Antibacterial activity of plant essential oils and extracts: The role of thyme essential oil, nisin, and their combination to control Listeria monocytogenes inoculated in minced fish meat

The antimicrobial effect of thyme and rosemary essential oils against Listeria monocytogenes in sous vide turkey meat during storage

The research was aimed to study the impact of sous vide thermal treatment on the microbiological quality of fresh turkey breast meat after treatment with thyme and rosemary EOs and the survival of Listeria monocytogenes on the turkey meat samples. The samples were vacuum-packed and cooked at 55 °C, 60 °C, and 65 °C for 5, 15, 30 and, 60 min. There was an amount of 5 g (5 ±0.2 g) of the sample placed in PA/PE film bags and inoculated with 100 μL of L. monocytogenes inoculum. The sample was incubated at 37 °C for 18 h after bag sealing. The samples were tested on the 1st and 3rd days of experiments. The microbiological quality of fresh turkey breast meat was assessed by the detection of total microbial counts and meat microbiota was identified by mass spectrometry using MALDI-TOF MS Biotyper (Bruker Daltonics, Germany). Microbial counts differed significantly depending on temperature and time and the microbial counts ranged from 2.21 log cfu.g-1 to 8.26 log cfu.g-1 on the 1st and 3rd day of the experiment. The study shows that the sous vide method with essential oils combination is an effective method and it can be used to protect the microbiota of turkey meat and L. monocytogens survival, however, the quality of raw material is crucial.

Recent developments of natural antimicrobials and antioxidants on fish and fishery food products

Fish and fishery products (FFP) are highly perishable due to their high nutritional value and moisture content. The spoilage is mainly caused by microorganisms and chemical reactions, especially lipid oxidation, leading to losses in quality and market value. Microbiological and lipid deteriorations of fishery-derived products directly lower their nutritive value and pose the risk of toxicity for human health. Increasing demand for safe FFP brings about the preservation using additives from natural origins without chemical additives due to their safety and strict regulation. Antimicrobials and antioxidants from natural sources have exhibited an excellent control over the growth of microorganisms causing fish spoilage via different mechanisms. They also play a major role in retarding lipid oxidation by acting at various stages of oxidation. Antimicrobials and antioxidants from natural sources are usually regarded as safe with no detrimental effects on the quality attributes of FFP. This review provides recent literature on the different antioxidant and antimicrobial agents from natural sources, focusing on microbial and oxidative spoilage mechanisms, their inhibition system, and their applications to retard spoilage, maintain safety, and extend the shelf life of FFP. Their applications and benefits have been revisited.

Antimicrobial Activity of Myrtus communis L. and Rosmarinus officinalis L. Essential Oils against Listeria monocytogenes in Cheese

Listeria monocytogenes has been referred to as a concern microorganism in cheese making due to its ability to survive and grow in a wide range of environmental conditions, such as refrigeration temperatures, low pH and high salt concentration at the end of the production process. Since cheese may be a potential hazard for consumers, especially high-risk consumers (e.g., pregnant, young children, the elderly, people with medical conditions), efforts of the dairy industry have been aimed at investigating new conservation techniques based on natural additives to meet consumers’ demands on less processed foods without compromising the food safety. Thus, the aim of this study was to evaluate the efficacy of Myrtus communis L. (myrtle) and Rosmarinus officinalis L. (rosemary) essential oils (EO) against Listeria monocytogenes ATCC 679 spiked in sheep cheese before ripening. After the cheesemaking process, the samples were stored at 8 °C for 2 h, 1 d, 3 d, 14 d and 28 d. The composition of EO was identified by gas chromatography-mass spectrometry (GC-MS) analysis. Constituents such as 1,8-cineole, limonene, methyl-eugenol, α-pinene, α-terpineol, α-terpinolene and β-pinene were present in both EO, accounting for 44.61% and 39.76% from the total of chemical compounds identified for myrtle and rosemary EO, respectively. According to the chemical classification, both EO were mainly composed of monoterpenes. Minimum inhibitory concentration (MIC) against L. monocytogenes was obtained at 31.25 μL/mL to myrtle EO and at 0.40 μL/mL to rosemary EO. Then, cheeses were inoculated with L. monocytogenes (Ca. 6 log CFU/mL) and EO was added at MIC value. The addition of rosemary and myrtle EO displayed lower counts of L. monocytogenes (p < 0.01) (about 1–2 log CFU/g) during the ripening period compared to control samples. Ripening only influences (p < 0.001) the growth of L. monocytogenes in control samples. Since rosemary and myrtle EO do not exert any negative impact on the growth of native microflora (p > 0.05), their use as natural antimicrobial additives in cheese demonstrated a potential for dairy processors to assure safety against L. monocytogenes.

Pulsed electric field assisted process for extraction of bioactive compounds from custard apple (Annona squamosa) leaves

Impact of pulsed electric field (PEF) assisted process on preparation of custard apple leaf extract (CALE) using ethanol (70%, v/v) was studied. Different electric field strengths (2-6 kV/cm), pulse numbers (100-300 pulses) with specific energies (45-142 kJ/kg) for 2.5 to 5 min were implemented. Cell disintegration index was higher in CALE when PEF 6 kV/cm, 300 pulses, 142 kJ/kg for 5 min was applied. Extraction yield was higher (+5.2%) than the untreated counterpart (13.28%). Chlorophyll A and B contents were negligible in PEF pre-treated CALE. PEF improved radical scavenging activities assessed by DPPH, ABTS radical scavening activities and FRAP. The antibacterial properties of CALE against Staphylococcus aureus and Escherichia coli were highest. Purpureacin 2 and rutin were abundant in PEF pre-treated CALE. Therefore PEF was the potential aid in augmenting extraction yield and bioactivities of the extract from custard apple leaves.

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.

Sustainable sources for antioxidant and antimicrobial compounds used in meat and seafood products

The contribution of food in promotion of health has become of most importance. The challenges that lie before the global food supply chain, such as climate changes, food contamination, and antimicrobial resistance may compromise food safety at international scale. Compounds with strong antimicrobial and antioxidant activity can be extracted from different natural and sustainable sources and may contribute to extend the shelf life of meat and seafood products, enhance food safety and enrich foods with additional biologically active and functional ingredients. This chapter describes the use of bioprotective cultures, essential oils, plant extracts, seaweed extracts and grape pomace compounds in production of value-added meat and seafood products with improved shelf life and safety, following the requests from the market and consumers.

Antilisterial Potential of Lactic Acid Bacteria in Eliminating Listeria monocytogenes in Host and Ready-to-Eat Food Application

Listeriosis is a severe food borne disease with a mortality rate of up to 30% caused by pathogenic Listeria monocytogenes via the production of several virulence factors including listeriolysin O (LLO), transcriptional activator (PrfA), actin (Act), internalin (Int), etc. It is a foodborne disease predominantly causing infections through consumption of contaminated food and is often associated with ready-to-eat food (RTE) and dairy products. Common medication for listeriosis such as antibiotics might cause an eagle effect and antibiotic resistance if it is overused. Therefore, exploration of the use of lactic acid bacteria (LAB) with probiotic characteristics and multiple antimicrobial properties is increasingly getting attention for their capability to treat listeriosis, vaccine development, and hurdle technologies. The antilisterial gene, a gene coding to produce antimicrobial peptide (AMP), one of the inhibitory substances found in LAB, is one of the potential key factors in listeriosis treatment, coupled with the vast array of functions and strategies; this review summarizes the various strategies by LAB against L. monocytogenes and the prospect in development of a ‘generally regarded as safe’ LAB for treatment of listeriosis.

Global transcriptomic response of Listeria monocytogenes exposed to Fingered Citron (Citrus medica L. var. sarcodactylis Swingle) essential oil

Listeria monocytogenes, which could cause severe disease of listeriosis, is one of the most concerned foodborne pathogens worldwide. Citrus medica L. var. sarcodactylis Swingle (Fingered Citron) is one of the citrus species cultivated in south China. Here, we investigated the efficacy of Fingered Citron essential oil (FCEO) against L. monocytogenes and explored the response of L. monocytogenes in the presence of FCEO using genome-wide transcriptome analysis. FCEO exhibited strong anti-listeria activity and obvious alterations of cell morphology were observed by scanning electron microscopy and transmission electron microscopy. Moreover, GO analysis demonstrated many potential cell responses, including metabolic process, cellular process, single-organism process, cell part, membrane, catalytic activity, binding, and transporter activity. KEGG analysis suggests that L. monocytogenes respond and adapt by (1) increasing motility through the enhancement of flagella rotation; (2) promoting cell tumbles and re-orientating to escape from FCEO; (3) enhancing the uptake of carbohydrates from environment to gain more energy; (4) changing the uptake of several metallic cations, including iron, zinc, cobalt, and nickel. Our research contributes to the understanding of the adaptive responses of L. monocytogenes exposed to FCEO and provides novel insights for finding new targets of anti-listeria therapy.

An Overview of the Potential Therapeutic Applications of Essential Oils

The emergence of antimicrobial resistance (AMR) has urged researchers to explore therapeutic alternatives, one of which includes the use of natural plant products such as essential oils (EO). In fact, EO obtained from clove, oregano, thymus, cinnamon bark, rosemary, eucalyptus, and lavender have been shown to present significant inhibitory effects on bacteria, fungi, and viruses; many studies have been done to measure EO efficacy against microorganisms. The strategy of combinatory effects via conventional and non-conventional methods revealed that the combined effects of EO-EO or EO-antibiotic exhibit enhanced efficacy. This paper aims to review the antimicrobial effects of EO, modes of EO action (membrane disruption, efflux inhibition, increase membrane permeability, and decrease in intracellular ATP), and their compounds' potential as effective agents against bacteria, fungi, and viruses. It is hoped that the integration of EO applications in this work can be used to consider EO for future clinical applications.

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 microbial safety of fish and fish products: Recent advances in understanding its significance, contamination sources, and control strategies

Microorganisms play a crucial and unique role in fish and fish product safety. The presence of human pathogens and the formation of histamine caused by spoilage bacteria make the control of both pathogenic and spoilage microorganisms critical for fish product safety. To provide a comprehensive and updated overview of the involvement of microorganisms in fish and fish product safety, this paper reviewed outbreak and recall surveillance data obtained from government agencies from 1998 to 2018 and identified major safety concerns associated with both domestic and imported fish products. The review also summarized all available literature about the prevalence of major and emerging microbial safety concerns, including Salmonella spp., Listeria monocytogenes, and Aeromonas hydrophila, in different fish and fish products and the survival of these pathogens under different storage conditions. The prevalence of antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs), two emerging food safety concerns, is also reviewed. Pathogenic and spoilage microorganisms as well as ARB and ARGs can be introduced into fish and fish products in both preharvest and postharvest stages. Many novel intervention strategies have been proposed and tested for the control of different microorganisms on fish and fish products. One key question that needs to be considered when developing and implementing novel control measures is how to ensure that the measures are cost and environment friendly as well as sustainable. Over the years, regulations have been established to provide guidance documents for good farming and processing practices. To be more prepared for the globalization of the food chain, harmonization of regulations is still needed.

M13 phage-based nanoprobe for SERS detection and inactivation of Staphylococcus aureus

Rapid and sensitive diagnosis of bacterial infections at early stage is of great significance for food safety monitoring as well as clinical treatment. Herein, we construct a surface-enhanced Raman scattering (SERS) nanoprobe based on M13 phages for the selective detection and inactivation of Staphylococcus aureus (S. aureus). M13 phage with specific S. aureus-binding heptapeptide displayed on the N-terminal of pIII protein is selected from phage display peptide library. The S. aureus-specific SERS probe is thus constructed by in situ growth of gold nanoparticles (AuNPs) on M13 phage surface, followed by modification with 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) as SERS active molecule. Upon the addition of this SERS probe, M13 phage selectively binds with S. aureus to induce anchoring of AuNPs on S. aureus surface, and the SERS probe-labeled S. aureus cells are collected by centrifugation for SERS detection. For the quantification of S. aureus, a linear range of 10-10⁶ cfu mL^-1 is achieved in aqueous medium. It is further demonstrated by spiking recovery in soft drinks. Furthermore, this SERS probe exhibits bactericidal capabilities towards S. aureus, which shows promising potential to serve as a multifunctional platform for simultaneous detection and inactivation of S. aureus.

Development of Hypericum perforatum oil incorporated antimicrobial and antioxidant chitosan cryogel as a wound dressing material

In this study, a herbal infused oil (Hypericum perforatum, HP) incorporated chitosan (CS) cryogel as a wound dressing material was produced in order to be used in wound healing process. The main strategy is to combine the traditional perspective of using medicinal oils with polymeric scaffolds manufactured by an engineering approach to fabricate a potential tissue engineering product that provides both new tissue formation and wound healing. The scaffolds manufactured by cryogelation were soft, spongy, highly porous, physically stable, elastic and could be easily cut in any desired shape. Physicochemical, mechanical and morphological analyzes were used to characterize the produced cryogels. Young modulus of the plain chitosan cryogel was about 21 kPa whereas it increased with increasing HP oil content and became 61 kPa for 20% HP oil ratio. Further, the antimicrobial studies, antioxidant and DNA cleavage effects were investigated. Samples including the highest ratio of oil (CS4) showed the highest DPPH scavenging activity as 69.9%. In addition, 20% HP oil loaded chitosan cryogel demonstrated single strain DNA cleavage activitiy at 500 μg/mL concentration. Antimicrobial studies were applied against seven strains. The lowest activities were obtained against E. hirae and B. cereus, the highest against E. coli and L. pneumophila. This study concluded that the newly developed HP oil loaded chitosan cryogel scaffolds with unique antimicrobial and antioxidant properties are promising candidates to be used in tissue engineering applications as wound dressing for exudative and long-term healing wounds.

Rosmarinus plants: Key farm concepts towards food applications

Rosmarinus species are aromatic plants that mainly grow in the Mediterranean region. They are widely used in folk medicine, food, and flavor industries and represent a valuable source of biologically active compounds (e.g., terpenoids, flavonoids, and phenolic acids). The extraction of rosemary essential oil is being done using three main methods: carbon dioxide supercritical extraction, steam distillation, and hydrodistillation. Furthermore, interesting antioxidant, antibacterial, antifungal, antileishmanial, anthelmintic, anticancer, anti-inflammatory, antidepressant, and antiamnesic effects have also been broadly recognized for rosemary plant extracts. Thus the present review summarized data on economically important Rosmarinus officinalis species, including isolation, extraction techniques, chemical composition, pharmaceutical, and food applications.

An innovative method to enhance protease tolerance of nisin in endogenous proteases

Nisin, a natural peptide produced by Lactococcus lactis cultivation in milk whey, is widely used as a preservative in industrial production. However, nisin can be degraded by endogenous enzymes in foods. In this study, we investigated the antibacterial activity of nisin-soybean protein and nisin-egg white protein and compared them with that of free nisin in cantaloupe juice, which was used as a model of endogenous protease environment. Results showed that endogenous proteases in the model resulted in a loss of nisin activity, but combining nisin with protein (soybean or egg white) resulted in greater protection of its antimicrobial activity by inhibiting endogenous proteases. The microbial addition experiment (Staphylococcus aureus and Micrococcus luteus) and preservation experiment in the food model showed that the antibacterial activity of nisin combined with either of the 2 proteins was higher than that of nisin alone in an endogenous protease environment. In summary, soybean protein and egg white protein improved the protease tolerance of nisin, expanding the application scope of nisin in food.

Chitosan-loaded nanoemulsion containing Zataria Multiflora Boiss and Bunium persicum Boiss essential oils as edible coatings: Its impact on microbial quality of turkey meat and fate of inoculated pathogens

This study was targeted to investigate the effect of chitosan-loaded nanoemulsion enriched with two types of essential oils on the microbial quality of turkey meat. To this end, the effects of essential oils of Zataria Multiflora Boiss (ZEO) and Bunium persicum Boiss (BEO) were evaluated at two concentrations (0.5% and 1% (w/v)) during 18 days of storage at 4 °C. Initially, in vitro evaluations were performed on the prepared nanoemulsions, namely essential oil nanoemulsions and chitosan-loaded nanoemulsions containing essential oils, using micro-dilution method and agar diffusion methods, respectively. Meat samples were analyzed for microbial indicators and inoculated salmonella Enteritidis, and Listeria monocytogenes during 3-day intervals. The highest reduction rate of total viable bacteria (2.06 log CFU/g), total psychrophilic (2.59 log CFU/g), Pseudomonas spp. (2.07 log CFU/g), Enterobacteriaceae (2.51 log CFU/g), lactic acid bacteria (2.51 log CFU/g), and yeast and mold count (2.10 log CFU/g) were observed in chitosan-loaded nanoemulsion containing ZEO 1%, in comparison with control samples. Moreover, the shelf life significantly increased due to the application of chitosan-loaded nanoemulsions (15-18 days), compared to that of the control group (6 days). Therefore, the edible chitosan-based nanoemulsion could play an effective role in the preservation of the microbial qualities of turkey meat.

A novel bilayer zein/MMT nanocomposite incorporated with H. perforatum oil for wound healing

Recently, layered structures composed of nanofibers have gained attention as a novel material to mimic skin tissue in wound healing applications. The aim of this study is to develop a novel hybrid bilayer material composed of zein based composite film and nanofiber layers as a wound dressing material. The upper layer was composed of H. perforatum oil incorporated zein film including MMT and the bottom layer was comprised of 3D electrospun zein/MMT nanofibers to induce wound healing with the controlled release of H. perforatum oil. The bilayer composites were characterized in terms of mechanical test, WVP, water uptake and surface wettability. Antimicrobial activity of the wound dressings against microorganisms were investigated by disc diffusion method. In vitro cytotoxicity of monolayer film and bilayer structure was performed using WST-1 assay on HS2 keratinocyte and 3T3 cell lines. Results indicated that the prepared monolayer films showed appropriate mechanical and gas barrier properties and surface wettability for wound healing. Controlled release of H. perforatum oil was obtained from fabricated membranes up to 48 h. Bilayer membranes showed antimicrobial activity against E. coli, S. aureus, and C. albicans and did not show any toxic effect on NIH3T3 mouse fibroblast and HS2 keratinocyte cell lines. In vitro scratch assay results indicated that H. perforatum oil had a wound healing effect by inducing fibroblast migration. The proliferation study supported these results by increasing fibroblast proliferation on H. perforatum oil loaded bilayer membranes.

Review on Natural Preservatives for Extending Fish Shelf Life

Fish is extremely perishable as a result of rapid microbial growth naturally present in fish or from contamination. Synthetic preservatives are widely used in fish storage to extend shelf life and maintain quality and safety. However, consumer preferences for natural preservatives and concerns about the safety of synthetic preservatives have prompted the food industry to search natural preservatives. Natural preservatives from microorganisms, plants, and animals have been shown potential in replacing the chemical antimicrobials. Bacteriocins and organic acids from bacteria showed good antimicrobial activities against spoilage bacteria. Plant-derived antimicrobials could prolong fish shelf life and decrease lipid oxidation. Animal-derived antimicrobials also have good antimicrobial activities; however, their allergen risk should be paid attention. Moreover, some algae and mushroom species can also provide a potential source of new natural preservatives. Obviously, the natural preservatives could perform better in fish storage by combining with other hurdles such as non-thermal sterilization processing, modified atmosphere packaging, edible films and coatings.

Antioxidative Activity of Thyme (Thymus vulgaris) and Oregano (Origanum vulgare) Essential Oils and Their Effect on Oxidative Stability of Minced Pork Packaged Under Vacuum and Modified Atmosphere

The antioxidant stability of minced pork treated with thyme and oregano essential oils (EOs) was determined. Minced pork containing different concentrations (0%, 0.3%, 0.6%, or 0.9%) of thyme (TEO) or oregano essential oil (OEO) and packaged under vacuum or modified atmosphere (MAP) (30%O₂ /50%CO₂ /20%N₂ ) was evaluated within 15 days of refrigeration (3 ± 1 °C) storage. EOs were examined for scavenging capacity toward 2,2-diphenyl-1-picrylhydrazyl, nitric oxide radicals, and hydroxyl, and inhibition of lipid peroxidation and ferric ion reducing antioxidant power (butylated hydroxytoluene was used as positive controls). The order of antioxidative effectiveness was as follows: butylated hydroxytoluene > OEO > TEO, with significant differences between agents (P < 0.05). Lipid oxidation in meat was determined by monitoring malondialdehyde (MDA) formation and lipolysis was assessed by measuring the acidity index immediately and after 3, 6, 9, 12, and 15 days of storage. EOs significantly (P < 0.05) increased the stability of minced pork with respect to lipid oxidation compared with the control, and the antioxidative effect was dose-dependent. Moreover, vacuum packaging resulted in mince with significantly lower oxidation and lipolysis levels than modified atmosphere packaged mince (P < 0.05). The results demonstrate that both EOs examined effectively reduced lipid oxidation in raw pork mince after 2 weeks' storage. PRACTICAL APPLICATION: The natural food preservatives market is growing rapidly, as is high demand for organic foods. These results are likely to be of interest to the scientists, researchers, and persons who work in the meat industry. Results and discussion can contribute to a better understanding of antioxidative properties of essential oils in food model. Furthermore, no study has reported the effect of these MAP on pork oxidative stability.

Antimicrobial activity of four essential oils extracted from plants commonly used in traditional medicine against some clinical strains

Introduction: Recently, efforts regarding the discovery of the effectual components of plants possessing antimicrobial properties are advanced. Herbal essential oils are widely used for treatment of various diseases, and they play an important role in healthcare considerations.

Objective: This study aims to evaluate the effectiveness of Cinnamomum verum, Eucalyptus globulus, Lavandula angustifolia and Mentha pulegium essential oils against Candida albicans and some pathogenic bacteria.

Methods: The antibacterial activity of four essential oils (EOs) against different microbial strains was evaluated using the disk diffusion method as well as determination of the minimal inhibitory concentration (MIC), and bactericidal concentration (MBC). For Candida albicans, the MFC of the plant oils was determined using a macro broth dilution assay. A range of concentrations (50 to 0.2 mg/ml) were prepared in Mueller Hinton Broth medium in flasks. Tween 80 (0.01% v/v) was included to enhance oil solubility. Each flask was inoculated with 108 CFU/ml of C. albicans. The flasks were incubated at 35°C for 48 hours. From each flask 13 μl of culture was inoculated onto Mueller-Hinton Agar plates and incubated at 35°C for 48 h. The plates were observed and the MFC was determined as the lowest concentration of plant oil completely inhibiting the growth of C. albicans.

Results: The obtained results showed that all bacteria and yeasts tested were sensitive to cinnamon essential oil with an inhibition zone ranging from 22 to 39.33 mm and a MIC ranging from 0.20 mg/ml to 1.56 mg/ml. At low concentrations ranging from 0.2 to 3.13 mg/ml, this essential oil has shown the most important bactericidal effect. Eucalyptus essential oil showed the highest inhibitory effect on Staphylococcus aureus with a diameter of 21.33±1.15 mm. The antibacterial effect of mint indicates that the most sensitive bacterium is A. boumannii. However, S. enteritidis, C. albicans, K. pneumoni and P. aeruginosa are resistant germs whose inhibition diameter varies from 7.33±1.15 mm to 11.33±1.15 mm. Lavender EO has an inhibitory effect against S. aureus (20.67±1.15 mm) and an intermediate effect against Streptococcus pyogenes, Serratia marcescens and Enterococcus faecalis.

Conclusions: The antibacterial activity of essential oils, especially those of cinnamon against the strains studied, supports their potential use as a remedy against infectious microbial diseases.

Novel natural food preservatives and applications in seafood preservation: a review

Food preservative additives are natural or synthetic substances which delay degradation in foods caused by microbial growth, enzyme activity, and oxidation. Until recently, the use of synthetic additives in food was more common. However, synthetic additives have not been widely accepted by consumers in recent years due to their assumed adverse effects on their health. Therefore, the tendency of consumers to natural additives is increasing day-by-day. Seafood is an easily perishable food due to its chemical composition. Immediately after harvest, changes in odor, taste, and texture in fishery products can be noticed. For this reason, measures to protect the product must be taken immediately after harvest or catching. Various preservation methods have been developed. In addition to various technological methods, preservative additives are used in fresh or processed seafood as well as in other foods. This review focuses on novel natural preservatives from different sources such as plants, bacteria, fungi, animals and algae, and their use in seafood to protect quality and prolong shelf life. © 2018 Society of Chemical Industry.

Chemical Composition, Antioxidant and Antibacterial Activity of Bunium persicum, Eucalyptus globulus, and Rose Water on Multidrug-Resistant Listeria Species

This research was aimed at investigating the antioxidant and antibacterial activity of Bunium persicum, Eucalyptus globulus, and rose water on multidrug-resistant Listeria species. The antibiotic resistance of Listeria spp obtained from seafood samples were determined by the Kirby-Bauer method. The antioxidant and antibacterial activity of the essential oils and extracts were evaluated using ferric reducing antioxidant power and microdilution methods, respectively. A total 2 samples (1.88%) were positive for Listeria spp. L monocytogenes was found to be resistant to ampicillin, amoxicillin/clavulanic acid, penicillin, vancomycin, and kanamycin. B persicum essential oil showed the greatest antioxidant activity (248.56 ± 1.09 µM Fe²⁺/g). The E globulus essential oil showed consistently strong antimicrobial activity against L monocytogenes and L grayi, while rose water showed no antimicrobial activity against any of the tested bacterial strains. The results showed that after adding the B persicum and E globulus essential oils to bacteria, the cell components’ release increased significantly.

Inhibitory effects of Inula britannica extract fermented by Lactobacillus plantarum KCCM 11613P on coagulase activity and growth of Staphylococcus aureus including methicillin-resistant strains

The aim of this study was to evaluate the antimicrobial efficacy of fermented Inula britannica extract (FIBE) against Staphylococcus aureus strains including methicillin-resistant S. aureus (MRSA). I. britannica extract was fermented by Lactobacillus plantarum KCCM 11613P, and the pathogenicity of S. aureus strains was determined via assessment of coagulase, DNase, and hemolytic activities. Epicatechin concentration increased from 4.38 to 6.05 μg/mg during fermentation (p < 0.01). FIBE treatment inhibited coagulase release from S. aureus to levels below the inhibitory concentration. FIBE promoted the release of intracellular nucleic acids and N-phenyl-1-naphthylamine absorption. In three S. aureus strains, damaged cells exhibited 21.58, 16.79, and 17.65% decreases in membrane potential induced by cell membrane depolarization, respectively (p < 0.05). Upon FIBE treatment in culture, the minimum inhibitory concentration of FIBE exerted a bacteriostatic effect. In conclusion, FIBE possesses antimicrobial properties, including inhibition of virulence factors, damage to cell membranes, and inhibition of bacterial growth. PRACTICAL APPLICATIONS: Methicillin-resistant Staphylococcus aureus (MRSA) is a serious concern in hospitals because of its known antibiotic resistance. Vancomycin and tigecycline are used for treating MRSA, but the appearance of vancomycin-intermediate and multidrug-resistant strains of these bacteria has created a demand for new antimicrobial agents. This study demonstrates the effective application of Inula britannica and fermentation technology for developing natural antimicrobial agents against methicillin-resistant Staphylococcus aureus.

Bacteriocins: Classification, synthesis, mechanism of action and resistance development in food spoilage causing bacteria

Huge demand of safe and natural preservatives has opened new area for intensive research on bacteriocins to unravel the novel range of antimicrobial compounds that could efficiently fight off the food-borne pathogens. Since food safety has become an increasingly important international concern, the application of bacteriocins from lactic acid bacteria that target food spoilage/pathogenic bacteria without major adverse effects has received great attention. Different modes of actions of these bacteriocins have been suggested and identified, like pore-forming, inhibition of cell-wall/nucleic acid/protein synthesis. However, development of resistance in the food spoilage and pathogenic bacteria against these bacteriocins is a rising concern. Emergence and spread of mutant strains resistant to bacteriocins is hampering food safety. It has spurred an interest to understand the bacteriocin resistance phenomenon displayed by the food pathogens, which will be helpful in mitigating the resistance problem. Therefore, present review is focused on the different resistance mechanisms adopted by food pathogens to overcome bacteriocin.

Antibacterial activity and sensory properties of Heracleum persicum essential oil, nisin, and Lactobacillus acidophilus against Listeria monocytogenes in cheese

AIM

The aim of this study was to evaluate the antibacterial and chemical effect of Heracleum persicum essential oil (EO), nisin, Lactobacillus acidophilus, and their combination against Listeria monocytogenes both in vitro and in Iranian white cheese model.

MATERIALS AND METHODS

Chemical compositions of H. persicum EO were analyzed by gas chromatography-mass spectrometry. After production of Iranian white cheese, minimum inhibitory concentration (MIC) and minimum bactericidal concentration of EO and nisin and agar spot test of L. acidophilus against L. monocytogenes were evaluated.

RESULTS

Hexyl butanoate (25.98%), octyl isobutyrate (17.82%), methyl butyrate (14.37%), and pentyl cyclopropane (12.77%) were the main components of the EO. MIC of the EO against L. monocytogenes was 2.5 mg/mL. Combination of nisin (5.3 IU/mL) and H. persicum EO (2500 µg/mL) showed increasing effect against L. monocytogenes (fractional inhibitory concentration = 0.9), while a higher concentration of EO and nisin showed undesirable effect on the cheese flavor. Furthermore, a combination of 1012 CFU/g L. acidophilus with H. persicum EO at the concentration of 2.5 mg/mL (T12) showed acceptable sensorial and also antibacterial results in Iranian white cheese.

CONCLUSION

Combination of H. persicum EO, L. acidophilus, and nisin can be recommended as natural preservatives and flavoring agents in cheese.

Estabelecimento de sistema bacteriano de expressão de peptídeos derivados da enzima vegetal RuBisCO

Resumo O objetivo do presente estudo foi estabelecer um sistema bacteriano de expressão de peptídeos derivados da proteólise simulada in silico da enzima ribulose-1,5-bisfosfato carboxilase oxigenase (RuBisCO), proveniente de soja, visando viabilizar um método sustentável de produção dessas moléculas para futura aplicação industrial. Inicialmente, foi conferida à cepa Escherichia coli S17-1 cálcio-competência para propagação do plasmídeo de expressão pET-30a(+) contendo o inserto codificante da sequência peptídica GSIKAFKEATKVDKVVVLWTALVPR. Após extração de DNA plasmidial, o material foi transformado em células de alto rendimento E. coli Rosetta™(DE3)pLysS. As células Rosetta portando o plasmídeo de expressão foram induzidas e a produção dos peptídeos foi verificada por meio de eletroforese em gel vertical, confirmando o estabelecimento de um sistema de expressão viável para peptídeos heterólogos. Assim, a produção em maior escala de peptídeos derivados de RuBisCO – associando-se futuramente etapas de purificação e ativação – torna-se possível. Além disso, o método aqui estabelecido pode também ser aplicado utilizando diferentes sequências peptídicas com atividade antimicrobiana.

Microbiological Safety of Fresh Tilapia ( Oreochromis niloticus) from Kenyan Fresh Water Fish Value Chains

This study evaluated the microbiological safety of fresh Nile tilapia ( Oreochromis niloticus) from Kenyan fresh water fish value chains. One hundred seventy-six fish samples were analyzed. The microbial counts of hygiene indicators, total viable aerobic count (TVC), total coliforms, and fecal coliforms isolated by using culture techniques were enumerated, and microbial pathogens present in the fish samples were identified and characterized by using molecular methods. The diversity of bacterial isolates was determined by using the Shannon-Weaver diversity index. The mean of TVC in the samples was 4.44 log CFU/g. A comparison with the European Commission and International Commission on Microbiological Specifications for Foods standards showed two fish samples had counts above the 5.00 log CFU/g limit for TVC, and all the fish samples had total coliform and fecal coliform counts above 2.00 and 1.00 log CFU/g, respectively. Pathogenic strains, including Shiga toxin-producing and enteropathogenic Escherichia coli, Listeria monocytogenes, Yersinia enterocolitica, Klebsiella pneumoniae, and Salmonella enterica, were identified in the fish samples. The diversity of 1,608 bacterial isolates was higher in semiregulated chains than unregulated chains. The diversity was also high at the retail stage of the fish value chain. In conclusion, fresh Nile tilapia samples were above some of the set food safety standards and may be a source of foodborne pathogens. Further microbial risk assessment for detected pathogens is recommended to further support public health protection, taking into account growth, inactivation through cooking, processing, survival, and consumption.