Bacterial Quorum Sensing and Food Industry

Tannin-Rich Fraction from Pomegranate Rind Inhibits Quorum Sensing in Chromobacterium violaceum and Biofilm Formation in Escherichia coli

Pomegranate rind has been found to inhibit numerous pathogens, mostly attributed to its tannin fraction. The present study was conducted to investigate the quorum sensing (QS) inhibition effect of tannin-rich fraction from pomegranate rind (TFPR) by using an indicator strain Chromobacterium violaceum. Meanwhile, its effect on biofilm formation and motility of Escherichia coli was evaluated. It was shown that TFPR inhibited QS-regulated violacein pigment production. Biofilm formation and motility of E. coli were also hindered by TFPR. Transcriptional analysis further showed that TFPR repressed expressions of curli genes (csgB and csgD) and various motility genes (fimA, fimH, flhD, motB, qseB, and qseC). Our findings indicated that TFPR has potential application for controlling E. coli contaminations or biofilms in the food industry.

Quercetin Influences Quorum Sensing in Food Borne Bacteria: In-Vitro and In-Silico Evidence

Quorum sensing (QS) plays a vital role in regulating the virulence factor of many food borne pathogens, which causes severe public health risk. Therefore, interrupting the QS signaling pathway may be an attractive strategy to combat microbial infections. In the current study QS inhibitory activity of quercetin and its anti-biofilm property was assessed against food-borne pathogens using a bio-sensor strain. In addition in-silico techniques like molecular docking and molecular dynamics simulation studies were applied to screen the quercetin's potentiality as QS inhibitor. Quercetin (80 μg/ml) showed the significant reduction in QS-dependent phenotypes like violacein production, biofilm formation, exopolysaccharide (EPS) production, motility and alginate production in a concentration-dependent manner. Synergistic activity of conventional antibiotics with quercetin enhanced the susceptibility of all tested pathogens. Furthermore, Molecular docking analysis revealed that quercetin binds more rigidly with LasR receptor protein than the signaling compound with docking score of -9.17 Kcal/mol. Molecular dynamics simulation predicted that QS inhibitory activity of quercetin occurs through the conformational changes between the receptor and quercetin complex. Above findings suggest that quercetin can act as a competitive inhibitor for signaling compound towards LasR receptor pathway and can serve as a novel QS-based antibacterial/anti-biofilm drug to manage food-borne pathogens.

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.

Lactobacillus acidophilus modulates the virulence of Clostridium difficile

Clostridium difficile is a spore-forming, toxin-producing, anaerobic bacterium that colonizes the human gastrointestinal tract. This pathogen causes antibiotic-associated diarrhea and colitis in animals and humans. Antibiotic-associated diseases may be treated with probiotics, and interest is increasing in such uses of probiotics. This study investigated the effect of Lactobacillus strains on the quorum-sensing signals and toxin production of C. difficile. In addition, an in vivo experiment was designed to assess whether Lactobacillus acidophilus GP1B is able to control C. difficile-associated disease. Autoinducer-2 activity was measured for C. difficile using the Vibrio harveyi coupled bioluminescent assay. Cell extract (10μg/mL) of L. acidophilus GP1B exhibited the highest inhibitory activity among 5 to 40μg/mL cell-extract concentrations. Real-time PCR data indicated decreased transcriptional levels in luxS, tcdA, tcdB, and txeR genes in the presence of 10μg/mL of cell extract of L. acidophilus GP1B. Survival rates at 5d for mice given the pathogen alone with L. acidophilus GP1B cell extract or L. acidophilus GP1B were 10, 70, and 80%, respectively. In addition, the lactic acid-produced L. acidophilus GP1B exhibits an inhibitory effect against the growth of C. difficile. Both the L. acidophilus GP1B and GP1B cell extract have significant antipathogenic effects on C. difficile.

Quorum sensing activity of Hafnia alvei isolated from packed food

Quorum sensing (QS) is a mechanism adopted by bacteria to regulate expression of genes according to population density. N-acylhomoserine lactones (AHLs) are a type of QS signalling molecules commonly found in Gram-negative bacteria which have been reported to play a role in microbial spoilage of foods and pathogenesis. In this study, we isolated an AHL-producing Hafnia alvei strain (FB1) from spherical fish pastes. Analysis via high resolution triple quadrupole liquid chromatography/mass spectrometry (LC/MS) on extracts from the spent supernatant of H. alvei FB1 revealed the existence of two short chain AHLs: N-(3-oxohexanoyl) homoserine lactone (3-oxo-C6-HSL) and N-(3-oxo- octanoyl) homoserine lactone (3-oxo-C8-HSL). To our knowledge, this is the first report of the production of AHLs, especially 3-oxo-C8-HSL, by H. alvei.

Development and Control of Bacterial Biofilms on Dairy Processing Membranes

Membrane fouling is a major operational problem that leads to reduced membrane performance and premature replacement of membranes. Bacterial biofilms developed on reverse osmosis membranes can cause severe flux declines during whey processing. Various types of biological, physical, and chemical factors regulate the formation of biofilms. Extracellular polymeric substances produced by constitutive microflora provide an effective barrier for the embedded cells. Cultural and microscopic techniques also revealed the presence of biofilms with attached bacterial cells on membrane surfaces. Presence of biofilms, despite regular cleaning processes, reflects ineffectiveness of cleaning agents. Cleaning efficiency depends upon factors such as pH of the cleaning agent, temperature, pressure, cleaning agent dose, optimum cleaning time, and cross-flow velocity during cleaning. Among different cleaning agents, surfactants help to prevent bacterial attachment to surfaces by reducing the surface tension of water and interfacial tension between the layers. Enzymes mixed with surfactants and chelating agents can be used to penetrate the biofilm matrix formed by microbes. Recent studies have shown the role of quorum-sensing-based cell-to-cell signaling, which provides communication within bacterial cells to form a mature biofilm, and also the role of applying quorum inhibitors to prevent biofilm formation. Major cleaning applications are also summarized in Table .

Quorum sensing in extreme environments

Microbial communication, particularly that of quorum sensing, plays an important role in regulating gene expression in a range of organisms. Although this phenomenon has been well studied in relation to, for example, virulence gene regulation, the focus of this article is to review our understanding of the role of microbial communication in extreme environments. Cell signaling regulates many important microbial processes and may play a pivotal role in driving microbial functional diversity and ultimately ecosystem function in extreme environments. Several recent studies have characterized cell signaling in modern analogs to early Earth communities (microbial mats), and characterization of cell signaling systems in these communities may provide unique insights in understanding the microbial interactions involved in function and survival in extreme environments. Cell signaling is a fundamental process that may have co-evolved with communities and environmental conditions on the early Earth. Without cell signaling, evolutionary pressures may have even resulted in the extinction rather than evolution of certain microbial groups. One of the biggest challenges in extremophile biology is understanding how and why some microbial functional groups are located where logically they would not be expected to survive, and tightly regulated communication may be key. Finally, quorum sensing has been recently identified for the first time in archaea, and thus communication at multiple levels (potentially even inter-domain) may be fundamental in extreme environments.