Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/16/2004
Publication Date: 8/1/2004
Citation: Leverentz, B., Conway, W.S., Janisiewicz, W.J., Camp, M.J. 2004. Optimizing concentration and timing of a phage spray application to reduce Listeria monocytogenes on fruit tissue. Journal of Food Protection. 67(8):1682-1686. Interpretive Summary: The fresh-cut produce industry is a rapidly growing $10 to $12 billion a year industry, accounting for over 10% of all produce sales in the U.S., and has an annual growth rate in the double digits. However, along with the rapid development of this industry, new problems have arisen in the food safety area. Various sanitizers, which are effective in reducing foodborne pathogen populations on whole produce, are not as effective on fresh-cut produce. Also, the extensive use of these sanitizers has resulted in various foodborne pathogens developing resistance to them. Naturally occurring bacteriophages, or viruses of bacteria, may be viable alternatives to sanitizers. We have shown that when a mixture of bacteriophages, which specifically target the foodborne pathogen Listeria monocytogenes, is applied at a rate of 108 PFU/ml from 1 hour before until 30 minutes after contamination with L. monocytogenes, populations of this pathogen on fresh-cut honeydew melons are significantly reduced. The fresh-cut produce industry can use bacteriophages to implement a successful biocontrol strategy to reduce the potential for outbreaks of foodborne diseases. This will benefit not just the fresh-cut processors, but retail outlets, foodservice organizations and consumers by providing a high quality and safe food supply.
Technical Abstract: A phage cocktail was applied to honeydew melon pieces 1, 0.5 and 0 h before contamination with Listeria monocytogenes strain LCDC 81-861 and 0.5, 1, 2, and 4 h after contamination. The phage application was most effective when applied 1, 0.5, or 0 h before contamination with L. monocytogenes, reducing pathogen populations by up to 6.8 log units after seven days of storage. This indicates that under commercial conditions, if contamination occurs at the time of cutting, phages would have to be applied no later than 0.5 h after cutting the produce. However, all phage applications, from one hour before to four hours after contamination at concentrations ranging from 104 to 108 PFU/ml, reduced bacterial populations on honeydew melon pieces. Higher phage concentrations were more effective in reducing pathogen populations. A phage concentration of approximately 108 PFU/ml was necessary to reduce the pathogen populations to non-detectable levels immediately after treatment, and suppress pathogen growth throughout the storage period of seven days at 10 degree C. In an attempt to enhance the effectiveness of the phage cocktail on low pH fruit, such as apples, the phages were applied in combination with MnCl2. This combination, however, did not enhance the effectiveness of the phages on apple tissue. The results from this study indicate that the effectiveness of the phage application on honeydew melon pieces can be optimized by using a phage concentration of at least 108 PFU/ml applied from one hour before contamination until 0.5 h after contamination of the fruit.