Antimicrobial and anti-virulence activities of 4-shogaol from grains of paradise against gram-negative bacteria: Integration of experimental and computational methods

Repurposing Nitroimidazoles: A New Frontier in Combatting Bacterial Virulence and Quorum Sensing via In Silico, In Vitro, and In Vivo Insights

The global antibiotic resistance crisis demands innovative strategies targeting bacterial virulence rather than survival. Quorum sensing (QS), a key regulator of virulence and biofilm formation, offers a promising avenue to mitigate resistance by disarming pathogens without bactericidal pressure. This study investigates the repurposing of nitroimidazoles as anti-QS and anti-virulence agents at subminimum inhibitory concentrations (sub-MICs). In Silico analyses, including molecular docking and molecular dynamics (MD) simulations, were performed to investigate ligand-receptor interactions with structurally distinct Lux-type QS receptors and assess binding stability and conformational dynamics over time. In Vitro assays evaluated the effects of representative nitroimidazoles, metronidazole (MET) and secnidazole (SEC), on QS-controlled phenotypes, including violacein production in Chromobacterium violaceum and biofilm formation and protease activity in Pseudomonas aeruginosa, Acinetobacter baumannii, Salmonella enterica, and Proteus mirabilis. In Vivo efficacy was assessed using a murine infection model and HeLa cell invasion assays. Molecular docking revealed high-affinity binding to QS receptors, corroborating their mechanistic interference. Sub-MIC MET/SEC significantly suppressed violacein synthesis, biofilm biomass, and protease secretion in Gram-negative pathogens. Both compounds reduced bacterial invasiveness in HeLa cells and In Vivo protected mice from lethal P. aeruginosa infections. Crucially, nitroimidazoles attenuated virulence without affecting bacterial viability, preserving microbial ecology. These findings position nitroimidazoles as dual-function agents; antimicrobial at bactericidal doses and anti-virulence at sub-MICs. Their validated efficacy across In Silico, In Vitro, and In Vivo models underscores their potential as adjunctive therapies, bridging the gap between drug repurposing and next-generation anti-infective development.

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.

Reprofiling lamivudine as an antibiofilm and anti-pathogenic agent against Pseudomonas aeruginosa

Resistance to antibiotics is a critical growing public health problem that needs urgent action to combat. To avoid the stress on bacterial growth that evokes the development of resistance, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. There are FDA approved drugs have been screened for their anti-virulence activities. Lamivudine (LAM) is a synthetic nucleoside analogue used as an antiretroviral in treatment of HIV and can be used in treatment of HBV. The present study aimed to assess the anti-virulence activities of LAM against a clinically important pathogen Pseudomonas aeruginosa. The LAM's antibiofilm and anti-virulence activities were evaluated. The impact of LAM on the quorum sensing (QS) systems which control the production of these virulence factors was assessed virtually and by quantification of the expression of QS-encoding genes. Furthermore, in vivo mice protection assay was conducted to attest the LAM's anti-pathogenic activity. The current findings elaborated the promising anti-pathogenic and anti-QS activities of LAM. LAM interfered with biofilm formation in P. aeruginosa PAO1 strain. Moreover, swarming motility and production of pyocyanin and protease were significantly diminished. At the molecular level, LAM downregulated the QS-encoding genes LasI, LasR, RhlR, PqsA and PqsR. Additionally, the detailed in silico docking and molecular simulation studies showed the considered high LAM's ability to bind and hinder the QS receptors in the P. aeruginosa. In an agreement with in vitro and in silico, the in vivo results showed the LAM full protection of mice against P. aeruginosa. In conclusion, LAM could be repurposed to be employed as adjunct therapy with traditional antibiotics for treating serious pseudomonal infections.

Piceatannol: a renaissance in antibacterial innovation unveiling synergistic potency and virulence disruption against serious pathogens

In the relentless battle against multi-drug resistant Gram-negative bacteria, piceatannol emerges as a beacon of hope, showcasing unparalleled antibacterial efficacy and a unique ability to disrupt virulence factors. Our study illuminates the multifaceted prowess of piceatannol against prominent pathogens-Proteus mirabilis, Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. Notably, piceatannol demonstrated a remarkable ability to inhibit biofilm formation, reduce bacterial mobility, and diminish extracellular enzyme synthesis.Mechanistic insights into piceatannol's activity unraveled its impact on membrane potential, proton motive force, and ATP production. Furthermore, our study delved into piceatannol's anti-quorum sensing (QS) activity, showcasing its potential to downregulate QS-encoding genes and affirming its affinity to critical QS receptors through molecular docking. Crucially, piceatannol exhibited a low propensity for resistance development, positioning it as a promising candidate for combating antibiotic-resistant strains. Its mild effect on red blood cells (RBCs) suggests safety even at higher concentrations, reinforcing its potential translational value. In an in vivo setting, piceatannol demonstrated protective capabilities, significantly reducing pathogenesis in mice infected with P. aeruginosa and P. mirabilis. This comprehensive analysis positions piceatannol as a renaissance in antibacterial innovation, offering a versatile and effective strategy to confront the evolving challenges posed by resilient Gram-negative pathogens.

Enoxacin adversely affects Salmonella enterica virulence and host pathogenesis through interference with type III secretion system type II (T3SS-II) and disruption of translocation of Salmonella Pathogenicity Island-2 (SPI2) effectors

Salmonella enterica is a clinically significant oro-fecal pathogen that causes a wide variety of illnesses and can lead to epidemics. S. enterica expresses a lot of virulence factors that enhance its pathogenesis in host. For instance, S. enterica employs a type three secretion system (T3SS) to translocate a wide array of effector proteins that could change the surrounding niche ensuring suitable conditions for the thrive of Salmonella infection. Many antimicrobials have been recently introduced to overcome the annoying bacterial resistance to antibiotics. Enoxacin is member of the second-generation quinolones that possesses a considerable activity against S. enterica. The present study aimed to evaluate the effect of enoxacin at sub-minimum inhibitory concentration (sub-MIC) on S. enterica virulence capability and pathogenesis in host. Enoxacin at sub-MIC significantly diminished both Salmonella invasion and intracellular replication within the host cells. The observed inhibitory effect of enoxacin on S. enterica internalization could be attributed to its ability to interfere with translocation of the T3SS effector proteins. These results were further confirmed by the finding that enoxacin at sub-MIC down-regulated the expression of the genes encoding for T3SS-type II (T3SS-II). Moreover, enoxacin at sub-MIC lessened bacterial adhesion to abiotic surface and biofilm formation which indicates a potential anti-virulence activity. Importantly, in vivo results showed a significant ability of enoxacin to protect mice against S. enterica infection and decreased bacterial colonization within animal tissues. In nutshell, current findings shed light on an additional mechanism of enoxacin at sub-MIC by interfering with Salmonella intracellular replication. The outcomes presented herein could be further invested in conquering bacterial resistance and open the door for additional effective clinical applications.

Celastrol boosts fluconazole efficacy against vaginal candidiasis: in vitro and in vivo evidence

Candida albicans is a commensal fungus that naturally inhabits the vagina. However, overgrowth of C. albicans can result in vulvovaginal candidiasis (VVC), one of the most prevalent fungal infections affecting women. The rapid emergence of azole resistance in C. albicans, in addition to the limited available antifungal agents, complicates the treatment and emphasizes the urgent need for novel therapeutic options. Efflux-mediated azole resistance is a common resistance mechanism in fluconazole (FLZ)-resistant C. albicans. Combination therapy using natural compounds is a potential approach that can restore fluconazole's antifungal activity in azole-resistant isolates via efflux pump inhibition. This study aimed to evaluate the ability of celastrol, a natural triterpene, to retrieve FLZ antifungal activity against azole-resistant C. albicans in vitro and in vivo. Celastrol did not exhibit antifungal activity against the tested clinical isolates; however, the sub-MIC of celastrol inhibited rhodamine 6G (R6G) efflux and increased R6G accumulation inside celastrol-treated C. albicans cells. Synergy was spotted between celastrol and FLZ via a checkerboard assay. Quantification of m-RNA levels of efflux-mediated azole resistance genes within azole-resistant C. albicans demonstrated CDR1 overexpression. Upon celastrol treatment, a significant decline in ABC transporters transcript levels were detected. Moreover, molecular docking demonstrated that celastrol is a potential ABC efflux transporters blocker that successfully fits into target binding pockets. A negligible hemolytic effect of celastrol against human erythrocytes was observed. In the in vivo model of VVC, the combination of FLZ and celastrol in vaginal gel revealed a drastic reduction in the fungal burden with apparently normal vaginal tissue. Celastrol promising in vitro and in vivo findings strengthen its future use for the treatment of azole-resistant C. albicans.

Sulforaphane Is Not Only a Food Supplement: It Diminishes the Intracellular Survival and Colonization of Salmonella enterica

Sulforaphane is a main bioactive component in several edible cruciferous vegetables. It acquires several benefits to health in addition to its considered antibacterial and antivirulence activities. Herein, we aimed at evaluating the antivirulence activity of sulforaphane against the worldwide clinically important enteric pathogen Salmonella enterica serovar Typhimurium. The influence of sulforaphane on bacterial adhesion, invasion, biofilm formation, and intracellular replication was assayed. Additionally, the effect of sulforaphane on the type III secretion system (TTSS) in S. enterica was quantified. The outcome of the combination with different antibiotics was assessed, and an in vivo protection assay was conducted to assess the influence on S. enterica pathogenesis. The results showed the significant antibiofilm activity of sulforaphane at subinhibitory effect in addition to its significant reduction in bacterial invasion and intracellular replication inside the host cells. The in vivo findings emphasized the decreased capacity of S. enterica to induce pathogenesis in the presence of sulforaphane. Our finding attributed these antivirulence activities to the interference of sulforaphane with TTSS-type II and the downregulation of its encoding genes. In a nutshell, the edible cruciferous vegetable bioactive sulforaphane is a safe adjunct therapy that can be administrated alongside traditional antibiotics for treating clinically significant enteric pathogens as S. enterica.

Arctigenin from Burdock Root Exhibits Potent Antibacterial and Anti-Virulence Properties against Pseudomonas aeruginosa

Arctium lappa (Burdock) root is used in various culinary applications especially in Asian Cuisine. Arctigenin (ARC) is a polyphenolic compound abundant in the roots of the burdock plant from which it derives its name. The emergence of bacterial resistance is a growing global worry, specifically due to the declining availability of new antibiotics. Screening for the antibacterial candidates among the safe natural products is a promising approach. The present study was aimed to assess the antibacterial activity of ARC against Pseudomonas aeruginosa exploring its effect on the bacterial cell membrane. Furthermore, the anti-virulence activities and anti-quorum sensing (QS) activities of ARC were in vitro, in vivo and in silico assessed against P. aeruginosa. The current results showed the ARC antibacterial activity was owed to its disruption effect of the cell membrane. ARC at sub-MIC significantly decreased the formation of biofilm, motility, production of extracellular enzymes and in vivo protected mice against P. aeruginosa. These anti-virulence activities of ARC are owed to its interference with bacterial QS and its expression. Furthermore, ARC showed mild effect on mammalian erythrocytes, low probability to induce resistance and synergistically combined with antibiotics. In summary, the promising anti-virulence properties of ARC indicate its potential as an effective supplement to conventional antibiotics for treating severe P. aeruginosa infections.

Cilostazol is a promising anti-pseudomonal virulence drug by disruption of quorum sensing

Resistance to antibiotics is a critical growing public health problem that desires urgent action to combat. To avoid the stress on bacterial growth that evokes the resistance development, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. Quorum sensing (QS) systems play main roles in controlling the production of diverse virulence factors and biofilm formation in bacteria. Thus, interfering with QS systems could result in mitigation of the bacterial virulence. Cilostazol is an antiplatelet and a vasodilator FDA approved drug. This study aimed to evaluate the anti-virulence activities of cilostazol in the light of its possible interference with QS systems in Pseudomonas aeruginosa. Additionally, the study examines cilostazol's impact on the bacterium's ability to induce infection in vivo, using sub-inhibitory concentrations to minimize the risk of resistance development. In this context, the biofilm formation, the production of virulence factors and influence on the in vivo ability to induce infection were assessed in the presence of cilostazol at sub-inhibitory concentration. Furthermore, the outcome of combination with antibiotics was evaluated. Cilostazol interfered with biofilm formation in P. aeruginosa. Moreover, swarming motility, biofilm formation and production of virulence factors were significantly diminished. Histopathological investigation revealed that liver, spleen and kidney tissues damage was abolished in mice injected with cilostazol-treated bacteria. Cilostazol exhibited a synergistic outcome when used in combination with antibiotics. At the molecular level, cilostazol downregulated the QS genes and showed considerable affinity to QS receptors. In conclusion, Cilostazol could be used as adjunct therapy with antibiotics for treating Pseudomonal infections. This research highlights cilostazol's potential to combat bacterial infections by targeting virulence mechanisms, reducing the risk of antibiotic resistance, and enhancing treatment efficacy against P. aeruginosa. These findings open avenues for repurposing existing drugs, offering new, safer, and more effective infection control strategies.

Investigating Sulforaphane's anti-virulence and anti-quorum sensing properties against Pseudomonas aeruginosa

Background

P. aeruginosa, a significant bacterium, can cause severe illness and resistance to antibiotics. Quorum sensing (QS) systems regulate virulence factors production. Targeting QS could reduce bacteria pathogenicity and prevent antibiotic resistance. Cruciferous vegetables contain sulforaphane, known for its anti-inflammatory, antioxidant, anticancer, and antimicrobial properties.

Aim

We aimed to examine the inhibitory influences of sulforaphane, at a sub-inhibitory concentration (¼ minimum inhibitory concentration, MIC), on virulence and QS in P. aeruginosa.

Materials and methods

The sulforaphane's anti-virulence actions at sub-inhibitory concentrations were explored in vitro and in vivo. A sub-MIC concentration of sulforaphane was combined with anti-pseudomonal drugs, and the results of this combination were assessed. The virtual affinity of sulforaphane for the receptors of QS was studied, and its effect on the expression of QS genes was quantified.

Results

Sulforaphane significantly decreased the biofilm formation, motility, ability to withstand oxidative stress, and the synthesis of virulence extracellular enzymes such as proteases, hemolysins, and elastase, as well as other virulence factors like pyocyanin. In addition, sulforaphane lessened the severity of P. aeruginosa infection in mice. Sulforaphane reduced the antipseudomonal antibiotics' MICs when used together, resulting in synergistic effects. The observed anti-virulence impacts were attributed to the ability of sulforaphane to inhibit QS via suppressing the QS genes' expression.

Conclusion

Sulforaphane shows promise as a potent anti-virulence and anti-QS agent that can be used alongside conventional antimicrobials to manage severe infections effectively. Furthermore, this study paves the way for further investigation of sulforaphane and similar structures as pharmacophores for anti-QS candidates.

Thymoquinone is a natural antibiofilm and pathogenicity attenuating agent in Pseudomonas aeruginosa

Pseudomonas aeruginosa belongs to the critical pathogens that represent a global public health problem due to their high rate of resistance as listed by WHO. P. aeruginosa can result in many nosocomial infections especially in individuals with compromised immune systems. Attenuating virulence factors by interference with quorum sensing (QS) systems is a promising approach to treat P. aeruginosa-resistant infections. Thymoquinone is a natural compound isolated from Nigella sativa (black seed) essential oil. In this study, the minimum inhibitory concentration of thymoquinone was detected followed by investigating the antibiofilm and antivirulence activities of the subinhibitory concentration of thymoquinone against P. aeruginosa PAO1. The effect of thymoquinone on the expression of QS genes was assessed by quantitative real-time PCR, and the protective effect of thymoquinone against the pathogenesis of PAO1 in mice was detected by the mouse survival test. Thymoquinone significantly inhibited biofilm, pyocyanin, protease activity, and swarming motility. At the molecular level, thymoquinone markedly downregulated QS genes lasI, lasR, rhlI, and rhlR. Moreover, thymoquinone could protect mice from the pathologic effects of P. aeruginosa increasing mouse survival from 20% to 100%. In conclusion, thymoquinone is a promising natural agent that can be used as an adjunct therapeutic agent with antibiotics to attenuate the pathogenicity of P. aeruginosa.