Examination of Bacteriophage as a Biocontrol Method for Salmonella on Fresh-Cut Fruit: A Model Study

Abstract

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 Salmonella Enteritidis populations can (i) survive on fresh-cut melons and apples stored at 5 degrees C, (ii) increase up to 2 log units on fresh-cut fruits stored at 10 degrees C, and (iii) increase up to 5 log units at 20 degrees C during a storage period of 168 h. In addition, we examined the effect of lytic, Salmonella-specific phages on reducing Salmonella numbers in experimentally contaminated fresh-cut melons and apples stored at various temperatures. We found that the phage mixture reduced Salmonella populations by approximately 3.5 logs on honeydew melon slices stored at 5 and 10 degrees C and by approximately 2.5 logs on slices stored at 20 degrees C, which is greater than the maximal amount achieved using chemical sanitizers. However, the phages did not significantly reduce Salmonella populations 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 Salmonella contamination 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 Salmonella contamination of fresh-cut produce with a low pH.

Bacteriophage biocontrol ofListeria monocytogeneson soft ripened white mold and red-smear cheeses

“…In other studies, no phage resistant Listeria emerged on phage-treated ready-to-eat foods over 6 to 13 days, 31 or red-smear cheese over 3 weeks. 24 Resistance to a specific phage added to food was also not observed with Salmonella Enteritidis on fresh-cut fruit during a 7 day period, 39 or Campylobacter jejuni on chicken skin after 10 days. 40 However, some phage-insensitive Brochothrix thermosphacta emerged on pork adipose tissue 8 days after phage was added.…”

Bacteriophage biocontrol of foodborne pathogens

“…The result maybe explained as phage particles were inactivated due to low pH on apple surface Leverentz et al 2001 No survival during 89 days in pasteurized cheeses containing phage SJ2 (MOI 10 4 ) M o d i e t a l . 2001…”

Phage-based biocontrol strategies to reduce foodborne pathogens in foods

“…39 Other studies have confirmed that low pH can reduce or eliminate Salmonella phage populations. 40,41 As with the Dykes and Moorhead 5 study, Leverentz' group showed that the efficacy of phage reduction was shown to increase when phage were employed in combination with the nisin. In a follow up study with honey dew melons, the authors showed that a cocktail of six phages resulted in a larger reduction in the L. monocytogenes concentration, when the phages were applied at higher concentrations, 42 highlighting once again the importance of phage dosage.…”