Purification and mass spectrometry based characterization of a pediocin produced by Pediococcus acidilactici 13.

Bacteriocins are antimicrobial peptides produced by several bacterial species. Among the bacteriocins pediocin-like bacteriocins have a significant inhibitory activity on the foodborne pathogens especially on Listeria monocytogenes. This study aims to select a simple and usable purification method to purify/concentrate the antimicrobial peptide and characterization of the bacteriocin produced by Pediococcus acidilactici 13 by using proteomic approaches which is a recent omic technology. For purification dialysis, ultrafiltration method was used, and as a result of this study the bacteriocin activity reached 819,200 AU/mL from 102,400 AU/mL initially. Two dimensional gel electrophoresis and then matrix-assisted laser desorption ionization/time of flight mass spectrometry (MALDI-TOF MS) analysis were carried out to identify the current bacteriocin and related proteins. Obtained data revealed similarity to pediocin PA-1 transport/processing ATP-binding protein PedD (accession number: P36497), pediocin operon PedC (accession number: Q68GC4) and bacteriocin pediocin PA-1 (accession number: P29430) from UniProtKB/Swiss-Prot databank, thus the bacteriocin produced by P. acidilactici 13 is considered similar to pediocin PA-1.

Predictive model for the reduction of heat resistance of Listeria monocytogenes in ground beef by the combined effect of sodium chloride and apple polyphenols.

We investigated the combined effect of three internal temperatures (57.5, 60, and 62.5°C) and different concentrations (0 to 3.0 wt/wt.%) of sodium chloride (NaCl) and apple polyphenols (APP), individually and in combination, on the heat-resistance of a five-strain cocktail of Listeria monocytogenes in ground beef. A complete factorial design (3×4×4) was used to assess the effects and interactions of heating temperature, NaCl, and APP. All 48 combinations were tested twice, to yield 96 survival curves. Mathematical models were then used to quantitate the combined effect of these parameters on heat resistance of the pathogen. The theoretical analysis shows that compared with heat alone, the addition of NaCl enhanced and that of APP reduced the heat resistance of L. monocytogenes measured as D-values. By contrast, the protective effect of NaCl against thermal inactivation of the pathogen was reduced when both additives were present in combination, as evidenced by reduction of up to ~68% in D-values at 57.5°C; 65% at 60°C; and 25% at 62.5°C. The observed high antimicrobial activity of the combination of APP and low salt levels (e.g., 2.5% APP and 0.5% salt) suggests that commercial and home processors of meat could reduce the salt concentration by adding APP to the ground meat. The influence of the combined effect allows a reduction of the temperature of heat treatments as well as the salt content of the meat. Meat processors can use the predictive model to design processing times and temperatures that can protect against adverse effects of contaminated meat products. Additional benefits include reduced energy use in cooking, and the addition of antioxidative apple polyphenols may provide beneficial health affects to consumers.

Comparison of methods for the microbiological identification and profiling of Cronobacter species from ingredients used in the preparation of infant formula.

Cronobacter spp. (formerly Enterobacter sakazakii) can be isolated from a wide range of foods and environments, and its association with neonatal infections has drawn considerable attention from regulatory authorities. The principle route of neonatal infection has been identified as the ingestion of contaminated infant formula. A number of methods have been developed to identify Cronobacter spp., however these were before the most recent (2012) taxonomic revision of the genus into seven species. In this study, phenotyping, protein profiling and molecular methods were used to identify Cronobacter strains which had been recently isolated from ingredients used in the preparation of infant formula. Pulsed field gel electrophoresis revealed that different Cronobacter strains had been recovered from the same food products. All isolates were identified as Cronobacter sakazakii according to four genus specific PCR-probes and protein profiling using MALDI-TOF analysis. However, 16S rDNA sequence analyses and fusA allele sequencing gave more accurate identification: four strains were C. sakazakii, one strain was Cronobacter malonaticus and the remaining strain was Cronobacter universalis. Multilocus sequence typing showed the strains were different sequence types. These results demonstrate the presence of different Cronobacter species in food ingredients used in the preparation of infant formula, and also the need for molecular identification and profiling methods to be revised according to taxonomic revisions.

Some growth parameters and antimicrobial activity of a bacteriocin-producing strain Pediococcus acidilactici 13.

Some growth parameters and bacteriocin production by the strain Pediococcus acidilactici 13, were screened in this study. The inhibitor substance produced by this strain showed strong antimicrobial activity at 204,800 AU/mL (Activity Units/mL) against the gram positive food borne pathogen, Listeria monocytogenes, when the incubation temperature was 37 degrees C and the initial pH of the medium, TGE (Trypton Glucose Yeast Extract), was 6.0. The bacteriocin-producing strain had considerable resistance NaCl, since the strain maintained to growth up to 10% NaCl concentrations at TGE broth and was able to grow in a wide temperature range (25-50 degrees C). The strain was identified as P. acidilactici with API 50 CHL, as well as with 16S rRNA gene sequencing.