The 65 isolates 43 from food and 22 from clinical samples that were collected from various food and healthcare units were positive for esculin hydrolysis on bile esculin agar and for l -pyroglutamic acid beta-naphthylamide hydrolysis on PYR discs results not shown. They were identified at the species level as E.
Phylogenetic tree of bacteriocinogenic isolates based on partial 16S rDNA gene sequences. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test replicates are shown next to the branches. Interestingly, when the putative bacteriocinogenic E. Of them, the food-isolated E. Some Gram-positive bacteria, such as L.
Still, other Gram-positive bacteria, such as Listeria , Bacillus , and Staphylococcus , and all tested Gram-negative bacteria were resistant. The most potent antimicrobial activity was shown against L. All selected 11 isolates with antimicrobial activities demonstrated bile salt hydrolase activity except strains OS11, 13, 16, and Furthermore, all strains were non-hemolytic and gelatinase-positive.
They were sensitive to ampicillin and vancomycin Table S2 but resistant to clindamycin, fusidic acid, apramycin, streptomycin, tetracycline, and polymyxin B Table S2 , Fig. Other antibiotics sensitivities and resistance patterns are listed Table S2. Clustering based on the resistance pattern of these isolates is presented in Fig. ST, representing E. The final step of reverse-phase chromatography using a Sephasil Peptide C8 column allowed the separation of two peaks with antimicrobial activity, eluted at approximately Second reversed-phase chromatography using the Sephasil peptide C 8 column.
This shows two peaks with antimicrobial activity eluted at approximately The solid line shows the absorbance at nm, while the broken line shows the elution gradient of isopropanol.
A single diffuse band with a molecular weight of 7— A peptide mass similarity search using ExPASy revealed that there were no molecular weight similarities with any other AMPs except holotricin-2 Da SDS-PAGE A of protein marker i compared to partially purified BLIS after cation exchange chromatography ii and showed a single diffused band in the bioassay experiment iii with a molecular weight between 7 and Enterococcus faecalis are widely spread in the environment and are commonly isolated from foodstuffs and clinical samples The identification of antimicrobial agents to treat antibiotic-resistant nosocomial enterococci is crucial because the treatment of such infections is becoming increasingly problematic.
In addition, enterococci gained greater medical and public attention since the mids when vancomycin resistance was first present in clinical isolates VRE BLIS with the potential to inhibit the growth of such bacteria could remedy infections without affecting endogenous beneficial microbiota or risking dissemination of R-factors to non-enterococcal pathogens e.
The 11 unknown putative bacteriocinogenic E. Our study showed that, E. Generally, the bacteriocins produced from Gram-positive bacteria are active against closely related species and not directly active against Gram-negative bacteria. However, some other bacteriocins from LAB showed antagonistic activities against both Gram-positive and Gram-negative bacteria, like enterocin E 41 , enterocin E 42 , and salivaricin SMXD51 Especially during infancy and early childhood, exposure to broad-spectrum antibiotics is often unfavorable, as the early microbiota lacks diversity and stability, rendering it distinctly vulnerable to disturbance, in addition to the importance of intestinal microbiota in early development and education of the immune system Noticeably, bacteriocins from isolate OS13 were active against multi-resistant nosocomial enterococci as Enterococcus faecalis V, which was the first VRE Enterococcus isolated in the United States, and it was also resistant to high levels of aminoglycosides, macrolides, lincosamides, and streptogramin B Therefore, BLIS could represent a non-conventional alternative of interest to combat pathogens like enterococci, recognizing that the presence of natural resistance prevents a variety of modern drugs widely used, such as cephalosporins and quinolones, from working effectively against enterococcal infections Most VREs are also resistant to antibiotics as ampicillin, vancomycin, and aminoglycosides, widely used in the hospital environment.
Therefore, only a few therapeutic options are commercially available to treat multidrug-resistant VRE infections, including linezolid, tedizolid, tigecycline, and daptomycin 46 , The increased use of these last-source antibiotics and the ability of enterococci to readily acquire new resistance determinants are currently raising the need to find alternative therapeutics and explore the effectiveness of natural antimicrobials such as bacteriocins.
At each purification level, the antimicrobial activity decreased, especially after reverse-phase chromatography, which was observed in other studies 34 , There are previous reports of many BLIS becoming less heat-stable during subsequent purification steps 55 , Generally, Enterococcus spp. Regarding the virulence traits of strain OS13, neither hemolytic activity nor bile salt hydrolase activity was demonstrated, while gelatinase activity was observed.
Cytolysin also called hemolysin is a lantibiotic, but it differs from most lantibiotics because it is both antibacterial and hemolytic In our study, PCR analysis was used to confirm the absence of the cytolysin gene cluster cyl. Although E. The gelatinase enzyme is involved in the virulence of Enterococcus sp. The primary role of gelatinase in enterococcal pathogenesis is to provide nutrients to the bacteria by degrading host tissue. However, it also appears to play a role in biofilm formation The food chain is considered the primary transmission route of antibiotic-resistant bacteria between populations.
Enterococcus sp. In biosafety evaluations of enterococci, their resistance to glycopeptides, such as vancomycin, should be considered In our study, the pathogenic potential of the food isolated E. OS13 was sensitive to ampicillin, penicillin G, vancomycin, erythromycin, kanamycin, and gentamicin. It was resistant to chloramphenicol, streptomycin, tetracycline, clindamycin, fusidic acid, and polymyxin B.
These results are in agreement with previous publications 71 , 72 , where all tested E. Resistance to chloramphenicol, tetracycline, erythromycin, gentamicin, and kanamycin is becoming common among enterococci from different sources due to the abuse of antibiotics in clinics, animal and fish farming, and agriculture. Thus, enterococcal antibiotic resistance is not exclusive to the clinical field and is also prevalent in the food industry Although MLST is a tool for global epidemiological studies, the possible role of plasmids in transferring virulence between different strains should be considered MLST analysis of E.
To our knowledge, ours is the first report of the isolation of E. The ability of CC to spread in hospitals and cause infection is unknown. MLST of E. Although our BLIS showed sensitivity to heat treatments, they could be used for preservation of raw or minimally processed foods stored at low temperatures besides their likely role in the treatment of clinical infections with VRE and MDRE.
Future works are still required to figure out the amino acid sequences, structures, encoding genes, and mode of actions of such BLIS.
Chun, W. Action of lysozyme and nisin mixtures against lactic acid bacteria. Food Microbiol. Parada, J. Bacteriocins from lactic acid bacteria: Purification, properties and use as biopreservatives. Article Google Scholar. Aakra, A. Survey of genomic diversity among Enterococcus faecalis strains by microarray-based comparative genomic hybridization. Baldassarri, L. Pathogenesis of implant infections by enterococci. Organs 28 , — Coates, A. Novel approaches to developing new antibiotics for bacterial infections.
Kristich, C. Massachusetts Eye and Ear Infirmary, Antimicrobial and safety aspects, and biotechnological potential of bacteriocinogenic enterococci isolated from mallard ducks Anas platyrhynchos. Nilsen, T. Franz, C. Diversity of enterococcal bacteriocins and their grouping in a new classification scheme. FEMS Microbiol. Acedo, J. The expanding structural variety among bacteriocins from Gram-positive bacteria.
Nes, I. Bacteriocin diversity in Streptococcus and Enterococcus. On the contrary, enterococci have important implications in the dairy industry. They play an acknowledged role in the development of organoleptic characteristics during the ripening of many cheeses and they have been also used as components of cheese starter cultures [1].
Some enterococci of food origin also share a number of useful biotechnological traits e. Unfortunately, enterococci have recently assumed major importance in clinical microbiology as well. Enterococci have traditionally been regarded as low-grade pathogens. However, there is no consensus on the significance of their presence in foodstuffs. Their newly accentuated ambiguity concerning the relationships of enterococci with human beings is related to their enteric habitat , their entering the food chain, their antibiotic resistance and their possible involvement in food-borne illnesses due to the presence of virulence factors, such as the production of adhesins and aggregation substances.
Over the last two decades, enterococci have emerged as important hospital-acquired pathogens in immune-suppressed patients and intensive-care units. The rise in hospital-acquired enterococcal infections has been in part due to the increased use of broad-spectrum antibiotics and the rising number of severely ill patients.
Enterococci are not only intrinsically resistant to several antibiotics, but are also characterised by a potent and unique ability to exchange genetic material. The increasing prevalence of strains resistant to ampicillin, aminoglycosides and glycopeptides and the acquisition of resistance to the few antibiotics available for treatment such as vancomycin pose serious difficulties in clinical therapy.
In addition, selective pressure exerted by the use of antibiotics as growth promoters in food animals appears to have created large reservoirs of transferable antibiotic resistance in various ecosystems. With the emergence of glycopeptide resistance in Enterococcus faecium outside hospitals, a large reservoir of transferable resistance vanA gene cluster was identified in animal husbandry due to the use of avoparcin as a feed additive.
The spread of resistance, which enters the human enterococcal flora via the food chain, and the transfer of this trait to pathogenic species i. Therefore, the barrier separating enterococci as inoffensive contaminants from pathogens appears most fragile. The identification of the enterococci has always been problematic.
Numerous enterococcal isolates, especially from an environmental source, often remain unidentified when their identification is based on phenotypic traits alone. It is difficult to unequivocally categorise isolates into one of the Enterococcus species by physiological tests because heterogeneity in phenotypic features is very high, regardless of the origin of the isolate [ 2—5 ].
The problem with the taxonomy of enterococci is generally that they are a heterogeneous group of Gram-positive cocci sharing many characteristics with the genera Streptococcus and Lactococcus. On the basis of 16S rRNA cataloguing, the genus Streptococcus was separated during the s into the three genera Enterococcus, Lactococcus and Streptococcus.
Since this transfer, the total number of species presently included in the Enterococcus genus on the basis of chemotaxonomic and phylogenetic studies is This situation continues to fluctuate from time to time as individual species are moved into other genera or new taxa are discovered.
More recently, other species of enterococci have been proposed on the basis of chemotaxonomic studies and phylogenetic evidence provided by 16S rDNA sequencing [ 7 , 8 ]. It is highly probable that phylogenetic system of the genus Enterococcus has not yet been completely elucidated and that some re-classifications may be necessary in the near future.
Over the last two decades, enterococci, formerly viewed as organisms of minimal clinical impact, have emerged as important hospital-acquired pathogens in immunosuppressed patients and intensive care units. Enterococci do not possess the common virulence factors found in many other bacteria, but they have a number of other characteristics, e.
Foodborne enterococci have not yet been clearly involved as direct causes of clinical infections [9]. In this context, reports of hospital-acquired infections attributed to enterococci are difficult to interpret because these bacteria are generally identified in mixed cultures with other primary pathogens, such as staphylococci and others [10].
Enterococci have been implicated in cases of food poisoning, e. Enterococci are now among the most common nosocomial pathogens; they have been implicated as an important cause of endocarditis, bacteraemia, urinary tract, central nervous system, intra-abdominal and pelvic infections [12]. Epidemiological data also indicate that E. In addition, there is strong evidence that enterococci causing bacteraemias commonly originate from the urinary tract.
Malone et al. In addition to these well-documented infections, the incidence of intra-abdominal infections caused by vancomycin-resistant enterococci is increasing [19]. Enterococci may also contribute to cause abdominal and pelvic abscess formation and sepsis [20]. The clinical significance of enterococci in human infections is poorly understood because of the scarcity of well-documented reports confirming their occurrence in mixed cultures. The increasing resistance of enterococci to antibiotics and the presence of active mechanisms of gene transfer are exacerbating the increasing findings of these bacteria as nosocomial opportunists.
However, the antibiotic resistance alone cannot explain the virulence of these bacteria in the absence of pathogenicity factors. Virulence traits in enterococci include adherence to host tissue, invasion and abscess formation, resistance to and modulation of host defense mechanisms, secretion of cytolysins and other toxic products and production of plasmid-encoded pheromones [ 12 , 14 , 21 ].
A number of genes encoding for virulence factors especially in E. Recent molecular screenings of Enterococcus virulence determinants indicated that medical E. Multiple determinants, e. Many of these enterococcal virulence traits, such as haemolysin—cytolysin production, the adhesion ability and the antibiotic resistance see later , have been shown to be transmissible by gene transfer mechanisms [ 23—26 ].
Often, the same plasmid may encode a sex pheromone response and either antibiotic resistance or haemolysin production genes [ 12 , 26 , 27 ]. The exchange of genetic material in E. In a recent study, multiple pheromone-encoding genes were identified in both clinical and food enterococcal strains, indicating the potential of these latter to acquire other sex pheromone plasmids.
Trans-conjugation in which starter strains acquired virulence determinants from medical strains was also demonstrated [21]. Sex pheromones are also thought to act as virulence factors by eliciting an inflammatory host response [ 28—30 ].
Virulence of enterococci is strongly enhanced by their frequent resistance to commonly used antibiotics. Antibiotic resistance, which can be both intrinsic and acquired, makes enterococci effective opportunists in nosocomial infections. Intrinsic resistance to many antibiotics suggests that treatment of infection could be difficult.
In addition to these constitutive resistances, enterococci have acquired genetic determinants that confer resistance to all classes of antimicrobials, including chloramphenicol, tetracyclines and glycopeptides. The major risk related to these latter resistance traits is that they are for the most part transferable. The genes coding for all of these antibiotic-resistant traits may be transferred by pheromone-mediated, conjugative often multiresistant plasmids or transposons to both enterococci and more virulent pathogens, such as S.
Within acquired antibiotic resistances, vancomycin-resistant enterococci VRE are possibly the most serious concern that has recently emerged in human clinical infections.
Two distinct forms of transferable vancomycin-resistant phenotypes have been described in enterococci: the VanA phenotype associated with a high level of inducible resistance to vancomycin and cross resistance to teicoplanin and the VanB phenotype usually displaying variable levels of inducible resistance only to vancomycin. Enterococci can be readily isolated from foods, including a number of traditional fermented foods.
A clear picture of the microbial ecology of these bacteria easily explains their presence in foods. Enterococci constitute a large proportion of the autochthonous bacteria associated with the mammalian gastrointestinal tract. Once rejected from the environment by means of human faeces or animal ejecta, they are able to colonise diverse niches because of their exceptional aptitude to resist or grow in hostile environments.
Therefore, enterococci are not only associated with warm-blooded animals, but they also occur in soil, surface waters and on plant and vegetables. By intestinal or environmental contamination they can then colonise raw foods e. They can also contaminate finished products during food processing. Therefore, many fermented foods made from meat and milk especially fermented meats and cheeses contain enterococci.
A wide variety of fermented meat products is produced in many parts of the world. In Europe the predominant types are Italian salami and German raw sausage with numerous national and regional variants. The technology for the production of most of these products is essentially similar. After a period of fermentation to biologically stabilise the product, processed meats are typically salted or smoked, and for the most part eaten raw [34].
It was therefore suggested that a proper heat treatment during processing, such as in the case of cooked, unfermented meats, would be necessary to eliminate enterococci as spoilage microflora in fermented meats [36]. In many cases, however, enterococci are a spoilage problem also in cooked, processed meats because they are able to survive heat processing, especially if initially present in high numbers [12].
To this regard, both E. Gordon and Ahmad [39] stated that E. Therefore, the presence of enterococci in fermented or non-fermented meat products appears unavoidable by present day applied technologies. The presence of enterococci in dairy products has long been considered an indication of insufficient sanitary conditions during the production and processing of milk. To the contrary, many authors suggest that certain strains of enterococci in some cheeses may be highly desirable on the basis of their positive contribution to flavour development during the cheese ripening.
This beneficial role led to the inclusion of enterococcal strains in certain starter cultures. Enterococci occur in a variety of cheeses, especially artisanal cheeses produced in southern Europe from raw or pasteurised milk, and in natural milk starters. The isolation of enterococci from natural milk starter cultures, which are still widely used for many Italian soft cheeses made with raw or pasteurised milk, can be explained by their thermal resistance.
The presence of enterococci in pasteurised cheeses is generally due to recontamination after the heat treatment and to their heat resistance.
The recovery and persistence of the enterococci in some cheeses during ripening can be attributed to their wide range of growth temperatures and their tolerance to pH and salt. Clearly, the presence of enterococci is ineluctable also in many dairy products. The extremely high level of antibiotic resistance observed in enterococci and their widespread finding in raw foods are two key elements contributing to the frequent recovery of antibiotic-resistant enterococci ARE in both unfermented and fermented foods.
ARE have been found in meat products, dairy products, ready-to-eat foods and even within enterococcal strains proposed as probiotics [ 36 , 40—44 ].
In previous studies on European cheeses, enterococci mainly belonging to E. Although ARE are found in both pasteurised and, to a much higher extent, raw milk cheeses, their presence in these latter products may represent a more serious risk of expanding antibiotic resistance through the food chain.
Strains with high-level resistance to kanamycin and gentamicin were recently isolated from French raw milk cheeses and hospitalised patients [45]. The same picture emerges from data on meat products. Enterococci resistant to one or more antibiotics including bacitracin, chloramphenicol, erythromycin, gentamicin, penicillin, rifampicin, streptomycin and tetracycline were isolated from minced meat, raw meat sausages, ham and tenderloin beef [ 36 , 42 ].
The overall data on antibiotic resistance within food-associated enterococci open the question of their entering the food chain. There is strong epidemiological evidence of a link between the use of antibiotics in human medicine and animal husbandry and the emergence, spreading and persistence of resistant strains in animal products [ 46 , 47 ].
Antibiotic-resistant enterococci can be provided to the human gut by contaminated foods especially of animal origin and environment, including people and animals. A recent epidemiological study carried out in France, which showed common pulsed field gel electrophoresis PFGE patterns in antibiotic-resistant E.
Food-associated enterococci could therefore be a reservoir for antibiotic resistance. Once ingested, ARE can survive gastric passage and multiply, thus leading to sustained intestinal carriage [48].
The emergence of ARE in nosocomial infections poses the problems of i the role played by these bacteria, as possible natural food reservoirs, in the dissemination of antibiotic-resistant traits in the environment, and ii the risk for human health of using antimicrobial drugs in agriculture. These two aspects, with almost exclusive emphasis on the selection and microbial ecology of VRE in foods, will be treated later. Among ARE, the emergence, selection and spreading of enterococci resistant to the glycopeptide antibiotics vancomycin and teicoplanin in a hospital environment is a clinical emergence.
The use of this class of antimicrobials is of utmost importance in clinical therapy against multiple antibiotic-resistant strains or in the case of allergy to other antibiotics, e. Although nosocomial acquisition and subsequent colonisation of VRE has been emphasised among hospitalised persons, colonisation appears to occur frequently in persons not associated with the health care setting [ 52—55 ].
Several reports carried out in European countries and the USA in recent years indicate that colonisation with VRE frequently occurs in the community, and that many animal, food and environmental reservoirs can act as community sources for VRE outside the health care setting.
In this mechanism, the transport of these resistances via the food chain to humans appears most probable. High level VRE strains, especially belonging to E.
The vanA type glycopeptide resistance, which confers coupled resistance to both vancomycin and teicoplanin, seems the most frequent vancomycin-resistant phenotype among food-associated VRE.
The chronic use of antibiotics as growth promoters in livestock is a recognised factor acting as a selective agent in promoting resistant enterococci. With the emergence of glycopeptide resistance in enterococci especially E. Similar mechanisms have been suggested for streptogamin, avilamycin and tylosin resistance.
Streptogamin resistance has been found in E. Because virginiamycin has been used as a growth promoter in animal feed but streptogamins have rarely been used in human therapy, this again appears to be another example of resistance of animal origin [47]. The fact that vancomycin resistance is common not only in animals fed with avoparcin as a growth promoter, but also in the human population outside hospitals, makes clear that either a clonal spread of resistant strains or a transfer of resistance genes between animal and human bacteria may occur.
Epidemiological studies of farms that use avoparcin have shown a significant association with the presence of VRE in animal stools. VRE generally reach foods through environmental contamination from various sources. VRE have been found in waste water samples from sewage treatment plants, livestock faeces, uncooked chicken samples, manure samples from pig and poultry farms [ 12 , 36 , 62 ].
These findings suggest that a possible link between the use of avoparcin and other antibiotics used in livestock, the selection of VRE or ARE , and humans becoming colonised via the food chain exists.
To prove such a link is beset with many difficulties: it is necessary to explain the presence of VRE within non-hospitalised people in the United States where avoparcin has never been approved for use. To this regard, it was suggested that other modes of community transmission, such as household contact e. It is also difficult to prove that animal, environmental and human strains are identical by means of molecular typing. To date, molecular typing of strains only suggests a link [ 40 , 63 ].
Human vancomycin-resistant E. Molecular typing by PFGE carried out on VRE isolated from hospitalised patients and non-hospitalised controls in France revealed a different pattern for each VRE that originated from an individual subject [65].
Therefore, although a connection between the occurrence of VRE in meat and nosocomial infections has not yet been clearly proved, epidemiological data would suggest that both clonal dissemination through the food chain and horizontal gene transfer between a variety of different strains are involved in the VRE spreading outside the hospital. Concerning gene transfer route of transmission, recent molecular studies on sequence polymorphism of Tn , encoding vancomycin resistance, within VRE from humans, pigs and poultry suggest that the primary transmission is from animals to humans and not the other way around [66].
On the other hand, although many reports of cases of VRE infection suggested inter-strain transmission of resistance genes, cross colonisation of single resistant clones seem the most frequent mechanisms of VRE spreading within farms or hospitals [ 11 , 61 , 64 , 67—70 ]. High levels of biogenic amines in many fermented foods, such as fermented sausages, cheeses, wines, beers, olives and fish products, involved in food intoxication may be a clinical concern.
Their ubiquitous nature determines their frequent finding in foods as contaminants. In addition, the notable resistance of enterococci to adverse environmental conditions explains their ability to colonise different ecological niches and their spreading within the food chain through contaminated animals and foods.
Strains E. The probiotics E. Probiotics have been shown to have positive effects on the performance characteristics of the growth and health of farm animals. Feeding pigs with the probiotic Enterococcus was found to reduce intestinal pathogens Liao and Nyachoti, Similarly, the probiotic E.
Likewise, oral administration of E. In chickens , E. Additionally, enterocin E Line et al. Enterococci are also used as probiotics for dogs based on their tolerance to bile, adhesion activity, antimicrobial activity and their impact on high levels of serum cholesterol and alanine aminotransferase Bybee et al. Numerous studies have shown the beneficial effects of enterococci in aquaculture. Several studies reported a wide spectrum of inhibition by E. In addition, several trials have investigated the efficacy of E.
Bacteriocins are an interesting alternative to the use of antibiotics, which have created great public concerns due to the emergence of antimicrobial resistance. New compounds and therapeutic methods for treating infections caused by antibiotic-resistant pathogens and limiting their spread are urgently needed. Hence, there is a need to discover new antimicrobial agents and to develop innovative strategies to fight against those pathogens Hammami et al.
Gastrointestinal diseases are usually associated with gut microbiota dysbiosis. Probiotics affect the functionality of the GIT by a variety of mechanisms such as interfering with the attachment of pathogens to adhesion sites, out-competing pathogens for nutrients, degradation or other alterations of toxin receptors, production of inhibitory substances e. Species such as H. The broad inhibitory spectra of bacteriocins produced by Enterococcus make them appropriate candidates, alone or in combination with other antibiotics, to prevent or treat these infections.
For example, administration of enterocin CRL35 alone showed significant activity against L. Likewise, enterocin E has effectively been used to treat infection in birds Svetoch et al. More recently, durancin 61 A has demonstrated a significant activity when combined with reuterin against C. Although immunomodulation is one of the main mechanisms of action of probiotic bacteria, very few studies have actually documented immunomodulatory properties of Enterococcus.
In a lesser extent, Kanda and collaborators have demonstrated that the administration of E. Another recent study have reported that E. Enterocins are being extensively studied for use in treatment of acne Figure 2. Previously, a patent was issued for the use of AS combined with lysozyme for applications against acne and other skin bacterial infections targeting P. Nosocomial infections involving drug-resistant bacteria are a major concern in hospitals.
They contribute to increased morbidity, length of stay and the cost of care. The main multi-resistant organisms include methicillin-resistant S. Because of their activity against clinically important strains and synergistic activity with other bacteriocins and antibiotics, enterocins could be used in the treatment of nosocomial infections caused by these resistant bacteria Hammami et al.
Methicillin-resistant S. They may also be resistant to tetracycline, clindamycin, cephalosporins, macrolides, quinolones and other antibiotics. In community, most MRSA infections are skin and soft tissue infections. In medical establishment, MRSA causes bacteraemia, septicemia, endocarditis, pneumonia and surgical site infections Lee et al.
The efficacy of vancomycin, the traditional antibiotic chosen to treat these infections, has declined with the emergence of resistant strains Fair and Tor, Alternatively, bacteriocins E and B have been proven effective against antibiotic-resistant strains in nosocomial infections Svetoch et al. Similarly, durancin 61A alone or in combination with vancomycin was shown effective against clinical MRSA Hanchi et al. The spread of VRE may lead to clinical isolates resistant to all antibiotics because enterococci have become important nosocomial pathogens and a reservoir for resistance genes Fair and Tor, Interestingly, two peptides produced by E.
This novel anti-inflammatory bacterium may be preferentially useful as a prophylactic treatment to avoid inflammatory bowel disease Avram-Hananel et al. More recently, administration of E. A growing number of studies have illustrated the beneficial effects of probiotics on health including the elimination of pathogens. Until recently, the most commonly used probiotic strains are related to Bifidobacterium, Lactobacillus , and Lactococcus species.
In order to identify new members, other microorganisms with probiotic potential should be evaluated for probiotic candidacy. Among these candidates, Enterococcus spp. However, for safety reasons, the application of enterococci as probiotic or feed additive has not been sufficiently exploited despite their significant antibacterial activity and probiotic potential Franz et al.
This genus has bad reputation due to members associated with severe health-care associated infections such as vancomycin-resistant enterococci VRE. There is a major concern about use of enterococci strains in food supplements, which could lead to the spread of multi-resistance and virulence genes Jahan et al. In an even more alarming development, transfer of vancomycin resistance from enterococci to methicillin-resistant strains of S.
Thus, strains carrying acquired resistance should not be intentionally introduced to the food and feed chain. In the case of feed and novel foods, a pre-market safety assessment is required where the safety of the candidate strains is assessed at species-level. Recent advances in molecular biology have demonstrated that enterococcal food strains are safe and can be differentiated from the nosocomial strains carrying virulence and antimicrobial resistance genes Montealegre et al.
This will enable possible improvement of the safety assessment of enterococci used in food and feed. Some Enterococcus strains have many interesting properties such as multi-bacteriocin production and viability in different matrices including food and GIT, which highlight their potential use as natural preservatives in food, as probiotics, or as viable alternatives to antibiotics. In addition, enterococci bacteriocins are recognized for their wide spectrum antimicrobial activity including Gram-positive foodborne pathogens, such as biogenic amines producing bacteria Laukova et al.
These features provide the rationale to nominate bacteriocinogenic Enterococcus strains as important candidates for food, human and animal health applications. Furthermore, bacteriocin production is an important element in competition among bacteria.
Bacteriocin-producing probiotics could compete with intestinal pathogens for colonization or modulate the microbiota homeostasis. In this context, it has been reported that bacteriocins can be produced in the gut by probiotic bacteria where it can modulate gut microbiota to reduce gastrointestinal diseases Salvucci et al.
However, the mechanisms by which probiotics attenuate gastrointestinal infections need to be evaluated in order to determine their efficacy more accurately. Bacteriocins are target specific, safe, can synergize with antibiotics, and are heat stable, interesting features for the development of drug candidates to the treatment of antibiotic-resistant bacterial infections. Considering the emergence of resistance, it is believed that multiple bacteriocin productions can help the producer strain to abolish resistance problem of some target strains Perez et al.
The use of bacteriocins in combination with other antimicrobials Hanchi et al. In general, the mainstream use of bacteriocin therapies will need careful and controlled implementation to limit possible resistance development. Finally, probiotics have been defined as live microorganisms which, when administered in adequate amounts, confer a health benefit to the host.
This definition suggests that safety and efficacy of probiotics have to be demonstrated for each strain and each product. As probiotic properties have been shown to be strain specific, accurate identification of candidate strains is also very important. In spite of their pathogenic potential, commensal enterococci generally display low levels of virulence, as evidenced by their presence as natural colonizers of the GIT of humans and most animals and by the fact that they have been used safely for decades as probiotics in humans and farm animals Arias and Murray, Therefore, their application as promising probiotics in food and feed industry needs implementation of appropriate guidance and relevant legislation of valid scientific methods to distinguish between pathogenic and non-pathogenic stains, and to prevent horizontal transfer of pathogenic genes.
Despite the several hurdles that must be overcome for the exploitation of enterococci and their bacteriocins in food systems, as probiotics and in drug discovery, the innovations and developments discussed in this review offer a taste of future trends in food, veterinary and pharmaceutical applications of these intriguing microbes.
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