Genes lasI Research Articles

Biofilm production by clinical isolates of Pseudomonas aeruginosa and structural changes in LasR protein of isolates non biofilm-producing

IntroductionBiofilm production is an important mechanism for the survival of Pseudomonas aeruginosa and its relationship with antimicrobial resistance represents a challenge for patient therapeutics. P. aeruginosa is an opportunistic pathogen frequently associated to nosocomial infections, especially in imunocompromised hosts. ObjectivesAnalyze the phenotypic biofilm production in P. aeruginosa isolates, describe clonal profiles, and analyze quorum sensing (QS) genes and the occurrence of mutations in the LasR protein of non-biofilm producing isolates. MethodsIsolates were tested for biofilm production by measuring cells adherence to the microtiter plates. Clonal profile analysis was carried out through ERIC-PCR, QS genes were by specific PCR. ResultsThe results showed that 77.5% of the isolates were considered biofilm producers. The results of genotyping showed 38 distinct genetic profiles. As for the occurrence of the genes, 100% of the isolates presented the lasR, rhlI and rhlR genes, and 97.5%, presented the lasI gene. In this study nine isolates were not biofilm producers. However, all presented the QS genes. Amplicons related to genes were sequenced in three of the nine non-biofilm-producing isolates (all presenting different genetic similarity profile) and aligned to the sequences of those genes in P. aeruginosa strain PAO1 (standard biofilm-producing strain). Alignment analysis showed an insertion of three nucleotides (T, C and G) causing the addition of an amino acid valine in the sequence of the LasR protein, in position 53. ConclusionThe modeling of the resulting LasR protein showed a conformational change in its structure, suggesting that this might be the reason why these isolates are unable to produce biofilm.

Evaluating ginger extract, wild blueberry extract, and polysorbates (PS20, PS80) on Pseudomonas aeruginosa biofilm formation.

Pseudomonas aeruginosa is a biofilm forming pathogen that challenges clinical and industrial settings. Many natural products and surfactants have been screened and valued for their anti-biofilm capacity. In this study we assessed the inhibitory effect and molecular mechanism of action of ginger extract (Zingiber officinale Rosc.), wild blueberry extract (Vaccinium angustifolium), and polysorbates (PS20/PS80) on biofilm formation. Ginger and wild blueberry extractions were done using ethanol and distilled water, respectively. Hexane and methanol were used for extracts' liquid-liquid portioning. LC-HRMS was performed to obtain extract fractions. Efficacy of the crude extracts, fractions, and polysorbates was assessed on P. aeruginosa PAN14 growth and biofilm. Transcription levels of biofilm encoding genes ndvB, pelC, algC and quorum sensing genes lasI, lasR, rhlI, rhlR were evaluated by RT-qPCR. Extracts and polysorbates concentrations did not affect P. aeruginosa growth. Biofilm assay showed a reduction in biofilm when 5% ginger, 25% wild blueberry extracts, 0.2% PS20, and 0.25% PS80 were added. LC-HRMS analysis of ginger extract showed abundant gingerol in the hexane layer. Wild blueberry chromatograms showed various constituents differing between their peel and pulp, and pulp extracts. RT-qPCR showed decreased transcription levels of exopolysaccharide and quorum sensing genes with a 363.6 folds reduction in ndvB upon treatment with 25% wild blueberry peel and pulp extract. These results shed light on the mechanism of action of ginger and wild blueberry constituents as well as PS20/80 on P. aeruginosa biofilm formation. Future mouse model experiments are useful to test biofilm inhibition in-vivo.

A complex hierarchical quorum-sensing circuitry modulates phenazine gene expression in Pseudomonas aeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) modulates the expression of a myriad of virulence factors via two complicated hierarchical quorum-sensing (QS) cascade. This study shed light on the interrelation between P. aeruginosa QS systems and pyocyanin production. Transcription analysis of lasR, rhlR, rhlI and phz genes using quantitative real time-reverse transcriptase PCR (qRT-PCR) assay, followed by sequencing of the autoinducer synthase (lasI gene) were applied for 15 P. aeruginosa strains recovered from diverse animal clinical sources. Expression studies revealed that most P. aeruginosa strains demonstrated statistically significant differences (p < 0.05) with a very wide range of transcript levels of QS and phz genes in comparison to P. aeruginosa ATCC 27853. We have identified significant positive correlations (r ≥ 0.3) between the expressions of QS and phz genes in eleven analyzed strains, whereas pyocyanin production positively correlated with the expression of lasR only in three strains (r ≥ 0.6). We further found that there was a negative correlation between the transcript levels of QS and phz genes in one bacterial strain. Analysis of lasI sequences showed point mutations explaining the alterations in pyocyanin expression. The deficiencies of lasI, lasR and rhlI with rhlR-dependent expression of phz in one strain were also recorded. These results provided new insights to the pivotal role of QS signal molecules on pyocyanin production presenting the las system as the dominant regulator.

Association of furanone C-30 with biofilm formation & antibiotic resistance in Pseudomonas aeruginosa.

Background & objectives:Pseudomonas aeruginosa is an opportunistic pathogen that can cause nosocomial bloodstream infections in humans. This study was aimed to explore the association of furanone C-30 with biofilm formation, quorum sensing (QS) system and antibiotic resistance in P. aeruginosa.Methods:An in vitro model of P. aeruginosa bacterial biofilm was established using the standard P. aeruginosa strain (PAO-1). After treatment with 2.5 and 5 μg/ml of furanone C-30, the change of biofilm morphology of PAO-1 was observed, and the expression levels of QS-regulated virulence genes (lasB, rhlA and phzA2), QS receptor genes (lasR, rhlR and pqsR) as well as QS signal molecule synthase genes (lasI, rhlI, pqsE and pqsH) were determined. Besides, the AmpC expression was quantified in planktonic and mature biofilm induced by antibiotics.Results:Furanone C-30 treatment significantly inhibited biofilm formation in a dose-dependent manner. With the increase of furanone C-30 concentration, the expression levels of lasB, rhlA, phzA2, pqsR, lasI, rhlI, pqsE and pqsH significantly decreased in mature biofilm bacteria while the expression levels of lasR and rhlR markedly increased. The AmpC expression was significantly decreased in both planktonic and biofilm bacteria induced by imipenem and ceftazidime.Interpretation & conclusions:Furanone C-30 may inhibit biofilm formation and antibiotic resistance in P. aeruginosa through regulating QS genes. The inhibitory effect of furanone C-30 on las system appeared to be stronger than that on rhl system. Further studies need to be done with different strains of P. aeruginosa to confirm our findings.

PHENOTYPIC AND GENOTYPIC CHARACTERIZATION OF PSEUDOMONAS AERUGINOSA RECOVERED FROM KIDNEY LESIONS OF BROILER CHICKENS.

This work was planned to investigate the prevalence of P. aeruginosa in broiler chickens kidneys suffered from naked eye pathological lesions. Out of 240 examined kidneys samples, 25 isolates (10.4%) of P. aeruginosa were recovered. Antimicrobial sensitivity pattern against 14 different antimicrobials comprising nine groups proved that isolates were resistant to most of the used antimicrobial agents. Phenotypic detection of extended spectrum beta-lactamases (ESBLs) producing isolates using modified double disk diffusion test revealed that, ten (40%) were ESBLs producers. Genotypically using PCR, three ESBLs genes (TEM, Ctx-M and Shv) and three virulence genes (lasI, Tox A and Plc H) were detected with different percentages. Cinnamon and carvacrol oils were found bactericidal for P. aeruginosa at concentrations of 4% and 0.4% respectively.

Perturbation of Quorum Sensing in &amp;lt;i&amp;gt;Pseudomonas aeruginosa&amp;lt;/i&amp;gt; by Febuxostat

Quorum sensing is a signal-based communication system in bacteria. It is an attractive target because it regulates the production of virulence factors in Pseudomonas aeruginosa. As a result, interference with quorum sensing could result in inhibition of virulence of Pseudomonas aeruginosa with the merit of lack of selective pressure on growth that leads to development of resistance. This study investigated the anti-quorum sensing and anti-virulence activities of febuxostat in Pseudomonas aeruginosa PAO1 strain. At 1/8 MIC of febuxostat, the production of the quorum-sensing regulated violacein pigment of Chromobacterium violaceum CV026 was significantly reduced. Moreover, it markedly reduced pyocyanin, hemolysin, protease and elastase production. Significant inhibitory activities were also found against biofilm, swimming, twitching and swarming motilities. Molecular docking showed the ability of febuxostat to inhibit quorum sensing by competing with the autoinducers to bind with LasR and RhlR receptors. Febuxostat could bind to both receptors by hydrogen bonding and hydrophobic interaction. From the Molecular docking scores, febuxostat is a very promising quorum sensing inhibitor. Febuxostat could also significantly decrease the level of expression of all QS genes LasI, LasR, RhlI, RhlR, PqsA and PqsR that regulate the production of virulene factors as confirmed by qRT-PCR.

Detection of ( LasI ) Gene in Pseudomonas aeruginosa and its Role in Biofilm Formation.

The present study included the collection of 120 samples from various clinical sources. The samples collected from some hospitals in Baghdad city which included burns ,wound , cystic fibrosis, ear infections and urinary tract infections ( 52 ,28, 4, 23 and 13). Samples respectively. Samples were identified based on the morphological and microscopical characteristics of the colonies when they were culturing in a number of culture media as well as biochemical tests. The molecular detection was used to confirm diagnostic test for the isolates based on the 16SrRNA gene, as a detection gene, which has specific sequences for DNA of P.aeruginosa bacteria.The results of molecular detection showed that 51 isolates belong to target bacteria were distributed as follow 21 of burns, 14 isolates of wounds, 7 isolates of ear infection, 4 isolates of cystic fibrosis, 5 isolates of urinary tract infection. The results of phenotypic detection of biofilm formation showed that 44/51 (86.2%) of isolates differences in their ability to biofilm formation. The results of screed QS genes by Polymerase chain reaction (PCR) amplify based on specific sequences for lasI gene showed that 48 (94.1%) of isolates have lasI gene.

Deficiency of quorum sensing system inhibits the resistance selection of Pseudomonas aeruginosa to ciprofloxacin and levofloxacin in vitro.

The objective was to investigate how deficient of quorum sensing system (QS) affects minimal inhibitory concentrations (MICs) of Pseudomonas aeruginosa strains to ciprofloxacin (CIP) and levofloxacin (LEV) in vitro. Collected the clinical Pseudomonas aeruginosa isolates. Screened the strains deficient of QS genes by the PCR agarose electrophoresis, and then randomly picked out normal strains with the same number of deficient ones. All strains incubated on the different CIP-concentration Mueller-Hinton agars for five days, the different concentrations of CIP respectively refered to 0.5×MIC, 1×MIC, 2×MIC and 4×MIC. Strains incubated on the first, third and fifth days were saved. MICs of saved strains to CIP and LEV were measured by the agar dilution method. Statistical analysis methods were the repeated measures analysis of variance and the rank sum test. The study totally collected 40 Pseudomonas aeruginosa isolates. 5 deficient strains screened were as follows: one strain lacked of rhlR and lasI genes, one strain lacked of lasI, lasR, rhlI and rhlR genes, four strains lacked of lasR gene. All the final selected strains were sensitive to both CIP and LEV. Statistical analysis results showed deficient strains became resistant more slowly and difficultly than normal strains, whether the resistance was to CIP or LEV. What's more, MICs to LEV showed the half and delayed increase than those to CIP in the vitro selection. Deficient of QS inhibits the resistance selection of P. aeruginosa to CIP and LEV in vitro.

The Role of Quorum Sensing Genes (Las and Rhl) in Biofilm Forming Pseudomonas Aeruginosa Isolates

Background: Quorum sensing (QS) is a bacterial cell-cell communication process that involves the production, detection, and response to extracellular signaling molecules called autoinducers (AIs). Processes controlled by QS include bioluminescence, sporulation, competence, antibiotic production, biofilm formation, and virulence factor secretion. Pseudomonas aeruginosa (P. aeruginosa) produces multiple virulence factors and causes different types of infections. Objectives: to determine if deficiency within the QS system decreases the ability of P. aeruginosa to establish biofilm formation and infections in humans or not. Methodology: This was achieved through determination of the levels of P. aeruginosa autoinducers as well as the presence of QS-controlled genes (lasI, lasR, rhlI and rhlR) within the biofilm-forming clinical samples. Results: We collected 186 P. aeruginosa isolates, 89.3% were significantly biofilm producer strains. About 66% were strong, 28% were moderate and 15% were weak biofilm producer clinical isolates. Autoinducers evaluation revealed that, 8-clinical isolates (CIs) for 3OC 12 -HSL and/or C 4 -HSL concentration were deficient. The amount of 3OC 12 -HSL produced by 8-CIs was significantly lower than that produced by PAO1. While 6-CIs produced no C 4 -HSL and 2-CIs produced detectable levels of C 4 -HSL. Polymerase chain reaction (PCR) analysis of autoinducers deficient CIs revealed that, two isolates contained all four QS genes (lasI, lasR, rhlI and rhlR) and were moderate-biofilm producers while three isolates lacked all QS genes and were non-biofilm producer strains. Analysis of remaining autoinducers deficient CIs revealed that, they were weak-biofilm producer strains and they had intact las system in two strains and lacked lasR in third one while they were completely lacked the rhl system. Patients had autoinducers deficient CIs were isolated from cardiac catheterization, tracheostomy tubes, sputum, and wound infections. Conclusion: Naturally occurring QS-deficient strains of P. aeruginosa were capable of causing different infections despite the loss of optimum gene. QS-deficient genes affected the severity of biofilm formation. So the development of efficient cell-to-cell signaling blockers may reduce P. aeruginosa biofilm formation on medical devices.

Quorum Sensing - Dependent Virulence Factors and Biofilm Formation of Pseudomonas Aeruginosa Isolates from Retrieved Orthopedic Implants

Background: Quorum sensing (QS) plays a crucial role in medical device-related infections. However, epidemiological analysis of QS- dependent virulence factors among Pseudomonas aeruginosa (P. aeruginosa) isolates from orthopedic implants-related infections has rarely been reported. Objective: to assess some QS-dependent virulence factors (as pyocyanin, elastase, protease, rhamnolipid, and biofilm production) in P. aeruginosa isolates from retrieved different orthopedic implants. Methodology: Twenty-four P. aeruginosa isolates obtained from 300 retrieved orthopedic implants with proven diagnosis of osteoarticular infection directly related to orthopedic implants were investigated for production of QS-dependent virulence factors. The pyocyanin production was assayed using King A media, rhamnolipid production was checked utilizing cetyltrimethylammonium bromide (CTAB) agar test. Elastin lytic activity was assayed using elastin Congo red, total protease was estimated using the modified skimmed milk assay technique, and the biofilm forming ability was assayed by microtiter plate assay. N-acyl homoserine lactones (3-oxo-C 12 -HSL, C 4 -HSL) were detected by Cross-feeding bioassay. Polymerase chain reaction (PCR) was used to assess the presence of the QS genes lasI, lasR, rhlI, and rhlR in P. aeruginosa isolates. Results: Seventeen isolates (70.8%) displayed the QS-dependent phenotypes and seven isolates were found to be lacking all tested virulence factors. The lack of production of pyocyanin, Rhamnolipid, las B elastase, total protease, and biofilm formation by the seven isolates proposed that they might have a defective QS system. Among the Seven isolates exhibiting impaired QS-dependent phenotypes, AHLs autoinducers were present in three isolates, though the residual four isolates were lacking both autoinducers and therefore are considered QS-deficient. PCR analysis declared that two isolates contained lasI, lasR, rhlI and rhlR genes while one isolate lacked lasR gene, and one isolate was lacking the four tested genes. Conclusion: Although QS seems to be a crucial regulator of virulence factors and biofilm formation in P. aeruginosa, it is equipped to produce implant infection in humans despite an impaired QS system. These results do not challenge the concept that QS plays a foremost role in P. aeruginosa pathogenicity, but highlight that along with known virulence factors, perhaps there are other virulence factors, that may not be strictly under QS control.

Hyperoside inhibits biofilm formation of Pseudomonas aeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) is a common pathogen in hospital-acquired infection and is readily able to form biofilms. Due to its high antibiotic resistance, traditional antibacterial treatments exert a limited effect on P. aeruginosa biofilm infections. It has been indicated that hyperoside inhibits P. aeruginosa PAO1 (PAO1) biofilm formation without affecting growth. Therefore, the current study examined the biofilm formation and quorum sensing (QS) system of PAO1 in the presence of hyperoside. Confocal laser scanning microscopy analysis demonstrated that hyperoside significantly inhibited biofilm formation. It was also observed that hyperoside inhibited twitching motility in addition to adhesion. Data from reverse transcription-quantitative polymerase chain reaction indicated that hyperoside inhibited the expression of lasR, lasI, rhlR and rhlI genes. These results suggest that the QS-inhibiting effect of hyperoside may lead to a reduction in biofilm formation. However, the precise mechanism of hyperoside on P. aeruginosa pathogenicity remains unclear and requires elucidation in additional studies.

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

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

Synergistic activity of sub-inhibitory concentrations of curcumin with ceftazidime and ciprofloxacin against Pseudomonas aeruginosa quorum sensing related genes and virulence traits.

Quorum sensing (QS) system in Pseudomonas aeruginosa may be an important target for pharmacological intervention. The present study aimed to investigate the synergetic activity of sub-MIC concentrations of curcumin (C) with ceftazidime (CAZ) and ciprofloxacin (CIP) against P. aeroginusa QS system. We determined the MIC and synergistic activity of C, CAZ and CIP against P. aeroginusa PAO1 using broth microdilution and checkerboard titration methods. The activity of sub-MIC (1/4 and 1/16 MIC) concentrations of C on the QS signal molecules was assessed using a reporter strain assay. The influence of sub-MIC of C, CAZ and CIP alone and in combination on motility and biofilm formation was also determined and confirmed by RT-PCR to test the expression of QS regulatory genes lasI, lasR, rhlI and rhlR. The addition of C decreased the MIC of CAZ and CIP. Curcumin showed synergistic effects with CAZ and additive activity with CIP. Treated PAO1 cultures in the presence of C showed significant reduction of signals C12-HSL and C4-HSL (P < 0.05). Sub-MIC concentrations (1/4 and 1/16 MIC) of C, CAZ and CIP alone and in combination significantly reduced swarming and twitching motilities and biofilm formation. Expression of QS regulatory genes lasI, lasR, rhlI, and rhlR using 1/4 MIC of C, CAZ and CIP alone and in combination was repressed significantly relative to untreated PAO1. Our results indicate that a combination of the sub-MIC concentration of C and CAZ exhibited synergism against P. aeroginusa QS system. This combination could lead to the development of a new combined therapy against P. aeruginosa.

Histone-like protein H-NS as a negative regulator of quorum sensing systems in gram-negative bacteria

The effects of histone-like protein H-NS on transcription of promoters of the Quorum Sensing regulated operons from marine luminescent mesophilic bacterium Aliivibrio fischeri and psychrophilic Aliivibrio logei, as well as from pathogenic Pseudomonas aeruginosa, are studied. In the present work, the plasmids carrying DNA fragments with the promoters Pr1f (upstream of the luxICDABEG operon from A. fischeri), Pr1l (upstream of the luxCDABEG operon from A. logei), Pr2l (upstream of luxI gene from A. logei), PluxCf (upstream of luxC gene from A. fischeri), and PlasI (upstream of lasI gene from P. aerugenosa) are used. In these plasmids, promoter-operator regions are transcriptionally fused to the reporter genes cassette luxCDABE from Photorhabdus luminescens. Here we have shown that the transcription of the QS-regulated promoters in E. coli hns::kan cells increases 100 to 1000 times. Furthermore, transcription of the QS-regulated promoters in E. coli hns + cells increases 10 to 100 times in the cells transformed with the plasmid carrying gene ardA ColIb-P9 encoding DNA mimic antirestriction protein ArdA, inhibitor of the type I restriction-modification systems.

Molecular cloning and characterization of α-amylase/subtilisin inhibitor from rhizome of Ligusticum chuanxiong.

To clone and characterize a novel bi-functional α-amylase/subtilisin inhibitor (LASI) from the rhizome of Ligusticum chuanxiong, a traditional Chinese medicine. The LASI showed strong homology with members of the Kunitz trypsin inhibitor family. Its putative amino acid sequence has a 40% identity with that of the α-amylase/subtilisin inhibitor from rice. LASI gene without signal peptide was expressed in E. coli Rosetta. After purification, the recombinant LASI protein was inhibitory against not only α-amylase from porcine pancreas, Helicoverpa armigera, Spodoptera litura and Plutella xylostella, but also subtilisin A, but not against trypsin or chymotrypsin. In addition, the expression level of LASI in rhizome was higher than that in leaf and LASI expression was enhanced by salt, chilling and drought treatment. This is the first member of the Kunitz-protease inhibitor family identified in traditional Chinese medicine and it might be involved in the plant defense responses against lepidopterous pests, microorganisms and abiotic stresses.

Quorum Sensing Inhibiting Activity of Streptomyces coelicoflavus Isolated from Soil.

Quorum sensing (QS) systems communicate bacterial population and stimulate microbial pathogenesis through signaling molecules. Inhibition of QS signals potentially suppresses microbial infections. Antimicrobial properties of Streptomyces have been extensively studied, however, less is known about quorum sensing inhibitory (QSI) activities of Streptomyces. This study explored the QSI potential of Streptomyces isolated from soil. Sixty-five bacterial isolates were purified from soil samples with morphological characteristics of Streptomyces. The three isolates: S6, S12, and S17, exhibited QSI effect by screening with the reporter, Chromobacterium violaceum. Isolate S17 was identified as Streptomyces coelicoflavus by sequencing of the hypervariable regions (V1–V6) of 16S rRNA and was assigned gene bank number KJ855087. The QSI effect of the cell-free supernatant of isolate S17 was not abolished by proteinase K indicating the non-enzymatic activity of QSI components of S17. Three major compounds were isolated and identified, using spectroscopic techniques (1D, 2D NMR, and Mass spectrometry), as behenic acid (docosanoic acid), borrelidin, and 1H-pyrrole-2-carboxylic acid. 1H-pyrrole-2-carboxylic acid inhibited QS and related virulence factors of Pseudomonas aeruginosa PAO1 including; elastase, protease, and pyocyanin without affecting Pseudomonas viability. At the molecular level, 1H-pyrrole-2-carboxylic acid suppressed the expression of QS genes (lasI, lasR, lasA, lasB, rhlI, rhlR, pqsA, and pqsR). Moreover, QSI activity of S17 was assessed under different growth conditions and ISP2 medium supplemented with glucose 0.4% w/v and adjusted at pH 7, showed the highest QSI action. In conclusion, 1H-pyrrole-2-carboxylic acid, one of the major metabolites of Streptomyces isolate S17, inhibited QS and virulence determinants of P. aeruginosa PAO1. The findings of the study open the scope to exploit the in vivo efficacy of this active molecule as anti-pathogenic and anti-virulence of P. aeruginosa.

Correlation of quorum sensing and virulence factors in Pseudomonas aeruginosa isolates in Egypt.

Pseudomonas aeruginosa is one of the most virulent nosocomial pathogens worldwide. Quorum sensing (QS) regulates the production of pathogenic virulence factors and biofilm formation in P. aeruginosa. The four genes lasR, lasI, rhlR,and rhlI were found to regulate this QS system. In this study, we aimed to assess the correlation between these four genes and QS-dependent virulence factors and to detect the inhibitory effect of clove oil on QS. Fifty P. aeruginosa clinical isolates were collected. Susceptibility to different antibiotics was tested. Virulence factors including biofilm formation, pyocyanin production, and twitching motility were phenotypically detected. QS genes were amplified by polymerase chain reaction (PCR), and one strain subsequently underwent sequencing. The inhibitory effect of clove oil on virulence factors was also tested. A positive correlation was found between biofilm formation and the presence of lasR and rhlI genes. Twitching motility was positively correlated with the presence of lasR, lasI, and rhlI genes. On the other hand, no correlation was found between pyocyanin production and any of the studied genes. Only one isolate amplified all the tested QS gene primers, but it did not express any of the tested virulence factors phenotypically. Sequence analyses of this isolate showed that the four genes had point mutations. Results emphasize the importance of QS in P. aeruginosa virulence; however, QS-deficient clinical isolates occur and are still capable of causing clinical infections in humans. Also, clove oil has an obvious inhibitory effect on QS, which should be clinically exploited.

Promotion of acute-phase skin wound healing by Pseudomonas aeruginosa C4 -HSL.

A Pseudomonas aeruginosa quorum-sensing system, which produces N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C12 -HSL) and N-butanoyl-l-homoserine lactone (C4 -HSL), regulates the virulence factors. In our previous study, 3-oxo-C12 -HSL, encoded by lasI gene, was shown to promote wound healing. However, the effect of C4 -HSL, encoded by rhlI gene, remains to be elucidated. We addressed the effect of C4 -HSL on wounds in P. aeruginosa infection. Wounds were created on the backs of Sprague-Dawley SD rats, and P. aeruginosa PAO1 (PAO1) or its rhlI deletion mutant (ΔrhlI) or lasI deletion mutant (ΔlasI) was inoculated onto the wound. Rats were injected intraperitoneally with anti-C4 -HSL antiserum or treated with C4 -HSL at the wound surface. PAO1 inoculation led to significant acceleration of wound healing, which was associated with neutrophil infiltration and TNF-α synthesis. These responses were reversed, except for TNF-α production, when ΔrhlI was inoculated instead of PAO1 or when rats were co-treated with PAO1 and anti-C4 -HSL antiserum. In contrast, the healing process and neutrophil infiltration, but not TNF-α synthesis, were accelerated when C4 -HSL was administered in the absence of PAO1. This acceleration was not affected by anti-TNF-α antibody. These results suggest that C4 -HSL may be involved in the acceleration of acute wound healing in P. aeruginosa infection by modifying the neutrophilic inflammation.

Cooperative pathogenicity in cystic fibrosis: Stenotrophomonas maltophilia modulates Pseudomonas aeruginosa virulence in mixed biofilm.

The present study was undertaken in order to understand more about the interaction occurring between S. maltophilia and P. aeruginosa, which are frequently co-isolated from CF airways. For this purpose, S. maltophilia RR7 and P. aeruginosa RR8 strains, co-isolated from the lung of a chronically infected CF patient during a pulmonary exacerbation episode, were evaluated for reciprocal effect during planktonic growth, adhesion and biofilm formation onto both polystyrene and CF bronchial cell monolayer, motility, as well as for gene expression in mixed biofilms. P. aeruginosa significantly affected S. maltophilia growth in both planktonic and biofilm cultures, due to an inhibitory activity probably requiring direct contact. Conversely, no effect was observed on P. aeruginosa by S. maltophilia. Compared with monocultures, the adhesiveness of P. aeruginosa on CFBE41o- cells was significantly reduced by S. maltophilia, which probably acts by reducing P. aeruginosa's swimming motility. An opposite trend was observed for biofilm formation, confirming the findings obtained using polystyrene. When grown in mixed biofilm with S. maltophilia, P. aeruginosa significantly over-expressed aprA, and algD—codifying for protease and alginate, respectively—while the quorum sensing related rhlR and lasI genes were down-regulated. The induced alginate expression by P. aeruginosa might be responsible for the protection of S. maltophilia against tobramycin activity we observed in mixed biofilms. Taken together, our results suggest that the existence of reciprocal interference of S. maltophilia and P. aeruginosa in CF lung is plausible. In particular, S. maltophilia might confer some selective “fitness advantage” to P. aeruginosa under the specific conditions of chronic infection or, alternatively, increase the virulence of P. aeruginosa thus leading to pulmonary exacerbation.

Involvement of quorum sensing genes in biofilm development and degradation of polycyclic aromatic hydrocarbons by a marine bacterium Pseudomonas aeruginosa N6P6.

Biofilm-forming and acyl homoserine lactone (AHL) synthase-positive Pseudomonas aeruginosa N6P6 was isolated from seawater after selective enrichment with two polycyclic aromatic hydrocarbons (PAHs), viz. phenanthrene and pyrene. AHL synthesis was detected qualitatively using bioreporter strains. This marine bacterium putatively synthesized N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone, which were identified by TLC, GC-MS, and HPLC. Two quorum sensing (QS) genes coding for AHL synthase, i.e., lasI and rhlI, were identified in the bacterium. lasI and rhlI gene expression was studied during biofilm mode of growth at different phases using quantitative real-time PCR (qRT-PCR). The expression of lasI increased with increase in biofilm growth. In contrast, the expression of rhlI decreased during log phase of biofilm growth. The changes in lasI/rhlI expression level had significant effects (P<0.05) on biofilm architecture and subsequent PAH degradation rate. Degradation of phenanthrene and pyrene by P. aeruginosa N6P6 was affected by biofilm growth and lasI expression. The respective phenanthrene degradation for 15, 24, 48, and 72 h old biofilm after 7 days was 21.5, 54.2, 85.6, and 85.7%. However, the corresponding pyrene degradation was 15, 18.28, 47.56, and 46.48%, respectively, after 7 days. A significant positive correlation (P<0.05) was observed between lasI expression and PAHs degradation. However, in the presence of tannic acid, a QS inhibitor (QSI), PAHs degradation, biofilm formation, and pyocyanin production reduced significantly which confirmed the pivotal role of QS in biodegradation of PAHs. The findings suggest that AHLs play a pivotal role during biofilm development and subsequent bioremediation of PAHs.