Research Note: Phageguard L (PGL) protects smoked salmon against naturally present Listeria monocytogenes

Objective

Study the efficacy of phages applied on smoked salmon that contains Listeria monocytogenes naturally present in- and on the salmon.

Protocol

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 L (PGL). 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).

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.

Conclusions

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.

Source: Ofimer research report 2011. Use of phages to control Listeria monocytogenes in smoked salmon. Research partners CITPPM, Adria and Micreos Food Safety.