Quorum sensing and its relevance to infectious diseases

Co-exposure to environmental microplastic and the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) induce distinctive alterations in the metabolome and microbial community structure in the gut of the earthworm Eisenia andrei

Microplastics (MPs) are recognized as emergent pollutants and have become a significant environmental concern, especially when combined with other contaminants. In this study, earthworms, specifically Eisenia andrei, were exposed to MPs (at a concentration of 10 μg kg-1 of soil), herbicide 2,4-D (7 mg kg-1 of soil), and a combination of the two for 7 and 14 days. The chemical uptake in the earthworms was measured, and the bacterial and archaeal diversities in both the soil and earthworm gut were analyzed, along with the metabolomic profiles. Additionally, data integration of the two omics approaches was performed to correlate changes in gut microbial diversity and the different metabolites. Our results demonstrated that earthworms ingested MPs and increased 2,4-D accumulation. More importantly, high-throughput sequencing revealed a shift in microbial diversity depending on single or mixture exposition. Metabolomic data demonstrated an important modulation of the metabolites related to oxidative stress, inflammatory system, amino acids synthesis, energy, and nucleic acids metabolism, being more affected in case of co-exposure. Our investigation revealed the potential risks of MPs and 2,4-D herbicide combined exposure to earthworms and soil fertility, thus broadening our understanding of MPs' toxicity and impacts on terrestrial environments.

Phenotypic assay for cytotoxicity assessment of Balamuthia mandrillaris against human neurospheroids

Introduction

The phenotypic screening of drugs against Balamuthia mandrillaris, a neuropathogenic amoeba, involves two simultaneous phases: an initial step to test amoebicidal activity followed by an assay for cytotoxicity to host cells. The emergence of three-dimensional (3D) cell cultures has provided a more physiologically relevant model than traditional 2D cell culture for studying the pathogenicity of B. mandrillaris. However, the measurement of ATP, a critical indicator of cell viability, is complicated by the overgrowth of B. mandrillaris in coculture with host cells during drug screening, making it challenging to differentiate between amoebicidal activity and drug toxicity to human cells.

Methods

To address this limitation, we introduce a novel assay that utilizes three-dimensional hanging spheroid plates (3DHSPs) to evaluate both activities simultaneously on a single platform.

Results and discussion

Our study showed that the incubation of neurospheroids with clinically isolated B. mandrillaris trophozoites resulted in a loss of neurospheroid integrity, while the ATP levels in the neurospheroids decreased over time, indicating decreased host cell viability. Conversely, ATP levels in isolated trophozoites increased, indicating active parasite metabolism. Our findings suggest that the 3DHSP-based assay can serve as an endpoint for the phenotypic screening of drugs against B. mandrillaris, providing a more efficient and accurate approach for evaluating both parasite cytotoxicity and viability.

Wild Wheat Rhizosphere-Associated Plant Growth-Promoting Bacteria Exudates: Effect on Root Development in Modern Wheat and Composition

Diazotrophic bacteria isolated from the rhizosphere of a wild wheat ancestor, grown from its refuge area in the Fertile Crescent, were found to be efficient Plant Growth-Promoting Rhizobacteria (PGPR), upon interaction with an elite wheat cultivar. In nitrogen-starved plants, they increased the amount of nitrogen in the seed crop (per plant) by about twofold. A bacterial growth medium was developed to investigate the effects of bacterial exudates on root development in the elite cultivar, and to analyze the exo-metabolomes and exo-proteomes. Altered root development was observed, with distinct responses depending on the strain, for instance, with respect to root hair development. A first conclusion from these results is that the ability of wheat to establish effective beneficial interactions with PGPRs does not appear to have undergone systematic deep reprogramming during domestication. Exo-metabolome analysis revealed a complex set of secondary metabolites, including nutrient ion chelators, cyclopeptides that could act as phytohormone mimetics, and quorum sensing molecules having inter-kingdom signaling properties. The exo-proteome-comprised strain-specific enzymes, and structural proteins belonging to outer-membrane vesicles, are likely to sequester metabolites in their lumen. Thus, the methodological processes we have developed to collect and analyze bacterial exudates have revealed that PGPRs constitutively exude a highly complex set of metabolites; this is likely to allow numerous mechanisms to simultaneously contribute to plant growth promotion, and thereby to also broaden the spectra of plant genotypes (species and accessions/cultivars) with which beneficial interactions can occur.

Quorum Sensing Regulation of Virulence Gene Expression in Vibrio harveyi during its Interaction with Marine Diatom Skeletonema marinoi

Communication between species from different kingdoms may be as important as intra-kingdom communication. It has recently been confirmed that co-existing bacteria and phytoplankton in aquatic ecosystems do cross-talk. This study examined the signs of possible cross signalling between V. harveyi, one of the predominant bacterial species of the marine ecosystem and a dominant diatom species, S.marinoi, to understand communication over species borders. It is known that V.harveyi employ quorum sensing for cell-to-cell communication, bioluminescence (luxR), and the regulation of the virulence gene (vhp, chiA). Former studies have also shown, this kind of interactions being disrupted by compounds secreted by a few algal species existing in the aquatic ecosystem. We investigated the QS communication by quantifying the expression levels of virulence regulator luxR and virulence factors metalloprotease (vhp) and chitinase (chiA) in four different V. harveyi strains grown in the presence of S. marinoi strain. Results obtained in this study indicate that quorum sensing was activated in strains of V. harveyi analysed but did not regulate the expressions of vhp and chiA virulence factors. This observation suggests that the existence of S. marinoi did not interfere with the QS behaviour of V. harveyi and its interaction with marine diatom; it may be due to the commensalism relationship.

Engineering acyl-homoserine lactone-interfering enzymes toward bacterial control

Enzymes able to degrade or modify acyl-homoserine lactones (AHLs) have drawn considerable interest for their ability to interfere with the bacterial communication process referred to as quorum sensing. Many proteobacteria use AHL to coordinate virulence and biofilm formation in a cell density-dependent manner; thus, AHL-interfering enzymes constitute new promising antimicrobial candidates. Among these, lactonases and acylases have been particularly studied. These enzymes have been isolated from various bacterial, archaeal, or eukaryotic organisms and have been evaluated for their ability to control several pathogens. Engineering studies on these enzymes were carried out and successfully modulated their capacity to interact with specific AHL, increase their catalytic activity and stability, or enhance their biotechnological potential. In this review, special attention is paid to the screening, engineering, and applications of AHL-modifying enzymes. Prospects and future opportunities are also discussed with a view to developing potent candidates for bacterial control.

Bacterial Sensing and Biofilm Monitoring for Infection Diagnostics

Recent insights into the rapidly emerging field of bacterial sensing and biofilm monitoring for infection diagnostics are discussed as well as recent key developments and emerging technologies in the field. Electrochemical sensing of bacteria and bacterial biofilm via synthetic, natural, and engineered recognition, as well as direct redox-sensing approaches via algorithm-based optical sensing, and tailor-made optotracing technology are discussed. These technologies are highlighted to answer the very critical question: "how can fast and accurate bacterial sensing and biofilm monitoring be achieved? Following on from that: "how can these different sensing concepts be translated for use in infection diagnostics? A central obstacle to this transformation is the absence of direct and fast analysis methods that provide high-throughput results and bio-interfaces that can control and regulate the means of communication between biological and electronic systems. Here, the overall progress made to date in building such translational efforts at the level of an individual bacterial cell to a bacterial community is discussed.

The β-Lactamase Inhibitor Boronic Acid Derivative SM23 as a New Anti-Pseudomonas aeruginosa Biofilm

Pseudomonas aeruginosa is a Gram-negative nosocomial pathogen, often causative agent of severe device-related infections, given its great capacity to form biofilm. P. aeruginosa finely regulates the expression of numerous virulence factors, including biofilm production, by Quorum Sensing (QS), a cell-to-cell communication mechanism used by many bacteria. Selective inhibition of QS-controlled pathogenicity without affecting bacterial growth may represent a novel promising strategy to overcome the well-known and widespread drug resistance of P. aeruginosa. In this study, we investigated the effects of SM23, a boronic acid derivate specifically designed as β-lactamase inhibitor, on biofilm formation and virulence factors production by P. aeruginosa. Our results indicated that SM23: (1) inhibited biofilm development and production of several virulence factors, such as pyoverdine, elastase, and pyocyanin, without affecting bacterial growth; (2) decreased the levels of 3-oxo-C₁₂-HSL and C₄-HSL, two QS-related autoinducer molecules, in line with a dampened lasR/lasI system; (3) failed to bind to bacterial cells that had been preincubated with P. aeruginosa-conditioned medium; and (4) reduced both biofilm formation and pyoverdine production by P. aeruginosa onto endotracheal tubes, as assessed by a new in vitro model closely mimicking clinical settings. Taken together, our results indicate that, besides inhibiting β-lactamase, SM23 can also act as powerful inhibitor of P. aeruginosa biofilm, suggesting that it may have a potential application in the prevention and treatment of biofilm-associated P. aeruginosa infections.

Quorum quenching activity of Bacillus cereus isolate 30b confers antipathogenic effects in Pseudomonas aeruginosa

Background: Quorum quenching, the interference of a Quorum sensing (QS) system that contributes to the pathogenesis through triggering the production of various virulence determinants, is among the newly suggested antivirulence strategies. Purpose: This study aimed at screening of N-Acyl homoserine lactonase activity from local bacterial isolate, and investigating its effect on Pseudomonas aeruginosa (P. aeruginosa) virulence and biofilm formation. Materials and methods: Soil bacteria were screened for aiiA gene coding for lactonase enzyme by Polymerase Chain reaction and sequencing of aiiA gene homologs. Lactonase activity and spectrum were assessed in the cell-free lysate by well diffusion assay using Agrobacterium tumafaciens KYC55. A bacterial isolate showing the highest N-acyl-homoserine lactones degradation percentage was identified by gene amplification and sequencing of the 16S rRNA gene and its aiiA gene homolog. High performance liquid chromatography was used to confirm N-acyl-homoserine lactone degradation. The effect of cell-free lysate on the biofilm formation ability and cytotoxicity of P. aeruginosa PAO1 and P. aeruginosa clinical isolates from different clinical sources were assessed by static microtiter plate and viability assay, respectively Results: Lactonase gene and activity were identified in three Bacillus spp. isolates. They showed broad catalytic activities against tested N-acyl-homoserine lactones. However, The lactonase activity in the cell- free lysate of isolate 30b showed the highest significant degradation percentage on all tested signals; N-butanoyl-L-homoserine lactone (71%), N-hexanoyl-l-homoserine lactone (100%), N-decanoyl-homoserine lactone (100%), N-(3-oxohexanoyl)-L-homoserine lactone (37.5%), N-(oxodecanoyl)-L-homoserine lactone (100%), and N-(3-oxododecanoyl)-L-homoserine lactone (100%). Alignment of the amino acid sequences of AiiA protein of isolate 30b showed 96% identity with Bacillus cereus (B. cereus) homologous lactonases in the GenBank database, and the isolate was designated as B. cereus isolate 30b. Cell-free lysate of B. cereus isolate 30b reduced biofilm formation significantly in 93% of P. aeruginosa isolates. The highest mean percentage of reduction in the biofilm was 86%. Moreover, the viability percentage of human lung carcinoma A549 cells infected by P. aeruginosa and treated with cell-free lysate of B. cereus isolate 30b increased up to 15%. Conclusion: The results of this study highlight the potential of lactonases as a promising strategy to combat Pseudomonas aeruginosa virulence.

Clarithromycin Plus Intravenous Immunoglobulin Therapy Can Reduce the Relapse Rate of Kawasaki Disease: A Phase 2, Open-Label, Randomized Control Study

Background

We previously reported that biofilms and innate immunity contribute to the pathogenesis of Kawasaki disease. Therefore, we aimed to assess the efficacy of clarithromycin, an antibiofilm agent, in patients with Kawasaki disease.

Methods and Results

We conducted an open‐label, multicenter, randomized, phase 2 trial at 8 hospitals in Japan. Eligible patients included children aged between 4 months and 5 years who were enrolled between days 4 and 8 of illness. Participants were randomly allocated to receive either intravenous immunoglobulin (IVIG) or IVIG plus clarithromycin. The primary end point was the duration of fever after the initiation of IVIG treatment. Eighty‐one eligible patients were randomized. The duration of the fever did not differ between the 2 groups (mean±SD, 34.3±32.4 and 31.1±31.1 hours in the IVIG plus clarithromycin group and the IVIG group, respectively [P=0.66]). The relapse rate of patients in the IVIG plus clarithromycin group was significantly lower than that in the IVIG group (12.5% versus 30.8%, P=0.046). No serious adverse events occurred during the study period. In a post hoc analysis, the patients in the IVIG plus clarithromycin group required significantly shorter mean lengths of hospital stays than those in the IVIG group (8.9 days versus 10.3 days, P=0.049).

Conclusions

Although IVIG plus clarithromycin therapy failed to shorten the duration of fever, it reduced the relapse rate and shortened the duration of hospitalization in patients with Kawasaki disease.

Clinical Trial Registration

URL: http://www.umin.ac.jp/ctr/index.htm. Unique identifier: UMIN000015437.

MicroRNA-induced negative regulation of TLR-5 in grass carp, Ctenopharyngodon idella

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that play crucial roles in numerous biological processes. However, the role of miRNAs in antibacterial defence in fish has not been fully determined. Here, we identified that nine miRNAs are differentially expressed in kidney between susceptible and resistant grass carp strains. Analysis of spatial and temporal miRNA expression patterns suggests that cid-miRn-115 and miR-142a-3p are potential regulators of anti-bacterial activity. Overexpressing of cid-miRn-115 and miR-142a-3p results in a visible change in Ctenopharyngodon idella kidney (CIK) cells immune effector activity. Bioinformatics analysis and overexpressing assay shows that cid-miRn-115 and miR-142a-3p directly regulate tlr5 expression. cid-miRn-115 and miR-142a-3p overexpressing leads to a significant decrease in tlr5 expression in CIK, thereby repressing its downstream genes, such as il-1β, il-8 and tnf-α. These findings provide a novel insight into the determination of anti-bacterial compounds in grass carp.

Cell Density Effects of Frog Skin Bacteria on Their Capacity to Inhibit Growth of the Chytrid Fungus, Batrachochytrium dendrobatidis

Bacterial symbionts on frog skin can reduce the growth of the chytrid fungus Batrachochytrium dendrobatidis (Bd) through production of inhibitory metabolites. Bacteria can be effective at increasing the resistance of amphibians to chytridiomycosis when added to amphibian skin, and isolates can be screened for production of metabolites that inhibit Bd growth in vitro. However, some bacteria use density-dependent mechanism such as quorum sensing to regulate metabolite production. It is therefore important to consider cell density effects when evaluating bacteria as possible candidates for bioaugmentation. The aim of our study was to evaluate how the density of cutaneous bacteria affects their inhibition of Bd growth in vitro. We sampled cutaneous bacteria isolated from three frog species in the tropical rainforests of northern Queensland, Australia, and selected ten isolates that were inhibitory to Bd in standardised pilot trials. We grew each isolate in liquid culture at a range of initial dilutions, sub-sampled each dilution at a series of times during the first 48 h of growth and measured spectrophotometric absorbance values, cell counts and Bd-inhibitory activity of cell-free supernatants at each time point. The challenge assay results clearly demonstrated that the inhibitory effects of most isolates were density dependent, with relatively low variation among isolates in the minimum cell density needed to inhibit Bd growth. We suggest the use of minimum cell densities and fast-growing candidate isolates to maximise bioaugmentation efforts.

Dynamics of history-dependent epidemics in temporal networks

The structural properties of temporal networks often influence the dynamical processes that occur on these networks, e.g., bursty interaction patterns have been shown to slow down epidemics. In this paper, we investigate the effect of link lifetimes on the spread of history-dependent epidemics. We formulate an analytically tractable activity-driven temporal network model that explicitly incorporates link lifetimes. For Markovian link lifetimes, we use mean-field analysis for computing the epidemic threshold, while the effect of non-Markovian link lifetimes is studied using simulations. Furthermore, we also study the effect of negative correlation between the number of links spawned by an individual and the lifetimes of those links. Such negative correlations may arise due to the finite cognitive capacity of the individuals. Our investigations reveal that heavy-tailed link lifetimes slow down the epidemic, while negative correlations can reduce epidemic prevalence. We believe that our results help shed light on the role of link lifetimes in modulating diffusion processes on temporal networks.

The role of quorum sensing system in antimicrobial induced ampC expression in Pseudomonas aeruginosa biofilm

The aim of this study was to evaluate the effects of quorum sensing (QS) systems in Pseudomonas aeruginosa (P. aeruginosa) on the expression of ampC gene induced by antibiotics. An in vitro dynamic model of P. aeruginosa biofilms was established in a silicon tube in once-flowthrough system at 37 °C. Biofilm generation was identified by argentation. Biofilm morphology of standard P. aeruginosa strain (PAO-1) and QS systems deficient strains (PDO100, rhlI deficient strain; PAO-JP1, lasI deficient strain; and PAO-MW1, rhlI and lasI deficient strain) were observed by optical microscope. The expression of ampC in PAO1, PAO1 with QS inhibitor (furanone C-30) and the QS deficient strains before and after induced by antibiotics were quantified by real-time quantitative PCR. The biofilms of PAO-1 and PDO100 were much thicker and denser than that of PAO-JP1 and PAO-MW1. Being induced by antibiotics, the expression of ampC in PAO1 and PDO100 was significantly higher than that in PAO-MW1 and PAO-JP1. With the effect of furanone C-30, the expression of ampC in PAO1 induced by antibiotics was reduced in a dose-dependent manner. QS system, especially the las system, plays an important role in both biofilm formation and antimicrobials induced ampC expression and furanone C-30 is a potent inhibitor for P. aeruginosa QS system.

Acyl-homoserine lactones suppresses IEC-6 cell proliferation and increase permeability of isolated rat colon

We investigated to determine whether a variety of acyl-homoserine lactones (AHLs) influences epithelial cell proliferation and mucosal permeability. 3-Oxo-C12-homoserine lactone (HSL) and 3-oxo-C14-HSL significantly suppressed IEC-6 cell proliferation. A significant increase in mucosal permeability was observed in isolated rat colon tissue exposed to C12-HSL, 3-oxo-C12-HSL, and 3-oxo-C14-HSL. These data indicate that AHLs suppress epithelial proliferation and disrupt barrier function in intestinal mucosa.

Vita-PAMPs: signatures of microbial viability

Can the innate immune system detect and respond to microbial viability? Using bacteria as a model, we found that indeed the very essence of microbial infectivity, viability itself, can be detected, and notably, in the absence of the activity of virulence factors. The microbial molecule that serves as the signature of viability is bacterial messenger RNA (mRNA), common to all bacteria, and without which bacteria cannot survive. Prokaryotic mRNAs also differ from eukaryotic mRNAs in several ways, and as such, these features all fulfill the criteria, and more, for a pathogen-associated molecular pattern (PAMP) as originally proposed by Charles Janeway. Because these mRNAs are lost from dead bacteria, they belong to a special class of PAMPs, which we call vita-PAMPs. Here we discuss the possible receptors and pathways involved in the detection of bacterial mRNAs, and thus microbial viability. We also consider examples of vita-PAMPs other than bacterial mRNA.

Disruption of bacterial cell-to-cell communication by marine organisms and its relevance to aquaculture

Bacterial disease is one of the most critical problems in commercial aquaculture. Although various methods and treatments have been developed to curb the problem, yet they still have significant drawbacks. A novel and environmental-friendly approach in solving this problem is through the disruption of bacterial communication or quorum sensing (QS). In this communication scheme, bacteria regulate their own gene expression by producing, releasing, and sensing chemical signals from the environment. There seems to be a link between QS and diseases through the regulation of certain phenotypes and the induction of virulence factors responsible for pathogen-host association. Several findings have reported that numerous aquatic organisms such as micro-algae, macro-algae, invertebrates, or even other bacteria have the potential to disrupt QS. The mechanism of action varies from degradation of signals through enzymatic or chemical inactivation to antagonistic as well as agonistic activities. This review focuses on the existing marine organisms that are able to interfere with QS with potential application for aquaculture as bacterial control.

Attenuation of colistin bactericidal activity by high inoculum of Pseudomonas aeruginosa characterized by a new mechanism-based population pharmacodynamic model

Colistin is increasingly being utilized against Gram-negative pathogens, including Pseudomonas aeruginosa, resistant to all other antibiotics. Since limited data exist regarding killing by colistin at different initial inocula (CFUo), we evaluated killing of Pseudomonas aeruginosa by colistin at several CFUo and developed a mechanism-based mathematical model accommodating a range of CFUo. In vitro time-kill experiments were performed using >or=8 concentrations up to 64 x the MIC of colistin against P. aeruginosa PAO1 and two clinical P. aeruginosa isolates at CFUo of 10(6), 10(8), and 10(9) CFU/ml. Serial samples up to 24 h were simultaneously modeled in the NONMEM VI (results shown) and S-ADAPT software programs. The mathematical model was prospectively "validated" by additional time-kill studies assessing the effect of Ca(2+) and Mg(2+) on killing of PAO1 by colistin. Against PAO1, killing of the susceptible population was 23-fold slower at the 10(9) CFUo and 6-fold slower at the 10(8) CFUo than at the 10(6) CFUo. The model comprised three populations with different second-order killing rate constants (5.72, 0.369, and 0.00210 liters/h/mg). Bacteria were assumed to release signal molecules stimulating a phenotypic change that inhibits killing. The proposed mechanism-based model had a good predictive performance, could describe killing by colistin for all three studied strains and for two literature studies, and performed well in a prospective validation with various concentrations of Ca(2+) and Mg(2+). The extent and rate of killing of P. aeruginosa by colistin were markedly decreased at high CFUo compared to those at low CFUo. This was well described by a mechanism-based mathematical model, which should be further validated using dynamic in vitro models.

Quorum sensing and fungal-bacterial interactions in Candida albicans: a communicative network regulating microbial coexistence and virulence

Microorganisms have evolved a complex signature of communication termed quorum sensing (QS), which is based on the exchange and sensing of low molecular- weight signal compounds. The ability to communicate within the microbial population gives the advantage to coordinate a groups behaviour leading to a higher fitness in the environment. The polymorphic fungus Candida albicans is an opportunistic human pathogen able to regulate virulence traits through the production of at least two QS signal molecules: farnesol and tyrosol. The ability to adopt multiple morphotypes and form biofilms on infected surfaces are the most important pathogenic characteristics regulated by QS and are of clinical relevance. In fact, traditional antimicrobial approaches are often ineffective towards these characteristics. Moreover, the intimate association between C. albicans and other pathogens, such as Pseudomonas aeruginosa, increases the complexity of the infection system. This review outlines the current knowledge on fungal QS and fungal-bacterial interactions emphasizing on C. albicans. Further investigations need to concentrate on the molecular mechanisms and the genetic regulation of these phenomena in order to identify putative novel therapeutic options.

[Usefulness of macrolides as anti-inflammatories in respiratory diseases]

The macrolides are antibiotics that, besides their anti-bacterial action, have an anti-inflammatory effect, by decreasing the activity of the immune cells and bacteria cell changes. An increase the survival of patients suffering from diffuse panbronchiolitis was already seen in the 1980s, after being treated with erythromycin. Currently, the use of macrolides in various chronic inflammatory diseases has increased significantly. Clinical improvements associated to the administration of macrolides have been observed in diseases such as, cystic fibrosis, asthma, and bronchiectasis. However, despite the apparent clinical benefit they seem to provide, the published results up until now are controversial and conclusive results are unable to be obtained. This means that further clinical trials are necessary to confirm or refute the long-term use of these drugs, which are not free of adverse effects, mainly the appearance of resistant bacteria.

Theoretical and structural analysis of the active site of the transcriptional regulators LasR and TraR, using molecular docking methodology for identifying potential analogues of acyl homoserine lactones (AHLs) with anti-quorum sensing activity

In the present study the homology of transcriptional receptors LuxR type were evaluated using as point of reference the receptors TraR and LasR of the bacterial types Agrobacterium tumefaciens and Pseudomonas aureginosa respectively. A series of alignments were performed in order to demonstrate that the active site of the protein is conserved in wide range of gram negative bacteria. Moreover, some docking calculations were carried out for analogs of the acyl homoserin lactones (AHLs) and regulatory proteins LasR and TraR, to understand the complex microenvironment in which the ligands are exposed. The molecular alignments show clearly that there are preserved motifs in the residues (Y53, Y61, W57, D70, W85 to TraR, Y56, Y64, W60, D73, W88 to LasR) analyzed, which may serve as site-specific targets for the development of potential antagonists. In this study was found that the anti-quorum sensing activity of the AHLs molecular analogs appears to depend on; the structure of the lactone ring and on appropriate combination of absolute and relative stereochemistry of the carbonyl (C=O) and amide (NH(2)) groups of the side chain of these AHLs molecular analogs, in combination with the interactions with the conserved amino acids (D73, W60, Y56, S129 to LasR and D70, W57, Y53 to TraR) of the LuxR type protein family.

Revisiting the quorum-sensing hierarchy in Pseudomonas aeruginosa: the transcriptional regulator RhlR regulates LasR-specific factors

Pseudomonas aeruginosa uses the two major quorum-sensing (QS) regulatory systems las and rhl to modulate the expression of many of its virulence factors. The las system is considered to stand at the top of the QS hierarchy. However, some virulence factors such as pyocyanin have been reported to still be produced in lasR mutants under certain conditions. Interestingly, such mutants arise spontaneously under various conditions, including in the airways of cystic fibrosis patients. Using transcriptional lacZ reporters, LC/MS quantification and phenotypic assays, we have investigated the regulation of QS-controlled factors by the las system. Our results show that activity of the rhl system is only delayed in a lasR mutant, thus allowing the expression of multiple virulence determinants such as pyocyanin, rhamnolipids and C(4)-homoserine lactone (HSL) during the late stationary phase. Moreover, at this stage, RhlR is able to overcome the absence of the las system by activating specific LasR-controlled functions, including production of 3-oxo-C(12)-HSL and Pseudomonas quinolone signal (PQS). P. aeruginosa is thus able to circumvent the deficiency of one of its QS systems by allowing the other to take over. This work demonstrates that the QS hierarchy is more complex than the model simply presenting the las system above the rhl system.

Advancements in molecular epidemiology of implant infections and future perspectives

Implant infection remains the major and often irreducible complication in clinical use of biomaterials, demanding new therapeutic and preventive strategies. Etio-pathogenesis of biomaterials-related infections is being more and more studied, and various virulence bacterial factors have progressively been identified, but little is still known about the weight of the distinct molecules in the context of specific peri-implant infection sites. Molecular epidemiology has become recently integrated into the research on implant infections. What distinguishes molecular epidemiology from the simple molecular biology is that the use of molecular techniques is applied to the study of the distribution and prevalence of virulence and resistance genes in collections of bacterial clinical isolates from implant infections. Here, the authors comment on the range of molecular techniques available, reviewing the various applications of molecular epidemiology to the study of implant infections and providing some experimental examples related to the field of orthopaedic implant infections. They highlight the new opportunities arising from molecular epidemiology of designing measures useful to prevent and treat implant infections. The knowledge of the relative weight of virulence factors and of their regulatory mechanisms at molecular level can open the way to new strategies also including gene therapies aimed at silencing or knocking out crucial genes responsible for the aggressive tools (adhesins, biofilm production, antibiotic resistance) of the aetiological agents of implant-related infections.

From quorum to cooperation: lessons from bacterial sociality for evolutionary theory

The study of cooperation and altruism, almost since its inception, has been carried out without reference to the most numerous, diverse and very possibly most cooperative domain of life on the planet: bacteria. This is starting to change, for good reason. Far from being clonal loners, bacteria are highly social creatures capable of astonishingly complex collective behaviour that is mediated, as it is in colonial insects, by chemical communication. The article discusses recent experiments that explore different facets of current theories of the evolution and maintenance of cooperation using bacterial models. Not only do bacteria hold great promise as experimentally tractable, rapidly evolving systems for testing hypotheses, bacterial experiments have already raised interesting questions about the assumptions on which our current understanding of cooperation and altruism rests.

Macrolides beyond the conventional antimicrobials: a class of potent immunomodulators

The historical change in the natural course of diffuse panbronchiolitis (DPB), a fatal disorder of the airways, following the introduction of erythromycin in its treatment has focused attention of researchers on the anti-inflammatory properties of macrolides. Chronic inflammation of the airways accompanied by infiltration by neutrophils and overproduction of mucus and pro-inflammatory cytokines is observed in bronchial asthma, cystic fibrosis (CF), DPB, chronic obstructive pulmonary disease (COPD) and bronchiectasis. The airways of these patients are often colonised by mucoid Pseudomonas aeruginosa attached to epithelium by a biofilm. Bacteria intercommunicate for biofilm formation by a system of lactones known as quorum sensing. Macrolides inhibit mobility and quorum sensing of P. aeruginosa; they also decrease production of mucus by epithelial cells and biosynthesis of pro-inflammatory cytokines from monocytes and epithelial cells by inhibiting nuclear factor-kappaB. Large, randomised clinical trials for the management of these disorders with macrolides are not available, with the sole exception of four trials denoting benefit following long-term administration of azithromycin in patients with CF. That benefit is consistent with an increase in forced expiratory volume in 1s (FEV(1)) and a decrease in the rate of bacterial exacerbations. Studies with small numbers of patients with COPD revealed attenuation of the inflammatory reaction by macrolides. Experimental studies of Gram-negative sepsis have shown considerable attenuation of the systemic inflammatory response following intravenous administration of clarithromycin. Results of the effects of clarithromycin in patients with ventilator-associated pneumonia and sepsis in a large, randomised study of 200 patients are awaited.

Inhibition of quorum sensing-controlled virulence factor production in Pseudomonas aeruginosa by South Florida plant extracts

Quorum sensing (QS) is a key regulator of virulence and biofilm formation in Pseudomonas aeruginosa and other medically relevant bacteria. Aqueous extracts of six plants, Conocarpus erectus, Chamaesyce hypericifolia, Callistemon viminalis, Bucida buceras, Tetrazygia bicolor, and Quercus virginiana, were examined in this study for their effects on P. aeruginosa virulence factors and the QS system. C. erectus, B. buceras, and C. viminalis caused a significant inhibition of LasA protease, LasB elastase, pyoverdin production, and biofilm formation. Additionally, each plant presented a distinct effect profile on the las and rhl QS genes and their respective signaling molecules, suggesting that different mechanisms are responsible for efficacy. Extracts of all plants caused the inhibition of QS genes and QS-controlled factors, with marginal effects on bacterial growth, suggesting that the quorum-quenching mechanisms are unrelated to static or cidal effects.

Contribution of AhyR to virulence of Aeromonas hydrophila J-1

Aeromonas hydrophila is a broad-host-range pathogen and its pathogenesis is multifactorial. A regulatory mechanism known as quorum sensing has been found to be involved in the regulation of virulence in many bacteria. In A. hydrophila the ahyR gene encodes LuxR-type response regulator. Here we describe the inactivation of the ahyR gene of A. hydrophila J-1 by the insertion of a DNA fragment containing a kanamycin resistance determinant and reintroduced by allelic exchange into the chromosome of A. hydrophila J-1 by means of the suicide plasmid pJP5603. Cytotoxic effects on EPC cells assay and LD(50) determinations in fish demonstrated that the ahyR mutant was highly attenuated relative to the wild-type strain. Compared with the parent strain, some characteristics, such as biochemical characters and outer membrane protein profiles, had changed. Some main virulent determinants could not be detected, including proteases, amylase, Dnase, hemolysin and S layer. This article confirmed the important function of AhyR in the pathogenesis of A. hydrophila J-1.

Unifying mechanism for bacterial cell signalers (4,5-dihydroxy-2,3-pentanedione, lactones and oligopeptides): Electron transfer and reactive oxygen species. Practical medical features

Cell signaling has attracted much attention involving higher organisms, and more recently is of considerable interest concerning involvement in the bacterial realm. Many aspects can apply, including quorum sensing. Of the participating molecules, designated autoinducers, 4,5-dihydroxy-2,3-pentanedione (DPD) is one of the most important. It is in equilibrium with a furanone and a furanosyl-borate diester (AI-2). A prior hypothesis for cell signaling in higher organisms invoked a key role for electron transfer (ET) and reactive oxygen species (ROS), as well as conduits, relays and electrical effects. The principal ET functionalities are quinones, metal complexes, ArNO(2), and iminium species. A lesser known type is the alpha-dicarbonyl class. Diacetyl, a member, as well as its imine derivatives, can serve as a model for DPD, since the parent possesses a reduction potential amenable to ET in the biological domain. Hence, it is conceivable that DPD and its imine derivatives may be involved in ET-ROS processes. Presence of hydroxy groups should facilitate ET by DPD vs. diacetyl. Extensive prior literature supports participation of ET functionalities in action of therapeutic drugs, toxins and various illnesses. This biochemical behavior also applies to the alpha-dicarbonyl parent models. A second important bacterial autoinducer is the lactone category. Although ET functionality is lacking, the presence of the 1,3-dicarbonyl structure can provide a site for avid chelation with redox metal, e.g., iron or copper, followed by ET-ROS. Findings with added iron furnish support for the proposal. Oligopeptides comprise the third principal type of bacterial signaling agent. A prior review incorporates these within the theoretical framework based on ET by redox amino acids and redox enzymes. In recent years there has been a rapid increase in resistance to antibiotics by pathogenic bacteria. Infectious diseases are the leading cause of death worldwide and the third leading cause in the US. An alternate approach to antibiotics that are becoming less and less effective is to attenuate bacterial virulence. Bacterial infections appear to be importantly associated with biofilm formation. Since quorum sensors play a crucial role in this connection, they provide attractive targets for much-needed, novel approaches. Two of the main autoinducers investigated are the AHL and AI-2 systems. This review summarizes the literature, mostly recent, on this topic. Leads are provided by higher organisms that appear to have evolved means for disrupting bacterial cell communication and, hence, escape colonization. The main types in this category are the furanones, for which both natural and synthetic types have been investigated with promising results.

Induction of neutrophil chemotaxis by the quorum-sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone

Acyl homoserine lactones are synthesized by Pseudomonas aeruginosa as signaling molecules which control production of virulence factors and biofilm formation in a paracrine manner. We found that N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), but not its 3-deoxo isomer or acyl-homoserine lactones with shorter fatty acids, induced the directed migration (chemotaxis) of human polymorphonuclear neutrophils (PMN) in vitro. By use of selective inhibitors a signaling pathway, comprising phosphotyrosine kinases, phospholipase C, protein kinase C, and mitogen-activated protein kinase C, could be delineated. In contrast to the well-studied chemokines complement C5a and interleukin 8, the chemotaxis did not depend on pertussis toxin-sensitive G proteins, indicating that 3OC12-HSL uses another signaling pathway. Strong evidence for the presence of a receptor for 3OC12-HSL on PMN was derived from uptake studies; by use of radiolabeled 3OC12-HSL, specific and saturable binding to PMN was seen. Taken together, our data provide evidence that PMN recognize and migrate toward a source of 3OC12-HSL (that is, to the site of a developing biofilm). We propose that this early attraction of PMN could contribute to prevention of biofilm formation.

Development of bioluminescent Edwardsiella ictaluri for noninvasive disease monitoring

Edwardsiella ictaluri is a facultative intracellular bacterium that causes enteric septicemia of catfish (ESC). In this study, we aimed to develop bioluminescent E. ictaluri that can be monitored by noninvasive bioluminescence imaging (BLI). To accomplish this, the luxCDABE operon of Photorhabdus luminescens was cloned downstream of the lacZ promoter in the broad host range plasmid pBBR1MCS4. Edwardsiella ictaluri strain 93-146 transformed with the new plasmid, pAKlux1, was highly bioluminescent. pAKlux1 was stably maintained in E. ictaluri without any apparent effect on growth or native plasmid stability. To assess the usefulness of the bioluminescent strain in disease studies, catfish were infected with 93-146 pAKlux1 by intraperitoneal injection and by bath immersion, and in vivo bacterial dissemination was observed using BLI. This study demonstrated that bioluminescent E. ictaluri can be used for real-time monitoring of ESC in live fish, which should enable observation of pathogen attachment sites and tissue predilections.

Discovery of potent inhibitors of pseudomonal quorum sensing via pharmacophore modeling and in silico screening

HipHop-Refine was employed to derive a binding hypothesis for pseudomonal quorum sensing (QS) antagonists. The model was employed as 3D search query to screen the National Cancer Institute (NCI) database. One of the hits illustrated nanomolar QS inhibitory activity. The fact that this compound contained tetravalent lead (Pb) prompted us to evaluate the activities of phenyl mercuric nitrate and thimerosal, both fit the binding pharmacophore. The two mercurials illustrated nanomolar to low micromolar IC50 inhibitory values against pseudomonal QS. The three compounds represent a new class of QS inhibitors.

Immune modulation by Pseudomonas aeruginosa quorum-sensing signal molecules

There is burgeoning recent interest in the potential of bacterial quorum-sensing signal molecules (QSSMs) such as the long chain N-acylhomoserine lactones (AHLs) and 4-quinolones produced by Pseudomonas aeruginosa for modulating immune function. While it is clear that QSSMs have well defined immune modulatory potential in vitro, and are detectable in body fluids (such as sputum from cystic fibrosis patients infected with P. aeruginosa) at levels which might be expected to modify immune competence, the true impact of bacterial QSSMs on host physiology in vivo has yet to be fully determined.

Killing of cryptococcus neoformans by Staphylococcus aureus: the role of cryptococcal capsular polysaccharide in the fungal-bacteria interaction

Microbes compete for the environmental niche which is their host. To investigate the effects of a pathogenic bacterium on invasion and colonization by a pathogenic yeast, Cryptococcus neoformans was co-cultured with Staphylococcus aureus. We found that the number of colony forming units of C. neoformans was decreased by Staphylococcus aureus. In contrast, the viability of Candida albicans was not affected. Under the microscope, wild-type C. neoformans cells were shown to be surrounded by S. aureus, while cells of a capsuleless mutant of C. neoformans were not. C. neoformans was not killed when a membrane separated it from S. aureus in co-culture. Killing was confirmed by staining with cyanoditolyl tetrazolium chloride: S. aureus stained red, indicating viability, while C. neojormans did not stain, indicating lethality. The in situ terminal deoxynucleotidyl transferase-mediated dUTR nick end labeling (TUNEL) assay indicated cell death with fragmentation of DNA of C. neoformans. Capsular polysaccharide from C. neoformans inhibited the killing. Treatment of the crude polysaccharide with protease increased the inhibition. The protective activity resided in the glucuronoxylomannan (GXM) fraction, although the concentration required for the inhibition was high. These results suggest that S. aureus kills C. neoformans by a process that involves attachment to the cryptococcal capsule.

The Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone stimulates phagocytic activity in human macrophages through the p38 MAPK pathway

Quorum-sensing is an important mechanism for the regulation of bacteria-to-bacteria communication. Recent advances have demonstrated that the Pseudomonas aeruginosa signaling molecule N-(3-oxododecanoyl)-L-homoserine lactone (3O-C(12)-HSL) is also a potent modulator of eukaryotic cells and may thus play an important role in the host response during P. aeruginosa infections. Little is known, however, about specific effects of 3O-C(12)-HSL molecules on human macrophages. To address this issue, we investigated the influence of 3O-C(12)-HSL on the phagocytic activity, production of reactive oxygen species, and activation of p38 and p42/44 MAPK signaling pathways in human macrophages. We show an effect of 3O-C(12)-HSL on the phagocytic capacity in human macrophages, which depends on concentration and time of exposure. When cells were exposed to 100 microM 3O-C(12)-HSL for 30 min or 1 h, the phagocytic activity increased 1.8 and 1.6 times, respectively. The 3O-C(12)-HSL treatments had no significant effect on the level of reactive oxygen species production. Furthermore, the p38 MAPK, but not the p42/44 MAPK, signaling pathway was activated in response to 3O-C(12)-HSL. In addition, specific blocking of p38 MAPK activation with 10 microM SB 203580 prevented the 3O-C(12)-HSL-induced increase in the phagocytic activity. These findings demonstrate that the bacterial quorum-sensing can play a significant role also in regulation of macrophage activity during infections caused by P. aeruginosa.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

Quorum quenching: enzymatic disruption of N-acylhomoserine lactone-mediated bacterial communication in Burkholderia thailandensis

Many species of gram-negative bacteria communicate by synthesizing, secreting, and responding to N-acylhomoserine lactones (AHLs), a mechanism termed quorum sensing. Several investigations have characterized numerous AHL-degrading enzymes (AiiA lactonases) encoded by environmental isolates of Bacillus spp. The Burkholderia thailandensis quorum system is comprised of at least three AHL synthases (AHSs) and five transcriptional regulators belonging to the LuxIR class of proteins. Expression of the Bacillus anthracis (Ames strain) AiiA lactonase in B. thailandensis completely abolished the accumulation of N-decanoylhomoserine lactone (C(10)-HSL) and N-octanoylhomoserine lactone (C(8)-HSL), reduced N-hexanoylhomoserine lactone (C(6)-HSL) levels, altered both swarming and twitching motility, caused a significant increase in generation time, and affected carbon metabolism. In contrast, heterologous expression of the Bacillus cereus strain A24 AiiA lactonase in B. thailandensis reduced the concentrations of C(6)-HSL, C(8)-HSL, and C(10)-HSL to nondetectable levels; altered both swarming and twitching motility; and caused fluctuations in carbon utilization. Individual disruption of the B. thailandensis AHSs, specifically disruption of the btaI1 and btaI3 genes, which encode the proteins that direct the synthesis of C(8)-HSL and C(6)-HSL, respectively, caused the hyper-beta-hemolysis of sheep erythrocytes on blood agar plates. In contrast, AHL cleavage in B. thailandensis by the Bacillus AiiA lactonases failed to enhance beta-hemolytic activity. The results of this study demonstrate that heterologous expression of Bacillus sp. AiiA lactonases in B. thailandensis reduced AHL accumulation, affected both swarming and twitching motility, increased generation time, altered substrate utilization, and prevented the beta-hemolysis of sheep erythrocytes.

Role of quorum sensing in the pathogenicity of Burkholderia pseudomallei

Burkholderia pseudomallei is the causative agent of human and animal melioidosis. The role of quorum sensing (QS) in the in vivo pathogenicity of B. pseudomallei via inhalational exposure of BALB/c mice and intraperitoneal challenge of Syrian hamsters has not been reported. This investigation demonstrates that B. pseudomallei encodes a minimum of three luxI and five luxR homologues that are involved in animal pathogenicity. Mass spectrometry analysis of culture supernatants revealed that wild-type B. pseudomallei and the luxI mutants synthesized numerous signalling molecules, including N-octanoyl-homoserine lactone, N-decanoyl-homoserine lactone, N-(3-hydroxyoctanoyl)-l-homoserine lactone, N-(3-hydroxydecanoyl)-l-homoserine lactone and N-(3-oxotetradecanoyl)-l-homoserine lactone, which was further confirmed by heterologous expression of the B. pseudomallei luxI alleles in Escherichia coli. Mutagenesis of the B. pseudomallei QS system increased the time to death and reduced organ colonization of aerosolized BALB/c mice. Further, intraperitoneal challenge of Syrian hamsters with the B. pseudomallei QS mutants resulted in a significant increase in the LD50. Using semi-quantitative plate assays, preliminary analysis suggests that QS does not affect lipase, protease and phospholipase C biosynthesis/secretion in B. pseudomallei. The findings of the investigation demonstrate that B. pseudomallei encodes multiple luxIR genes, and disruption of the QS alleles reduces animal pathogenicity, but does not affect exoproduct secretion.

Quorum sensing: a transcriptional regulatory system involved in the pathogenicity of Burkholderia mallei

Numerous gram-negative bacterial pathogens regulate virulence factor expression by using a cell density mechanism termed quorum sensing (QS). An in silico analysis of the Burkholderia mallei ATCC 23344 genome revealed that it encodes at least two luxI and four luxR homologues. Using mass spectrometry, we showed that wild-type B. mallei produces the signaling molecules N-octanoyl-homoserine lactone and N-decanoyl-homoserine lactone. To determine if QS is involved in the virulence of B. mallei, we generated mutations in each putative luxIR homologue and tested the pathogenicities of the derivative strains in aerosol BALB/c mouse and intraperitoneal hamster models. Disruption of the B. mallei QS alleles, especially in RJ16 (bmaII) and RJ17 (bmaI3), which are luxI mutants, significantly reduced virulence, as indicated by the survival of mice who were aerosolized with 10(4) CFU (10 50% lethal doses [LD50s]). For the B. mallei transcriptional regulator mutants (luxR homologues), mutation of the bmaR5 allele resulted in the most pronounced decrease in virulence, with 100% of the challenged animals surviving a dose of 10 LD50s. Using a Syrian hamster intraperitoneal model of infection, we determined the LD50s for wild-type B. mallei and each QS mutant. An increase in the relative LD50 was found for RJ16 (bmaI1) (>967 CFU), RJ17 (bmaI3) (115 CFU), and RJ20 (bmaR5) (151 CFU) compared to wild-type B. mallei (<13 CFU). These findings demonstrate that B. mallei carries multiple luxIR homologues that either directly or indirectly regulate the biosynthesis of an essential virulence factor(s) that contributes to the pathogenicity of B. mallei in vivo.

IMMUNOMODULATION AND SEPSIS: IMPACT OF THE PATHOGEN

Infection begins when microorganisms overcome host barriers and multiply within host tissues. To contain the infection, the host mounts an inflammatory response that mobilizes defense systems and kills the invading microorganisms. A focal inflammatory response is usually sufficient to eradicate the organisms. However, when it fails to contain the infection, the organisms, their toxins, and numerous host mediators are released into the bloodstream, producing a systemic inflammatory response and organ failure. Microorganisms have coevolved with their hosts, thereby acquiring means of overcoming host defense mechanisms or even taking advantage of innate host responses. Many pathogens avoid recognition by the host or dampen host immune responses via sophisticated pathogen-host interactions. Some pathogens benefit from the inflammatory response. According to current hypotheses regarding the pathogenesis of sepsis, the host generates both an innate immune response identical for all pathogens and an adaptive pathogen-specific response. Determining whether the innate response benefits the pathogen or the host is essential for understanding host-pathogen interactions. In this review, we discuss how pathogens interfere with innate and adaptive immune responses to escape eradication by the host.

Quorum sensing regulates type III secretion in Vibrio harveyi and Vibrio parahaemolyticus

In a process known as quorum sensing, bacteria communicate with one another by producing, releasing, detecting, and responding to signal molecules called autoinducers. Vibrio harveyi, a marine pathogen, uses two parallel quorum-sensing circuits, each consisting of an autoinducer-sensor pair, to control the expression of genes required for bioluminescence and a number of other target genes. Genetic screens designed to discover autoinducer-regulated targets in V. harveyi have revealed genes encoding components of a putative type III secretion (TTS) system. Using transcriptional reporter fusions and TTS protein localization studies, we show that the TTS system is indeed functional in V. harveyi and that expression of the genes encoding the secretion machinery requires an intact quorum-sensing signal transduction cascade. The newly completed genome of the closely related marine bacterium Vibrio parahaemolyticus, which is a human pathogen, shows that it possesses the genes encoding both of the V. harveyi-like quorum-sensing signaling circuits and that it also has a TTS system similar to that of V. harveyi. We show that quorum sensing regulates TTS in V. parahaemolyticus. Previous reports connecting quorum sensing to TTS in enterohemorrhagic and enteropathogenic Escherichia coli show that quorum sensing activates TTS at high cell density. Surprisingly, we find that at high cell density (in the presence of autoinducers), quorum sensing represses TTS in V. harveyi and V. parahaemolyticus.

Effects of natural and chemically synthesized furanones on quorum sensing in Chromobacterium violaceum

Background

Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions:

1. Do these compounds affect growth?

2) Do these compounds activate the quorum sensing system of C. violaceum CV026?

3) Do these compounds inhibit violacein formation induced by the addition of the natural inducer N-hexanoylhomoserine lactone (HHL)?

4) Do these compounds enhance violacein formation in presence of HHL?

Results

The naturally produced N-acylhomoserine lactones showed a strong non-linear concentration dependent influence on violacein production in C. violaceum with a maximum at 3.7*10^-8 M with HHL. Apart from the N-acylhomoserine lactones only one furanone (emoxyfurane) was found to simulate N-acylhomoserine lactone activity and induce violacein formation. The most effective substances acting negatively both on growth and quorum sensing were analogs and intermediates in synthesis of the butenolides from Streptomyces antibioticus.

Conclusion

As the regulation of many bacterial processes is governed by quorum sensing systems, the finding of natural and synthetic furanones acting as agonists or antagonists suggests an interesting tool to control and handle detrimental AHL induced effects.

Some effects are due to general toxicity; others are explained by a competitive interaction for LuxR proteins. For further experiments it is important to be aware of the fact that quorum sensing active compounds have non-linear effects. Inducers can act as inhibitors and inhibitors might be able to activate or enhance the quorum sensing system depending on chemical structure and concentration levels.

Plants as models for the study of human pathogenesis

There are many common disease mechanisms used by bacterial pathogens of plants and humans. They use common means of attachment, secretion and genetic regulation. They share many virulence factors, such as extracellular polysaccharides and some type III secreted effectors. Plant and human innate immune systems also share many similarities. Many of these shared bacterial virulence mechanisms are homologous, but even more appear to have independently converged on a common function. This combination of homologous and analogous systems reveals conserved and critical steps in the disease process. Given these similarities, and the many experimental advantages of plant biology, including ease of replication, stringent genetic and reproductive control, and high throughput with low cost, it is proposed that plants would make excellent models for the study of human pathogenesis.

Cell death in Escherichia coli dnaE(Ts) mutants incubated at a nonpermissive temperature is prevented by mutation in the cydA gene

Cells of the Escherichia coli dnaE(Ts) dnaE74 and dnaE486 mutants die after 4 h of incubation at 40 degrees C in Luria-Bertani medium. Cell death is preceded by elongation, is inhibited by chloramphenicol, tetracycline, or rifampin, and is dependent on cell density. Cells survive at 40 degrees C when they are incubated at a high population density or at a low density in conditioned medium, but they die when the medium is supplemented with glucose and amino acids. Deletion of recA or sulA has no effect. We isolated suppressors which survived for long periods at 40 degrees C but did not form colonies. The suppressors protected against hydroxyurea-induced killing. Sequence and complementation analysis indicated that suppression was due to mutation in the cydA gene. The DNA content of dnaE mutants increased about eightfold in 4 h at 40 degrees C, as did the DNA content of the suppressed strains. The amount of plasmid pBR322 in a dnaE74 strain increased about fourfold, as measured on gels, and the electrophoretic pattern appeared to be normal even though the viability of the parent cells decreased 2 logs. Transformation activity also increased. 4',6'-diamidino-2-phenylindole staining demonstrated that there were nucleoids distributed throughout the dnaE filaments formed at 40 degrees C, indicating that there was segregation of the newly formed DNA. We concluded that the DNA synthesized was physiologically competent, particularly since the number of viable cells of the suppressed strain increased during the first few hours of incubation. These observations support the view that E. coli senses the rate of DNA synthesis and inhibits septation when the rate of DNA synthesis falls below a critical level relative to the level of RNA and protein synthesis.