Listeria monocytogenes is a food-borne pathogen which causes listeriosis and is difficult to eradicate from seafood processing environments; therefore, more effective control methods need to be developed. This study investigated the effectiveness of three bacteriophages (LiMN4L, LiMN4p and LiMN17), individually or as a three-phage cocktail at ≈9 log₁₀ PFU/ml, in the lysis of three seafood-borne L. monocytogenes strains (19CO9, 19DO3 and 19EO3) adhered to a fish broth layer on stainless steel coupon (FBSSC) and clean stainless steel coupon (SSC), in 7-day biofilm, and dislodged biofilm cells at 15 ± 1 °C. Single phage treatments (LiMN4L, LiMN4p or LiMN17) decreased bacterial cells adhered to FBSSC and SSC by ≈3-4.5 log units. Phage cocktail reduced the cells on both surfaces (≈3.8-4.5 and 4.6-5.4 log10 CFU/cm², respectively), to less than detectable levels after ≈75 min (detection limit = 0.9 log₁₀ CFU/cm²). The phage cocktail at ≈5.8, 6.5 and 7.5 log₁₀ PFU/cm² eliminated Listeria contamination (≈1.5-1.7 log₁₀ CFU/cm²) on SSC in ≈15 min. One-hour phage treatments (LiMN4p, LiMN4L and cocktail) in three consecutive applications resulted in a decrease of 7-day L. monocytogenes biofilms (≈4 log₁₀ CFU/cm²) by ≈2-3 log units. Single phage treatments reduced dislodged biofilm cells of each L. monocytogenes strain by ≈5 log₁₀ CFU/ml in 1 h. The three phages were effective in controlling L. monocytogenes on stainless steel either clean or soiled with fish proteins which is likely to occur in seafood processing environments. Phages were more effective on biofilm cells dislodged from the surface compared with undisturbed biofilm cells. Therefore, for short-term phage treatments of biofilm it should be considered that some disruption of the biofilm cells from the surface prior to phage application will be required.

Aim: To isolate and characterize listeriaphages from seafood environments. Methods and Results: Listeriaphages (phages) isolated from seafood environments were distinguished by physical and biological techniques including restriction digestion of phage DNA. Three phages belonged to order Caudovirales and showed psychrotrophic characteristics. The phages had broad host ranges against 23 Listeria strains by productive infection or at least by adsorption. At 15 AE 1°C, adsorption rate constants of the three phages ranged from 8Á93 9 10 À9 to 3Á24 9 10 À11 ml min À1 across different Listeria monocytogenes strains. In indicator hosts, the mean burst sizes of phages LiMN4L, LiMN4p and LiMN17 were c. 17, 17 and 11 plaque-forming units (PFU) per cell, respectively, at 15 AE 1°C. The respective latent periods were c. 270 min for phages LiMN4p and LiMN17, whereas for phage LiMN4L, it was c. 240 min. Conclusions:The three virulent psychrotrophic phages isolated from seafoodprocessing environments had broad host ranges and low productive replication. These characteristics suggest that the phages may be suitable as passive biocontrol agents against seafood-borne L. monocytogenes. Significance and Impact of the Study: This is the first report on the isolation of autochthonous virulent listeriaphages from seafood-processing environments and information on single-step replication and adsorption characteristics of such listeriaphages.

Listeria-infecting bacteriophages (listeriaphages) can be used to control Listeria monocytogenes in the food industry. However, the sensitivity of many of seafood-borne Listeria strains to phages has not been reported. This research investigated the host ranges of three listeriaphages (FWLLm1, FWLLm3 and FWLLm5) by the formation of lytic zones and plaques on host lawns and in vitro lysis kinetics of listeriaphage FWLLm3. The study also predicted the phage titres required to lyse host cells. The host ranges of the phages were determined using 50 L. monocytogenes strains, of which 48 were isolated from the seafood industry and two from clinical cases. Of the 50 strains, 36 were tested at 25 and 30 ℃ and the remainder (14) at 15 and 25 ℃. Based on the formation of either discrete plaques or lytic zones (host kill zones), the host ranges of FWLLm1, FWLLm3 and FWLLm5 were about 87%, 81% and 87%, respectively, at 25 ℃. Six L. monocytogenes strains from the seafood environment were insensitive to all three phages, while the other seafood strains (42) were phage-sensitive. The adsorption rate constant (k value) of listeriaphage FWLLm3 was between 1.2 × 10(-9) and 1.6 × 10(-9 )ml/min across four host strains in tryptic soy broth at 25 ℃. The cultures (at 3-4 log colony-forming unit (CFU/ml) were completely lysed (<1 log CFU/ml) when cultures were infected with FWLLm3 at > 8.7 log phage-forming units (PFU/ml) for 30 min. Re-growth of phage-infected cultures was not detected after 24 h. The effective empirical phage titre was similar to the calculated titre using a kinetic model. Results indicate the potential use of the three phages for controlling L. monocytogenes strains in seafood processing environments.

Dried fish is one of the traditionally preserved foods in Sri Lanka.Since dried fish is often an important component of daily meal, this study was aimed to assess the quality of selected dried fish varieties in the local market. Dried fish samples of nine selected varieties were collected under three categories, viz. locally produced, imported dried fish before and after distribution to retail market. They were analyzed for microbiological and chemical parameters. Water activity of the samples was also measured. Samples were found to be negative for Escherichia coli, Staphylococcus aureus and halophilic bacteria. Aerobic Plate Count and yeast and mould count of the majority of the samples were within the acceptable limit. Histamine content exceeded 100 mg/kg level in 33% and 13% of imported and local samples respectively. Water activity of the samples was <0.75 except for imported prawn samples of retail outlets. There was no significant difference (p>0.05) between the analyzed parameters of all three categories.

This study aimed to identify histamine-forming bacteria (HFB) and the sources of introduction of such bacteria to recommend control measures to mitigate histamine formation in yellowfin tuna (YFT). Field samples were collected from multi-day boats that landed at Dikkowita, Negombo, Trincomalee and Dondra fishery harbours. Ice from the fish holds (n=63) and chill transport vehicles (n=63), and swabs from the fish holds (n=63), the boat decks (n=63) and the skin of YFT (n=63) were collected. Fish loin samples (n=15), ice samples (n=36) and swabs from the skin of YFT (n=18), floor (n=18) and chill transport vehicles (n=18) were collected from fish processing plants. Presumptive HFB isolated from Nivens medium and Violet Red Bile Glucose (VRBG) agar were screened for histamine forming ability in Tripticase soy broth (TSB) supplemented with 1.0% L-histidine. HFB isolates were characterized by sequencing approximately 1400 bp of the 16S rDNA. Seven isolates that produced histamine in the range of 3000–4000 ppm in TSB isolated from ice samples, and a swab sample collected from the boat deck, were confirmed as Klebsiella aerogens (n=6) and Morganella morganii (n=1) respectively. Hafnia alvei (n=1), Serratia sp. (n=2), Citrobacter freundii (n=1), Rahnella sp. (n=1) and Aeromonas salmonicida (n=8) were also among the isolated histamine forming bacteria. Pseudomonas sp. (n=24) and Shewanella baltica (n=7), which are known as spoilage bacteria were also isolated and showed weak histamine formation. Hence, it is evident that histamineforming bacteria could be introduced into the fish from ice and contacting surfaces. This necessitates the practice of rigorous cleaning procedures and adaptation of proper postharvest handling procedures to minimize contamination of the fish.