Antimicrobial activity of pediocin-producing Lactococcus lactis on Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 in cheese

The Potential of Pediococcus acidilactici Cell-Free Supernatant as a Preservative in Food Packaging Materials

This study delves into the production and antimicrobial characteristics of cell-free supernatants from Pediococcus acidilactici (CFSs-Pa). Antimicrobial activity was initially observed in CFS-Pa harvested after 12 h of incubation and increased up to the late stationary phase at 48 h. The increase in antimicrobial activity did not align with total protein content, pointing to other factors linked to the accumulation of organic acids, particularly lactic acid. The SDS-PAGE analysis also indicated that the expected proteinaceous compound (pediocin) was not observed in CFS-Pa. Further investigations suggested that the antimicrobial properties of CFS-Pa were exclusively due to organic acids. The MIC values confirmed potent antimicrobial activity, particularly at a 10% dilution of CFS-Pa in MRS broth. The time-kill assays demonstrated bactericidal activity against EHEC, Listeria monocytogenes, and Staphylococcus aureus by 12 h, 18 h, and 24 h using a 10% dilution of CFS-Pa. Additionally, CFS-Pa exhibited dose-dependent antioxidant activity, requiring a 70% (v/v) concentration to inhibit DPPH scavenging activity by 50%. All the experimental results suggested potential applications of CFS-Pa in food preservation. An attempt to incorporate CFS-Pa into bacterial cellulose (BC) for edible food packaging demonstrated promising antimicrobial results, particularly against L. monocytogenes and S. aureus, with room for optimization.

Metabolites from Lactococcus lactis subsp. lactis: Isolation, Structure Elucidation, and Antimicrobial Activity

Herein, we disclose the identification of novel metabolites from a potential probiotic strain, Lactococcus lactis subsp. lactis, obtained from traditional dairy milk samples collected in Maharashtra, India (in January 2021). Isolated metabolites include pyrazin-2-carboxamide [1, pyrazinamide, a potential antitubercular drug], 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one (2, DDMP), 2,4-di-tert-butylphenol (3), and hexadecanoic acid (4, palmitic acid). The chemical structures of these metabolites were elucidated through extensive 1D NMR (1H and 13C) and 2D NMR (HSQC, HMBC, and NOESY) analyses, high-resolution mass spectrometry, high-performance liquid chromatography, and single-crystal X-ray crystallography. Furthermore, these novel metabolites exhibited potent inhibitory activities against various bacteria, fungi, and yeast strains with minimum inhibitory concentrations ranging between 1.56 and 25 μg/mL, and compounds 1 and 3 were found to be most active against a wide range of microbial strains tested.

Effect of Disulfide Bonds on the Thermal Stability of Pediocin: In-silico Screening Using Molecular Dynamics Simulation

The thermal stability properties of pediocin at 310, 313, 323, 333, 343, and 348 K (37, 40, 50, 60, 70, and 75°C, respectively) are reported in this study. A theoretical approach, such as the molecular dynamics method, was used to analyze the structure. Molecular dynamics simulation confirms the stability of molecules with Cys. Furthermore, this study reveals that Cys residues play an essential role in structure stability at high temperatures. To understand the structural basis for the stability of pediocin, a detailed in-silico analysis using molecular dynamics simulations to explore the thermal stability profiles of the compounds was conducted. This study shows that thermal effects fundamentally alter the functionally crucial secondary structure of pediocin. However, as previously reported, pediocin's activity was strictly conserved due to the disulfide bond between Cys residues. These findings reveal, for the first time, the dominant factor behind the thermodynamic stability of pediocin.

Effectiveness of raw bacteriocin produced from lactic acid bacteria on biofilm of methicillin-resistant Staphylococcus aureus

Background and Aim

Probiotics are proven beneficial to health since they enhance immunity against dangerous pathogens and increase resistance to illness. Bacteriocin produced by lactic acid bacteria (LAB), demonstrates a broad inhibitory spectrum and therapeutic potential. This study aimed to isolate LAB-producing bacteriocin and investigate the effect of crude bacteriocin on biofilm from methicillin-resistant Staphylococcus aureus (MRSA).

Materials and Methods

This study used randomly collected 80 white soft local cheeses (40 each from cows and sheep) from different supermarkets in Basrah Province. The obtained samples were cultured and the bacterial suspension of S. aureus was prepared at 1.5 × 10⁸ cells/mL. The crude bacteriocin extracted from LAB was obtained, and the tube was dried and inverted to detect the biofilm loss at the bottom.

Results

There were 67 (83.75%) LAB isolates. Among 40 milk samples collected directly and indirectly, there were 36 (83.33%). Staphylococcus aureus isolates based on conventional bacteriological analysis and biochemical tests. Molecular testing was conducted to identify LAB and MRSA. Depending on genotypic results, the effect of white soft local cheese (cows and sheep) and the amplification results of the 16S rRNA gene were detected in 46 LAB isolates from white soft local cheese from cows and sheep. Based on the molecular identification of the mecA, results on Staphylococcus determined that only 2 of 36 isolates of S. aureus carried the mecA. Moreover, there were 26 (86.66%) isolates (MRSA) from samples of raw milk from local markets and subclinical mastitis in cows. The ability of LAB isolates was tested. The effects of bacteriocin production on preventing biofilm growth and formation were investigated. Results demonstrated that bacteriocin has high activity. Microtiter plates applied to investigate the ability of S. aureus to produce biofilms revealed that all isolates were either weak or moderate biofilm producers, with neither non-biofilm nor strong biofilm producers found among the tested isolates.

Conclusion

Lactic acid bacteria demonstrate a high ability to produce bacteriocin. Crude bacteriocin from LAB has a restrictive effect on biofilms produced by MRSA; thus, it can be used to reduce the pathogenicity of this bacterium.

Potentials of Natural Preservatives to Enhance Food Safety and Shelf Life: A Review

Food-borne illnesses are a significant concern for consumers, the food industry, and food safety authorities. Natural preservatives are very crucial for enhancing food safety and shelf life. Therefore, this review aimed to assess the literature regarding the potential of natural preservatives to enhance food safety and extend the shelf life of food products. The review paper indicated that natural antimicrobial agents that inhibit bacterial and fungal growth for better quality and shelf life have been of considerable interest in recent years. Natural antimicrobials are mainly extracted and isolated as secondary metabolites of plants, animals, and microorganisms. Plants, especially herbs and spices, are given more attention as a source of natural antimicrobials. Microorganisms used in food fermentation also produce different antimicrobial metabolites, including organic acids, hydrogen peroxide, and diacetyl, in addition to bacteriocins. Products of animal origin, such as tissues and milk, contain different antimicrobial agents. Natural antimicrobials are primarily extracted and purified before utilization for food product development. The extraction condition and purification of natural preservatives may change their structure and affect their functionality. Selecting the best extraction method coupled with minimal processing such as direct mechanical extraction seems to preserve active ingredients. The activity of natural antimicrobials could also be influenced by the source, time of harvesting, and stage of development. The effectiveness of natural antimicrobial compounds in food applications is affected by different factors, including food composition, processing method, and storage conditions. Natural antimicrobials are safe because they can limit microbial resistance and meet consumers’ demands for healthier foods.

Antibiofilm, AntiAdhesive and Anti-Invasive Activities of Bacterial Lysates Extracted from Pediococcus acidilactici against Listeria monocytogenes

This study aimed to investigate whether bacterial lysates (BLs) extracted from Pediococcus acidilactici reduce Listeria monocytogenes biofilm formation, as well as adhesion to and invasion of human intestinal epithelial cells. Pretreatment with P. acidilactici BLs (20, 40, and 80 μg/mL) significantly inhibited L. monocytogenes biofilm formation on the surface of polystyrene (p < 0.05). Fluorescence and scanning-electron-microscopic analyses indicated that L. monocytogenes biofilm comprised a much less dense layer of more-dispersed cells in the presence of P. acidilactici BLs. Moreover, biofilm-associated genes, such as flaA, fliG, flgE, motB, degU, agrA, and prfA, were significantly downregulated in the presence of P. acidilactici BLs (p < 0.05), suggesting that P. acidilactici BLs prevent L. monocytogenes biofilm development by suppressing biofilm-associated genes. Although P. acidilactici BLs did not dose-dependently inhibit L. monocytogenes adhesion to and invasion of intestinal epithelial cells, the BLs effectively inhibited adhesion and invasion at 40 and 80 μg/mL (p < 0.05). Supporting these findings, P. acidilactici BLs significantly downregulated L. monocytogenes transcription of genes related to adhesion and invasion, specifically fbpA, ctaP, actA, lapB, ami, and inlA. Collectively, these results suggest that P. acidilactici BLs have the potential to reduce health risks from L. monocytogenes.

Whole genome sequencing for the risk assessment of probiotic lactic acid bacteria

Probiotic bacteria exhibit beneficial effects on human and/or animal health, and have been widely used in foods and fermented products for decades. Most probiotics consist of lactic acid bacteria (LAB), which are used in the production of various food products but have also been shown to have the ability to prevent certain diseases. With the expansion of applications for probiotic LAB, there is an increasing concern with regard to safety, as cases with adverse effects, i.e., severe infections, transfer of antimicrobial resistance genes, etc., can occur. Currently, in vitro assays remain the primary way to assess the properties of LAB. However, such methodologies are not meeting the needs of strain risk assessment on a high-throughput scale, in the context of the evolving concept of food safety. Analyzing the complete genetic information, including potential virulence genes and other determinants with a negative impact on health, allows for assessing the safe use of the product, for which whole-genome sequencing (WGS) of individual LAB strains can be employed. Genomic data can also be used to understand subtle differences in the strain level important for beneficial effects, or protect patents. Here, we propose that WGS-based bioinformatics analyses are an ideal and cost-effective approach for the initial in silico microbial risk evaluation, while the technique may also increase our understanding of LAB strains for food safety and probiotic property evaluation.

Inhibitory Effect of Lactiplantibacillusplantarum and Lactococcus lactis Autochtonous Strains against Listeria monocytogenes in a Laboratory Cheese Model

In the present study, six Lactococcus lactis and seven Lactiplantibacillus plantarum strains isolated from artisanal Sardinian dairy products were evaluated for their efficacy in controlling the growth of Listeria monocytogenes during the storage of miniature fresh cheese manufactured on a laboratory scale to exploit their possible use as biopreservatives. The strains were tested for antimicrobial activity and some technological characteristics before using them in miniature fresh cheese to evaluate their in situ antilisterial effect. Our results showed that five strains (L. lactis 16FS16-9/20234-11FS16 and Lpb. plantarum 1/14537-4A/20045) could be considered suitable candidates for use as protective cultures in fresh cheese manufacture since they significantly lowered the pathogen counts by 3–4 log units compared to the control; however, all strains tested were capable of decreasing L. monocytogenes numbers. Our results suggest that the single and combined action of the acidifying power and the production of bacteriocin of these strains was capable of controlling and/or reducing the growth of L. monocytogenes. Considering their technological characteristics, they might be used as starter/adjunct cultures to increase the safety of the products, perhaps in association with other antimicrobial hurdles.

Biofloc Microbiome With Bioremediation and Health Benefits

The biofloc system has recently attracted great attention as a cost-effective, sustainable, and environmentally friendly technology and expected to contribute toward human food security (Zero Hunger SDG 2). It is also expected that this endeavor can be adopted widely because of its characteristics of zero water exchange and reduced artificial feeding features. In the biofloc system, the flocs which are generally formed by aggregation of heterotrophic microorganisms, serve as natural bioremediation candidates. These microbes effectively maintain water quality by utilizing the nutrient wastes, mostly originated from digested, unconsumed, and metabolic processes of feed. Additionally, the flocs are important sources of nutrients, mainly a protein source, and when these are consumed by aquaculture animals they improve the growth performance, immunity, and disease tolerance of host against pathogenic microbial infection. Here in this review, we focus on recent advances that could provide a mechanistic insight on how the microbial community developed in the biofloc system helps in the bioremediation process and enhances the overall health of the host. We have also tried to address the possible role of these microbial communities against growth and virulence of pathogenic microbes.

Spirulina platensis extract nanoliposomes: preparation, characterization and application to white cheese

BACKGROUND

Ultrafiltration cheese is produced in large scale from treated and pasteurized treated and pasteurized milk with mesophilic starter and to expand its shelf life preservatives addition is needed.

OBJECTIVE

The purpose of the present study was preparation of encapsulate Spirulina platensis algae nanoliposomes to evaluate the characteristics of the nanoliposomes loaded with Spirulina extract (SE-NLs). In addition, the chemical and microbiological properties of white cheese produced with SE-NLs were studied.

METHODS

Nanoliposomes are composed of lecithin and cholesterol, used for the encapsulation of SE. The SE-NLs were prepared using the thin layer hydration method. The characteristics of produced SE-NLs including particle size, zeta potential, morphology and the encapsulation efficiency (EE) was studied during 4 weeks in different storage conditions (4 °C and 25 °C). In addition, the effect of SE and SE-NLs on the chemical and microbiological properties of white cheese was evaluated during 60 days of ripening.

RESULTS

The results showed that the nanoliposomes loaded with 3 mg/g of SE had the optimum formulation due to the higher EE, smaller particle size, and higher negatively charged zeta potential. The quality of the produced nanoliposomes decreased by increasing the time of storage but the SE-NLs stored at 4 °C were more stable and possessed higher EE and smaller particle sizes. While the chemical composition of the cheeses manufactured by the nanoliposome loaded with 3 mg/g SE- NLs were comparable to that of control cheese at 60 days of ripening, it showed a significant inhibitory effect on Staphylococcus aureus and Listeria monocytogenes after 30 days.

CONCLUSION

The utilization of SE-NLs can be considered as a natural antimicrobial and an alternative to the use of synthetic preservatives in the production of white cheese.

HIGHLIGHTS

Nanoliposomes of Spirulina platensis extracts was prepared.UF white cheese prepared by nanoliposomes and then were evaluated.

In vitro and in silico approach for characterization of antimicrobial peptides from potential probiotic cultures against Staphylococcus aureus and Escherichia coli

The focus of the present study was to characterize antimicrobial peptide produced by potential probiotic cultures of Enterococcus durans DB-1aa (MCC4243), Lactiplantibacillus plantarum Cu2-PM7 (MCC4246) and Limosilactobacillus fermentum Cu3-PM8 (MCC4233) against Staphylococus aureus MTCC 96 and Escherichia coli MTCC118. The growth kinetic assay revealed 24 h of incubation to be optimum for bacteriocin production. The partially purified compound of all the three selected cultures after ion-exchange chromatography was found to be thermoresistant and stable under a wide range of pH. The compound was sensitive to proteinase-K, but resistant to trypsin, α-amylase and lipase. Comparatively, bacteriocins from L. fermentum Cu3-PM8 and L. plantarum Cu2-PM7 showed higher stability under studied parameter, hence was taken up for further investigation. The apparent molecular weight of bacteriocin from L. fermentum MCC4233 and L. plantarum MCC4246 was found to be 3.5 kDa. Further, plantaricin gene from MCC4246 was characterized in silico. The translated partial amino acid sequence of the plnA gene in MCC4246 displayed 48 amino acids showing 100 % similarity with plantaricin A of Lactobacillus plantarum (WP_0036419). The sequence revealed 7 β sheets, 6 α sheets, 6 predicted coils and 9 predicted turns. The predicted properties of the peptide included an isoelectric point of 10.82 and a hydrophobicity of 48.6 %. The molecular approach of using Geneious Prime software and protein prediction data base for characterization of bacteriocin is novel and predicts "KSSAYSLQMGATAIKQVKKLFKKWGW" to be a peptide responsible for antimicrobial activity. The study provides information about a broad spectrum bacteriocin in native probiotic culture and paves a way towards its application in functional foods as a biopreservative agent.

Autochthonous Enterococcus durans PFMI565 and Lactococcus lactis subsp. lactis BGBU1-4 in Bio-Control of Listeria monocytogenes in Ultrafiltered Cheese

Nowadays, consumers are interested in cheese produced without chemical additives or high-temperature treatments, among which, protective lactic acid bacteria (LAB) cultures could play a major role. In this study, the aims were to isolate, identify and characterize antilisterial LAB from traditionally produced cheese, and utilize suitable LAB in cheese production. Among 200 isolated LAB colonies, isolate PFMI565, with the strongest antilisterial activity, was identified as Enterococcus durans. E. durans PFMI565 was sensitive to clinically important antibiotics (erytromicin, tetracycline, kanamycin, penicillin, vancomycin) and had low acidifying activity in milk. E. durans PFMI565 and the previously isolated bacteriocin producer, Lactococcus lactis subsp. lactis BGBU1–4, were tested for their capability to control Listeria monocytogenes in experimentally contaminated ultrafiltered (UF) cheeses during 35 days of storage at 4 °C. The greatest reductions of L. monocytogenes numbers were achieved in UF cheese made with L. lactis subsp. lactis BGBU1–4 or with the combination of L. lactis subsp. lactis BGBU1–4 and E. durans PFMI565. This study underlines the potential application of E. durans PFMI565 and L. lactis subsp. lactis BGBU1–4 in bio-control of L. monocytogenes in UF cheese.

Use of Starter Cultures in Foods from Animal Origin to Improve Their Safety

Starter cultures can be defined as preparations with a large number of cells that include a single type or a mixture of two or more microorganisms that are added to foods in order to take advantage of the compounds or products derived from their metabolism or enzymatic activity. In foods from animal origin, starter cultures are widely used in the dairy industry for cheese, yogurt and other fermented dairy products, in the meat industry, mainly for sausage manufacture, and in the fishery industry for fermented fish products. Usually, microorganisms selected as starter culture are isolated from the native microbiota of traditional products since they are well adapted to the environmental conditions of food processing and are responsible to confer specific appearance, texture, aroma and flavour characteristics. The main function of starter cultures used in food from animal origin, mainly represented by lactic acid bacteria, consists in the rapid production of lactic acid, which causes a reduction in pH, inhibiting the growth of pathogenic and spoilage microorganisms, increasing the shelf-life of fermented foods. Also, production of other metabolites (e.g., lactic acid, acetic acid, propionic acid, benzoic acid, hydrogen peroxide or bacteriocins) improves the safety of foods. Since starter cultures have become the predominant microbiota, it allows food processors to control the fermentation processes, excluding the undesirable flora and decreasing hygienic and manufacturing risks due to deficiencies of microbial origin. Also, stater cultures play an important role in the chemical safety of fermented foods by reduction of biogenic amine and polycyclic aromatic hydrocarbons contents. The present review discusses how starter cultures contribute to improve the microbiological and chemical safety in products of animal origin, namely meat, dairy and fishery products.

Bacteriocins as an alternative in the treatment of infections by Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a highly versatile Gram-positive bacterium that is carried asymptomatically by up to 30% of healthy people, while being a major cause of healthcare-associated infections, making it a worldwide problem in clinical medicine. The adaptive evolution of S. aureus strains is demonstrated by its remarkable capacity to promptly develop high resistance to multiple antibiotics, thus limiting treatment choice. Nowadays, there is a continuous demand for an alternative to the use of antibiotics for S. aureus infections and a strategy to control the spread or to kill phylogenetically related strains. In this scenario, bacteriocins fit as with a promising and interesting alternative. These molecules are produced by a range of bacteria, defined as ribosomally synthesized peptides with bacteriostatic or bactericidal activity against a wide range of pathogens. This work reviews ascertained the main antibiotic-resistance mechanisms of S. aureus strains and the current, informative content concerning the applicability of the use of bacteriocins overlapping the use of conventional antibiotics in the context of S. aureus infections. Besides, we highlight the possible application of these biomolecules on an industrial scale in future work.

Bryndza cheese of Slovak origin as potential resources of probiotic bacteria

Bryndza cheese includes several predominant lactic acid bacteria. The aim of our study was the antagonistic effect of lactic acid bacteria supernatant isolated from ewes´ cheese bryndza against ten Gram-positive and Gram-negative bacteria. Isolated strains of bacteria were obtained from bryndza which were produced in five different regions of Slovakia. Isolated strains of lactic acid bacteria were identified with mass spectrometry MALDI-TOF MS Biotyper. A total of one hundred and thirty lactic bacteria include Enterococcus faecalis, Enterococcus faecium, Enterococcus hirae, Lactobacillus brevis, Lactobacillus harbinensis, Lactobacillus johnsonii, Lactobacillus plantarum, Lactobacillus paracasei ssp. paracasei, Lactobacillus paraplantarum, Lactobacillus suebicus, Lactococcus lactis ssp. lactis, Lactococcus lactis, and Pediococcus acidilactici were tested in this study against Gram-negative bacteria: Escherichia coli CCM 3988, Klebsiella pneumoniae CCM 2318, Salmonella enterica subsp. enterica CCM 3807, Shigella sonnei CCM 1373, Yersinia enterocolitica CCM 5671 and Gram-positive bacteria: Bacillus thuringiensis CCM 19, Enterococcus faecalis CCM 4224, Listeria monocytogenes CCM 4699, Staphylococcus aureus subsp. aureus CCM 2461, Streptococcus pneumonia CCM 4501 with agar diffusion method. Lactic acid bacteria showed activity 92% against Yersinia enterocolitica, 91% against Klebsiella pneumoniae, 88% against Escherichia coli, 84% against Listeria monocytogenes. The most effective bacteria against Gram-positive and Gram-negative bacteria tested was Lactobacillus paracasei ssp. paracasei.

Suitability of the Nisin Z-producer Lactococcus lactis subsp. lactis CBM 21 to be Used as an Adjunct Culture for Squacquerone Cheese Production

This research investigated the technological and safety effects of the nisin Z producer Lactococcus lactis subsp. lactis CBM 21, tested as an adjunct culture for the making of Squacquerone cheese in a pilot-scale plant. The biocontrol agent remained at a high level throughout the cheese refrigerated storage, without having a negative influence on the viability of the conventional Streptococcus thermophilus starter. The inclusion of CBM 21 in Squacquerone cheesemaking proved to be more effective compared to the traditional one, to reduce total coliforms and Pseudomonas spp. Moreover, the novel/innovative adjunct culture tested did not negatively modify the proteolytic patterns of Squacquerone cheese, but it gave rise to products with specific volatile and texture profiles. The cheese produced with CBM 21 was more appreciated by the panelists with respect to the traditional one.

Phylogenetic distribution of the bacteriocin repertoire of lactic acid bacteria species associated with artisanal cheese

The microbiota contributes to artisanal cheese bioprotection and biopreservation through inter and intraspecific competition. This work aimed to investigate the phylogenetic distribution of the repertoire of bacteriocin structural genes of model lactic acid bacteria (LAB) in order to investigate its respective role in the artisanal cheeses microenvironment. A phylogenetic analysis of the rRNA 16S gene from 445 model strains of LAB was conducted using bayesian inference and the repertoire of bacteriocin genes was predicted from these strains by BAGEL software. Bacterial strains were clustered in five monophyletic clades (A, B, C, D and E) with high posterior probability values (PP > 0.99). One bacteriocin structural gene was predicted for 88.5% of the analyzed strains. The majority of the species encoded different classes of bacteriocins. Greater diversity of bacteriocin genes was found for strains included in clade A, comprising Lactococcus lactis, Streptococcus agalactiae, Streptococcus thermophilus, Streptococcus macedonicus, Enterococcus faecalis and Enterococcus faecium. In addition, Lactococcus lactis presented higher diversity of bacteriocin classes, encoding glycocins, lanthipeptides, sactipeptides, cyclic and linear azole-containing peptides, included in bacteriocins class I, besides class II and III. The results suggest that the distribution of bacteriocin structural genes is related to the phylogenetic clades of LAB species, with a higher frequency in some specific clades. Information comprised in this study contributes to comprehend the bacterial competition mechanisms in the artisanal cheese microenvironment.

Food Safety through Natural Antimicrobials

Microbial pathogens are the cause of many foodborne diseases after the ingestion of contaminated food. Several preservation methods have been developed to assure microbial food safety, as well as nutritional values and sensory characteristics of food. However, the demand for natural antimicrobial agents is increasing due to consumers' concern on health issues. Moreover, the use of antibiotics is leading to multidrug resistant microorganisms reinforcing the focus of researchers and the food industry on natural antimicrobials. Natural antimicrobial compounds from plants, animals, bacteria, viruses, algae and mushrooms are covered. Finally, new perspectives from researchers in the field and the interest of the food industry in innovations are reviewed. These new approaches should be useful for controlling foodborne bacterial pathogens; furthermore, the shelf-life of food would be extended.

Ocins for Food Safety

The food industry produces highly perishable products. Food spoilage represents a severe problem for food manufacturers. Therefore, it is important to identify effective preservation solutions to prevent food spoilage. Ocins (e.g., bacteriocins, lactocins, and enterocins) are antibacterial proteins synthesized by bacteria that destroy or suppress the growth of related or unrelated bacterial strains. Ocins represent a promising strategy for food preservation, because of their antagonist effects toward food spoilage microorganisms, high potency, and low toxicity. Additionally, they can be bioengineered. The most common and commercially available ocins are nisin, plantaracin, sakacin P, and pediocin. Several ocins have been characterized and studied biochemically and genetically; however, their structure-function relationship, biosynthesis, and mechanism of action are not understood. This narrative review focuses primarily on ocins and their relevance to the food industry to help prevent food spoilage. In particular, the applications and limitations of ocins in the food industry are highlighted.

Growth, detection and virulence of Listeria monocytogenes in the presence of other microorganisms: microbial interactions from species to strain level

Like with all food microorganisms, many basic aspects of L. monocytogenes life are likely to be influenced by its interactions with bacteria living in close proximity. This pathogenic bacterium is a major concern both for the food industry and health organizations since it is ubiquitous and able to withstand harsh environmental conditions. Due to the ubiquity of Listeria monocytogenes, various strains may contaminate foods at different stages of the supply chain. Consequently, simultaneous exposure of consumers to multiple strains is also possible. In this context even strain-to-strain interactions of L. monocytogenes play a significant role in fundamental processes for the life of the pathogen, such as growth or virulence, and subsequently compromise food safety, affect the evolution of a potential infection, or even introduce bias in the detection by classical enrichment techniques. This article summarizes the impact of microbial interactions on the growth and detection of L. monocytogenes primarily in foods and food-associated environments. Furthermore it provides an overview of L. monocytogenes virulence in the presence of other microorganisms.

Selection of indigenous lactic acid bacteria presenting anti-listerial activity, and their role in reducing the maturation period and assuring the safety of traditional Brazilian cheeses

Artisanal raw milk cheeses are highly appreciated dairy products in Brazil and ensuring their microbiological safety has been a great need. This study reports the isolation and characterization of lactic acid bacteria (LAB) strains with anti-listerial activity, and their effects on Listeria monocytogenes during refrigerated shelf-life of soft Minas cheese and ripening of semi-hard Minas cheese. LAB strains (n = 891) isolated from Minas artisanal cheeses (n = 244) were assessed for anti-listerial activity by deferred antagonism assay at 37 °C and 7 °C. The treatments comprised the production of soft or semi-hard Minas cheeses using raw or pasteurized milk, and including the addition of selected LAB only [Lactobacillus brevis 2-392, Lactobacillus plantarum 1-399 and 4 Enterococcus faecalis (1-37, 2-49, 2-388 and 1-400)], L. monocytogenes only, selected LAB co-inoculated with L. monocytogenes, or without any added cultures. At 37 °C, 48.1% of LAB isolates showed anti-listerial capacity and 77.5% maintained activity at 7 °C. Selected LAB strains presented a bacteriostatic effect on L. monocytogenes in soft cheese. L. monocytogenes was inactivated during the ripening of semi-hard cheeses by the mix of LAB added. Times to attain a 4 log-reduction of L. monocytogenes were 15 and 21 days for semi-hard cheeses produced with raw and pasteurized milk, respectively. LAB with anti-listerial activity isolated from artisanal Minas cheeses can comprise an additional barrier to L. monocytogenes growth during the refrigerated storage of soft cheese and help shorten the ripening period of semi-hard cheeses aged at ambient temperature.

Human microbiome versus food-borne pathogens: friend or foe

As food safety advances, there is a great need to maintain, distribute, and provide high-quality food to a much broader consumer base. There is also an ever-growing "arms race" between pathogens and humans as food manufacturers. The human microbiome is a collective organ of microbes that have found community niches while associating with their host and other microorganisms. Humans play an important role in modifying the environment of these organisms through their life choices, especially through individual diet. The composition of an individual's diet influences the digestive system-an ecosystem with the greatest number and largest diversity of organisms currently known. Organisms living on and within food have the potential to be either friends or foes to the consumer. Maintenance of this system can have multiple benefits, but lack of maintenance can lead to a host of chronic and preventable diseases. Overall, this dynamic system is influenced by intense competition from food-borne pathogens, lifestyle, overall diet, and presiding host-associated microbiota.

Evaluation of technological properties of Enterococcus faecium CECT 8849, a strain isolated from human milk, for the dairy industry

In this work, a variety of biochemical properties of Enterococcus faecium CECT 8849, which had been isolated from breast milk, were analyzed. Its acidifying capacity and proteolytic activity were low but, in contrast, remarkable peptidase and esterase activities were observed. Ethanol and 3-hydroxy-2-butanone were the most abundant volatile compounds found in experimental model cheese manufactured with E. faecium CECT 8849. This strain inhibited the growth of several Listeria monocytogenes and Listeria innocua strains in vitro. Enterocin A and B structural genes were detected in E. faecium CECT 8849. Model fermented milk and cheeses were manufactured from milk inoculated or not with L. innocua CECT 8848 (2.5-3 log10 colony forming units mL(-1)) using E. faecium CECT 8849 or Lactococcus lactis ESI 153 as starter cultures. Although E. faecium CECT 8849 controlled Listeria growth in both dairy models, it led to lower reduction in Listeria counts when compared with L. lactis ESI 153.

Antimicrobial activity of lactic acid bacteria in dairy products and gut: effect on pathogens

The food industry seeks alternatives to satisfy consumer demands of safe foods with a long shelf-life able to maintain the nutritional and organoleptic quality. The application of antimicrobial compounds-producing protective cultures may provide an additional parameter of processing in order to improve the safety and ensure food quality, keeping or enhancing its sensorial characteristics. In addition, strong evidences suggest that certain probiotic strains can confer resistance against infection with enteric pathogens. Several mechanisms have been proposed to support this phenomenon, including antimicrobial compounds secreted by the probiotics, competitive exclusion, or stimulation of the immune system. Recent research has increasingly demonstrated the role of antimicrobial compounds as protective mechanism against intestinal pathogens and therefore certain strains could have an effect on both the food and the gut. In this aspect, the effects of the combination of different strains keep unknown. The development of multistrain probiotic dairy products with good technological properties and with improved characteristics to those shown by the individual strains, able to act not only as protective cultures in foods, but also as probiotics able to exert a protective action against infections, has gained increased interest.

Inhibitory activity of Lactobacillus plantarum TF711 against Clostridium sporogenes when used as adjunct culture in cheese manufacture

Bacteriocins produced by lactic acid bacteria are of great interest to the food-processing industry as natural preservatives. This work aimed to investigate the efficacy of bacteriocin-producing Lactobacillus plantarum TF711, isolated from artisanal Tenerife cheese, in controlling Clostridium sporogenes during cheese ripening. Cheeses were made from pasteurised milk artificially contaminated with 10(4) spores m/l C. sporogenes. Experimental cheeses were manufactured with Lb. plantarum TF711 added at 1% as adjunct to commercial starter culture. Cheeses made under the same conditions but without Lb. plantarum TF711 served as controls. Evolution of microbiological parameters, pH and NaCl content, as well as bacteriocin production was studied throughout 45 d of ripening. Addition of Lb. plantarum TF711 did not bring about any significant change in starter culture counts, NaCl content and pH, compared with control cheese. In contrast, clostridial spore count in experimental cheeses were significantly lower than in control cheeses from 7 d onwards, reaching a maximum reduction of 2·2 log units on day 21. Inhibition of clostridia found in experimental cheeses was mainly attributed to plantaricin activity, which in fact was recovered from these cheeses.

Behavior of Staphylococcus aureus in culture broth, in raw and thermized milk, and during processing and storage of traditional Greek Graviera cheese in the presence or absence of Lactococcus lactis subsp. cremoris M104, a wild, novel nisin A-producing raw milk isolate

This study was conducted to evaluate the behavior of Staphylococcus aureus during processing, ripening, and storage of traditional Greek Graviera cheese in accordance with European Union Regulation 1441/2007 for coagulase-positive staphylococci in thermized milk cheeses. Lactococcus lactis subsp. cremoris M104, a wild, novel nisin A-producing (NisA+) strain, also was evaluated as an antistaphylococcal adjunct. A three-strain cocktail of enterotoxigenic (Ent+) S. aureus increased by approximately 2 log CFU/ml when co-inoculated (at approximately 3 log CFU/ml) in thermized Graviera cheese milk (TGCM; 63°C for 30 s) with commercial starter culture (CSC) and/or strain M104 at approximately 6 log CFU/ml and then incubated at 37°C for 3 h. However, after 6 h at 37°C, significant retarding effects on S. aureus growth were noted in the order TGCM + M104 > TGCM + CSC = TGCM + CSC + M104 > TGCM. Additional incubation of TGCM cultures at 18°C for 66 h resulted in a 1.2-log reduction (P < 0.05) of S. aureus populations in TGCM + M104. The Ent + S. aureus cocktail did not grow but survived during ripening and storage when inoculated (at approximately 3 log CFU/g) postcooking into Graviera mini cheeses prepared from TGCM + CSC or TGCM + CSC + M104, ripened at 18°C and 90% relative humidity for 20 days, and stored at 4°C in vacuum packages for 2 months. A rapid 10-fold decrease (P < 0.05) in S. aureus populations occurred within the first 24 h of cheese fermentation. Reductions of S. aureus were greater by approximately 0.4 log CFU/g in CSC + M104 than in CSC only cheeses, concomitantly with the presence of NisA + M104 colonies and nisin-encoding genes in the CSC plus M104 cheeses and their corresponding microbial consortia only. A high level of selective survival of a naturally nisin-resistant EntC z S. aureus strain from the cocktail was noted in CSC + M104 cheeses and in coculture with the NisA + M104 strain in M-17 broth. In conclusion, although S. aureus growth inhibition is assured during Graviera cheese ripening, early growth of the pathogen during milk curdling and curd cooking operations may occur. Nisin-resistant S. aureus strains that may contaminate Graviera cheese milks postthermally may be difficult to control even by the application of the NisA + L. lactis subsp. cremoris strain M104 as a bioprotective adjunct culture.

Development of a potential probiotic fresh cheese using two Lactobacillus salivarius strains isolated from human milk

Cheeses have been proposed as a good alternative to other fermented milk products for the delivery of probiotic bacteria to the consumer. The objective of this study was to assess the survival of two Lactobacillus salivarius strains (CECT5713 and PS2) isolated from human milk during production and storage of fresh cheese for 28 days at 4°C. The effect of such strains on the volatile compounds profile, texture, and other sensorial properties, including an overall consumer acceptance, was also investigated. Both L. salivarius strains remained viable in the cheeses throughout the storage period and a significant reduction in their viable counts was only observed after 21 days. Globally, the addition of the L. salivarius strains did not change significantly neither the chemical composition of the cheese nor texture parameters after the storage period, although cheeses manufactured with L. salivarius CECT5713 presented significantly higher values of hardness. A total of 59 volatile compounds were identified in the headspace of experimental cheeses, and some L. salivarius-associated differences could be identified. All cheeses presented good results of acceptance after the sensory evaluation. Consequently, our results indicated that fresh cheese can be a good vehicle for the two L. salivarius strains analyzed in this study.

Technological properties of bacteriocin-producing lactic acid bacteria isolated from Pico cheese an artisanal cow's milk cheese

AIM

Evaluate technologically relevant properties from bacteriocin-producing strains to use as starter/adjunct cultures in cheese making.

METHODS AND RESULTS

Eight isolates obtained from Pico cheese produced in Azores (Portugal) were found to produce bacteriocins against Listeria monocytogenes and three isolates against Clostridium perfringens. They were identified as Lactococcus lactis and Enterococcus faecalis and submitted to technological tests: growth at different conditions of temperature and salt, acid production, proteolysis, lipolysis, coexistence, enzymatic profile and autolytic capacity. Safety evaluation was performed by evaluating haemolytic, gelatinase and DNase activity, resistance to antibiotics and the presence of virulence genes. Some isolates presented good technological features such as high autolytic activity, acid and diacetyl production. Lactococcus lactis was negative for all virulence genes tested and inhibit the growth of all Lactic acid bacteria (LAB) isolates. Enterococci were positive for the presence of some virulence genes, but none of the isolates were classified as resistant to important antibiotics.

CONCLUSIONS

The bacteriocin-producing Lc. lactis present good potential for application in food as adjunct culture in cheese production. The study also reveals good technological features for some Enterococcus isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriocin-producing strains presented important technological properties to be exploited as new adjunct culture for the dairy industry, influencing flavour development and improve safety.

Probiotics and its functionally valuable products-a review

During the past two decades probiotic bacteria have been increasingly proposed as health promoting bacteria in variety of food system, because of its safety, functional, and technological characteristics. Commonly, Lactobacillus spp., Bifidobacterium spp., Saccharomyces boulardii, and some other microorganisms have been considered as probiotic strains. Possibly these bacterial strains exerted several beneficial effects into gastrointestinal tract of host while administered with variety of food system. Lactic acid bacteria (LAB) usually produce antimicrobial substances like bacteriocin which have broad spectrum of antagonist effect against closely related Gram positive and Gram negative pathogens. LAB strains often produce polymeric substances such as exopolysaccharides (EPS) which increase the colonization of probiotic bacteria by cell-cell interactions in gastrointestinal tract. LAB also produces biosurfactant which showed that the wide range of antimicrobial activity against bacterial pathogen as well as its antiadhesive properties reduces the adhesion of pathogens into gastric wall membrane. Furthermore, LAB strains have also been reported for production of antioxidants which are ability to scavenge the free radicals such as superoxide anions and hydroxyl radicals. For this sense, this review article is mainly focused on the ecology, biosynthesis, genetics, target sites, and applications of bacteriocins and EPS from LAB strains. Moreover, this review discusses about the production and functions of nutritive essential element folate and iron chelating agent such as siderophores from LAB.

Bio-control of waterborne pathogens using Lactobacillus spp

Bacteria play a significant role in water contamination. Chemicals are mostly used for the treatment of bacteriologically contaminated water. The use of bacterial interactions is a new approach to limit the pathogens' growth. Detection of antimicrobial substances produced by lactic acid bacteria against the waterborne pathogens is the objective of this work. Microbiological and biochemical methods were used to identify lactic acid bacteria having an antimicrobial activity. Evaluation of antimicrobial activity with growth kinetic measurements was performed. Four isolates of lactic acid bacteria obtained from whey and curd were identified. The predominant species belonging to the Lactobacillus genera are: Lactobacillus rhamnosus, Lactobacillus sakei, Lactobacillus paracasei, and Lactobacillus paraplantarum. The present study revealed that the Lactobacillus consortium is able to inhibit Staphylococcus aureus's growth along with Escherichia coli and Vibrio species. In mixed culture, after 24 h, the Lactobacillus consortium reduces the growth of S. aureus by 2.03 log; moreover, the growth of the latter bacteria totally ceased after 72 h of incubation. The protein produced by the Lactobacillus consortium was responsible for arresting the growth of S. aureus.