Presence of Listeria spp. in fish samples, fish products and sea products

Influence of hot-smoking on the stability of fresh and frozen-thawed deep-skinned Atlantic mackerel fillets during cold storage

Atlantic mackerel (Scomber scombrus) caught during the summer months in Icelandic waters after intensive feeding is rich in lipids and, thus, sensitive to lipid degradation. Recent studies have led to improved cooling and handling on board, ensuring high-quality raw material. However, studies on the development of high-quality products for human consumption are lacking. The study aimed to investigate the effects of hot-smoking on the physicochemical, microbial, and sensory quality of deep-skinned Atlantic mackerel fillets during chilled storage (1 ± 0.6°C). In addition, the quality of smoked mackerel from frozen-thawed fillets (9 months at -25 ± 1.8°C) was compared to that of fresh-smoked fillets to evaluate the possibility of the industry being able to provide smoked fillets throughout the year, despite the short fishing season. Brining and hot-smoking reduced total viable counts and inactivated Listeria monocytogenes. Hot-smoking positively affected the sensory attributes of the fillets and sensory quality was largely maintained for at least 21 days of chilled storage. Although slightly lower sensory and texture scores were obtained for frozen-thawed smoked fillets, they remained within acceptable limits throughout the period of cold storage. The shelf-life of smoked Atlantic mackerel deep-skinned fillets stored at 1°C is, therefore, assessed to be at least 21 days. Well-fed Atlantic mackerel is suitable for developing high-quality and stable smoked fillet products from both fresh and frozen-thawed raw materials.

Prevalence of Listeria monocytogenes and other Listeria species in fish, fish products and fish processing environment: A systematic review and meta-analysis

Fish and seafood products are one of the most common causes of listeriosis in humans. A systematic review and meta-analysis were conducted using scientific literature to summarize available data on the prevalence of Listeria monocytogenes and Listeria sp. in fish, fish products and fish processing environment. Meta-analysis models were used to estimate the mean prevalence of the pathogen and to compare prevalence among the most popular fishes. Data from a total of 14,496 samples were analysed. Pooled prevalence of L. monocytogenes and Listeria sp. in raw fish was 5.8 % (95 % CI: 4.7-6.9) and 12.2 % (95 % CI: 8.9-15.5) respectively. Significantly higher results were observed for ready-to-eat products, occurrence of L. monocytogenes and Listeria sp. was 14.5 % (95 % CI: 11.1-18.0) and 21.7 % (95 % CI: 11.8-31.6) respectively. Moreover, meta-regression was performed to investigate changes in L. monocytogenes and Listeria sp. occurrence over the years and it shows a downward trend for both raw fish and RTE products. The results of the present study provide useful epidemiological information about the contamination level and distribution of Listeria sp. and L. monocytogenes among raw fish, fish products and fish processing environment.

Prevalence, genetic diversity and antimicrobial resistance of Listeria monocytogenes isolated from fresh and smoked fish in Poland

A total of 57 out of 301 (18.9%) fresh and smoked fish samples in Poland were positive for Listeria monocytotgenes. The bacteria were most frequently identified in fresh and smoked salmon (32.0% and 33.8% respectively) as well as in fresh cod (31.8%). Only three samples of smoked salmon were contaminated with the bacteria above 100 CFU/g. Four molecular serogroups were identified and the most prevalent, 1/2a-3a (40 isolates; 70.2%), was present in samples from both marine (33 strains; 71.7%) and freshwater fish (7 isolates; 63.6%). Similar duality of prevalence was observed only for L. monocytogenes of 1/2b-3b-7 serogroup (14 strains; 24.6%), which was identified in 11 (23.9%) marine and 3 (27.3%) freshwater fish. All isolates harboured 10 virulence-associated genes (inlA, inlB, inlC, inlJ, lmo2672, plcA, plcB, hlyA, actA, and mpl) and most of them (56; 98.2%) also possessed the flaA marker. Several strains displayed resistance to oxacillin (33; 57.9%), ceftriaxone (18; 31.6%), or clindamycin (5; 8.8%), and two isolates of serogroup 1/2a-3a showed multiresistance to all three. Genetic subtyping showed the presence of different pulsotypes belonging to six PFGE clusters. The obtained results provide useful information regarding fish contamination with L. monocytogenes which may have implications for public health.