Design, synthesis, molecular docking, anti-quorum sensing, and anti-biofilm activity of pyochelin-zingerone conjugate

Vitamin D3 potentiates antimicrobial and antibiofilm activities of streptomycin and thymoquinone against Pseudomonas aeruginosa

Biofilm formed by Pseudomonas aeruginosa is a three dimensional microbial matrix that confers multidrug resistance properties along with the proficiency to evade the host immune system. The present study aims to determine the combinatorial effects of vitamin D3 (cholecalciferol) with two already reported antibiofilm agents: streptomycin and thymoquinone separately against P. aeruginosa biofilms. The minimum inhibitory concentration of streptomycin, thymoquinone and D3 was found to be 20, 10 and 100 μg/mL respectively. The inhibition of biofilm formation and pre-formed biofilm disintegration properties of streptomycin and thymoquinone alone or in combination with D3 at their sub-MIC concentration was determined by crystal violet staining and confocal laser scanning microscopy. A significant inhibition of metabolic activities like oxygen consumption rate and reduction in quorum sensing related cellular activities like swarming motilities, pyocyanin production and extracellular protease secretion by P. aeruginosa were also observed as a result of this combinatorial effect. Both of these combinatorial applications were found to accumulate ROS in bacterial cells, which has been proved to be one of the main causes of their antibiofilm activity. Effect of these two drug combinations on bacterial lettuce leaf infection was also evaluated. Molecular docking analysis indicated that thymoquinone combined D3 can interact more efficiently with the quorum sensing proteins LasI and LasR. The host cell cytotoxicity of these two combinations was found to be negligible on the murine macrophage cell line. These findings suggest that D3 potentiates the antimicrobial and antibiofilm efficacy of both streptomycin and thymoquinone against P. aeruginosa. Although both combinations have shown significant antibiofilm and antimicrobial potential, combinatorial performances of D3 combined thymoquinone were found to be more promising.

Relationship between Pyochelin and Pseudomonas Quinolone Signal in Pseudomonas aeruginosa: A Direction for Future Research

Pseudomonas aeruginosa is an opportunistic pathogen that requires iron to survive in the host; however, the host immune system limits the availability of iron. Pyochelin (PCH) is a major siderophore produced by P. aeruginosa during infection, which can help P. aeruginosa survive in an iron-restricted environment and cause infection. The infection activity of P. aeruginosa is regulated by the Pseudomonas quinolone signal (PQS) quorum-sensing system. The system uses 2-heptyl-3-hydroxy-4-quinolone (PQS) or its precursor, 2-heptyl-4-quinolone (HHQ), as the signal molecule. PQS can control specific life processes such as mediating quorum sensing, cytotoxicity, and iron acquisition. This review summarizes the biosynthesis of PCH and PQS, the shared transport system of PCH and PQS, and the regulatory relationship between PCH and PQS. The correlation between the PQS and PCH is emphasized to provide a new direction for future research.

In vivo efficacy of pyochelin-mediated delivery of zingerone in Pseudomonas aeruginosa-induced peritonitis

Aim: The efficacy of a pyochelin-zingerone conjugate (PZC) against Pseudomonas aeruginosa in vivo in a mouse model of peritonitis, as well as mode of action in vitro, were investigated. Methods & results: Intraperitoneal administration of PZC (220 mg kg-1 b.wt.) resulted in a significant reduction in bacterial count in liver tissue by 2 log10 on the 4th day post infection. This was supported by reduced levels of inflammatory markers, liver function, inflammatory cytokines and improved histopathology. PZC showed its ability to disrupt the cellular membrane, increase permeability of the membrane and leakage of intracellular contents of P. aeruginosa, resulting in its death. Conclusion: The present study reports the hepatoprotective potential of PZC in an experimental model of P. aeruginosa-induced peritonitis.

Zingerone inhibits biofilm formation and enhances antibiotic efficacy against Salmonella biofilm

Salmonella enterica serovar Typhi is a significant cause of typhoid fever and a major public health problem. The ability of S. Typhi to form biofilms on living and non-living surfaces results in antibiotic resistance and poses a major challenge in health care. In this study, we assessed the ability of zingerone alone and in combination with antibiotics against the motility phenotypes and biofilm-forming ability of S. Typhi. Results showed that zingerone effectively reduced the swimming, swarming, and twitching phenotypes and exhibited biofilm inhibition potential. Moreover, zingerone enhanced the antibiofilm activity of ciprofloxacin and kanamycin. Microscopic analysis revealed a thinner biofilm in the presence of zingerone, which may have enhanced the antibiofilm efficacy of the antibiotics. The microscopic analysis showed that the presence of zingerone resulted in a reduction in the thickness of the biofilm, potentially increasing the antibiofilm efficacy of the antibiotics. In silico molecular docking and simulation studies further indicated that zingerone may bind to the fimbriae subunits (FimA, FimC, FimH, and FimY) of S. Typhi and form stable interactions. These findings provide important insights into the potential of zingerone to target biofilm-associated Salmonella infections. Further research is considered a promising option for designing innovative approaches to prevent infections associated with biofilms. Schematic representation of the role of zingerone in biofilm, motility inhibition and molecular interactions with biofilm associated proteins.

Antibiofilm Activity and Mechanism of Linalool against Food Spoilage Bacillus amyloliquefaciens

Pellicle biofilm-forming bacteria Bacillus amyloliquefaciens are the major spoilage microorganisms of soy products. Due to their inherent resistance to antibiotics and disinfectants, pellicle biofilms formed are difficult to eliminate and represent a threat to food safety. Here, we assessed linalool's ability to prevent the pellicle of two spoilage B. amyloliquefaciens strains. The minimum biofilm inhibitory concentration (MBIC) of linalool against B. amyloliquefaciens DY1a and DY1b was 4 μL/mL and 8 μL/mL, respectively. The MBIC of linalool had a considerable eradication rate of 77.15% and 83.21% on the biofilm of the two strains, respectively. Scanning electron microscopy observations revealed that less wrinkly and thinner pellicle biofilms formed on a medium supplemented with 1/2 MBIC and 1/4 MBIC linalool. Also, linalool inhibited cell motility and the production of extracellular polysaccharides and proteins of the biofilm matrix. Furthermore, linalool exposure reduced the cell surface hydrophobicity, zeta potential, and cell auto-aggregation of B. amyloliquefaciens. Molecular docking analysis demonstrated that linalool interacted strongly with quorum-sensing ComP receptor and biofilm matrix assembly TasA through intermolecular hydrogen bonds, hydrophobic contacts, and van der Waals forces interacting with site residues. Overall, our findings suggest that linalool may be employed as a potential antibiofilm agent to control food spoilage B. amyloliquefaciens.

Design, Synthesis, and Quorum Quenching Potential of Novel Catechol–Zingerone Conjugate to Find an Elixir to Tackle Pseudomonas aeruginosa Through the Trojan Horse Strategy

To address the issue of multidrug resistance in Pseudomonas aeruginosa, a novel catechol–zingerone conjugate (1) linked via a non-hydrolyzable 1,2,3-triazole linker was synthesized and subjected to biological evaluation based on the Trojan horse strategy. To enhance the efficacy, catechol, a xenosiderophore, utilized by P. aeruginosa for iron assimilation, and the dietary phytochemical zingerone, known for its anti-virulent activity against Pseudomonas aeruginosa, were exploited in the present study. Theoretical validation of conjugate (1) was conducted by in silico molecular docking analysis to determine the interaction with outer membrane transport receptor PirA and quorum sensing signal receptors. In addition, nine-fold binding affinity of Conjugate (1) toward PirA (5FP2) in comparison to its natural ligand catechol with D-score −1.13 Å authenticated the designed Trojan horse drug. Conjugate (1) showed stronger anti-virulent activity than zingerone; hence, it exhibited a promising anti-biofilm efficacy as assessed by crystal violet assay and visualized by FESEM toward P. aeruginosa. Encouraging results against P. aeruginosa in terms of quorum sensing regulated virulence factors, motility phenotypes, and biofilm formation with no cell cytotoxicity and could help open hitherto unexplored possibilities of establishing Trojan horse drugs as a successful approach against multidrug resistance in P. aeruginosa.

Repurposing phytochemicals as anti-virulent agents to attenuate quorum sensing-regulated virulence factors and biofilm formation in Pseudomonas aeruginosa

Unregulated consumption and overexploitation of antibiotics have paved the way for emergence of antibiotic‐resistant strains and ‘superbugs’. Pseudomonas aeruginosa is among the opportunistic nosocomial pathogens causing devastating infections in clinical set‐ups globally. Its artillery equipped with diversified virulence elements, extensive antibiotic resistance and biofilms has made it a ‘hard‐to‐treat’ pathogen. The pathogenicity of P. aeruginosa is modulated by an intricate cell density‐dependent mechanism called quorum sensing (QS). The virulence artillery of P. aeruginosa is firmly controlled by QS genes, and their expression drives the aggressiveness of the infection. Attempts to identify and develop novel antimicrobials have seen a sharp rise in the past decade. Among different proposed mechanisms, a novel anti‐virulence approach to target pseudomonal infections by virtue of anti‐QS and anti‐biofilm drugs appears to occupy the centre stage. In this respect, bioactive phytochemicals have gained prominence among the scientific community owing to their significant quorum quenching (QQ) properties. Recent studies have shed light on the QQ activities of various phytochemicals and other drugs in perturbing the QS‐dependent virulence in P. aeruginosa. This review highlights the recent evidences that reinforce the application of plant bioactives for combating pseudomonal infections, their advantages and shortcomings in anti‐virulence therapy.

Revisiting the virulence hallmarks of Pseudomonas aeruginosa: a chronicle through the perspective of quorum sensing

Pseudomonas aeruginosa is an opportunistic pathogen and the leading cause of mortality among immunocompromised patients in clinical setups. The hallmarks of virulence in P. aeruginosa encompass six biologically competent attributes that cumulatively drive disease progression in a multistep manner. These multifaceted hallmarks lay the principal foundation for rationalizing the complexities of pseudomonal infections. They include factors for host colonization and bacterial motility, biofilm formation, production of destructive enzymes, toxic secondary metabolites, iron-chelating siderophores and toxins. This arsenal of virulence hallmarks is fostered and stringently regulated by the bacterial signalling system called quorum sensing (QS). The central regulatory functions of QS in controlling the timely expression of these virulence hallmarks for adaptation and survival drive the disease outcome. This review describes the intricate mechanisms of QS in P. aeruginosa and its role in shaping bacterial responses, boosting bacterial fitness. We summarize the virulence hallmarks of P. aeruginosa, relating them with the QS circuitry in clinical infections. We also examine the role of QS in the development of drug resistance and propose a novel antivirulence therapy to combat P. aeruginosa infections. This can prove to be a next-generation therapy that may eventually become refractory to the use of conventional antimicrobial treatments.