Microbial diversity of seafood

Seafood production is the key to meet the food and nutrition requirements for the growing human population. Nevertheless, billions tonnes of fish are lost or wasted due to problems in fishing and in post-harvest, thereby threatening food security. To improve microbial quality and safety of seafood along the food value chain, food microbiologists now attempt to describe and to understand seafood spoilers and seafood-borne pathogens using novel research tools and methodologies such as Next Generation Sequencing (NGS) technologies and PCR based methodologies, for example, Real-Time PCR and High Resolution Melting (HRM). The exploration of microbial diversity of seafood is now needed as never before, since we have to tackle new challenges that can affect microbial safety and quality of seafood; Climate Change and Antimicrobial Resistance. The establishment of intelligent strategies towards seafood safety and quality assurance in the context of such challenges will contribute to Sustainable Development Goals and One Health. © 2020 Elsevier Lt

Specific Spoilage Organisms (SSOs) in Fish

Fresh and minimally processed fish and seafood spoil due to the action of a consortium of microorganisms, the so-called specific spoilage organisms (SSOs) that have the ability to dominate and produce metabolites that directly affect the sensory properties of the product, resulting in its rejection by the consumers. The selection of SSOs is affected by fish origination, processing, and storage conditions and various implicit factors such as antagonism for nutrients and microbial interactions. The metabolic products of SSOs causing the spoilage are various volatile compounds that mainly come from the assimilation of nonprotein-nitrogen of fish flesh. Qualitative and quantitative determination of SSOs is of great interest, and current molecular techniques provide us with powerful tools for exploring the diversity and dynamics of SSOs. The inhibition of SSOs by applying appropriate preservation strategies can retain fish freshness and extend shelf life. Elucidation of SSOs' metabolic potential and activity and the estimation of the growth and population level provide us with tools for rapid evaluation of fish freshness/spoilage status and remaining shelf life. © 2017 Elsevier Ltd. All rights reserved

Monitoring of spoilage and determination of microbial communities based on 16S rRNA gene sequence analysis of whole sea bream stored at various temperatures

Exploration of initial and spoilage microbiota grown on plates of whole sea bream stored aerobically at 0 (ice), 5 and 15 °C, was conducted by 16S rRNA gene sequence analysis. The course of spoilage was recorded by monitoring microbiological, sensory and chemical changes. Shelf-life of sea bream determined by sensory assessment was 16, 5 and 2 days at 0 (ice), 5 and 15οC, respectively. Pseudomonas spp. was the dominant spoilage population of whole sea bream at all temperatures tested. A sum of 144 colonies were isolated from TSA (Tryptone Soy Agar) plates and identified by genotypic approach at the beginning and at the sensory rejection time points. Regarding initial microbiota, Pseudomonas fragi was the most abundant compared to the rest bacteria (Pseudomonas fluorescens, Enterobacter hormaechei, Chryseobacterium carnipullorum). P. fragi was also the dominant microorganism of fish stored at 0 and 5, while P. fluorescens at 15 οC. Concluding, genotypic approach gives accurate identification of the dominant spoilage microorganisms providing us with valuable information regarding microbiological spoilage of fish. © 2015 Elsevier Ltd

The evolution of knowledge on seafood spoilage microbiota from the 20th to the 21st century: Have we finished or just begun?

Backround: The modern dietary trends have led to a continuously increasing demand for seafood. Both high quality and extended shelf-life of seafood is required to satisfy the nowadays dietary tendency, as well as the industrial interest to increase the added value of such products. However, microbial spoilage is the main factor linked with the rapid seafood sensorial degradation, resulting in high food losses along the production and distribution chain and thus, noteworthy economic losses for seafood producingcountries. In the past, the low technological capability permitted a limited and non-representative study of microbial community and thus, the results of spoilage-related microbiota present in seafood, were led to both insufficient and disputed conclusions. Scope and approach: The scope of the present review is to evaluate how method development has improved our understanding on seafood spoilage microbiota during the past decades, discussing in parallel the current/emerging trends, as well as what could be recommended for future research efforts. Key findings and conclusions: The advent of novel molecular technologies, mainly high throughput sequencing (HTS) set of techniques, has changed our approach regarding the study of seafood microbiota, enriching our knowledge in this field. For improving and/or ensuring seafood quality along seafood value chain, the scientific community has now the option of using such modern tools to explore and understand the complex plenomena taking place during seafood spoilage.The study of seafood microbiota changes during processing, storage and distribution, in combination with the “meta-omics” approaches, is the key to unveil the functionalities in such complicated food matrix. In the current decade, the scientific community faces the challenge to establish novel and intelligent strategies that could prevent seafood spoilage as well as to extend or even predict the shelf-life of seafood. The contribution of multi-omics is expected to enhance this attempt. Those strategies will lead to the production of high quality added value seafood, in order to meet consumers’ demands. © 2022 Elsevier Lt

Pathogens and their sources in freshwater fish, sea finfish, shellfish, and algae

Fish production is one of the most important solutions to tackle the great challenges of the 21st century, such as how to feed people in the context of a growing population. However, pathogens such as bacteria, including antimicrobial-resistant populations and viruses, can be present in the water column and fish (also including shellfish) threatening food security and public health. Pathogens can be transferred from human settlements, cropping systems, livestock systems, animal slaughtering and processing industries, and from other sources of human and animal activity, into the aquatic environment and contaminate fish. Fish contamination can be also continued in harvesting, handling, packaging, processing, and distribution, because of poor hygiene or sanitary practices in the post-farm gate. Such pathogens can end up in humans through the food value chain and fall ill after eating contaminated fish. Several pathogenic strains, serotypes or serovars of Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio cholerae, Salmonella enterica, Aeromonas sp., Listeria monocytogenes, and Clostridium botulinum are responsible for thousands of cases and deaths associated with fish consumption around the globe. Of them, Vibrio, Salmonella, Aeromonas, and L. monocytogenes isolated from farmed fish, have been found to present antibiotic resistance to various antimicrobial agents. Researchers can now detect such pathogenic bacteria using cutting-edge methodologies for example, conventional PCR, Real-Time PCR, High-Resolution Melting, and technologies such as Next Generation Sequencing. Such innovations have immensely contributed to our understanding of how to solve problems of stakeholders related to seafood safety, minimize hazard related issues, and tackle food and economic losses in pre- and post- fish farm gate, thereby providing products of the highest safety in the world. © 2023 International Life Sciences Institute (ILSI) Published by Elsevier Inc. All rights reserved

High pressure processing at ultra-low temperatures: Inactivation of foodborne bacterial pathogens and quality changes in frozen fish fillets

High pressure processing (HPP) at ultra-low temperatures was conducted against Listeria monocytogenes and Salmonella enterica in frozen pink salmon fillets. Quality changes, such as drip loss, color and odor attributes were recorded in non-inoculated pollock, pink salmon and tuna fillets. Pressures at 250 and 400 MPa were applied from 0.5 to 10 min. Reductions up to 3.5 log cfu/g were recorded for the treatments performed at −32 °C, in contrast to −50 °C where the reductions were only up to 1.5 log cfu/g. Higher pressure did not cause higher reduction. It was apparent that the main factor contributing to the bacterial inactivation is the phase transition of ice structure from I to III, in contrast to transition from I to II. Drip loss was not higher than the expected with HPP at temperatures above 0 °C, while color changes were negligible. Finally, the odor evaluation did not exhibit considerable differences between untreated and treated samples. Industrial relevance: High pressure processing at ultra-low temperatures is a promising treatment for bacterial inactivation and retention of quality attributes of frozen fish. Treatment at 250 MPa for only 3 min at temperatures just below −22 °C, which is feasible and affordable, caused a more than 3-log reduction against Listeria monocytogenes and Salmonella enterica, without affecting considerably the quality properties. Thus, the application of low pressure and shorter processing times gives a great potential for industrial application for frozen fish or fish that wouldn't be undesirable to freeze before pressurization. © 2021 Elsevier Lt

Volatile organic compounds of microbial and non-microbial origin produced on model fish substrate un-inoculated and inoculated with gilt-head sea bream spoilage bacteria

Volatile organic compounds (VOCs) origination during fish spoilage is attributed to either decomposition of fish constituents or metabolic activity of spoilage bacteria. To identify microbiological spoilage markers it is essential to know which VOCs are microbial metabolites. VOCs produced in sterile fish juice agar (FJA) model substrate made from gilt-head sea bream (Sparus aurata) flesh juice, inoculated or not with spoilage bacteria isolated from sea bream fillets were detected using SPME/GC-MS technique. Three groups of spoilage bacteria (Pseudomonas, Shewanella and Carnobacterium/Lactobacillus strains) were used to inoculate Petridishes with FJA and stored at 0 and 15 °C under air and commercial Modified Atmosphere Package (MAP CO2: 60%, O2: 10%, N2: 30%). Bacterial growth was also monitored. VOCs that were detected in sterile substrate and their amounts were not higher in inoculated FJA were presumably of non-microbial origin. VOCs that were detected only in inoculated FJA were metabolic products of spoilage bacteria. Some of VOCs were associated with metabolic activity of a particular microbial group, e.g. ethyl esters were associated with Pseudomonas, while 2-, 3-methylbutanal and 3-hydroxy-2-butanone with LAB. Few microbial metabolites increased during storage showing their potential as spoilage markers of gilt-head sea bream and the possible use for rapid freshness assessment. © 2016 Elsevier Lt

Preservation status and microbial communities of vacuum-packed hot smoked rainbow trout fillets

Vacuum-packed hot smoked rainbow trout fillets from two different smokehouses of Greece were stored at 2 and 7.9 °C. Microbiological, sensory, and physicochemical changes were monitored. Microbial communities grown on MRS of three different pHs (5.4, 6.4 and 7.4) were also classified and identified using Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). Shelf-life was found to differ between products from the two smokehouses (A: 104 and 45 days, B: 100 and 45 days, at 2 and 7.9 °C, respectively). At the time point that sensory rejection was recorded, counts on MRS were found at higher population levels than the other microorganisms tested, almost in all cases. Out of the 567 colonies isolated from MRS of three different pHs, 71 classified as Enterococcus spp., 383 as Candida spp. and 113 as Lactobacillus spp. Candida zeylanoides dominated exclusively in fillets from the smokehouse A during storage at 2 °C, while Lactobacillus sakei dominated clearly against C. zeylanoides at 7.9 °C, in all pH values. For the smokehouse B, C. zeylanoides or Enterococcus faecalis found to dominate initially in MRS of three pHs, C. zeylanoides, and/or Candida famata in the middle and/or the time point that sensory rejection was recorded at 2 °C, while Lactobacillus curvatus or E. faecalis at 7.9 °C. This study reveals the predominant cultivable spoilage microbiota of vacuum-packed hot smoked rainbow trout, and provides valuable information to the researcher and producers towards the production of more stable products with improved shelf-life. © 202

Effect of ozone on the microbiological status of five dried aromatic plants

BACKGROUND: Aromatic plants may be contaminated with a wide range of microorganisms, making them a potential health hazard when infused or added to ready-to-eat meals. To ensure safety, the effect of gaseous ozone treatment on the population of aerobic plate counts (APC), hygienic indicators (Escherichia coli, Enterococcus spp. and Enterobacteriaceae) and fungi was investigated for five dried aromatic plants: oregano, thyme, mountain tea, lemon verbena and chamomile. Selection, isolation and further fungi identification were based on the phenotypic and macro- and microscopic characteristics. RESULTS: Prior to ozonation, APC on five dried aromatic plants was in the range 5–7 log colony-forming units (CFU) g–1. The APC exhibited a 4 log reduction, from around 6.5 to 2.5 in the case of oregano, and only a 1–2 log reduction for other herbs after 30 or 60 min of 4 ppm gaseous ozone treatment. Enterococcus spp. and E. coli were not detected on any of the tested dried aromatic plants. The fungi counts were 2–4 log CFU g–1 before ozonation. Aspergillus spp, Penicillium spp, Cladosporium spp, Alternaria spp, Fusarium spp., Ulocladium spp. and some unknown fungi were detected on plants before ozone treatment. Aspergillus spp. and/or Penicillium spp. were only detected on mountain tea and thyme plant material after 60 min of ozonation. CONCLUSION: The present study provides information about the efficiency of ozone on the microbial decontamination of dried aromatic plants. Treatment with gaseous ozone at 4 ppm for 30 min in the case of dried oregano and 60 min in the case of chamomile and lemon verbena could be used as alternative disinfection methods. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industr

HRM and 16S rRNA gene sequencing reveal the cultivable microbiota of the European sea bass during ice storage

The total cultivable microbiota of the ice-stored European sea bass (Dicentrarchus labrax), the most important commercial fish species of the Mediterranean aquaculture, was determined using 16S rRNA gene sequence analysis. High Resolution Melting (HRM) curve profiles and sequencing analysis (V3–V4 region of the 16S rRNA gene) were used respectively for the differentiation and identification of the collected isolates from six time intervals (day 0, 4, 8, 12, 14 and 16) while fish were stored in ice. HRM analysis differentiated the unknown microbiota in ten groups (208 isolates) and in two single isolates based on their HRM curve profiles. The isolates with HRM profiles which were >91% similar within each group were found to belong to the same species using sequencing analysis. Thus, the ten groups consist of representatives of Psychrobacter glacincola, Ps. alimentarius, Ps. cryohalolentis, Ps. maritimus, Ps. fozii, Pseudomonas sp., Paeniglutamicibacter sp., Carnobacterium sp., Leucobacter aridicolis and Bacillus thuringiensis. Based on this approach, Ps. cryohalolentis was found to be the most dominant phylotype at the beginning of fish shelf-life compared to other species. The abundance of this bacterium decreased throughout storage, while Ps. glacincola increased and dominated at the time of the sensory minimum acceptability (day 14) and rejection (day 16). To conclude, HRM could be used for the rapid determination of sea bass microbiota, using the representatives of each group as reference bacterial strains, in order for scientists to solve rapidly stakeholders problems related with microbial quality or safety of fish. © 2020 Elsevier B.V