Isolation and characterisation of an enterocin P-producing Enterococcus lactis strain from a fresh shrimp (Penaeus vannamei)

Anti-Listerial Activity of Bacteriocin-like Inhibitory Substance Produced by Enterococcus lactis LBM BT2 Using Alternative Medium with Sugarcane Molasses

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, thus reaching final products by cross-contamination. With the growing demand for clean-label products, the search for natural antimicrobials as biopreservants, such as bacteriocins, has shown promising potential. In this context, this study aimed to evaluate the anti-listerial action of bacteriocins produced by Enterococcus lactis LBM BT2 in an alternative medium containing sugarcane molasses (SCM). Molecular analyses were carried out to characterize the strain, including the presence of bacteriocin-related genes. In the kinetic study on SCM medium E. lactis, LBM BT2 showed biomass and bacteriocin productions similar to those observed on a sucrose-based medium (control), highlighting the potential of the sugarcane molasses as a low-cost substrate. Stability tests revealed that the molecule remained active in wide ranges of pH (4-10) and temperature (60-100 °C). Furthermore, the proteolytic treatment reduced the biomolecule's antimicrobial activity, highlighting its proteinaceous nature. After primary purification by salting out and tangential flow filtration, the bacteriocin-like inhibitory substance (BLIS) showed bacteriostatic activity on suspended L. monocytogenes cells and against biofilm formation at a concentration of 0.625 mg/mL. These results demonstrate the potential of the produced BLIS as a biopreservative in the food industry.

Screening of bacteriocin-producing dairy Enterococcus strains using low-cost culture media

This study was carried out to select the bacteriocinogenic strains among Enterococcus strains isolated from Ukrainian traditional dairy products using a low-cost media for screening, that containing molasses and steep corn liquor. A total of 475 Enterococcus spp. strains were screened for antagonistic activity against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes indicator strains. The initial screening revealed that 34 Enterococcus strains during growth in low-cost medium containing corn steep liquor, peptone, yeast extract, and sucrose produced metabolites with inhibition activity against at least of the indicator strains used. Enterocin genes entA, entP, and entB were detected in 5 Enterococcus strains by PCR assay. Genes of enterocins A and P were found in E. faecalis 58 and Enterococcus sp. 226 strains, enterocins B and P - in Enterococcus sp. 423, enterocin A - in E. faecalis 888 and E. durans 248 strains. Bacteriocin-like inhibitory substances (BLIS) produced by these Enterococcus strains were thermostable and sensitive to proteolytic enzymes. To our knowledge, this is the first report on the isolation of enterocin-producing wild Enterococcus strains from traditional Ukrainian dairy products using a low-cost media for screening bacteriocinogenic strains. Strains E. faecalis 58, Enterococcus sp. 423, and Enterococcus sp. 226 are promising candidates for practical use as producers of bacteriocins with inhibitory activity against L. monocytogenes using molasses and steep corn liquor as cheap sources of carbon and nitrogen, that can significantly reduce the cost of industrial bacteriocin production. Further studies will be required to determine the dynamic of bacteriocin production, its structure, and mechanisms of antibacterial action.

The control of Fusarium growth and decontamination of produced mycotoxins by lactic acid bacteria

Global crop and food contamination with mycotoxins are one of the primary worldwide concerns, while there are several restrictions regarding approaching conventional physical and chemical mycotoxins decontamination methods due to nutrition loss, sensory attribute reduction in foods, chemical residual, inconvenient operation, high cost of equipment, and high energy consumption of some methods. In this regard, the overarching challenges of mycotoxin contamination in food and food crops require the development of biological decontamination strategies. Using certain lactic acid bacteria (LAB) as generally recognized safe (GRAS) compounds is one of the most effective alternatives due to their potential to release antifungal metabolites against various fungal factors species. This review highlights the potential applications of LAB as biodetoxificant agents and summarizes their decontamination activities against Fusarium growth and Fusarium mycotoxins released into food/feed. Firstly, the occurrence of Fusarium and the instrumental and bioanalytical methods for the analysis of mycotoxins were in-depth discussed. Upgraded knowledge on the biosynthesis pathway of mycotoxins produced by Fusarium offers new insightful ideas clarifying the function of these secondary metabolites. Moreover, the characterization of LAB metabolites and their impact on the decontamination of the mycotoxin from Fusarium, besides the main mechanisms of mycotoxin decontamination, are covered. While the thematic growth inhibition of Fusarium and decontamination of their mycotoxin by LAB is very complex, approaching certain lactic acid bacteria (LAB) is worth deeper investigations.

Bacteriocins: Properties and potential use as antimicrobials

A variety of bacteriocins originate from lactic acid bacteria, which have recently been modified by scientists. Many strains of lactic acid bacteria related to food groups could produce bacteriocins or antibacterial proteins highly effective against foodborne pathogens such as Staphylococcus aureus, Pseudomonas fluorescens, P. aeruginosa, Salmonella typhi, Shigella flexneri, Listeria monocytogenes, Escherichia coli O157:H7, and Clostridium botulinum. A wide range of bacteria belonging primarily to the genera Bifidobacterium and Lactobacillus have been characterized with different health‐promoting attributes. Extensive studies and in‐depth understanding of these antimicrobials mechanisms of action could enable scientists to determine their production in specific probiotic lactic acid bacteria, as they are potentially crucial for the final preservation of functional foods or for medicinal applications. In this review study, the structure, classification, mode of operation, safety, and antibacterial properties of bacteriocins as well as their effect on foodborne pathogens and antibiotic‐resistant bacteria were extensively studied.

Anti-Proliferative and Anti-Biofilm Potentials of Bacteriocins Produced by Non-Pathogenic Enterococcus sp

The incidence of cancer is increasing worldwide; likewise, the emergence of antibiotic-resistant biofilm-forming pathogens has led to a tremendous increase in morbidity and mortality. This study aimed to evaluate the probiotic properties of bacteriocin-producing Enterococcus sp. with a focus on their anti-biofilm and anticancer activities. Three of 79 Enterococcus isolates (FM43, FM65, FM50) were identified as producers of broad-spectrum bioactive molecules and were molecularly characterized as Enterococcus faecium by 16S rRNA sequencing. Phenotypic and genotypic screening for potential virulence factors revealed no factors known to promote pathogenicity. Treatment with proteinase K resulted in diminished antimicrobial activity; PCR-based screening for bacteriocin genes suggested the presence of both entA and entB genes that encode enterocins A and B, respectively. Maximum antimicrobial activity was detected during the early stationary phase, while activity disappeared after 24 h in culture. Bacteriocins from these isolates were stable at high temperatures and over a wide range of pH. Interestingly, crude supernatants of Ent. faecium FM43 and Ent. faecium FM50 resulted in significant destruction (80% and 48%, respectively; P < 0.05) of Streptococcus mutans ATCC 25175-associated preformed biofilms. Moreover, in vitro cytotoxicity assays revealed that extracts from Ent. faecium isolates FM43, FM65, and FM50 inhibited Caco-2 cell proliferation by 76.9%, 70%, and 85.3%, respectively. Taken together, the multifunctional capabilities of the microbial-derived proteins identified in our study suggest potentially important roles as alternative treatments for biofilm-associated infections and cancer.

In vitro assessment of potential probiotic characteristics of indigenous Lactococcus lactis and Weissella oryzae isolates from rainbow trout (Oncorhynchus mykiss Walbaum)

AIM

The objective of this study was to evaluate the probiotic potential of lactic acid bacteria (LAB) isolated from the intestinal ecosystem of rainbow trout.

METHODS AND RESULTS

Among LAB isolates, 10 of them were selected and screened for resistance to acid and bile salts, pancreatin, sodium chloride and temperature, hydrophobicity, growth profile and antimicrobial activity against fish pathogens. Then, biosafety assessments were investigated. Selected LAB tolerated to gastrointestinal physiological conditions, pancreatin and a range of sodium chloride and temperature. They also exhibited hydrophobicity and showed antagonistic activity against Streptococcus iniae and Yersinia ruckeri. Results of 16S rRNA gene sequencing showed that selected LAB belonged to the Lactococcus lactis (n = 5) and Weissella oryzae (n = 5) species. They exhibited no β-haemolytic activity, while six selected LAB were resistant to some antibiotics. None of them harboured virulence factors.

CONCLUSIONS

This study revealed probiotic characteristics of indigenous LAB isolated from the intestinal ecosystem of rainbow trout. However, further studies are required to confirm the effectiveness of these isolates as probiotics in aquaculture.

SIGNIFICANCE AND IMPACT OF THE STUDY

To the best of our knowledge, for the first time, the presence of probiotic candidates belonging to W. Oryzae was confirmed in fish intestinal microbiota.

Purification, characterization and mode of action of enterocin, a novel bacteriocin produced by Enterococcus faecium TJUQ1

Enterococcus faecium TJUQ1 with high bacteriocin-producing ability was isolated from pickled Chinese celery. In this study, enterocin TJUQ1 was purified by ammonium sulfate precipitation, reversed-phase chromatography (Sep-Pak C₈) and cation-exchange chromatography. The activity of the purified bacteriocin was 44,566.41 ± 874.69 AU/mg, which corresponds to a purification fold of 35.89 ± 2.34. The molecular mass was 5520 Da by MALDI-TOF MS and Tris-Tricine SDS-PAGE. The result of LC-MS/MS showed that the bacteriocin shared 59.15% identity with enterocin produced by E. faecium GN (accession no. O34071). PCR amplification revealed that E. faecium TJUQ1 possesses a gene encoding enterocin B with 60% identity to enterocin B. Circular dichroism (CD) spectroscopy showed that the molecular conformation was 32.6% helix, 19.5% beta, 12.9% turn and 35.0% random. The stability of enterocin TJUQ1 was measured. After exposure at 121 °C for 15 min, the residual antimicrobial activity of enterocin TJUQ1 was 85.95 ± 1.32%. The antimicrobial activity of enterocin TJUQ1 was still active over a pH range of 3-11. Enterocin TJUQ1 was inactivated after exposure to proteolytic enzymes but was not inactivated by lipase or amylase. These results showed that enterocin TJUQ1 was a novel class II bacteriocin. Enterocin TJUQ1 showed wide antibacterial activity against food-borne gram-negative and gram-positive pathogens, such as Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella enterica. The MIC was 5.26 ± 0.24 μg/mL against L. monocytogenes CMCC 1595. SEM and TEM were used to observe the changes in the morphological and intracellular organization of L. monocytogenes CMCC 1595 cells treated with enterocin TJUQ1. The results demonstrated that enterocin TJUQ1 increased extracellular electrical conductivity, facilitated pore formation, triggered the release of UV-absorbing materials, ATP and LDH, and even caused cell lysis in L. monocytogenes CMCC 1595 cells. Based on the characterization, the wide inhibitory spectrum and mode of action determined so far, enterocin TJUQ1 is a potential preservative for the food industry.

Production of Bioactive Peptides from Lactic Acid Bacteria: A Sustainable Approach for Healthier Foods

Traditional fermented foods where lactic acid bacteria (LAB) are present have been associated with beneficial effects on human health, and some of those benefits are related to protein-derived products. Peptides produced by LAB have attracted the interest of food industries because of their diverse applications. These peptides include ribosomally produced (bacteriocins) and protein hydrolysates by-products (bioactive peptides), which can participate as natural preservatives and nutraceuticals, respectively. It is essential to understand the biochemical pathways and the effect of growth conditions for the production of bioactive peptides and bacteriocins by LAB, in order to suggest strategies for optimization. LAB is an important food-grade expression system that can be used in the simultaneous production of peptide-based products for the food, animal, cosmetic, and pharmaceutical industries. This review describes the multifunctional proteinaceous compounds generated by LAB metabolism and discusses a strategy to use a single-step production process, using an alternative protein-based media. This strategy will provide economic advantages in fermentation processes and will also provide an environmental alternative to industrial waste valorization. New technologies that can be used to improve production and bioactivity of LAB-derived peptides are also analyzed.

Enterococci: Between Emerging Pathogens and Potential Probiotics

Enterococci are ubiquitous microorganisms that could be found everywhere; in water, plant, soil, foods, and gastrointestinal tract of humans and animals. They were previously used as starters in food fermentation due to their biotechnological traits (enzymatic and proteolytic activities) or protective cultures in food biopreservation due to their produced antimicrobial bacteriocins called enterocins or as probiotics, live cells with different beneficial characteristics such as stimulation of immunity, anti-inflammatory activity, hypocholesterolemic effect, and prevention/treatment of some diseases. However, in the last years, the use of enterococci in foods or as probiotics caused an important debate because of their opportunistic pathogenicity implicated in several nosocomial infections due to virulence factors and antibiotic resistance, particularly the emergence of vancomycin-resistant enterococci. These virulence traits of some enterococci are associated with genetic transfer mechanisms. Therefore, the development of new enterococcal probiotics needs a strict assessment with regard to safety aspects for selecting the truly harmless enterococcal strains for safe applications. This review tries to give some data of the different points of view about this question.

PreliminaryIn VitroEvaluation of the Probiotic Potential of the Bacteriocinogenic StrainEnterococcus lactisPMD74 Isolated from Ezine Cheese

Ezine cheese is a nonstarter and long-ripened cheese produced in the Mount of Ida region of Çanakkale, Turkey, with a protected designation of origin (PDO) status. The nonstarter fermented foods serve as sources for the isolation of novel strains. The present study aimed to report the novelty of the bacteriocinogenicEnterococcus lactisPMD74 strain and thein vitroassessment of its potential as a probiotic candidate. Additionally, the present study aimed to describe the technological and safety-related properties of the aforementioned strain. The strain exhibited high viability at pH 3.0, in the presence of pepsin, pancreatin, and bile salts (0.3% and 0.5%), and considerable survival passage through the stimulated digestion tests. The strain PMD74 exhibited substantial autoaggregative (41%) and coaggregative properties, which increased as a function of time. The highest coaggregation percentage was obtained withSalmonella entericaserotype Typhimurium SL1344 (23%), followed byStaphylococcus aureusATCC 6538 (10.3%) andEscherichia coliATCC 26922 (7.4%), respectively. The strain PMD74 was able to inhibit the growth of a number of Gram-positive bacteria, includingListeria monocytogenes,Lactobacillus sake,Staphylococcus aureus, andE. faecalis. The antimicrobial activity of the proteinaceous compound was calculated as 6400 AU·mL−1by the critical dilution method againstE. faecalisATTC 29212.γ-Hemolytic PMD74 was observed to be sensitive to vancomycin, ampicillin, penicillin, gentamicin, tetracycline, chloramphenicol, and tylosin. Among the four genes tested,E. lactisPMD74 was observed to be positive for three virulence determinants,ace,sprE, andgelE, and negative foresp. The amino acid decarboxylase activities were detected negative for histidine, tyrosine, and ornithine.E. lactisPMD74 was classified as a low acidifier, which suggested its possible role as an adjunct culture.E. lactisPMD74 exhibited considerable survival ability (8.86 log CFU·mL−1) in the acidic condition of fermented milk for a four-week-long storage period.

Bio-guided Purification and Mass Spectrometry Characterisation Exploring the Lysozyme-like Protein from Enterococcus lactis Q1, an Unusual Marine Bacterial Strain

Lactic acid bacteria produce various antibacterial peptides such as bacteriocins that are active against pathogenic and spoilage microorganisms. Very little attention has been paid to the production of lysozyme as an antimicrobial enzyme. The present work represents one of the few studies reporting lysozyme production by enterococci. Indeed, this study was first conducted to evaluate the antimicrobial activity of Enterococcus lactis Q1, an enterocin P-producing strain previously isolated from fresh shrimp (Penaeus vannamei), against multidrug-resistant clinical isolates. Results showed significant inhibitory activity (P < 0.05) towards diverse pathogens. The purification of the antimicrobial substances produced by Q1 strain leads to the isolation of two active fractions. The SDS-PAGE and mass spectrometry analyses of fraction number 2 (fraction 2) revealed the presence of a protein with molecular mass of 14.3 kDa. Additionally, the experimental results are consistent with mass spectra of industrial lysozyme (Fluka ref. 62970). The lysozyme produced by Enterococcus lactis Q1 strain was confirmed by a plate method against Micrococcus luteus ATCC 4698. Also, sensitivity of the Q1 strain to different concentrations of lysozyme was investigated. For the first time, this study shows that E. lactis Q1 produces lysozyme which could be an excellent candidate in food biopreservation or production of functional foods to promote health benefits.

Antimicrobial Activity of a Bacteriocin Produced by Enterococcus faecalis KT11 against Some Pathogens and Antibiotic-Resistant Bacteria

In this study, the antimicrobial activity of a bacteriocin produced by Enterococcus faecalis KT11, isolated from traditional Kargı Tulum cheese, was determined, and bacteriocin KT11 was partially characterized. The results showed that bacteriocin KT11 was antagonistically effective against various Gram-positive and Gram-negative test bacteria, including vancomycin- and/or methicillin-resistant bacteria. The activity of bacteriocin KT11 was completely abolished after treatment with proteolytic enzymes (proteinase K, α-chymotrypsin, protease and trypsin), which demonstrates the proteinaceous nature of this bacteriocin. Additionally, bacteriocin KT11 remained stable at pH values ranging from 2 to 11 and after autoclaving at 121℃ for 30 min. In addition, the activity of bacteriocin KT11 was stable after treatment with several surfactants (EDTA, SDS, Triton X-100, Tween 80 and urea) and organic solvents (chloroform, propanol, methanol, ethyl alcohol, acetone, hexane and ethyl ether). Cell-free supernatant of E. faecalis KT11 was subjected to ammonium sulfate precipitation and then desalted by using a 3.5-kDa cut-off dialysis membrane. The bacteriocin activity was determined to be 711 AU/mL in the dialysate. After tricine-SDS-PAGE analysis, one peptide band, which had a molecular weight of ~3.5 kDa, exhibited antimicrobial activity. Because the bacteriocin KT11, isolated from E. faecalis KT11, exhibits a broad antimicrobial spectrum, heat stability and stability over a wide pH range, this bacteriocin can be used as a potential bio-preservative in foods. Additionally, bacteriocin KT11 alone or in combination with conventional antibiotics may provide a therapeutic option for the treatment of multidrug-resistant clinical pathogens after further in vivo studies.

Genetic Analysis with Random Amplified Polymorphic DNA of the Multiple Enterocin-Producing Enterococcus lactis 4CP3 Strain and Its Efficient Role in the Growth of Listeria monocytogenes in Raw Beef Meat

In this manuscript, a multiple enterocin-producing Enterococcus lactis strain named 4CP3 was used to control the proliferation of Listeria monocytogenes in refrigerated raw beef meat model. Also, the intraspecific genetic differentiation of 4CP3 strain was assessed by Random Amplified Polymorphic DNA Polymerase Chain Reaction (RAPD-PCR) analysis. E. lactis 4CP3 strain was found to produce the enterocins A, B, and P. It displayed activity against L. monocytogenes EGDe 107776 by agar-well diffusion method. The application of E. lactis 4CP3 culture at 107 CFU/g in raw beef meat was evaluated using both ANOVA and ANCOVA linear models in order to examine its effect on the growth of the pathogen L. monocytogenes during refrigerated storage. Hence, a very interesting result in decreasing (P<0.05) and suppressing the growth of L. monocytogenes in refrigerated raw beef meat was shown during 28 days of storage. In conclusion, E. lactis 4CP3 strain might be useful for prevention of the proliferation and survival of L. monocytogenes in raw meat during refrigerated storage.

Safety, potential biotechnological and probiotic properties of bacteriocinogenic Enterococcus lactis strains isolated from raw shrimps

The aims of this study are to isolate new bacteriocinogenic lactic acid bacterial strains from white (Penaeus vannamei) and pink (Palaemon serratus) raw shrimps and evaluate their technological and probiotic potentialities. Seven strains were selected, among fifty active isolates, as producing interesting antimicrobial activity. Identified as Enterococcus lactis, these isolates were able to produce enterocins A, B and/or P. The safety aspect, assessed by microbiological and molecular tests, demonstrated that the strains were susceptible to relevant antibiotics such as vancomycin, negative for haemolysin and gelatinase activities, and did not harbour virulence and antibiotic resistance genes. The assessment of potential probiotic and technological properties showed a low or no lipolytic activity, moderate milk-acidifying ability, high reducing power, proteolytic activity and tolerance to bile (P < 0.05) and good autoaggregation and coaggregation capacities. Two strains designated as CQ and C43 exhibiting high enzymatic activities and bile salt hydrolase activity were found to display high survival under simulated in vitro oral cavity and gastrointestinal tract conditions caused by presence of lysozyme, pepsin, pancreatin, bile salts and acidic pH. This study highlights safe Enterococcus lactis strains with great technological and probiotic potentials for future application as new starter, adjunct, protective or probiotic cultures in food industry.