• Proceedings of the PSK Conference
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• 2003.10b
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• pp.174.2-174.2
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• 2003

Quorum sensing, a gene expression in response to population density, is regulated by chemical signals, most of which are acylated homoserine lactones (AHLs). The AHL derivatives have been reported to regulate bioluminescence, virulence factors and / or swarming motility in bacteria. It is hypothesized that higher organisms may have evolved specific means to interfere with bacterial communication as exemplified in the AHL-antagonistic activity of halogenated furanones isolated from the Australian macroalga Delisea pulchra. (omitted)

• Journal of Microbiology and Biotechnology
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• v.21 no.10
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• pp.1001-1011
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• 2011

To explore bacterial diversity for elucidating genetic variability in acylhomoserine lactone (AHL) lactonase structure, we screened 800 bacterial strains. It revealed the presence of a quorum quenching (QQ) AHL-lactonase gene (aiiA) in 42 strains. These 42 strains were identified using rrs (16S rDNA) sequencing as Bacillus strains, predominantly B. cereus. An in silico restriction endonuclease (RE) digestion of 22 AHL lactonase gene (aiiA) sequences (from NCBI database) belonging to 9 different genera, along with 42 aiiA gene sequences from different Bacillus spp. (isolated here) with 14 type II REs, revealed distinct patterns of fragments (nucleotide length and order) with four REs; AluI, DpnII, RsaI, and Tru9I. Our study reflects on the biodiversity of aiiA among Bacillus species. Bacillus sp. strain MBG11 with polymorphism (115Alanine > Valine) may confer increased stability to AHL lactonase, and can be a potential candidate for heterologous expression and mass production. Microbes with ability to produce AHL-lactonases degrade quorum sensing signals such as AHL by opening of the lactone ring. The naturally occurring diversity of QQ molecules provides opportunities to use them for preventing bacterial infections, spoilage of food, and bioremediation.

• Journal of Microbiology and Biotechnology
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• v.15 no.6
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• pp.1197-1206
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• 2005

Vibrio vulnificus is an opportunistic pathogen that causes a septicemia and expresses numerous virulence factors, in which luxS and smcR are genes encoding for components responsible for quorum-sensing regulation. In the present study, null mutants were constructed with lesions in each or both of these two genes from the V. vulnificus Vv$\Delta$Z strain, which is a lacZ$^{-}$ and chloramphenicol/streptomycin-resistant derivative of the wild-type ATCC29307 strain, and their phenotypes related to virulence were compared with those of the parental cells. $LD_{50}$ and histopathological findings of luxS-, smcR-, or luxS- smcR- deficient mutant were not different from those of the parent strain, a lacZ-deficient streptomycin-resistant strain in mice. However, time of death in mice was delayed, and numbers of bacteria survived in bloodstream after intraperitoneal injection in mice were decreased by mutation, especially luxS and smcR double mutant (VvSR$\Delta$ZSR). These phenomena were supported by increased serum sensitivity and delayed bacterial proliferation in both murine blood and iron-restricted medium. These results suggest that the luxS and luxR homologous genes in V. vulnificus could playa role in bacterial survival in host by enhancing proliferation and adjusting to changed environment.

• Journal of Microbiology and Biotechnology
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• v.25 no.11
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• pp.1908-1919
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• 2015

This work investigated the potential of curcumin (CCM) and (-)-epigallocatechin gallate (EGCG) to inhibit N-acyl homoserine lactone (AHL)-mediated biofilm formation in gram-negative bacteria from membrane bioreactor (MBR) activated sludge. The minimum inhibitory concentrations (MICs) of CCM alone against all the tested bacteria were 200-350 μg/ml, whereas those for EGCG were 300-600 μg/ml. Biofilm formation at one-half MICs indicated that CCM and EGCG alone respectively inhibited 52-68% and 59-78% of biofilm formation among all the tested bacteria. However, their combination resulted in 95-99% of biofilm reduction. Quorum sensing inhibition (QSI) assay with known biosensor strains demonstrated that CCM inhibited the expression of C4 and C6 homoserine lactones (HSLs)-mediated phenotypes, whereas EGCG inhibited C4, C6, and C10 HSLs-based phenotypes. The Center for Disease Control biofilm reactor containing a multispecies culture of nine bacteria with one-half MIC of CCM (150 μg/ml) and EGCG (275 μg/ml) showed 17 and 14 μg/cm² of extracellular polymeric substances (EPS) on polyvinylidene fluoride membrane surface, whereas their combination (100 μg/ml of each) exhibited much lower EPS content (3 μg/cm²). Confocal laser scanning microscopy observations also illustrated that the combination of compounds tremendously reduced the biofilm thickness. The combined effect of CCM with EGCG clearly reveals for the first time the enhanced inhibition of AHL-mediated biofilm formation in bacteria from activated sludge. Thus, such combined natural QSI approach could be used for the inhibition of membrane biofouling in MBRs treating wastewaters.

• ALGAE
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• v.30 no.2
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• pp.147-161
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• 2015

Brown algal extracts have long been used as feed supplements to promote health of farm animals. Here, we show new molecular insights in to the mechanism of action of a fucose containing polymer (FCP) rich fraction from the brown seaweed Ascophyllum nodosum using the Caenorhabditis elegans-Pseudomonas aeruginosa PA14 infection model. FCP enhanced survival of C. elegans against pathogen stress, correlated with up-regulation of key immune response genes such as: lipases, lysozyme (lys-1), saponin-like protein (spp-1), thaumatin-like protein (tlp-1), matridin SK domain protein (msk-1), antibacterial protein (abf-1), and lectin family protein (lfp). Further, FCP caused down regulation of P. aeruginosa quorum sensing genes: (lasI, lasR, rhlI, and rhlR), secreted virulence factors (lipase, proteases, and elastases) and toxic metabolites (pyocyanin, hydrogen cyanide, and siderophore). Biofilm formation and motility of pathogenic bacteria were also greatly attenuated when the culture media were treated with FCP. Interestingly, FCP failed to mitigate the pathogen stress in skn-1, daf-2, and pmk-1 mutants of C. elegans. This indicated that, FCP treatment acted on the regulation of fundamental innate immune pathways, which are conserved across the majority of organisms including humans. This study suggests the possible use of FCP, a seaweed component, as a functional food source for healthy living.

• Journal of Dairy Science and Biotechnology
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• v.33 no.1
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• pp.59-67
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• 2015

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is well-characterized as an important food-borne pathogen worldwide and causes human diseases such as diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS) by producing shiga-like toxin (Stx). It has been reported that a number of dairy foods, including cheese, can act as the source of EHEC O157:H7 infections. In addition to the toxicity of Stx, recently it has been indicated that EHEC O157:H7 possesses virulence factors related to attachment, quorum sensing, and biofilms. Moreover, these novel virulence factors might become critical points to be considered in the future production of food derived from animals. Here, we review the evidences that support these insights on new virulence factors and discuss the potential mechanisms mediating the pathogenesis of EHEC O157:H7 in the dairy food industry.

• Molecules and Cells
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• v.37 no.6
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• pp.480-486
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• 2014

Growth restriction by antibiotics is a common feature that pathogenic bacteria must overcome for survival. The struggle of bacteria to escape from growth restriction eventually results in development of antibiotic-resistance through the expression of a set of genes. Here we found that some physiologically important transcriptional regulators of Pseudomonas aeruginosa including QscR, a quorum sensing (QS) receptor, SoxR, a superoxide sensor-regulator, and AntR, a regulator of anthranilate-related secondary metabolism, are activated by various growth-restricted conditions. We generated the growth-restricted conditions by various methods, such as overexpression of PA2537 and treatment with antibiotics or disinfectants. The overexpression of PA2537, encoding an acyltransferase homologue, tightly restricted the growth of P. aeruginosa and significantly activated QscR during the growth restriction. Similarly, treatments with gentamycin, tetracycline, and ethanol also activated QscR near their minimal inhibitory concentrations (MICs). Some non-QS regulators, such as AntR and SoxR, were also activated near the MICs in the same conditions. However, LasR and PqsR, other QS receptors of P. aeruginosa, were not activated, suggesting that only a specific set of transcriptional regulators is activated by growth restriction. Since paraquat, a superoxide generator, significantly activated QscR and AntR, we suggest that the oxidative stress generated by growth restriction may be partly involved in this phenomenon.

• Journal of Microbiology and Biotechnology
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• v.25 no.8
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• pp.1299-1306
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• 2015

This study aims to investigate the mechanism of action of the cinnamon bark essential oil (CB), when used singly and also in combination with piperacillin, for its antimicrobial and synergistic activity against beta-lactamase TEM-1 plasmid-conferred Escherichia coli J53 R1. Viable count of bacteria for this combination of essential oil and antibiotic showed a complete killing profile at 20 h and further confirmed its synergistic effect by reducing the bacteria cell numbers. Analysis on the stability of treated cultures for cell membrane permeability by CB when tested against sodium dodecyl sulfate revealed that the bacterial cell membrane was disrupted by the essential oil. Scanning electron microscopy observation and bacterial surface charge measurement also revealed that CB causes irreversible membrane damage and reduces the bacterial surface charge. In addition, bioluminescence expression of Escherichia coli [pSB1075] and E. coli [pSB401] by CB showed reduction, indicating the possibility of the presence of quorum sensing (QS) inhibitors. Gas-chromatography and mass spectrometry of the essential oil of Cinnamomum verum showed that trans-cinnamaldehyde (72.81%), benzyl alcohol (12.5%), and eugenol (6.57%) were the major components in the essential oil. From this study, CB has the potential to reverse E. coli J53 R1 resistance to piperacillin through two pathways; modification in the permeability of the outer membrane or bacterial QS inhibition.

• Animal Bioscience
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• v.37 no.2_spc
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• pp.337-345
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• 2024

Ruminants possess a specialized four-compartment forestomach, consisting of the reticulum, rumen, omasum, and abomasum. The rumen, the primary fermentative chamber, harbours a dynamic ecosystem comprising bacteria, protozoa, fungi, archaea, and bacteriophages. These microorganisms engage in diverse ecological interactions within the rumen microbiome, primarily benefiting the host animal by deriving energy from plant material breakdown. These interactions encompass symbiosis, such as mutualism and commensalism, as well as parasitism, predation, and competition. These ecological interactions are dependent on many factors, including the production of diverse molecules, such as those involved in quorum sensing (QS). QS is a density-dependent signalling mechanism involving the release of autoinducer (AIs) compounds, when cell density increases AIs bind to receptors causing the altered expression of certain genes. These AIs are classified as mainly being N-acyl-homoserine lactones (AHL; commonly used by Gram-negative bacteria) or autoinducer-2 based systems (AI-2; used by Gram-positive and Gram-negative bacteria); although other less common AI systems exist. Most of our understanding of QS at a gene-level comes from pure culture in vitro studies using bacterial pathogens, with much being unknown on a commensal bacterial and ecosystem level, especially in the context of the rumen microbiome. A small number of studies have explored QS in the rumen using 'omic' technologies, revealing a prevalence of AI-2 QS systems among rumen bacteria. Nevertheless, the implications of these signalling systems on gene regulation, rumen ecology, and ruminant characteristics are largely uncharted territory. Metatranscriptome data tracking the colonization of perennial ryegrass by rumen microbes suggest that these chemicals may influence transitions in bacterial diversity during colonization. The likelihood of undiscovered chemicals within the rumen microbial arsenal is high, with the identified chemicals representing only the tip of the iceberg. A comprehensive grasp of rumen microbial chemical signalling is crucial for addressing the challenges of food security and climate targets.

• Journal of Microbiology and Biotechnology
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• v.34 no.8
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• pp.1642-1652
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• 2024

Arctium lappa (Burdock) root is used in various culinary applications especially in Asian Cuisine. Arctigenin (ARC) is a polyphenolic compound abundant in the roots of the burdock plant from which it derives its name. The emergence of bacterial resistance is a growing global worry, specifically due to the declining availability of new antibiotics. Screening for the antibacterial candidates among the safe natural products is a promising approach. The present study was aimed to assess the antibacterial activity of ARC against Pseudomonas aeruginosa exploring its effect on the bacterial cell membrane. Furthermore, the anti-virulence activities and anti-quorum sensing (QS) activities of ARC were in vitro, in vivo and in silico assessed against P. aeruginosa. The current results showed the ARC antibacterial activity was owed to its disruption effect of the cell membrane. ARC at sub-MIC significantly decreased the formation of biofilm, motility, production of extracellular enzymes and in vivo protected mice against P. aeruginosa. These anti-virulence activities of ARC are owed to its interference with bacterial QS and its expression. Furthermore, ARC showed mild effect on mammalian erythrocytes, low probability to induce resistance and synergistically combined with antibiotics. In summary, the promising anti-virulence properties of ARC indicate its potential as an effective supplement to conventional antibiotics for treating severe P. aeruginosa infections.