Lactic acid bacteria (LAB) in fish flesh has long been disregarded because the high
post-mortem pH, the low percentage of sugars, the high content of low molecular weight nitrogenous molecules and ...the low temperature of temperate waters favor the rapid growth of pH-sensitive psychrotolerant marine Gram-negative bacteria like
Pseudomonas, Shewanella and
Photobacterium. In seafood packed in both vacuum (VP) and modified atmosphere (MAP) packaging commonly CO
2 enriched, the growth of the Gram-negative aerobic bacteria group (predominantly pseudomonads) is effectively inhibited and the number reached by LAB during storage is higher than that achieved in air but always several log units lower than the trimethylamine oxide (TMA-O) reducing and CO
2-resistant organisms (
Shewanella putrefaciens and
Photobacterium phosphoreum). Accordingly, LAB are not of much concern in seafood neither aerobically stored nor VP and MAP. However, they may acquire great relevance in lightly preserved fish products (LPFP), including those VP or MAP. Fresh fish presents a very high water activity (aw) value (0.99). However, aw is reduced to about 0.96 when salt (typically 6% WP) is added to the product. As a result, aerobic Gram-negative bacteria are inhibited, which allows the growth of other organisms more resistant to reduced aw, i.e. LAB, and then they may acquire a central role in the microbial events occurring in the product. Changes in consumers’ habits have led to an increase of convenient LPFP with a relative long shelf-life (at least 3 weeks) which, on the other hand, may constitute a serious problem from a safety perspective since
Listeria monocytogenes and sometimes
Clostridium botulinum (mainly type E) may able to grow. In any case the LAB function in marine products is complex, depending on species, strains, interaction with other bacteria and the food matrix. They may have no particular effect or they may be responsible for spoilage and, in certain cases, they may even exert a bioprotective effect in relation to undesirable bacteria. The bioprotective potential of endogenous LAB in relation to pathogens and spoiling bacteria has often been highlighted. However, the technology is still in its infancy compared with foods dairy and meat products in which either the carbohydrate content (dairy products) or sugar and salt added (meat products) favor the acidification by LAB that enable a natural preservation of the product. Successful studies on LAB as probiotic for fish intensify, but this potential is still to be explored for human. Although not usual, some applications of LAB for fermentation of marine products and by-products are described.
Quantification of lactic acid bacteria (LAB) is essential to control quality of seafood products like cold-smoked salmon (CSS). In the present study, we report the design and optimization of a ...dual-labelled TaqMan ™ probe targeting the V7 region of 16S rRNA gene for the detection of LAB in CSS. This quantitative PCR (qPCR) assays is useful for the simultaneous detection of the ten LAB genera communally encountered in CSS as Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Macrococcus, Streptococcus, Vagococcus and Weissella. The specificity of this method was demonstrated against 14 genera (44 isolates, 35 species) of Gram-positive bacteria and 19 genera of Gram-negative (40 isolates, 34 species). Calibration of the method was performed in CSS matrix using a mix of equimolar cultured solution of five LAB. Quantification with the qPCR method range from 3.5 to 8.5 Log CFU/g in CSS matrix, covering 5 orders of magnitude. On these artificially contaminated CSS slices, PCR method results correlated successfully (R2 = 0.9945) with the conventional enumeration on Elliker medium. In addition, the new method was successful on commercial CSS from five different origins with a quantification range from 3.7 Log CFU/g to 8.0 Log CFU/g. This one-step quantitative methodology is proposed as a rapid and complementary tool of the cultural methods to investigate the LAB microbiota and biodiversity of CSS.
•Simultaneous detection and quantification by qPCR of 10 lactic acid bacteria genera in cold-smoked salmon.•qPCR method ranges from 3.5 to 8.5 Log CFU/g in cold-smoked salmon matrix.•One-step quantitative methodology performed successfully on various commercial cold-smoked salmon products.
The effect of vacuum (VP – 4°C) and CO2/N2–atmosphere (MAP – 4°C) packaging on the quality of red drum fillets compared with whole gutted iced fish was investigated.
A metagenomic approach, bacterial ...enumeration and isolation, biochemical and sensory analyses were carried out. The organoleptic rejection of whole fish was observed at day 15 whereas VP and MAP fillets appeared unacceptable only after 29days. At these dates, total mesophilic counts reached 107–108CFU g−1. According to Illumina MiSeq sequencing, Arthrobacter, Chryseobacterium, Brevibacterium, Staphylococcus and Kocuria were the main genera of the fresh red drum fillets. At the sensory rejection time, lactic acid bacteria (LAB), particularly Carnobacterium sp., dominated the microbiota of both types of packaging. The pH value of fresh samples was between 5.96 and 6.37 and did not vary greatly in all trials. Total volatile basic nitrogen (TVBN) and trimethylamine (TMA) concentrations were low and not represent reliable indicators of the spoilage, contrary to some biogenic amines (cadaverine, putrescine and tyramine).
Chilled packed fillets of red drum have an extended shelf-life compared to whole gutted iced fish. Overall, few differences in sensory and microbial quality were observed between the VP and MAP samples.
Next-Generation Sequencing (NGS) provided data on the microbiota of a tropical fish.
•A polyphasic approach to characterize the microbial ecosystem of red drum is used•At day 0, less common genera (Chryseobacterium, Brevibacterium, etc.) dominated•Chilled packed fillets had a longer shelf-life than whole gutted iced fish•Packaging favored the dominance of the LAB (particularly Carnobacterium spp.)•Cadaverine, putrescine and tyramine could be good indicators of the fillets spoilage
Biopreservation is a natural technology of food preservation, which consists of inoculating food with microorganisms selected for their antibacterial properties. The objective of this study was to ...select lactic acid bacteria (LAB) to improve the quality of cold-smoked salmon (CSS). In this work, different strains representative of the 4 dominant species, identified in a previous study by pyrosequencing the 16S rRNA gene, were isolated and their spoiling potential in CSS blocks, sterilized by ionization, was assessed by twelve trained panelists along the vacuum storage at 8°C. Photobacterium phosphoreum, Brochothrix thermosphacta and Serratia proteamaculans released strong off-odors whereas the spoiling potential of Carnobacterium divergens was weaker. The spoiling capacity of Lactococcus piscium EU2241, Leuconostoc gelidum EU2247, Lactobacillus sakei EU2885, Staphylococcus equorum S030674 and 4 commercial starters was tested by the same method and 2 strains were eliminated due to off-odor production. The effect of the 6 selected LAB against the 4 specific spoiling organisms (SSOs) selected was tested by challenge tests in sterile CSS blocks. The protective effect of the LAB differed from one SSO to another and no correlation could be established between the sensory improvement, SSO inhibition, and the implantation or acidification of protective cultures (PCs). All the PCs except L. piscium reduced the off-odors released by P. phosphoreum although some of them had no effect on its growth. S. equorum, which did not grow in CSS, favored the implantation of P. phosphoreum but prevented its off-odor formation. L. piscium was the only strain that prevented the spoilage of B. thermosphacta and S. proteamaculans although it did not grow very well and did not acidify the product. L. gelidum EU2247 inhibited the growth of these 2 SSOs and lowered the pH but had no effect on the sensory quality. Finally, L. piscium was tested in 2 naturally contaminated products, with a positive effect on 1 batch. This effect was not correlated with the microbial ecosystem as determined by acultural and cultural techniques. Based on these results, the selection strategy is discussed.
•Four specific spoilage bacteria of cold-smoked salmon were identified.•Eight protective cultures were tested in situ against the four spoilage bacteria.•Lactococcus piscium EU2241 improved the sensory quality of cold-smoked salmon.•There was no correlation between sensory improvement and microbial ecosystem.
Listeria monocytogenes is a pathogenic Gram positive bacterium and the etiologic agent of listeriosis, a severe food-borne disease. Lactococcus piscium CNCM I-4031 has the capacity to prevent the ...growth of L. monocytogenes in contaminated peeled and cooked shrimp. To investigate the inhibititory mechanism, a chemically defined medium (MSMA) based on shrimp composition and reproducing the inhibition observed in shrimp was developed. In co-culture at 26 °C, L. monocytogenes was reduced by 3–4 log CFU g−1 after 24 h. We have demonstrated that the inhibition was not due to secretion of extracellular antimicrobial compounds as bacteriocins, organic acids and hydrogen peroxide. Global metabolomic fingerprints of these strains in pure culture were assessed by liquid chromatography coupled with high resolution mass spectrometry. Consumption of glucose, amino-acids, vitamins, nitrogen bases, iron and magnesium was measured and competition for some molecules could be hypothesized. However, after 24 h of co-culture, when inhibition of L. monocytogenes occurred, supplementation of the medium with these compounds did not restore its growth. The inhibition was observed in co-culture but not in diffusion chamber when species were separated by a filter membrane. Taken together, these data indicate that the inhibition mechanism of L. monocytogenes by L. piscium is cell-to-cell contact-dependent.
•A chemically defined medium (MSMA) was developed to study bacterial interactions.•Lactococcus piscium CNCM I-4031 inhibits the growth of L. monocytogenes as in shrimp.•This interaction requires contact between both strains.•First report of contact dependant inhibition between a LAB and L. monocytogenes.
Biopreservation is a sustainable approach to improve food safety and maintain or extend food shelf life by using beneficial microorganisms or their metabolites. Over the past 20 years, omics ...techniques have revolutionised food microbiology including biopreservation. A range of methods including genomics, transcriptomics, proteomics, metabolomics and meta-omics derivatives have highlighted the potential of biopreservation to improve the microbial safety of various foods. This review shows how these approaches have contributed to the selection of biopreservation agents, to a better understanding of the mechanisms of action and of their efficiency and impact within the food ecosystem. It also presents the potential of combining omics with complementary approaches to take into account better the complexity of food microbiomes at multiple scales, from the cell to the community levels, and their spatial, physicochemical and microbiological heterogeneity. The latest advances in biopreservation through omics have emphasised the importance of considering food as a complex and dynamic microbiome that requires integrated engineering strategies to increase the rate of innovation production in order to meet the safety, environmental and economic challenges of the agri-food sector.
Tropical shrimp is of considerable economic importance in the world but is highly perishable due to microbial and chemical degradation. Biopreservation is a food preservation technology based on the ...addition of “positive” bacteria able to kill or prevent the growth of undesirable microorganisms. Two strains of lactic acid bacteria (LAB) have previously been selected for a biopreservation strategy: Lactococcus piscium CNCM I-4031, for its ability to prevent the sensory deterioration of seafood and Carnobacterium divergens V41, which inhibits growth of Listeria monocytogenes. The objective was to test the association of the two strains to improve both the quality and safety of shrimp. In a first trial, the two LAB were inoculated alone or in a cocktail in cooked and peeled shrimp (CPS) Penaeus vannamei at 5×105CFU/g. Chemical, sensory and microbiological analyses by culture-dependent and -independent methods were performed during storage under modified atmosphere packaging (MAP) at 8°C. The results were compared to a non-inoculated batch. In a second trial, the same experiments were repeated in the presence of 102CFU/g of L. monocytogenes RF191. The microbiota of CPS was composed of LAB, Shewanella spp. and Enterobacteriaceae. Brochothrix thermosphacta was not detected. L. piscium and C. divergens reached 108 and 109CFU/g, respectively, in 7days and did not inhibit each other when co-inoculated. L. piscium reduced L. monocytogenes by 1Log (CFU/g) for 28days. C. divergens had an immediate listericidal effect lasting 7days. A regrowth of L. monocytogenes was then observed but the count was always 2 to 5Log (CFU/g) lower than in the control. No additional or synergic effect between protective strains was observed and the cocktail had the same inhibitory effect as C. divergens alone. C. divergens was very effective at preventing the sensory deterioration of CPS. This may be related to the inhibition of Shewanella and Enterobacteriaceae. However, the panelists could detect the presence of C. divergens during the first 10days of storage, with slight unpleasant odors and flavors. L. piscium improved the sensory quality of CPS for 14days only. In co-culture, L. piscium eliminated the off-odors and flavors released by C. divergens in the early stage of storage and the co-culture allowed maintaining a good quality of CPS throughout the storage. Therefore, the use of a cocktail of L. piscium CNCM I-4031 and C. divergens V41 is recommended in a strategy of biopreservation of shrimp.
•A cocktail of L. piscium and C. divergens was tested to biopreserve cooked shrimp.•L. piscium CNCM-I4031 and C. divergens V41 have no antagonist effect on each other.•L. piscium inhibited L. monocytogenes by 1Log and C. divergens by 2 to 5Log CFU/g.•The cocktail showed no additional or synergetic effect on inhibition of Listeria.•The cocktail was more efficient to improve sensory quality than the strains alone.
Beneficial bacteria with antibacterial properties are attractive alternatives to chemical-based antibacterial or bactericidal agents. Our study sourced such bacteria from horticultural produce and ...environments to explore the mechanisms of their antimicrobial properties. Five strains of
were studied that possessed antibacterial activity against the pathogen
. The vegetative culture of these strains (
-PFR46I06,
-PFR46H06,
-PFR46H07,
-PFR46H08 and
-PFR46H09) were tested against
(n = 31),
(n = 1) and
(n = 1) isolated from seafood and horticultural sources and from clinical cases (n = 2) using solid media coculture and liquid media coculture. All
strains were inhibited by all strains of
; however,
-PFR46H07,
-PFR46H08 and
-PFR46H09 on solid media showed good inhibition, with average zones of inhibition of 14.8 mm, 15.1 mm and 18.2 mm, respectively, and the other two strains and
-PFR46H09 had a significantly greater zone of inhibition than the others (
< 0.05). There was no inhibition observed in liquid media coculture or in
culture supernatants against
spp. by any of the
strains. Therefore, we hypothesized that the structural apparatus that causes cell-to-cell contact may play a role in the ejection of ant-listeria molecules on solid media to inhibit
isolates, and we investigated the structural protein differences using whole-cell lysate proteomics. We paid special attention to the type VI secretion system (
-T6SS) for the transfer of effector proteins or bacteriocins. We found significant differences in the peptide profiles and protein summaries between these isolates' lysates, and PFR46H06 and PFR46H07 possessed the fewest secretion system structural proteins (12 and 11, respectively), while PFR46H08 and PFR46H09 had 18 each.
-PFR46H09, which showed the highest antimicrobial effect, had nine
-T6SS structural proteins compared to only four in the other three strains.
In recent years, bacteriocins produced by lactic acid bacteria (LAB) have shown great potential for food safety preservation, especially for ready-to-eat products. In this study, bio-protective ...membrane was made from plasma-treated polypropylene film and functionalized with Carnobacterium divergens V41 (bacteriocin-producing strain) for the purpose of inhibiting Listeria monocytogenes growth in culture media and cold-smoked salmon (CSS) at refrigerated temperatures. In semi solid Brain Heart Infusion (BHI) agar, bio-protective plastic membrane led to a 3-Log reduction in L. monocytogenes count compared to the control, after 14 days of aerobic incubation at 8 °C. In vacuum-packed CSS, L. monocytogenes growth was inhibited by bio-protective plastic membrane after 7 days of storage at 4 °C and 21 days at 8 °C. Antilisterial activity of plastic membrane was even better than C. divergens cells added in CSS by direct spraying. Stability test has shown that bio-protective plastic membrane stored for 42 days at 4 °C still exerted antimicrobial activity against L. monocytogenes on BHI agar (2-Log reduction compared to the control). These preliminary results demonstrate that bio-protective plastic membrane can be used to control pathogenic bacteria in food products with potential industrial development.
●Modification of polypropylene surface by plasma treatment in order to fix bioprotective Carnobacterium divergens bacteria.●Antilisterial activity of bio-protective plastic film tested in BHI and smoked salmon.●Assessment of stability of bio-protective polypropylene film in BHI over storage time.●Potentiality of development of a new active food packaging
Tenacibaculum discolor develops biofilm in marine aquaculture production tanks and is identified as one of the causative agents of tenacibaculosis, a bacterial disease that causes significant losses ...in marine aquaculture production. In this study, the biofilm characteristics of T. discolor strain FMCC B487 were evaluated. Cell growth and biofilm formation and development were studied in miniaturized assays to assess the effect of different levels of environmental factors temperature and salinity, as well as the presence of monosaccharides potentially found in aquaculture hatcheries. The ability of the strain to grow and develop strong biofilms in ambient to high temperatures and at salinities above 20 g/L was shown. Mannose was the monosaccharide with the most prominent impact on the T. discolor strain FMCC B487 biofilm. The composition of planktonic cell extract, biofilm extracts, and extracellular polymeric substances (EPS) produced by T. discolor strain FMCC B487 were investigated by means of colorimetric and fluorometric assays as well as analyses by electrophoresis, gas chromatography, and high-performance size-exclusion chromatography coupled with a multiangle light scattering detector, revealing the dominance of proteins and lipids and the absence of high-molecular-weight polysaccharides. This information may serve as a basis for considering anti-biofilm strategies against the pathogen T. discolor.
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