Evaluation on the potential application of bacteriophages mixture to control the growth of Escherichia coli strains on selected vegetables

Abstract

Fresh vegetables are being identified as a source of foodborne outbreaks with increasing cases around the world. Escherichia coli has been used as one of the hygiene indicators to assess the hygiene status of a food product. Bacteriophages may offer a more natural means to eliminate or reduce microbial load to a safe level when compared to some commonly used conventional methods. This study evaluated the ability of bacteriophages mixture to reduce or eliminate mixed E. coli strains in selected vegetables. The bacteriophages mixture contained several types of bacteriophages isolates and was suspended in a phage buffer. An amount of 10 g of selected vegetables (cherry tomato, green mustard, bean sprout and lettuce respectively), was washed and subsequently added with high-density E. coli strains (108 CFU/mL) to create artificial contamination. Later, 100 µL of bacteriophages mixture (109 PFU/mL) was applied to each of the vegetables and allowed to dry for 15 min in a biosafety cabinet. Evaluation of the reduced number of viable E. coli cells (CFU/g) in each sample was done at 0 hr, 6 hrs, 24 hrs, 48 hrs and 72 hrs intervals, for two different storage conditions which were room temperature (30oC) and chilled temperature (4oC). The artificially contaminated sample not treated with bacteriophages mixture was used as a control. The overall results showed that the application of bacteriophage mixture was able to reduce viable E. coli cell numbers if compared with the control sample. Its application was found most efficient in reducing E. coli numbers in cherry tomatoes stored at room temperature if compared to other types of vegetables stored at either room or chilled temperature. It is safe to conclude that the efficiency of the bacteriophage mixture in controlling E. coli growth in the vegetables varied depending on the type of vegetables and also on the storage condition (chilled and room temperature). These findings will provide some preliminary data for the potential application of bacteriophage as a natural agent in controlling the growth of E. coli species in food, especially in minimally processed vegetables.