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A phage cocktail was applied to honeydew melon pieces 1, 0.5, and 0 h before contamination with Listeria monocytogenesstrain 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 7 days of storage. This indicates that under commercial conditions, if contamination occurs at the time of cutting, phage would have to be applied as soon as possible after cutting the produce. However, all phage applications from 1 h before to 4 h after contamination and all phage concentrations ranging from 104to 108PFU/ml reduced bacterial populations on honeydew melon pieces. Higher phage concentrations were more effective in reducing pathogen populations. A phage concentration of approximately 108PFU/ml was necessary to reduce the pathogen populations to nondetectable levels immediately after treatment, and pathogen growth was suppressed by phage concentrations of 106through 108throughout the storage period of 7 days at 10°C. In an attempt to enhance the effectiveness of the phage cocktail on low pH fruit, such as apples, the phage was applied in combination with MnCl2. This combination, however, did not enhance the effectiveness of the phage 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 108PFU/ml applied up to 1 h after processing of the honeydew melons.

The preparation and distribution of fresh-cut produce is a rapidly developing industry that provides the consumer with convenient and nutritious food. However, fresh-cut fruits and vegetables may represent an increased food safety concern because of the absence or damage of peel and rind, which normally help reduce colonization of uncut produce with pathogenic bacteria. In this study, we found that SalmonellaEnteritidis populations can (i) survive on fresh-cut melons and apples stored at 5°C, (ii) increase up to 2 log units on fresh-cut fruits stored at 10°C, and (iii) increase up to 5 log units at 20°C during a storage period of 168 h. In addition, we examined the effect of lytic, Salmonella-specific phages on reducing Salmonellanumbers in experimentally contaminated fresh-cut melons and apples stored at various temperatures. We found that the phage mixture reduced Salmonellapopulations by approximately 3.5 logs on honeydew melon slices stored at 5 and 10°C and by approximately 2.5 logs on slices stored at 20°C, which is greater than the maximal amount achieved using chemical sanitizers. However, the phages did not significantly reduce Salmonellapopulations on the apple slices at any of the three temperatures. The titer of the phage preparation remained relatively stable on melon slices, whereas on apple slices the titer decreased to nondetectable levels in 48 h at all temperatures tested. Inactivation of phages, possibly by the acidic pH of apple slices (pH 4.2 versus pH 5.8 for melon slices), may have contributed to their inability to reduce Salmonellacontamination in the apple slices. Higher phage concentrations and/or the use of low-pH-tolerant phage mutants may be required to increase the efficacy of the phage treatment in reducing Salmonellacontamination of fresh-cut produce with a low pH.