Research Note: Phage protects smoked salmon, naturally contaminated with Listeria monocytogenes
Study the efficacy of phages applied on smoked salmon that have been naturally contaminated with Listeria monocytogenes.
A total of 48 smoked salmon slices were divided in three parts:
- Part A was analyzed at day zero (D0) in order to detect the presence/absence of Listeria monocytogenes (control without phages D0)
- Part B was treated with Phageguard Listex at 109 PFU/cm2. This part was analyzed for Listeria at the end of the shelf-life.
Part C was analyzed at the end of the shelf life in order to detect the presence/absence of Listeria monocytogenes (control without phages D28).
For the slices were part A was positive for Listeria monocytogenes, parts B and C were vacuum packaged and stored for 10 days at 4°C and for 18 days at 8°C. Enrichment of L. monocytogenes was performed according to the validated AFNOR Aloa One Day method and numerations were done according to either the validated AFNOR ALOA One Count method or the AFNOR NF V 45-008 method.
48 samples of sliced smoked salmons were analyzed at day zero, see table below. Listeria monocytogenes was detected on 21% of the samples (10 out 48). The initial contamination level on these 10 samples was low (< 2 CFU/g).
Of the 10 samples that tested positive at day zero for Listeria monocytogenes, 6 control samples were negative on Day 28 and at 4 samples the Listeria counts were ranging from 100 to 1400 per gram. For the smoked salmon treated with phage, Listeria monocytogenes was not detected in any of the samples.
These results demonstrate that phage effectively controls Listeria on sliced smoked salmon naturally contaminated with L. monocytogenes and stored during 28 days at low temperature.
- Listeria monocytogenes was detected at day zero on 10 out of 48 samples 21%
For 4 samples, the contamination levels at the end of shelf-life were ranging from 100 to 1400 Listeria monocytogenes per gram for the slice part not treated with phages (control) while for the slice part treated with phages, Listeria monocytogenes was not detected.
Ofimer research report 2011. Use of phages to control Listeria monocytogenes in smoked salmon. Research partners CITPPM, Adria and Micreos Food Safety.