Antimicrobial and safety aspects, and biotechnological potential of bacteriocinogenic enterococci isolated from mallard ducks (Anas platyrhynchos)

Bacteriocinogenic anti-listerial properties and safety assessment of Enterococcus faecium and Lactococcus garvieae strains isolated from Brazilian artisanal cheesemaking environment

AIMS

This study aimed to prospect and isolate lactic acid bacteria (LAB) from an artisanal cheese production environment, to assess their safety, and to explore their bacteriocinogenic potential against Listeria monocytogenes.

METHODS AND RESULTS

Samples were collected from surfaces of an artisanal-cheese production facility and after rep-PCR and 16S rRNA sequencing analysis, selected strains were identified as to be belonging to Lactococcus garvieae (1 strain) and Enterococcus faecium (14 isolates, grouped into three clusters) associated with different environments (worktables, cheese mold, ripening wooden shelves). All of them presented bacteriocinogenic potential against L. monocytogenes ATCC 7644 and were confirmed as safe (γ-hemolytic, not presenting antibiotic resistance, no mucus degradation properties, and no proteolytic or gelatinase enzyme activity). Additionally, cell growth, acidification and bacteriocins production kinetics, bacteriocin stability in relation to different temperatures, pH, and chemicals were evaluated. According to performed PCR analysis all studied strains generated positive evidence for the presence of entA and entP genes (for production of enterocins A and enterocins P, respectively). However, pediocin PA-1 associated gene was recorded only in DNA obtained from E. faecium ST02JL and Lc. garvieae ST04JL.

CONCLUSIONS

It is worth considering the application of these safe LAB or their bacteriocins in situ as an alternative means of controlling L. monocytogenes in cheese production environments, either alone or in combination with other antimicrobials.

Revisiting the Multifaceted Roles of Bacteriocins : The Multifaceted Roles of Bacteriocins

Bacteriocins are gene-encoded antimicrobial peptides produced by bacteria. These peptides are heterogeneous in terms of structure, antimicrobial activities, biosynthetic clusters, and regulatory mechanisms. Bacteriocins are widespread in nature and may contribute to microbial diversity due to their capacity to target specific bacteria. Primarily studied as food preservatives and therapeutic agents, their function in natural settings is however less known. This review emphasizes the ecological significance of bacteriocins as multifunctional peptides by exploring bacteriocin distribution, mobility, and their impact on bacterial population dynamics and biofilms.

Purification and characterization of bacteriocins-like inhibitory substances from food isolated Enterococcus faecalis OS13 with activity against nosocomial enterococci

Nosocomial infections caused by enterococci are an ongoing global threat. Thus, finding therapeutic agents for the treatment of such infections are crucial. Some Enterococcus faecalis strains are able to produce antimicrobial peptides called bacteriocins. We analyzed 65 E. faecalis isolates from 43 food samples and 22 clinical samples in Egypt for 17 common bacteriocin-encoding genes of Enterococcus spp. These genes were absent in 11 isolates that showed antimicrobial activity putatively due to bacteriocins (three from food, including isolate OS13, and eight from clinical isolates). The food-isolated E. faecalis OS13 produced bacteriocin-like inhibitory substances (BLIS) named enterocin OS13, which comprised two peptides (enterocin OS13α OS13β) that inhibited the growth of antibiotic-resistant nosocomial E. faecalis and E. faecium isolates. The molecular weights of enterocin OS13α and OS13β were determined as 8079 Da and 7859 Da, respectively, and both were heat-labile. Enterocin OS13α was sensitive to proteinase K, while enterocin OS13β was resistant. Characterization of E. faecalis OS13 isolate revealed that it belonged to sequence type 116. It was non-hemolytic, bile salt hydrolase-negative, gelatinase-positive, and sensitive to ampicillin, penicillin, vancomycin, erythromycin, kanamycin, and gentamicin. In conclusion, BLIS as enterocin OS13α and OS13β represent antimicrobial agents with activities against antibiotic-resistant enterococcal isolates.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

Probiotic Properties of Enterococcus Isolated From Artisanal Dairy Products

The present study focused on probiotic characterization and safety evaluation of Enterococcus isolates from different artisanal dairy products. All the isolates exhibited inhibitory activity against several food spoilage bacteria and food-borne pathogens, including Shigella flexneri, Staphylococcus aureus, Listeria monocytogenes, Yersinia enterocolitica, Klebsiella pneumoniae, Escherichia coli, and Bacillus subtilis. The PCR results indicated the presence of at least one enterocin structural gene in all the tested strains. The Enterococcus isolates were further evaluated regarding their safety properties and functional features. The isolates were susceptible to vancomycin, gentamycin, and chloramphenicol. The results of PCR amplification revealed that all the tested isolates harbored none of the tested virulence genes except E. faecalis (ES9), which showed the presence of esp gene. The Enterococcus isolates showed cholesterol lowering properties. The selected isolates showed a high tolerance to low pH, and toward bile salts. They also demonstrated hydrophobicity activity, auto-aggregation, and adhesion ability to the human intestinal Caco-2 cell line. These properties may contribute the bacteria colonizing the gut. This study revealed that the Enterococcus isolates, especially E. durans ES11, ES20 and ES32, might be excellent candidates for production of functional foods to promote health benefits.

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.

Novel Group of Leaderless Multipeptide Bacteriocins from Gram-Positive Bacteria

From raw milk we found 10 Lactococcus garvieae isolates that produce a new broad-spectrum bacteriocin. Though the isolates were obtained from different farms, they turned out to possess identical inhibitory spectra, fermentation profiles of sugars, and repetitive sequence-based PCR (rep-PCR) DNA patterns, indicating that they produce the same bacteriocin. One of the isolates (L. garvieae KS1546) was chosen for further assessment. Purification and peptide sequencing combined with genome sequencing revealed that the antimicrobial activity was due to a bacteriocin unit composed of three similar peptides of 32 to 34 amino acids. The three peptides are produced without leader sequences, and their genes are located next to each other in an operon-like structure, adjacent to the genes normally involved in bacteriocin transport (ABC transporter) and self-immunity. The bacteriocin, termed garvicin KS (GarKS), showed sequence homology to four multipeptide bacteriocins in databases: the known staphylococcal aureocin A70, consisting of four peptides, and three unannotated putative multipeptide bacteriocins produced by Bacillus cereus All these multipeptide bacteriocin loci show conserved genetic organization, including being located adjacent to conserved genetic determinants (Cro/cI and integrase) which are normally associated with mobile genetic elements or genome rearrangements. The antimicrobial activity of all multipeptide bacteriocins was confirmed with synthetic peptides, and all were shown to have broad antimicrobial spectra, with GarKS being the most active of them. The inhibitory spectrum of GarKS includes important pathogens belonging to the genera Staphylococcus, Bacillus, Listeria, and Enterococcus

IMPORTANCE

Bacterial resistance to antibiotics is a very serious global problem. There are no new antibiotics with novel antimicrobial mechanisms in clinical trials. Bacteriocins use antimicrobial mechanisms different from those of antibiotics and can kill antibiotic-resistant bacteria, but the number of bacteriocins with very broad antimicrobial spectra is very small. In this study, we have found and purified a novel three-peptide bacteriocin, garvicin KS. By homology search, we were able to find one known and three novel sequence-related bacteriocins consisting of 3 or 4 peptides. None of the peptides has modified amino acids in its sequence. Thus, the activity of all bacteriocins was confirmed with chemically synthesized peptides. All of them, especially garvicin KS, have very broad antibacterial spectra, thus representing a great potential in antimicrobial applications in the food industry and medicine.

Draft Genome Sequence of the Bacteriocinogenic Strain Enterococcus faecalis DBH18, Isolated from Mallard Ducks (Anas platyrhynchos)

Here, we report the draft genome sequence of Enterococcus faecalis DBH18, a bacteriocinogenic lactic acid bacterium (LAB) isolated from mallard ducks (Anas platyrhynchos). The assembly contains 2,836,724 bp, with a G+C content of 37.6%. The genome is predicted to contain 2,654 coding DNA sequences (CDSs) and 50 RNAs.

Identification of Microorganisms in Duck Meat Products Available in Korea and the Effect of High Hydrostatic Pressure

The objective of this study was to investigate the microbial count of duck meat and duck meat products commercially available in Korea. High hydrostatic pressure (HHP) treatment was applied at 0.1, 300, 400, and 500 MPa for 5 min to enhance the microbiological safety of duck meats. The levels of total aerobic bacteria were in the ranges of 3.53-6.19 and 3.62-6.85 Log CFU/g in raw and smoked duck products, respectively. By DNA sequence analysis, we identified microorganisms responsible for spoilage, with the most common species in the raw and smoked duck products being Aeromonas spp. or Pseudomonas spp. and Leuconostoc mesenteroides, respectively. HHP treatment significantly reduced the levels of total aerobic bacteria in raw and smoked duck products. This study demonstrates that HHP treatment may be used to effectively improve the safety of raw and smoked duck meat products.

Draft Genome Sequence of the Bacteriocin-Producing Strain Enterococcus faecium M3K31, Isolated from Griffon Vultures (Gyps fulvus subsp. fulvus)

Enterococcus faeciumM3K31 is a bacteriocinogenic lactic acid bacterium (LAB) isolated from griffon vulture (Gyps fulvussubsp.fulvus) feces. The draft genome sequence of this strain provides genetic data that support its biotechnological potential.

Antimicrobial activity and the presence of virulence factors and bacteriocin structural genes in Enterococcus faecium CM33 isolated from ewe colostrum

Screening of lactic acid bacteria (LAB) isolated from ewe colostrum led to the identification and isolation of Enterococcus faecium CM33 with interesting features like high survival rates under acidic or bile salts condition, high tolerance for the simulated gastrointestinal condition, and high adhesive potential to Caco-2 cells. According the inhibition of pathogen adhesion test results, this strain can reduce more than 50% adhesion capacity of Escherichia coli, Shigella flexneri, Klebsiella pneumoniae, Listeria monocytogenes, and Staphylococcus aureus to Caco-2 cells. Based on the antibiotic sensitivity test findings, E. faecium CM33 was susceptible to gentamycin, vancomycin, erythromycin, ampicillin, penicillin, tetracycline, and rifampicin, but resistant to chloramphenicol, clindamycin, and kanamycin. Upon assessment of the virulence determinants for E. faecium CM33, this strain was negative for all tested virulence genes. Furthermore, the genome of this strain was evaluated for the incidence of the known enterocin genes by specific PCR amplification and discovered the genes encoding enterocins A, 31, X, and Q. Based on this study findings, the strain E. faecium CM33 can be considered as a valuable nutraceutical and can be introduced as a new potential probiotic.

Antimicrobial activity and safety evaluation of Enterococcus faecium KQ 2.6 isolated from peacock feces

Background

The objective of this paper was to study antimicrobial activity and safety of Enterococcus faecium KQ 2.6 (E. faecium KQ 2.6) isolated from peacock feces.

Methods

Agar well diffusion method was adopted in antimicrobial activity assay. Disk diffusion test was used to determine the antibiotic resistance. The identification and virulence potential of E. faecium KQ 2.6 were investigated using PCR amplification.

Results

The results indicated that cell free supernatant (CFS) of the strain had the good antimicrobial activity against selected gram-positive and gram-negative bacteria. The biochemical characteristics of antimicrobial substances were investigated. The results indicated that the antimicrobial substances were still active after treatment with catalase and proteinase, respectively. Moreover, the stability of antimicrobial substances did not change after heat treatment at 40, 50, 60, 70 and 80°C for 30 min, respectively. The activity of antimicrobial substances remained stable at 4 and −20°C after long time storage. The antimicrobial activity of CFS was compared with that of the buffer with similar strength and pH. The inhibitory zone of the buffer was apparently smaller than that of CFS, which meant that the acid in CFS was not the only factor that was contributed to antibacterial activity of CFS. The antibiotic resistance and virulence potential were evaluated using disk diffusion test and PCR amplification. The results showed that E. faecium KQ 2.6 did not harbor any tested virulence genes such as gelE, esp, asa1, cylA, efaA and hyl. It was susceptible to most of tested antibiotics except for vancomycin and polymyxin B.

Conclusion

E. faecium KQ 2.6 may be used as bio-preservative cultures for the production of fermented foods.

Genetic and biochemical evidence that recombinant Enterococcus spp. strains expressing gelatinase (GelE) produce bovine milk-derived hydrolysates with high angiotensin converting enzyme-inhibitory activity (ACE-IA)

In this work, genes encoding gelatinase (gelE) and serine proteinase (sprE), two extracellular proteases produced by Enterococcus faecalis DBH18, were cloned in the protein expression vector pMG36c, containing the constitutive P32 promoter, generating the recombinant plasmids pCG, pCSP, and pCGSP encoding gelE, sprE, and gelE-sprE, respectively. Transformation of noncaseinolytic E. faecalis P36, E. faecalis JH2-2, E. faecium AR24, and E. hirae AR14 strains with these plasmids permitted detection of caseinolytic activity only in the strains transformed with pCG or pCGSP. Complementation of a deletion (knockout) mutant of E. faecalis V583 for production of gelatinase (GelE) with pCG unequivocally supported that gelE is responsible for the caseinolytic activity of the transformed strain grown in bovine skim milk (BSM). RP-HPLC-MS/MS analysis of hydrolysates of transformed Enterococcus spp. strains grown in BSM permitted the identification of 38 major peptide fragments including peptides with previously reported angiotensin converting enzyme-inhibitory activity (ACE-IA), antihypertensive activity, and antioxidant activity.

Functional genetic analysis of the GarML gene cluster in Lactococcus garvieae DCC43 gives new insights into circular bacteriocin biosynthesis

Garvicin ML (GarML) is a circular bacteriocin produced by Lactococcus garvieae DCC43. The recently published draft genome of this strain allowed determination of the genetic background for bacteriocin production. Bioinformatic analysis identified a gene cluster consisting of nine open reading frames likely involved in the production of and immunity to GarML. The garA gene encodes the bacteriocin precursor, garX a large transmembrane protein, garBCDE a putative immunity protein (garB) followed by an ATPase and two transmembrane proteins, and garFGH a putative ABC transporter complex. Functional genetic analysis revealed that deletion of garFGH had no effect on sensitivity to or production of GarML. In contrast, deletion of garBCDE or inactivation of garX resulted in high-level sensitivity to GarML and completely abolished production of active bacteriocin. Mass spectrometry of culture supernatants revealed that wild-type cultures contained the mature circular form as well as the linear forms of the bacteriocin, both with and without the three-amino-acid leader sequence, while bacteriocin-negative mutants contained only the linear forms. These results indicate that cleavage of the leader peptide precedes circularization and is likely performed by a functional entity separate from the GarML gene cluster. To our knowledge, this is the first conclusive evidence for these processes being separated in time. Loss of immunity and antimicrobial activity in addition to our inability to detect the circular bacteriocin in the ΔgarBCDE and garX::pCG47 mutants demonstrate that both these units are indispensable for GarML biosynthesis as well as immunity. Furthermore, the results indicate that these genes are implicated in the circularization of the bacteriocin and that their functions are probably interlinked.

Diversity of bacteriocinogenic lactic acid bacteria isolated from Mediterranean fish viscera

Nine lactic acid bacteria strains showing bacteriocin-like activity were isolated from various fresh fish viscera. The following species were identified based on 16S rDNA sequences: Enterococcus durans (7 isolates), Lactococcus lactis (1) and Enterococcus faecium (1). These strains were active against Listeria innocua and other LAB. Random amplified polymorphic DNA analyses showed four major patterns for the E. durans species. PCR analyses revealed a nisin gene in the genome of the Lc. lactis strain. Genes coding enterocins A, B and P were found in the genome of the E. faecium isolate. Enterocins A and B genes were also present in the genome of E. durans GM19. Hence, this is the first report describing E. durans strains producing enterocins A and B. Electrospray ionization mass spectrometry revealed that the purified bacteriocin produced by the E. durans GMT18 strain had an exact molecular mass of 6,316.89 Da. This bacteriocin was designated as durancin GMT18. Edman sequencing failed to proceed; suggesting that durancin GTM18 may contain terminal lanthionine residues. Overall, the results obtained revealed the presence of a variety of enterococci in Mediterranean fish viscera, as evidenced by their genetic profiles and abilities to produce different bacteriocins. These strains could be useful for food biopreservation or as probiotics.

Anti-infective properties of bacteriocins: an update

Bacteriocin production is a widespread phenomenon among bacteria. Bacteriocins hold great promise for the treatment of diseases caused by pathogenic bacteria and could be used in the future as alternatives to existing antibiotics. The anti-infective potential of bacteriocins for inhibiting pathogens has been shown in various food matrices including cheese, meat, and vegetables. However, their inhibition of pathogens in vivo remains unclear and needs more investigation, due mainly to difficulties associated with demonstrating their health benefits. Many bacteriocins produced by established or potential probiotic organisms have been evaluated as potential therapeutic agents and interesting findings have been documented in vitro as well as in a few in vivo studies. Some recent in vivo studies point to the efficacy of bacteriocin-based treatments of human and animal infections. While further investigation remains necessary before the possibilities for bacteriocins in clinical practice can be described more fully, this review provides an overview of their potential applications to human and veterinary health.

Genome sequence of the bacteriocin-producing strain Lactococcus garvieae DCC43

This work describes the draft genome sequence of Lactococcus garvieae DCC43. The 2.2-Mb draft genome contains 2,227 predicted protein-coding genes, among which is a region encoding the bacteriocin garvicin ML. No antibiotic resistance genes or capsule-related virulence genes were identified. Two plasmid replication regions indicate that this strain likely contains plasmids. Comparative genomics suggests that this strain displays a high degree of sequence variation from the previously sequenced L. garvieae strains.

The maltose ABC transporter in Lactococcus lactis facilitates high-level sensitivity to the circular bacteriocin garvicin ML

We generated and characterized a series of spontaneous mutants of Lactococcus lactis IL1403 with average 6- to 11-fold-lowered sensitivities to the circular bacteriocin garvicin ML (GarML). Carbohydrate fermentation assays highlighted changes in carbohydrate metabolism, specifically loss of the ability to metabolize starch and maltose, in these mutants. PCR and sequencing showed that a 13.5-kb chromosomal deletion encompassing 12 open reading frames, mainly involved in starch and maltose utilization, had spontaneously occurred in the GarML-resistant mutants. Growth experiments revealed a correlation between sensitivity to GarML and carbon catabolite repression (CCR); i.e., sensitivity to GarML increased significantly when wild-type cells were grown on maltose and galactose as sole carbohydrates, an effect which was alleviated by the presence of glucose. Among the genes deleted in the mutants were malEFG, which encode a CCR-regulated membrane-bound maltose ABC transporter. The complementation of mutants with these three genes recovered normal sensitivity to the bacteriocin, suggesting an essential role of the maltose ABC transporter in the antimicrobial activity of GarML. This notion was supported by the fact that the level of sensitivity to GarML was dose dependent, increasing with higher expression levels of malEFG over a 50-fold range. To our knowledge, this is the first time a specific protein complex has been demonstrated to be involved in sensitivity to a circular bacteriocin.

Garvieacin Q, a novel class II bacteriocin from Lactococcus garvieae BCC 43578

Lactococcus garvieae BCC 43578 produces a novel class II bacteriocin, garvieacin Q (GarQ), 70 amino acids in length and containing a 20-amino-acid N-terminal leader peptide. It is cleaved at the Gly-Gly site to generate the mature GarQ (5,339 Da), which is especially inhibitory against Listeria monocytogenes ATCC 19115 and other L. garvieae strains.

Protein expression vector and secretion signal peptide optimization to drive the production, secretion, and functional expression of the bacteriocin enterocin A in lactic acid bacteria

Replacement of the leader sequence (LS) of the bacteriocin enterocin A (LS(entA)) by the signal peptides (SP) of the protein Usp45 (SP(usp45)), and the bacteriocins enterocin P (SP(entP)), and hiracin JM79 (SP(hirJM79)) permits the production, secretion, and functional expression of EntA by different lactic acid bacteria (LAB). Chimeric genes encoding the SP(usp45), the SP(entP), and the SP(hirJM79) fused to mature EntA plus the EntA immunity genes (entA+entiA) were cloned into the expression vectors pNZ8048 and pMSP3545, under control of the inducible P(nisA) promoter, and in pMG36c, under control of the constitutive P(32) promoter. The amount, antimicrobial activity, and specific antimicrobial activity of the EntA produced by the recombinant Lactococcus lactis, Enterococcus faecium, E. faecalis, Lactobacillus sakei and Pediococcus acidilactici hosts varied depending on the signal peptide, the expression vector, and the host strain. However, the antimicrobial activity and the specific antimicrobial activity of the EntA produced by most of the LAB transformants was lower than expected from their production. The supernatants of the recombinant L. lactis NZ9000 (pNZUAI) and L. lactis NZ9000 (pNZHAI), overproducers of EntA, showed a 1.2- to 5.1-fold higher antimicrobial activity than that of the natural producer E. faecium T136 against different Listeria spp.

Identification of bacteriocin genes in enterococci isolated from game animals and saltwater fish

Bacteriocins produced by enterococci, referred to as enterocins, possess great interest for their potential use as biopreservatives in food and feed, as well as alternative antimicrobials in humans and animals. In this context, the aim of the present study was to determine the antimicrobial activity and the presence of bacteriocin structural genes in fecal enterococcal isolates from animal origins. Evaluation of the direct antimicrobial activity of 253 isolates from wild boars (Sus scrofa, n = 69), mullets (Liza ramada, n = 117), and partridges (Perdix perdix, n = 67) against eight indicator bacterial strains (including Listeria monocytogenes, Pediococcus pentosaceus, and Enterococcus spp.) showed that 177 (70%) exerted antimicrobial activity against at least one indicator microorganism. From these isolates, 123 were further selected on the basis of their inhibition group, and 81 were found to be producers of bacteriocins active against Listeria monocytogenes. Analysis of the presence of enterocin structural genes in a subset of 36 isolates showed that 70% harbored one or more of the evaluated genes, those of enterocin P and hiracin JM79 being the most prevalent. These results show that wild animals constitute an appropriate source for the isolation of bacteriocinogenic enterococci.

Characterization of garvicin ML, a novel circular bacteriocin produced by Lactococcus garvieae DCC43, isolated from mallard ducks (Anas platyrhynchos)

Lactococcus garvieae DCC43 produces a bacteriocin, garvicin ML (GarML), with a molecular mass of 6,004.2 Da. Data from de novo amino acid sequencing by tandem mass spectrometry and nucleotide sequencing by reverse genetics suggested that the bacteriocin is synthesized as a 63-amino-acid precursor with a 3-amino-acid leader peptide that is removed by cleavage. Subsequently, a covalent linkage between the N and C termini forms the mature version of this novel 60-amino-acid circular bacteriocin.

Use of the usp45 lactococcal secretion signal sequence to drive the secretion and functional expression of enterococcal bacteriocins in Lactococcus lactis

Replacement of the signal peptide (SP) of the bacteriocins enterocin P (EntP) and hiracin JM79 (HirJM79), produced by Enterococcus faecium P13 and Enterococcus hirae DCH5, respectively, by the signal peptide of Usp45 (SP(usp45)), the major Sec-dependent protein secreted by Lactococcus lactis, permits the production, secretion, and functional expression of EntP and HirJM79 by L. lactis. Chimeric genes encoding the SP(usp45) fused to either mature EntP (entP), with or without the immunity gene (entiP) or to mature HirJM79 (hirJM79), with or without the immunity gene (hiriJM79), were cloned into the expression vector pMG36c, carrying the P(32) constitutive promoter, and into pNZ8048 under control of the inducible PnisA promoter. The production of EntP and HirJM79 by most of the L. lactis recombinant strains was 1.5- to 3.7-fold higher and up to 3.6-fold higher than by the E. faecium P13 and E. hirae DCH5 control strains, respectively. However, the specific antimicrobial activity of the recombinant EntP was 1.1- to 6.2-fold higher than that produced by E. faecium P13, while that of the HirJM79 was a 40% to an 89% of that produced by E. hirae DCH5. Chimeras of SP(usp45) fused to mature EntP or HirJM79 drive the production and secretion of these bacteriocins in L. lactis in the absence of specific immunity and secretion proteins. The supernatants of the recombinant L. lactis NZ9000 strains, producers of EntP, showed a much higher antimicrobial activity against Listeria spp. than that of the recombinant L. lactis NZ9000 derivatives, producers of HirJM79.

Contribution of hydrogen peroxide to the inhibition of Staphylococcus aureus by Lactococcus garvieae in interaction with raw milk microbial community

The response of Staphylococcus aureus growth inhibition by Lactococcus garvieae to catalase and milk lactoperoxidase, and its efficiency in raw milk cheese were evaluated. S. aureus and L. garvieae were co-cultivated in broth buffered at pH 6.8, and in raw, pasteurized and microfiltered milk, in presence and absence of catalase. Although H2O2 production by L. garvieae was detected only in agitated broth, the inhibition of S. aureus by L. garvieae was reduced by catalase both in static and shaking cultures by 2.7 log, pasteurized milk (approximately 0.7 log), microfiltered milk (approximately 0.6 log) and raw milk (approximately 0.2 log). The growth of S. aureus alone in microfiltered milk was delayed compared with that in pasteurized milk and inhibition of S. aureus by L. garvieae was stronger in microfiltered milk. The inhibition of coagulase-positive staphylococci (CPS) by L. garvieae in raw milk cheese was similar to that in raw milk (approximately 0.8 log), but weaker than that in pasteurized and microfiltered milks. L. garvieae also had an early antagonistic effect on the growth of several other microbial groups, which lastingly affected populations levels and balance during cheese ripening.

Functional and safety aspects of enterococci in dairy foods

The genus Enterococcus like other LAB has also been featured in dairy industry for decades due to its specific biochemical traits such as lipolysis, proteolysis, and citrate breakdown, hence contributing typical taste and flavor to the dairy foods. Furthermore, the production of bacteriocins by enterococci (enterocins) is well documented. These technological applications have led to propose enterococci as adjunct starters or protective cultures in fermented foods. Moreover, enterococci are nowadays promoted as probiotics, which are claimed for the maintenance of normal intestinal microflora, stimulation of the immune system and improvement of nutritional value of foods. At the same time, enterococci present an emerging pool of opportunistic pathogens for humans as they cause disease, possess agents for antibiotic resistance, and are frequently armed with potential virulence factors. Because of this "dualistic" nature, the use of enterococci remains a debatable issue. However, based on a long history of safe association of particular enterococci with some traditional food fermentations, the use of such strains appears to bear no particular risk for human health. Abundance of knowledge as well as progress in molecular techniques has, however, enabled exact characterization and safety assessment of strains. Therefore, a balanced evaluation of both, beneficial and undesirable nature of enterococci is required. A clear understanding of their status may, therefore, allow their safe use as a starter, or a probiotic strain. The present review describes the broader insight of the benefits and risks of enterococci in dairy foods and their safety assessment.

Antimicrobial activity of Enterococcus faecium L50, a strain producing enterocins L50 (L50A and L50B), P and Q, against beer-spoilage lactic acid bacteria in broth, wort (hopped and unhopped), and alcoholic and non-alcoholic lager beers

Enterococcus faecium L50 produces enterocin L50 (L50A and L50B) (EntL50, EntL50A and EntL50B), enterocin P (EntP) and enterocin Q (EntQ) and displays a broad antimicrobial spectrum against the most relevant beer-spoilage lactic acid bacteria (LAB) (i.e., Lactobacillus brevis and Pediococcus damnosus), which is mainly due to the production of EntL50 (EntL50A and EntL50B). Bacteriocin assays using in vitro-synthesized EntL50 (EntL50A and EntL50B) showed that both individual peptides possess antimicrobial activity on their own, EntL50A being the most active, but when the two peptides were combined a synergistic effect was observed. The only virulence genes detected in E. faecium L50 were efaAfm (cell wall adhesin) and ccf (sex pheromone), and this strain was susceptible to most clinically relevant antibiotics. E. faecium L50 survived but did not grow nor showed antimicrobial activity in hopped and unhopped wort, and alcoholic (1 and 5% ethanol, v/v) and non-alcoholic (0% ethanol, v/v) commercial lager beers. However, when unhopped wort was supplemented with 50% (v/v) MRS broth, E. faecium L50 grew and exerted antimicrobial activity similarly as in MRS broth. The enterocins produced by this strain were bactericidal (5 log decrease) against P. damnosus and Lb. brevis in a dose- and substrate-dependent manner when challenged in MRS broth, wort (hopped and unhopped), and alcoholic (1 and 5% ethanol, v/v) and non-alcoholic (0% ethanol, v/v) lager beers at 32 degrees C, and no bacterial resistances were detected even after incubation for 6-15 days. The enterocins in wort and lager beer (5% ethanol, v/v) withstood the heat treatments commonly employed in the brewing industry during mashing, wort boiling, fermentation, and pasteurization, and retained most of their antimicrobial activity in lager beer (5% ethanol, v/v) after long-term storage at 8 and 25 degrees C.

Cloning and heterologous production of Hiracin JM79, a Sec-dependent bacteriocin produced by Enterococcus hirae DCH5, in lactic acid bacteria and Pichia pastoris

Hiracin JM79 (HirJM79), a Sec-dependent bacteriocin produced by Enterococcus hirae DCH5, was cloned and produced in Lactococcus lactis, Lactobacillus sakei, Enterococcus faecium, Enterococcus faecalis, and Pichia pastoris. For heterologous production of HirJM79 in lactic acid bacteria (LAB), the HirJM79 structural gene (hirJM79), with or without the HirJM79 immunity gene (hiriJM79), was cloned into the plasmid pMG36c under the control of the constitutive promoter P(32) and into the plasmid pNZ8048 under the control of the inducible P(NisA) promoter. For the production of HirJM79 in P. pastoris, the gene encoding the mature HirJM79 protein was cloned into the pPICZalphaA expression vector. The recombinant plasmids permitted the production of biologically active HirJM79 in the supernatants of L. lactis IL1403, L. lactis NZ9000, L. sakei Lb790, E. faecalis JH2-2, and P. pastoris X-33, the coproduction of HirJM79 and nisin A in L. lactis DPC5598, and the coproduction of HirJM79 and enterocin P in E. faecium L50/14-2. All recombinant LAB produced larger quantities of HirJM79 than E. hirae DCH5, although the antimicrobial activities of most transformants were lower than that predicted from their production of HirJM79. The synthesis, processing, and secretion of HirJM79 proceed efficiently in recombinant LAB strains and P. pastoris.