonas aeruginosa, and inoculated L. monocytogenes (1 × 105 cfu/g) survival at 4°C for 12 days. The best sensory evaluation score was observed for the samples treated with 0.8% and 1.5% ZEO. Overall, this study results indicated that the treatment of rainbow trout fillet with 1.5% ZEO is the best method for controlling the growth of L. monocytogenes at refrigerator temperature without any undesirable sensory effects.

Effect of Zataria multiflora Boiss. essential oil, NaCl, acid, time, and temperature on the growth of Listeria monocytogenes strains in broth and minced rainbow trout

The small outbreaks of listeriosis as one of the leading causes of food poisoning-associated deaths occur more than previously reported. In current study, the growth ability of Listeria monocytogenes strains isolated from different sources of food and human origin was measured under salt stress (0.5%, 2.5%, 5%, 7.5%, and 10%) and acid environments (pH = 6.64 and 5.77) for 96 hr by using a Bioscreen C microbiology reader at 37°C. In further steps of this study, after analysis of constituents of Zataria multiflora Boiss. essential oil (ZMEO), the sensory evaluation of the treated fish meat with ZMEO was performed. Then, the fish isolate of L. monocytogenes was exposed to sensory acceptable and subminimum inhibitory concentrations (subMICs) of ZMEO in fish broth and minced fish meat during incubation at abuse (12°C), room (22°C), and optimum (37°C) temperatures for 48 hr. The MIC of NaCl against four strains of L. monocytogenes was 10% at 37°C. The maximum optical densities (ODs) and under curve areas (AUC) of growth patterns in higher pH value and lower contents of NaCl followed the order of 21C > 6F > 66C > 22C of L. monocytogenes strains, while the lag time was prolonged in the reverse order. The maximum OD, growth, and lag times of samples treated with higher contents of NaCl and lower pH value were affected in a different order. The organoleptic evaluation showed that the fish meat treated with less than 0.5% of ZMEO was sensory acceptable. The population of L. monocytogenes remained relatively constant at the inoculation level of 107 cfu/ml (or g) at 12°C in broth and minced fish mediums. The inhibitory antilisterial activity of essential oil as an extensive-used plant for food and pharmacological applications is negligible due to possible adverse sensory and toxic effects at relevant high doses.

Potential Application of Essential Oils for Mitigation of Listeria monocytogenes in Meat and Poultry Products

One of the most important challenges in the food industry is to provide healthy and safe food. Therefore, it is not possible to achieve this without different processes and the use of various additives. In order to improve safety and extend the shelf life of food products, various synthetic preservatives have been widely utilized by the food industry to prevent growth of spoilage and pathogenic microorganisms. On the other hand, consumers' preference to consume food products with natural additives induced food industries to use natural-based preservatives in their production. It has been observed that herbal extracts and their essential oils could be potentially considered as a replacement for chemical antimicrobials. Antimicrobial properties of plant essential oils are derived from some main bioactive components such as phenolic acids, terpenes, aldehydes, and flavonoids that are present in essential oils. Various mechanisms such as changing the fatty acid profile and structure of cell membranes and increasing the cell permeability as well as affecting membrane proteins and inhibition of functional properties of the cell wall are effective in antimicrobial activity of essential oils. Therefore, our objective is to revise the effect of various essential oils and their bioactive components against Listeria monocytogenes in meat and poultry products.

The efficiency of technologies used for epidemiological characterization of Listeria monocytogenes isolates: an update

The characterization of pathogenic bacteria by providing information regarding the identification and source-tracking of the causes of outbreaks is vital for the epidemiological investigations of foodborne diseases. The knowledge of transmission of Listeria monocytogenes (L. monocytogenes) strains from the environment, directly or indirectly (through food processing facilities) to the final food products, due to the complexity of evaluating numerous, affecting parameters is quite limited. The food trade globalization also adds difficulties in tracking the association between the infection occurrence and causative pathogens, aiming to prevent their spread. The occurrence of listeriosis, a notifiable disease throughout the world, can either be sporadic or outbreak-related. Due to the importance of foodborne outbreaks from a public health aspect and its correspondence enormous economic losses, cross-linked surveillance studies regarding the contamination of foods by L. monocytogenes, besides identifying clusters and tracing the sources of infections on an international-scale to prevent and control L. monocytogenes outbreaks sounds very crucial. Contrary to the conventional typing methods, molecular-based techniques, such as whole-genome sequencing, owing to the capacity to discriminate L. monocytogenes strains down to single nucleotide differences, provide an accurate characterization of strains and tracking the causes of outbreaks. However, routinely using molecular-based methods depends on the required improvements in the affordability, proper timing, and preparing reliable, standardized bioinformatics facilities. This work was conducted to critically review the practical potential of diverse typing methods have been used for the characterization of L. monocytogenes and discuss how they might change the future of efforts for control of listeriosis.

Comparative Effects of Carum copticum Essential Oil on Bacterial Growth and Shiga-Toxin Gene Expression of Escherichia coli O157:H7 at Abused Refrigerated Temperatures

Abused refrigerated temperatures are described as unacceptable deviations from the optimal temperature, occurring frequently during transportation of food products. Escherichia coli O157:H7 is a serious contaminant of meats and meat products due to its ability to grow at abused temperatures (> 10 °C). The aim of this study was to evaluate the antibacterial activity of Carum copticum essential oil for the control of Escherichia coli O157:H7 using laboratory media and minced beef at severe abused refrigerated temperature (15 °C). A comparative quantitative reverse transcription real-time PCR was used to assess effects of temperature and Carum copticum essential oil at sub-minimum inhibitory concentrations on bacterial growth and Shiga-toxin gene (stx1A and stx2A) expression. Results indicated that Carum copticum essential oil inhibited growth of E. coli O157:H7 in tryptone soy broth (TSB) media at all sub-MIC values until Hour 48. However, bacterial population increased progressively until Hour 72 at essential oil concentration of 0.75% (ml g^-1) and reached 8.6 log CFU g^-1 in minced beef. The essential oil at concentration of 0.005% (ml g^-1) increased stx gene expression at all times, but increased stx gene expression (0.015%) at Hour 24 in TSB media. The expression rate of stx1A in minced beef decreased progressively (10.39 and 7.67 folds for 0.5 and 0.75%, respectively) and expression of stx2A was variable in minced beef during storage. In conclusion, results from this study have shown that effects of Carum copticum essential oil on growth and virulence gene expression are not necessarily correlated and temperature, essential oil concentration, investigated gene type, and bacterial growth environment (in vivo or in vitro) are effective as well.

Antimicrobial-loaded nanocarriers for food packaging applications

Increasing the demands of consumers for organic and safer foods has led to applying new technologies for food preservation. Active packaging (AP) containing natural antimicrobial agents is a good candidate for promoting the shelf life of food products. The efficiency of AP has been enhanced through nanoencapsulation methods, in which antimicrobial-loaded nanocarriers could provide a controlled release of antimicrobial active packaging for keeping the quality of foods during storage. The main objective of this review is to introduce common methods for designing novel encapsulation delivery systems offering controlled release of antimicrobials in the AP systems. The common nanocarriers for enveloping antimicrobial agents are described and the current state of art in the application of nanoencapsulated antimicrobials in development of antimicrobial APs have been summarized and tabulated. Incorporation of a carrier loaded with natural antimicrobial agents is the most effective method for developing AP in the food packaging sector which has become possible by using nanoencapsulated antimicrobials in films or coating structures, instead of using their free form. Nanoencapsulation approaches provide many advantages including protection against environmental stresses, release control, and improving the solubility and absorption of natural antimicrobials in AP, which are the main achievements overcoming the barriers for using natural antimicrobials in food packaging.