Bacteriocin-producing Lactic Acid Bacteria Research Articles

Evaluation of Market Curd for Sanitary Quality and Bacteriocin-Producing Lactic acid Bacteria for Potential Application as a Natural, Healthy Food Preservative

The quality of curd in local market varies as there are no well described standards for milk products, making evaluation of their microbiological quality, important. Curd is a great source of lactic acid bacteria, important producers of bacteriocins (proteinaceous antimicrobials). The study evaluates curd samples, collected from local market of Jalandhar, for sanitary quality and presence of bacteriocin-producing lactic acid bacteria (LAB). Of the total 21 curd samples tested, only 14% showed confluent microbial growth and categorized as ‘poor quality’ in terms of microbial load. Sample 6 exhibited best sanitary quality. 3 isolates (LABI, II, and III), of the total of 42 bacterial colonies tested, were promising bacteriocin producers against Vibrio parahemolyticus and E.coli with, LABIII (17357 U mL -1) as the best bacteriocin producer, exhibiting 13.1% higher activity than standard reference, Lactococcous lactis subspecies lactis MTCC440, against E.coli. LABI and II showed similar bacteriocin activity against V. parahemolyticus while, against E.coli, bacteriocin activity was 7539 U mL -1 and 10995 U mL -1 for LABI and II, respectively. The future work will explore efficiency of LABIII as bio-preservative in different food materials in cost effective manner. This would help to provide economic solutions for food preservation with distinct and well proved health benefits for the consumers.

Characteristics and potential applications of circular bacteriocins

Abstract Bacteriocins are ribosomally synthesized peptides or proteins exerting anatagonistic activity toward organisms which are closely related to the producer strain. Circular bacteriocins are produced by Gram-positive bacteria, mainly lactic acid bacteria, and to a lesser extent by Bacillus, Clostridium and Staphylococcus genera. These bacteriocins are characterized by the head-to-tail cyclization of their backbone. The circular nature of these peptides makes them resistant to many proteolytic enzymes and provides great thermal and pH stability. Circular bacteriocins are divided into 2 subgroups based on their physicochemical properties and sequence identity. These bacteriocins are synthesized as linear precursors with a leader sequence which is cleaved off during maturation. The mature circular peptides are composed of 58–70 amino acid residues. Biosynthesis of circular bacteriocins requires three stages: cleavage of the leader sequence, circularization and export out of the cell. Circular bacteriocins have broad antimicrobial activity spectrum, including many food spoilage bacteria and pathogens, such as Listeria, Staphylococcus and Clostridum spp. Circular bacteriocins permeabilize the membrane of sensitive bacteria, causing loss of ions and dissipation of the membrane potential, and finally cell death. Enterocin AS-48 was the first identified circular bacteriocin and is best characterized so far. Circular bacteriocins or bacteriocin-producing lactic acid bacteria have great potential in food preservation, and possibly in pharmaceutical and cosmetic industries. Thanks to their properties, circular bacteriocins could be an alternative not only to preservatives and methods used to provide microbial food safety presently, but also to less stable, linear bacteriocins. 1. Characteristics and classification of circular bacteriocins. 2. Genetics of circular bacteriocins. 3. Biosynthesis of circular bacteriocins. 4. Structure of circular bacteriocins. 5. Modes of action of circular bacteriocins. 6. Enterocin AS-48. 7. Potential applications of circular bacteriocins. 8. Summary

Inhibitory effect of bacteriocin-producing lactic acid bacteria against histamine-forming bacteria isolated from Myeolchi-jeot

The objectives of this study were to identify the histamine-forming bacteria and bacteriocin- producing lactic acid bacteria (LAB) isolated from Myeolchi-jeot according to sequence analysis of the 16S rRNA gene, to evaluate the inhibitory effects of the bacteriocin on the growth and histamine accumulation of histamine-forming bacteria, and to assess the physico-chemical properties of the bacteriocin. Based on 16S rRNA gene sequences, histamine-forming bacteria were identified as Bacillus licheniformis MCH01, Serratia marcescens MCH02, Staphylococcus xylosus MCH03, Aeromonas hydrophila MCH04, and Morganella morganii MCH05. The five LAB strains identified as Pediococcus acidilactici MCL11, Leuconostoc mesenteroides MCL12, Enterococcus faecium MCL13, Lactobacillus sakei MCL14, and Lactobacillus acidophilus MCL15 were found to produce an antibacterial compound with inhibitory activity against the tested histamine-producing bacteria. The inhibitory activity of these bacteriocins obtained from the five LAB remained stable after incubation at pH 4.0–8.0 and heating for 10 min at 80 °C; however, the bacteriocin activity was destroyed after treatment with papain, pepsin, proteinase K, α-chymotrypsin, or trypsin. Meanwhile, these bacteriocins produced by the tested LAB strains also exhibited histamine-degradation ability. Therefore, these antimicrobial substances may play a role in inhibiting histamine formation in the fermented fish products and preventing seafood-related food-borne disease caused by bacterially generated histamine.

Potential use of bacteriocin producing lactic acid bacterial strain isolated from milk products and its application as the fish feed

Bacteriocins are gene-encoded inhibitory proteins and those produced by Gram-positive Lactic acid bacteria. Some bacteriocins even display antagonistic activity towards Gram-positive food borne pathogens and spoilage organisms. This present study involves isolation of Bacteriocin-producing lactic acid bacteria from a variety of milk and milk products. The physico-chemical properties of the isolated bacteriocin producing bacterial strains were screened. The isolated bacteriocin bacterial strains were biochemically characterized and identified. Further, the isolated effective bacterial strain was used as a fish feed and its effect on their growth was evaluated. The evaluated data continue to demonstrate that the bacteriocin producing bacterial strains will have greater potential in the food products industry.

Evaluation of bacteriocinogenic activity, safety traits and biotechnological potential of fecal lactic acid bacteria (LAB), isolated from Griffon Vultures (Gyps fulvus subsp. fulvus).

BackgroundLactic acid bacteria (LAB) are part of the gut microbiota and produce ribosomally synthesized antimicrobial peptides or bacteriocins with interest as natural food preservatives and therapeutic agents. Bacteriocin-producing LAB are also attractive as probiotics. Griffon vultures (Gyps fulvus subspecies fulvus) are scavenger birds that feed almost exclusively on carrion without suffering apparent ill effects. Therefore, griffon vultures might be considered a reservoir of bacteriocin-producing lactic acid bacteria (LAB) with potential biotechnological applications.ResultsGriffon vulture feces were screened for LAB with antimicrobial activity, genes encoding bacteriocins, potential virulence determinants, susceptibility to antibiotics, genotyping and characterization of bacteriocins. In this study, from 924 LAB evaluated 332 isolates (36 %) showed direct antimicrobial activity against Gram-positive bacteria only. The molecular identification of the most antagonistic 95 isolates showed that enterococci was the largest LAB group with antimicrobial activity (91 %) and E. faecium (40 %) the most identified antagonistic species. The evaluation of the presence of bacteriocin structural genes in 28 LAB isolates with the highest bacteriocinogenic activity in their supernatants determined that most enterococcal isolates (75 %) encoded multiple bacteriocins, being enterocin A (EntA) the largest identified (46 %) bacteriocin. Most enterococci (88 %) were resistant to multiple antibiotics. ERIC-PCR and MLST techniques permitted genotyping and recognition of the potential safety of the bacteriocinogenic enterococci. A multiple-step chromatographic procedure, determination of the N-terminal amino acid sequence of purified bacteriocins by Edman degradation and a MALDI TOF/TOF tandem MS procedure permitted characterization of bacteriocins present in supernatants of producer cells.ConclusionsEnterococci was the largest LAB group with bacteriocinogenic activity isolated from griffon vulture feces. Among the isolates, E. faecium M3K31 has been identified as producer of enterocin HF (EntHF), a bacteriocin with remarkable antimicrobial activity against most evaluated Listeria spp. and of elevated interest as a natural food preservative. E. faecium M3K31 would be also considered a safe probiotic strain for use in animal nutrition.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0840-2) contains supplementary material, which is available to authorized users.

Antibacterial Activity and Optimisation of Bacteriocin Producing Lactic Acid Bacteria Isolated from Beef (Red Meat) Samples

Bacteriocin producing bacteria are commonly found in meat products to enhance theirshelf-life. In the present study, bacterial species were isolated from meat samples (beef) from differentlocalities of Lahore, Pakistan. MRS agar medium was used to isolate lactic acid bacteria (LAB) throughspread and streak methods (incubated for 72 h at 37 °C). Identification of bacteriocinogenic LAB strainswas done by using staining techniques, morphology based characteristics and biochemical tests. Thesestrains were BSH 1b, BSH 3a, BIP 4a, BIP 3a, BIP 1b and BRR 3a. Antibacterial activity of LAB wasperformed against food borne pathogens viz., Escherichia coli and Staphylococcus aureus through paperdisc diffusion method. Three bacterial strains showed maximum inhibition and characterised by ribotypingviz., BIP 4a was identified as Lactobacillus curvatus, BIP 3a was Staphylococcus warneri and BIP 1b wasLactobacillus graminis. Optimum pH 5-6.5 and 30-37 °C temperature for isolated bacterial strains wasrecorded. Protein concentration measured was 0.07 mg/mL for BSH 1b, 0.065 mg/mL for BSH 3a,0.057 mg/mL for BIP 4a, 0.062 mg/mL for BIP 1b, 0.065 mg/mL for BIP 3a and for BRR 3a 0.078 mg/mL,respectively. Bacteriocin of all isolates except BIP 3a was found to be sensitive towards pepsin and resistanttowards Rnase. Bacteriocin production was stable at between pH 5.0 and 6.0 and resistant temperaturewas 40 °C. It was concluded that lactic acid bacteria (LAB) from meat can be helpful as antibacterialagents against food-borne bacterial pathogens because of thermostable producing bacteriocin.

Development of antimicrobial packaging materials for food preservation using bacteriocin from Lactobacillus casei

Bacteriocins are proteinaceous toxin produced by bacteria to inhibit the growth of similar or closely related bacteria. Among lactic acid bacteria (LAB), bacteriocins are produced by <em>Streptococcus</em>, <em>Pediococcus</em>, <em>Lactobacillus</em>, etc. In recent years, bacteriocin-producing LAB have attracted significant attention because of their generally recognized as safe status and potential use as safe additives for food preservation. Incorporation of bacteriocins into packaging films to control food spoilage and pathogenic organisms has been an area of active research for last decade. Antimicrobial packaging film prevents microbial growth on food surface by direct contact of the package with the surface of food. The objectives of this study were to isolate bacteriocin-producing LAB from Yakult®, develop antimicrobial packaging system and evaluate their antimicrobial effects on selected spoilage and pathogenic microorganisms. For this reason, the antimicrobial packaging film was made by using the bacteriocin by <em>Lactobacillus casei</em> and coating it or adsorbing it onto the surface of different packaging materials. The antimicrobial activity of the coated films was tested by agar diffusion assay against the test organisms <em>Escherichia coli</em> and <em>Staphylococcus aureus</em>. The results obtained proved that bacteriocins can be used to inhibit both the test organisms. Thus antimicrobial packaging systems can be developed using bacteriocins thereby reducing the risk of pathogen development, as well as extending the shelf life of foods.

Protection of honeybee Apis mellifera by its endogenous and exogenous lactic flora against bacterial infections

Abstract Lactic acid bacteria (LAB) symbionts of honeybees are certainly playing key roles in their host's colony functioning. The defense against bacterial pathogen invasion by endogenous LAB has been considered as promising and usable phenomenon. This study addresses bacteriocinogeny as one of antibacterial action mode displayed by bacteria. The honeybee endogenous LAB isolated from worker honeybee intestines (61 strains), queen honeybee intestines (16 strains) and beebread (25 strains) were tested for bacteriocin production ability. We checked also well characterized bacteriocin producing LAB strains against bacteria causing American foulbrood (AFB) – Paenibacillus larvae aiming possible use of exogenous LAB for control AFB in honeybees and in the same time to observe the vulnerability of endogenous bacteria exposed to bacteriocin producers. We demonstrated that none of 102 studied LAB strains, isolated from worker honeybee intestines, from queen honeybee intestines and from beebread, produced bacteriocins detectable by the well diffusion method (WDM). All of them failed to inhibit two strains of P. larvae . Three exogenous bacteriocin-producing LAB strains were tested against the same pathogens and against 25 endogenous bacterial isolates representing 11 different LAB species. The screening showed that all the tested exogenous bacteriocin-producing strains inhibited the tested P. larvae strains. The endogenous LAB strains exhibited varied sensitivity profiles when treated with bacteriocin-producing strains. This raises similar challenges to those observed in antibiotic applications leading to dysbacteriosis, even though the efficacy of these bacteriocins against P. larvae in an in vitro system is evident.

Biodiversity of Bacteriocin-Producing Lactic Acid Bacteria from Mexican Regional Cheeses and their Contribution to Milk Fermentation

ABSTRACTThe aim of this work was to examine the biodiversity of bacteriocin-producing lactic acid bacteria from homemade cheeses produced in Veracruz (México) and assess their contribution as adjunct cultures in dairy products. Ninety-three presumptive bacteriocinogenic strains were detected by direct antagonism assays and 29 of them were active against Enterococcus faecalis NRRL-B537, Listeria innocua 062 AST, or Listeria monocytogenes ATCC19115 by the well diffusion test using cell-free supernatants, adjusted to pH 6.0 to exclude inhibition by organic acids. Positive isolates were identified by partial sequencing of the 16s rDNA as Pediococcus acidilactici (four isolates), Enterococcus faecium (17 isolates), Lactobacillus plantarum (six isolates) and Lactobacillus fermentum (two isolates). RAPD-PCR discriminated seven groups with a 50% similarity and revealed the presence of the same isolates. The coding genes for the synthesis of plantaricin EF, plantaricin JK, plantaricin N, plantaricin NC8 and the inducing peptide plantaricin A were detected by PCR in L. plantarum. Similarly, enterocin P and pediocin PA-1 genes were amplified from Enterococcus and Pediococcus genomic DNA, respectively. Overall, co-culturing of bacteriocin producing Lactobacillus and Pediococcus strains with the dairy starter Lactococcus lactis IPLA947 did not interfere with milk acidification. Lactose consumption, acidification rate and production of lactic acid were unchanged. Nonetheless, higher levels of acetic acid, ethanol and succinic acid were detected depending on the strain. Our results demonstrate the diversity of bacteriocinogenic species in homemade Mexican cheeses which may be used as adjunct cultures to enhancing safety of this well-appreciated cheese while providing a richer range of metabolites.

Effect of bacteriocin-producing Pediococcus acidilactici K10 on beer fermentation

Beer is generally considered to be a beverage that has high microbiological stability. However, some undesirable lactic acid bacteria (LAB) can grow in beer and consequently spoil this beverage. In this study, bacteriocin-producing Pediococcus acidilactici K10 was used as a means of bio-acidifying the mash and reducing the spoilage LAB content of the beer. The K10 strain had antimicrobial activity against two beer spoilage LAB strains in wort and did not grow in a beer environment. The K10 strain was inoculated before the mashing step. The effect of K10 as a starter culture was investigated and compared with a control. As a result, filtration time was shortened by 17 min, alcohol content was increased by 137%, foam stability was increased by 156%, bitterness was increased by two bitterness units and there was a significant difference (p < 0.05) in aromatic and sour odour. The feasibility of using bacteriocin-producing LAB strain in beer brewing is envisaged. Copyright © 2016 The Institute of Brewing & Distilling

Antimicrobial Impact forLactococcus lactissubsp.lactisA15 andEnterococcus faeciumA15 Isolated from Some Traditional Egyptian Dairy Products on Some Pathogenic Bacteria

Lactococcus lactis subsp. lactis A15 and Enterococcus faecium A15 had antimicrobial activity against Listeria monocytogenes EGDEe 107776. Bacteriocins produced from isolated strains are stable between pH 5 and 8 and stable also until 100C for 10 min. The amount of bacteriocin produced by Lactococcus lactis subsp. lactis A15 reached to the maximum (2560 AU/mL) at the end of logarithmic phase while Enterococcus faecium A15 was observed in logarithmic phase. PCR results revealed the presence of nisin Z structural gene in Lactococcus lactis subsp. lactis A15 and enterocin B gene for Enterococcus faecium A15. Lactococcus lactis subsp. lactis A15 was free from genes of asa1, gelE, espfm, cylA, efaAfs. Otherwise, Enterococcus faecium A15 did not contain an asal, espfm and cylA genes. Tested strains were sensitive to kanamycin, vancomycin and gentamycin. Tested strains were not able to hydrolyze red blood cells. Practical Applications Nowadays, the addition of bacteriocins and/or bacteriocin-producing lactic acid bacteria (LAB) as natural food preservatives to food products (i.e. cheese and yoghurt) has been considered with the aim of increasing the food safety of these products. Bacteriocins have successfully been used to control Listeria monocytogenes. Lactococcus lactis subsp. lactis A15 could be used as starter culture or co-culture in food system for preventing the growth of Listeria monocytogenes and increasing the safety and shelf-life of dairy products. Enterococcus faecium A15 was able to produce gelatinase but not able to hydrolyze red blood cells. On the other hand, the bacteriocin produced from Enterococcus faecium A15 may find application as bio-preservatives for increasing the shelf-life of Egyptian Dairy products.

Identification, Characterization and Genetic Improvement of Bacteriocin Producing Lactic Acid Bacteria

Identification, Characterization and Genetic Improvement of Bacteriocin Producing Lactic Acid Bacteria

Bacteriocins from lactic acid bacteria and their applications in meat and meat products

Meat and meat products have always been an important part of human diet, and contain valuable nutrients for growth and health. Nevertheless, they are perishable and susceptible to microbial contamination, leading to an increased health risk for consumers as well as to the economic loss in meat industry. The utilization of bacteriocins produced by lactic acid bacteria (LAB) as a natural preservative has received a considerable attention. Inoculation of bacteriocin-producing LAB cell as starter or protective cultures is suitable for fermented meats, whilst the direct addition of bacteriocin as food additive is more preferable when live cells of LAB could not produce bacteriocin in the real meat system. The incorporation of bacteriocins in packaging is another way to improve meat safety to avoid direct addition of bacteriocin to meat. Utilization of bacteriocins can effectively contribute to food safety, especially when integrated into hurdle concepts. In this review, LAB bacteriocins and their applications in meat and meat products are revisited. The molecular structure and characteristics of bacteriocins recently discovered, as well as exemplary properties are also discussed.

Co-culture-inducible bacteriocin production in lactic acid bacteria.

It is common knowledge that microorganisms have capabilities, like the production of antimicrobial compounds, which do not normally appear in ideal laboratory conditions. Common antimicrobial discovery techniques require the isolation of monocultures and their individual screening against target microorganisms. One strategy to achieve expression of otherwise hidden antimicrobials is induction by co-cultures. In the area of bacteriocin-producing lactic acid bacteria, there has been some research focusing into the characteristics of co-culture-inducible bacteriocin production and particularly the molecular mechanism(s) of such interactions. No clear relationship has been seen between bacteriocin-inducing and bacteriocin-producing microorganisms. The three-component regulatory system seems to be playing a central role in the induction, but inducing compounds have not been identified or characterized. However, the presence of the universal messenger molecule autoinducer-2 has been associated in some cases with the co-culture-inducible bacteriocin phenotype and it may play the role in the additional regulation of the three-component regulatory system. Understanding the mechanisms of induction would facilitate the development of strategies for screening and development of co-culture bacteriocin-producing systems and novel products as well as the perseverance of such systems in food and down to the intestinal tract, possibly conferring a probiotic effect on the host.

Encapsulation of Lactococcus lactis subsp. lactis on alginate/pectin composite microbeads: Effect of matrix composition on bacterial survival and nisin release

Alginate/pectin hydrogel microspheres were prepared by extrusion based on a vibrating technology to encapsulate bacteriocin-producing lactic acid bacteria. Effects of both alginate/pectin (A/P) biopolymers ratio and physiological state of Lactococcus lactis subsp. lactis (exponential phase, stationary phase) were examined for nisin release properties, L. lactis survival and beads physico-chemical properties. Results showed that A/P composites were more efficient to increase beads properties than those formulated with pure alginate or pectin. Association of alginate and pectin induces synergistic effect which improves microbeads mechanical properties. FTIR spectroscopy confirms possible interactions between alginate and pectin during inter-penetrating network formation. Physiological state of bacteria during encapsulation process and microbeads composition (A/P ratio, enrichment of internal medium with nutrients) were determining factors for both bacteria viability and bacteriocin release. Of the several matrices tested A/P (75/25) with glucose-enriched M17 gave the best results when L. lactis was encapsulated in exponential state.

Design of microcapsules containing Lactococcus lactis subsp. lactis in alginate shell and xanthan gum with nutrients core

Aqueous-core microcapsules with sodium alginate (SA) hydrogel in membrane and xanthan gum (XG) in core were prepared using ionotropic gelation method to encapsulate bacteriocin-producing lactic acid bacteria (LAB). In this study LAB were immobilized in microcapsule membrane. XG was applied to reinforce SA microcapsules. Molecular interaction between SA and XG in the microcapsules was investigated using FTIR spectroscopy. Microcapsules morphology and mechanical properties were examined. The impact of an enrichment with nutrients of core (M17 broth supplemented with 0.5% glucose vs physiological water) and physiological state of Lactococcus lactis during encapsulation step (exponential vs stationary state) was studied on L. lactis survival, nisin release. Furthermore, the antimicrobial effectiveness of the best system to preserve bacterial survival and permit nisin release was studied against Listeria monocytogenes. No differences were observed in terms of mechanical properties among studied systems. FTIR spectroscopy confirmed the establishment of possible hydrogen bonding between XG hydroxyls groups and SA carboxylate groups which could modify microcapsules release properties. Microcapsules with L. lactis in exponential state encapsulated in SA membrane and aqueous-core based on XG with nutrients gave the best results. At 30 °C, a complete inhibition of L. monocytogenes growth throughout the storage period was observed for these microcapsules.

Effect of the competitive growth of Lactobacillus sakei MN on the growth kinetics of Listeria monocytogenes Scott A in model meat gravy

Listeria monocytogenes is a foodborne pathogen capable of growth under refrigeration temperatures. The use of bacteriocin-producing lactic acid bacteria to inhibit Gram-positive pathogen growth may be an important tool to enhance the safety of refrigerated foods. The influence of three different populations of the bacteriocin-producing strain Lactobacillus sakei MN on the growth kinetic parameters of three different populations of L. monocytogenes Scott A co-cultured in model meat gravy at 4, 10, 16, and 22 °C was studied. The Baranyi growth model was used to estimate the kinetic parameters of L. monocytogenes and L. sakei for each strain cultured alone or in co-culture. The highest L. monocytogenes populations were achieved by pure cultures, decreasing in co-culture with the different inocula of L. sakei, at all temperatures. A modified logistic model was applied which includes a factor β that adjusts the effect of L. sakei on L. monocytogenes depending on the environmental conditions. The co-cultures of low (∼1log) L. monocytogenes inocula showed a decrease in β values when temperature increased, indicating that inter-species competition changes with temperature; the 2log- and 4log-inocula of L. monocytogenes co-cultures also showed this behavior but only with the higher initial population of L. sakei.

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.

In vitro Characterization of Bacteriocin Produced by Lactic Acid Bacteria Isolated from Nem Chua, a Traditional Vietnamese Fermented Pork.

The aim of this study was to screen and In vitro characterize the properties of bacteriocin produced by lactic acid bacteria isolated from Vietnamese fermented pork (Nem chua). One hundred and fifty LAB were isolated from ten samples of Nem chua and screened for bacteriocin-producing lactic acid bacteria. Antimicrobial activity of bacteriocin was carried out by spot on lawn method against both gram positive and gram negative bacteria. One isolate, assigned as KL-1, produced bacteriocin and showed inhibitory activity against Lactobacillus sakei, Leuconostoc mesenteroides and Enterococcus faecalis. To characterize the bacteriocin-producing strain, optimum temperature, incubation period for maximum bacteriocin production and identification of bacteriocin-producing strain were determined. It was found that the optimum cultivation temperature of the strain to produce the maximum bacteriocin activity (12,800 AU/mL) was obtained at 30℃. Meanwhile, bacteriocin production at 6,400 AU/mL was found when culturing the strain at 37℃ and 42℃. The isolate KL-1 was identified as L. plantarum. Antimicrobial activity of cell-free supernatant was completely inhibited by proteolytic enzyme of trypsin, alpha-chymotrypsin and proteinase K. Bacteriocin activity was stable at high temperature up to 100℃ for 10 min and at 4℃ storage for 2 d. However, the longer heating at 100℃ and 4℃ storage, its activity was reduced.

Characterization and antimicrobial activity of lactic acid bacteria from fermentative bioreactors during hydrogen production using cassava processing wastewater

Fermentative hydrogen production was evaluated using two anaerobic fluidized bed reactors (AFBRs). The reactors were fed cassava processing wastewater and operated with varying organic loading rates (OLR: 4–30kgCODm−3d−1) for up to 160d under mesophilic conditions. The effects and roles of lactic acid bacteria (LAB) and their antimicrobial peptides in hydrogen-producing bioreactors and on hydrogen producers were evaluated. A maximum hydrogen yield of 2.0mmolg−1COD and a maximum hydrogen production rate of 2.1LH2d−1L−1 were achieved with OLRs of 10kgCODm−3d−1 and 14kgCODm−3d−1, respectively, which coincided with the absence of bacteriocin-producing lactic acid bacteria. The major metabolites were lactic acid, ethanol, methanol, acetic acid and butyric acid. After growth on MRS agar, gram-staining and catalase tests, 47 strains were classified as presumptive lactic acid bacteria, with counts ranging from <10 to 1.5×109CFUmL−1 for both reactors, providing evidence that lactic acid bacteria are able to survive and persist in the reactors. Thirty-nine pure cultures of the LAB community were successfully identified by 16S rRNA sequencing. For AFBR1 (4–12kgCODm−3d−1), there was a prevalence of Lactobacillus sp. (45.4%), followed by Lactococcus lactis (31.8%). Lactobacillus sp. (78.6%) was the prevalent genus for AFBR2 (14–30kgCODm−3d−1).