Characterization of two safe Enterococcus strains producing enterocins isolated from Egyptian dairy products

Safety Evaluation, Biogenic Amine Formation, and Enzymatic Activity Profiles of Autochthonous Enterocin-Producing Greek Cheese Isolates of the Enterococcus faecium/durans Group

Autochthonous single (Ent+) or multiple (m-Ent+) enterocin-producing strains of dairy enterococci show promise for use as bioprotective adjunct cultures in traditional cheese technologies, provided they possess no pathogenic traits. This study evaluated safety, decarboxylase activity, and enzymatic (API ZYM) activity profiles of nine Ent+ or m-Ent+ Greek cheese isolates previously assigned to four distinct E. faecium (represented by the isolates KE64 (entA), GL31 (entA), KE82 (entA-entB-entP) and KE77 (entA-entB-entP-bac31)) and two E. durans (represented by the isolates KE100 (entP) and KE108 (entP-bac31-cyl)) strain genotypes. No strain was β-hemolytic or harbored vanA and vanB or the virulence genes agg, ace, espA, IS16, hyl, or gelE. All strains were of moderate to high sensitivity to ampicillin, ciprofloxacin, chloramphenicol, erythromycin, gentamicin, penicillin, tetracycline, and vancomycin, except for the E. faecium KE64 and KE82 strains, which were resistant to erythromycin and penicillin. All cheese strains showed moderate to strong esterase-lipase and aminopeptidase activities and formed tyramine, but none formed histamine in vitro. In conclusion, all Ent+ or m-Ent+ strain genotypes of the E. faecium/durans group, except for the cyl-positive E. durans KE108, were safe for use as adjunct cultures in traditional Greek cheeses. Further in situ biotechnological evaluations of the strains in real cheese-making trials are required.

Lipolytic Postbiotic from Lactobacillus paracasei Manages Metabolic Syndrome in Albino Wistar Rats

The current study investigates the capacity of a lipolytic Lactobacillus paracasei postbiotic as a possible regulator for lipid metabolism by targeting metabolic syndrome as a possibly safer anti-obesity and Anti-dyslipidemia agent replacing atorvastatin (ATOR) and other drugs with proven or suspected health hazards. The high DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS [2,2'-azino-bis (3-ethyl benzothiazoline-6-sulphonic acid)] scavenging activity and high activities of antioxidant enzyme such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-px) of the Lactobacillus paracasei postbiotic (cell-free extract), coupled with considerable lipolytic activity, may support its action against metabolic syndrome. Lactobacillus paracasei isolate was obtained from an Egyptian cheese sample, identified and used for preparing the postbiotic. The postbiotic was characterized and administered to high-fat diet (HFD) albino rats (100 and 200 mg kg^-1) for nine weeks, as compared to atorvastatin (ATOR; 10 mg kg^-1). The postbiotic could correct the disruption in lipid metabolism and antioxidant enzymes in HFD rats more effectively than ATOR. The two levels of the postbiotic (100 and 200 mg kg^-1) reduced total serum lipids by 29% and 34% and serum triglyceride by 32-45% of the positive control level, compared to only 25% and 35% in ATOR's case, respectively. Both ATOR and the postbiotic (200 mg kg^-1) equally decreased total serum cholesterol by about 40% and 39%, while equally raising HDL levels by 28% and 30% of the positive control. The postbiotic counteracted HFD-induced body weight increases more effectively than ATOR without affecting liver and kidney functions or liver histopathology, at the optimal dose of each. The postbiotic is a safer substitute for ATOR in treating metabolic syndrome.

Catfish Glycoprotein, a Highly Powerful Safe Preservative of Minced Beef Stored at 4 °C for 15 Days

Minced beef is a very perishable food product, due to its vulnerability to microbial contamination and its fast quality deterioration. In the current study, the biological efficiency of different concentrations (0, 50 and 100 µg g⁻¹) of the antibacterial catfish glycoprotein (CFG) was estimated as a possible improver of the storability and safety of minced beef preserved at 4 °C for 15 days. CFG (50 and 100 µg g⁻¹) could efficiently control the changes in meat pH during 15 days storage at 4 °C to be within the normal, acceptable levels (6.4 and 6.2, respectively), equalizing the level of the control for minced beef after 6 days of storage under similar conditions. Likewise, the level of metmyoglobin in minced beef stored at the same conditions was maintained at 53.67 and 46.67% by CFG supplementation at 50 and 100 µg g⁻¹, respectively, at the 15th day of storage, which is comparable to the 6th day in case of the control samples. However, the antioxidant effect of CFG against lipid peroxidation was less effective. The antibacterial action of CFG was most pronouncedly powerful and efficient. Supplementation of minced beef with CFG at 50 and 100 µg g⁻¹ significantly (p < 0.05) decreased the bacterial counts at all the time inspection points as compared to the control. After 15 days of storage, the total viable bacteria, psychrotrophic bacterial count and coliforms count were reduced to 3.12, 2.65 and 0.0 log CFU g⁻¹, respectively, in response to CFG (50 µg g⁻¹), and 2.41, 2.04 and 0.0 log CFU g⁻¹, respectively, in response to CFG (100 µg g⁻¹); this compared to 5.13, 4.78 and 2.5 in the control samples after only six days cold storage. Using CFG at 50, 100 and 200 µg g⁻¹ in rat diets did not affect their liver or kidney functions, reflecting the non-toxicity of this substance. Substantiating the antioxidant and antimicrobial potential of CFG in minced beef storage may support its use as a naturally powerful and safe food preservative, as well as a shelf-life extender.

Nisin Production by Enterococcus hirae DF105Mi Isolated from Brazilian Goat Milk

The purpose of this study was to select the promising biopreservation bacteriocin producer strain from goat milk and characterize the expressed bacteriocin, related to its physiological and biochemical properties and specificity of operon encoding production and expression of antimicrobial peptide. Brazilian goat milk was used as the source for the selection of bacteriocin-producing lactic acid bacteria. One strain (DF105Mi) stood out for its strong activity against several Listeria monocytogenes strains. Selected strain was identified based on the biochemical and physiological characteristics and 16s rRNA analysis. The bacteriocin production and inhibitory spectrum of strain DF105Mi were studied, together with the evaluation of the effect of temperature, pH, and chemicals on bacteriocin stability and production, activity, and adsorption to target cells as well as to the cell surface of bacteriocin producers. Physiological and bio-molecular analyses based on targeting of different genes, parts of nisin operon were performed in order to investigate the hypothesis that the studied strain can produce and express nisin. Based on biochemical, physiological, and 16s rRNA analysis, the strain DF105Mi was classified as Enterococcus hirae. The selected strain produces a bacteriocin which is stable in a wide range of pH (2.0-12.0), temperature (up to 120 °C), presence of selected chemicals and presents adsorption affinity to different test organisms, process influenced by environmental conditions. Higher bacteriocin production by Ent. hirae DF105Mi was recorded during stationary growth phase, but only when the strain was cultured at 37 °C. The strain's genetic analysis indicated presence of the genes coding for the production of the bacteriocin nisin. This result was confirmed by cross-checking the sensitivity of the produced strain to commercial nisin A. The strong anti-Listeria activity, bacteriocin adsorption, and stability of produced bacteriocin indicate that Ent. hirae DF105Mi presents a differentiated potential application for biopreservation of fermented dairy products.

Enterococcus faecium isolated from healthy dogs for potential use as probiotics

This study aimed to isolate and identify enterococci obtained from fresh faecal swabs of 16 healthy dogs. Following molecular identification, all isolates were screened against the most critical virulence factors as well as enterocin (bacteriocin) determinants to confirm that the isolated enterococcus was safe to be used as host-specific probiotic. Enterococcus faecium was isolated and confirmed in 8 out of the 16 samples. Regarding the assessment of the virulence determinants, E. faecium strains were negative for tested (gelE and esp) virulence genes. Furthermore, the genome was evaluated for the incidence of five known enterocin genes by specific PCR amplification. Four strains encoding entAS-48 gene were found, while only one strain harboured the entL50A/B gene. Based on these results, five of the E. faecium isolated in this study were considered as promising probiotic candidates for dogs.

Approaches for enhancing in situ detection of enterocin genes in thermized milk, and selective isolation of enterocin-producing Enterococcus faecium from Baird-Parker agar

Enterococci are naturally selected for growth in thermized ewes'/goats' milk mixtures used for traditional cooked hard cheese processing in Greece. A culture-independent PCR-based approach was applied to detect the presence of enterocin-encoding genes in naturally culture-enriched thermized milk (TM). Portions of TM (63 °C, 30 s) collected from a commercial cheese plant before addition of starters were fermented at 37 °C for 48 h to facilitate growth of indigenous enterococci. The multiple enterocin-producing (m-Ent+) Enterococcus faecium KE82 and the nisin A-producing Lactococcus lactis subsp. cremoris M104 served as bacteriocin-positive inocula in separate TM treatments. The PCR results revealed a constant presence of the enterocin A, B and P genes in TM fermented naturally at 37 °C. Eleven out of 42 (26.2%) lactic isolates from the enriched TM cultures without inoculation were Ent+ E. faecium assigned to three biotypes. Biotype I (4 isolates) included single entA possessors, whereas biotype II (5 isolates) and biotype III (2 isolates) were m-Ent+ variants profiling entA-entB-entP and entA-entB genes, respectively. Biotype II displayed the strongest antilisterial activity in vitro. Surprisingly, 85.7% (6/7) of the m-Ent+ E. faecium were selectively isolated from Baird-Parker agar, reflecting their natural resistance to 0.01% tellurite contained in the egg yolk supplement. No cytolysin-positive E. faecalis or other Ent+ Enterococcus spp. were isolated. In conclusion, commercially thermized Greek milk is a natural pool or 'reservoir' of antagonistic Ent+ or m-Ent+ E. faecium strains that can be easily detected and recovered by applying this PCR-based approach to naturally fermented milks or cheese products.

Evaluation of marine bacteriocinogenic enterococci strains with inhibitory activity against fish-pathogenic Gram-negative bacteria

Use of lactic acid bacteria (LAB) as probiotics may provide an alternative to the use of antibiotics in aquaculture. LAB strains isolated from wild fish viscera and skin were evaluated for bacteriocin production and safety aspects (lack of antibiotic resistance, production of virulence factors). 16S rRNA gene sequences revealed the presence of Enterococcus faecium (13 isolates) and Lactococcus lactis (3 isolates) from fish samples. Pulsed-field gel electrophoresis analyses of the 13 enterococci isolates showed that they were all clustered, with greater than 95% similarity. However, RAPD analysis revealed significant molecular diversity between enterococci strains. Six enterococci strains were chosen and evaluated for their antibacterial activities. These strains produced a bacteriocin-like substance and exhibited a broad spectrum of inhibition against pathogenic bacteria isolated from diseased fish, including Streptococcus parauberis, Vagococcus spp., and Carnobacterium maltaromaticum, and in particular against the Gram-negative bacteria Flavobacterium frigidarium, Vibrio pectenicida, V. penaeicida, and Photobacterium damselae. The inhibition activity towards bacterial indicator strains was at a maximum when bacteria were grown at 37°C. However, bacteriocin production was observed at 15°C after 12 h of incubation. Only structural genes of enterocins A and B were detected by PCR in the 6 enterococci strains, suggesting the production of these enterocins. In addition, these strains did not harbor any virulence factors or any significant antibiotic resistance, and they tolerated bile. Our results suggest that enterococci are an important part of the bacterial flora of fish and that some strains have the potential to be used as probiotics.

Bacteriocin-Producing Lactic Acid Bacteria Isolated from Mangrove Forests in Southern Thailand as Potential Bio-Control Agents: Purification and Characterization of Bacteriocin Produced by Lactococcus lactis subsp. lactis KT2W2L

The aim of this work was to purify and characterize the bacteriocin produced by Lactococcus lactis subsp. lactis KT2W2L previously isolated from mangrove forests in southern Thailand, in order to evaluate its potential as new food protective agent. The active peptide from the cell-free supernatant of this strain was purified in 4 steps: (1) precipitation with 70 % saturated ammonium sulfate, (2) elution on a reversed-phase cartridge using different concentrations of acetonitrile, (3) cation-exchange chromatography and (4) final purification by reversed-phase HPLC on a C8 column. The molecular mass of 3,329.5254 Da of the purified bacteriocin, determined by mass spectrometry, is nearly identical to that of peptide nisin Z. The activity of the purified bacteriocin was unaffected by pH (2.0-10.0), thermostable but was sensitive to proteolytic enzymes. The bacteriocin activity was stable after 8 weeks of storage at -20 °C and 7 weeks of storage at 4 °C, but decreased after 3 weeks of storage at 37 °C. It was stable when incubated for 1 month at 4 °C in 0-30 % NaCl. Inhibitory spectrum of this bacteriocin showed a wide range of activity against similar bacterial strains, food-spoilage and food-borne pathogens. L. lactis subsp. lactis KT2W2L was sensitive to kanamycin, penicillin and tetracycline but resistant to ampicillin, gentamicin and vancomycin. The fragment obtained after amplification of genomic DNA from L. lactis subsp. lactis KT2W2L, with specific primers for bacteriocin genes, presented 99 % homology to the nisin Z gene. PCR amplification demonstrated that L. lactis subsp. lactis KT2W2L does not harbor virulence genes cylA, cylB, efaAfs and esp. The bacteriocin and its producing strain may find application as bio-preservatives for reduction in food-spoilage and food-borne pathogens in food products.

Protective effect of Enterococcus faecalis DAPTO 512 on the intestinal tract and gut mucosa: milk allergy application

The allergenicity of β-lactoglobulin (β-Lg) was studied by using Ussing chamber in a murine model of β-Lg allergy supplemented with hydrolysates obtained after fermentation of milk for 48 h at 37 (°)C with Enterococcus faecalis DAPTO 512, isolated from cow milk and identified by 16S rDNA sequence analysis. Balb/c mice were sensitised intraperitoneally with β-Lg. Three groups of mice were formed: group 1, composed of naive mice used as control received only NaCl; group 2, positive control composed of mice sensitised intraperitoneally with β-Lg; group 3, formed by mice which were given hydrolysates of 48 h then sensitised with β-Lg. After 48 h of fermentation β-casein and β-Lg were degraded by E. faecalis DAPTO 512. β-Lg immunisation was associated with strong IgG and IgE production in case of positive controls and a significant increase in short current circuit (Isc) and high conductance (G) responses were observed. The control and the hydrolysate groups showed a significant decrease in the production of IgG and IgE anti β-Lg compared to the positive control. The allergenic potential of β-Lg was markedly reduced in the group that received hydrolysates (Isc and G remained unchanged after intestine challenge with β-Lg). The histological scrutiny showed villi atrophy, lymphocyte hyperplasia and a significant chorion detachment in the positive control group. In the group administered with hydrolysates of fermented milk, inflammatory signs were lower, the villi were long and thin and lymphocytes were less dense. The results showed that feeding of milk fermented with E. faecalis DAPTO 512 during 18 days prior to β-Lg allergy induction exerts a protecting effect on the murine intestine and induces a significant decrease in the β-Lg allergenicity.