Screening of lactic-acid bacteria from South African barley beer for the production of bacteriocin-like compounds

Characterization of a broad spectrum bacteriocin produced by Lactobacillus plantarum MXG-68 from Inner Mongolia traditional fermented koumiss

An agar well diffusion assay (AWDA) was used to isolate a high bacteriocin-producing strain with a broad spectrum of antibacterial activity, strain MXG-68, from Inner Mongolia traditional fermented koumiss. Lactobacillus plantarum MXG-68 was identified by morphological, biochemical, and physiological characteristics and 16S rDNA analysis. The production of antibacterial substance followed a growth-interrelated model, starting at the late lag phase of 4 h and arriving at a maximum value in the middle of the stationary phase at 24 h. Antibacterial activity was abolished or decreased in the presence of pepsin, chymotrypsin, trypsin, proteinase, and papain K. The results showed that antibacterial substances produced by L. plantarum MXG-68 were proteinaceous and could thus be classified as the bacteriocin, named plantaricin MXG-68. The molar mass of plantaricin MXG-68 was estimated to be 6.5 kDa, and the amino acid sequence of its N-terminal was determined to be VYGPAGIFNT. The mode of plantaricin MXG-68 action was determined to be bactericidal. Bacteriocin in cell-free supernatant (CFS) at pH 7 was stable at different temperatures (60 °C, 80 °C, 100 °C, 121 °C for 30 min; 4 °C and - 20 °C for 30 days), as well as at pH 2.0-10.0. Antibacterial activity maintained stable after treatment with organic solvents, surfactants, and detergents but increased in response to EDTA. Response surface methodology (RSM) revealed the optimum conditions of bacteriocin production in L. plantarum MXG-68, and the bacteriocin production in medium optimized by RSM was 26.10% higher than that in the basal MRS medium.

An evaluation and partial characterization of a bacteriocin produced by Lactococcus lactis subsp lactis ST1 isolated from goat milk

A bacteriocin-like inhibitory substance producing Lactococcus lactis subsp lactis strain, ST1, isolated from goat milk of Iranian origin and with broad spectrum of activity and desirable technical properties was used for evaluating some futures of bacteriocin inhibitory activity. Cell growth and bacteriocin production studies were carried out in MRS medium incubated statically under uncontrolled pH condition. The antibacterial activity presented a primary metabolite pattern and showed a rapid decrease at the stationary phase. Microaerobiosis and capnophily growth conditions resulted in higher bacteriocin production while aerobiosis showed negative effect on both cell growth and bacteriocin production. Bacteriocin production, on the other hand, was favored in MRS broth (pH; 6.5) inoculated with 0.1 ml l^-1 fresh culture when incubation was carried out at 30 °C. This indicated that the conditions resulted in higher levels of growth were frequently favoring bacteriocin production by ST1 as well. Decrease in activity, at the stationary growth phase, was much pronounced in favored growth condition. Nutrient depletion, deferent effect of low pH on bacteriocin production and/or protein degradation seemed more responsible for this phenomenon. The study also provided further data on new method for bacteriocin release from the cell wall of producer. It was clearly shown that both heating and ultrasound shock for 5 min at pH 2 could increase bacteriocin activity significantly. The release was more pronounced in the presence of 0.5% Tween80.

Comparing the efficacy of plasmid curing agents in Lactobacillus acidophilus

This study was mainly focused on plasmid profiling and plasmid characterisation of Lactobacillus acidophilus isolated from molasses. The secondary objective was to observe the efficacy of the plasmid curing agents acriflavine, ethidium bromide, novobiocin and SDS on L. acidophilus. Plasmid-free strains and cured derivatives harbouring only a single plasmid (6.2 kbp) were also obtained. Treatment of L. acidophilus with novobiocin at concentrations of 2.4 µg/ml could produce a large number of chloramphenicol- variants at a very high frequency (4.6%). These curing data confirmed that novobiocin acts as an effective curing agent for L. acidophilus.

Bacteriocins from Lactobacillus plantarum - production, genetic organization and mode of action: produção, organização genética e modo de ação

Bacteriocins are biologically active proteins or protein complexes that display a bactericidal mode of action towards usually closely related species. Numerous strains of bacteriocin producing Lactobacillus plantarum have been isolated in the last two decades from different ecological niches including meat, fish, fruits, vegetables, and milk and cereal products. Several of these plantaricins have been characterized and the aminoacid sequence determined. Different aspects of the mode of action, fermentation optimization and genetic organization of the bacteriocin operon have been studied. However, numerous of bacteriocins produced by different Lactobacillus plantarum strains have not been fully characterized. In this article, a brief overview of the classification, genetics, characterization, including mode of action and production optimization for bacteriocins from Lactic Acid Bacteria in general, and where appropriate, with focus on bacteriocins produced by Lactobacillus plantarum, is presented.

Antimicrobial activity of Enterococcus faecium L50, a strain producing enterocins L50 (L50A and L50B), P and Q, against beer-spoilage lactic acid bacteria in broth, wort (hopped and unhopped), and alcoholic and non-alcoholic lager beers

Enterococcus faecium L50 produces enterocin L50 (L50A and L50B) (EntL50, EntL50A and EntL50B), enterocin P (EntP) and enterocin Q (EntQ) and displays a broad antimicrobial spectrum against the most relevant beer-spoilage lactic acid bacteria (LAB) (i.e., Lactobacillus brevis and Pediococcus damnosus), which is mainly due to the production of EntL50 (EntL50A and EntL50B). Bacteriocin assays using in vitro-synthesized EntL50 (EntL50A and EntL50B) showed that both individual peptides possess antimicrobial activity on their own, EntL50A being the most active, but when the two peptides were combined a synergistic effect was observed. The only virulence genes detected in E. faecium L50 were efaAfm (cell wall adhesin) and ccf (sex pheromone), and this strain was susceptible to most clinically relevant antibiotics. E. faecium L50 survived but did not grow nor showed antimicrobial activity in hopped and unhopped wort, and alcoholic (1 and 5% ethanol, v/v) and non-alcoholic (0% ethanol, v/v) commercial lager beers. However, when unhopped wort was supplemented with 50% (v/v) MRS broth, E. faecium L50 grew and exerted antimicrobial activity similarly as in MRS broth. The enterocins produced by this strain were bactericidal (5 log decrease) against P. damnosus and Lb. brevis in a dose- and substrate-dependent manner when challenged in MRS broth, wort (hopped and unhopped), and alcoholic (1 and 5% ethanol, v/v) and non-alcoholic (0% ethanol, v/v) lager beers at 32 degrees C, and no bacterial resistances were detected even after incubation for 6-15 days. The enterocins in wort and lager beer (5% ethanol, v/v) withstood the heat treatments commonly employed in the brewing industry during mashing, wort boiling, fermentation, and pasteurization, and retained most of their antimicrobial activity in lager beer (5% ethanol, v/v) after long-term storage at 8 and 25 degrees C.

Isolation and purification of enterocin E-760 with broad antimicrobial activity against gram-positive and gram-negative bacteria

Strain NRRL B-30745, isolated from chicken ceca and identified as Enterococcus durans, Enterococcus faecium, or Enterococcus hirae, was initially identified as antagonistic to Campylobacter jejuni. The isolate produced a 5,362-Da bacteriocin (enterocin) that inhibits the growth of Salmonella enterica serovar Enteritidis, S. enterica serovar Choleraesuis, S. enterica serovar Typhimurium, S. enterica serovar Gallinarum, Escherichia coli O157:H7, Yersinia enterocolitica, Citrobacter freundii, Klebsiella pneumoniae, Shigella dysenteriae, Pseudomonas aeruginosa, Proteus mirabilis, Morganella morganii, Staphylococcus aureus, Staphylococcus epidermidis, Listeria monocytogenes, Campylobacter jejuni, and 20 other Campylobacter species isolates. The enterocin, E-760, was isolated and purified by cation-exchange and hydrophobic-interaction chromatographies. The proteinaceous nature of purified enterocin E-760 was demonstrated upon treatment with various proteolytic enzymes. Specifically, the antimicrobial peptide was found to be sensitive to beta-chymotrypsin, proteinase K, and papain, while it was resistant to lysozyme and lipase. The enterocin demonstrated thermostability by retaining activity after 5 min at 100 degrees C and was stable at pH values between 5.0 and 8.7. However, activity was lost below pH 3.0 and above pH 9.5. Administration of enterocin E-760-treated feed significantly (P < 0.05) reduced the colonization of young broiler chicks experimentally challenged and colonized with two strains of C. jejuni by more than 8 log(10) CFU. Enterocin E-760 also significantly (P < 0.05) reduced the colonization of naturally acquired Campylobacter species in market age broiler chickens when administered in treated feed 4 days prior to analysis.

Improvement of enterocin P purification process

Purification and heterologous expression of enterocin P (EntP), a sec-dependent bacteriocin produced by Enterococcus faecium, in Escherichia coli is described. PCR-amplified product of the enterocin P structural gene entP was cloned into plasmid pET-32b under the control of the inducible T7lac promoter. The neo-synthesized EntP was genetically modified by an addition of 3 extra amino acids, leading to recombinant EntRP. Active EntRP was recovered from the cytoplasmic soluble fraction of E. coli harboring appropriate recombinant plasmid, characterized by ELISA and Western-blot analysis and purified by immunoaffinity chromatography. The use of E. coli as heterologous host and pET-32b as expressing vector offers promising tools for heterologous production of class IIa bacteriocin.

The effect of prebiotics on production of antimicrobial compounds, resistance to growth at low pH and in the presence of bile, and adhesion of probiotic cells to intestinal mucus

AIMS

Screening of five bile salt-resistant and low pH-tolerant lactic acid bacteria for inhibitory activity against lactic acid bacteria and bacterial strains isolated from the faeces of children with HIV/AIDS. Determining the effect of prebiotics and soy milk-base on cell viability and adhesion of cells to intestinal mucus.

METHODS AND RESULTS

Lactobacillus plantarum 423, Lactobacillus casei LHS, Lactobacillus salivarius 241, Lactobacillus curvatus DF 38 and Pediococcus pentosaceus 34 produced the highest level of antimicrobial activity (12,800 AU ml(-1)) when grown in MRS broth supplemented with 2% (m/v) dextrose. Growth in the presence of Raftilose Synergy1, Raftilose L95 and Raftiline GR did not lead to increased levels of antimicrobial activity. Cells grown in the presence of Raftilose Synergy1 took longer to adhere to intestinal mucus, whilst cells grown in the absence of prebiotics showed a linear rate of binding.

CONCLUSIONS

A broad range of gram-positive and gram-negative bacteria were inhibited. Dextrose stimulated the production of antimicrobial compounds. Adhesion to intestinal mucus did not increase with the addition of prebiotics.

SIGNIFICANCE AND IMPACT OF THE STUDY

The strains may be incorporated in food supplements for HIV/AIDS patients suffering from gastro-intestinal disorders.

Characterization of a 3944 Da bacteriocin, produced by Enterococcus mundtii ST15, with activity against Gram-positive and Gram-negative bacteria

Strain ST15, isolated from soy beans, and identified as Enterococcus mundtii, produces a 3944 Da bacteriocin that inhibits the growth of Lactobacillus sakei, Enterococcus faecalis, Bacillus cereus, Propionibacterium sp., Clostridium tyrobutyricum, Acinetobacter baumanii, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus caprinus. Bacteriocin ST15 is inactivated by proteinase K, pronase, pepsin, protease and Triton X-114, but not when treated with catalase, alpha-amylase, Triton X-100, SDS, Tween 20, Tween 80, urea and EDTA. No change in activity was recorded after 2 h at pH values between 2.0 and 12.0, and after treatment at 100 degrees C for 90 min. Activity was, however, lost after treatment at 121 degrees C for 20 min. The mode of activity is bactericidal. The highest level of activity (51200 AU ml(-1)) was recorded when cells were grown in MRS broth, pH 6.5. Bacteriocin ST15 differs from other broad-spectrum bacteriocins described for Enterococcus spp. by being active against Gram-negative bacteria and by being smaller.

Effect of medium components on bacteriocin production by Lactobacillus plantarum strains ST23LD and ST341LD, isolated from spoiled olive brine

Bacteriocin ST23LD levels of 2930AU/OD were recorded in MRS broth (pH of 6.5) and in the presence of tryptone and yeast extract as sole nitrogen sources. Growth in MRS broth at an initial pH of 6.0 yielded only 1460AU/OD bacteriocin ST23LD. Activities of 5861AU/OD were recorded with maltose (20, 30 and 40 g/l) as sole carbon source and 9036AU/OD with the addition of 2.0-10.0 g/l KH2PO4. Bacteriocin ST341LD levels of 2850 and 2841AU/OD were recorded in MRS broth at an initial pH of 6.0 or 5.5, respectively. Only 709AU/OD was recorded in the same medium with an initial pH of 6.5. Bacteriocin ST341LD production was stimulated by the presence of tryptone. However, glucose at 10 and 40 g/l, or the presence of 5.0 or 10.0 g/l K2HPO4, resulted in a 50% reduction of bacteriocin activity. Glycerol in the growth medium repressed bacteriocin production. No increased bacteriocin production was recorded in medium supplemented with vitamins.

Application of PCR, rep-PCR and RAPD techniques for typing ofLactococcus lactis strains

A collection of 34 lactococcal strains were characterized using the polymerase chain reaction (PCR) for the acmA gene, and for the 16S rDNA gene, and DNA fingerprinting methods for randomly amplified polymorphic DNA (RAPD) and repetitive extragenic palindrome-PCR (rep-PCR). PCR experiments corroborated the genotypic identification of Lactococcus lactis strains by RAPD; rep-PCR did not distinguish between L. lactis subspecies. In some cases, phenotypic classification of L. lactis subspecies did not correlate with genotypic characterization.