Title: Phytochemicals in lowbush wild blueberry inactivate Escherichia coli O157:H7 by damaging its cell membrane Authors
|Lacombe, Alison -|
|Tadepalli, Shravani -|
|Wu, Vivian -|
Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 2013
Publication Date: N/A
Interpretive Summary: Extracts from lowbush blueberry fruits have been shown to kill microbes. This study identified the chemicals in the extract and the mechanism against a foodborne pathogen, Escherichia coli O157:H7. Blueberries extract was separated into four phenolic fractions, blueberry phenolics, monomeric phenolic acids, anthocyanins plus proanthocyanidins, anthocyanins. The effects of these polyphenols in killing E. coli O157:H7 and damaging the cell membrane of E. coli O157:H7 were determined. Monomeric phenolic acids at 0.4 g/L gallic acid equivalent (GAE), anthocyanins plus proanthocyanidins at 0.9 g/L GAE, or anthocyanins at 0.65 g/L GAE were capable of killing 5 log CFU/ml of E. coli O157:H7. These polyphenols killed E. coli O157:H7 by damaging and increasing the permeability of the cell membrane. Findings from this study will help food producers in using blueberry constituents as natural preservatives in food products.
Technical Abstract: The antimicrobial activity and model of action of polyphenolic compounds extracted from lowbush wild blueberries (LWB) were studied against E. coli O157:H7. Polyphenols in LWB were extracted using methanol:H20 (80:20, v/v), dried and reconstituted in water 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% w/v NaCl, inoculated with E. coli O157:H7 to achieve 8 log CFU/ml and incubated at 25 C for one hour. The survival populations of E. coli O157:H7 in the phenolic fractions were determined by a viable cell counts method. The permeability of the membrane of was determined using live/dead viability assay and the damage of membrane was examined by using transmission electron microscopy (TEM). Significant (P less than less than 0.05) reductions of 5 log CFU/ml of E. coli O157:H7 were observed for MPA at 0.4 g/L gallic acid equivalent (GAE), A&P at 0.9 g/L GAE, and anthocyanins at 0.65 g/L GAE. Significant (P less than 0.05) reductions of 6-7 log 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 on selective agar compared to the control. The cells of E. coli O157:H7 exhibited significant increase in membrane permeability 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 that the inactivation and increased membrane permeability of E. coli O157:H7 were due to damages to the cell membrane caused by the phenolic fractions. This study demonstrated the antimicrobial effect of polyphenols from LWB against E. coli O157:H7 and the probable mode of action.