Enhancement of the enterocin CRL35 activity by a synthetic peptide derived from the NH2-terminal sequence

Improvement of Key Molecular Events Linked to Alzheimer's Disease Pathology Using Postbiotics

In the past 50 years, life expectancy has increased by more than 20 years. One consequence of this increase in longevity is the rise of age-related diseases such as dementia. Alzheimer's disease (AD) is the most common form of dementia, accounting for 60-70% of cases. AD pathogenesis is not restricted to the neuronal compartment but includes strong interactions with other brain cells, particularly microglia triggering the release of inflammatory mediators, which contribute to disease progression and severity. There is growing evidence revealing the diverse clinical benefits of postbiotics in many prevalent conditions, including neurodegenerative diseases. Here, we tested the ability of bacterial conditioned media (BCM) derived from selected lactic acid bacteria (LAB) strains to regulate core mechanisms relevant to AD pathophysiology in the microglia cell line BV-2. Levilactobacillus brevis CRL 2013, chosen for its efficient production of the neurotransmitter GABA, and Lactobacillus delbrueckii subsp. lactis CRL 581, known for its anti-inflammatory properties, were selected alongside Enterococcus mundtii CRL 35, a LAB strain that can significantly modulate cytokine production. BCM from all 3 strains displayed antioxidant capabilities, reducing oxidative stress triggered by beta-amyloid oligomers (oAβ1-42). Additionally, BCM effectively mitigated the expression of inflammatory cytokines, namely, TNF-α, IL-1β, and IL-6 triggered by oAβ1-42. Furthermore, our study identified that BCM from CRL 581 inhibit the activity of acetylcholinesterase (AChE), a crucial enzyme in AD progression, in both human erythrocytes and mouse brain tissues. Notably, the inhibitory effect was mediated by low-molecular-weight components of the BCM. L. delbrueckii subsp. lactis CRL 581 emerged as a favorable candidate for production of postbiotics with potential benefits for AD therapy since it demonstrated potent antioxidant activity, reduction of cytokine expression, and partial AChE inhibition. On the other hand, E. mundtii CRL 35 showed that the antioxidant activity failed to inhibit AChE and caused induction of iNOS expression, rendering it unsuitable as a potential therapeutic for AD. This study unveils the potential benefits of LAB-derived postbiotics for the development of new avenues for therapeutic interventions for AD.

Bacteriocin production and technological properties of Enterococcus mundtii and Enterococcus faecium strains isolated from sheep and goat colostrum

Enterococci are lactic acid bacteria (LAB) that play a role in the aroma formation, maturation, and sensory development of fermented foods such as meat and dairy products. They also contribute to the improvement of the extended shelf life of fermented foods by producing bacteriocin. The aim of this study was to isolate bacteriocin-producing LAB from sheep and goat colostrum, to characterize the bacteriocin-producing strains, and determine the technological properties of the strains. A total of 13 bacteriocin-producing LAB was isolated and identified as 11 Enterococcus mundtii and two Enterococcus faecium. The strains were found to be genetically different from each other by phylogenetic analysis of 16S rRNA gene sequences and random amplified polymorphic-DNA (RAPD-PCR). It has been determined that bacteriocins show activity in a wide pH range and are resistant to heat, lose their activity with proteolytic enzymes and α-amylase, but are resistant to detergents. While the presence of the munKS gene was detected in all of the strains, it was determined that E. faecium HC121.4, HC161.1, E. mundtii HC147.1, HC166.5, and HC166.8 strains contained multiple enterocin genes. Trisin-SDS-PAGE analysis revealed two active protein bands of approximately 5.1 and 5.5 kDa in E. faecium HC121.4 and one active protein band with a weight of approximately 4.96 kDa in other strains. E. mundtii strains and E. faecium HC161.1 were identified as mundticin KS producers, and E. faecium HC121.4 was defined as an enterocin A and B producer. Except for E. mundtii HC166.8, acid production of strains was found to be slow at 6 h and moderate at 24 h. None of them showed extracellular proteolytic and lipolytic activities. It was found that the strains had esterase, esterase lipase, leucine arylamidase, acid phosphatase, and naphthol-AS-Bl-phosphohydrolase activities, while protease activities were low and peptidase activities were high. In conclusion, bacteriocin producer 13 Enterococcus strains isolated from sheep and goat colostrum were found to have the potential to be included in starter culture combinations.

Biotechnological use of dairy by-products for the production and microencapsulation of the food preservative enterocin CRL35

Bacteriocins from Gram-positive bacteria have been proposed as natural food preservative and there is a need for large-scale production for commercial purposes. The aim of the present work is to evaluate whey, a cheese industrial by-product, for the production and microencapsulation of enterocin CRL35. Whey proved to be a promising basal medium for bacterial growth although the bacteriocin production was quite low. However, it could be much favored with the addition of yeast extract at concentrations as low as 0.5%. Besides improving bacteriocin production, this peptide was successfully microencapsulated by spray drying using whey protein concentrate and a chitosan derivative as wall materials. Microcapsules averaging 10 ± 5 μm diameter were obtained, with good structural integrity and high antimicrobial activity with a stability of at least 12 weeks at 4°C. In summary, sustainable bacteriocin production and microencapsulation was achieved recycling whey or its derivatives. In addition, the formulation owns high antimicrobial activity with a long shelf life. The development of a food preservative may represent a green solution for handling whey.

A bacteriocin-based treatment option for Staphylococcus haemolyticus biofilms

Bacteriocins are ribosomally-synthesized antimicrobial peptides, showing great potential as novel treatment options for multidrug-resistant pathogens. In this study, we designed a novel hybrid bacteriocin, Hybrid 1 (H1), by combing the N-terminal part and the C-terminal part of the related bacteriocins enterocin K1 (K1) and enterocin EJ97 (EJ97), respectively. Like the parental bacteriocins, H1 used the membrane-bound protease RseP as receptor, however, it differed from the others in the inhibition spectrum. Most notably, H1 showed a superior antimicrobial effect towards Staphylococcus haemolyticus—an important nosocomial pathogen. To avoid strain-dependency, we further evaluated H1 against 27 clinical and commensal S. haemolyticus strains, with H1 indeed showing high activity towards all strains. To curtail the rise of resistant mutants and further explore the potential of H1 as a therapeutic agent, we designed a bacteriocin-based formulation where H1 was used in combination with the broad-spectrum bacteriocins micrococcin P1 and garvicin KS. Unlike the individual bacteriocins, the three-component combination was highly effective against planktonic cells and completely eradicated biofilm-associated S. haemolyticus cells in vitro. Most importantly, the formulation efficiently prevented development of resistant mutants as well. These findings indicate the potential of a bacteriocins-based formulation as a treatment option for S. haemolyticus.

Draft Genome Sequence of Enterococcus mundtii SCPM-O-B-8398 (E28), Isolated from Fermented Milk in the Moscow Region, Russian Federation

We report the draft genome sequence of the bacteriocin-producing Enterococcus mundtii strain SCPM-O-B-8398 (E28), which was isolated from fermented milk in the Moscow region, Russian Federation.

Probiotic Potential and Wide-spectrum Antimicrobial Activity of Lactic Acid Bacteria Isolated from Infant Feces

In this study, we aimed to characterize lactic acid bacteria strains derived from infants' feces, to evaluate the probiotic potential and explore the wide-spectrum antimicrobial activity. Of 800 isolates, 20 inhibited the growth of enterotoxigenic Escherichia coli K88 and Salmonella enterica ATCC 13076. On the basis of 16S rRNA sequence analysis, the 20 isolates were assigned to Lactobacillus casei (7), Lactobacillus paracasei (2), Lactobacillus plantarum (4), Lactobacillus rhamnosus (2), Enterococcus avium (3), Enterococcus faecium (1), and Enterococcus lactis (1) species. In addition, 12 strains with high antimicrobial activity were investigated for the presence of probiotic properties such as physiological-biochemical characteristics, antimicrobial susceptibility, hemolytic activity, hydrophobicity, and aggregation activity. Wide-spectrum antimicrobial activity analysis revealed that approximately all tested strains inhibited the ten pathogens, and four strains (ZX221, ZX633, ZX3131, and ZX3875) had good probiotic properties and survived after being exposed to simulated gastrointestinal tract conditions. Moreover, we investigated the influence of pH on the wide-spectrum antimicrobial activity and found that four strains inhibited most pathogens at pH 4.5 and pH 5, whereas only ZX633 had an inhibitory effect on Bacillus subtilis ATCC 6633 and Micrococcus luteus ATCC 4698 at pH 5.5. Overall, Lact. casei ZX633 had wide-spectrum antimicrobial activity and could be considered a potential probiotic.

Characterization of Partially Purified Bacteriocins Produced by Enterococcus faecium Strains Isolated from Soybean Paste Active Against Listeria spp. and Vancomycin-Resistant Enterococci

Three out of one hundred eighty putative LAB isolates from Korean traditional fermented soybean paste were identified to be unique and bacteriocinogenic strains. Based on phenotypic and 16S rRNA sequencing analysis, selected strains were identified as Enterococcus faecium ST651ea, E. faecium ST7119ea and E. faecium ST7319ea. The bacteriocinogenic properties of the studied strains were evaluated against Listeria monocytogenes ATCC15313, Listeria innocua ATCC33090 and vancomycin-resistant E. faecium VRE19 of clinical origin. The strains E. faecium ST651ea, ST7119ea and ST7319ea expressed bacteriocins with an activity of 12,800 AU/mL, 25,600 AU/mL and 25,600 AU/mL, respectively, recorded against L. monocytogenes ATCC15131. According to the PCR-based screening of bacteriocin-related genes, which was further confirmed through amplicon sequencing, showed that strain E. faecium ST651ea carries entB and entP genes, whereas both E. faecium ST7119ea and ST7319ea strains harbor entA and entB genes. The molecular size of expressed bacteriocins was estimated by tricine-SDS-PAGE showing an approximative protein size of 4.5 kDa. The assessment of the spectrum of activity of bacteriocins ST651ea, ST7119ea and ST7319ea showed strong activity against most of clinical VRE isolates, majority of other Enterococcus spp. and Listeria spp. Bacteriocins ST651ea, ST7119ea and ST7319ea were partially purified by combination of 60% ammonium sulfate precipitation and hydrophobic chromatography on the SepPakC₁₈ column. Challenge test with semi-purified (60% 2-propanol fraction) bacteriocins resulted in a significant reduction of viable cells for all test organisms. Thus, indicating that all the bacteriocins evaluated can be used as potential biocontrol in food and feed industries as well as an alternative treatment for VRE-related infections in both veterinary and clinical settings.

Assessment of exopolysaccharides, bacteriocins and in vitro and in vivo hypocholesterolemic potential of some Egyptian Lactobacillus spp

Lactobacilli probiotics have been suggested to reduce cholesterol with low side effects to host. Bacteriocins and exopolysaccharides (EPSs) production are two meaningful examples of functional applications of lactobacilli in the food industry. Eight Lactobacillus strains were isolated from some Egyptian fermented food and tested for their probiotic properties. Analysis of the monosaccharide composition by thin layer chromatography showed the presence of glucose, galactose and unknown sugar. The main functional groups of EPSs were elucidated by Fourier-Transform Infrared Spectroscopy. Their fermentation cultures displayed powerful antioxidant activities extending from 97.5 to 99%, 40-75% for their EPSs and free cells, respectively, and exhibited in vitro cholesterol downgrading from 48 to 82% and 72 to 91% after 48 and 120 h, respectively. Their EPSs showed good anticancer activities against carcinoma cells with low IC₅₀ values for HCT-116, PC-3 and HepG-2 cells. To the best of our knowledge, there have been no previous reports on the potential of Lactobacillus EPSs activity against PC-3. The selected strains, L. plantarum KU985433 and L. rhamnosus KU985436 produced two different bacteriocins as detected by gel permeation chromatography with good antimicrobial activities. In vivo study demonstrated that feeding Westar rats with fermented milk exhibited greater cholesterol, LDL and blood triglyceride reduction for both strains. Whereas, HDL was increased by about 43 and 38%, respectively, and the atherogenic indices decreased.

Application of isolated Lactobacillus sakei and Staphylococcus xylosus strains as a probiotic starter culture during the industrial manufacture of Tunisian dry-fermented sausages

For decades, lactic acid bacteria has been isolated and selected to be used as starter cultures in meat fermentation for standardization and management of quality of dry-fermented sausage which constitute a considerable challenge. The aim of this study was to evaluate the effect of Lactobacillus sakei strains, isolated from different origins, on qualities of dry-fermented sausages. These last, manufactured with different combinations of starter cultures (L. sakei + Staphylococcus xylosus), were ripened, using the same raw materials and conditions, for 45 days. Samples were collected during this period, and microbiological, physicochemical, fatty acid profile, and sensorial analyses determined. Lactic acid bacteria were the dominant flora during ripening. A desirable PUFA/SFA ratio, corresponding to 1:1.7 (0.6), was detected after 24 days of maturation in sausages inoculated by L. sakei BMG 95 and S. xylosus. Sensory analysis showed that fermented sausages manufactured with L. sakei and S. xylosus had a more desirable odor, flavor, and texture and consequently were preferred overall. In particular, sensory panellists preferred sausages produced with either L. sakei 23K or L. sakei BMG 95 when compared to fermented sausage produced with a commercial starter or no starter at all.

Obtaining an Ent35-MccV derivative with mutated hinge region that exhibits increased activity against Listeria monocytogenes and Escherichia coli

The present paper describes the generation of derivatives from the hybrid peptide called Ent35-MccV, active against Gram-positive and Gram-negative bacteria. This peptide has a triple glycine hinge region between enterocin CRL35 and microcin V. In order to obtain variants of Ent35-MccV with greater biotechnological potential, a saturation mutagenesis was carried out in the hinge region. As a result, we obtained a bank of E. coli strains expressing different mutated hybrid bacteriocins in the central position of the hinge region. From all these variants, we found that the one bearing a tyrosine in the central region of the hinge (Ent35-GYG-MccV) is 2-fold more active against E. coli and 4-fold more active against Listeria than the original peptide Ent35-MccV. This derivative was purified and characterized. The development and evaluation of alternative hinges for Ent35-MccV represents a step forward in the bioengineering of antimicrobial peptides. This approach fosters the rational design of peptides with enhanced antimicrobial activity.

Physiological and proteomic response of Escherichia coli O157:H7 to a bioprotective lactic acid bacterium in a meat environment

The enterohemorrhagic Escherichia (E.) coli (EHEC) is a pathogen of great concern for public health and the meat industry all over the world. The high economic losses in meat industry and the high costs of the illness highlight the necessity of additional efforts to control this pathogen. Previous studies have demonstrated the inhibitory activity of Enterococcus mundtii CRL35 towards EHEC, showing a specific proteomic response during the co-culture. In the present work, additional studies of the EHEC-Ent. mundtii interaction were carried out: i) differential protein expression of E. coli O157:H7 NCTC12900 growing in co-culture with Ent. mundtii in a meat environment, ii) the reciprocal influence between these two microorganisms in the adhesion to extracellular matrix (ECM) proteins and iii) the possible induction of the phage W933, coding for Shiga toxin (Stx1), by Ent. mundtii CRL35. Proteomic analysis showed a significant repression of a number of E. coli NCTC12900 proteins in co-culture respect to its single culture, these mostly related to the metabolism and transport of amino acids and nucleotides. On the other hand, statistically significant overexpression of EHEC proteins involved in stress, energy production, amino acid metabolism and transcription was observed at 30 h respect to 6 h when EHEC grew in co-culture. Data are available via ProteomeXchange with identifier PXD014588. Besides, EHEC showed a decreased adhesion capacity to ECM proteins in the presence of the bioprotective strain. Finally, Ent. mundtii CRL35 did not induce the lytic cycle of W933 bacteriophage, thus indicating its potential safe use for eliminating this pathogen. Overall, this study expands the knowledge of EHEC- Ent. mundtii CRL35 interaction in a meat environment, which will certainly contribute to find out effective biological strategies to eliminate this pathogen.

Pediocin-Like Antimicrobial Peptides of Bacteria

Bacteriocins are bacterial antimicrobial peptides that, unlike classical peptide antibiotics, are products of ribosomal synthesis and usually have a narrow spectrum of antibacterial activity against species closely related to the producers. Pediocin-like bacteriocins (PLBs) belong to the class IIa of the bacteriocins of Gram-positive bacteria. PLBs possess high activity against pathogenic bacteria from Listeria and Enterococcus genera. Molecular target for PLBs is a membrane protein complex - bacterial mannose-phosphotransferase. PLBs can be synthesized by components of symbiotic microflora and participate in the maintenance of homeostasis in various compartments of the digestive tract and on the surface of epithelial tissues contacting the external environment. PLBs could give a rise to a new group of antibiotics of narrow spectrum of activity.

The Genus Enterococcus: Between Probiotic Potential and Safety Concerns-An Update

A considerable number of strains belonging to different species of Enterococcus are highly competitive due to their resistance to wide range of pH and temperature. Their competitiveness is also owed to their ability to produce bacteriocins recognized for their wide-range effectiveness on pathogenic and spoilage bacteria. Enterococcal bacteriocins have attracted great research interest as natural antimicrobial agents in the food industry, and as a potential drug candidate for replacing antibiotics in order to treat multiple drugs resistance pathogens. However, the prevalence of virulence factors and antibiotic-resistance genes and the ability to cause disease could compromise their application in food, human and animal health. From the current regulatory point of view, the genus Enterococcus is neither recommended for the QPS list nor have GRAS status. Although recent advances in molecular biology and the recommended methods for the safety evaluation of Enterococcus strains allowed the distinction between commensal and clinical clades, development of highly adapted methods and legislations are still required. In the present review, we evaluate some aspects of Enterococcus spp. related to their probiotic properties and safety concerns as well as the current and potential application in food systems and treatment of infections. The regulatory status of commensal Enterococcus candidates for food, feed, probiotic use, and recommended methods to assess and ensure their safety are also discussed.

Screening of the Enterocin-Encoding Genes and Their Genetic Determinism in the Bacteriocinogenic Enterococcus faecium GHB21

Enterococci are well-known for their ability to produce a variety of antimicrobial peptides called enterocins. Most of these enterocins withstand extreme conditions and are very effective against a broad spectrum of undesirable bacteria including some Gram-negative bacteria. The same enterococci strain can produce multiple enterocins simultaneously. The genetic determinants of these bacteriocins can either be located on plasmids or on bacterial chromosome. Digestion of Enterococcus faecium GHB21 plasmids with various restriction endonucleases suggests the presence of two plasmids named pGHB-21.1 and pGHB-21.2 whose respective sizes are ~ 10.0 kb and ~ 3.3 kb. The screening of enterocin-encoding genes among E. faecium GHB21 genome by PCR followed by amplicon sequencing indicated the presence of three different enterocin structural genes similar to entA, entB, and entP genes previously detected in other E. faecium strains. These enterocin genes were, subsequently, localized on the bacterial chromosome based on PCR-targeted screening using total DNA and plasmids of E. faecium GHB21 as separate templates.

Differential Proteomic Analysis of Lactic Acid Bacteria-Escherichia coli O157:H7 Interaction and Its Contribution to Bioprotection Strategies in Meat

Human infection by Enterohemorrhagic Escherichia (E.) coli (EHEC) occurs through the ingestion of contaminated foods such as milk, vegetable products, water-based drinks, and particularly minced meats. Indeed EHEC is a pathogen that threatens public health and meat industry. The potential of different Lactic Acid Bacteria (LAB) strains to control EHEC in a meat-based medium was evaluated by using a simple and rapid method and by analyzing the growth kinetics of co-cultures (LAB-EHEC) in a meat-based medium. The activity of LAB toward EHEC in co-cultures showed variable inhibitory effect. Although, LAB were able to control EHEC, neither the produced acid nor bacteriocins were responsible of the inhibition. The bacteriocinogenic Enteroccus (Ent.) mundtii CRL35 presented one of the highest inhibition activities. A proteomic approach was used to evaluate bacterial interaction and antagonistic mechanisms between Ent. mundtii and EHEC. Physiological observations, such as growth kinetics, acidification ability and EHEC inhibitory potential were supported by the proteomic results, demonstrating significant differences in protein expression in LAB: (i) due to the presence of the pathogen and (ii) according to the growth phase analyzed. Most of the identified proteins belonged to carbohydrate/amino acid metabolism, energy production, transcription/translation, and cell division. These results contribute to the knowledge of competition strategies used by Ent. mundtii during its co-culture with EHEC setting new perspectives for the use of LAB to control this pathogen in meat.

Recent Progress in the Chemical Synthesis of Class II and S-Glycosylated Bacteriocins

A wide variety of antimicrobial peptides produced by lactic acid bacteria (LAB) have been identified and studied in the last decades. Known as bacteriocins, these ribosomally synthesized peptides inhibit the growth of a wide range of bacterial species through numerous mechanisms and show a great variety of spectrum of activity. With their great potential as antimicrobial additives and alternatives to traditional antibiotics in food preservation and handling, animal production and in veterinary and medical medicine, the demand for bacteriocins is rapidly increasing. Bacteriocins are most often produced by fermentation but, in several cases, the low isolated yields and difficulties associated with their purification seriously limit their use on a large scale. Chemical synthesis has been proposed for their production and recent advances in peptide synthesis methodologies have allowed the preparation of several bacteriocins. Moreover, the significant cost reduction for peptide synthesis reagents and building blocks has made chemical synthesis of bacteriocins more attractive and competitive. From a protein engineering point of view, the chemical approach offers many advantages such as the possibility to rapidly perform amino acid substitution, use unnatural or modified residues, and make backbone and side chain modifications to improve potency, modify the activity spectrum or increase the stability of the targeted bacteriocin. This review summarized synthetic approaches that have been developed and used in recent years to allow the preparation of class IIa bacteriocins and S-linked glycopeptides from LAB. Synthetic strategies such as the use of pseudoprolines, backbone protecting groups, microwave irradiations, selective disulfide bridge formation and chemical ligations to prepare class II and S-glycosylsated bacteriocins are discussed.

New insights into enterocin CRL35: mechanism of action and immunity revealed by heterologous expression in Escherichia coli

The role of the class IIa bacteriocin membrane receptor protein remains unclear, and the following two different mechanisms have been proposed: the bacteriocin could interact with the receptor changing it to an open conformation or the receptor might act as an anchor allowing subsequent bacteriocin insertion and membrane disruption. Bacteriocin-producing cells synthesize an immunity protein that forms an inactive bacteriocin-receptor-immunity complex. To better understand the molecular mechanism of enterocin CRL35, the peptide was expressed as the suicidal probe EtpM-enterocin CRL35 in Escherichia coli, a naturally insensitive microorganism since it does not express the receptor. When the bacteriocin is anchored to the periplasmic face of the plasma membrane through the bitopic membrane protein, EtpM_, E. coli cells depolarize and die. Moreover, co-expression of the immunity protein prevents the deleterious effect of EtpM-enterocin CRL35. The binding and anchoring of the bacteriocin to the membrane has demonstrated to be a sufficient condition for its membrane insertion. The final step of membrane disruption by EtpM-enterocin CRL35 is independent from the receptor, which means that the mannose PTS might not be involved in the pore structure. In addition, the immunity protein can protect even in the absence of the receptor.

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

Background

Lactic 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.

Results

Griffon 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.

Conclusions

Enterococci 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 material

The online version of this article (doi:10.1186/s12866-016-0840-2) contains supplementary material, which is available to authorized users.

Maltaricin CPN, a new class IIa bacteriocin produced by Carnobacterium maltaromaticum CPN isolated from mould-ripened cheese

AIMS

The purpose of this study was to isolate, characterize and determine the structure and the antibacterial activities of a bacteriocin produced by Carnobacterium maltaromaticum CPN, a strain isolated from unpasteurized milk Camembert cheese.

METHODS AND RESULTS

This bacteriocin, termed maltaricin CPN, was produced at higher amounts in MRS broth at temperatures between 15°C and 25°C. It was purified to homogeneity from culture supernatant by using a simple method consisting of cation-exchange and reversed-phase chromatographies. Mass spectrometry showed that maltaricin was a 4427·29 Da bacteriocin. Its amino acid sequence was determined by Edman degradation which showed that it had close similarity with bacteriocins of the class IIa. Maltaricin CPN consisted in fact of 44 unmodified amino acids including two cysteine residues at positions 9 and 14 linked by a disulphide bond. The antimicrobial activity of maltaricin CPN covered a range of bacteria, with strong activity against many species of Gram-positive bacteria, especially the food-borne pathogen Listeria monocytogenes, but no activity against Gram-negative ones.

CONCLUSIONS

In the studied conditions, C. maltaromaticum CPN produced a new class IIa bacteriocin with strong anti-Listeria activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study covers the purification and the structural characterization of a new bacteriocin produced by strain C. maltaromaticum CPN isolated from Camembert cheese. Its activity against strains of L. monocytogenes and higher production rates at relatively low temperatures show potential technological applications to improve the safety of refrigerated food.

Anti-MRSA Activities of Enterocins DD28 and DD93 and Evidences on Their Role in the Inhibition of Biofilm Formation

Methicillin-resistant Staphylococcus aureus (MRSA) has become a worrisome superbug. This work aimed at studying the effects of two class IIb bacteriocins, enterocins DD28 and DD93 as anti-MRSA agents. Thus, these bacteriocins were purified, from the cultures supernatants of Enterococcus faecalis 28 and 93, using a simplified purification procedure consisting in a cation exchange chromatography and a reversed-phase high-performance liquid chromatography. The anti-Staphylococcal activity was shown in vitro by the assessment of the minimal inhibitory concentration (MIC), followed by a checkerboard and time-kill kinetics experiments. The data unveiled a clear synergistic effect of enterocins DD28 and DD93 in combination with erythromycin or kanamycin against the clinical MRSA-S1 strain. Besides, these combinations impeded as well the MRSA-S1 clinical strain to setup biofilms on stainless steel and glace devices.

Use of Lactobacillus plantarum Strains as a Bio-Control Strategy against Food-Borne Pathogenic Microorganisms

Lactobacillus plantarum is one of the most versatile species extensively used in the food industry both as microbial starters and probiotic microorganisms. Several L. plantarum strains have been shown to produce different antimicrobial compounds such as organic acids, hydrogen peroxide, diacetyl, and also bacteriocins and antimicrobial peptides, both denoted by a variable spectrum of action. In recent decades, the selection of microbial molecules and/or bacterial strains able to produce antagonistic molecules to be used as antimicrobials and preservatives has been attracting scientific interest, in order to eliminate or reduce chemical additives, because of the growing attention of consumers for healthy and natural food products. The aim of this work was to investigate the antimicrobial activity of several food-isolated L. plantarum strains, analyzed against the pathogenic bacteria Listeria monocytogenes, Salmonella Enteritidis, Escherichia coli O157:H7 and Staphylococcus aureus. Antagonistic activity was assayed by agar spot test and revealed that strain L. plantarum 105 had the strongest ability to contrast the growth of L. monocytogenes, while strains L. plantarum 106 and 107 were the most active microorganisms against E. coli O157:H7. The antimicrobial ability was also screened by well diffusion assay and broth micro-dilution method using cell-free supernatants (CFS) from each Lactobacillus strain. Moreover, the chemical nature of the molecules released in the CFS, and possibly underlying the antagonistic activity, was preliminary characterized by exposure to different constraints such as pH neutralization, heating, catalase, and proteinase treatments. Our data suggest that the ability of L. plantarum cultures to contrast pathogens growth in vitro depends, at least in part, on a pH-lowering effect of supernatants and/or on the presence of organic acids. Cluster analysis was performed in order to group L. plantarum strains according to their antimicrobial effect. This study emphasizes the tempting use of the tested L. plantarum strains and/or their CFS as antimicrobial agents against food-borne pathogens.

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.

Draft Genome Sequence of the Nonstarter Bacteriocin-Producing Strain Enterococcus mundtii CRL35

Enterococcus mundtii CRL35 is a bacteriocinogenic strain isolated from an artisanal cheese of northwestern Argentina. Here we report its draft genome sequence, consisting of 82 contigs. In silico genomic analysis of biotechnological properties was performed to determine the potential of this microorganism to be used in a food model system.

Class IIa bacteriocins: diversity and new developments

Class IIa bacteriocins are heat-stable, unmodified peptides with a conserved amino acids sequence YGNGV on their N-terminal domains, and have received much attention due to their generally recognized as safe (GRAS) status, their high biological activity, and their excellent heat stability. They are promising and attractive agents that could function as biopreservatives in the food industry. This review summarizes the new developments in the area of class IIa bacteriocins and aims to provide uptodate information that can be used in designing future research.

A new hybrid bacteriocin, Ent35-MccV, displays antimicrobial activity against pathogenic Gram-positive and Gram-negative bacteria

Bacteriocins and microcins are ribosomally synthesized antimicrobial peptides that are usually active against phylogenetically related bacteria. Thus, bacteriocins are active against Gram-positive while microcins are active against Gram-negative bacteria. The narrow spectrum of action generally displayed by bacteriocins from lactic acid bacteria represents an important limitation for the application of these peptides as clinical drugs or as food biopreservatives. The present study describes the design and expression of a novel recombinant hybrid peptide combining enterocin CRL35 and microcin V named Ent35–MccV. The chimerical bacteriocin displayed antimicrobial activity against enterohemorrhagic Escherichia coli and Listeria monocytogenes clinical isolates, among other pathogenic bacteria. Therefore, Ent35–MccV may find important applications in food or pharmaceutical industries.

Enterocin CRL35 inhibits Listeria monocytogenes in a murine model

Listeria monocytogenes is a foodborne pathogen causative of opportunistic infections. Listeriosis is associated with severe infections in pregnant women causing abortion or neonatal listeriosis. An alternative to antibiotics are safe novel bacteriocins peptides such as enterocin CRL35 with strong antilisterial activity produced by Enterococcus mundtii CRL35. In the present paper, our goal is to study the effectiveness of this peptide and the producer strain in a murine model of pregnancy-associated listeriosis. A single dose of 5×10(9) colony-forming unit of L. monocytogenes FBUNT (Faculty of Biochemistry-University of Tucumán) resulted in translocation of pathogen to liver and spleen of BALB/c pregnant mice. The maximum level of Listeria was observed on day 3 postinfection. Interestingly, the intragastric administration of enterocin CRL35 significantly reduced the translocation of the pathogen to vital organs. On the other hand, the preadministration of E. mundtii CRL35 slightly inhibited this translocation. Listeria infection caused a significant increase in polymorphonuclear leukocytes at day 3 postinfection compared to the noninfected group. This value was reduced after the administration of enterocin CRL35. No significant changes were observed in either white blood cells or lymphocytes counts. Based on the data presented in the present work enterocin CRL35 would be a promising alternative for the prevention of Listeria infections.

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.

Lactic acid bacteria isolated from young calves--characterization and potential as probiotics

Lactic acid bacteria (LAB) are widely used as probiotics in humans and animals to restore the ecological balance of different mucosa. They help in the physiological functions of newborn calves that are susceptible to a variety of syndromes. The criteria for the selection of strains for the design of probiotic products are not available. Based in the host-specificity of the indigenous microbiota, 96 LAB isolates from faeces and oral cavity of calves were obtained. The surface properties were screened showing a small number of highly hydrophobic or autoagglutinating isolates. Also, a group produced H(2)O(2) and were able to inhibit pathogens, and two strains were bacteriocin-producers. Some grew at very low pH and high bile concentrations. The strains sharing some of the specific properties evaluated were identified genetically, assayed their compatibility and exopolysaccharide production. The results allow going further in the establishment of criteria to select strains to be included in a multi-strain-probiotic-product to be further assayed in animals.

Mutational analysis of residues in the helical region of the class IIa bacteriocin pediocin PA-1

A 15-mer fragment that is derived from the helical region in the C-terminal half of pediocin PA-1 inhibited the activity of pediocin PA-1. Of 13 other pediocin-like (hybrid) bacteriocins, only the hybrid bacteriocin Sak/Ped was markedly inhibited by the 15-mer fragment. Sak/Ped was the only one of these bacteriocins that had a sequence (in the C-terminal helix-containing half) identical to that of the 15-mer fragment, indicating that the fragment inhibits pediocin-like bacteriocins in a sequence-dependent manner. By replacing (one at a time) all 15 residues in the fragment with Ala or Leu, five residues (K1, A2, T4, N8, and A15) were identified as being especially important for the inhibitory action of the fragment. The results suggest that the corresponding residues (K20, A21, T23, N27, and A34, respectively) in pediocin PA-1 might be involved in interactions between pediocin PA-1 and its receptor. To characterize the environment surrounding these five residues when pediocin PA-1 interacts with target cells, these residues were replaced (one at a time) with a hydrophobic large (Leu) residue, a hydrophilic charged (Asp or Arg) residue, and a small (Ala or Gly) residue. The results revealed that residues A21 and A34 are in a spatially constrained environment, since the replacement with a small (Gly) residue was the only substitution that did not markedly reduce the bacteriocin activity. The positive charge in K20 and the polar amide group in N27 appeared to interact with electronegative groups, since the replacement of these two residues with a positive (Arg) residue was well tolerated, while replacement with a negative (Asp) residue was detrimental to the bacteriocin activity. K20 was in a less constrained environment than N27, since the replacement of K20 with a large hydrophobic (Leu) residue was tolerated fairly well and to a greater extent than N27. T23 seemed to be in an environment that was not restricted with respect to size, polarity, and charge, since replacements with large (Leu) and small (Ala) hydrophobic residues and a hydrophilic negative (Asp) residue were tolerated fairly well (2- to 6-fold reduction in activity). Moreover, the replacement of T23 with a large positive (Arg) residue resulted in wild-type or better-than-wild-type activity.

Combined effect of synthetic enterocin CRL35 with cell wall, membrane-acting antibiotics and muranolytic enzymes against Listeria cells

AIMS

To evaluate the inhibition effectiveness of enterocin CRL35 in combination with cell wall, membrane-acting antibiotics and muranolytic enzymes against the foodborne pathogen Listeria.

METHODS AND RESULTS

Synthetic enterocin CRL35 alone and in combination with monensin, bacitracin, gramicidin, mutanolysin and lysozyme were used in this study. Minimal inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) index assays were performed using Listeria innocua 7 and Listeria monocytogenes FBUNT as sensitive strains. Antibiotics showed positive interactions with the bacteriocin in both strains tested. On the other hand, when mutanolysin and enterocin CRL35 were added to resting cells in a buffer system, the lytic effect of mutanolysin was enhanced. However, the addition of mutanolysin showed no effect on the growth of L. innocua 7 cells in a culture medium. Moreover, mutanolysin allowed the overgrowth of L. innocua 7 cells to an OD similar to control cells in the presence of inhibitory concentration of enterocin CRL35. In contrast, the combination of lysozyme and enterocin CRL35 resulted in a 50% inhibition of the L. innocua 7 growth.

CONCLUSIONS

Based on our results, we conclude that the combination of synthetic enterocin CRL35 with some antibiotics is effective against L. innocua 7 and L. monocytogenes FBUNT cells, and more importantly the amount of these agents to be used was considerably reduced. The effectiveness of the combination of synthetic enterocin CRL35 with muramidases seems to depend on complex environments, and more detailed studies need to be performed to elucidate this issue.

SIGNIFICANCE AND IMPACT OF THE STUDY

Enterocin CRL35 represents a promising agent that not only can ensure the quality and safety of food but it can also be combined with several antimicrobial agents important in the medical field.

Molecular and genetic characterization of a novel bacteriocin locus in Enterococcus avium isolates from infants

Enterococci are among the most common human intestinal lactic acid bacteria, and they are known to produce bacteriocins. In this study, fecal enterococci were isolated from infants and screened for bacteriocin production. Bacteriocin-producing Enterococcus avium isolates were obtained, and a new pediocin-like bacteriocin was purified and characterized. This bacteriocin, termed avicin A, was found to be produced by isolates from two healthy infants. It was purified to homogeneity from culture supernatant by ion-exchange and reversed-phase chromatography, and part of its amino acid sequence was obtained. The sequence of a 7-kb DNA fragment of a bacteriocin locus was determined by PCR and DNA sequencing. The bacteriocin locus was organized into four operon-like structures consisting of (i) the structural genes encoding avicin A and its immunity protein, (ii) a divergicin-like bacteriocin (avicin B) gene, (iii) an ABC bacteriocin transporter gene and two regulatory genes (histamine protein kinase- and response regulator-encoding genes), and (iv) induction peptide pheromone- and transport accessory protein-encoding genes. It was shown that the production of avicin A was regulated by the peptide pheromone-inducible regulatory system. Avicin A shows very high levels of similarity to mundticin KS and enterocin CRL35. This bacteriocin showed strong antimicrobial activity against many species of Gram-positive bacteria, including the food-borne pathogen Listeria monocytogenes. The avicin A locus is the first bacteriocin locus identified in E. avium to be characterized at the molecular level.

Characterization of mundticin L, a class IIa anti-Listeria bacteriocin from Enterococcus mundtii CUGF08

Enterococcus mundtii CUGF08, a lactic acid bacterium isolated from alfalfa sprouts, was found to produce mundticin L, a new class IIa bacteriocin that has a high level of inhibitory activity against the genus Listeria. The plasmid-associated operons containing genes for the mundticin L precursor, the ATP binding cassette (ABC) transporter, and immunity were cloned and sequenced. The fifth residue of the conservative consensus sequence YGNGX in the mature bacteriocin is leucine instead of valine in the sequences of the homologous molecules mundticin KS (ATO6) and enterocin CRL35. The primary structures of the ABC transporter and the immunity protein are homologous but unique.

Crystal structure and mutagenic analysis of a bacteriocin immunity protein, Mun-im

Bacteriocin-producing lactic acid bacteria (LAB) possess a self-protection factor, which is generally called an immunity protein. In this study, we determine the crystal structure of an immunity protein, designated Mun-im, which was classified into subgroup B immunity proteins for class IIa bacteriocins. The Mun-im protein takes a left-turning antiparallel four-helix bundle structure with the flexible N- and C-terminal parts. Although the amino acid sequences of the subgroup B immunity proteins are distinguished from those of the subgroup A, the core structure of Mun-im is well-superimposed with that of the subgroup A immunity protein, EntA-im, and the C-terminus of both proteins is flexible. However, the C-terminus of Mun-im is obviously shorter than that of the subgroup A. We found through mutagenic study of Mun-im that the C-terminus and the K86 residue on the helix 4 in the immunity protein molecule are important for expression of the immunity activity on the subgroup B immunity proteins.

Screening of surface properties and antagonistic substances production by lactic acid bacteria isolated from the mammary gland of healthy and mastitic cows

Bovine mastitis (BM) is a costly disease in dairy cattle production. The prevention and treatment of mastitis is performed by applying antimicrobial products that negatively affect milk quality. In the last years, the use of probiotic microorganisms to prevent infections in humans and animals has being aggressively studied. Samples from teat canal and milk (foremilk and stripping) were taken from healthy and mastitic mammary quarters. A screening of the surface properties and antagonistic substances production of lactic acid bacteria (LAB) isolated from the mammary gland was performed to select potential probiotic strains to prevent mastitis. Somatic cell count, physico-chemical and microbiological studies were carried out. Pre-selected microorganisms were genetically identified. Compared with stripping milk, foremilk showed lower levels of fat and higher levels of pH, density, microorganism numbers, lower percentage of strains with mean and high hydrophobicity and mean autoaggregation and higher number of strains able to produce hydrogen peroxide and bacteriocins. The other parameters analyzed were not statistically significant. One hundred and two LAB strains were isolated. Most of them had low degrees of hydrophobicity and autoaggregation. No correlation between these properties was found. Antagonistic metabolites were mainly produced by strains isolated from healthy quarters. Most of the pre-selected strains were identified as Streptococcus bovis and Weissella paramesenteroides. Three bacteriocin-producers were found and their products partially characterized. The results of this work are the basis for the further design of a specie-specific probiotic product able to prevent BM.

Mutational analysis of the class IIa bacteriocin curvacin A and its orientation in target cell membranes

To analyze the orientation in target cell membranes of the pediocin-like bacteriocin (antimicrobial peptide) curvacin A, 55 variants were generated by site-directed mutagenesis and their potencies against four different target cells determined. The result suggest that the somewhat hydrophilic short central helix (residues 19 to 24), along with the N-terminal beta-sheet-like structure (residues 1 to 16), inserts in the interface region of the target cell membrane, with Ala22 close to the hydrophobic core of the membrane. The following hinge region, with Gly28 as an important residue, may then form a turn wherein Gly28 becomes positioned near the border between the interface and the hydrophobic regions, thus permitting the longer and more-hydrophobic C-terminal helix (residues 29 to 41) to insert into the hydrophobic core of the membrane. This helix contains three glycine residues (G33, G37, and G40) that form a putative helix-helix-interacting GxxxGxxG motif. The replacement of any of these glycines with a larger residue was very detrimental, suggesting their possible involvement in helix-helix interactions with a membrane-embedded receptor protein.