Cobalt Complex with Thiazole-Based Ligand as New Pseudomonas aeruginosa Quorum Quencher, Biofilm Inhibitor and Virulence Attenuator

Dual action of benzaldehydes: Inhibiting quorum sensing and enhancing antibiotic efficacy for controlling Pseudomonas aeruginosa biofilms

Quorum sensing (QS) has a central role in biofilm lifestyle and antimicrobial resistance, and disrupting these signaling pathways is a promising strategy to control bacterial pathogenicity and virulence. In this study, the efficacy of three structurally related benzaldehydes (4-hydroxybenzaldehyde, 4-hydroxy-3-methoxybenzaldehyde (vanillin) and 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde)) in disrupting the las and pqs systems of Pseudomonas aeruginosa was investigated using bioreporter strains and computational simulations. Additionally, these benzaldehydes were combined with tobramycin and ciprofloxacin antibiotics to evaluate their ability to increase antibiotic efficacy in preventing and eradicating P. aeruginosa biofilms. To this end, the total biomass, metabolic activity and culturability of the biofilm cells were determined. In vitro assays results indicated that the aromatic aldehydes have potential to inhibit the las and pqs systems by > 80 %. Molecular docking studies supported these findings, revealing the aldehydes binding in the same pocket as the natural ligands or receptor proteins (LasR, PQSA, PQSE, PQSR). Benzaldehydes were shown to act as virulence factor attenuators, with vanillin achieving a 48 % reduction in pyocyanin production. The benzaldehyde-tobramycin combination led not only to a 60 % reduction in biomass production but also to a 90 % reduction in the metabolic activity of established biofilms. A similar result was observed when benzaldehydes were combined with ciprofloxacin. 4-Hydroxybenzaldehyde demonstrated relevant action in increasing biofilm susceptibility to ciprofloxacin, resulting in a 65 % reduction in biomass. This study discloses, for the first time, that the benzaldehydes studied are potent QS inhibitors and also enhancers of antibiotics antibiofilm activity against P. aeruginosa.

Promoter Identification and Optimization for the Response of Lactobacillus plantarum WCFS1 to the Gram-Negative Pathogen-Associated Molecule N-3-Oxododecanoyl Homoserine Lactone

Quorum sensing (QS) in bacteria has been well studied as a cellular communication phenomenon for decades. In recent years, such systems have been repurposed for the use of biosensors in both cellular and cell-free contexts as well as for inducible protein expression in nontraditional chassis organisms. Such biosensors are particularly intriguing when considering the association between the pathogenesis of some bacteria and their signaling intermediates. Considering this relationship and considering the recent demonstration of the species Lactobacillus plantarum WCFS1 as both a synthetic biology chassis and an organism capable of detecting a pathogen-associated QS molecule, we wanted to develop this organism as a QS sentinel. We used an approach combining techniques from both systems and synthetic biology to identify a number of native QS-response genes and to alter associated promoter activity to tune the output of L. plantarum cultures exposed to N-3-oxododecanoyl homoserine lactone. The resulting engineered QS sentinel reinforces the potential of modified lactic acid bacteria (LAB) for use in human-health-promoting applications and also demonstrates a simple rational workflow to engineer sentinel organisms to respond to any environmental or chemical stimuli.

It is the time for quorum sensing inhibition as alternative strategy of antimicrobial therapy

Multiple drug resistance poses a significant threat to public health worldwide, with a substantial increase in morbidity and mortality rates. Consequently, searching for novel strategies to control microbial pathogenicity is necessary. With the aid of auto-inducers (AIs), quorum sensing (QS) regulates bacterial virulence factors through cell-to-cell signaling networks. AIs are small signaling molecules produced during the stationary phase. When bacterial cultures reach a certain level of growth, these molecules regulate the expression of the bound genes by acting as mirrors that reflect the inoculum density.Gram-positive bacteria use the peptide derivatives of these signaling molecules, whereas Gram-negative bacteria use the fatty acid derivatives, and the majority of bacteria can use both types to modulate the expression of the target gene. Numerous natural and synthetic QS inhibitors (QSIs) have been developed to reduce microbial pathogenesis. Applications of QSI are vital to human health, as well as fisheries and aquaculture, agriculture, and water treatment. Video Abstract.

Metal Complexes—A Promising Approach to Target Biofilm Associated Infections

Microbial biofilms are represented by sessile microbial communities with modified gene expression and phenotype, adhered to a surface and embedded in a matrix of self-produced extracellular polymeric substances (EPS). Microbial biofilms can develop on both prosthetic devices and tissues, generating chronic and persistent infections that cannot be eradicated with classical organic-based antimicrobials, because of their increased tolerance to antimicrobials and the host immune system. Several complexes based mostly on 3D ions have shown promising potential for fighting biofilm-associated infections, due to their large spectrum antimicrobial and anti-biofilm activity. The literature usually reports species containing Mn(II), Ni(II), Co(II), Cu(II) or Zn(II) and a large variety of multidentate ligands with chelating properties such as antibiotics, Schiff bases, biguanides, N-based macrocyclic and fused rings derivatives. This review presents the progress in the development of such species and their anti-biofilm activity, as well as the contribution of biomaterials science to incorporate these complexes in composite platforms for reducing the negative impact of medical biofilms.

Quorum Sensing Inhibiting Activity of Cefoperazone and Its Metallic Derivatives on Pseudomonas aeruginosa

The last decade has witnessed a massive increase in the rate of mortalities caused by multidrug-resistant Pseudomonas aeruginosa. Therefore, developing new strategies to control virulence factors and pathogenicity has received much attention. One of these strategies is quorum sensing inhibition (QSI) which was developed to control Pseudomonas infection. This study aims to validate the effect of one of the most used β-lactam antibiotics; cefoperazone (CFP) and its metallic-derivatives on quorum sensing (QS) and virulence factors of P. aeruginosa. Assessment of quorum sensing inhibitory activity of CFP, cefoperazone Iron complex (CFPF) and cefoperazone Cobalt complex (CFPC) was performed by using reporter strain Chromobacterium violaceum ATCC 12472. Minimal inhibitory concentration (MIC) was carried out by the microbroth dilution method. The influence of sub-MICs (1/4 and 1/2 MICs) of CFP, CFPF and CFPC on virulence factors of P. aeruginosa was evaluated. Data was confirmed on the molecular level by RT-PCR. Also, molecular docking analysis was conducted to figure out the possible mechanisms of QSI. CFP, CFPF, and CFPC inhibited violacein pigment production of C. violaceum ATCC 12472. Sub-MICs of CFP (128- 256 μg/mL), and significantly low concentrations of CFPC (0.5- 16 μg/mL) and CFPF (0.5- 64 μg/mL) reduced the production of QS related virulence factors such as pyocyanin, protease, hemolysin and eliminated biofilm assembly by P. aeruginosa standard strains PAO1 and PA14, and P. aeruginosa clinical isolates Ps1, Ps2, and Ps3, without affecting bacterial viability. In addition, CFP, CFPF, and CFPC significantly reduced the expression of lasI and rhlI genes. The molecular docking analysis elucidated that the QS inhibitory effect was possibly caused by the interaction with QS receptors. Both CFPF and CFPC interacted strongly with LasI, LasR and PqsR receptors with a much high ICM scores compared to CFP that could be the cause of elimination of natural ligand binding. Therefore, CFPC and CFPF are potent inhibitors of quorum sensing signaling and virulence factors of P. aeruginosa.

Quantitative mapping of mRNA 3' ends in Pseudomonas aeruginosa reveals a pervasive role for premature 3' end formation in response to azithromycin

Pseudomonas aeruginosa produces serious chronic infections in hospitalized patients and immunocompromised individuals, including patients with cystic fibrosis. The molecular mechanisms by which P. aeruginosa responds to antibiotics and other stresses to promote persistent infections may provide new avenues for therapeutic intervention. Azithromycin (AZM), an antibiotic frequently used in cystic fibrosis treatment, is thought to improve clinical outcomes through a number of mechanisms including impaired biofilm growth and quorum sensing (QS). The mechanisms underlying the transcriptional response to AZM remain unclear. Here, we interrogated the P. aeruginosa transcriptional response to AZM using a fast, cost-effective genome-wide approach to quantitate RNA 3’ ends (3pMap). We also identified hundreds of P. aeruginosa genes with high incidence of premature 3’ end formation indicative of riboregulation in their transcript leaders using 3pMap. AZM treatment of planktonic and biofilm cultures alters the expression of hundreds of genes, including those involved in QS, biofilm formation, and virulence. Strikingly, most genes downregulated by AZM in biofilms had increased levels of intragenic 3’ ends indicating premature transcription termination, transcriptional pausing, or accumulation of stable intermediates resulting from the action of nucleases. Reciprocally, AZM reduced premature intragenic 3’ end termini in many upregulated genes. Most notably, reduced termination accompanied robust induction of obgE, a GTPase involved in persister formation in P. aeruginosa. Our results support a model in which AZM-induced changes in 3’ end formation alter the expression of central regulators which in turn impairs the expression of QS, biofilm formation and stress response genes, while upregulating genes associated with persistence.

Pseudomonas aeruginosa is a common source of hospital-acquired infections and causes prolonged illness in patients with cystic fibrosis. P. aeruginosa infections are often treated with the macrolide antibiotic azithromycin, which changes the expression of many genes involved in infection. By examining such expression changes at nucleotide resolution, we found azithromycin treatment alters the locations of mRNA 3’ ends suggesting most downregulated genes are subject to premature 3’ end formation. We further identified candidate RNA regulatory elements that P. aeruginosa may use to control gene expression. Our work provides new insights in P. aeruginosa gene regulation and its response to antibiotics.

Growing emergence of drug-resistant Pseudomonas aeruginosa and attenuation of its virulence using quorum sensing inhibitors: A critical review

A perilous increase in the number of bacterial infections has led to developing throngs of antibiotics for increasing the quality and expectancy of life. Pseudomonas aeruginosa is becoming resistant to all known conventional antimicrobial agents thereby posing a deadly threat to the human population. Nowadays, targeting virulence traits of infectious agents is an alternative approach to antimicrobials that is gaining much popularity to fight antimicrobial resistance. Quorum sensing (QS) involves interspecies communication via a chemical signaling pathway. Under this mechanism, cells work in a concerted manner, communicate with each other with the help of signaling molecules called auto-inducers (AI). The virulence of these strains is driven by genes, whose expression is regulated by AI, which in turn acts as transcriptional activators. Moreover, the problem of antibiotic-resistance in case of infections caused by P. aeruginosa becomes more alarming among immune-compromised patients, where the infectious agents easily take over the cellular machinery of the host while hidden in the QS mediated biofilms. Inhibition of the QS circuit of P. aeruginosa by targeting various signaling pathways such as LasR, RhlR, Pqs, and QScR transcriptional proteins will help in blocking downstream signal transducers which could result in reducing the bacterial virulence. The anti-virulence agent does not pose an immediate selective pressure on growing bacterium and thus reduces the pathogenicity without harming the target species. Here, we review exclusively, the growing emergence of multi-drug resistant (MDR) P. aeruginosa and the critical literature survey of QS inhibitors with their potential application of blocking P. aeruginosa infections.

Posttranslational chemical installation of azoles into translated peptides

Azoles are five-membered heterocycles often found in the backbones of peptidic natural products and synthetic peptidomimetics. Here, we report a method of ribosomal synthesis of azole-containing peptides involving specific ribosomal incorporation of a bromovinylglycine derivative into the nascent peptide chain and its chemoselective conversion to a unique azole structure. The chemoselective conversion was achieved by posttranslational dehydrobromination of the bromovinyl group and isomerization in aqueous media under fairly mild conditions. This method enables us to install exotic azole groups, oxazole and thiazole, at designated positions in the peptide chain with both linear and macrocyclic scaffolds and thereby expand the repertoire of building blocks in the mRNA-templated synthesis of designer peptides.

Azoles are five-membered heterocycles found in peptidic natural products and synthetic peptiodomimetics. Here the authors demonstrate a posttranslational chemical modification method for in vitro ribosomal synthesis of peptides with exotic azole groups at specific positions.