Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/27/2003
Publication Date: 8/1/2003
Citation: Leverentz, B., Conway, W.S., Camp, M.J., Janisiewicz, W.J., Abuladze, T., Saftner, R.A., Sulakvelidze, A. 2003. Biocontrol of Listeria monocytogenes on fresh-cut produce by combining bacteriophages and a bacteriocin. Applied and Environmental Microbiology. 69(8):4519-4526. Interpretive Summary: Fresh-cut produce is a rapidly growing $10 to $12 billion a year industry and accounts for over 10% of all produce sales in the U.S.; it 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 a mixture of bacteriophages, which specifically target the foodborne pathogen Listeria monocytogenes, alone and in combination with another natural antimicrobial compound, reduces populations of this pathogen on fresh-cut honeydew melons. The fresh-cut produce industry can use bacteriophages combined with an antimicrobial compound to implement a successful biocontrol strategy to reduce the potential for outbreaks of foodborne diseases. This will benefit not just the fresh produce processors, but retail outlets, foodservice organizations and consumers by providing a high quality and safe food supply.
Technical Abstract: The fresh-cut produce industry has been the fastest growing portion of the food retail market during the past ten years, providing consumers with convenient and nutritious food. However, fresh-cut fruits and vegetables raise food safety concerns, because exposed fruit tissue may be colonized more easily by pathogenic bacteria than intact produce. We found that Listeria monocytogenes populations survived and increased only slightly on fresh-cut 'Red Delicious' apples, but increased significantly on honeydew melons stored at 10 degrees C. In addition, we examined the effect of lytic, L. monocytogenes - specific phages via two phage application methods, spraying and pipetting, on L. monocytogenes populations in artificially contaminated fresh-cut melons and apples. The phage mixture reduced L. monocytogenes populations by approximately 2 - 4 log units over the control on honeydew melons. This is greater than the reduction achieved using chemical sanitizers. In combination with nisin (a bacteriocin), the phage mixture reduced L. monocytogenes populations by 5.8 log units to 1.4 CFU/ml and by 3.5 log units to 0.6 CFU/ml on honeydew and apple, respectively. The phage titer was stable on melon slices. The spray application of the phage and phage plus nisin reduced the bacterial numbers at least as much as the pipette application. This combination of treatments lowered the L. monocytogenes contamination of apple slices by up to 2.3 log units and on honeydew melons by up to 5.7 log units. The effectiveness of the phage treatment also depends on the initial concentration of L. monocytogenes and the application method of the phage.