A model to study the inhibition of bacterial contamination of vegetable sprouts by plant based polyphenols

Abstract or Summary

Consumption of sprouts is popular worldwide due to their high nutritional value. Sprouts are an inexpensive food containing essential vitamins, minerals and anti-oxidants. However, several outbreaks of food borne diseases associated with sprouts have resulted in public concern of sprout consumption in some countries. A common cause of food-borne diseases is contamination by shiga-toxin producing Escherichia coli. These bacteria can form biofilms on the surface of sprouts and are difficult to eradicate. We investigated the ability of plant bioactives, particularly polyphenols, to reduce or eliminate bacterial adhesion and therefore contamination on a sprouted legume (alfalfa) model. Three day old alfalfa sprouts were inoculated with two concentration levels (103 and 105 CFU g/L) of a non-toxigenic E. coli strain for 4 h before washing and enumerating adhered cells by direct plating on MacConkey Agar and Plate Count Agar. A range of plant polyphenols were screened for antibacterial capacity, using a micro broth dilution assay to determine their minimum inhibitory concentration (MIC). The most effective polyphenol was selected for treatment of bacterial biofilms both in vitro (by the crystal violet (CV) method), and in-vivo (on sprouts), which were then examined by scanning electron microscopy (SEM). Of the polyphenols assayed, the MIC experiments showed that the gallic acid had greatest antibacterial activity against E. coli. Biofilm assays (CV and SEM) experiments showed a reduction in biofilm formation on sprouts in the presence of gallic acid also. The results of our study suggest polyphenols are potentially effective and natural intervention strategy to retard bacterial adhesion and biofilm formation on sprouts.