Characterization of a Cryptic Rolling-Circle Replication Plasmid pMK8 from Enterococcus durans 1-8

A novel cryptic plasmid from Enterococcus durans 1-8, designated as pMK8, was sequenced and analyzed in this study. It consists of 3337 bp with a G + C content of 33.11%. Sequence analysis of pMK8 revealed three putative open reading frames (ORFs). Based on homology, two of them were identified as genes encoding replication initiation (RepC) and mobilization (Mob) protein, respectively. Sequence analysis revealed a pT181 family double-strand origin (dso) and a putative single-strand origin (sso) located upstream of the repC gene. Sequence homology analysis indicated that the sso belongs to the ssoW family. Southern hybridization confirmed the presence of single-strand DNA (ssDNA) intermediates, suggesting that pMK8 replicates via the RCR mechanism. Furthermore, the relative copy number of pMK8 was estimated by real-time PCR to be 175 ± 14 copies in each cell.

Characterization of Enterococcus durans 152 bacteriocins and their inhibition of Listeria monocytogenes in ham

Listeria monocytogenes is a nonfastidious, widely occurring foodborne pathogen that is a major challenge to the food industry. Enterococcus durans 152, a confirmed L. monocytogenes-control microorganism, was isolated from floor drain samples from a food processing facility. In this study, the two bacteriocins produced by E. durans 152 were characterized and identified as Dur 152A (an enterocin L50A derivative with two amino acid substitutions of I→M) and enterocin L50B. The bacteriocins were then partially purified and evaluated for inhibitory activity to L. monocytogenes in deli ham. Results revealed that at 400 AU/ml, the bacteriocins prevented growth of listeria in deli ham for at least 10 weeks at 8 °C and at least 30 days at 15 °C. For comparison, 500 ppm Nisin controlled listeria growth for up to 6 weeks at 8 °C and up to 18 days at 15 °C. These findings reveal the potential for the bacteriocins of E. durans 152 to serve as anti-listerial agents in deli meat.

Phenotypic and Genotypic Alterations of Durancin GL-Resistant Enterococcus durans Strains

The emergence and spread of bacteriocin-resistant bacteria threaten the efficiency of bacteriocin usage as food preservatives. In this experiment, 19 selected Enterococcus durans strains acquired resistance after exposure to durancin GL, and the mutants had similar intermediate levels of resistance. One wild-type E. durans KLDS 6.0603 and its two resistant mutants, E. durans KLDS 6.0603-2 and E. durans KLDS 6.0603-3, were used to characterize phenotypic and genotypic differences. Approximately 100 μg/mL of durancin GL can penetrate the cytoplasmic membrane of E. durans KLDS 6.0603, causing damage to bacterial cells, but cannot penetrate E. durans KLDS 6.0603-2 and KLDS 6.0603-3 membranes. Unsaturated fatty acid content in resistant strains was significantly increased compared with wild-type strains, indicating that the former has more fluidity of cell membrane than the latter. Decreased mannose phosphotransferase system gene expression (mptD) was observed in the two resistant strains. Results showed that the factors, including the increased unsaturated fatty acid and decreased mptD expression, could contribute to durancin GL resistance.

Alanine-Scanning Mutational Analysis of Durancin GL Reveals Residues Important for Its Antimicrobial Activity

Durancin GL is a novel class IIa bacteriocin with 43 residues produced by Enterococcus durans 41D. This bacteriocin demonstrates narrow inhibition spectrum and potent antimicrobial activity against several Listeria monocytogenes strains, including nisin-resistant L. monocytogenes NR30. A systematic alanine-scanning mutational analysis with site-directed mutagenesis was performed to analyze durancin GL residues important for antimicrobial activity and specificity. Results showed that three mutations lost their antimicrobial activity, ten mutations demonstrated a decreased effect on the activity, and seven mutations exhibited relatively high activity. With regard to inhibitory spectrum, four mutants demonstrated a narrower antimicrobial spectrum than wild-type durancin GL. Another four mutants displayed a broader target cell spectrum and increased potency relative to wild-type durancin GL. These findings broaden our understanding of durancin GL residues important for its antimicrobial activity and contribute to future rational design of variants with increased potency.

Individual responses of mother sows to a probiotic Enterococcus faecium strain lead to different microbiota composition in their offspring

Pregnant gilts were fed the probiotic Enterococcus faecium NCIMB10415 (SF68) one month before birth of piglets. DNA extracts of sow faeces taken in weekly intervals as well as extracts from the intestine of their offspring during the suckling period at 12 and 26 days of life were analysed by denaturing gradient gel electrophoresis (DGGE) and quantitative PCR. DGGE profiles of faecal bacterial communities from three out of six probiotic-fed sows were distinctly different from the control and other probiotic-fed sows at all time points after probiotic supplementation. The probiotic-fed sows and their offspring were therefore divided into non-responder (n=3) and responder (n=3) groups. The probiotic strain significantly increased faecal lactobacilli cell numbers in mother sows, which could be assigned to a significant increase of Lactobacillus amylovorus and Lactobacillus acidophilus. Responding sows showed a more pronounced increase than non-responding sows. Similarly, suckling piglets from non-responding and responding sows showed numeric and significant differences for different bacterial groups and species. DGGE profiles of suckling piglets from responding sows also grouped more closely than profiles from control animals. Non-metric multiscaling of suckling piglets showed the same tendency for suckling piglets, but not for post-weaning piglets. This study showed that the probiotic E. faecium strain modified the faecal microbiota of sows. This modification is carried over to their offspring, but leads to changes that do not mirror the quantitative composition in the mother sow. Individual variations in the bacterial composition of mother sows before probiotic feed intake may influence the impact of a probiotic in sows and their offspring.

Enterocin TW21, a novel bacteriocin from dochi-isolated Enterococcus faecium D081821

AIMS

Purification and characterization of a novel bacteriocin produced by strain Enterococcus faecium D081821.

METHODS AND RESULTS

Enterococcus faecium D081821, isolated from the traditional Taiwanese fermented food dochi (fermented black beans), was previously found to produce a bacteriocin against Listeria monocytogenes and some Gram-positive bacteria. This bacteriocin, termed enterocin TW21, was purified from culture supernatant by ammonium sulfate precipitation, Sep-Pak C18 cartridge, ion-exchange and gel filtration chromatography. Mass spectrometry analysis showed the mass of the peptide to be approximately 5300·6 Da. The N-terminal amino acid sequencing yielded a partial sequence NH2 -ATYYGNGVYxNTQK by Edman degradation, and it contains the consensus class IIa bacteriocin motif YGNGV in the N-terminal region. The open reading frame (ORF) encoding the bacteriocin was identified from the draft genome sequence of Enterococcus faecium D081821, and sequence analysis of this peptide indicated that enterocin TW21 is a novel bacteriocin.

CONCLUSIONS

Enterococcus faecium D081821 produced a bacteriocin named enterocin TW21, the molecular weight and amino acid sequence both revealed it to be a novel bacteriocin.

SIGNIFICANT AND IMPACT OF STUDY

A new member of class IIa bacteriocin was identified. This bacteriocin shows great inhibitory ability against L. monocytogenes and could be applied as a natural food preservative.

Strategies to improve the bacteriocin protection provided by lactic acid bacteria

Lactic acid bacteria (LAB) produce a wide variety of antimicrobial peptides (bacteriocins) which contribute to the safety and preservation of fermented foods. This review discusses strategies that have been or could be employed to further enhance the commercial application of bacteriocins and/or bacteriocin-producing LAB for food use.

BlpC-regulated bacteriocin production in Streptococcus thermophilus

Streptococcus thermophilus B59671 produces a bacteriocin with anti-pediococcal activity, but genes required for its production are not characterized. Genome sequencing of S. thermophilus has identified a genetic locus encoding a quorum sensing (QS) system that regulates production of class II bacteriocins. However, in strains possessing this gene cluster, production of bacteriocin like peptides (Blp) was only observed when excess pheromone was provided. PCR analysis revealed this strain possessed blpC, which encodes the 30-mer QS pheromone. To investigate if BlpC regulates bacteriocin production in S. thermophilus B59671, an integrative vector was used to replace blpC with a gene encoding for kanamycin resistance and the resulting mutant did not inhibit the growth of Pediococcus acidilactici. Constitutive expression of blpC from a shuttle vector restored the bacteriocin production, confirming the blp gene cluster is essential for bacteriocin activity in S. thermophilus B59671.