Spoilage of refrigerated Litopenaeus vannamei: eavesdropping on Acinetobacter acyl-homoserine lactones promotes the spoilage potential of Shewanella baltica

The inhibition mechanism of PostbioYDFF-3 on quality deterioration of refrigerated grass carp fillets from the perspective of endogenous enzyme and microorganisms changes

The protective mode of PostbioYDFF-3 (referred to as postbiotics) on the quality stability of refrigerated fillets was explored from the aspects of endogenous enzyme activity and the abundance of spoilage microorganisms. Compared to the control group, the samples soaked in postbiotics showed significant reductions in TVC, TVB-N and TBARS values by 39.6%, 58.6% and 25.5% on day 5, respectively. In addition, the color changes, biogenic amine accumulation and texture softening of the fish fillets soaked in postbiotics were effectively suppressed. Furthermore, the activity of endogenous enzyme activities was detected. The calpain activities were significantly inhibited (p < 0.05) after soaking in postbiotics, which declined by 23%. Meanwhile, high throughput sequencing analysis further indicated that the growth of spoilage microorganism such as Acinetobacter and Pseudomonas were suppressed. Overall, the PostbioYDFF-3 was suitable for preserving fish meat.

Sustainable food packaging: Harnessing biowaste of Terminalia catappa L. for chitosan-based biodegradable active films for shrimp storage

Shrimp, a globally consumed perishable food, faces rapid deterioration during storage and marketing, causing nutritional and economic losses. With a rising environmental consciousness regarding conventional plastic packaging, consumers seek sustainable options. Utilizing natural waste resources for packaging films strengthens the food industry. In this context, we aim to create chitosan-based active films by incorporating Terminalia catappa L. leaves extract (TCE) to enhance barrier properties and extend shrimp shelf life under refrigeration. Incorporation of TCE improves mechanical, microstructural, UV, and moisture barrier properties of the chitosan film due to cross-linking interactions, resulting in robust, foldable packaging film. Active TCE film exhibits high antioxidant property due to polyphenols. These films also exhibited low wettability and showed hydrophobicity than neat CH films which is essential for meat packaging. These biodegradable films offer an eco-friendly end-of-life option when buried in soil. TCE-loaded films effectively control spoilage organisms, prevent biochemical spoilage, and maintain shrimp freshness compared to neat CH films during refrigerated condition. The active TCE film retains sensory attributes better than neat chitosan, aligning with consumer preference. The developed edible and active film from waste sources might offer sustainable, alternative packaging material with a lower carbon footprint than petroleum-based sources.

Response surface methodology to optimize the sterilization process of slightly acidic electrolyzed water for Chinese shrimp (Fenneropenaeus chinensis) and to investigate its effect on shrimp quality

Chinese shrimps are popular among consumers for their delicious taste and high nutritional value, but they are highly susceptible to deterioration due to microbial contamination with degradation of texture, color and flavor. The aim of this study was to evaluate the effects of available chlorine concentration (ACC), processing time and material-liquid ratio on the bacterial inhibition rate of shrimp treated with slightly acidic electrolyzed water (SAEW). The effective parameters were optimized by response surface methodology to the optimal bactericidal conditions: ACC 88 mg/L, processing time 12 min, and material-liquid ratio 1:4. The actual bactericidal inhibition rate of shrimp under these conditions was 37.60 %. On this basis, the quality, color difference and textural changes of shrimp treated with SAEW, sodium hypochlorite and alkaline electrolytic water were compared and investigated during storage at 4 °C. The combined results showed that the SAEW treatment could extend the shelf-life by more than 2 d.

Joining the bacterial conversation: increasing the cultivation efficiency of soil bacteria with acyl-homoserine lactones and cAMP

IMPORTANCE

Microorganisms are a repository of interesting metabolites and functions. Therefore, accessing them is an important exercise for advancing not only basic questions about their physiology but also to advance technological applications. In this sense, increasing the culturability of environmental microorganisms remains an important endeavor for modern microbiology. Because microorganisms do not live in isolation in their environments, molecules can be added to the cultivation strategies to "inform them" that they are present in growth-permissive environmental conditions. Signaling molecules such as acyl-homoserine lactones and 3',5'-cyclic adenosine monophosphate belong to the plethora of molecules used by bacteria to communicate with each other in a phenomenon called quorum sensing. Therefore, including quorum sensing molecules can be an incentive for microorganisms, specifically soil bacteria, to increase their numbers on solid media.

A comprehensive review of the spoilage of shrimp and advances in various indicators/sensors for shrimp spoilage monitoring

Shrimp is a popular internationally traded shellfish due to its unique taste, texture, and nutritional value. Shrimp is highly perishable because it has enough free amino acids, high moisture levels, non-nitrogenous compounds used for microbial growth, and melanosis. Shrimp spoilage after death is caused by various reasons, like autolysis (endogenous proteinases actions during shrimp storage), growth of spoilage microorganisms, ATP degradation, melanin formation, and lipid peroxidation. A microbial byproduct, total volatile basic nitrogen, is one of the major reasons for the generation of foul odors from shrimp spoilage. Shrimp freshness monitoring is crucial for market sellers and exporters. Traditional methods for estimating shrimp freshness are expensive and inaccessible to the general public. Sensors are rapid, sensitive, selective, and portable food toxins' detection tools, devoid of expensive instruments, skilled people, sample pretreatment, and a long detection time. This review addresses shrimp spoilage causes. The mechanisms of different stages of shrimp spoilage after death, like rigor mortis, dissolution of rigor mortis, autolysis, and microbial spoilage mechanisms, are discussed. This review highlights the last five years' advances in shrimp freshness detection sensors and indicators like colorimetric pH indicators, fluorescence sensors, electronic noses, and biosensors, their working principles, and their sensitivities. Commercially available indicators and sensors for shrimp spoilage monitoring are also discussed. A review highlighting the applications of the different sensors and indicators for monitoring shrimp freshness is unavailable to date. Challenges and future perspectives in this field are explained at the end.

Quorum sensing autoinducers AHLs protect Shewanella baltica against phage infection

Quorum sensing (QS) plays an important role in phage-host interactions. Shewanella baltica can't produce the N-acyl-homoserine lactones (AHLs) signal molecules but can eavesdrop on exogenous AHLs through its LuxR receptor. However, no clear evidence exists regarding the involvement of AHLs-mediated QS systems in S. baltica in regulating phage infection. Here, we report that AHLs modulated the phage resistance of S. baltica OS155. Specifically, we characterized a S. baltica phage vB_Sb_QDWS and preliminarily identified that lipopolysaccharide (LPS) is an important receptor for phage vB_Sb_QDWS. AHLs could protect S. baltica against phage infection by decreasing LPS-mediated phage adsorption. The expression of genes galU and tkt, which are essential for LPS synthesis, down-regulated significantly in response to AHLs autoinducers. Our finding confirms the important roles of QS in virus-host interactions and would be helpful to develop novel phage strategies for food spoilage control.

Chitosan coating with grape peel extract: A promising coating to enhance the freeze-thaw stability of beef

This study investigated the effect of chitosan coating with grape peel extracts (CH + GPE) on the physiochemical properties, protein and lipid oxidation, microstructure, and bacterial community diversity of beef during freeze-thaw (F-T) cycles. The results indicated that the CH + GPE groups had lower pH values, total aerobic count, total volatile base nitrogen, and thiobarbituric acid reactive substance values and better protection against color, water holding capacity, and sensory quality after five F-T cycles. The CH + GPE coating effectively inhibited beef microstructure destruction during the F-T cycles. High-throughput sequencing analysis revealed that the CH + GPE coating contributed to a decline in the bacterial diversity of beef and inhibited the growth of pathogenic bacteria. Interestingly, the CH + GPE coating affected the correlation between quality parameters and bacteria in beef. Consequently, the CH + GPE coating can be used as a novel packaging for preventing the loss of frozen meat quality due to temperature fluctuations.

Differences in Bacterial Communities of Retail Raw Pork in Different Market Types in Hangzhou, China

Pork is widely consumed globally, and pigs' microbiota can potentially harbor foodborne pathogens. Contaminated pork in retail markets poses significant implications for food quality and safety. However, limited studies have compared pork microbiomes in various marketing environments. In this study, we utilized traditional microbial culture methods and high-throughput 16S rRNA sequencing to assess pathogen contamination and bacterial diversity in raw pork samples purchased from farmers' markets and two types of supermarkets (upscale and ordinary) in Hangzhou, China. Traditional microbial plate cultures identified E. coli and Salmonella spp. in 32.1% (27/84) and 15.5% (13/84) of the collected pork samples, respectively. Moreover, 12 out of 13 Salmonella strains were found in farmers' markets. The MIC results indicated a high prevalence of MDR strains, accounting for 51.9% in E. coli and 53.8% in Salmonella. The prevalence of NaClO tolerant strains was 33.3% and 92.3% for E. coli and Salmonella, respectively. Sequencing results indicated significantly higher microbial diversity in farmers' market samples compared to supermarket samples. Farmers' market pork samples exhibited a greater abundance of Acinetobacter, while Pseudomonas and Brochothrix were predominant in supermarket samples. The total abundance of pathogenic and spoilage bacteria was also higher for the farmers' market samples. Cross-contamination during market trading was evident through a high correlation between bacterial abundance in pork from different stalls within the same farmers' market. PICRUSt2 analysis identified significant differences in the average proportions of genes for carbohydrate, energy, and lipid metabolism from the farmers' markets, suggesting an exacerbation of microbial metabolic activity and increased perishability of pork in this environment. In conclusion, this study revealed variations in the characteristics of raw pork bacterial contamination across different types of retail stores, as well as differences in the composition and diversity of their respective bacterial communities.

Bacterial Skin Microbiota of Seabass from Aegean Fish Farms and Antibiotic Susceptibility of Psychrotrophic Pseudomonas

Farming seabass (Dicentrarchus labrax) is an essential activity in the Mediterranean basin including the Aegean Sea. The main seabass producer is Turkey accounting for 155,151 tons of production in 2021. In this study, skin swabs of seabass farmed in the Aegean Sea were analysed with regard to the isolation and identification of Pseudomonas. Bacterial microbiota of skin samples (n = 96) from 12 fish farms were investigated using next-generation sequencing (NGS) and metabarcoding analysis. The results demonstrated that Proteobacteria was the dominant bacterial phylum in all samples. At the species level, Pseudomonas lundensis was identified in all samples. Pseudomonas, Shewanella, and Flavobacterium were identified using conventional methods and a total of 46 viable (48% of all NGS+) Pseudomonas were isolated in seabass swab samples. Additionally, antibiotic susceptibility was determined according to standards of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Clinical and Laboratory Standards Institute (CLSI) in psychrotrophic Pseudomonas. Pseudomonas strains were tested for susceptibility to 11 antibiotics (piperacillin-tazobactam, gentamicin, tobramycin, amikacin, doripenem, meropenem, imipenem, levofloxacin, ciprofloxacin, norfloxacin, and tetracycline) from five different groups of antibiotics (penicillins, aminoglycosides, carbapenems, fluoroquinolones, and tetracyclines). The antibiotics chosen were not specifically linked to usage by the aquaculture industry. According to the EUCAST and CLSI, three and two Pseudomonas strains were found to be resistant to doripenem and imipenem (E-test), respectively. All strains were susceptible to piperacillin-tazobactam, amikacin, levofloxacin, and tetracycline. Our data provide insight into different bacteria that are prevalent in the skin microbiota of seabass sampled from the Aegean Sea in Turkey, and into the antibiotic resistance of psychrotrophic Pseudomonas spp.

Quorum-Sensing Inhibitors from Probiotics as a Strategy to Combat Bacterial Cell-to-Cell Communication Involved in Food Spoilage and Food Safety

Experience-based knowledge has shown that bacteria can communicate with each other through a cell-density-dependent mechanism called quorum sensing (QS). QS controls specific bacterial phenotypes, such as sporulation, virulence and pathogenesis, the production of degrading enzymes, bioluminescence, swarming motility, and biofilm formation. The expression of these phenotypes in food spoiling and pathogenic bacteria, which may occur in food, can have dramatic consequences on food production, the economy, and health. Due to the many reports showing that the use of conventional methods (i.e., antibiotics and sanitizers) to inhibit bacterial growth leads to the emergence of antibiotic resistance, it is necessary to research and exploit new strategies. Several studies have already demonstrated positive results in this direction by inhibiting autoinducers (low-molecular-weight signaling compounds controlling QS) and by other means, leading to QS inhibition via a mechanism called quorum quenching (QQ). Thus far, several QS inhibitors (QSIs) have been isolated from various sources, such as plants, some animals from aqueous ecosystems, fungi, and bacteria. The present study aims to discuss the involvement of QS in food spoilage and to review the potential role of probiotics as QSIs.

Unraveling the effect of the combination of modified atmosphere packaging and ε-polylysine on the physicochemical properties and bacterial community of greater amberjack (Seriola dumerili)

The combined effect of ε-polylysine (PL) and modified atmosphere packaging (MAP; 60% CO2/40% N2) on the bacterial community of greater amberjack filets and their physicochemical properties was evaluated at 4°C. The total viable counts (TVC), psychrotrophic bacterial count, sensory index, texture analysis, and total volatile basic nitrogen (TVB-N) revealed that PL, MAP, and MAP + PL treatment delayed the deterioration of greater amberjack filets. These treatment groups also showed decreased accumulation of biogenic amines. High-throughput 16S rRNA gene sequencing results indicated that these treatments suppressed the growth of Pseudomonas in greater amberjack filets. Furthermore, the MAP + PL treatment group was observed to be more effective than the PL and MAP groups, extending the shelf life of greater amberjack filets by 6 days. This investigation showed that the combination of PL and MAP has the potential to retain the quality and extend the shelf life of greater amberjack.

Microbiota Succession of Whole and Filleted European Sea Bass (Dicentrarchus labrax) during Storage under Aerobic and MAP Conditions via 16S rRNA Gene High-Throughput Sequencing Approach

In the present work, the profiles of bacterial communities of whole and filleted European sea bass (Dicentrarchus labrax), during several storage temperatures (0, 4, 8 and 12 °C) under aerobic and Modified Atmosphere Packaging (MAP) conditions, were examined via the 16S rRNA High-Throughput Sequencing (HTS) approach. Sensorial attributes were also assessed to determine products’ shelf-life. Results indicated that shelf-life was strongly dependent on handling, as well as on temperature and atmosphere conditions. HTS revealed the undisputed dominance of Pseudomonas from the very beginning and throughout storage period in the majority of treatments. However, a slightly different microbiota profile was recorded in MAP-stored fillets at the middle stages of storage, which mainly referred to the sporadic appearance of some bacteria (e.g., Carnobacterium, Shewanella, etc.) that followed the dominance of Pseudomonas. It is noticeable that a major difference was observed at the end of shelf-life of MAP-stored fillets at 12 °C, where the dominant microbiota was constituted by the genus Serratia, while the relative abundance of Pseudomonas and Brochothrix was more limited. Furthermore, at the same temperature under aerobic storage of both whole and filleted fish, Pseudomonas almost co-existed with Acinetobacter, while the presence of both Erwinia and Serratia in whole fish was noteworthy. Overall, the present study provides useful information regarding the storage fate and spoilage status of whole and filleted European sea bass, suggesting that different handling and storage conditions influence the shelf-life of sea bass by favoring or delaying the dominance of Specific Spoilage Organisms (SSOs), affecting in parallel to some extent the formation of their consortium that is responsible for products’ sensorial deterioration. Such findings enrich the current knowledge and should be used as a benchmark to develop specific strategies aiming to delay spoilage and thus increase the products’ added value.

New Sesquiterpenoids From Plant-Associated Irpex lacteus

Bacteria produce a large number of virulence factors through the quorum sensing (QS) mechanism. Inhibiting such QS system of the pathogens without disturbing their growth is a potential strategy to control multi-drug-resistant pathogens. To accomplish this, two new tremulane-type sesquiterpenoids, irpexolaceus H (1) and I (2), along with two known furan compounds, irpexlacte B (3) and C (4), were isolated from Orychophragmus violaceus (L.) OE Schulz endophytic fungus Irpex lacteus (Fr.) Fr. Their structures were elucidated by detailed spectroscopic data (NMR, HRESIMS, IR, and UV), single-crystal X-ray diffraction, and electronic circular dichroism (ECD) analysis. Furthermore, those compounds were evaluated for anti-quorum sensing (anti-QS) activity, and compound 3 was found contributing to the potential QS inhibitory activity.

Changes in the Microbial Communities of Tiger Frog (Rana tigrina) Meat during Refrigerated Storage

ABSTRACT

Microbial activity is the major cause of the spoilage of aquatic meat products during storage. This study investigated the changes of the microbial compositions of the tiger frog (Rana tigrina) meat stored aerobically at 4°C for 12 days using 16S rRNA amplicon high-throughput sequencing analysis. The microbial diversity and species richness of the frog meat were abundant at the initial phase of storage but decreased substantially with prolongation of the storage time. Proteobacteria was the prevalent phylum identified from the frog meat, with a relative abundance of 40.29% at day 0 increasing to 96.77% at day 6 and 95.41% at day 12. At the genus level, Shewanella, Pseudomonas, and Acinetobacter were the three dominant genera in the spoiled samples and contributed to frog meat spoilage. Their proportions were 41.67, 28.48, and 5.94% at day 6 and 29.94, 23.48, and 18.44% at day 12, respectively. The present study is conducive to understanding the pattern and process of frog meat spoilage during refrigeration and could be used to develop efficient control measures to mitigate the predominant psychrotrophic spoilers in aerobically stored frog meat.

HIGHLIGHTS

Diversity and succession of the microbial community and its correlation with lipid oxidation in dry-cured black carp (Mylopharyngodon piceus) during storage

This study aimed to achieve deeper insights into the microbiota composition and dynamic succession of the dry-cured black carp during storage using a high-throughput sequencing technique (HTS). The effect of lipid oxidation on microorganisms was also evaluated. Over 651 bacterial genera belonging to 37 phyla were identified. Firmicutes, Proteobacteria and Actinobacteria were the main bacterial phylum, some are highly associated with meat spoilage. Staphylococcus, Macrococcus and Acinetobacter were the most three microbial genera throughout the entire storage period (30 days). Between two different storage temperature, refrigeration at 4 °C could facilitate maintaining the microbial diversity, while 25 °C storage led to the formation of dominant microflora and the reduction of community diversity. Canonical correspondence analysis (CCA) showed that acid value (AV), malondialdehyde (MDA) and 4-hydroxy-2-hexenal (HHE) contents were three key environmental factors (oxidation products) affecting the profile of the microbiota. Staphylococcus presented a positive correlation with HHE content, while Macrococcus and Acinetobacter were negatively correlated with HHE content. These results could expand our knowledge on the effect of lipid oxidation on change of microbial distribution, it could also present an guideline to develop advanced storage methods for the vacuum packed dry-cured fish products.

Involvement of Exogenous N-Acyl-Homoserine Lactones in Spoilage Potential of Pseudomonas fluorescens Isolated From Refrigerated Turbot

Some bacteria can modulate their spoilage potential by responding to environmental signaling molecules via the quorum sensing (QS) system. However, the ability of Pseudomonas fluorescens, the specific spoilage organism (SSO) of turbot, to response to environmental signaling molecules remains unclear. This study investigated the effects of six synthetic N-acyl homoserine lactones (AHLs) on typical behaviors mediated by QS in P. fluorescens, such as biofilm formation and extracellular protease activity. Total volatile basic nitrogen (TVB-N) was used as a spoilage indicator to evaluate quality changes in AHL-treated turbot filets during storage. The results confirm the enhancing effect of environmental AHLs on QS-dependent factors of P. fluorescens and quality deterioration of turbot filets, with C₄-HSL and C₁₄-HSL being the most effective. Moreover, the content decrease of exogenous AHLs was also validated by gas chromatography–mass spectrometry analysis. Further, changes in rhlR transcription levels in P. fluorescens suggest that this bacterium can sense environmental AHLs. Finally, molecular docking analysis demonstrates the potential interactions of RhlR protein with various exogenous AHLs. These findings strongly implicate environmental AHLs in turbot spoilage caused by P. fluorescens, suggesting preservation of turbot should not exclusively consider the elimination of SSO-secreted AHLs.

Involvement of Exogenous N-Acyl-Homoserine Lactones in Spoilage Potential of Pseudomonas fluorescens Isolated From Refrigerated Turbot

Some bacteria can modulate their spoilage potential by responding to environmental signaling molecules via the quorum sensing (QS) system. However, the ability of Pseudomonas fluorescens, the specific spoilage organism (SSO) of turbot, to response to environmental signaling molecules remains unclear. This study investigated the effects of six synthetic N-acyl homoserine lactones (AHLs) on typical behaviors mediated by QS in P. fluorescens, such as biofilm formation and extracellular protease activity. Total volatile basic nitrogen (TVB-N) was used as a spoilage indicator to evaluate quality changes in AHL-treated turbot filets during storage. The results confirm the enhancing effect of environmental AHLs on QS-dependent factors of P. fluorescens and quality deterioration of turbot filets, with C₄-HSL and C₁₄-HSL being the most effective. Moreover, the content decrease of exogenous AHLs was also validated by gas chromatography-mass spectrometry analysis. Further, changes in rhlR transcription levels in P. fluorescens suggest that this bacterium can sense environmental AHLs. Finally, molecular docking analysis demonstrates the potential interactions of RhlR protein with various exogenous AHLs. These findings strongly implicate environmental AHLs in turbot spoilage caused by P. fluorescens, suggesting preservation of turbot should not exclusively consider the elimination of SSO-secreted AHLs.

Effects of temperature on paocai bacterial succession revealed by culture-dependent and culture-independent methods

Paocai is a widely consumed Chinese traditional fermented vegetable product. To understand the effect of temperature on paocai fermentation flora, the bacterial community structure of paocai fermented at 10 °C, 15 °C, 25 °C and 35 °C was analyzed by culture-dependent and culture-independent methods. The results showed that increasing the fermentation temperature in a certain range is beneficial for rapid paocai acid production and shortening of the maturity period. Illumina Miseq sequencing was performed on 56 samples at different fermentation process temperatures using a culture-independent method. A total of 1,964,231 high-quality reads of 16S rRNA V3-V4 regions were obtained, and they were divided into 405 operational taxonomic units (OTUs) and identified as 213 bacterial genera. The bacterial diversity decreased with the progression of fermentation, and some spoiled samples had an increased diversity. The culture-independent method found that at 10 °C, Lactococcus appeared at the start of fermentation, Leuconostoc and Weissella appeared in the middle of fermentation, and Lactobacillus and Leuconostoc dominated fermentation in the late stage. At 15 °C, Lactococcus started fermentation, Leuconostoc appeared in the middle stage, and Lactobacillus was dominant in the late stage. At 25 °C, Lactococcus started fermentation, Weissella and Lactobacillus appeared in the middle stage, and Lactobacillus dominated fermentation in the late stage. Finally, at 35 °C, Lactococcus, Weissella, and Lactobacillus started fermentation, Weissella and Lactobacillus appeared in the middle stage, and Lactobacillus dominated fermentation in the late stage. A total of 647 strains of bacteria were isolated by culture-dependent methods and were divided into 12 genera and 19 species by randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) and 16S ribosomal RNA gene (rDNA) sequencing technology. More types of bacteria were isolated in the early stage of fermentation. At 10 °C, Lactococcus lactis began fermentation, and Lactobacillus brevis and Leuconostoc mesenteroides dominated acid production in the middle and late stages of paocai fermentation. At 15 °C, L. lactis initiates fermentation, while Lactobacillus plantarum dominates the acid fermentation of paocai. At 25 °C and 35 °C, there were a large number of Enterobacteriaceae bacteria in the start-up fermentation stage, and L. plantarum was dominant after 1-2 days of fermentation. Redundancy analysis (RDA) found that the lower the temperature, the more bacterial species that are produced, and the higher the temperature and the longer the time, the more obvious are the effects of L. plantarum on paocai. The results of dominant bacteria studied by culture-dependent and culture-independent methods are similar. The results indicate that most of the dominant microorganisms in the paocai fermentation system are culturable. This discovery can provide data and physical support for modernization and regulation of different types of paocai production.

Quorum sensing in food spoilage and natural-based strategies for its inhibition

Food can harbor a variety of microorganisms including spoilage and pathogenic bacteria. Many bacterial processes, including production of degrading enzymes, virulence factors, and biofilm formation are known to depend on cell density through a process called quorum sensing (QS), in which cells communicate by synthesizing, detecting and reacting to small diffusible signaling molecules - autoinducers (AI). The disruption of QS could decisively contribute to control the expression of many harmful bacterial phenotypes. Several quorum sensing inhibitors (QSI) have been extensively studied, being many of them of natural origin. This review provides an analysis on the role of QS in food spoilage and biofilm formation within the food industry. QSI from natural sources are also reviewed towards their putative future applications to prolong shelf life of food products and decrease foodborne pathogenicity.

AHLs-produced bacteria in refrigerated shrimp enhanced the growth and spoilage ability of Shewanella baltica

Shewanella baltica is the predominant bacteria in spoiled shrimp (Litopenaeus vannamei), however, the spoilage ability and the mechanism of S. baltica is still unknown. S. baltica can't produce the signal molecule of acyl-homoserine-lactones (AHLs), so the aim of this study was to investigate how wild type S. baltica SA03 (WT SA03) eavesdrop exogenous AHLs to enhance its spoilage ability through LuxR receptor. The results indicated that Aeromonas spp. (Aer), Acinetobacter spp. (Aci) and Serratia spp. (Ser) isolated from refrigerated shrimp can produce different AHLs. WT SA03 can eavesdrop the AHLs of Aer (C4-HSL), Aci (O-C6-HSL) and Ser (C6-HSL, O-C6-HSL) to enhance its growth, especially Ser. Exogenous C4-HSL and C6-HSL enhanced biofilm formation of WT SA03, and C6-HSL and O-C6-HSL enhanced thioredoxin reductase trxB mRNA expression. However, the luxR mutant of WT SA03 (ΔluxR SA03) lost or weakened the role of using environmental AHLs. In vivo experiments, the lag time of WT SA03 was shortened by 6.4 h, 6.2 h and 14.4 h by co-inoculated with Aer, Aci and Ser, respectively. The total volatile basic nitrogen (TVB-N) were significantly enhanced in the samples co-inoculated with WT SA03 and Aer (or Aci, Ser) than those of ΔluxR SA03 and Aer (or Aci, Ser) (p < 0.05). The results showed that S. baltica SA03 can utilize AHLs produced by other bacteria to enhance its growth and spoilage ability through LuxR receptor system. Quorum sensing based on AHLs of bacteria might as the potential targets for food spoilage control.