Effects of antibiotics on quorum sensing in Pseudomonas aeruginosa. Antimicrob Agents Chemother. 2008;52:3648-3663. [PMID: 18644954 DOI: 10.1128/aac.01230-07]

Antimicrobial peptide GH12 suppresses cariogenic virulence factors of Streptococcus mutans

Cariogenic virulence factors of Streptococcus mutans include acidogenicity, aciduricity, and extracellular polysaccharides (EPS) synthesis. The de novo designed antimicrobial peptide GH12 has shown bactericidal effects on S. mutans, but its interaction with virulence and regulatory systems of S. mutans remains to be elucidated. The objectives were to investigate the effects of GH12 on virulence factors of S. mutans, and further explore the function mechanisms at enzymatic and transcriptional levels. To avoid decrease in bacterial viability, we limited GH12 to subinhibitory levels. We evaluated effects of GH12 on acidogenicity of S. mutans by pH drop, lactic acid measurement and lactate dehydrogenase (LDH) assay, on aciduricity through survival rate at pH 5.0 and F₁F₀-ATPase assay, and on EPS synthesis using quantitative measurement, morphology observation, vertical distribution analyses and biomass calculation. Afterwards, we conducted quantitative real-time PCR to acquire the expression profile of related genes. GH12 at 1/2 MIC (4 mg/L) inhibited acid production, survival rate, EPS synthesis, and biofilm formation. The enzymatic activity of LDH and F₁F₀-ATPase was inhibited, and ldh, gtfBCD, vicR, liaR, and comDE genes were significantly downregulated. In conclusion, GH12 inhibited virulence factors of S. mutans, through reducing the activity of related enzymes, downregulating virulence genes, and inactivating specific regulatory systems.

Antibiotics Promote Escherichia coli-Pseudomonas aeruginosa Conjugation through Inhibiting Quorum Sensing

The effect of antibiotics on horizontal gene transfer (HGT) is controversial, and the underlying mechanism remains poorly understood. Here, using Escherichia coli SM10λπ as the donor strain, which carries a chromosomally integrated RP4 plasmid, we investigated the effect of antibiotics on conjugational transfer of a mobilizable gentamicin (Gm) resistance plasmid. The results showed that an exposure to gentamicin that restricted the survival of recipient cells significantly enhanced SM10λπ-Pseudomonas aeruginosa PAO1 conjugation, which was attenuated by a deficiency of lasI-rhlI, genes associated with the generation of the quorum sensing signals N-acyl homoserine lactones (AHLs) in PAO1, or the deletion of the AHL receptor SdiA in SM10λπ. Subsequent mechanistic investigations revealed that a treatment with Gm repressed the mRNA expression of lasI and rhlI in PAO1 and upregulated traI expression in SM10λπ. Moreover, PAO1 treated with other quorum sensing (QS)-inhibiting antibiotics such as azithromycin or chloramphenicol also showed a conjugation-promoting ability. On the other hand, when using non-AHL-producing E. coli strain EC600 as the recipient cells, the promoting effect of Gm on conjugation could not be observed. These data suggest that AHL-SdiA contributes to the effectiveness of antibiotics on plasmid conjugation. Collectively, our findings highlight the HGT-promoting effect of antibiotics and suggest quorum sensing as a promising target for controlling antibiotic resistance dissemination. These findings have implications for assessing the risks of antibiotic use and developing advisable antibiotic treatment protocols.

Bacterial Biofilm Control by Perturbation of Bacterial Signaling Processes

The development of effective strategies to combat biofilm infections by means of either mechanical or chemical approaches could dramatically change today’s treatment procedures for the benefit of thousands of patients. Remarkably, considering the increased focus on biofilms in general, there has still not been invented and/or developed any simple, efficient and reliable methods with which to “chemically” eradicate biofilm infections. This underlines the resilience of infective agents present as biofilms and it further emphasizes the insufficiency of today’s approaches used to combat chronic infections. A potential method for biofilm dismantling is chemical interception of regulatory processes that are specifically involved in the biofilm mode of life. In particular, bacterial cell to cell signaling called “Quorum Sensing” together with intracellular signaling by bis-(3′-5′)-cyclic-dimeric guanosine monophosphate (cyclic-di-GMP) have gained a lot of attention over the last two decades. More recently, regulatory processes governed by two component regulatory systems and small non-coding RNAs have been increasingly investigated. Here, we review novel findings and potentials of using small molecules to target and modulate these regulatory processes in the bacterium Pseudomonas aeruginosa to decrease its pathogenic potential.

A SAR-based mechanistic study on the combined toxicities of sulfonamides and quorum sensing inhibitors on Escherichia coli

Quorum sensing inhibitors (QSIs) are promising alternatives to antibiotics, but they are discharged into the environment after their use cycle. This poses joint effects on the organisms in the environment. Therefore, it is of great importance to study the combined toxicities of QSIs and antibiotics. In this study, we investigated the single and combined toxicities of four potential QSIs and 11 sulfonamides (SAs) on Escherichia coli. The results revealed that the single toxicities of SAs were greater than those of QSIs, and the toxicities were found positively related to the binding energies (E_bind) with their target proteins, for both antibiotics and QSIs. The combined toxicities of the binary mixtures were observed to be either antagonism or addition. The antagonism could be explained by the phenomenon that QSIs changed SAs molecules into ionic forms, preventing the SA molecules entering the bacteria. Furthermore, it was found that the ratios of the effective concentration (the actual concentration involved in the interaction with the proteins) in the antagonistic cases were higher than those in the additive cases. This study would benefit both rational use of the drug combination and ecological risk assessment of antibiotics and QSIs in the real environment.

Inhibition of Pseudomonas aeruginosa quorum sensing by subinhibitory concentrations of curcumin with gentamicin and azithromycin

OBJECTIVES

Pseudomonas aeruginosa quorum sensing (QS) circuits regulate virulence factors and co-ordinate bacterial pathogenicity. This study aimed to investigate the inhibitory activity of subinhibitory concentrations of curcumin with azithromycin and gentamicin against P. aeruginosa QS-related genes and virulence factors.

METHODS

The minimum inhibitory concentrations (MICs) and synergistic activity of curcumin with azithromycin and gentamicin against P. aeruginosa PAO1 were determined using broth microdilution and checkerboard titration methods, respectively. The activity of sub-MICs (1/4× and 1/16× MIC) of curcumin on the QS signal molecules was assessed using a reporter strain assay. The influence of sub-MICs of curcumin, azithromycin and gentamicin alone and in combination on motility and biofilm formation was also determined and was confirmed by RT-PCR to test the expression of the QS regulatory genes lasI, lasR, rhlI and rhlR.

RESULTS

Addition of curcumin drastically decreased the MIC of azithromycin and gentamicin. Curcumin showed synergistic effects with azithromycin and gentamicin. Treated PAO1 cultures in the presence of curcumin showed a significant reduction of signals C12-HSL and C4-HSL (P<0.05). Sub-MICs (1/4× and 1/16× MIC) of curcumin, azithromycin and gentamicin alone and in combination significantly reduced swarming and twitching motilities as well as biofilm formation. Expression of QS regulatory genes lasI, lasR, rhlI and rhlR using 1/4× MIC of curcumin, azithromycin and gentamicin alone and in combination was decreased significantly compared with untreated PAO1.

CONCLUSIONS

These results indicate that a combination of sub-MIC of curcumin with azithromycin and gentamicin exhibited synergism against P. aeruginosa QS systems.

Subinhibitory concentration of ciprofloxacin targets quorum sensing system of Pseudomonas aeruginosa causing inhibition of biofilm formation & reduction of virulence

Background & objectives:

Biofilms formed by Pseudomonas aeruginosa lead to persistent infections. Use of antibiotics for the treatment of biofilm induced infection poses a threat towards development of resistance. Therefore, the research is directed towards exploring the property of antibiotics which may alter the virulence of an organism besides altering its growth. The aim of this study was to evaluate the role of subinhibitory concentration of ciprofloxacin (CIP) in inhibiting biofilm formation and virulence of P. aeruginosa.

Methods:

Antibiofilm potential of subinhibitory concentration of CIP was evaluated in terms of log reduction, biofilm forming capacity and coverslip assay. P. aeruginosa isolates (grown in the presence and absence of sub-MIC of CIP) were also evaluated for inhibition in motility, virulence factor production and quorum sensing (QS) signal production.

Results:

Sub-minimum inhibitory concentration (sub-MIC) of CIP significantly reduced the motility of P. aeruginosa stand and strain and clinical isolates and affected biofilm forming capacity. Production of protease, elastase, siderophore, alginate, and rhamnolipid was also significantly reduced by CIP.

Interpretation & conclusions:

Reduction in virulence factors and biofilm formation was due to inhibition of QS mechanism which was indicated by reduced production of QS signal molecules by P. aeruginosa in presence of subinhibitory concentration of CIP.

Pulse Generation in the Quorum Machinery of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium that is responsible for a wide range of infections in humans. Colonies employ quorum sensing (QS) to coordinate gene expression, including for virulence factors, swarming motility and complex social traits. The QS signalling system of P. aeruginosa is known to involve multiple control components, notably the las, rhl and pqs systems. In this paper, we examine the las system and, in particular, the repressive interaction of rsaL, an embedded small regulative protein, employing recent biochemical information to aid model construction. Using analytic methods, we show how this feature can give rise to excitable pulse generation in this subsystem with important downstream consequences for rhamnolipid production. We adopt a symmetric competitive inhibition to capture the binding in the lasI–rsaL intergenic region and show our results are not dependent on the exact choice of this functional form. Furthermore, we examine the coupling of lasR to the rhl system, the impact of the predicted capacity for pulse generation and the biophysical consequences of this behaviour. We hypothesize that the interaction between the las and rhl systems may provide a quorum memory to enable cells to trigger rhamnolipid production only when they are at the edge of an established aggregation.

Transcriptomic Analyses Elucidate Adaptive Differences of Closely Related Strains of Pseudomonas aeruginosa in Fuel

Pseudomonas aeruginosa can utilize hydrocarbons, but different strains have various degrees of adaptation despite their highly conserved genome. P. aeruginosa ATCC 33988 is highly adapted to hydrocarbons, while P. aeruginosa strain PAO1, a human pathogen, is less adapted and degrades jet fuel at a lower rate than does ATCC 33988. We investigated fuel-specific transcriptomic differences between these strains in order to ascertain the underlying mechanisms utilized by the adapted strain to proliferate in fuel. During growth in fuel, the genes related to alkane degradation, heat shock response, membrane proteins, efflux pumps, and several novel genes were upregulated in ATCC 33988. Overexpression of alk genes in PAO1 provided some improvement in growth, but it was not as robust as that of ATCC 33988, suggesting the role of other genes in adaptation. Expression of the function unknown gene PA5359 from ATCC 33988 in PAO1 increased the growth in fuel. Bioinformatic analysis revealed that PA5359 is a predicted lipoprotein with a conserved Yx(FWY)xxD motif, which is shared among bacterial adhesins. Overexpression of the putative resistance-nodulation-division (RND) efflux pump PA3521 to PA3523 increased the growth of the ATCC 33988 strain, suggesting a possible role in fuel tolerance. Interestingly, the PAO1 strain cannot utilize n-C₈ and n-C₁₀ The expression of green fluorescent protein (GFP) under the control of alkB promoters confirmed that alk gene promoter polymorphism affects the expression of alk genes. Promoter fusion assays further confirmed that the regulation of alk genes was different in the two strains. Protein sequence analysis showed low amino acid differences for many of the upregulated genes, further supporting transcriptional control as the main mechanism for enhanced adaptation.IMPORTANCE These results support that specific signal transduction, gene regulation, and coordination of multiple biological responses are required to improve the survival, growth, and metabolism of fuel in adapted strains. This study provides new insight into the mechanistic differences between strains and helpful information that may be applied in the improvement of bacterial strains for resistance to biotic and abiotic factors encountered during bioremediation and industrial biotechnological processes.

Alternative strategies for the study and treatment of clinical bacterial biofilms

Biofilms represent an adaptive lifestyle where microbes grow as structured aggregates in many different environments, e.g. on body surfaces and medical devices. They are a profound threat in medical (and industrial) settings and cause two-thirds of all infections. Biofilm bacteria are especially recalcitrant to common antibiotic treatments, demonstrating adaptive multidrug resistance. For this reason, novel methods to eradicate or prevent biofilm infections are greatly needed. Recent advances have been made in exploring alternative strategies that affect biofilm lifestyle, inhibit biofilm formation, degrade biofilm components and/or cause dispersal. As such, naturally derived compounds, molecules that interfere with bacterial signaling systems, anti-biofilm peptides and phages show great promise. Their implementation as either stand-alone drugs or complementary therapies has the potential to eradicate resilient biofilm infections. Additionally, altering the surface properties of indwelling medical devices through bioengineering approaches has been examined as a method for preventing biofilm formation. There is also a need for improving current biofilm detection methods since in vitro methods often do not accurately measure live bacteria in biofilms or mimic in vivo conditions. We propose that the design and development of novel compounds will be enabled by the improvement and use of appropriate in vitro and in vivo models.

Dual function of tropodithietic acid as antibiotic and signaling molecule in global gene regulation of the probiotic bacterium Phaeobacter inhibens

Antibiotics are typically regarded as microbial weapons, but whereas their function at concentrations lethal for bacteria is often well characterized, the role of antibiotics at much lower concentrations as possibly found under natural conditions remains poorly understood. By using whole-transcriptome analyses and phenotypic screenings of the marine bacterium Phaeobacter inhibens we found that the broad-spectrum antibiotic tropodithietic acid (TDA) causes the same regulatory effects in quorum sensing (QS) as the common signaling molecule N-acyl-homoserine lactone (AHL) at concentrations 100-fold lower than the minimal inhibitory concentration against bacteria. Our results show that TDA has a significant impact on the expression of ~10% of the total genes of P. inhibens, in the same manner as the AHL. Furthermore, TDA needs the AHL associated LuxR-type transcriptional regulator, just as the AHL molecule. Low concentrations of antibiotics can obviously have a strong influence on the global gene expression of the bacterium that produces it and drastically change the metabolism and behaviour of the bacterium. For P. inhibens this includes motility, biofilm formation and antibiotic production, all important for settlement on new host-associated surfaces. Our results demonstrate that bacteria can produce antibiotics not only to antagonise other bacteria, but also to mediate QS like endogenous AHL molecules.

Strategies for inhibiting quorum sensing

The ability of bacterial cells to synchronize their behaviour through quorum sensing (QS) regulatory networks enables bacterial populations to mount co-operative responses against competing micro-organisms and host immune defences and to adapt to environmental challenges. Since QS controls the ability of many pathogenic bacteria to cause disease, it is an attractive target for novel antibacterial agents that control infection through inhibition of virulence and by rendering biofilms more susceptible to conventional antibiotics and host clearance pathways. QS systems provide multiple druggable molecular targets for inhibitors (QSIs) that include the enzymes involved in QS signal molecule biosynthesis and the receptors involved in signal transduction. Considerable advances in our understanding of the chemical biology of QS systems and their inhibition have been made, some promising QS targets structurally characterized, QSI screens devised and inhibitors identified. However, much more work is required before any QSI ‘hits’ with the appropriate pharmacological and pharmacokinetic properties can enter human clinical trials. Indeed, the relative efficacy of QSIs alone or as prophylactics or therapeutics or as adjuvants in combination with conventional antibiotics still needs to be extensively evaluated in vivo. Particular attention must be given to the measurement of successful QSI therapy outcomes with respect to bacterial clearance, immune response and pathophysiology. Currently, our understanding of the potential of QS as a promising antibacterial target suggests that it is likely to be of value with respect to a limited number of major pathogens.

Quorum sensing inhibitory activity of sub-inhibitory concentrations of β-lactams

INTRODUCTION

The virulence factors of Pseudomonas aeruginosa are under the control of quorum sensing (QS) signals. Hence, interference with QS prevents its pathogenesis.

OBJECTIVE

The aim of the present research is to assess the influence of some β-lactam antibiotics on cell communication and the release of different virulence factors.

METHODS

The minimal inhibitory concentrations of ceftazidime, cefepime and imipenem were evaluated by microbroth dilution method. The effect of sub-inhibitory concentration of the tested antibiotics on QS signals was investigated using reporter strain assay. In addition, different virulence factors (elastase, protease, pyocyanin and hemolysin) were estimated in the presence of their sub-inhibitory concentrations.

RESULTS

Low concentrations of ceftazidime, cefepime and imipenem caused significant elimination of the QS signals 3OH-C12-HSL and C4-HSL up to 1/20 MIC. Furthermore, low concentrations of the tested antimicrobials suppressed virulence factors elastase and hemolysin. Moreover, 1/20 of their MICs reduced elastase, protease, pyocyanin and hemolysin.

CONCLUSION

Utilization of β-lactam antibiotics at low concentrations could be an effective approach for prevention and treatment of P. aeruginosa infection.

Plakofuranolactone as a Quorum Quenching Agent from the Indonesian Sponge Plakortis cf. lita

There is an urgent need for novel strategies to fight drug resistance and multi-drug resistance. As an alternative to the classic antibiotic therapy, attenuation of the bacteria virulence affecting their Quorum sensing (QS) system is a promising approach. Quorum sensing (QS) is a genetic regulation system that allows bacteria to communicate with each other and coordinate group behaviors. A new γ-lactone that is capable of inhibiting the LasI/R QS system, plakofuranolactone (1), was discovered in the extract of the marine sponge Plakortis cf. lita, and its structure, including absolute configuration, was determined by NMR spectroscopy, MS spectrometry, and quantum-mechanical prediction of optical rotation. The quorum quenching activity of plakofuranolactone was evaluated using reporter gene assays for long- and short-chain signals (E. coli pSB1075, E. coli pSB401, and C. violeaceum CV026) and was confirmed by measuring the total protease activity (a virulence factor which is under control of the LasI/R system) of the wild-type P. aeruginosa PAO1. Further research will be pursued to assess the potential of plakofuranolactone as a new antivirulence lead compound and a chemical tool to increase the knowledge in this field.

Plant phenolic volatiles inhibit quorum sensing in pectobacteria and reduce their virulence by potential binding to ExpI and ExpR proteins

Quorum sensing (QS) is a population density-dependent regulatory system in bacteria that couples gene expression to cell density through accumulation of diffusible signaling molecules. Pectobacteria are causal agents of soft rot disease in a range of economically important crops. They rely on QS to coordinate their main virulence factor, production of plant cell wall degrading enzymes (PCWDEs). Plants have evolved an array of antimicrobial compounds to anticipate and cope with pathogens, of which essential oils (EOs) are widely recognized. Here, volatile EOs, carvacrol and eugenol, were shown to specifically interfere with QS, the master regulator of virulence in pectobacteria, resulting in strong inhibition of QS genes, biofilm formation and PCWDEs, thereby leading to impaired infection. Accumulation of the signal molecule N-acylhomoserine lactone declined upon treatment with EOs, suggesting direct interaction of EOs with either homoserine lactone synthase (ExpI) or with the regulatory protein (ExpR). Homology models of both proteins were constructed and docking simulations were performed to test the above hypotheses. The resulting binding modes and docking scores of carvacrol and eugenol support potential binding to ExpI/ExpR, with stronger interactions than previously known inhibitors of both proteins. The results demonstrate the potential involvement of phytochemicals in the control of Pectobacterium.

Synergistic Nisin-Polymyxin Combinations for the Control of Pseudomonas Biofilm Formation

The emergence and dissemination of multi-drug resistant pathogens is a global concern. Moreover, even greater levels of resistance are conferred on bacteria when in the form of biofilms (i.e., complex, sessile communities of bacteria embedded in an organic polymer matrix). For decades, antimicrobial peptides have been hailed as a potential solution to the paucity of novel antibiotics, either as natural inhibitors that can be used alone or in formulations with synergistically acting antibiotics. Here, we evaluate the potential of the antimicrobial peptide nisin to increase the efficacy of the antibiotics polymyxin and colistin, with a particular focus on their application to prevent biofilm formation of Pseudomonas aeruginosa. The results reveal that the concentrations of polymyxins that are required to effectively inhibit biofilm formation can be dramatically reduced when combined with nisin, thereby enhancing efficacy, and ultimately, restoring sensitivity. Such combination therapy may yield added benefits by virtue of reducing polymyxin toxicity through the administration of significantly lower levels of polymyxin antibiotics.

Synthesis, characterization and in vitro evaluation of amphiphilic ion pairs of erythromycin and kanamycin antibiotics with liposaccharides

The hydrophilic ion paring strategy (HIP) is a method explored to improve the cell/tissue uptake of poorly adsorbed drugs and to optimize their physico-chemical characteristics. In this context, we here describe the synthesis of some ion pairs of two model cationic antibiotics, erythromycin (ERY) and kanamycin A (KAN), with liposaccharides having different levels of lipophilicity and charge. The formation of drug-liposaccharide complexes was confirmed by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) analysis. The effect of the amphiphilic liposaccharide moieties on the antimicrobial activity of ERY and KAN was assessed by measuring the minimal inhibitory concentration (MIC) of the compounds against a panel of bacterial strains that were susceptible or resistant to the parent antibiotics. The ion pairing did not depress the in vitro antibiotic activity, although no lowering of MIC values was registered. The experimental findings would motivate the future investigation of this ion pairing strategy in drug design, for instance allowing improvement of the encapsulation efficiency of hydrophilic antibiotics in lipid-based nanocarriers, or changing their in vivo biodistribution and pharmacokinetic profile.

Control of quorum sensing and virulence factors of Pseudomonas aeruginosa using phenylalanine arginyl β-naphthylamide

The spread of multidrug-resistant Pseudomonas aeruginosa isolates constitutes a serious clinical challenge. Bacterial efflux machinery is a crucial mechanism of resistance among P. aeruginosa. Efflux inhibitors such as phenylalanine arginyl β-naphthylamide (PAβN) promote the bacterial susceptibility to antimicrobial agents. The pathogenesis of P. aeruginosa is coordinated via quorum sensing (QS). This study aims to find out the impact of efflux pump inhibitor, PAβN, on QS and virulence attributes in clinical isolates of P. aeruginosa. P. aeruginosa isolates were purified from urine and wound samples, and the antimicrobial susceptibility was carried out by disc diffusion method. The multidrug-resistant and the virulent isolates U16, U21, W19 and W23 were selected. PAβN enhanced their susceptibility to most antimicrobial agents. PAβN reduced QS signalling molecules N-3-oxo-dodecanoyl-l-homoserine lactone and N-butyryl-l-homoserine lactone without affecting bacterial viability. Moreover, PAβN eliminated their virulence factors such as elastase, protease, pyocyanin and bacterial motility. At the transcription level, PAβN significantly (P<0.01) diminished the relative expression of QS cascade (lasI, lasR, rhlI, rhlR, pqsA and pqsR) and QS regulated-type II secretory genes lasB (elastase) and toxA (exotoxin A) compared to the control untreated isolates U16 and U21. In addition, PAβN eliminated the relative expression of pelA (exopolysaccharides) in U16 and U21 isolates. Hence, P. aeruginosa-tested isolates became hypo-virulent upon using PAβN. PAβN significantly blocked the QS circuit and inhibited the virulence factors expressed by clinical isolates of P. aeruginosa. PAβN could be a prime substrate for development of QS inhibitors and prevention of P. aeruginosa pathogenicity.

Difference of Type 3 secretion system (T3SS) effector gene genotypes (exoU and exoS) and its implication to antibiotics resistances in isolates of Pseudomonas aeruginosa from chronic otitis media

OBJECTIVE

Type 3 secretion system (T3SS) is the most important virulence factor in Pseudomonas aeruginosa infection. Of the various T3SS effector genes, exoS and exoU showed mutually exclusive distributions, and these two genes showed varied virulence. In many pseudomonal infections, the distribution of these genes showed different pattern and it influenced severity of infection. This study was aimed to evaluate differences of virulence factors and antibiotics resistance between chronic otitis media and other body infection caused by P. aeruginosa.

METHODS

To estimate the prevalence of effector genes of T3SS, especially the distributions of exoS and exoU genes and their association with antibiotic resistance in COM, we compared the prevalence of T3SS genes in isolates from COM with those from lower respiratory infection and bacteremia. Other virulence genes, including groEL, pilA, ndvB, lasB, rhlI, and apr, were also studied to evaluate prevalence. These isolates were tested for antibiotic susceptibility, and we examined the association between antibiotic susceptibility and the prevalence of T3SS effector genes.

RESULTS

The COM group showed a significantly higher exoU-positive rate than the control group (70.6% vs. 6.7%; P<0.01). Furthermore, COM patients with exoU showed significant antibiotic resistance to ciprofloxacin and tobramycin (P=0.035), whereas there was no significant difference in the control group.

CONCLUSIONS

The high incidence of exoU-positive P. aeruginosa and ciprofloxacin resistance can explain the chronicity and intractability of infection in COM. Elucidation of this pathogenicity will facilitate the development of new treatment options for COM patients.

Increased therapeutic efficacy of combination of azithromycin and ceftazidime on Pseudomonas aeruginosa biofilm in an animal model of ureteral stent infection

Background

Infection caused by ureteral stent indwelling is one of the most difficult medical problems, since once bacteria reside in biofilms they are extremely resistant to antibiotics as well as to the host immune defences. In this study we assessed the in vitro and in vivo efficacy of azithromycin and ceftazidime in preventing ureteral stent infection by Pseudomonas aeruginosa.

Results

The susceptibility testing with adherent bacteria showed that the biofilm was strongly inhibited by azithromycin treatment, ceftazidime against adherent bacteria in the presence of azithromycin showed the minimum inhibitory concentrations (MICs) and minimum bacteriocidal concentrations (MBCs) dramatically lower than those obtained in the absence of azithromycin. Moreover, ceftazidime plus azithromycin reduced twitching motility and production of rhamnolipid. For the single-treatment groups, in vivo intravenous injection of ceftazidime showed the highest inhibitory effect on bacterial load. Azithromycin prophylactic injection combined with ceftazidime showed increased inhibitory effect on bacterial load than that of each single antibiotic.

Conclusions

Combination of azithromycin and ceftazidime effectively prevent the formation of biofilm and reduced bacteria load of Pseudomonas aeruginosa compared to separate treatment of either of these two antibiotics. This combined treatment option have the potential to contribute to the success of Pseudomonas biofilm elimination in the clinical environment.

Network-assisted investigation of virulence and antibiotic-resistance systems in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium of clinical significance. Although the genome of PAO1, a prototype strain of P. aeruginosa, has been extensively studied, approximately one-third of the functional genome remains unknown. With the emergence of antibiotic-resistant strains of P. aeruginosa, there is an urgent need to develop novel antibiotic and anti-virulence strategies, which may be facilitated by an approach that explores P. aeruginosa gene function in systems-level models. Here, we present a genome-wide functional network of P. aeruginosa genes, PseudomonasNet, which covers 98% of the coding genome, and a companion web server to generate functional hypotheses using various network-search algorithms. We demonstrate that PseudomonasNet-assisted predictions can effectively identify novel genes involved in virulence and antibiotic resistance. Moreover, an antibiotic-resistance network based on PseudomonasNet reveals that P. aeruginosa has common modular genetic organisations that confer increased or decreased resistance to diverse antibiotics, which accounts for the pervasiveness of cross-resistance across multiple drugs. The same network also suggests that P. aeruginosa has developed mechanism of trade-off in resistance across drugs by altering genetic interactions. Taken together, these results clearly demonstrate the usefulness of a genome-scale functional network to investigate pathogenic systems in P. aeruginosa.

PA3297 Counteracts Antimicrobial Effects of Azithromycin in Pseudomonas aeruginosa

Pseudomonas aeruginosa causes acute and chronic infections in human. Its increasing resistance to antibiotics requires alternative treatments that are more effective than available strategies. Among the alternatives is the unconventional usage of conventional antibiotics, of which the macrolide antibiotic azithromycin (AZM) provides a paradigmatic example. AZM therapy is associated with a small but consistent improvement in respiratory function of cystic fibrosis patients suffering from chronic P. aeruginosa infection. Besides immunomodulating activities, AZM represses bacterial genes involved in virulence, quorum sensing, biofilm formation, and motility, all of which are due to stalling of ribosome and depletion of cellular tRNA pool. However, how P. aeruginosa responds to and counteracts the effects of AZM remain elusive. Here, we found that deficiency of PA3297, a gene encoding a DEAH-box helicase, intensified AZM-mediated bacterial killing, suppression of pyocyanin production and swarming motility, and hypersusceptibility to hydrogen peroxide. We demonstrated that expression of PA3297 is induced by the interaction between AZM and ribosome. Importantly, mutation of PA3297 resulted in elevated levels of unprocessed 23S-5S rRNA in the presence of AZM, which might lead to increased susceptibility to AZM-mediated effects. Our results revealed one of the bacterial responses in counteracting the detrimental effects of AZM.

Quercetin is an effective inhibitor of quorum sensing, biofilm formation and virulence factors in Pseudomonas aeruginosa

AIMS

The study aimed to perform a systematic investigation of the effects of quercetin on biofilm formation and virulence factors in Pseudomonas aeruginosa.

METHODS AND RESULTS

The Ps. aeruginosa strain PAO1 was selected as the test strain. The results indicated that quercetin did not impact the growth of PAO1 as determined by MIC and growth curve analysis. However, this compound significantly inhibited (P < 0·05) biofilm formation and production of virulence factors including pyocyanin, protease and elastase at a lower concentration than those for most previously reported plant extracts and substances. Considering the central role of quorum sensing (QS) in the regulation of biofilm and virulence factor, we further detected the transcriptional changes associated with QS and found that the expression levels of lasI, lasR, rhlI and rhlR were significantly reduced (P < 0·05) by 34, 68, 57 and 50%, respectively, in response to 16 μg ml(-1) quercetin.

CONCLUSIONS

This study indicated that quercetin is an effective inhibitor of biofilm formation and virulence factors in Ps. aeruginosa.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to demonstrate that quercetin is an effective inhibitor of QS, biofilm formation and virulence factors in Ps. aeruginosa. Furthermore, quercetin might have potential in fighting biofilm-related infections.

The phenotypic evolution of Pseudomonas aeruginosa populations changes in the presence of subinhibitory concentrations of ciprofloxacin

Ciprofloxacin is a widely used antibiotic, in the class of quinolones, for treatment of Pseudomonas aeruginosa infections. The immediate response of P. aeruginosa to subinhibitory concentrations of ciprofloxacin has been investigated previously. However, the long-term phenotypic adaptation, which identifies the fitted phenotypes that have been selected during evolution with subinhibitory concentrations of ciprofloxacin, has not been studied. We chose an experimental evolution approach to investigate how exposure to subinhibitory concentrations of ciprofloxacin changes the evolution of P. aeruginosa populations compared to unexposed populations. Three replicate populations of P. aeruginosa PAO1 and its hypermutable mutant ΔmutS were cultured aerobically for approximately 940 generations by daily passages in LB medium with and without subinhibitory concentration of ciprofloxacin and aliquots of the bacterial populations were regularly sampled and kept at  - 80 °C for further investigations. We investigate here phenotypic changes between the ancestor (50 colonies) and evolved populations (120 colonies/strain). Decreased protease activity and swimming motility, higher levels of quorum-sensing signal molecules and occurrence of mutator subpopulations were observed in the ciprofloxacin-exposed populations compared to the ancestor and control populations. Transcriptomic analysis showed downregulation of the type III secretion system in evolved populations compared to the ancestor population and upregulation of denitrification genes in ciprofloxacin-evolved populations. In conclusion, the presence of antibiotics at subinhibitory concentration in the environment affects bacterial evolution and further studies are needed to obtain insight into the dynamics of the phenotypes and the mechanisms involved.

Control of biofilm-associated infections by signaling molecules and nanoparticles

As the severe infections caused by resistant pathogens and biofilm embedded bacteria continue to emerge, alternative antimicrobial strategies could represent a solution. Recent studies support the development of molecular approaches (through signaling molecules) aiming to fight infections by modulating the virulence, behavior and formation of resistance structures such as biofilms. The utilization of such formulations would offer the advantage of reducing the selection of resistant isolates, since most of the proposed molecules do not interfere with the population fitness if utilized in low amounts. Despite the promising results, these therapies are delaying to be applied in the clinical context mainly because of the following: (i) limited knowledge regarding their long and medium term effect, (ii) specific properties that make most of these molecules difficult to be utilized in pharmacological formulations, (iii) low stability, (iv) difficulty to reach a target within the host body, and (v) limited availability. For reducing most of these disadvantages, nanotechnology seem to offer the best option through the development of nanostructured materials and nanoparticles able to improve the efficiency of molecular virulence modulators and novel antimicrobial compounds and to ensure their targeted delivery and controlled release.

Impact of Azithromycin on the Quorum Sensing-Controlled Proteome of Pseudomonas aeruginosa

The macrolide antibiotic, azithromycin (AZM), has been reported to improve the clinical outcome of cystic fibrosis patients, many of whom are chronically-infected with Pseudomonas aeruginosa. However, the highest clinically-achievable concentrations of this drug are well-below the minimum inhibitory concentration for P. aeruginosa, raising the question of why AZM exhibits therapeutic activity. One possibility that has been raised by earlier studies is that AZM inhibits quorum sensing (QS) by P. aeruginosa. To explicitly test this hypothesis the changes brought about by AZM treatment need to be compared with those associated with specific QS mutants grown alongside in the same growth medium, but this has not been done. In this work, we used quantitative 2D-difference gel electrophoresis and 1H-NMR spectroscopy footprint analysis to examine whether a range of clinically-relevant AZM concentrations elicited proteomic and metabolomic changes in wild-type cultures that were similar to those seen in cultures of defined QS mutants. Consistent with earlier reports, over half of the AZM-induced spot changes on the 2D gels were found to affect QS-regulated proteins. However, AZM modulated very few protein spots overall (compared with QS) and collectively, these modulated proteins comprised only a small fraction (12-13%) of the global QS regulon. We conclude that AZM perturbs a sub-regulon of the QS system but does not block QS per se. Reinforcing this notion, we further show that AZM is capable of attenuating virulence factor production in another Gram-negative species that secretes copious quantities of exoenzymes (Serratia marcescens), even in the absence of a functional QS system.

Exploiting Quorum Sensing Interfering Strategies in Gram-Negative Bacteria for the Enhancement of Environmental Applications

Quorum sensing (QS) is a widespread intercellular form of communication to coordinate physiological processes and cooperative activities of bacteria at the population level, and it depends on the production, secretion, and detection of small diffusible autoinducers, such as acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2. In this review, the function of QS autoinducers of gram-negative bacteria in different aspects of wastewater treatment systems is examined. Based on research primarily performed over the past 10 years, QS involvement in the formation of biofilm and aerobic granules and changes of the microbial community and degradation/transformation pathways is discussed. In particular, the QS pathway in the role of bacterial infections and disease prevention in aquaculture is addressed. Interference of QS autoinducer-regulated pathways is considered potential treatment for a variety of environmentally related problems. This review is expected to serve as a stepping stone for further study and development strategies based on the mediation of QS-regulated pathways to enhance applications in both wastewater treatment systems and aquaculture.

Exploiting the antivirulence efficacy of an ajoene-ciprofloxacin combination against Pseudomonas aeruginosa biofilm associated murine acute pyelonephritis

The study investigated the in vitro, ex vivo and in vivo efficacy of ajoene and ciprofloxacin (CIP) alone and in combination against Pseudomonas aeruginosa biofilms and biofilm-associated murine acute pyelonephritis. The ajoene-CIP combination exhibited significant greater (p < 0.05) antimotility and biofilm inhibitory effects than those obtained when they were applied individually. The combined action of the agents resulted in a significant increase in serum sensitivity and phagocytic uptake and killing of P. aeruginosa (p < 0.001) compared to the untreated control. Mice groups treated with an ajoene (25 mg kg(-1)) and CIP (30 mg kg(-1) or 15 mg kg(-1)) combination showed a significantly (p < 0.001) reduced bacterial load in the kidney and bladder as compared to that of infected controls and mice treated with solo agents on the fifth day post-infection. The decreased levels of biomarkers and photomicrographs of the kidney tissue of the treated mice showed a reduced severity of damage. Hence, the study highlights the antivirulent and therapeutic efficacy of the ajoene-CIP combination at the minimal dosage of CIP.

Broad-spectrum inhibition of AHL-regulated virulence factors and biofilms by sub-inhibitory concentrations of ceftazidime

Quorum sensing in bacteria is a density dependent communication system that regulates the expression of genes. In this study we have shown the broad spectrum anti-quorum sensing and biofilm inhibiting activity of ceftazidime against 3 different bacterial pathogens.

Maniwamycins: new quorum-sensing inhibitors against Chromobacterium violaceum CV026 were isolated from Streptomyces sp. TOHO-M025

Quorum sensing is an important microbial signaling system that controls the expression of many virulence genes. Maniwamycins C-F, new compounds and quorum-sensing inhibitors, were isolated from the culture broth of Streptomyces sp. TOHO-M025 using a silica gel column and preparative HPLC. The structures of maniwamycins were elucidated by spectroscopic analyses, including NMR. The compounds each have an azoxy moiety. All maniwamycins inhibited violacein synthesis, which is controlled by quorum sensing, in Chromobacterium violaceum CV026.

Adjuvant effect of cranberry proanthocyanidin active fraction on antivirulent property of ciprofloxacin against Pseudomonas aeruginosa

Quorum sensing inhibitors (QSIs) act as antivirulent agents since quorum sensing (QS) plays a vital role in regulating pathogenesis of Pseudomonas aeruginosa. However, application of single QSI may not be effective as pathogen is vulnerable to successful mutations. In such conditions, combination of QSIs can be exploited as there can be synergistic or adjuvant action. In the present study, we evaluated the antivirulence efficacy of combination of Vaccinium macrocarpon proanthocyanidin active fraction (PAF) and ciprofloxacin (CIP) at their sub-MICs using standard methods followed by analysis of their mode of action on QS using TLC and molecular docking. There was significant improvement in action of CIP when it was combined with PAF in reducing the QS controlled virulence factors (p < 0.05), motilities and biofilm of P. aeruginosa. TLC profiles of QS signals [(Acyl homoserine lactone (AHL) and Pseudomonas quinolone signal (PQS)] indicated that CIP in combination with PAF, besides showing inhibitory action on production of AHLs, also modulated production and inactivation of PQS. Docking scores also supported the observation. We therefore hypothesize that PAF-CIP combination, having improved anti-virulence property; can be exploited as a potent drug pairing against P. aeruginosa.

Antisense RNA-based High-Throughput Screen System for Directed Evolution of Quorum Quenching Enzymes

Quorum quenching (QQ) enzymes, which disrupt the quorum sensing signaling process, have attracted considerable attention as new antimicrobial agents. However, their low catalytic efficiency for quorum sensing molecules remains a challenge. Herein, we present an antisense RNA-based high-throughput screen system for directed evolution of a quorum quenching enzyme. The screening system was constructed by incorporating an antisense RNA (RyhB) into a synthetic module to quantitatively regulate the expression of a reporter gene fused with a sense RNA (sodB). To control the expression of a reporter gene in response to the catalytic activity of a quorum quenching enzyme, the region of interaction and mode between a pair of antisense (RyhB) and sense (sodB) RNAs was designed and optimized through the prediction of the secondary structure of the RNA pair. The screening system constructed was shown to lead to a significant reduction in the false-positive rate (average 42%) in the screening of N-acyl-homoserine lactonase (AiiA) with increased catalytic activity, resulting in a true-positive frequency of up to 76%. The utility and efficiency of the screening system were demonstrated by selecting an AiiA with 31-fold higher catalytic efficiency than the wild-type in three rounds of directed evolution. The present approach can be widely used for the screening of quorum quenching enzymes with the desired catalytic property, as well as for a synthetic network for a stringent regulation of the gene expression.

Whole-Cell Biosensors as Tools for the Detection of Quorum-Sensing Molecules: Uses in Diagnostics and the Investigation of the Quorum-Sensing Mechanism

Genetically engineered bacterial whole-cell biosensors are powerful tools that take advantage of bacterial proteins and pathways to allow for detection of a specific analyte. These biosensors have been employed for a broad range of applications, including the detection of bacterial quorum-sensing molecules (QSMs). Bacterial QSMs are the small molecules bacteria use for population density-dependent communication, a process referred to as quorum sensing (QS). Various research groups have investigated the presence of QSMs, including N-acyl homoserine lactones (AHLs) and autoinducer-2 (AI-2), in physiological samples in attempts to enhance our knowledge of the role of bacteria and QS in disease states. Continued studies in these fields may allow for improved patient care and therapeutics based upon QSMs. Furthermore, bacterial whole-cell biosensors have elucidated the roles of some antibiotics as QS agonists and antagonists. Graphical Abstract.

Cystic fibrosis - a multiorgan protein misfolding disease

Cystic fibrosis (CF) is a heterogeneous multiorgan disease caused by mutations in the CFTR gene leading to misfolding (and other defects) and consequent dysfunction of CFTR protein. The majority of mutations cause a severe CF phenotype, and people with this condition will require a wide variety of medical interventions and therapies throughout their lives to address the symptoms of their condition. CF affects many different organ systems, but the most serious consequence of the disease is degeneration of lung function due to chronic respiratory infection and colonization of the airways with opportunistic microbial pathogens. Improvements in therapeutics, particularly the effective use of antibiotics, have led to significant gradual increases in life expectancy. There remains, however, a continuing need for newer, safer and more effective antimicrobials and mucolytic agents to maintain and improve our ability to combat CF lung infections before other curative approaches which target the root cause of the disease become available.

Efficacy of ciprofloxacin-clarithromycin combination against drug-resistant Pseudomonas aeruginosa mature biofilm using in vitro experimental model

Pseudomonas aeruginosa is the main cause of mortality in cystic fibrosis patients and eradication of its biofilm represents a substantial problem clinically. In this study, biofilm of a cystic fibrosis strain P. aeruginosa PACI22 was established and confocal laser scanning microscopy was utilized for biofilm visualization. A quantitative time-kill biofilm model was implemented in vitro to assess the biocidal effect of ciprofloxacin, clarithromycin, and their combination at concentration levels ranged from 0.5× to 64× minimum biofilm inhibitory concentrations (MBIC) against the biofilm and the mean log bacterial densities (Log CFU/ml) retrieved from the biofilm were monitored by frequent sampling at 0, 3, 6, 9, 12, and 24 hr throughout the experiment. The results revealed that none of the tested antibiotics alone could completely eradicate the biofilm-ensconced bacteria at 0.5-64× MBIC values after 24 hr of treatment. Conversely, ciprofloxacin-clarithromycin combination at 32-64× MBIC entirely exterminated the biofilm. Furthermore, a substantial in vitro synergism between ciprofloxacin and clarithromycin against the biofilm was experimentally verified. This promising synergism affords scientific rationale for further in vivo investigations to evaluate the therapeutic potential of this combination for treatment of chronic pulmonary infections caused by P. aeruginosa biofilms.

Role of quorum sensing in bacterial infections

Quorum sensing (QS) is cell communication that is widely used by bacterial pathogens to coordinate the expression of several collective traits, including the production of multiple virulence factors, biofilm formation, and swarming motility once a population threshold is reached. Several lines of evidence indicate that QS enhances virulence of bacterial pathogens in animal models as well as in human infections; however, its relative importance for bacterial pathogenesis is still incomplete. In this review, we discuss the present evidence from in vitro and in vivo experiments in animal models, as well as from clinical studies, that link QS systems with human infections. We focus on two major QS bacterial models, the opportunistic Gram negative bacteria Pseudomonas aeruginosa and the Gram positive Staphylococcus aureus, which are also two of the main agents responsible of nosocomial and wound infections. In addition, QS communication systems in other bacterial, eukaryotic pathogens, and even immune and cancer cells are also reviewed, and finally, the new approaches proposed to combat bacterial infections by the attenuation of their QS communication systems and virulence are also discussed.

Pseudomonas aeruginosa quorum sensing molecules correlate with clinical status in cystic fibrosis

Pseudomonas aeruginosa produces quorum sensing signal molecules that are potential biomarkers for infection.

A prospective study of 60 cystic fibrosis patients with chronic P. aeruginosa, who required intravenous antibiotics for pulmonary exacerbations, was undertaken. Clinical measurements and biological samples were obtained at the start and end of the treatment period. Additional data were available for 29 of these patients when they were clinically stable.

Cross-sectionally, quorum sensing signal molecules were detectable in the sputum, plasma and urine of 86%, 75% and 83% patients, respectively. They were positively correlated between the three biofluids. Positive correlations were observed for most quorum sensing signal molecules in sputum, plasma and urine, with quantitative measures of pulmonary P. aeruginosa load at the start of a pulmonary exacerbation. Plasma concentrations of 2-nonyl-4-hydroxy-quinoline (NHQ) were significantly higher at the start of a pulmonary exacerbation compared to clinical stability (p<0.01). Following the administration of systemic antibiotics, plasma 2-heptyl-4-hydroxyquinoline (p=0.02) and NHQ concentrations (p<0.01) decreased significantly.

In conclusion, quorum sensing signal molecules are detectable in cystic fibrosis patients with pulmonary P. aeruginosa infection and are positively correlated with quantitative measures of P. aeruginosa. NHQ correlates with clinical status and has potential as a novel biomarker for P. aeruginosa infection.

P. aeruginosa QS molecules correlate with clinical status in cystic fibrosis and are biomarkers for infectionhttp://ow.ly/MhzZp

Antimicrobial resistance, respiratory tract infections and role of biofilms in lung infections in cystic fibrosis patients

Lung infection is the main cause of morbidity and mortality in patients with cystic fibrosis and is mainly dominated by Pseudomonas aeruginosa. The biofilm mode of growth makes eradication of the infection impossible, and it causes a chronic inflammation in the airways. The general mechanisms of biofilm formation and antimicrobial tolerance and resistance are reviewed. Potential anti-biofilm therapeutic targets such as weakening of biofilms by quorum-sensing inhibitors or antibiotic killing guided by pharmacokinetics and pharmacodynamics of antibiotics are presented. The vicious circle of adaptive evolution of the persisting bacteria imposes important therapeutic challenges and requires development of new drug delivery systems able to reach the different niches occupied by the bacteria in the lung of cystic fibrosis patients.

Drug repurposing as an alternative for the treatment of recalcitrant bacterial infections

Bacterial infection remains one of the leading causes of death worldwide, and the options for treating such infections are decreasing, due the rise of antibiotic-resistant bacteria. The pharmaceutical industry has produced few new types of antibiotics in more than a decade. Researchers are taking several approaches toward developing new classes of antibiotics, including (1) focusing on new targets and processes, such as bacterial cell–cell communication that upregulates virulence; (2) designing inhibitors of bacterial resistance, such as blockers of multidrug efflux pumps; and (3) using alternative antimicrobials such as bacteriophages. In addition, the strategy of finding new uses for existing drugs is beginning to produce results: antibacterial properties have been discovered for existing anticancer, antifungal, anthelmintic, and anti-inflammatory drugs. In this review, we discuss the antimicrobial properties of gallium compounds, 5-fluorouracil, ciclopirox, diflunisal, and some other FDA-approved drugs and argue that their repurposing for the treatment of bacterial infections, including those that are multidrug resistant, is a feasible strategy.

The formation of biofilms by Pseudomonas aeruginosa: a review of the natural and synthetic compounds interfering with control mechanisms

P. aeruginosa is an opportunistic pathogenic bacterium responsible for both acute and chronic infections. Beyond its natural resistance to many drugs, its ability to form biofilm, a complex biological system, renders ineffective the clearance by immune defense systems and antibiotherapy. The objective of this report is to provide an overview (i) on P. aeruginosa biofilm lifestyle cycle, (ii) on the main key actors relevant in the regulation of biofilm formation by P. aeruginosa including QS systems, GacS/GacA and RetS/LadS two-component systems and C-di-GMP-dependent polysaccharides biosynthesis, and (iii) finally on reported natural and synthetic products that interfere with control mechanisms of biofilm formation by P. aeruginosa without affecting directly bacterial viability. Concluding remarks focus on perspectives to consider biofilm lifestyle as a target for eradication of resistant infections caused by P. aeruginosa.

6-Gingerol reduces Pseudomonas aeruginosa biofilm formation and virulence via quorum sensing inhibition

Pseudomonas aeruginosa is a well-known pathogenic bacterium that forms biofilms and produces virulence factors via quorum sensing (QS). Interfering with normal QS interactions between signal molecules and their cognate receptors is a developing strategy for attenuating its virulence. Here we tested the hypothesis that 6-gingerol, a pungent oil of fresh ginger, reduces biofilm formation and virulence by antagonistically binding to P. aeruginosa QS receptors. In silico studies demonstrated molecular binding occurs between 6-gingerol and the QS receptor LasR through hydrogen bonding and hydrophobic interactions. Experimentally 6-gingerol reduced biofilm formation, several virulence factors (e.g., exoprotease, rhamnolipid, and pyocyanin), and mice mortality. Further transcriptome analyses demonstrated that 6-gingerol successfully repressed QS-induced genes, specifically those related to the production of virulence factors. These results strongly support our hypothesis and offer insight into the molecular mechanism that caused QS gene repression.

Antipseudomonal agents exhibit differential pharmacodynamic interactions with human polymorphonuclear leukocytes against established biofilms of Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most common pathogen infecting the lower respiratory tract of cystic fibrosis (CF) patients, where it forms tracheobronchial biofilms. Pseudomonas biofilms are refractory to antibacterials and to phagocytic cells with innate immunity, leading to refractory infection. Little is known about the interaction between antipseudomonal agents and phagocytic cells in eradication of P. aeruginosa biofilms. Herein, we investigated the capacity of three antipseudomonal agents, amikacin (AMK), ceftazidime (CAZ), and ciprofloxacin (CIP), to interact with human polymorphonuclear leukocytes (PMNs) against biofilms and planktonic cells of P. aeruginosa isolates recovered from sputa of CF patients. Three of the isolates were resistant and three were susceptible to each of these antibiotics. The concentrations studied (2, 8, and 32 mg/liter) were subinhibitory for biofilms of resistant isolates, whereas for biofilms of susceptible isolates, they ranged between sub-MIC and 2 × MIC values. The activity of each antibiotic alone or in combination with human PMNs against 48-h mature biofilms or planktonic cells was determined by XTT [2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] assay. All combinations of AMK with PMNs resulted in synergistic or additive effects against planktonic cells and biofilms of P. aeruginosa isolates compared to each component alone. More than 75% of CAZ combinations exhibited additive interactions against biofilms of P. aeruginosa isolates, whereas CIP had mostly antagonistic interaction or no interaction with PMNs against biofilms of P. aeruginosa. Our findings demonstrate a greater positive interaction between AMK with PMNs than that observed for CAZ and especially CIP against isolates of P. aeruginosa from the respiratory tract of CF patients.

Pseudomonas aeruginosa biofilm infections: from molecular biofilm biology to new treatment possibilities

Bacteria in natural, industrial and clinical settings predominantly live in biofilms, i.e., sessile structured microbial communities encased in self-produced extracellular matrix material. One of the most important characteristics of microbial biofilms is that the resident bacteria display a remarkable increased tolerance toward antimicrobial attack. Biofilms formed by opportunistic pathogenic bacteria are involved in devastating persistent medical device-associated infections, and chronic infections in individuals who are immune-compromised or otherwise impaired in the host defense. Because the use of conventional antimicrobial compounds in many cases cannot eradicate biofilms, there is an urgent need to develop alternative measures to combat biofilm infections. The present review is focussed on the important opportunistic pathogen and biofilm model organism Pseudomonas aeruginosa. Initially, biofilm infections where P. aeruginosa plays an important role are described. Subsequently, current insights into the molecular mechanisms involved in P. aeruginosa biofilm formation and the associated antimicrobial tolerance are reviewed. And finally, based on our knowledge about molecular biofilm biology, a number of therapeutic strategies for combat of P. aeruginosa biofilm infections are presented.

The problems of antibiotic resistance in cystic fibrosis and solutions

Chronic respiratory infection is the main cause of morbidity and mortality in cystic fibrosis (CF) patients. One of the hallmarks of these infections, led by the opportunistic pathogen Pseudomonas aeruginosa, is their long-term (lifelong) persistence despite intensive antimicrobial therapy. Antimicrobial resistance in CF is indeed a multifactorial problem, which includes physiological changes, represented by the transition from the planktonic to the biofilm mode of growth and the acquisition of multiple (antibiotic resistance) adaptive mutations catalyzed by frequent mutator phenotypes. Emerging multidrug-resistant CF pathogens, transmissible epidemic strains and transferable genetic elements (such as those encoding class B carbapenemases) also significantly contribute to this concerning scenario. Strategies directed to combat biofilm growth, prevent the emergence of mutational resistance, promote the development of novel antimicrobial agents against multidrug-resistant strains and implement strict infection control measures are thus needed.

Bacterial responses to antibiotics and their combinations

Antibiotics affect bacterial cell physiology at many levels. Rather than just compensating for the direct cellular defects caused by the drug, bacteria respond to antibiotics by changing their morphology, macromolecular composition, metabolism, gene expression and possibly even their mutation rate. Inevitably, these processes affect each other, resulting in a complex response with changes in the expression of numerous genes. Genome-wide approaches can thus help in gaining a comprehensive understanding of bacterial responses to antibiotics. In addition, a combination of experimental and theoretical approaches is needed for identifying general principles that underlie these responses. Here, we review recent progress in our understanding of bacterial responses to antibiotics and their combinations, focusing on effects at the levels of growth rate and gene expression. We concentrate on studies performed in controlled laboratory conditions, which combine promising experimental techniques with quantitative data analysis and mathematical modeling. While these basic research approaches are not immediately applicable in the clinic, uncovering the principles and mechanisms underlying bacterial responses to antibiotics may, in the long term, contribute to the development of new treatment strategies to cope with and prevent the rise of resistant pathogenic bacteria.

Sodium houttuyfonate affects production of N-acyl homoserine lactone and quorum sensing-regulated genes expression in Pseudomonas aeruginosa

Quorum sensing (QS) is a means of cell-to-cell communication that uses diffusible signaling molecules that are sensed by the population to determine population density, thus allowing co-ordinate gene regulation in response to population density. In Pseudomonas aeruginosa, production of the QS signaling molecule, N-acyl homoserine lactone (AHL), co-ordinates expression of key factors of pathogenesis, including biofilm formation and toxin secretion. It is predicted that the inhibition of AHL sensing would provide an effective clinical treatment to reduce the expression of virulence factors and increase the effectiveness of antimicrobial agents. We previously demonstrated that sodium houttuyfonate (SH), commonly used in traditional Chinese medicine to treat infectious diseases, can effectively inhibit QS-regulated processes, including biofilm formation. Here, using a model system, we demonstrate that SH causes the dose-dependent inhibition of AHL production, through down-regulation of the AHL biosynthesis gene, lasI. Addition of SH also resulted in down-regulation of expression of the AHL sensor and transcriptional regulator, LasR, and inhibited the production of the QS-regulated virulence factors, pyocyanin and LasA. These results suggest that the antimicrobial activity of SH may be due to its ability to disrupt QS in P. aeruginosa.