Antilisterial Bacteriocin Research Articles

Reduction and Growth Inhibition of Listeria monocytogenes by Use of Anti-Listerial Nisin, P100 Phages and Buffered Dry Vinegar Fermentates in Standard and Sodium-Reduced Cold-Smoked Salmon.

Cold-smoked salmon are ready-to-eat products that may support the growth of pathogenic Listeria monocytogenes during their long shelf-life. Consumption of such contaminated products can cause fatal listeriosis infections. Another challenge and potential risk associated with CS salmon is their high levels of sodium salt. Excess dietary intake is associated with serious health complications. In the present study, anti-listerial bacteriocin (nisin), P100 bacteriophages (Phageguard L, PGL) and fermentates (Verdad N6, P-NDV) were evaluated as commercial bio-preservation strategies for increased control of L. monocytogenes in standard (with NaCl) and sodium-reduced (NaCl partially replaced with KCl) CS salmon. Treatments of CS salmon with nisin (1 ppm) and PGL (5 × 107 pfu/cm2) separately yielded significant initial reductions in L. monocytogenes (up to 0.7 log) compared to untreated samples. Enhanced additive reductions were achieved through the combined treatments of nisin and PGL. Fermentates in the CS salmon inhibited the growth of Listeria but did not lead to its eradication. The lowest levels of L. monocytogenes during storage were observed in nisin- and PGL-treated CS salmon containing preservative fermentates and stored at 4 °C, while enhanced growth was observed during storage at an abusive temperature of 8 °C. Evaluation of industry-processed standard and sodium-replaced CS salmon confirmed significant effects with up to 1.7 log reductions in L. monocytogenes levels after 34 days of storage of PGL- and nisin-treated CS salmon-containing fermentates. No differences in total aerobic plate counts were observed between treated (PGL and nisin) or non-treated standard and sodium-reduced CS salmon at the end of storage. The microbiota was dominated by Photobacterium, but with a shift showing dominance of Lactococcus spp. and Vagococcus spp. in fermentate-containing samples. Similar and robust reductions in L. monocytogenes can be achieved in both standard and sodium-replaced CS salmon using the bio-preservation strategies of nisin, PGL and fermentates under various and relevant processing and storage conditions.

Control of Listeria monocytogenes in chicken dry-fermented sausages with bioprotective starter culture and high-pressure processing.

Listeria monocytogenes is one of the most relevant pathogens for ready-to-eat food, being a challenge for the food industry to comply with microbiological criteria. The aim of the work was to assess the behavior of L. monocytogenes in two types of chicken-based dry-fermented sausages during the fermentation and ripening, with or without a bioprotective starter culture (Latilactobacillus sakei CTC494). To complement the challenge testing approach, simulations with different predictive models were performed to better understand the role of contributing factors. The impact of post-processing strategies, such as high-pressure processing and/or corrective storage was assessed. The chicken meat was inoculated with a cocktail of three L. monocytogenes strains, mixed with other ingredients/additives and stuffed into small (snack-type) or medium (fuet-type) casings. Snack-type was fermented (22°C/3 days) and ripened (14°C/7 days), while fuet-type was ripened (13°C/16 days). At the end of ripening, HPP (600 MPa/5 min) and/or corrective storage (4 or 15°C/7 days) were applied. The suitability of HPP after fermentation was evaluated in the snack-type sausages. Pathogen growth (>3 Log10) was observed only during the fermentation of the snack type without a starter. The bioprotective starter prevented the growth of L. monocytogenes in the snack-type sausages and enhanced the inactivation (1.55 Log10) in fuet-type sausages, which could be related to the higher lactic acid production and consequent decrease of pH, but also the production of the antilisterial bacteriocin sakacin k. The gamma concept model allowed us to identify the main factors controlling the L. monocytogenes’ growth, i.e., the temperature during the early stages and aw at the end of the production process. The earlier acidification linked with the addition of starter culture made the interaction with the other factors (undissociated lactic acid, aw and temperature) to be the growth-preventing determinants. High-pressure processing only caused a significant reduction of L. monocytogenes in snack-type, which showed higher aw. The application of HPP after fermentation did not offer a relevant advantage in terms of efficacy. Corrective storage did not promote further pathogen inactivation. The findings of the work will guide the food industry to apply effective strategies (e.g., fermentation temperature and bioprotective starter cultures) to control L. monocytogenes in chicken dry-fermented sausages.

Biofilm genes expression of Listeria monocytogenes exposed to Latilactobacillus curvatus bacteriocins at 10 °C

Listeria monocytogenes is a foodborne pathogen able to survive in a wide range of conditions, including low temperatures, being highly persistent in the food-processing environments. Anti-listerial bacteriocins produced by Latilactobacillus curvatus CRL705 and CRL1579 were used to prevent/control biofilm formation of L. monocytogenes FBUNT, Scott A and CECT 4031T strains at 10 °C and genes transcription was evaluated. Sub-inhibitory concentrations of bacteriocins were able to reduce biofilm after six days at 10 °C, which was confirmed by crystal violet staining, motility assay and confocal laser scanning microscopy. When a set of thirty genes related to adhesion, virulence and stress response were investigated by using RT-qPCR, adaptation of L. monocytogenes to the concurrence of cold and bacteriocin stresses induced the expression of luxS, agrA, agrB, cspB and cell surface proteins related to biofilm formation genes for the three Listeria strains, whereas actA gene decreased and sigB gene increased its transcription, showing changes in the relative expression (log2) between −2 and 4-fold for Scott A and CECT 4031T strains in presence of lactocin AL705. Results showed that bacteriocin treatment affected the expression levels of most genes, while a lack of transcription of the virulence regulatory prfA was observed in the assayed strains. In addition, some genes related to energy production and sugar transport were up-regulated, exhibiting up to 1.8-fold changes in the presence of the bacteriocins. A better understanding of bacteriocins, particularly of lactocin AL705, to control biofilm formation of L. monocytogenes strains on abiotic surfaces at 10 °C, was achieved. Bacteriocins represent a successful intervention strategy to mitigate post-processing contamination.

Effect of Bacteriocin (ALC102) of Enterococcus faecium GRD AA on Biofilm Forming Listeria monocytogenes MTCC 657

Antilisterial bacteriocin producing strain were isolated from milk samples and were subjected to 16S rRNA sequencing and found to be of genus Enterococcus faecium. The bacteriocin ALC102 were partially purified by Amberlite XAD-16 adsorption followed by column chromatography. The biofilm formation capacity of Listeria monocytogenes MTCC 657 were evaluated by tube method and CV binding assay. Biofilm formation on different abiotic substrates were also evaluated. Among three substrates stainless steel had a strong biofilm formation followed by glass and aluminum foil. From the results of biofilm eradication studies, the bacteriocin ALC102 showed almost similar activity of commercial bacteriocin nisin on all the substrates at 45°C, 30°C, 4°C and -20°C. Based on CBD® biofilm eradication assay, the eradication potential of ALC102 and nisin were found to be similar on high (45°C) and freezing (-20°C) temperatures. From the study, antilisterial bacteriocin ALC102 found to be able to inhibit the biofilm formed Listeria monocytogenes MTCC 657 at different temperatures and different incubation periods (24h, 48h and 72h). The biofilm eradication potential of antilisterial bacteriocin ALC102 was similar to nisin. Neither incubation temperature nor incubation period doesn’t altered the activity of the bacteriocin. So this bacteriocin can be considered as a potential competitor in food industry and we strongly recommend the use of this bacteriocin from Enterococcus faecium GRD AA in the food preservation industry to a higher temperature (45°C) to freezing temperature (-20°C).

Antioxidant Activity of Antilisterial Bacteriocns Isolated from Paenibacillus polmyxa and Enterococcus faecium GRD AA

Anti-listerial bacteriocin producing strain was isolated, purified and characterized from fermented food source toddy and milk and found to be the genus Paenibacillus polymyxa and Enterococcus faecium GRD AA. The bacteriocins ALC101 and ALC102 were partially purified by Amberlite XAD-16 purification method and anti-listerial activity were checked. Both the bacteriocins ALC101 and ALC102 along with Nisin showed a maximum of 85% of DPPH and 85.5% of ABTS radical scavenging activity like BHT which was the standard used in the assay. The bacteriocins also showed a maximum of 87.6% Fe2+ reduction potential. From the results it can be concluded as bacteriocin produced by Paenibacillus polymyxa ALC101, and bacteriocin from Enterococcus faecium GRD AA ALC102 has a good antioxidant potential when compared to Nisin and BHT (positive control).

Comparative Genomics of Leuconostoc carnosum.

Leuconostoc carnosum is a known colonizer of meat-related food matrices. It reaches remarkably high loads during the shelf life in packaged meat products and plays a role in spoilage, although preservative effects have been proposed for some strains. In this study, the draft genomes of 17 strains of L. carnosum (i.e., all the strains that have been sequenced so far) were compared to decipher their metabolic and functional potential and to determine their role in food transformations. Genome comparison and pathway reconstruction indicated that L. carnosum is a compact group of closely related heterofermentative bacteria sharing most of the metabolic features. Adaptation to a nitrogen-rich environment, such as meat, is evidenced by 23 peptidase genes identified in the core genome and by the autotrophy for nitrogen compounds including several amino acids, vitamins, and cofactors. Genes encoding the decarboxylases yielding biogenic amines were not present. All the strains harbored 1–4 of 32 different plasmids, bearing functions associated to proteins hydrolysis, transport of amino acids and oligopeptides, exopolysaccharides, and various resistances (e.g., to environmental stresses, bacteriophages, and heavy metals). Functions associated to bacteriocin synthesis, secretion, and immunity were also found in plasmids. While genes for lactococcin were found in most plasmids, only three harbored the genes for leucocin B, a class IIa antilisterial bacteriocin. Determinants of antibiotic resistances were absent in both plasmids and chromosomes.

Partial Characterization of an Anti-Listerial Bacteriocin from Enterococcus faecium CJNU 2524.

Listeria monocytogenes is a representative foodborne pathogen and causes listeriosis. Enterococcus faecium CJNU 2524 was confirmed to produce a bacteriocin with anti-listerial activity. To establish optimal culture conditions for the production of the bacteriocin from E. faecium CJNU 2524, different media (MRS and BHI broth) and temperatures (25°C, 30°C, and 37°C) were investigated. The results showed that the optimal culture conditions were MRS broth and 25°C or 30°C temperatures. The crude bacteriocin was stable in a broad range of pH conditions (2.0–10.0), temperatures (60°C–100°C), and organic solvents (methanol, ethanol, acetone, acetonitrile, and chloroform). The bacteriocin activity was abolished when treated with protease but not α-amylase or lipase, indicating the proteinaceous nature of the bacteriocin. Finally, the bacteriocin showed a bactericidal mode of action against L. monocytogenes. Therefore, it can be a biopreservative candidate for controlling L. monocytogenes in dairy and meat products.

Characterization, Cytotoxic Analysis and Action Mechanism of Antilisterial Bacteriocin Produced by Lactobacillus plantarum Isolated from Cheddar Cheese

Emergence of food borne pathogens and multidrug resistant organisms has enforced the screening of natural antimicrobial compounds. Bacteriocins are ribosomally synthesized natural antimicrobial peptides produced by numerous bacteria. These antimicrobial peptides are gaining more attention as alternative therapeutics in pharmaceutical industry as next-generation antibiotics targeting the multi-drug resistant pathogens and as a bio preservative in food industry. The current study is aimed to purify and characterize a broad spectrum bacteriocin (Bac-IB45) with the determination of its plausible mode/mechanism of action. In this research, Bac-IB45 from Lactobacillus plantarum KIBGE-IB45 was 41.71-fold purified with the molecular mass of 20.5 kDa estimated using tricine SDS-PAGE. This bacteriocin is highly thermostable and pH stable in nature. It also exhibited stability against various metal ions, surfactants and organic solvents. Purified Bac-IB45 showed broad antimicrobial potential against various multidrug resistant, food borne bacterial and fungal pathogens. However, Bac-IB45 was found to be sensitive to various proteolytic enzymes. The time-kill assay of Bac-IB45 and scanning electron microscopic analysis revealed the bactericidal mode/mechanism of action against Listeria monocytogenes ATCC 7644. This unique Bac-IB45 with broad spectrum of inhibition and bactericidal mode of action could be used as a natural food preservative and as alternative therapeutics to solve the unrestrained problems of industries.

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

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

Draft genome sequence, disease-resistance genes, and phenotype of a Paenibacillus terrae strain (NK3-4) with the potential to control plant diseases.

Paenibacillus terrae NK3-4 is a plant growth-promoting rhizobacterium that may be useful for controlling plant diseases. We conducted a genomic analysis and identified the genes mediating antimicrobial functions. Additionally, an extracellular antifungal protein component was isolated and identified. The draft genome sequence was assembled into 54 contigs, with 5 458 568 bp and a G+C content of 47%. Moreover, 4 690 015 bp encoded 5090 proteins, 7 rRNAs, and 54 tRNAs. Forty-four genes involved in antimicrobial functions were detected. They mainly encode 19 non-ribosomal peptide synthetases (NRPSs); one polyketide synthase/NRPSs hybrid enzyme; four Zn-dependent metalloproteases; three antilisterial bacteriocin subtilosin biosynthesis proteins (AlbA); four serine proteases; five pectate lyases; three beta-glucanases; and four 1,4-beta-xylanases. These include four novel NRPSs that have not been found in any species of Paenibacillus. Furthermore, five proteins exhibiting antifungal activity were identified from the antifungal extracellular protein component based on MS/MS and the strain NK3-4 predicted protein library. On the basis of these features, we propose that strain NK3-4 represents a promising biocontrol agent for protecting plant from diseases. The draft genome sequence described herein may provide the genetic basis for the characterization of the molecular mechanisms underlying the biocontrol functions. It may also facilitate the development of rational strategies for improving the strain.

Combined effect of NaCl and low temperature on antilisterial bacteriocin production of Lactobacillus plantarum ST202Ch

The aim of our study was to examine the combined effect of NaCl and low temperature on antilisterial bacteriocin production of L. plantarum. Traditionally, the activity of the bacteriocin (arbitrary unit/ml) is determined as an adaptation of the critical dilution method. With that methodology, the value of AU/ml is a discrete variable, which may cause information loss. Therefore, redox potential measurement technique was applied. Bacteriocin producer L. plantarum and a bacteriocin sensitive L. monocytogenes strain were selected for this study. The measure of the inhibition activity of bacteriocin was expressed in ΔTTD terms which means the difference between the detection times of L. monocytogenes in inhibited and non-inhibited culture media. During the L. plantarum fermentations the antilisterial activity proved to be the highest in the transient section between the late linear and stationer phase of the logarithmic growth curves. Multiple regression model was established to describe the combined effect of temperature and NaCl concentration on the bacteriocin production of L. plantarum.

High hydrostatic pressure effects on Listeria monocytogenes and L. innocua: Evidence for variability in inactivation behaviour and in resistance to pediocin bacHA-6111-2

The effect of high hydrostatic pressure (HHP) on the survival of 14 strains of Listeria monocytogenes from food or clinical origins, selected to represent different pheno and genotypes, was evaluated. Stationary phase cells were submitted to 300, 400 and 500 MPa at 10 °C, for 5 min. A high variability in the resistance of L. monocytogenes to pressure was observed, and particularly two strains isolated from food were significantly more baroresistant than the rest. Strains of L. monocytogenes resistant to one or more antibiotics exhibited significantly higher levels of survival after the high pressure treatment at 400 MPa. No correlation was found between strains' origin or thermal tolerance and resistance to HHP. The suitability of two strains of L. innocua as surrogates of L. monocytogenes, was also investigated. These exhibited significantly higher sensitivities to HHP than observed for some L. monocytogenes. The antimicrobial effect of the antilisterial bacteriocin (bacHA-6111-2) increased after L. monocytogenes cells had been exposed to pressure. The data obtained underlines the importance of strain selection for studies aiming to evaluate HHP efficacy to ensure safety of HHP-treated foods.

Draft Genome Sequence of Leuconostoc mesenteroides 406 Isolated from the Traditional Fermented Mare Milk Airag in Tuv Aimag, Mongolia.

Leuconostoc mesenteroides 406 was isolated from the traditional fermented mare milk airag in Tuv Aimag, Mongolia. This strain produces an antilisterial bacteriocin. Here, we report the draft genome sequence of this organism.

Prevalence, acquired antibiotic resistance and bacteriocin production of Enterococcus spp. isolated from tunisian fermented food products

In this study, a total of 100 fermented food products including dairy (Lben, Rayeb, Rigouta, and Jben) olive and vegetable products, harvested in Northwestern Tunisia, were investigated for the presence of Enterococcus spp. Our results showed high levels of contamination with Enterococcus spp., identified according to standard bacteriological, biochemical and phenotypic criteria. 143 isolates were recovered; E. faecium (46.15%) was the predominant species, followed by E. faecalis (27.27%), E. casseliflavus (12.58%), E. durans (8.39%) and E. mundtii (5.59%). None of the isolates showed acquired resistance againts clinically relevant drugs used for enterococcal infections treatment in human medicins, and no haemolytic activity was demonstrated. Furthermore, over 50% of the isolates within each species exhibited antilisterial bacteriocin production. Further data are needed to enhance understanding of bacteriocin production of enterococci in fermented food products as well as the potential risks to quality and safety, including possible transmission of antibiotic resistant organisms to human consumers.

Solution Structure of Enterocin HF, an Antilisterial Bacteriocin Produced by Enterococcus faecium M3K31.

The solution structure of enterocin HF (EntHF), a class IIa bacteriocin of 43 amino acids produced by Enterococcus faecium M3K31, was evaluated by CD and NMR spectroscopy. Purified EntHF was unstructured in water, but CD analysis supports that EntHF adopts an α-helical conformation when exposed to increasing concentrations of trifluoroethanol. Furthermore, NMR spectroscopy indicates that this bacteriocin adopts an antiparallel β-sheet structure in the N-terminal region (residues 1-17), followed by a well-defined central α-helix (residues 19-30) and a more disordered C-terminal end (residues 31-43). EntHF could be structurally organized into three flexible regions that might act in a coordinated manner. This is in agreement with the absence of long-range nuclear Overhauser effect signals between the β-sheet domain and the C-terminal end of the bacteriocin. The 3D structure recorded for EntHF fits emerging facts regarding target recognition and mode of action of class IIa bacteriocins.

Cloning strategies for heterologous expression of the bacteriocin enterocin A by Lactobacillus sakei Lb790, Lb. plantarum NC8 and Lb. casei CECT475.

BackgroundBacteriocins produced by lactic acid bacteria (LAB) attract considerable interest as natural and nontoxic food preservatives and as therapeutics whereas the bacteriocin-producing LAB are considered potential probiotics for food, human and veterinary applications, and in the animal production field. Within LAB the lactobacilli are increasingly used as starter cultures for food preservation and as probiotics. The lactobacilli are also natural inhabitants of the gastrointestinal (GI) tract and attractive vectors for delivery of therapeutic peptides and proteins, and for production of bioactive peptides. Research efforts for production of bacteriocins in heterologous hosts should be performed if the use of bacteriocins and the LAB bacteriocin-producers is ever to meet the high expectations deposited in these antimicrobial peptides. The recombinant production and functional expression of bacteriocins by lactobacilli would have an additive effect on their probiotic functionality.ResultsThe heterologous production of the bacteriocin enterocin A (EntA) was evaluated in different Lactobacillus spp. after fusion of the versatile Sec-dependent signal peptide (SPusp45) to mature EntA plus the EntA immunity gene (entA + entiA) (fragment UAI), and their cloning into plasmid vectors that permitted their inducible (pSIP409 and pSIP411) or constitutive (pMG36c) production. The amount, antimicrobial activity (AA) and specific antimicrobial activity (SAA) of the EntA produced by Lactobacillus sakei Lb790, Lb. plantarum NC8 and Lb. casei CECT475 transformed with the recombinant plasmids pSIP409UAI, pSIP411UAI and pMGUAI varied depending of the expression vector and the host strain. The Lb. casei CECT475 recombinant strains produced the largest amounts of EntA, with the highest AA and SAA. Supernatants from Lb. casei CECT (pSIP411UAI) showed a 4.9-fold higher production of EntA with a 22.8-fold higher AA and 4.7-fold higher SAA than those from Enterococcus faecium T136, the natural producer of EntA. Moreover, supernatants from Lb. casei CECT475 (pSIP411UAI) showed a 15.7- to 59.2-fold higher AA against Listeria spp. than those from E. faecium T136.ConclusionLb. casei CECT457 (pSIP411UAI) may be considered a promising recombinant host and cell factory for the production and functional expression of the antilisterial bacteriocin EntA.

Production of Antilisterial Bacteriocins from Lactic Acid Bacteria in Dairy-Based Media: A Comparative Study.

One hundred and eight strains of lactic acid bacteria (LAB) were screened for bacteriocin production by the modified deferred antagonism and agar well diffusion methods. When the modified deferred antagonism method was employed, 82 LAB strains showed inhibitory action against Listeria monocytogenes v7 ½a, whereas 26 LAB strains expressed no inhibition. Only 12 LAB strains exhibited inhibitory activity when the agar well diffusion method was used, 11 of which had been previously recognized as bacteriocin production positive (Bac(+)). Lactobacillus viridescens NRRL B-1951 was determined, for the first time, to produce an inhibitory compound with a proteinaceous nature. The inhibitory activity was observed in the presence of lipase, α-chymotrypsin, and trypsin, but no inhibition zone could be detected in the presence of proteinase K, indicating the proteinaceous nature of the inhibitory compound. The inhibitory compound was active against Lact. sake ATCC 15521 and Lact. plantarum NCDO 995. Bacteriocin production by the Bac(+) LAB strains was assessed in Lactobacillus MRS Broth as well as in dairy-based media such as nonfat milk, demineralized whey powder, and cheddar cheese whey supplemented with complex nutrient sources that are rich in nitrogen. Lact. sake ATCC 15521 and L. monocytogenes CWD 1002, CWD 1092, CWD 1157, CWD 1198, and v7 ½a were used as indicators. The inhibitory activities of the bacteriocins varied depending on the indicator strains and the growth media used. The LAB indicator strains were found to be more sensitive to inhibition by bacteriocins when compared to the listerial indicator strains. Among the listerial indicators, L. monocytogenes CWD 1002 and CWD 1198 were the most sensitive strains to the bacteriocins investigated in this study. Media composition had a significant influence on bacteriocin production and activity. When compared to demineralized whey powder medium and cheddar cheese whey medium supplemented with whey protein concentrate, cheddar cheese whey medium supplemented with complex nutrient sources such as yeast extract, polypeptone, proteose peptone nr. 3, or soytone appeared to be more supportive of bacteriocin production.

Survival and Metabolic Activity of Pediocin Producer Pediococcus acidilactici UL5: Its Impact on Intestinal Microbiota and Listeria monocytogenes in a Model of the Human Terminal Ileum.

Pediococcus acidilactici UL5 is a promising probiotic candidate due to its high survival rate under gastric and duodenal conditions and to its ability to produce the antilisterial bacteriocin pediocin PA-1. Its survival, metabolic activity, and impact on Listeria monocytogenes in a continuous stirred tank reactor containing immobilized human intestinal microbiota were studied over a period of 32days of feeding a nutrient medium simulating ileal chyme. The impact of P. acidilactici UL5 on different bacterial groups of intestinal origin as well as its survival and its impact on L. monocytogenes were quantified using quantitative polymerase chain reaction coupling with propidium monoazide (PMA-qPCR), which was shown to detect and quantify viable bacteria only. P. acidilactici UL5 and its non-pediocin-producing mutant had no effect on the microbiota, but the producing strain induced an increase in the production of acetic and propionic acids. P. acidilactici survived but appeared to be a poor competitor with intestinal microbiota, dropping by 1.3 and 2.8 log10 after 8h of fermentation to 104colony-forming units (cfu) mL-1. A 1.64 log but non-significant reduction of Listeria was observed when P. acidilactici UL5 was added at 108cfumL-1. P. acidilactici UL5 isolated from the reactor after 3days was still able to produce the active bacteriocin. These data demonstrate that P. acidilactici UL5 is capable of surviving transit through the ileum without losing its ability to produce pediocin PA-1 but seems to not be enough competitive with the great diversity of organisms found in the ileum.

Biopreservation of Fresh Orange Juice Using Antilisterial Bacteriocins101 and Antilisterial Bacteriocin103 Purified from Leuconostoc mesenteroides

Recently, as the consumption of fresh fruit juice has been increasing the demand for natural and potent biopreservative has also been increased. Listeria monocytogenes is one of the most important and serious intracellular foodborne pathogen that threatens immunocompromised individuals. The main objective of this study is to investigate the biopreservative potential of Antilisterial Bacteriocin101 and Antilisterial Bacteriocin103 on comparison with a chemical preservative. Preservation of fresh orange juice was carried out in two sets i.e., unpasteurized (no heat pretreatment) and pasteurized (pretreated at 72oC for 2 min). Listeria monocytogenes MTCC 657 at an initial concentration of 6.75 log CFU/ml was inoculated into both unpasteurized and pasteurized fresh orange juice then chemical preservative (12 ppm), Antilisterial Bacteriocin101 (40 ppm) and Antilisterial Bacteriocin103 (40 ppm) were added and stored for 12 days at 4oC and checked for the viability of the indicator strain at 24 h regular intervals. Antilisterial Bacteriocins showed potential reduction of viable counts upto 4th day in unpasteurized fresh orange juice and upto 6th day in case of pasteurized fresh orange juice. This study has revealed that both the Antilisterial Bacteriocins show high potential in reduction of microbial population and is more effective than chemical preservative even at low concentration.

Molecular Characterization of Bacteriocinogenic, Antifungal and Probiotic Lactic Acid Bacteria Isolated from Chicken Gastrointestinal Tract

In this study, bacteriocinogenic Lactobacillus plantarum isolates capable of inhibiting food- and feed-borne filamentous fungi from the gastrointestinal tract (GIT) of broiler chicken were identified using 16S rRNA gene sequencing and further evaluated for probiotic properties in vitro. Six potent lactobacilli were selected from one hundred and thirteen isolates for the present study based on their ability to inhibit both pathogenic bacteria and filamentous fungi. They were characterized using various physiological, biochemical and molecular methods. They were acetoin producers, homo fermentative, catalase-negative and producing racemic lactic acid (10 - 20 mM). All the six isolates exhibited varied sugar utilization and RAPD pattern, indicated their strain level genotypic variation. The 16S rRNA gene sequence and multiplex PCR analysis confirmed that these isolates were Lactobacillus plantarum. The isolates being resistant to low pH (2.0) and bile salt (0.6%) could survive in the gastrointestinal tract of host indicating their potential probiotic application. The isolates were non-pathogenic (γ-hemolytic) and exhibited resistance to antibiotics ciprofloxacin, nalidixic acid, norfloxacin, nitrofurantoin, colistin and streptomycin. They demonstrated strong autoaggregating phenotype ranging from 78% to 86% and showed 49% - 61% and 30% - 46% coaggregation with E. coli MTCC 728 and L. monocytogenes MTCC 657, respectively. The percentage of hydrophobicity ranged from 16% - 33% for all the isolates showing that surface was rather hydrophilic. They exhibited β-galactosidase activity ranging from 1036 - 1179 MU, bile salt hydrolase activity assisting to reduce serum cholesterol and produced the anti-Listerial bacteriocin. The strong inhibitory activity of these isolates against food spoilage molds and bacteria with probiotic properties indicates their potential application as food preservatives.