Phytochemicals in lowbush wild blueberry inactivate Escherichia coli O157:H7 by damaging its cell membrane.
The antimicrobial activity and model of action of polyphenolic compounds extracted from lowbush wild blueberries (LWB) were studied against Escherichia coli O157:H7. Polyphenols in LWB were extracted using 80% vol/vol methanol and designated as total blueberry phenolics (TBP). The fraction was further separated by a C-18 Sep-Pak cartridge into monomeric phenolics acids (MPA) and anthocyanins plus proanthocyanidins (A&P). The A&P fraction was further separated into anthocyanins and proanthocyanidins using a LH-20 Sephadex column. Each fraction was diluted in 0.85% wt/vol NaCl, inoculated with E. coli O157:H7 to achieve 8 log colony-forming units (CFU)/mL, and incubated at 25 °C for 1 h. The survival populations of E. coli O157:H7 in the phenolic fractions were determined by a viable cell counts method. The permeability of the cell membrane of E. coli O157:H7 was determined using LIVE/DEAD viability assay, and the damage was visualized by using transmission electron microscopy (TEM). Significant (p<0.05) reductions of 5 log CFU/mL of E. coli O157:H7 were observed for MPA at 0.4 g/L gallic acid equivalents (GAE), A&P at 0.9 g/L GAE, and anthocyanins at 0.65 g/L GAE. Reductions of 6-7 CFU/mL were observed for MPA at 0.8 g/L GAE, A&P at 1.8 g/L GAE, and anthocyanins at 1.3 g/L GAE compared to the control. The cell membrane of E. coli O157:H7 exhibited a significantly increased permeability when treated with proanthocyanidins (0.15 g/L GAE), A&P (0.45 g/L GAE), anthocyanins (0.65 g/L GAE), and TBP (0.14 g/L GAE). TEM confirmed the inactivation and increased membrane permeability of E. coli O157:H7. This study demonstrated the antimicrobial effect of polyphenols from LWB against E. coli O157:H7 and the probable mode of action.
1 School of Food and Agriculture, The University of Maine , Orono, Maine.
Alison
A
Lacombe
Shravani
S
Tadepalli
Chen-An
CA
Hwang
Vivian C H
VC
Wu
D000872:Anthocyanins / Q000494:pharmacology; D029798:Blueberry Plants / Q000737:chemistry*; D002462:Cell Membrane / Q000187:drug effects*; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development; D005506:Food Contamination / Q000517:prevention & control; D005516:Food Microbiology; D050296:Microbial Viability / Q000187:drug effects; D046529:Microscopy, Electron, Transmission; D064209:Phytochemicals / Q000494:pharmacology*; D059808:Polyphenols / Q000494:pharmacology; D044945:Proanthocyanidins / Q000494:pharmacology
D000872:Anthocyanins; D064209:Phytochemicals; D059808:Polyphenols; D044945:Proanthocyanidins