Effect of combined physico-chemical treatments based on enterocin AS-48 on the control of Listeria monocytogenes and Staphylococcus aureus in a model cooked ham

Bioprotective cultures and bacteriocins as food preservatives

Food preservation technologies face the challenge of extending product shelf life applying different factors to prevent the microbiological spoilage of food and inhibit/inactivate food borne pathogens maintaining or even enhancing its quality. One such preservation strategy is the application of bacteriocins or bacteriocin-producer cultures as a kind of food biopreservation. Bacteriocins are ribosomally synthesized small polypeptide molecules that exert antagonistic activity against closely related and unrelated bacteria without harming the producing strain by specific immunity proteins. This chapter aims to contribute to current knowledge about innovative natural preservative agents and their application in the food industry. Specifically, its purpose is to analyze the classification of bacteriocins from lactic acid bacteria (LAB), desirable characteristics of bacteriocins that position them in a privileged place in food biopreservation technology, their success story as well as the bacteriocinogenic LAB in various food systems. Finally, challenges and barrier strategies used to enhance the efficiency of the bacteriocins antimicrobial effect are presented in this chapter.

Embedding Biomimetic Magnetic Nanoparticles Coupled with Peptide AS-48 into PLGA to Treat Intracellular Pathogens

Among the strategies employed to overcome the development of multidrug-resistant bacteria, directed chemotherapy combined with local therapies (e.g., magnetic hyperthermia) has gained great interest. A nano-assembly coupling the antimicrobial peptide AS-48 to biomimetic magnetic nanoparticles (AS-48-BMNPs) was demonstrated to have potent bactericidal effects on both Gram-positive and Gram-negative bacteria when the antimicrobial activity of the peptide was combined with magnetic hyperthermia. Nevertheless, intracellular pathogens remain challenging due to the difficulty of the drug reaching the bacterium. Thus, improving the cellular uptake of the nanocarrier is crucial for the success of the treatment. In the present study, we demonstrate the embedding cellular uptake of the original nano-assembly into THP-1, reducing the toxicity of AS-48 toward healthy THP-1 cells. We optimized the design of PLGA[AS-48-BMNPs] in terms of size, colloidal stability, and hyperthermia activity (either magnetic or photothermal). The stability of the nano-formulation at physiological pH values was evaluated by studying the AS-48 release at this pH value. The influence of pH and hyperthermia on the AS-48 release from the nano-formulation was also studied. These results show a slower AS-48 release from PLGA[AS-48-BMNPs] compared to previous nano-formulations, which could make this new nano-formulation suitable for longer extended treatments of intracellular pathogens. PLGA[AS-48-BMNPs] are internalized in THP-1 cells where AS-48 is liberated slowly, which may be useful to treat diseases and prevent infection caused by intracellular pathogens. The treatment will be more efficient combined with hyperthermia or photothermia.

Combined antimicrobial effect of bacteriocins with other hurdles of physicochemic and microbiome to prolong shelf life of food: A review

Bacteriocins are ribosomally synthesized peptides to inhibit food spoilage bacteria, which are widely used as a kind of food biopreservation. The role of bacteriocins in therapeutics and food industries has received increasing attention across a number of disciplines in recent years. Despite their advantages as alternative therapeutics over existing strategies, the application of bacteriocins suffers from shortcomings such as the high isolation and purification cost, narrow spectrum of activity, low stability and solubility and easy enzymatic degradation. Previous studies have studied the synergistic or additive effects of bacteriocins when used in combination with other hurdles including physics, chemicals, and microbes. These combined treatments reduce the adverse effects of chemical additives, extending the shelf life of food products while guaranteeing food quality. This review highlights the advantages and disadvantages of bacteriocins in food preservation. It then reviews the combined effect and mechanism of different hurdles and bacteriocins in enhancing food preservation in detail. The combination of bacterioncins and other hurdles provide potential approaches for maintaining food quality and food safety.

Enterocins: Classification, Synthesis, Antibacterial Mechanisms and Food Applications

Enterococci, a type of lactic acid bacteria, are widely distributed in various environments and are part of the normal flora in the intestinal tract of humans and animals. Although enterococci have gradually evolved pathogenic strains causing nosocomial infections in recent years, the non-pathogenic strains have still been widely used as probiotics and feed additives. Enterococcus can produce enterocin, which are bacteriocins considered as ribosomal peptides that kill or inhibit the growth of other microorganisms. This paper reviews the classification, synthesis, antibacterial mechanisms and applications of enterocins, and discusses the prospects for future research.

Nitrite reduction in fermented meat products and its impact on aroma

Fermented meat products are important not only for their sensory characteristics, nutrient content and cultural heritage, but also for their stability and convenience. The aroma of fermented meat products is unique and its formation mechanisms are not completely understood; however, the presence of nitrite and nitrate is essential for the development of cured aroma. The use of nitrite and nitrate as curing agents in meat products is based on its preservation activity. Even though their presence has been associated with several risks due to the formation of nitrosamines, their use is guarantee due to their antimicrobial action against Clostridium botulinum. Recent trends and recommendations by international associations are directed to use nitrite but at the minimum concentration necessary to provide the antimicrobial activity against Clostridium botulinum. This chapter discuss the actual limits of nitrite and nitrite content and their role as curing agents in meat products with special impact on dry fermented products. Regulatory considerations, antimicrobial mechanisms and actual trends regarding nitrite reduction and its effect on sensory and aroma properties are also considered.

Mutagenicity and genotoxicity assessment of a new biopreservative product rich in Enterocin AS-48

A biopreservative derived from the fermentation of a dairy byproduct by Enterococcus faecalis UGRA10 strains being developed. This product possesses a strong and wide antibacterial spectrum mainly due to the presence of Enterocin AS-48 in its composition. To assess its potential as food additive, the mutagenicicity and genotoxicity has been assayed by means of the bacterial reverse-mutation assay in Salmonella typhimurium TA97A, TA98, TA100, TA102, TA1535 strains (Ames test, OECD 471, 2020) and the micronucleus test (MN) (OECD 487, 2016) in L5178Y/Tk ± cells. The results in the Ames test after exposure to the byproduct (6.75-100 μg/plate) with absence and presence of the metabolic activation system from rat liver (S9 fraction), revealed not mutagenicity at the conditions tested. For the MN test, the exposition to five enterocin AS-48 concentrations (0.2-1 μg/μl) was tested in the absence and presence of S9 fraction, with no evidence of genotoxicity. Negative results in the mutagenicity and genotoxicity assays point out the good safety profile of the byproduct and support its use as additive. Further toxicological studies are required before its approval and commercial application.

Application of bacteriocins in food preservation and infectious disease treatment for humans and livestock: a review

Infectious diseases caused by bacteria that can be transmitted via food, livestock and humans are always a concern to the public, as majority of them may cause severe illnesses and death. Antibacterial agents have been investigated for the treatment of bacterial infections. Antibiotics are the most successful antibacterial agents that have been used widely for decades to ease human pain caused by bacterial infections. Nevertheless, the emergence of antibiotic-resistant bacteria has raised awareness amongst public about the downside of using antibiotics. The threat of antibiotic resistance to global health, food security and development has been emphasized by the World Health Organization (WHO), and research studies have been focused on alternative antimicrobial agents. Bacteriocin, a natural antimicrobial peptide, has been chosen to replace antibiotics for its application in food preservation and infectious disease treatment for livestock and humans, as it is less toxic.

Killing or inhibition actions of (a) antibiotics and (b) bacteriocin on gut microbiota.

Micro/nanoencapsulation strategy to improve the efficiency of natural antimicrobials against Listeria monocytogenes in food products

Listeria monocytogenes (Lm), the etiological agent of listeriosis diseases in humans, is a serious pathogenic microorganism threatening the food safety especially in ready-to-eat food products. Adhesion on both biotic and abiotic surfaces is making it a potential source of contamination by Lm. Also, this bacterium has become more tolerant in food processing conditions, including in the presence of adverse conditions such as cold and dehydration. One of the attractive and effective methods to inhibit the growth of Lm in the food products is using natural antimicrobial agents, which can be a suitable alternative to synthetic preservatives for producing organic food products. The use of pure natural antimicrobials has some limitations including low stability against harsh conditions, low solubility and absorption, and un-controlled release, which can decrease their functions. These limitations have been overcome by using new advanced encapsulation techniques, which have boosted the anti-listerial activity of natural agents. Therefore, the current paper is aiming to review the results of recent studies conducted on using natural antimicrobials added directly or as encapsulated forms into the food formulation to control the growth of Lm. The information of current study can be used by the researchers as well as the food companies for the optimization of food formulations through encapsulation strategies to control Lm and potentially produce safe foods for the consumers.

Impact of sodium lactate, encapsulated or unencapsulated polyphosphates and their combinations on Salmonella Typhimurium, Escherichia coli O157:H7 and Staphylococcus aureus growth in cooked ground beef

Foodborne illnesses affect the health of consumers worldwide, and thus searching for potential antimicrobial agents against foodborne pathogens is given an increased focus. This research evaluated the influence of sodium lactate (SL), encapsulated (e) and unencapsulated (u) polyphosphates (PP; sodium tripolyphosphate, STP; sodium acid pyrophosphate, SPP), and their combinations on Salmonella Typhimurium, Escherichia coli O157:H7 and Staphylococcus aureus growth in cooked ground beef during 30 day storage at 4 or 10 °C. pH, water activity (a_w), oxidation-reduction potential (ORP) and S. Typhimurium, E. coli O157:H7 and S. aureus counts were determined. S. Typhimurium was not found in SPP-SL combination groups after 30 day storage at 4 °C (P <0.05). Lower S. Typhimurium levels were determined in only SL containing groups stored at 10 °C than group with only tested microorganism (MO, P < 0.05). Although there was no change in S. Typhimurium load in all SL incorporated groups during 10 °C storage, S. Typhimurium count increased in other groups (P < 0.05). E. coli O157:H7 in MO and STP groups showed an increase at 4 °C, whereas it decreased in SPP-SL combination groups (P < 0.05). A gradual increase in E. coli O157:H7 at 10 °C was determined in MO and only PP incorporated groups, whereas there was a decrease in STP-SL or SPP-SL combination groups (P < 0.05). E. coli O157:H7 count was stable in SL containing groups during 10 °C storage. A gradual decrease in S. aureus was determined in all treatments at 4 °C, whereas S. aureus count increased in MO and uSTP groups during 10 °C storage (P < 0.05). There was no change in S. aureus level in only eSTP or uSPP or ueSTP containing groups at 10 °C, meantime it decreased in other groups (P < 0.05). The lowest S. aureus load was achieved by uSPP-SL or eSPP-SL or ueSPP-SL combinations after 30 days at both storage temperatures (P < 0.05). In general, pH was higher in samples with STP than those with SPP and control (P < 0.05). The lowest a_w was generally obtained in all SL containing groups at both storage temperatures (P < 0.05). Lower ORP was determined in all PP incorporated groups during storage at both temperatures compared to others (P < 0.05). ORP in all treatments generally increased (P < 0.05) during storage at both storage temperatures. This study showed that encapsulation is not a factor affecting antimicrobial efficiency of PP and using PP-SL combinations have synergistic effect on reducing the viability of S. Typhimurium, E. coli O157:H7 and S. aureus and their subsequent growth ability in cooked ground beef.

Subchronic toxicity study in BALBc mice of enterocin AS-48, an anti-microbial peptide produced by Enterococcus faecalis UGRA10

Few studies have examined the use of animal models to evaluate the in-vivo toxicity of antimicrobial peptides, but such research is essential to their safe use in foods. This study was performed to evaluate any adverse effects of enterocin AS-48, a circular bacteriocin produced by Enterococcus strains, when administered to BALB/c mice at concentrations of 50, 100, and 200 mg/kg in the diet for 90 days. Animals dosed with nisin at a dietary concentration of 200 mg/kg served as a reference treated group. There were no deaths in any of the animal groups, and the AS-48 treatment produced no abnormalities or clinical signs on body weights, food consumption, urinalysis, haematology, or blood biochemistry. Furthermore, there were no significant differences in the weights of liver, spleen, heart, kidneys, and intestines between control mice and those treated with AS-48 or nisin. The histopathological study showed moderate vacuolar degeneration in hepatocytes of some animals fed 100 or 200 mg/kg AS-48 (3/10 and 2/10 respectively). However, this anomaly was lower than in the group treated with nisin (5/10). Conclusively, no toxicologically significant changes were associated in BALB/c mice fed with 50, 100, and 200 mg/kg enterocin AS-48 for 90 days.

Antilisterial efficacy of Lactobacillus bacteriocins and organic acids on frankfurters. Impact on sensory characteristics

Dipping solutions containing bacteriocins produced by Lactobacillus curvatus CRL705 and Lactobacillus sakei CRL1862 (Bact705/1862), nisin and organic acids (lactic acid, LA; acetic acid, AA) were tested alone or in combination against Listeria monocytogenes inoculated by immersion on vacuum-packaged frankfurters stored at 10 °C during 36 days. LA/AA solution (2.5% v/v each) reduced pathogen population by 1.50 log10 CFU/ml during storage. Semi-purified Bact705/1862 prevented L. monocytogenes growth, while nisin was not able to avoid its regrowth after 20 days. The combined addition of Bact705/1862 + LA/AA was the most effective approach for pathogen reduction below detection level from day 6 to final storage. Frankfurters treated with Bact705/1862 + LA/AA compared to fresh-purchased samples did not show significant differences in flavor, juiciness, color intensity and overall preference at 22 days-storage at 5 °C. Meat processors should not only validate the antimicrobial efficacy of combined treatments but also their sensory impact on the product, which is directly related to consumer acceptability.

Liquid-liquid extraction of antimicrobial peptide P34 by aqueous two-phase and micellar systems

Antimicrobial peptide P34 is a promising biopreservative for utilization in the food industry. In this work, aqueous biphasic systems (ABS) and aqueous biphasic micellar systems (ABMS) were studied as prestep for purification of peptide P34. The ABS was prepared with polyethylene glycol (PEG) and inorganic salts and the ABMS with Triton X-114 was chosen as the phase-forming surfactant. Results indicate that peptide P34 partitions preferentially to PEG-rich phase and extraction with ammonium sulfate [(NH₄)₂SO₄], yielding a 75% recovery of the antimicrobial activity, specific activity of 1,530 antimicrobial units per mg of protein, and purification fold of 2.48. Protein partition coefficient and partition coefficient for the biological activity with (NH₄)₂SO₄ system were 0.48 and 64, respectively. Addition of sodium chloride did not affect recovery, but decreased protein amount in the PEG-rich phase, indicating a higher partition of biomolecules. ABMS did not yield good recovery of antimicrobial activity. Purification fold using PEG-(NH₄)₂SO₄ and 1.0 mol l^-1 sodium chloride was twice higher than that obtained by conventional protocol, indicating a successful utilization of ABS as a step for purification of peptide P34.

Inactivation of Listeria in Foods Packed in Films Activated with Enterocin AS-48 plus Thymol Singly or in Combination with High-Hydrostatic Pressure Treatment

The aim of the present study was to determine the efficacy of films activated with enterocin AS-48 plus thymol singly, or in combination with high-hydrostatic pressure (HHP) on the inactivation of Listeria innocua in sea bream fillets and in fruit puree stored under refrigeration for 10 days. L. innocua proliferated in control fish fillets during storage. The activated film reduced viable Listeria counts in fillets by 1.76 log cycles and prevented growth of survivors until mid-storage. Application of HHP treatment to fillets packed in films without antimicrobials reduced Listeria counts by 1.83 log cycles, but did not prevent the growth of survivors during storage. The combined treatment reduced viable counts by 1.88 log cycles and delayed growth of survivors during the whole storage period. L. innocua survived in puree during storage. The activated film reduced Listeria counts by 1.80 and 2.0 log cycles at days 0 and 3. After that point, Listeria were below the detection limit. No viable Listeria were detected in the purees after application of HHP treatment singly, or in combination with the activated film. Results from the study indicate that the efficacy of activated films against Listeria is markedly influenced by the food type.

Potential Applications of the Cyclic Peptide Enterocin AS-48 in the Preservation of Vegetable Foods and Beverages

Bacteriocins are antimicrobial peptides produced by bacteria. Among them, the enterococcal bacteriocin (enterocin) AS-48 stands for its peculiar characteristics and broad-spectrum antimicrobial activity. AS-48 belongs to the class of circular bacteriocins and has been studied in depth in several aspects: peptide structure, genetic determinants, and mode of action. Recently, a wealth of knowledge has accumulated on the antibacterial activity of this bacteriocin against foodborne pathogenic and spoilage bacteria in food systems, especially in vegetable foods and drinks. This work provides a general overview on the results from tests carried out with AS-48 in different vegetable food categories (such as fruit juices, ciders, sport and energy drinks, fresh fruits and vegetables, pre-cooked ready to eat foods, canned vegetables, and bakery products). Depending on the food substrate, the bacteriocin has been tested alone or as part of hurdle technology, in combination with physico-chemical treatments (such as mild heat treatments or high-intensity pulsed electric fields) and other antimicrobial substances (such as essential oils, phenolic compounds, and chemical preservatives). Since the work carried out on bacteriocins in preservation of vegetable foods and drinks is much more limited compared to meat and dairy products, the results reported for AS-48 may open new possibilities in the field of bacteriocin applications.

Revisão: Aspectos gerais das bacteriocinas

Resumo Bacteriocinas são peptídeos antimicrobianos sintetizados nos ribossomos, tendo sido descrita uma grande diversidade de bacteriocinas, as quais diferem entre si quanto a composição de aminoácidos, biossíntese, transporte e modo de ação. Nos alimentos, as bacteriocinas podem ser encontradas naturalmente como produtos da microbiota normal ou introduzida (cultura starter ou probióticos). Devido às suas aplicabilidades frente a organismos patogênicos contaminantes em alimentos, vários estudos têm sido publicados, tornando o uso destes peptídeos uma alternativa aos conservantes químicos tradicionais. Considerando-se as propriedades das bacteriocinas e sua potencial aplicação como bioconservadores de alimentos e alternativa aos antibióticos, o presente estudo busca acercar-se de uma visão geral das bacteriocinas quanto aos aspectos históricos, sistemas de classificação, biossíntese e transporte, modo de ação, abordando também algumas de suas aplicações na indústria de alimentos.

Effects of Two Application Methods of Plantaricin BM-1 on Control of Listeria monocytogenes and Background Spoilage Bacteria in Sliced Vacuum-Packaged Cooked Ham Stored at 4°C

Two application methods were used to investigate the effect of plantaricin BM-1 on the control of Listeria monocytogenes and background spoilage bacteria in sliced vacuum-packaged cooked ham without the addition of any chemical preservatives, including sodium nitrite, during 35 days of storage at 4°C. Regardless of the application method, plantaricin BM-1 treatment (320, 640, or 1,280 arbitrary units [AU]/g of sliced cooked ham) significantly (P < 0.05) reduced the survival of L. monocytogenes (inoculated at 4 log CFU/g of sliced ham) compared with its survival in the control during the first 21 days of storage at 4°C. The inhibitory effect of plantaricin applied to the surface of the ham was significantly better than the same concentration of plantaricin incorporated into the cooked ham (P < 0.0001) during storage. Even 320 AU/g plantaricin applied to the surface exhibited greater inhibition of L. monocytogenes than 1,280 AU/g plantaricin incorporated into the cooked ham on days 1, 14, and 28. A level of 1,280 AU/g plantaricin applied to the surface of the ham reduced L. monocytogenes counts to below the detection limit from the 1st to the 21st day of storage at 4°C. Afterwards, L. monocytogenes was able to regrow, and the viable counts of L. monocytogenes at the end of storage reached 2.76 log CFU/g (6.11 log CFU/g lower than in the control). In the control ham, the counts of background spoilage bacteria increased gradually and surpassed the microbiological spoilage limitation level on the 21st day of storage. However, plantaricin BM-1 treatment significantly (P < 0.05) reduced the survival of background spoilage bacteria in ham compared with their survival in the control from day 21 to 35 of storage at 4°C. A level of 1,280 AU/g plantaricin incorporated into cooked ham was the most effective, reducing the count of background spoilage bacteria count from an initial 2.0 log CFU/g to 1.5 log CFU/g on day 7. This was then maintained for another 14 days and finally increased to 2.76 log CFU/g at the end of the storage at 4°C (2.85 log CFU/g lower than in the control). In conclusion, plantaricin BM-1 application inhibited the growth of L. monocytogenes and background spoilage bacteria in cooked ham during storage at 4°C and could be used as an antimicrobial additive for meat preservation.

The Cyclic Antibacterial Peptide Enterocin AS-48: Isolation, Mode of Action, and Possible Food Applications

Enterocin AS-48 is a circular bacteriocin produced by Enterococcus. It contains a 70 amino acid-residue chain circularized by a head-to-tail peptide bond. The conformation of enterocin AS-48 is arranged into five alpha-helices with a compact globular structure. Enterocin AS-48 has a wide inhibitory spectrum on Gram-positive bacteria. Sensitivity of Gram-negative bacteria increases in combination with outer-membrane permeabilizing treatments. Eukaryotic cells are bacteriocin-resistant. This cationic peptide inserts into bacterial membranes and causes membrane permeabilization, leading ultimately to cell death. Microarray analysis revealed sets of up-regulated and down-regulated genes in Bacillus cereus cells treated with sublethal bacteriocin concentration. Enterocin AS-48 can be purified in two steps or prepared as lyophilized powder from cultures in whey-based substrates. The potential applications of enterocin AS-48 as a food biopreservative have been corroborated against foodborne pathogens and/or toxigenic bacteria (Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Escherichia coli, Salmonella enterica) and spoilage bacteria (Alicyclobacillus acidoterrestris, Bacillus spp., Paenibacillus spp., Geobacillus stearothermophilus, Brochothrix thermosphacta, Staphylococcus carnosus, Lactobacillus sakei and other spoilage lactic acid bacteria). The efficacy of enterocin AS-48 in food systems increases greatly in combination with chemical preservatives, essential oils, phenolic compounds, and physico-chemical treatments such as sublethal heat, high-intensity pulsed-electric fields or high hydrostatic pressure.

Bovicin HC5 and nisin reduce Staphylococcus aureus adhesion to polystyrene and change the hydrophobicity profile and Gibbs free energy of adhesion

Staphylococcus aureus is an opportunistic pathogen often multidrug-resistant that not only causes a variety of human diseases, but also is able to survive on biotic and abiotic surfaces through biofilm communities. The best way to inhibit biofilm establishment is to prevent cell adhesion. In the present study, subinhibitory concentrations of the bacteriocins bovicin HC5 and nisin were tested for their capability to interfere with the adhesion of S. aureus to polystyrene. Subinhibitory dosages of the bacteriocins reduced cell adhesion and this occurred probably due to changes in the hydrophobicity of the bacterial cell and polystyrene surfaces. After treatment with bovicin HC5 and nisin, the surfaces became more hydrophilic and the free energy of adhesion (∆G(adhesion)) between bacteria and the polystyrene surface was unfavorable. The transcriptional level of selected genes was assessed by RT-qPCR approach, revealing that the bacteriocins affected the expression of some important biofilm associated genes (icaD, fnbA, and clfB) and rnaIII, which is involved in the quorum sensing mechanism. The conditioning of food-contact surfaces with bacteriocins can be an innovative and powerful strategy to prevent biofilms in the food industry. The results are relevant for food safety as they indicate that bovicin HC5 and nisin can inhibit bacterial adhesion and consequent biofilm establishment, since cell adhesion precedes biofilm formation.

The impact of enterocin AS-48 on the shelf-life and safety of sardines (Sardina pilchardus) under different storage conditions

The purpose of this study was to determine the effect of enterocin AS-48, packaged under normal atmosphere (NA), vacuum (VP) or modified atmosphere (MAP) on the shelf life and safety of fresh sardines (Sardina pilchardus) stored at 5 °C. We studied the effect of these hurdles, alone or combined, on the relevant autochthonous bacterial populations. Total volatile basic nitrogen (TVB-N) content was used as indicative of freshness. Levels of biogenic amines cadaverine, putrescine, tyramine, and histamine were also determined. The application of AS-48 did not reduce the mesophilic, psychrotrophic, or Gram negative bacteria viable cell counts under any of the storage conditions tested. AS-48 did cause significant reductions in viable staphylococci counts, especially under VP. In sardines under NA treated with AS-48, the populations of histamine- and tyramine-forming total and lactic acid bacteria (LAB) showed no significant reductions. MAP or VP with AS-48 allowed reductions (significant at some storage times) in histamine- and tyramine-forming LAB. The TVB-N content was also reduced under normal atmosphere and, especially, in sardines stored under MAP. The most interesting results are those concerning the decrease (by several fold) in the levels of the biogenic amines cadaverine, putrescine, tyramine, and histamine determined after treatment with AS-48.

Characterization of functional, safety, and probiotic properties of Enterococcus faecalis UGRA10, a new AS-48-producer strain

Enterococcus faecalis UGRA10, a new AS-48-producer strain, has been isolated from a Spanish sheep's cheese. The inhibitory substance produced by E. faecalis UGRA10 was purified and characterized using matrix-assisted laser desorption ionization-time of flight mass spectrometry, confirming its identity with AS-48 enterocin (7.150 Da). Subsequent genetic analysis showed the existence of the as-48 gene cluster on a plasmid of approximately 70-kb. The UGRA10 strain was examined for safety properties such as enterococci virulence genes, biogenic amine production, and antibiotic resistance. As for most E. faecalis strains, PCR amplification revealed the existence of gene encoding for GelE, Asa1, Esp, EfaA, and Ace antigens and for tyrosine decarboxylase. This strain was sensitive to most of the antibiotics tested, being resistant only to aminoglycosides, lincosamide, and pristinamicins. In addition, UGRA10 developed an ability to form biofilms and to adhere to Caco 2 and HeLa 229 cells. More interestingly, this strain shows a high ability to interfere with the adhesion of Listeria monocytogenes to Caco 2 cells. Altogether, the results suggest that this broad-spectrum bacteriocin-producing strain has biotechnological potential to be developed as a protective agent in food preservation and as a probiotic.