Genotypic and phenotypic characterization of the food spoilage bacterium Brochothrix thermosphacta

Modeling the growth and volatile metabolite production of spoilage-causing Brochothrix thermosphacta on solid meat substrates under modified atmospheres

Spoilage microorganisms including Brochothrix thermosphacta are associated with various volatile organic compounds (VOCs) and off-odors in meat. Modified atmosphere packaging (MAP) limits microbial growth and affects metabolic activities. However, the exact impact of gas compositions on B. thermosphacta still remains unclear, especially regarding the direct relationship between its growth and VOC accumulation. This study thus aimed to investigate and model these behaviors by growing B. thermosphacta on solid pork simulation media under different packaging atmospheres. Five O2/CO2/N2 ratios (v/v%: air, 0/0/100, 60/40/0, 5/40/55, 0/40/60) were examined to study the synergy of MAP gases on the aerobic/anaerobic metabolism of B. thermosphacta. The quantities of VOCs (ppbv) were fitted against respective bacterial numbers (log CFU/g) of different individual samples assessed at regular storage intervals. Results suggest that VOCs including acetoin, ethanol, benzaldehyde, and 3-methyl-1-butanol are the major metabolites of B. thermosphacta. Under air, the observable increase of multiple VOCs started at 5.9-6.6 log CFU/g and was closely correlated with microbial growth. In contrast, 100 % N2 caused low acetoin levels and high ethanol emission because of shifting to an anaerobic metabolism. Under high-CO2 atmospheres, concentrations of most VOCs were reduced, likely linked to limited microbial counts. Through this study, predictive modeling offers novel insights into the impact of the atmosphere on bacterial growth and VOC production. This helps to fully understand microbial spoilage and contributes to the development of suitable meat storage strategies.

Preservation strategies for processed grass carp products: Analyzing quality and microbial dynamics during chilled and ice temperature storage

This study investigated the impact of ice temperature storage on quality and bacterial composition of processed fish paste products (PFP). Freezing curve revealed the ice temperature was -1 °C. Electric nose (e-nose) showed significant changes in volatile components within 8 days. Results of total volatile basic nitrogen (TVB-N) showed that PFP stored at 4 °C reached its limit after 2 days, whereas PFP stored at ice temperature remained stable for 6 days. Thiobarbituric acid reactive substances (TBARS) demonstrated delayed oxidation in PFP stored at ice temperature compared to 4 °C. TCA-soluble peptides indicated that the protein degradation was suppressed by ice temperature. Additionally, ice temperature inhibited microbial growth and altered bacterial composition. High-throughput sequencing revealed that Pseudomonas, Brochothrix, Carnobacterium were dominant at 4 °C, while Acinetobacter, Pseudomonas, Janthinobacterium and Brochothrix were dominant at ice temperature. In summary, ice temperature might be a potential method for maintaining the freshness of PFP.

Post-harvest bacterial contamination of fish, their assessment and control strategies

Healthy fish populations lead to healthy aquatic ecosystems and it is our responsibility to be a part of the solution. Fish is one of the most favored foods and is suitable for people of all ages. Fish is an essential source of protein, vitamins, and minerals and a source of income for millions of people. Human population growth and climate change are putting a strain on our food system, demanding the development of sustainable services to enhance global food production and its security. Food safety is an intricate problem in both developed and developing countries. Fresh fish is a highly perishable food with a limited life span; as a result, it must be delivered and kept carefully to minimize deterioration and assure safety. Fish spoilage is linked to biochemical changes that occur post-harvest, such as storage and transportation. These modifications can account for fish spoilage by altering the taste, texture, and appearance. Fish harvesting, distribution, and post-harvest handling are all unhygienic, resulting in poor and unpredictable fish quality in the market. Many innovative and effective control measurements of various bacteria in fish have been proposed and evaluated. This review is a systematic approach to investigating post-harvest fish spoilage, its assessment, and control strategies.

The complete genomic sequence of the type strain Brochothrix thermosphacta DSM 20171 highlights a diversity of prophages in this species

The bacterium Brochothrix thermosphacta is a known muscle food spoiler. Here, the complete genome sequence of the B. thermosphacta type strain, DSM 20171, is reported. Prediction of prophages and genomic islands reveals an unsuspected diversity in this bacterial species that deserves further investigation.

Effects of lactic acid and ascorbic acid electrostatic spraying on the physicochemical attributes and microbial diversity of beef aged at mild temperature (10 °C)

This study aimed to clarify the effect of electrostatic spraying of lactic acid (LE) and ascorbic acid (AE) on vacuum-packaged beef aged at 10 °C. The physicochemical attributes, flavor profiles, and microbial diversities were evaluated. Beef steaks were electrostatically sprayed twice with 4% LE, 0.5% AE, or a mixture of them (LAE). Afterward, the beef was vacuum-packaged and aged. All treated beef exhibited a decrease in quality and sensory scores over time. At the end of the study period, the total viable count (TVC) and the total volatile basic nitrogen values in the control group (7.34 log CFU/g and 15.52 mg/100 g, respectively) were higher than those in the acid-treated groups. The LAE group exhibited the best color stability and the lowest TVC and Enterobacteriaceae counts after aging. High-throughput sequencing analysis revealed that acid types and electrostatic spray could change the microbiota structure. Leuconostoc was the dominant bacteria in the AE and LAE groups, while Enterococcus became the predominant bacteria in the NLE and LE groups with aging. This indicates that electrostatic spray combined with acid treatment can ensure beef quality and microbiological safety at mild temperatures.

Complete sequences of two Paenibacillus sp. strains and one Lysinibacillus strain isolated from the environment on STAA medium highlight biotechnological potential

Streptomycin thallous acetate actidione medium is typically used to isolate Brochothrix thermosphacta bacteria from food. Using this medium, three bacterial strains were isolated from the environment. Genomic sequences demonstrated that these bacteria are of the genera Lysinibacillus and Paenibacillus and are of biotechnological interest.

Biofilm formation of the food spoiler Brochothrix thermosphacta on different industrial surface materials using a biofilm reactor

Brochothrix thermosphacta is considered as a major food spoiler bacteria. This study evaluates biofilm formation by B. thermosphacta CD337(2) - a strong biofilm producer strain - on three food industry materials (polycarbonate (PC), polystyrene (PS), and stainless steel (SS)). Biofilms were continuously grown under flow at 25 °C in BHI broth in a modified CDC biofilm reactor. Bacterial cells were enumerated by plate counting, and biofilm spatial organization was deciphered by combining confocal laser scanning microscopy and image analysis. The biofilms had the same growth kinetics on all three materials and reach 8log CFU/cm2 as maximal concentration. Highly structured biofilms were observed on PC and PS, but less structured ones on SS. This difference was confirmed by structural quantification analysis using the image analysis software tool BiofilmQ. Biofilm on SS show less roughness, density, thickness and volume. The biofilm 3D structure seemed to be related to the coupon topography and roughness. The materials used in this study do not affect biofilm growth. However, their roughness and topography affect the biofilm architecture, which could influence biofilm behaviour.

Formulation of food grade Limosilactobacillus fermentum for antifungal properties isolated from home-made curd

Food spoilage has become a worldwide problem. Limosilactobacillus fermentum LAB212, isolated from home-made curd produces some potent antifungal compounds which can combat a wide range of spoilage and pathogenic fungi by disrupting their cell wall. Dual culture overlay assay and co-culture assay have confirmedly shown the potentiality of the strain. DOWEX50H + extraction and chemical characterization by high performance liquid chromatography show that lactic acid and acetic acid are playing the key roles in executing the antifungal activity. DPPH scavenging assay proves that the strain also exhibits a good antioxidant activity. After observing all the beneficial features and social need of the chemical preservative free food it is becoming highly prospective to exploite the strain commercially. In an experiment conducted for 180 days it was standardized that LAB212 supplemented with MRS and inulin is found most effective combination when challenged against the spoilage fungal species of Aspergillus flavus VBAH14, Penicillium rubens VBCA11, thus can be used as a very effective preservative agent. Using this strain as bio-preservative agent will also minimize the food borne diseases.

A culture-based assessment of the microbiota of conventional and free-range chicken meat from Irish processing facilities

Chicken meat is the most popularly consumed meat worldwide, with free-range and ethically produced meat a growing market among consumers. However, poultry is frequently contaminated with spoilage microbes and zoonotic pathogens which impact the shelf-life and safety of the raw product, constituting a health risk to consumers. The free-range broiler microbiota is subject to various influences during rearing such as direct exposure to the external environment and wildlife which are not experienced during conventional rearing practices. Using culture-based microbiology approaches, this study aimed to determine whether there is a detectable difference in the microbiota from conventional and free-range broilers from selected Irish processing plants. This was done through analysis of the microbiological status of bone-in chicken thighs over the duration of the meat shelf-life. It was found that the shelf-life of these products was 10 days from arrival in the laboratory, with no statistically significant difference (P > 0.05) evident between free-range and conventionally raised chicken meat. A significant difference, however, was established in the presence of pathogenesis-associated genera in different meat processors. These results reinforce past findings which indicate that the processing environment and storage during shelf-life are key determinants of the microflora of chicken products reaching the consumer.

Genomic Characterization of a Tetracycline-Resistant Strain of Brochothrix thermosphacta Highlights Plasmids Partially Shared between Various Strains

The Gram-positive bacterium Brochothrix thermosphacta is a spoilage agent commonly found on meat products. While the tet(L) gene, which confers resistance to tetracycline, has been identified in certain strains of B. thermosphacta, only a limited number of studies have investigated this gene and its potential presence on mobile DNA elements. This study aims to analyze the tetracycline-resistant strain B. thermosphacta BT469 at the genomic level to gain insight into the molecular determinants responsible for this resistance. Three plasmids have been identified in the strain: pBT469-1, which contains a tetR gene; pBT469-2, which harbours the tet(L) gene responsible for tetracycline resistance; and pBT469-3, which carries genes encoding for a thioredoxin and a phospholipase A2. Homology searches among sequences in public databases have revealed that the plasmid pBT469-2 is currently unique to the BT469 strain. However, the pBT469-1 plasmid is also found in three other strains of B. thermosphacta. Notably, sequences similar to pBT469-1 and pBT469-2 were also found in other bacterial genera, suggesting that these plasmids may be part of a diverse family present in several bacterial genera. Interestingly, sequences of various strains of B. thermosphacta show a high level of similarity with pBT469-3, suggesting that variants of this plasmid could be frequently found in this bacterium.

Microbial and Biochemical Profile of Different Types of Greek Table Olives

Analysis of table olives microbiome using next-generation sequencing has enriched the available information about the microbial community composition of this popular fermented food. In this study, 16S and 18S rRNA sequencing was performed on table olives of five Greek popular cultivars, Halkidikis, Thassou, Kalamon, Amfissis, and Konservolia, fermented either by Greek style (in brine or salt-drying) or by Spanish style, in order to evaluate their microbial communities. Moreover, analytical methods were used to evaluate their biochemical properties. The prevailing bacterial species of all olives belonged to Lactobacillaceae, Leuconostocaceae, and Erwiniaceae families, while the most abundant yeasts were of the Pichiaceae family. Principal coordinates analysis showed a clustering of samples cured by salt-drying and of samples stored in brine, regardless of their cultivar. The biochemical evaluation of total phenol content, antioxidant activity, hydroxytyrosol, oleuropein, oleocanthal, and oleacein showed that salt-dried olives had low amounts of hydroxytyrosol, while Spanish-style green olives had the highest amounts of oleocanthal. All the other values exhibited various patterns, implying that more than one factor affects the biochemical identity of the final product. The protocols applied in this study can provide useful insights for the final product, both for the producers and the consumers.

Microbial spoilage mechanisms of vacuum-packed lamb meat: A review

Lamb meat is an important export commodity, however chilled vacuum-packed (VP) lamb has approximately half the shelf-life of beef under the same storage conditions. This makes the industry more vulnerable to financial losses due to long shipping times and unexpected spoilage. Understanding the spoilage mechanisms of chilled VP lamb in relation to VP beef is important for developing effective strategies to extend the shelf-life of lamb. This review has discussed various key factors (i.e., pH, fat, and presence of bone) that have effects on microbial spoilage of VP lamb contributing to its shorter shelf-life relative to VP beef. A range of bacterial organisms and their metabolisms in relevance to lamb spoilage are also discussed. The data gap in the literature regarding the potential mechanisms of spoilage in VP red meat is highlighted. This review has provided the current understanding of key factors affecting the shelf-life of VP lamb relative to VP beef. It has also identified key areas of research to further understand the spoilage mechanisms of VP lamb. These include investigating the potential influence of fat and bone (including bone marrow) on the shelf-life, as well as assessing changes in the meat metabolome as the spoilage microbial community is developing using an integrated approach. Such new knowledge would aid the development of effective approaches to extend the shelf-life of VP lamb.

Exploring the Diversity of Biofilm Formation by the Food Spoiler Brochothrix thermosphacta

Brochothrix thermosphacta is considered as a major spoiler of meat and seafood products. This study explores the biofilm formation ability and the biofilm structural diversity of 30 multi-origin B. thermosphacta strains using a set of complementary biofilm assays (biofilm ring test, crystal violet staining, and confocal laser scanning microscopy). Two major groups corresponding to low and high biofilm producers were identified. High biofilm producers presented flat architectures characterized by high surface coverage, high cell biovolume, and high surface area.

Systematic review and critical reflection on the isolation and identification methods for spoilage associated bacteria in fresh marine fish

Consumers demand more fresh, safe, and high-quality food. As this is partiallycorrelated to the microbial profile, several microbiological examination tools are available. Incontrast to meat, no microbiological normalized methods to assess the microbiological quality of fresh marine fish have been agreed on. As a result, studies on the detection and diversity of spoilage associated organisms (SAOs) in fish often apply various detection, isolation, and identification techniques. This complicates the comparison and interpretation of data reported, and often results in different or inconclusive results. Therefore, the present review aimed to present a critical overview of the isolation/cultivation and detection techniques currently applied in fish microbiology. After a comprehensive search in the PubMed, Web of Science and Scopus databases, a total of 111 studies fulfilled the review selection criteria. Results revealed that when relying on culture media for the isolation of SAOs in fish, it is essential to include a salt-containing medium next to plate count agar that is currently used as the reference medium for the enumeration of bacteria on fish. In terms of identification, MALDI-TOF MS and 16S rRNA gene sequencing are currently the most promising tools, though other housekeeping genes should be targeted as well, and, the biggest challenge at this point is still the lack of comprehensive proteomic and sequence databases for SAOs. A full replacement of cultivation by next generation sequencing is difficult to recommend due to the absence of a standardized experimental methodology, especially for fish, and the relatively high sequencing costs. Additionally, a discrepancy between culture-dependent and independent methods in revealing the bacterial diversity, and abundancy, from marine fish was demonstrated by several authors. It is therefore recommended to consider both approaches as complements of one another, rather than substitutes, and to include them simultaneously to yield more complete results regarding the SAOs in fresh marine fish. As such, a thorough understanding of the biology of spoilage organisms and process will be obtained to prolong the shelf-life and deliver a high-quality product.

Application of MALDI-TOF MS for identification of environmental bacteria: A review

Bacteria play a variety of roles in the environment. They maintain the balance in the ecosystem and provide different ecosystem services such as in biogeochemical cycling of nutrients, biodegradation of toxic pollutants, and others. Therefore, isolation and identification of different environmental bacteria are important to most environmental research. Due to the high cost and time associated with the conventional molecular techniques, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has gained considerable attention for routine identification of bacteria. This review aims to provide an overview of the application of MALDI-TOF MS in various environmental studies through bibliometric analysis and literature review. The bibliometric analysis helped to understand the time-variable application of MALDI-TOF MS in various environmental studies. The categorical literature review covers various environmental studies comprising areas like ecology, food microbiology, environmental biotechnology, agriculture, and plant sciences, which show the application of the technique for identification and characterization of pollutant-degrading, plant-associated, disease-causing, soil-beneficial, and other environmental bacteria. Further research should focus on bridging the gap between the phylogenetic identity of bacteria and their specific environmental functions or metabolic traits that can help in rapid advancements in environmental research, thereby, improving time and cost savings.

Εvaluation of the microbial stability and shelf life of 50% NaCl-reduced traditional Greek pork meat product "Syglino of Monemvasia" stored under vacuum at different temperatures

Nowadays, consumers are increasingly concerned about nutrition and health issues. "Syglino of Monemvasia" is a traditional Greek cooked and smoked, sliced pork meat product. Although this is a nutritious food, its consumption should be done in moderation due to the pickling process of its preparation. This product was thus here optimized to contain half salt (NaCl) amount and its microbial stability and shelf life was then assessed in comparison to the already available commercial product. For this, the total viable counts (TVCs) and some critical specific spoilage associations were enumerated at each product type during vacuum incubation at four different temperatures (0, 5, 10, and 15 °C). The alterations in pH, a_w, color, and some other crucial sensory attributes of each product were also periodically monitored. The new low-salt product was found to remain microbiologically stable under refrigerated vacuum storage for approximately two weeks, being finally spoiled by Brochothrix thermosphacta grown above 10⁷ CFU/g, ultimately resulting in the deterioration of taste, odor, and overall appearance of the product, and thus leading to its subsequent organoleptic rejection. Despite its limited shelf life, the 50% NaCl-reduced "Syglino" could be released in the local market provided that the cooling chain is maintained throughout its distribution (≤5 °C) and at the same time consumers are willing to accept its milder taste. Although salt replacers could have been used to improve its flavor and at the same time increase its shelf life, the product here developed without the use of such alternatives will hopefully contribute to the taste training of its consumers for less salt in their diet, keeping in parallel its clean label with no added preservatives and other food additives.

Novel Bio-Based Materials and Applications in Antimicrobial Food Packaging: Recent Advances and Future Trends

Food microbial contamination not only poses the problems of food insecurity and economic loss, but also contributes to food waste, which is another global environmental problem. Therefore, effective packaging is a compelling obstacle for shielding food items from outside contaminants and maintaining its quality. Traditionally, food is packaged with plastic that is rarely recyclable, negatively impacting the environment. Bio-based materials have attracted widespread attention for food packaging applications since they are biodegradable, renewable, and have a low carbon footprint. They provide a great opportunity to reduce the extensive use of fossil fuels and develop food packaging materials with good properties, addressing environmental problems and contributing significantly to sustainable development. Presently, the developments in food chemistry, technology, and biotechnology have allowed us to fine-tune new methodologies useful for addressing major safety and environmental concerns regarding packaging materials. This review presents a comprehensive overview of the development and potential for application of new bio-based materials from different sources in antimicrobial food packaging, including carbohydrate (polysaccharide)-based materials, protein-based materials, lipid-based materials, antibacterial agents, and bio-based composites, which can solve the issues of both environmental impact and prevent foodborne pathogens and spoilage microorganisms. In addition, future trends are discussed, as well as the antimicrobial compounds incorporated in packaging materials such as nanoparticles (NPs), nanofillers (NFs), and bio-nanocomposites.

The pathogenic and spoilage bacteria associated with red meat and application of different approaches of high CO2 packaging to extend product shelf-life

With the fast-global development of packaging techniques, the potential antimicrobial effect of CO₂, as a safe, cheap and readily available gas, makes it the integral component for packaging of meat products. The associated spoilage and/or pathogenic bacteria on raw meat may respond in different ways to elevated CO₂ concentrations. The growth of some aerobic Gram-negative bacteria such as Pseudomonas spp. is significantly inhibited but some LAB bacteria may be allowed to grow faster and dominate the product. The antimicrobial efficacy of enriched CO₂ packaging is attributed to the rate of CO₂ solubility in the product which is itself affected by the level of headspace CO₂, product pH, temperature and the ratio of headspace gas to product (G:P). This review, first, explores the varied range of beef and sheep meat spoilage and pathogenic bacteria and the intrinsic and extrinsic parameters that may influence the pattern of microbial growth and meat spoilage rate during storage. Then, the antimicrobial mechanism of elevated CO₂ packaging will be discussed and the different approaches of achieving enriched CO₂ packaging i.e. the traditional technique of flushing a desired gas mixture and/or using the new commercially developed CO₂ emitters will then be compared in terms of their strengths, limitations and technical mode of action.

Effect of Adding Essential Oils of Caraway and Rosemary on Volatile Aroma Compounds Derived from Stored Vacuum Packaged Minced Turkey Meat

Changes in the odor of meat during its storage are one of the basic indicators affecting its assessment and possible disqualification. The aim of the study was to determine whether the addition of essential oils may affect the composition and concentration of volatile compounds included in the aroma of stored turkey meat. We investigated the effect of adding essential oil (EO) of caraway (0.02% v/w), rosemary (0.02% v/w) and a mixture of the two (0.01% each) on the composition of volatile compound fractions formed during 10-day storage of vacuum-packed minced turkey meat. The EOs used were also evaluated for their influence on microbial contamination (total viable count and lactic acid bacteria count), sensory quality (odor and taste) and the level of fat rancidity (acid value, peroxide value and p-anisidine value) and pH in chill-stored samples. In terms of sensory indicators, the greatest beneficial effect of adding EOs was noted in the odor of raw meat. Use of the HS-SPME/GC-MS (headspace-solid phase microextraction/gas chromatography-mass spectrometry) method showed that the addition of essential oils significantly reduced the amounts of benzeneacetaldehyde, 2-octenal and ethyl 2-methyloctanoate compared with the control sample. In addition, in the presence of essential oils of rosemary and caraway, decreases were noted in benzaldehyde and 9-octadecenal, respectively. These changes may potentially affect the reception of the odor. There was a beneficial effect of the EOs in reducing the levels of fat oxidation indicators, including peroxides. However, the oils at applied concentrations had no significant effect on the total viable count and LAB count.

Quantification of Viable Brochothrix thermosphacta in Cold-Smoked Salmon Using PMA/PMAxx-qPCR

The aim of this study was to develop a rapid and accurate PMA-qPCR method to quantify viable Brochothrix thermosphacta in cold-smoked salmon. B. thermosphacta is one of the main food spoilage bacteria. Among seafood products, cold-smoked salmon is particularly impacted by B. thermosphacta spoilage. Specific and sensitive tools that detect and quantify this bacterium in food products are very useful. The culture method commonly used to quantify B. thermosphacta is time-consuming and can underestimate cells in a viable but not immediately culturable state. We designed a new PCR primer set from the single-copy rpoC gene. QPCR efficiency and specificity were compared with two other published primer sets targeting the rpoC and rpoB genes. The viability dyes PMA or PMAxx were combined with qPCR and compared with these primer sets on viable and dead B. thermosphacta cells in BHI broth and smoked salmon tissue homogenate (SSTH). The three primer sets displayed similar specificity and efficiency. The efficiency of new designed rpoC qPCR on viable B. thermosphacta cells in SSTH was 103.50%, with a linear determination coefficient (r²) of 0.998 and a limit of detection of 4.04 log CFU/g. Using the three primer sets on viable cells, no significant difference was observed between cells treated or untreated with PMA or PMAxx. When dead cells were used, both viability dyes suppressed DNA amplification. Nevertheless, our results did not highlight any difference between PMAxx and PMA in their efficiency to discriminate viable from unviable B. thermosphacta cells in cold-smoked salmon. Thus, this study presents a rapid, specific and efficient rpoC-PMA-qPCR method validated in cold-smoked salmon to quantify viable B. thermosphacta in foods.

Assessment of the potential use of MALDI-TOF MS for the identification of bacteria associated with chilled vacuum-packaged lamb meat

The focus of this study was to compare the effectiveness of MALDI-TOF MS and partial 16S rRNA gene sequencing for the identification of bacteria isolated from VP lamb meat stored chilled at 5 °C for 21 days, at the same time gaining insights into bacterial changes over time. The identity of bacterial isolates on non-selective and selective agars was determined by both methods and results compared. Results showed that total bacterial numbers increased over the 21 days (as expected) with Staphylococcus and Pseudomonas (day 0) being replaced by Carnobacterium, Brochothrix and members of the Enterobacteriaceae family by day 21. A high level of agreement (86-100%) for bacterial isolates' identity at genus level was observed between MALDI-TOF MS and partial 16S rRNA gene-based sequencing for isolates where identification was possible. With its cheaper cost and faster turnaround time, once optimized, MALDI-TOF MS could become a useful alternative to 16S rRNA gene-sequencing for the rapid identification of red meat bacterial isolates.

Characterization of Bacterial Communities of Cold-Smoked Salmon during Storage

Cold-smoked salmon is a widely consumed ready-to-eat seafood product that is a fragile commodity with a long shelf-life. The microbial ecology of cold-smoked salmon during its shelf-life is well known. However, to our knowledge, no study on the microbial ecology of cold-smoked salmon using next-generation sequencing has yet been undertaken. In this study, cold-smoked salmon microbiotas were investigated using a polyphasic approach composed of cultivable methods, V3—V4 16S rRNA gene metabarcoding and chemical analyses. Forty-five cold-smoked salmon products processed in three different factories were analyzed. The metabarcoding approach highlighted 12 dominant genera previously reported as fish spoilers: Firmicutes Staphylococcus, Carnobacterium, Lactobacillus, β-Proteobacteria Photobacterium, Vibrio, Aliivibrio, Salinivibrio, Enterobacteriaceae Serratia,Pantoea, γ-Proteobacteria Psychrobacter, Shewanella and Pseudomonas. Specific operational taxonomic units were identified during the 28-day storage study period. Operational taxonomic units specific to the processing environment were also identified. Although the 45 cold-smoked salmon products shared a core microbiota, a processing plant signature was found. This suggest that the bacterial communities of cold-smoked salmon products are impacted by the processing environment, and this environment could have a negative effect on product quality. The use of a polyphasic approach for seafood products and food processing environments could provide better insights into residential bacteria dynamics and their impact on food safety and quality.

Metataxonomic profiling of bacterial communities and their predictive functional profiles in traditionally preserved meat products of Sikkim state in India

Traditionally preserved meat products are common food items in Sikkim state of India. We studied the high-throughput sequencing of four traditionally preserved meat products viz. beef kargyong, pork kargyong, yak satchu and khyopeh to profile the bacterial communities and also inferred their predictive functional profiles. Overall abundant OTUs in samples showed that Firmicutes was the abundant phylum followed by Proteobacteria and Bacteroidetes. Abundant species detected in each product were Psychrobacter pulmonis in beef kargyong, Lactobacillus sakei in pork kargyong, Bdellovibrio bacteriovorus and Ignatzschinera sp. in yak satchu and Lactobacillus sakei and Enterococcus sp. in khyopeh. Several genera unique to each product, based on analysis of shared OTUs contents, were observed among the samples except in khyopeh. Goods coverage recorded to 1.0 was observed, which reflected the maximum bacterial diversity in the samples. Alpha diversity metrics showed a maximum bacterial diversity in khyopeh and lowest in pork kargyong Community dissimilarities in the products were observed by PCoA plot. A total of 133 KEGG predictive functional pathways was observed in beef kargyong, 131 in pork kargyong, 125 in yak satchu and 101 in khyopeh. Metagenome contribution of the OTUs was computed using PICTRUSt2 and visualized by BURRITO software to predict the metabolic pathways. Several predictive functional profiles were contributed by abundant OTUs represented by Enterococcus, Acinetobacter, Agrobacterium, Bdellovibrio, Chryseobacterium, Lactococcus, Leuconostoc, Psychrobacter, and Staphylococcus.

Characterization of Clostridium tyrobutyricum Strains Using Three Different Typing Techniques

Clostridium tyrobutyricum is well known as one of the main causative agents of severe cheese spoilage. The metabolism of this anaerobic bacterium during ripening leads to textural and sensory defects in cheese and consequential loss of product value. The potential to induce cheese spoilage, however, may vary among different strains of the same species. Therefore, a better understanding of the intra-species diversity of C. tyrobutyricum may be of practical relevance for the dairy industry. In the present study, we compared the ability of three typing techniques to differentiate 95 C. tyrobutyricum strains on the subspecies level: (1) repetitive element palindromic PCR (rep-PCR) fingerprinting combined with conventional agarose gel electrophoresis, (2) hexaplex-PCR followed by an automated capillary electrophoresis and (3) matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) typing. MALDI-TOF MS fingerprinting provided only moderate reproducibility and low discriminatory power. Both PCR-based methods were highly reproducible and discriminative, with hexaplex-PCR fingerprinting being slightly more discriminative than rep-PCR typing. Overall, a high intra-species diversity was observed among the tested strains, indicating that further investigations on the strain level may be of interest.

Metatranscriptomic analysis of modified atmosphere packaged poultry meat enables prediction of Brochothrix thermosphacta and Carnobacterium divergens in situ metabolism

In this study, in situ-expressed metabolic routes of Brochothrix (B.) thermosphacta and Carnobacterium (C.) divergens were evaluated based on a metatranscriptomic dataset from bacteria growing on MAP chicken meat (O₂/CO₂; N₂/CO₂). Both species exhibited no (C. divergens) or minor transcription regulation (B. thermosphacta) within their main metabolic routes in response to different atmospheres. Both employ pathways related to glucose and ribose. Gluconeogenesis from lipid-borne glycerol is active in the progressing lack of carbohydrates. Pyruvate fates in both species comprise lactate, ethanol, acetate, CO₂, formate, C4-compounds and H₂O₂ (only B. thermosphacta). Both species express genes for a minimal aerobic respiratory chain, but do not possess the genetic setting for a functional citric acid cycle. While products of carbohydrate and glycerol metabolism display mild to medium sensorial off-characteristics, predicted end products of their amino acid metabolism comprise, e.g., isobutyrate and isovalerate (B. thermosphacta) or cadaverine and tyramine (C. divergens) as potent spoilage compounds.

The complex multicellular morphology of the food spoilage bacteria Brochothrix thermosphacta strains isolated from ground chicken

Herein we describe a highly structured, filamentous growth phenotype displayed by an isolate of the food spoilage microorganism Brochothrix thermosphacta. The growth morphology of this B. thermosphacta strain (strain BII) was dependent on environmental factors such as the growth media, incubation temperatures, and the inoculum concentration. Inoculation of cultures in highly dilute suspensions resulted in the formation of isolated, tight aggregates resembling fungal growth in liquid media. This same strain also formed stable, mesh-like structures in 6-well tissue culture plates under specific growth conditions. The complex growth phenotype does not appear to be unique to strain BII but was common among B. thermosphacta strains isolated from chicken. Light and electron micrographs showed that the filaments of multiple BII cells can organize into complex, tertiary structures resembling multistranded cables. Time-lapse microscopy was employed to monitor the development of such aggregates over 18 h and revealed growth originating from short filaments into compact ball-like clusters that appeared fuzzy due to protruding filaments or cables. This report is the first to document this complex filamentous growth phenotype in a wild-type bacterial isolate of B. thermosphacta.

Understanding spoilage microbial community and spoilage mechanisms in foods of animal origin

The increasing global population has resulted in increased demand for food. Goods quality and safe food is required for healthy living. However, food spoilage has resulted in food insecurity in different regions of the world. Spoilage of food occurs when the quality of food deteriorates from its original organoleptic properties observed at the time of processing. Food spoilage results in huge economic losses to both producers (farmers) and consumers. Factors such as storage temperature, pH, water availability, presence of spoilage microorganisms including bacteria and fungi, initial microbial load (total viable count-TVC), and processing influence the rate of food spoilage. This article reviews the spoilage microbiota and spoilage mechanisms in meat and dairy products and seafood. Understanding food spoilage mechanisms will assist in the development of robust technologies for the prevention of food spoilage and waste.

Transcriptome and Volatilome Analysis During Growth of Brochothrix thermosphacta in Food: Role of Food Substrate and Strain Specificity for the Expression of Spoilage Functions

Brochothrix thermosphacta is one of the main spoilers in food, responsible for meat and seafood spoilage through the production of malodorous volatile organic compounds. The molecules produced by this bacterium depend on the substrate (meat or seafood) and the storage conditions such as gas mixtures used in the packaging. It seems also that the spoilage potential is strain dependent as production of diacetyl and acetoin, two molecules responsible for seafood spoilage, varies with strains. Therefore, this suggests the involvement of different metabolic functions depending on both food substrate and strain capacities. In this study, we selected two strains with different abilities to produce diacetyl and acetoin and compared their behavior after grown in beef or cooked peeled shrimp juices. We determined the genes upregulated by both strains depending on the growth substrate and those that were specifically upregulated in only one strain. The genes upregulated by both strains in meat or in shrimp juice revealed the importance of the substrate for inducing specific metabolic pathways. The examination of genes that were specifically upregulated in only one of the two strains revealed strain features associated to specific substrates and also strain-specific regulations of metabolic pathways putatively leading to different levels of spoilage molecule production. This shows that the spoilage potential of B. thermosphacta depends on nutrients provided by food substrate and on metabolic activity potential that each strain possesses.

Quality and Safety of Fresh Chicken Fillets after High Pressure Processing: Survival of Indigenous Brochothrix thermosphacta and Inoculated Listeria monocytogenes

The effect of high-pressure processing (HPP) on Listeriamonocytogenes, the indigenous microbiota and the shelf-life of chicken fillets was evaluated. Chicken fillets were inoculated with different inocula (2, 4, and 6 log CFU/g) of a 4-strain cocktail of L. monocytogenes, vacuum-packed, processed or not with HPP (500 MPa/10 min) and stored at 4 °C and 12 °C. Total viable counts (TVC), L. monocytogenes, Pseudomonas spp., Brochothrix thermosphacta, lactic acid bacteria (LAB), Enterobacteriaceae and yeasts/molds were determined along with the pH and sensory analysis. Pulsed-field gel electrophoresis (PFGE) was used to monitor the succession of indigenous Brochothrix isolates and inoculated Listeria strains. The main spoilage microorganism of HPP-treated samples was B. thermosphacta detected after 3 days of storage. HPP decreased the inoculated Listeria population. For the low and medium inoculum case it was detected throughout the shelf-life at both temperatures in populations near to the detection limit or after enrichment. In the high inoculum case, the pathogen decreased ≥5-log cycles after HPP, while increased subsequently to 1.6 and 4.5 log CFU/g at 4 °C and 12 °C, respectively, by the end of the shelf-life. PFGE showed that Brochothrix isolates exhibited a significant diversity among control samples, whereas this was limited for the HPP-treated samples. The survival and distribution of different Listeria strains depended on the initial inoculum and storage temperature. In conclusion, HPP increased the shelf-life (for 5 and 4 days, at 4 °C and 12 °C, respectively) and enhanced the safety of chicken meat.