Characterisation of an antiviral pediocin-like bacteriocin produced by Enterococcus faecium

Isolation and identification of bacteriocinogenic strain of Lactobacillus plantarum with potential beneficial properties from donkey milk

AIMS

The goal of this study was to isolate and characterize a lactic acid bacteria (LAB) from donkey milk with potential beneficial properties.

METHODS AND RESULTS

Lactic acid bacteria were isolated from donkey milk and identified based on physiological, biochemical and molecular methods. The isolate that presented highest bacteriocin potential (Lactobacillus plantarum LP08AD) was evaluated for the production of bacteriocin, including stability in the presence of various enzymes, surfactants, salts, pH and temperatures. Bactericidal effect of bacteriocin LP08AD on Listeria monocytogenes, Enterococcus faecium and Lactobacillus curvatus was shown for actively growing and stationary cells. Similar growth and bacteriocin production were observed when strain LP08AD was cultured in MRS broth at 30°C or 37°C. Bacteriocin LP08AD adhered at low levels on the producer cells (200 AU ml(-1) ). The presence of plantaricin W gene on the genomic DNA was recorded based on PCR. Good growth for strain LP08AD was recorded in MRS broth with pH from 5·0 to 9·0 and LP08AD grew well in the absence of oxbile or concentration below 0·8%. Lact. plantarum LP08AD was applied to the small intestinal epithelial polarized monolayers of H4, PSIc1 and CLAB and demonstrated low attachment ability on all cell lines studied, with values with a similar behaviour for cells from human and pig origin.

CONCLUSIONS

Bacteriocin-producing Lact. plantarum LP08AD might be useful in the design of novel functional foods with potential probiotic or biopreservation properties.

SIGNIFICANCE AND IMPACT OF THE STUDY

To the best of our knowledge, this is the first report on detection and characterization of bacteriocinogenic Lact. plantarum from donkey milk. The strain LP08AD shows to have potential beneficial properties, as demonstrated by the use of noncancerogenic cell lines.

Bacteriocin PJ4 active against enteric pathogen produced by Lactobacillus helveticus PJ4 isolated from gut microflora of wistar rat (Rattus norvegicus): partial purification and characterization of bacteriocin

The increase of multidrug-resistant pathogens and the restriction on the use antibiotics due to its side effects have drawn attention to the search for possible alternatives. Bacteriocins are small antimicrobial peptides produced by numerous bacteria. Much interest has been focused on bacteriocins because they exhibit inhibitory activity against pathogens. Lactic acid bacteria possess the ability to synthesize antimicrobial compounds (like bacteriocin) during their growth. In this study, an antibacterial substance (bacteriocin PJ4) produced by Lactobacillus helveticus PJ4, isolated from rat gut microflora, was identified as bacteriocin. It was effective against wide assay of both Gram-positive and Gram-negative bacteria involved in various diseases, including Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus. The antimicrobial peptide was relatively heat-resistant and also active over a wide pH range of 2-10. It has been partially purified to homogeneity using ammonium sulfate precipitation and size exclusion chromatography and checked on reverse-phase high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of bacteriocin PJ4 purified through size exclusion chromatography resolved ~6.5 kDa protein with bacteriocin activity. The peptide is inactivated by proteolytic enzymes, trypsin, and lipase but not when treated with catalase, α-amylase, and pepsin. It showed a bactericidal mode of action against the indicator strains E. coli MTCC443, Lactobacillus casei MTCC1423, and E. faecalis DT48. Such characteristics indicate that this bacteriocin may be a potential candidate for alternative agents to control important pathogens.

Biochemical, antimicrobial and molecular characterization of a noncytotoxic bacteriocin produced by Lactobacillus plantarum ST71KS

Lactobacillus (Lb.) plantarum ST71KS was isolated from homemade goat feta cheese and identified using biochemical and molecular biology techniques. As shown by Tricine-SDS-PAGE, this lactic acid bacterium produces a bacteriocin (ST71KS) with an estimated molecular weight of 5.0 kDa. Bacteriocin ST71KS was not affected by the presence of α-amylase, catalase and remained stable in a wide range of pH and after treatment with Triton X-100, Triton X-114, Tween 20, Tween 80, NaCl, SDS, urea and EDTA. This bacteriocin also remained active after being heated at 100 °C for 2 h and even after 20 min at 121 °C; however, it was inactivated by proteolitic enzymes. Production of bacteriocin ST71KS reached 6400 AU/mL during stationary growth phase of Lb. plantarum cultivated in MRS at 30 °C and 37 °C. Bacteriocin ST71KS displayed a bactericidal effect against Listeria monocytogenes strains 603 and 607 and did not adsorb to the producer cells. Lb. plantarum ST71KS harbors two bacteriocin genes with homology to plantaricin S and pediocin PA-1. These characteristics indicate that bacteriocin ST71KS is a class IIa bacteriocin. The peptide presented no toxic effect when tested in vitro with kidney Vero cells, indicating safe technological application to control L. monocytogenes in foods.

Enterococcus faecium isolated from Lombo, a Portuguese traditional meat product: characterisation of antibacterial compounds and factors affecting bacteriocin production

Strain ST211CH, identified as a strain of Enterococcus faecium, isolated from Lombo produced a bacteriocin that inhibited the growth of Enterococcus spp., Listeria spp., Klebsiella spp., Lactobacillus spp., Pseudomonas spp., Staphylococcus spp. and Streptococcus spp. The mode of action of the bacteriocin named as bacteriocin ST211Ch was bactericidal against Enterococcus faecalis ATCC19443. As determined by Tricine-SDS-PAGE, the approximate molecular mass of the bacteriocin was 8.0 kDa. Loss in antimicrobial activity was recorded after treatment with proteolytic enzymes. Maximum activity of bacteriocin ST211Ch was measured in broth cultures of E. faecium strain ST211Ch after 24 h; thereafter, the activity was reduced. Bacteriocin ST211Ch remained active after exposure to various temperatures and pHs, as well as to Triton X-100, Tween-80, Tween-20, sodium dodecyl sulfate, NaCl, urea and EDTA. Effect of media components on production of bacteriocin ST211Ch was also studied. On the basis of PCR reactions targeting different bacteriocin genes, i.e. enterocins, curvacins and sakacins, no evidences for the presence of these genes in the total DNA of E. faecium strain ST211Ch was obtained. The bacterium most probably produced a bacteriocin different from those mentioned above. Based on the antimicrobial spectrum, stability and mode of action of bacteriocin ST211CH, E. faecium strain ST211Ch might be considered as a potential candidate with beneficial properties for use in biopreservation to control food spoilage bacteria.

Oral administration of milk fermented with Lactococcus lactis subsp. cremoris FC protects mice against influenza virus infection

AIMS

To evaluate the protective effects of oral administration of milk fermented with a Lactococcus strain against influenza virus (IFV) infection in a mouse model.

METHODS AND RESULTS

Milk fermented with exopolysaccharide-producing Lactococcus lactis subsp. cremoris (L. cremoris) FC was orally administered to BALB/c mice for 12 days. Mice were intranasally infected with IFV A/New Caledonia/20/99 (H1N1) on day 8, and survival was determined for 14 days after IFV infection. Survival rate and body weight loss after IFV infection in the L. cremoris FC fermented milk-administered group were significantly improved compared with those in the control group. In the unfermented milk-administered group, survival rate was not improved, whereas body weight loss was slightly improved compared with that in the control group. The mean virus titre in the lung of the L. cremoris FC fermented milk-administered group 3 days after infection was significantly decreased compared with that in the control group.

CONCLUSIONS

These results suggest that oral administration of milk fermented with L. cremoris FC protects mice against IFV infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results demonstrate that oral administration of milk fermented with exopolysaccharide-producing Lactococcus strains might protect host animals against IFV infection.

Inactivation of feline calicivirus and murine norovirus during Dongchimi fermentation

Among the traditional fermented vegetables in Korea, Dongchimi is a type of kimchi with a large water base. We aimed to investigate the survival of norovirus surrogates during Dongchimi fermentation. Dongchimi spiked with feline calicivirus (FCV) or murine norovirus (MNV) was prepared following a traditional recipe. Dongchimi was initially fermented at room temperature overnight and then kept at 4 °C. The number of lactic acid bacteria, pH, acidity, and virus titer were measured 0, 1, 2, 3, 5, 7, 10, 15, 20 days after fermentation. During the fermentation process, lactic acid bacteria and acidity increased. At the end of the fermentation, population of FCV and MNV decreased about 4.12 and 1.47 log units, respectively. Based on the significant reduction of norovirus surrogate during Dongchimi fermentation, we conclude that the risk of norovirus in Dongchimi may be low.

Identification, characterization, and recombinant expression of epidermicin NI01, a novel unmodified bacteriocin produced by Staphylococcus epidermidis that displays potent activity against Staphylococci

We describe the discovery, purification, characterization, and expression of an antimicrobial peptide, epidermicin NI01, which is an unmodified bacteriocin produced by Staphylococcus epidermidis strain 224. It is a highly cationic, hydrophobic, plasmid-encoded peptide that exhibits potent antimicrobial activity toward a wide range of pathogenic Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA), enterococci, and biofilm-forming S. epidermidis strains. Purification of the peptide was achieved using a combination of hydrophobic interaction, cation exchange, and high-performance liquid chromatography (HPLC). Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis yielded a molecular mass of 6,074 Da, and partial sequence data of the peptide were elucidated using a combination of tandem mass spectrometry (MS/MS) and de novo sequencing. The draft genome sequence of the producing strain was obtained using 454 pyrosequencing technology, thus enabling the identification of the structural gene using the de novo peptide sequence data previously obtained. Epidermicin NI01 contains 51 residues with four tryptophan and nine lysine residues, and the sequence showed approximately 50% identity to peptides lacticin Z, lacticin Q, and aureocin A53, all of which belong to a new family of unmodified type II-like bacteriocins. The peptide is active in the nanomolar range against S. epidermidis, MRSA isolates, and vancomycin-resistant enterococci. Other unique features displayed by epidermicin include a high degree of protease stability and the ability to retain antimicrobial activity over a pH range of 2 to 10, and exposure to the peptide does not result in development of resistance in susceptible isolates. In this study we also show the structural gene alone can be cloned into Escherichia coli strain BL21(DE3), and expression yields active peptide.

Dextransucrase from the mutant of Pediococcus pentosaceus (PPm) is more stable than the wild type

A comparative study on both wild type and mutant of Pediococcus pentosaceus for dextransucrase activity, its stability, dextran synthesizing activity, antibiotic sensitivity and carbohydrate utilization was performed. The wild type P. pentosaceus had specific activity of 0.58 U/mg whereas the mutant showed that of 1.0 U/mg with 72% enhancement. The antibiogram of 27 antibiotics tested against mutant showed significant differences with 9 antibiotics when compared to wild type. In carbohydrate fermentation profile, trehalose, galactose, maltose, lactose and fructose are metabolized by both the strains, but weakly in case of mutant. Stabilization of purified dextransucrase from wild type and mutant with various stabilizers was studied at 30 and 4 °C. Both enzymes were more stable at 4 °C. Among various stabilizers such as dextran (100 kDa, 10 μg/ml), glycerol (0.5%, v/v), PEG 8000 (10 μg/ml) and Tween 80 (0.5%, v/v), Tween 80 provided maximum stabilization at 4 and 30 °C. The mutant showed better stabilization than that of the wild type at both 30 and 4 °C. The loss of activity at 30 °C after 24 h in wild type and mutant in the presence of Tween 80 was only 34 and 32%, respectively, whereas the loss of activity in control of wild type and mutant was 76 and 59%, respectively. After 15 days at 4 °C, the loss of activity in control of wild type and mutant in the presence of Tween 80 was only 15 and 8%, respectively, whereas at 30 °C, the loss of activity in control of wild type and mutant was 49 and 42% respectively. Half-life of the enzyme with Tween 80 was 28.5 and 33.5 h for wild type and mutant, respectively, at 30 °C and 52.1 and 106.6 days for wild type and mutant respectively, at 4 °C.

Purification and characterization of enterocin MC13 produced by a potential aquaculture probiontEnterococcus faeciumMC13 isolated from the gut ofMugil cephalus

A bacteriocin producer strain MC13 was isolated from the gut of Mugil cephalus (grey mullet) and identified as Enterococcus faecium . The bacteriocin of E. faecium MC13 was purified to homogeneity, as confirmed by Tricine sodium dodecyl sulphate – polyacrylamide gel electrophoresis (SDS–PAGE). Reverse-phase high-performance liquid chromatography (HPLC) analysis showed a single active fraction eluted at 26 min, and matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry analysis showed the molecular mass to be 2.148 kDa. The clear zone in native PAGE corresponding to enterocin MC13 band further substantiated its molecular mass. A dialyzed sample (semicrude preparation) of enterocin MC13 was broad spectrum in its action and inhibited important seafood-borne pathogens: Listeria monocytogenes , Vibrio parahaemolyticus , and Vibrio vulnificus . This antibacterial substance was sensitive to proteolytic enzymes: trypsin, protease, and chymotrypsin but insensitive to catalase and lipase, confirming that inhibition was due to the proteinaceous molecule, i.e., bacteriocin, and not due to hydrogen peroxide. Enterocin MC13 tolerated heat treatment (up to 90 °C for 20 min). Enterococcus faecium MC13 was effective in bile salt tolerance, acid tolerance, and adhesion to the HT-29 cell line. These properties reveal the potential of E. faecium MC13 to be a probiotic bacterium. Enterococcus faecium MC13 could be used as potential fish probiotic against pathogens such as V. parahaemolyticus, Vibrio harveyi , and Aeromonas hydrophila in fisheries. Also, this could be a valuable seafood biopreservative against L. monocytogenes.

Development of Class IIa Bacteriocins as Therapeutic Agents

Class IIa bacteriocins have been primarily explored as natural food preservatives, but there is much interest in exploring the application of these peptides as therapeutic antimicrobial agents. Bacteriocins of this class possess antimicrobial activity against several important human pathogens. Therefore, the therapeutic development of these bacteriocins will be reviewed. Biological and chemical modifications to both stabilize and increase the potency of bacteriocins are discussed, as well as the optimization of their production and purification. The suitability of bacteriocins as pharmaceuticals is explored through determinations of cytotoxicity, effects on the natural microbiota, and in vivo efficacy in mouse models. Recent results suggest that class IIa bacteriocins show promise as a class of therapeutic agents.

Effect of recombinant divercin RV41, structural variants and the activators of potassium channels on Listeria monocytogenes EGDe

The effect of recombinant divercin RV41 (DvnRV41) and its structural variants on the K-channel formation was determined. The growth of Listeria monocytogenes EGDe (sensitive phenotype) and its isogenic strain (resistant phenotype) was assessed in the presence of DvnRV41 combined or not with pinacidil, NS1619, cromakalim (as K-channel activators), iberiotoxin and glipizide (as K-channel blockers). The combined action of DvnRV41 and K activators permitted formation of ATP-dependent pores. The combination of DvnRV41 and ATP-dependent pore activator cromakalim inhibited the growth of sensitive strain. The antilisterial activity of structural variants was less important than that of DvnRV41 but their mode of action remained overall similar.