Detection and preliminary characterization of a bacteriocin (plantaricin 35d) produced by a Lactobacillus plantarum strain

Use of Bacteriocins and Bacteriocinogenic Beneficial Organisms in Food Products: Benefits, Challenges, Concerns

This review’s objective was to critically revisit various research approaches for studies on the application of beneficial organisms and bacteriocins as effective biopreservatives in the food industry. There are a substantial number of research papers reporting newly isolated bacterial strains from fermented food products and their application as potential probiotics, including partial characterization of bacteriocins produced by these microorganisms. Most of these studies follow scientific community-accepted standard procedures and propose various applications of the studied strains and bacteriocins as potential biopreservatives for the food industry. A few investigations go somewhat further, performing model studies, exploring the application of expressed bacteriocins in a designed food product, or trying to evaluate the effectiveness of the studied potential probiotics and bacteriocins against foodborne pathogens. Some authors propose applications of bacteriocin producers as starter cultures and are exploring in situ bacteriocin production to aid in the effective control of foodborne pathogens. However, few studies have evaluated the possible adverse effects of bacteriocins, such as toxicity. This comes from well-documented reports on bacteriocins being mostly non-immunogenic and having low cytotoxicity because most of these proteinaceous molecules are small peptides. However, some studies have reported on bacteriocins with noticeable cytotoxicity, which may become even more pronounced in genetically engineered or modified bacteriocins. Moreover, their cytotoxicity can be very specific and is dependent on the concentration of the bacteriocin and the nature of the targeted cell. This will be discussed in detail in the present review.

Applications of Bacteriocins of Lactic Acid Bacteria in Biotechnology and Food Preservation: A Bibliometric Review

Introduction:

Due to the growing prevalence of antibiotic resistance in microorganisms and the demand for safe food, there is increasing interest in using natural bioproducts such as the antimicrobial peptides bacteriocins to extend the shelf-life of foods. This is because of their spectrum of activity, ease of synthesis and applicability. This study reports on the global trends in lactic acid bacteria (LAB) bacteriocins based research publications in the Web of Science core collections within the last 20 years (2000-2019), with specific focus to their applications in biotechnology and food science.

Methods:

Data analysis was undertaken using VOSviewer and HistCite software to evaluate relationships between articles and visualise research linkages amongst authors, institutions and countries.

Results:

In the 20 years under review, a total of 1741 bacteriocin related articles were published, with the most cited publication examining the anti-infective activity of Lactobacillus salivarius. The highest research output was recorded by the United States, followed by Spain and China. However, Europe as a continent had the highest research output with a higher inter-institution collaboration network and stronger food safety legislations.

Discussion:

The bibliometric analysis gave insights into the research areas, cooperation network of authors, co-citation maps and co-occurrence of keywords utilized in the research field and indicates that bacteriocin-based research is highly multidisciplinary with a global reach.

Conclusion:

Key focus is on the control of foodborne disease pathogens, search for new producer organisms and approaches to improve bacteriocin yield and application. This class of antimicrobial peptides has the potential to replace chemical food preservatives in the future.

Multi-Omics Approach in Amelioration of Food Products

Determination of the quality of food products is an essential key factor needed for safe-guarding the quality of food for the interest of the consumers, along with the nutritional and sensory improvements that are necessary for delivering better quality products. Bacteriocins are a group of ribosomally synthesized antimicrobial peptides that help in maintaining the quality of food. The implementation of multi-omics approach has been important for the overall enhancement of the quality of the food. This review uses various recent technologies like proteomics, transcriptomics, and metabolomics for the overall enhancement of the quality of food products. The matrix associated with the food products requires the use of sophisticated technologies that help in the extraction of a large amount of information necessary for the amelioration of the food products. This review would provide a wholesome view of how various recent technologies can be used for improving the quality food products and for enhancing their shelf-life.

Tapioca starch and skim milk support probiotic efficacy of Lactiplantibacillus plantarum post-fermentation medium against pathogens and cancer cells

The production of functional foods containing prebiotic ingredients is an area of particular interest and a very promising market with the potential to dominate the food industry. This study aims to explore the potential of starch-based prebiotic tapioca and skim milk, as low-cost and easily accessible food sources and as natural and "clean label" food ingredients on the probiotic activities of Lactiplantibacillus plantarum (formerly Lactobacillus plantarum). The results show that concomitant use of the modified tapioca starch and skim milk promotes the antibacterial and anti-cancer properties of L. plantarum post-fermentation media pointing out how the functionality of probiotic products can be regulated by growth supplements.

Diversity and Antimicrobial Activity towards Listeria spp. and Escherichia coli among Lactic Acid Bacteria Isolated from Ready-to-Eat Seafood

Biopreservation is a food preservation technology using microorganisms and/or their inherent antimicrobial metabolites to inhibit undesirable microorganisms. The aim of the present study was to explore the diversity and antimicrobial activity of lactic acid bacteria (LAB) strains (n = 99) isolated from ready-to-eat (RTE) seafood (cold-smoked salmon (CSS), gravlax, and sushi) towards two strains of Listeria monocytogenes (CCUG 15527, F11), Listeria innocua (CCUG 15531) and Escherichia coli (CCUG 38079). The LAB strains were assigned to five different genera (Carnobacterium spp., Lactobacillus spp., Leuconostoc spp., Weissella spp., and Enterococcus sp.) by sequencing a 1150 bp stretch of the 16S rRNA gene. A significant association between the seafood source and the distribution of LAB genera was found (p < 0.001), of which Leuconostoc spp. were most prevalent in sushi and Carnobacterium sp. and Lactobacillus sp. were most frequently isolated from CSS and gravlax. Antimicrobial activity among the LAB was significantly affected by LAB genera (F= 117.91, p < 0.001, one-way ANOVA), product of origin (F = 3.47, p < 0.05), and target (F = 4.64, p = 0.003). LAB isolated from sushi demonstrated a significantly higher antimicrobial effect than LAB from CSS and gravlax (p < 0.05). In general, a significantly higher antimicrobial activity was found towards Listeria spp. than E. coli (p < 0.05). However, Leuconostoc spp. demonstrated similar antimicrobial effects towards E. coli and Listeria spp., except for L. monocytogenes F11 being more sensitive (p < 0.05). This study suggested that seafood-derived LAB strains could be selected for technological application in RTE seafood systems.

Antilisterial Activity of Bacteriocins Produced by Lactic Bacteria Isolated from Dairy Products

Sixty-nine Lactic Acid Bacteria (LAB) and bifidobacteria were isolated and identified from Italian dairy products (raw milk, cream, butter, soft cheese and yoghurt) to find new antimicrobial compounds to use as food bio-preservatives. All the isolates were preliminarily screened by the deferred antagonism method for bacteriocin production. Afterwards, to evaluate the release of bacteriocin in liquid medium, the Cell-Free Supernatant Fluid (CFSF) of the best producers was tested by agar well diffusion assay. The study allowed the selection of three bacteriocin producing strains (Enterococcus faecium E23, Bifidobacterium thermophilum B23 and Lactobacillus bulgaricus L21), endowed with the strongest and broadest inhibitory capability against the pathogen Listeria monocytogenes. The molecular characteristics and the chemical–physical properties of both producers and the respective bacteriocins were studied and compared. The results showed that E. faecium E23 was the best producer strain and its class IIa bacteriocins, called enterocin E23, exhibited a good spectrum of activity towards L. monocytogenes. Enterocin E23 was stable over a wide range of pH and at low temperatures for at least four months and, for this reason, it can be employed in refrigerated foods for the control of L. monocytogenes, the major concern in dairy products.

Cell-free supernatant of Streptococcus salivarius M18 impairs the pathogenic properties of Pseudomonas aeruginosa and Klebsiella pneumonia

M18 strain of Streptococcus salivarius is a bacterial replacement probiotic that has been suggested for use in the oral cavity. Here, we have shown that S. salivarius M18 cell-free supernatant reduced the growth of the two most common human pathogens Pseudomonas aeruginosa and Klebsiella pneumonia and sensitized the pathogenic bacteria to antibiotic. Besides, the supernatant inhibited biofilm formation of P. aeruginosa drastically. For pinpointing the biomolecular changes that occurred in P. aeruginosa incubated with the probiotic supernatant, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used. Unsupervised learning algorithms, principal component analysis (PCA) and hierarchical cluster analysis (HCA), and intensity analyses of individual spectral bands exhibited comprehensive alterations in the polysaccharide and lipid contents and compositions of P. aeruginosa cultivated with S. salivarius M18 cell-free supernatant. These results indicate that S. salivarius M18 has the potential for the prevention or alleviation of different pathogen-induced infections along with the infections of oral pathogens.

Identification of a bacteriocin-like compound from Lactobacillus plantarum with antimicrobial activity and effects on normal and cancerogenic human intestinal cells

In this paper, we demonstrate that the antimicrobial activity of L. plantarum PBS067 strain against antagonist microorganisms was mediated by the production of a bacteriocin-like compound secreted at the stationary phase of the growth. The novel bacteriocin-like compound, designed plantaricin P1053, was identified by using sorption–desorption method, butanol extraction and SEC-HPLC. The molecular mass of plantaricin P1053 was shown to be 1053 Da by ESI-MS analysis. Plantaricin P1053 exhibited a broad-spectrum antimicrobial activity against Gram-positive bacteria as S. aureus and Gram-negative bacteria as E. coli. In addition to the antimicrobial activity, the isolated bacteriocin-like compound showed effects on normal and cancerogenic epithelial intestinal cell lines through an enhancing of viability of healthy cells and a proliferation reduction of cancer cells. Moreover, in this paper we demonstrate that the isolated bacteriocin-like compound acts on healthy cells through the epidermal growth factor receptor (EGFR) pathways. In conclusion, plantaricin P1053 isolated from L. plantarum PBS067 strain could represent one of the first multifunctional bacteriocin-like compound acting on human epithelial intestinal cells.

Bacteriocins of Gram-positive bacteria having activity spectra extending beyond closely-related species

Bacteriocins are bacterially-produced antimicrobial peptides that have killing activity principally against other relatively closely-related bacteria. Some bacteriocins of the lactic acid bacteria (LAB) have for many years been extensively applied in food biopreservation. However, especially during the last decade, a number of reports have appeared about unanticipated extensions to the generally rather narrow anti-bacterial activity spectrum of some of the LAB bacteriocins and novel applications have been proposed for bacteriocins ranging from controlling the growth of an increasingly-heterogeneous variety of pathogens, including Gram-negative multidrug resistant bacteria, viruses, yeasts, and in particular, difficult to control Mycobacterium spp., to their potential application as anticancer agents. How best can we assess this now rapidly-accumulating stream of reports on potential future applications of bacteriocins? Where is the line between realistic, science-based proposals and highly-speculative fiction and what are the ‘critical points’ that might help us to draw this line? In this review, we have attempted to analyse a selection of the presently-available data concerning relatively ‘unorthodox’ (i.e. beyond food preservation) applications of bacteriocins, and, by utilising our set of ‘critical points’, we endeavour to identify essential or/and missing information that appear crucial for success of the proposed applications.

Lactic Acid Bacteria (LAB) and Their Bacteriocins as Alternative Biotechnological Tools to Control Listeria monocytogenes Biofilms in Food Processing Facilities

Bacteriocins are antimicrobial peptides produced by bacteria Gram-negative and Gram-positive, including lactic acid bacteria (LAB), organisms that are traditionally used in food preservation practices. Bacteriocins have been shown to have an aptitude as biofilm controlling agents in Listeria monocytogenes biofilms, a major risk for consumers and the food industry. Biofilms protect pathogens from sanitization procedures, allowing them to survive and persist in processing facilities, resulting in the cross-contamination of the end products. Studies have been undertaken on bacteriocinogenic LAB, their bacteriocins, and bioengineered bacteriocin derivatives for controlling L. monocytogenes biofilms on different surfaces through inhibition, competition, exclusion, and displacement. These alternative strategies can be considered promising in preventing the development of resistance to conventional sanitizers and disinfectants. Bacteriocins are "friendly" antimicrobial agents, and with high prevalence in nature, they do not have any known associated public health risk. Most trials have been carried out in vitro, on food contact materials such as polystyrene and stainless steel, while there have been few studies performed in situ to consolidate the results observed in vitro. There are strategies that can be employed for prevention and eradication of L. monocytogenes biofilms (such as the establishment of standard cleaning procedures using the available agents at proper concentrations). However, commercial cocktails using alternatives compounds recognized as safe and environmental friendly can be an alternative approach to be applied by the industries in the future.

Lactobacillus plantarum with Functional Properties: An Approach to Increase Safety and Shelf-Life of Fermented Foods

Lactobacillus plantarum (widespread member of the genus Lactobacillus) is one of the most studied species extensively used in food industry as probiotic microorganism and/or microbial starter. The exploitation of Lb. plantarum strains with their long history in food fermentation forms an emerging field and design of added-value foods. Lb. plantarum strains were also used to produce new functional (traditional/novel) foods and beverages with improved nutritional and technological features. Lb. plantarum strains were identified from many traditional foods and characterized for their systematics and molecular taxonomy, enzyme systems (α-amylase, esterase, lipase, α-glucosidase, β-glucosidase, enolase, phosphoketolase, lactase dehydrogenase, etc.), and bioactive compounds (bacteriocin, dipeptides, and other preservative compounds). This review emphasizes that the Lb. plantarum strains with their probiotic properties can have great effects against harmful microflora (foodborne pathogens) to increase safety and shelf-life of fermented foods.

Edible Films and Coatings as Carriers of Living Microorganisms: A New Strategy Towards Biopreservation and Healthier Foods

Edible films and coatings have been extensively studied in recent years due to their unique properties and advantages over more traditional conservation techniques. Edible films and coatings improve shelf life and food quality, by providing a protective barrier against physical and mechanical damage, and by creating a controlled atmosphere and acting as a semipermeable barrier for gases, vapor, and water. Edible films and coatings are produced using naturally derived materials, such as polysaccharides, proteins, and lipids, or a mixture of these materials. These films and coatings also offer the possibility of incorporating different functional ingredients such as nutraceuticals, antioxidants, antimicrobials, flavoring, and coloring agents. Films and coatings are also able to incorporate living microorganisms. In the last decade, several works reported the incorporation of bacteria to confer probiotic or antimicrobial properties to these films and coatings. The incorporation of probiotic bacteria in films and coatings allows them to reach the consumers' gut in adequate amounts to confer health benefits to the host, thus creating an added value to the food product. Also, other microorganisms, either bacteria or yeast, can be incorporated into edible films in a biocontrol approach to extend the shelf life of food products. The incorporation of yeasts in films and coatings has been suggested primarily for the control of the postharvest disease. This work provides a comprehensive review of the use of edible films and coatings for the incorporation of living microorganisms, aiming at the biopreservation and probiotic ability of food products.

Purification and Characterization of Plantaricin JLA-9: A Novel Bacteriocin against Bacillus spp. Produced by Lactobacillus plantarum JLA-9 from Suan-Tsai, a Traditional Chinese Fermented Cabbage

Bacteriocins are ribosomally synthesized peptides with antimicrobial activity produced by numerous bacteria. A novel bacteriocin-producing strain, Lactobacillus plantarum JLA-9, isolated from Suan-Tsai, a traditional Chinese fermented cabbage, was screened and identified by its physiobiochemical characteristics and 16S rDNA sequence analysis. A new bacteriocin, designated plantaricin JLA-9, was purified using butanol extraction, gel filtration, and reverse-phase high-performance liquid chromatography. The molecular mass of plantaricin JLA-9 was shown to be 1044 Da by MALDI-TOF-MS analyses. The amino acid sequence of plantaricin JLA-9 was predicted to be FWQKMSFA by MALDI-TOF-MS/MS, which was confirmed by Edman degradation. This bacteriocin exhibited broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria, especially Bacillus spp., high thermal stability (20 min, 121 °C), and narrow pH stability (pH 2.0-7.0). It was sensitive to α-chymotrypsin, pepsin, alkaline protease, and papain. The mode of action of this bacteriocin responsible for outgrowth inhibition of Bacillus cereus spores was studied. Plantaricin JLA-9 had no detectable effects on germination initiation over 1 h on monitoring the hydration, heat resistance, and 2,6-pyridinedicarboxylic acid (DPA) release of spores. Rather, germination initiation is a prerequisite for the action of plantaricin JLA-9. Plantaricin JLA-9 inhibited growth by preventing the establishment of oxidative metabolism and disrupting membrane integrity in germinating spores within 2 h. The results suggest that plantaricin JLA-9 has potential applications in the control of Bacillus spp. in the food industry.

Encapsulation of Lactobacillus plantarum 423 and its Bacteriocin in Nanofibers

Plantaricin 423, produced by Lactobacillus plantarum 423, was encapsulated in nanofibers that were produced by the electrospinning of 18% (w/v) polyethylene oxide (200 000 Da). The average diameter of the nanofibers was 288 nm. Plantaricin 423 activity decreased from 51 200 AU/ml to 25 600 AU/ml and from 204 800 AU/ml to 51 200 AU/ml after electrospinning, as determined against Lactobacillus sakei DSM 20017 and Enterococcus faecium HKLHS, respectively. Cells of L. plantarum 423 encapsulated in nanofibers decreased from 2.3 × 10(10) cfu/ml before electrospinning to 4.7 × 10(8) cfu/ml thereafter. Cells entrapped in the nanofibers continued to produce plantaricin 423. This is the first report on the encapsulation of a bacteriocin and cells of L. plantarum in nanofibers. The method may be used to design a drug delivery system for bacteriocins and the encapsulation of probiotic lactic acid bacteria. The technology is currently being optimized.

Molecular characterisation of new organisation of plnEF and plw loci of bacteriocin genes harbour concomitantly in Lactobacillus plantarum I-UL4

Background

Bacteriocin-producing Lactic acid bacteria (LAB) have vast applications in human and animal health, as well as in food industry. The structural, immunity, regulatory, export and modification genes are required for effective bacteriocin biosynthesis. Variations in gene sequence, composition and organisation will affect the antimicrobial spectrum of bacteriocin greatly. Lactobacillus plantarum I-UL4 is a novel multiple bacteriocin producer that harbours both plw and plnEF structural genes simultaneous which has not been reported elsewhere. Therefore, molecular characterisation of bacteriocin genes that harboured in L. plantarum I-UL4 was conducted in this study.

Results and discussion

Under optimised conditions, 8 genes (brnQ1, napA1, plnL, plnD, plnEF, plnI, plnG and plnH) of plnEF locus and 2 genes (plw and plwG) of plw locus were amplified successfully from genomic DNA extracted from L. plantarum I-UL4 using specific primers designed from 24 pln genes selected randomly from reported plw, plS, pln423 and plnEF loci. DNA sequence analysis of the flanking region of the amplified genes revealed the presence of two pln loci, UL4-plw and UL4-plnEF loci, which were chromosomally encoded as shown by Southern hybridisation. UL4-plw locus that contained three ORFs were arranged in one operon and possessed remarkable amino acid sequence of LMG2379-plw locus, suggesting it was highly conserved. Interestingly, the UL4-plnEF locus appeared to be a composite pln locus of JDM1-plnEF and J51-plnEF locus in terms of genetic composition and organisation, whereby twenty complete and one partial open reading frames (ORFs) were aligned and organised successfully into five operons. Furthermore, a mutation was detected in plnF structural gene which has contributed to a longer bacteriocin peptide.

Conclusions

Plantaricin EF and plantaricin W encoded by plnEF and plnW loci are classified as class I bacteriocin and class II bacteriocin molecules respectively. The concurrent presence of two pln loci encoding bacteriocins from two different classes has contributed greatly to the broad inhibitory spectrum of L. plantarum I-UL4. The new genetic composition and organisation of plnEF locus and concurrent presence of plnEF and plnW loci indicated that L. plantarum I-UL4 is a novel multiple bacteriocin producer that possesses vast potentials in various industries.

Isolation and partial characterization of a bacteriocin produced by Lactobacillus plantarum BM-1 isolated from a traditionally fermented Chinese meat product

Lactobacillus plantarum BM-1 isolated from a traditionally fermented Chinese meat product was found to produce a novel bacteriocin that is active against a wide range of gram-positive and gram-negative bacteria. Production of the bacteriocin BM-1 started early in the exponential phase and its maximum activity (5120 AU/mL) was recorded early during the stationary phase (16 hr). Bacteriocin BM-1 is sensitive to proteolytic enzymes but stable in the pH range of 2.0-10.0 and heat-resistant (15 min at 121°C). This bacteriocin was purified through pH-mediated cell adsorption-desorption and cation-exchange chromatography on an SP Sepharose Fast Flow column. The molecular weight of the purified bacteriocin BM-1 was determined to be 4638.142 Da by electrospray ionization Fourier transform mass spectrometry. Furthermore, the N-terminal amino acid sequence was obtained through automated Edman degradation and found to comprise the following 15 amino acid residues: H2 N-Lys-Tyr-Tyr-Gly-Asn-Gly-Val-Tyr-Val-Gly-Lys-His-Ser-Cys-Ser. Comparison of this sequence with that of other bacteriocins revealed that bacteriocin BM-1 contains the consensus YGNGV amino acid motif near the N-terminus. Based on its physicochemical characteristics, molecular weight, and N-terminal amino acid sequence, plantaricin BM-1 is a novel class IIa bacteriocin.

Anti-listerial Bactericidal Activity of Lactobacillus plantarum DM5 Isolated from Fermented Beverage Marcha

The strain Lactobacillus plantarum DM5 was isolated from fermented beverage Marcha of Sikkim and explored for its antagonistic activity against food-borne pathogens. The cell-free supernatant of L. plantarum DM5 showed antibacterial activity of 6,400 AU/mL in MRS medium (pH 6.0) against the indicator strain Staphylococcus aureus. MRS medium supplemented with 15 g/L of maltose at 37 °C under static condition yielded highest antimicrobial activity (6,400 AU/mL) with 3 % increase in specific activity when compared to 20 g/L glucose. The antimicrobial compound was heat stable (60 min at 100 °C) and was active over a wide pH range. It showed bactericidal effect on S. aureus and Listeria monocytogenes by causing 96 and 98 % of cell lysis, respectively. The cell morphology of the treated S. aureus and L. monocytogenes was completely deformed as revealed by scanning electron microscopy, suggesting the high potential of L. plantarum DM5 as natural preservatives in food industry. The antimicrobial compound was purified by 80 % ammonium sulphate precipitation and showed antimicrobial activity of 12,800 AU/mL with 19-fold purification and a molecular mass of 15.2 kDa, indicating the proteinaceous nature of the compound.

Lantibiotics biosynthesis genes and bacteriocinogenic activity of Lactobacillus spp. isolated from raw milk and cheese

Lactobacillus species are usually used as starters for the production of fermented products, and some strains are capable of producing antimicrobial substances, such as bacteriocins. Because these characteristics are highly desirable, research are continually being performed for novel Lactobacillus strains with bacteriocinogenic potential for use by food industries. The aim of this study was to characterise the bacteriocinogenic potential and activity of Lactobacillus isolates. From a lactic acid bacteria culture collection obtained from raw milk and cheese, 27 isolates were identified by 16S rDNA as Lactobacillus spp. and selected for the detection of lantibiotics biosynthesis genes, bacteriocin production, antimicrobial spectra, and ideal incubation conditions for bacteriocin production. Based on the obtained results, 21 isolates presented at least one of the three lantibiotics biosynthesis genes (lanB, lanC or lamM), and 23 isolates also produced antimicrobial substances with sensitivity to at least one proteinase, indicating their bacteriocinogenic activity. In general, the isolates had broad inhibitory activity, mainly against Listeria spp. and Staphylococcus spp. strains, and the best antimicrobial performance of the isolates occurred when they were cultivated at 25 °C for 24 or 48 h or at 35 °C for 12 h. The present study identified the bacteriocinogenic potential of Lactobacillus isolates obtained from raw milk and cheese, suggesting their potential use as biopreservatives in foods.

Production of two bacteriocins in various growth conditions produced by gram-positive bacteria isolated from chicken cecum

Lactobacillus plantarum CLP29 and Enterococcus faecium CLE34 isolated from the cecal contents of young broiler chicks were identified based on physiological and biochemical characteristics, and identification was confirmed by 16S rRNA sequencing. Both bacteria showed a broad range of inhibitory action against bacteria such as Salmonella and Escherichia coli and produced two peptides, plantaricin CLP29 and enterocin CLE34. Treatment with proteinase K, trypase, or benase resulted in the loss of activity of the two peptides, confirming their proteinaceous nature. The highest activity levels for both bacteria were recorded in de Man – Rogosa – Sharpe agar at pH 5.0, 6.0, and 7.0, at 37 °C. Carbon and nitrogen sources affected the antibacterial activities of the two bacteriocins in different combinations, which suggested that the antibacterial abilities of different bacteriocins produced in nutrient sources were various.

Probiotic lactic acid bacteria in the gastro-intestinal tract: health benefits, safety and mode of action

Lactic acid bacteria (LAB) have received considerable attention as probiotics over the past few years. This concept has grown from traditional dairy products to a profitable market of probiotic health supplements and functional foods. Extensive research is done on novel potential probiotic strains, with specific emphasis on their health benefits and mode of action. Criteria for the selection of probiotic strains have only recently been formulated by the Food and Agriculture Organization of the United Nations and the World Health Organization (FAO/WHO). Several in vitro techniques have been developed to evaluate the probiotic properties of strains. In many cases, this is followed by in vivo tests. Safety studies are also obligatory, as a few cases of bacteremia caused by LAB have been reported. This review focuses on the health benefits and safety of LAB probiotics, the criteria used to select a probiotic, mode of action and the impact these organisms have on natural microbiota in the gastro-intestinal tract.

Discovery of novel biopreservation agents with inhibitory effects on growth of food-borne pathogens and their application to seafood products

Selection of protective cultures is relevant in order to biopreserve and improve the functional safety of food products, mainly through inhibition of spoilage and/or pathogenic bacteria. Accordingly, the present study investigated potential applications of lactic acid bacteria (LAB) in the biopreservation of fish and shellfish products. For this purpose, a collection of 84 LAB strains isolated from sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) was identified and characterized for their inhibitory activities against the most relevant seafood-spoilage and pathogenic bacteria potentially present in commercial products. The bioactive strains belonged to the genus Enterococcus and exhibited inhibition against Carnobacterium sp, Bacillus sp, Listeria monocytogenes, Aeromonas salmonicida, Aeromonas hydrophila and Vibrio anguillarum. Treatment of cell-free extracts of the LAB strains with proteases revealed the proteinaceous nature of the inhibition. Interestingly, the cell-free extracts containing bacteriocins remained 100% active after treatment up to 100 °C for 30 min or 121 °C for 15 min. Molecular analysis led to identification of the bacteriocins investigated, including enterocins A, B, L50 and P. All of these proteins demonstrated remarkable anti-Listeria activity and were found to be heat-resistant small class IIa bacteriocins. The results presented in this work open the way for potential applications of these LAB strains to the biopreservation of minimally-processed seafood products.