Discrimination among Pediocin AcH/PA-1 producer strains by comparison of pedB and pedD amplified genes and by multiplex PCR assay

Beneficial features of pediococcus: from starter cultures and inhibitory activities to probiotic benefits

Pediococci are lactic acid bacteria (LAB) which have been used for centuries in the production of traditional fermented foods. There fermentative abilities were explored by the modern food processing industry in use of pediococci as starter cultures, enabling the production of fermented foods with distinct characteristics. Furthermore, some pediococci strains can produce bacteriocins and other antimicrobial metabolites (AMM), such as pediocins, which are increasingly being explored as bio-preservatives in various food matrices. Due to their versatility and inhibitory spectrum, pediococci bacteriocins and AMM are being extensively researched not only in the food industry, but also in veterinary and human medicine. Some of the pediococci were evaluated as potential probiotics with different beneficial areas of application associated with human and other animals' health. The main taxonomic characteristics of pediococci species are presented here, as well as and their potential roles and applications as starter cultures, as bio-preservatives and as probiotic candidates.

Heterologous expression of pediocin/papA in Bacillus subtilis

Listeria monocytogenes is a food-borne pathogen. Pediocin is a group IIα bacteriocin with anti-listeria activity that is naturally produced by Pediococcus acidilactic and Lactobacillus plantarum. The pedA/papA gene encodes pediocin/plantaricin. In native hosts, the expression and secretion of active PedA/PapA protein rely on the accessory protein PedC/PapC and ABC transporter PedD/PapD on the same operon. The excretion machines were also necessary for pediocin protein expression in heterologous hosts of E. coli, Lactobacillus lactis, and Corynebacterium glutamicum. In this study, two vectors carrying the codon sequence of the mature PapA peptide were constructed, one with and one without a His tag. Both fragments were inserted into the plasmid pHT43 and transformed into Bacillus subtilis WB800N. The strains were induced with IPTG to secrete the fused proteins PA1 and PA2. Supernatants from both recombinant strains can inhibit Listeria monocytogenes ATCC54003 directly. The fused protein possesses inhibition activity as a whole dispense with removal of the leading peptide. This is the first report of active pediocin/PapA expression without the assistance of PedCD/PapCD in heterogeneous hosts. In addition, the PA1 protein can be purified by nickel-nitrilotriacetic acid (Ni-NTA) metal affinity chromatography.

Functional properties of novel protective lactic acid bacteria and application in raw chicken meat against Listeria monocytogenes and Salmonella enteritidis

In this study 635 lactic acid bacteria of food origin were evaluated for their potential application as protective cultures in foods. A stepwise selection method was used to obtain the most appropriate strains for application as protective cultures in chicken meat. Specifically, all strains were examined for antimicrobial activity against various Gram positive and Gram negative pathogenic and spoilage bacteria. Strains exhibiting anti-bacterial activity were subsequently examined for survival in simulated food processing and gastrointestinal tract conditions, such as high temperatures, low pH, starvation and the presence of NaCl and bile salts. Selected strains where then examined for basic safety properties such as antibiotic resistance and haemolytic potential, while their antimicrobial activity was further investigated by PCR screening for possession of known bacteriocin genes. Two chosen strains were then applied on raw chicken meat to evaluate their protective ability against two common food pathogens, Listeria monocytogenes and Salmonella enteritidis, but also to identify potential spoilage effects by the application of the protective cultures on the food matrix. Antimicrobial activity in vitro was evident against Gram positive indicators, mainly Listeria and Brochothrix spp., while no antibacterial activity was obtained against any of the Gram negative bacteria tested. The antimicrobial activity was of a proteinaceous nature while strains with anti-listerial activity were found to possess one or more bacteriocin genes, mainly enterocins. Strains generally exhibited sensitivity to pH 2.0, but good survival at 45 degrees C, in the presence of bile salts and NaCl as well as during starvation, while variable survival rates were obtained at 55 degrees C. None of the strains was found to be haemolytic while variable antibiotic resistance profiles were obtained. Finally, when the selected strains Enterococcus faecium PCD71 and Lactobacillus fermentum ACA-DC179 were applied as protective cultures in chicken meat against L. monocytogenes and S. enteritidis respectively, a significantly reduced growth of these pathogenic bacteria was observed. In addition, these two strains did not appear to have any detrimental effect on biochemical parameters related to spoilage of the chicken meat.

Pediocins: The bacteriocins of Pediococci. Sources, production, properties and applications

Class IIa bacteriocins from lactic acid bacteria are small, cationic proteins with antilisterial activity. Within this class, the pediocins are those bacteriocins that share a highly conserved hydrophilic and charged N-terminal part harboring the consensus sequence -YGNGV- and a more variable hydrophobic and/or amphiphilic C-terminal part. Several pediocins have been isolated and characterized. Despite the structural similarities, their molecular weight varies, as well as their spectrum of antimicrobial activity. They exhibit important technological properties, e.g. thermostability and retaining of activity at a wide pH range, which along with the bactericidal action against Gram-positive food spoilage and pathogenic bacteria, make them an important class of biopreservatives. Much new information regarding the pediocins has emerged during the last years. In this review, we summarize and discuss all the available information regarding the sources of pediocins, the characteristics of their biosynthesis and production in fermentation systems, the characteristics of the known pediocin molecules, and their antibacterial action. The advances made by genetic engineering in improving the features of pediocins are also discussed, as well as their perspectives for future applications.

Autolytic activity and pediocin-induced lysis in Pediococcus acidilactici and Pediococcus pentosaceus strains

AIMS

To evaluate the autolytic phenotype of Pediococcus acidilactici and P. pentosaceus, the peptidoglycan hydrolases content and the effect of pediocin AcH/PA-1 and autolysins on cell lysis.

METHODS AND RESULTS

The autolytic phenotype of Pediococcus strains was evaluated under starvation conditions in potassium phosphate buffer. The strains tested showed an extent of autolysis ranging between 40 and 90% after 48 h of starvation at 37 degrees C. Peptidoglycan hydrolase content was evaluated by renaturing sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) using cells of Micrococcus lysodeikticus as a target for the enzymatic activity and a major activity band migrating at about 116 kDa was detected. Additional secondary lytic bands migrating in a range of molecular weight between 45 and 110 kDa were also detected. The lytic activity, evaluated in the presence of different chemicals, was retained in 15 mM CaCl2 and in a range of pH between 5 and 9.5 but was strongly reduced in presence of 8% NaCl and in the presence of protease inhibitors. The substrate specificity of peptidoglycan hydrolases of Pediococcus strains was evaluated in renaturing SDS-PAGE incorporating cells of different bacterial species. Lytic activity was detected against cells of Lactococcus lactis subsp. lactis, L. delbrueckii subsp. bulgaricus, Lactobacillus helveticus and Listeria monocytogenes. The interaction between pediocin AcH/PA-1 and autolysis was evaluated and a relevant effect of bacteriocin in cell-induced lysis was observed.

CONCLUSIONS

The autolytic phenotype is widely distributed among P. acidilactici and P. pentosaceus and the rate of autolysis is high in the majority of the analysed strains. Several autolytic bands, detected by renaturing SDS-PAGE, retained their activity against several lactic acid bacteria and L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The characterization of the autolytic phenotype of Pediococcus acidilactici and P. pentosaceus strains should expand the knowledge of their role in fermentation processes where these species occur as primary or secondary bacterial population.

Genomic diversity within the genus Pediococcus as revealed by randomly amplified polymorphic DNA PCR and pulsed-field gel electrophoresis

The genomic diversity of 33 previously assigned strains from six species within the genus Pediococcus was assessed by randomly amplified polymorphic DNA (RAPD) PCR and pulsed-field-gel electrophoresis (PFGE). The RAPD PCR patterns produced by two separate random primers, termed P1 (ACGCGCCCT) and P2 (ATGTAACGCC), were compared by the Pearson correlation coefficient and the unweighted pair group method with arithmetic averages clustering algorithm. Pattern variations between repeat samples set a strain discrimination threshold of less than 70% similarity. P1 and P2 primers alone and in combination produced 14, 21, and 28 distinct patterns, respectively. When each strain was assigned with a type strain with which it shared the highest level of similarity, both primers grouped 17 of the 27 strains to their proposed species. PFGE following genomic digestion with the restriction enzymes ApaI, NotI, and AscI produced 30, 32, and 28 distinct macrorestriction patterns, respectively. Specific DNA fragments within the NotI and AscI macrorestriction patterns for each strain were observed that allowed 27 of the 33 strains to be assigned to their proposed species. For example, following digestion with AscI, all Pediococcus parvulus strains were characterized by two DNA fragments, one of approximately 220 kb and another between 700 and 800 kb. The exceptions correlated with those observed with both RAPD PCR primers and included three P. damnosus and two P. pentosaceus strains that grew at temperatures regarded as nonpermissive for their proposed species but not for those with which they grouped.

Genomic subpopulations within the species Pediococcus acidilactici detected by multilocus typing analysis: relationships between pediocin AcH/PA-1 producing and non-producing strains

A high degree of genetic polymorphism among P. acidilactici strains was highlighted by a multilocus typing approach analysing several housekeeping genes and by sampling the whole genome using random amplified polymorphic DNA (RAPD) fingerprint analysis performed by using a single primer pedA gene targeted in low-stringency amplification conditions. Restriction fragment length polymorphism of the rpoC, ldhD/L and mle genes, and a modified RAPD analysis, permitted the grouping of Pediococcus acidilactici strains in seven genotypes (I-VII). Genotypic results obtained by analysing housekeeping genes involved in the transcription/translation machinery and in primary metabolism were supported by phylogenetic analysis based on the partial 16S rDNA sequencing of a reference strain of each of the seven clusters obtained. Three of the seven genotypes detected showed relationships with pediocin AcH/PA-1 production and carbohydrate fermentation patterns: all pediocin-producing and sucrose-positive strains were grouped in genotype VII, melibiose-, sucrose- and raffinose-positive strains in genotype VI, and arabinose-positive strains in genotype V.