Spontaneously Fermented Fruiting Bodies of Agaricus bisporus as a Valuable Source of New Isolates of Lactic Acid Bacteria with Functional Potential

The aim of the investigation was the identification and initial study of lactic acid bacteria (LAB) isolated from spontaneously fermented (at 28 °C for 5 days) fruiting bodies of white button mushrooms (Agaricus bisporus). The isolated LAB were preliminarily characterized applying the MALDI-TOF Biotyper. Moreover, further phenotypical, genotypical characteristics as well as some functional and technological properties of the selected microorganisms (including the ability to produce exopolysaccharides, cell hydrophobicity, resistance to low pH, and bile salt) were also analyzed. Among autochthonous LAB (isolated from the tested mushroom raw material), Leuconostoc mesenteroides predominated in spontaneously fermented A. bisporus, while Lactiplantibacillus paraplantarum, Lactiplantibacillus plantarum, and Lactococcus lactis were less abundant. The highest dynamics of acidification of the mushroom material were exhibited by isolates EK55 and EK4 that, after 24 h of incubation, were able to decrease the pH of the raw material up to 5.06 ± 0.021 and 5.17 ± 0.015, respectively. Furthermore, the analysis of bacterial cell hydrophobicity indicated that the highest values of this parameter were noted for L. plantarum isolates EK12 (29.59 ± 0.7%), EK55 (28.75 ± 0.551%), and EK5 (27.33 ± 1.516%). It was revealed some of the analyzed LAB (especially isolates L. plantarum EK55 and L. paraplantarum EK4) exhibited functional and technological potential that might be used in the formulation of novel starter cultures.

Adhesion Conditions of Bifidobacterium pseudocatenulatum KAKii to Human Enterocyte-like Caco-2 Cell Lines

Attachment ability of bifidobacteria strains to the human intestinal surface is an important criterion as a probiotic candidate. However, attachment activity is influenced by external and internal conditions. This study was conducted to screen cell surface hydrophobicity and adhesion scores of bifidobacteria strains. Attachment conditions (pH and exposure time) of selected strains to human enterocyte-like Caco-2 cell lines were subsequently investigated. Three different solvents (n-hexadecane, Toluene, and Xylene) were used in cell surface hydrophobicity analysis. Based on the results obtained, xylene presented consistent cell hydrophobicity activity in all strains used. Bifidobacterium pseudocatenulatum KAKii (wild type strain) gave promising cell hydrophobicity activity with no significant difference (p > 0.05) when compared to Lactobacillus plantarum NBRC 3070 with xylene as a solvent, and also presented a significantly higher attachment score (p < 0.05) compared to all strains used. The influence of pH and time exposure on adhesion of B. pseudocatenulatum KAKii to Caco-2 cells revealed that this strain was favored to attach to the intestinal cell line at pH 6 and after 120 min of exposure. Further optimization of attachment conditions will be carried out.

Effects of natural antimicrobials on bacterial cell hydrophobicity, adhesion, and zeta potential / Vpliv naravnih protimikrobnih snovi na bakterijsko hidrofobnost, adhezijo in zeta potencial

Interactions between bacterial cells and contact materials play an important role in food safety and technology. As bacterial strains become ever more resistant to antibiotics, the aim of this study was to analyse adhesion of selected foodborne bacterial strains on polystyrene surface and to evaluate the effects of natural antimicrobials on bacterial cell hydrophobicity, adhesion, and zeta potential as strategies of adhesion prevention. The results showed strain-specific adhesion rate on polystyrene. The lowest and the highest adhesion were found for two B. cereus lines. Natural antimicrobials ferulic and rosmarinic acid substantially decreased adhesion, whereas the effect of epigallocatechin gallate was neglectful. Similar results were found for the zeta potential, indicating that natural antimicrobials reduce bacterial adhesion. Targeting bacterial adhesion using natural extracts we can eliminate potential infection at an early stage. Future experimental studies should focus on situations that are as close to industrial conditions as possible.