Purpose: The purpose of this study was to evaluate efficacy of a listeriophage cocktail as a Listeria spp. control strategy for nonfood contact surfaces (NFCS) in a meat processing facility.
Methods: Initial prevalence, persistence, and load of Listeria spp. was determined for 30 floor-wall (FW) junctions and 29 drain sampling sites, once weekly for three weeks, in a meat processing facility, using a modified FDA BAM protocol and standard PFGE typing. Positive sites were treated with listeriophage cocktail in liquid (1 ml/ft2 [109 pfu/ml]), three times at 12 h intervals. Treated and untreated sites were again sampled for Listeria spp. and concentrations were compared to pretreatment levels. Lytic capacity of an isolate from each postivie site was determined by standard spot assay.
Results: A total of 15, 21, and 14 samples (among 59 sites) were positive for Listeria spp. at weeks one, two, and three, respectively. PFGE analyses identified 38 strains. Twenty-three sites that were positive at least once were treated with listeriophage. Twelve sites remained positive after treatment; Listeria spp. were numerically reduced in four of 12 sites by an average of 2.1 log CFU/sponge. Among five PFGE types that were recovered more than once, PUL_0012-PUL_0045 was recovered, consecutively, in week three and four from the same drain. A total of 26% isolates (six of 23) showed low susceptibility (average lytic score zero to one) to listeriophage, 43% (10 of 23) showed moderate lysis (score one to two), and 31% (seven of 23) isolates showed confluent lysis (score two to three) across all temperatures and listeriophage concentrations tested.
Significance: Reductions in detected Listeria spp., postapplication of listeriophage, offers preliminary evidence that phages may be an effective Listeria spp. control strategy for nonfood contact surfaces.