Journal of food protection · 2026
Biocontrol Validation of a Strictly Lytic Phage A511 and a Commercial Phage PGL Shows Reduction of Listeria monocytogenes in Raw Scottish Salmon Fillet Postharvest.
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Mutai Ivy J, Maina Meshach, Kubala Anton, Dowah Ahmed, Wang Belinda, Gurusinghe Anuji, Crumlish Margaret, Rees Catherine E D, Bhandare Sudhakar
Аннотация
INTRODUCTION: Listeria monocytogenes is a known food-borne risk associated with ready-to-eat (RTE) foods, including fish. An estimated 90% of cases of invasive human listeriosis result from ingestion of foods containing >2.0 × 103 CFU/g, with growth after purchase being a significant factor. This study aimed to evaluate the biological characteristics, lytic spectra, and determine the biocontrol potential of a strictly lytic L. monocytogenes bacteriophage A511 in comparison with a commercial phage PGL (P100) on raw Scottish salmon fillets.
METHODOLOGY: The lytic spectra of phage A511 and the commercial phage PGL were determined using spot assays on a panel of 33 L. monocytogenes strains, and phage growth kinetics, such as burst and latent period, were evaluated using standard double agar layer methods. For the biocontrol study, ∼4 log10 CFU/ml of L. monocytogenes were inoculated on raw Scottish salmon fillets, and the two individual lytic phages (viz., phage A511 and commercial phage PGL) at three phage application rates (final concentrations of 105, 107, and 109 PFU/g) were used to control experimental Listeria contamination of fresh Scottish salmon fillets stored at 4 °C and 10 °C.
RESULTS: The phages A511 and PGL exhibited lytic spectra of 97% and 100%, respectively, against the strains tested while A511 produced burst sizes of ∼49 PFU/cell. There was a significant effect of phage titer (p < 0.0001) on the levels of L. monocytogenes, with reductions in bacterial numbers to below the limit of detection (i.e., no detectable counts were observed) after 1-day incubations at both 4 °C and 10 °C for both phage A511 and PGL applied at 109 PFU/g, with enhanced reductions at 4 °C.
CONCLUSION: This study conducted a lab‑scale evaluation of the archival phage A511 on raw salmon in direct comparison with a commercial phage (PGL) under a unified dose-time-temperature framework. To our knowledge, a direct comparison of A511 and PGL on raw salmon using an identical experimental design has not been previously reported. While the findings demonstrate effective reduction of L. monocytogenes under controlled laboratory conditions, further work, including broader strain coverage, naturally contaminated lots, sensory and shelf‑life assessments, and multi‑batch validation, is required before commercial implementation can be fully assessed.
METHODOLOGY: The lytic spectra of phage A511 and the commercial phage PGL were determined using spot assays on a panel of 33 L. monocytogenes strains, and phage growth kinetics, such as burst and latent period, were evaluated using standard double agar layer methods. For the biocontrol study, ∼4 log10 CFU/ml of L. monocytogenes were inoculated on raw Scottish salmon fillets, and the two individual lytic phages (viz., phage A511 and commercial phage PGL) at three phage application rates (final concentrations of 105, 107, and 109 PFU/g) were used to control experimental Listeria contamination of fresh Scottish salmon fillets stored at 4 °C and 10 °C.
RESULTS: The phages A511 and PGL exhibited lytic spectra of 97% and 100%, respectively, against the strains tested while A511 produced burst sizes of ∼49 PFU/cell. There was a significant effect of phage titer (p < 0.0001) on the levels of L. monocytogenes, with reductions in bacterial numbers to below the limit of detection (i.e., no detectable counts were observed) after 1-day incubations at both 4 °C and 10 °C for both phage A511 and PGL applied at 109 PFU/g, with enhanced reductions at 4 °C.
CONCLUSION: This study conducted a lab‑scale evaluation of the archival phage A511 on raw salmon in direct comparison with a commercial phage (PGL) under a unified dose-time-temperature framework. To our knowledge, a direct comparison of A511 and PGL on raw salmon using an identical experimental design has not been previously reported. While the findings demonstrate effective reduction of L. monocytogenes under controlled laboratory conditions, further work, including broader strain coverage, naturally contaminated lots, sensory and shelf‑life assessments, and multi‑batch validation, is required before commercial implementation can be fully assessed.