Presence of quorum sensing signal molecules in minced beef stored under various temperature and packaging conditions

Meat juice contributes to the stability of ethanol adaptation in Salmonella enterica serovar Enteritidis

Stability assessment of observed tolerance phenotypes is integral in understanding stress adaptation in food-borne pathogens. Therefore, the current work was carried out to determine whether ethanol adaptation induced by exposure to 5 per cent ethanol for 60 min is a stable phenomenon in Salmonella enterica serovar Enteritidis. The capacity of Salmonella Enteritidis (S. Enteritidis) to maintain the acquired ethanol adaptation in the absence of sublethal ethanol stress was investigated at 37 °C, 25 °C or 4 °C in Luria–Bertani broth and two types of meat juice. It was found that ethanol adaptation was completely reversed within 40 min at 37 °C or within 60 min at 25 °C, but was stable at 4 °C for at least 48 h in the broth assay. Ethanol adaptation was retained in chicken juice during 60-min incubation at 25 °C or 48-h incubation at 4 °C. Moreover, exposure to pork juice stored at either 25 °C or 4 °C significantly (P<0.05) increased the ethanol tolerance of ethanol-adapted cells. Collectively, these findings suggest that ethanol adaptation stability in S. Enteritidis under cold conditions and in meat juices should be taken into account when conducting a comprehensive risk analysis during food processing.

Sensorial, color, lipid oxidation, and visual acceptability of dry-aged beef from young bulls with different fat thickness

The reduction in slaughter age with minimum fat and dry aging process improves meat tenderness, however, its shelf-life in display has not been studied. It was evaluated the sensorial, and the color, lipid oxidation, and visual acceptance in display of dry-aged beef (0, 14, and 28 days) from young bulls slaughtered with different subcutaneous fat thickness (2.00, 3.00, and 4.00 mm). Meat with 2.00 and 3.00 mm fat had higher acceptability than 4.00 mm (p < .05). Dry aging improved overall acceptability of consumers. Meat with 2.00 and 3.00 mm fat presented higher lightness and lipid oxidation values than 4.00 mm (p < .05) but similar visual acceptance was observed. Dry-aged beef (14 and 28 days) had lower lightness, but higher redness (p < .05) than not dry aged (0 days). Display reduced color over time, for all dry-aged treatments (p < .05). Dry aging process increased lipid oxidation but these values were below 2.00 mg/kg of malonaldehyde only in the first day of display. Dry aged for 14 days had similar visual acceptability to not dry-aged beef until the third day of display (p < .05). Shelf-life of 0, 14, and 28 days of dry aged was 5.41, 2.55, and 0.23 days. Despite of the increase in lipid oxidation and lightness, the sensorial and display acceptability of meat from young bulls was not prejudiced by the reduction in fat thickness. Beef dry-aged for 14 days was visually well accepted and could be displayed for 2.55 days without compromising acceptability.

Spoilage of Chilled Fresh Meat Products during Storage: A Quantitative Analysis of Literature Data

A literature search was performed on spoilage of fresh meat products by combining keyword query, text mining and expert elicitation. From the 258 collected studies, a quantitative analysis was first performed to identify the methods which are the most used to evaluate spoilage beside the preservation strategies suggested. In a second step focusing on a subset of 24 publications providing quantitative data on spoilage occurrence time, associations between spoilage occurrence time of meat products and specific spoilage indicators were investigated. The analysis especially focused on factors well represented in the 24 publications, i.e., gas packaging (O2 and CO2) and storage temperature. Relationships between spoilage occurrence and several microbiological indicators were also sought. The results point out possible advantages of removing dioxygen in packaging to delay spoilage occurrence, whereas, in the presence of dioxygen, the carbon dioxide proportion in the gas mixtures was shown to influence spoilage occurrence. The collected data clearly reveal a potentially protective role of lactic acid bacteria. Besides, while a spoilage role could be attributed to Pseudomonas spp., the growth of mesophilic aerobic microbes, Brochothrix spp. and Enterobacteriaceae seemed independent of spoilage occurrence time.

Grapefruit essential oils inhibit quorum sensing of Pseudomonas aeruginosa

Citrus essential oils are used in food to confer flavor and aromas. The citrus essential oils have been granted as GRAS and could be used as antimicrobial additives to control bacterial quorum sensing from potential food bacterial pathogens. The chemical composition and inhibitory activity of Citrus paradisi (grapefruit) essential oils obtained by cold-pressed method (EOP) and cold-pressed method followed by steam distillation, against Pseudomonas aeruginosa were determined. The GC-MS analyses of the oil indicated the amount of the essential oil components was highest with D-limonene in both cases. However, the extraction method modified the chemical composition. EOP had higher amount of coumarins and flavonoid as well as less oxygenated terpenoids. At 0.1 mg/mL essential oils were not able to modify the bacterial development but inhibited the P. aeruginosa biofilm production between 52% and 55%, sessile viability between 45% and 48%, autoinducer production and elastase activity between 30% and 56%. Limonene was less effective at inhibiting P. aeruginosa than the essential oils, suggesting a synergistic effect of the minor components. According to our results, grapefruit essential oils could be used as a food preservative to control P. aeruginosa virulence.

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.

Cyclic Peptides in Neurological Disorders: The Case of Cyclo(His-Pro)

Communication between and within communities of cells or independent organisms is a crucial prerequisite for species survival. In response to variations in the extracellular environment, the collective behavior of cell populations can be coordinated by regulating community-level gene expression. This mechanism is strongly conserved during evolution, being shared both by bacterial communities and central nervous system cells. Notably, cyclic dipeptides (CDPs) are molecules that are implicated in these quorum sensing behaviors in both settings. Bacteria coordinate their collective behavior by producing CDPs (quorum sensing inducers) that enhance the capacity of individual members of the community to detect these signals and thus amplify the community-level response. In this review, we highlight recent data indicating that strikingly similar molecular mechanisms control communications between glial and neuronal cells to maintain homeostasis in the central nervous system, with a specific focus on the role of the thyrotropin-releasing hormone—derived CDP cyclo(His-Pro) in the protection against neurotoxic insults.

Quorum sensing system and influence on food spoilage in Pseudomonas fluorescens from turbot

The spoilage of aquatic products is mainly caused by the bacterial growth, and the specific spoilage organism (SSO) plays an important role. Quorum sensing (QS) is a microbial cell-cell communication system which is coordinated with the population density, and is controlled by N-acyl-homoserine lactone (AHLs) as the Gram-negative bacteria communication signals. In this study, the SSO was Pseudomonas fluorescens (PF-04), isolated from the turbot (Scophthalmus maximus L.) during aerobically refrigerated storage. The supernatant extract of PF-04 tested the AHLs activities utilizing biosensor Chromobacterium violaceum CV026. AHL production was influenced by the environment temperature, and AHL production reduced obviously at 10 °C compare with 25 °C. In Luria-Bertani (LB) supplemented with 0.5-1.0% NaCl, AHL production reached the maximum. The AHL production was also regulated by pH of culture medium, acidic condition was conducive to persistent existence of the AHL molecules, but the alkaline environment would cause chemically unstable of AHL molecules. QS system in P. flurosecens played an imperative role in biofilm formation, protease and siderophore production. AHLs could regulate above three factors in PF-04. In summary, this study showed that (1) the influence of different environmental conditions (temperature, NaCl and pH) on AHL production revealed the correlation of QS in foods and (2) that proved the effect of external AHLs to regulate the biofilm formation, protease and siderophore production in PF-04.

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

Shewanella baltica and Acinetobacter are among the predominant spoilage bacteria in refrigerated shrimp (Litopenaeus vannamei). S. baltica are incapable of producing acyl-homoserine lactone (AHL) quorum sensing signals, but can respond to environmental AHLs. In this paper, Acinetobacter was found to produce three AHLs, i.e. N-butanoyl-l-homoserine lactone (C4-HSL), N-(3-oxohexanoyl)-l-homoserine lactone (O-C6-HSL) and N-(3-oxooctanoyl)-l-homoserine lactone (O-C8-HSL), according to thin-layer chromatography using the bioreporter Agrobacterium tumefaciens A136. The agar diffusion and β-galactosidase assays revealed that S. baltica could eavesdrop on these three AHLs from Acinetobacter. Eavesdropping on Acinetobacter AHLs especially C4-HSL was found to boost the growth of S. baltica particularly under nutrient limiting conditions (up to 40-fold increase) in the co-culture experiments. The azocasein assay revealed that S. baltica produced fourfold more extracellular proteases in response to Acinetobacter AHLs. As demonstrated by the biofilm crystal violet staining assay and confocal laser scanning microscopy, eavesdropping also decreased the biofilm-forming capacity of Acinetobacter. By inoculation of S. baltica and Acinetobacter onto surface-sterilized shrimp, eavesdropping was found to endow a growth advantage to S. baltica in vivo, resulting in a 0.5 day shortened shelf life of shrimp according to total volatile basic nitrogen levels and sensory analysis. Overall, the AHL-dependent eavesdropping increased the spoilage potential of S. baltica, providing a fresh perspective on the spoilage process of refrigerated L. vannamei, and this may inspire the development of novel preservation techniques in the future to further reduce post-harvest loss of shrimp.

Effect of Environmental Factors on Intra-Specific Inhibitory Activity of Carnobacterium maltaromaticum

Carnobacterium maltaromaticum is frequently associated with foods having extended shelf-life due to its inhibitory activity to other bacteria. The quantification of such inhibition interactions affected by various environmental factors is limited. This study investigated the effect of environmental factors relevant to vacuum-packaged beef on inhibition between two model isolates of C. maltaromaticum, D0h and D8c, specifically D8c sensitivity to D0h inhibition and D0h inhibitor production. The effects of temperature (-1, 7, 15, 25 °C), atmosphere (aerobic and anaerobic), pH (5.5, 6, 6.5), lactic acid (0, 25, 50 mM) and glucose (0, 0.56, 5.55 mM) on D8c sensitivity (diameter of an inhibition zone) were measured. The effects of pH, glucose, lactic acid and atmosphere on D0h inhibitor production were measured at 25 °C. Sensitivity of D8c was the highest at 15 °C, under aerobic atmosphere, at higher concentrations of undissociated lactic acid and glucose, and at pH 5.5 (p < 0.001). pH significantly affected D0h inhibitor production (p < 0.001), which was the highest at pH 6.5. The effect of lactic acid depended upon pH level; at relatively low pH (5.5), lactic acid decreased the production rate (arbitrary inhibition unit (AU)/mL/h). This study provides a quantitative description of intra-species interactions, studied in in vitro environments that are relevant to vacuum-packaged beef.

Proteomic and genetics insights on the response of the bacteriocinogenic Lactobacillus sakei CRL1862 during biofilm formation on stainless steel surface at 10°C

Some lactic acid bacteria have the ability to form biofilms on food-industry surfaces and this property could be used to control food pathogens colonization. Lactobacillus sakei CR1862 was selected considering its bacteriocinogenic nature and ability to adhere to abiotic surfaces at low temperatures. In this study, the proteome of L. sakei CRL1862 grown either under biofilm on stainless steel surface and planktonic modes of growth at 10°C, was investigated. Using two-dimensional gel electrophoresis, 29 out of 43 statistically significant spots were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Ten proteins resulted up-regulated whereas 16 were down-regulated during biofilm formation. Differentially expressed proteins were found to belong to carbohydrate, nucleotide, aminoacid and lipid metabolisms as well as translation, peptide hydrolysis, cell envelope/cell wall biosynthesis, adaption to atypical conditions and protein secretion. Some proteins related to carbohydrate and nucleotide metabolisms, translation and peptide degradation were overexpressed whereas those associated to stress conditions were synthesized in lower amounts. It seems that conditions for biofilm development would not imply a stressful environment for L. sakei CRL1862 cells, directing its growth strategy towards glycolytic flux regulation and reinforcing protein synthesis. In addition, L. sakei CRL1862 showed to harbor nine out of ten assayed genes involved in biofilm formation and protein anchoring. By applying qRT-PCR analysis, four of these genes showed to be up regulated, srtA2 being the most remarkable. The results of this study contribute to the knowledge of the physiology of L. sakei CRL1862 growing in biofilm on a characteristic food contact surface. The use of this strain as green biocide preventing L. monocytogenes post-processing contamination on industrial surfaces may be considered.

Use of Foodomics for Control of Food Processing and Assessing of Food Safety

Food chain, food safety, and food-processing sectors face new challenges due to globalization of food chain and changes in the modern consumer preferences. In addition, gradually increasing microbial resistance, changes in climate, and human errors in food handling remain a pending barrier for the efficient global food safety management. Consequently, a need for development, validation, and implementation of rapid, sensitive, and accurate methods for assessment of food safety often termed as foodomics methods is required. Even though, the growing role of these high-throughput foodomic methods based on genomic, transcriptomic, proteomic, and metabolomic techniques has yet to be completely acknowledged by the regulatory agencies and bodies. The sensitivity and accuracy of these methods are superior to previously used standard analytical procedures and new methods are suitable to address a number of novel requirements posed by the food production sector and global food market.

Inhibition of biofilm development and spoilage potential of Shewanella baltica by quorum sensing signal in cell-free supernatant from Pseudomonas fluorescens

The objective of this study was to in vitro evaluate the effect of a cell-free supernatant (CFS) containing quorum sensing (QS) signal of Pseudomonas fluorescens on the growth, biofilm development and spoilage potential of Shewanella baltica, and preliminarily assess the interactive influences of various chemically synthesized autoinducers on spoilage phenotypes of S. baltica. PF01 strain isolated from spoiled Pseudosciaen crocea was identified P. fluorescens. The addition of 25% and 50% CFS to S. baltica culture had no effect on the growth rate during the lag and exponential phase, however, caused cell decline during the stationary phase. The presence of CFS from P. fluorescens significantly inhibited biofilm development, and greatly decreased the production of trimethylamine (TMA) and biogenic amino in S. baltica. Various signal molecules of QS in the CFS of P. fluorescens culture were detected, including seven N-acyl-l-homoserine lactones (AHLs), autoinducer-2 (AI-2) and two diketopiperazines (DKPs). Exogenous supplement of synthesized seven AHLs containing in the CFS decreased biofilm formation and TMA production in S. baltica, while exposure to exogenous cyclo-(l-Pro-l-Leu) was showed to promote spoilage potential, which revealed that S. baltica also sense the two QS molecules. Furthermore, the stimulating effect of cyclo-(l-Pro-l-Leu) was affected when AHL was simultaneously added, suggesting that the inhibitory activity of spoilage phenotypes in S. baltica might be attributed to a competitive effect of these QS compounds in the CFS of P. fluorescens. The present studies provide a good basis for future research on the role of QS in the regulation of spoilage microbial flora.

Assessment of the effect of a Salmonella enterica ser. Typhimurium culture supernatant on the single-cell lag time of foodborne pathogens

The objective of this study was the in vitro evaluation of the effect of a cell-free microbial supernatant, produced by a luxS-positive Salmonella enterica ser. Typhimurium strain, on the single-cell growth kinetic behavior of two strains of S. enterica (serotypes Enteritidis and Typhimurium) and a methicillin-resistant Staphylococcus aureus strain. The single-cell lag time (λ) of the pathogens was estimated in the absence and presence (20% v/v) of microbial supernatant based on optical density measurements. As demonstrated by the obtained results, the tested microbial supernatant had a strain-specific effect on the single-cell λ and its variability. Although the mean λ values were similar in the absence and presence of microbial supernatant in the case of Salmonella Enteritidis, a significant (P ≤ 0.05) reduction and increase in the mean value of this parameter in the presence of microbial supernatant were observed for Salmonella Typhimurium and St. aureus, respectively. With regard to the effect of the tested microbial supernatant on the single-cell variability of λ, similar λ distributions were obtained in its absence and presence for S. Enteritidis, while considerable differences were noted for the other two tested organisms; the coefficient of variation of λ in the absence and presence of microbial supernatant was 41.6 and 69.8% for S. Typhimurium, respectively, with the corresponding values for St. aureus being 74.0 and 56.9%. As demonstrated by the results of bioassays, the tested microbial supernatant exhibited autoinducer-2 activity, indicating a potential association of such quorum sensing compounds with the observed effects. Although preliminary in nature, the collected data provide a good basis for future research on the role of quorum sensing in the single-cell growth behavior of foodborne pathogens.

Interstrain interactions between bacteria isolated from vacuum-packaged refrigerated beef

The formation of bacterial spoilage communities in food is influenced by both extrinsic and intrinsic environmental factors. Although many reports describe how these factors affect bacterial growth, much less is known about interactions among bacteria, which may influence community structure. This study investigated interactions among representative species of bacteria isolated from vacuum-packaged (VP) beef. Thirty-nine effectors and 20 target isolates were selected, representing 10 bacterial genera: Carnobacterium, Pseudomonas, Hafnia, Serratia, Yersinia, Rahnella, Brochothrix, Bacillus, Leuconostoc, and Staphylococcus. The influence of live effectors on growth of target isolates was measured by spot-lawn agar assay and also in liquid culture medium broth using live targets and effector cell-free supernatants. Inhibition on agar was quantified by diameter of inhibition zone and in broth by measuring detection time, growth rate, and maximum population density. A number of interactions were observed, with 28.6% of isolates inhibiting and 4.2% promoting growth. The majority of Pseudomonas isolates antagonized growth of approximately one-half of target isolates. Two Bacillus spp. each inhibited 16 targets. Among lactic acid bacteria (LAB), Carnobacterium maltaromaticum inhibited a wider range of isolates compared to other LAB. The majority of effector isolates enhancing target isolate growth were Gram-negative, including Pseudomonas spp. and Enterobacteriaceae. These findings markedly improve the understanding of potential interactions among spoilage bacteria, possibly leading to more mechanistic descriptions of bacterial community formation in VP beef and other foods.

Complete Genome Sequence of Pluralibacter gergoviae FB2, an N-Acyl Homoserine Lactone-Degrading Strain Isolated from Packed Fish Paste

Pluralibacter gergoviae FB2, a bacterial strain isolated from packed food, has been found to exhibit quorum-quenching properties. Hence, we report the first, complete genome of P. gergoviae sequenced using the Pacific Biosciences single-molecule, real-time (SMRT) platform.