Broad-spectrum antimicrobial properties of linalool: supporting its pharmacological use in chronic wound infections by pathogens within the ESKAPE group and polymicrobial biofilms

Chronic wound infections are caused by biofilm forming opportunistic pathogenic bacteria. The persistence of infection, co-infecting pathogens and prolonged use of antibiotics promote antibiotic resistance hampering healing process due to increased inflammation. Hence, we tested the broad range antibacterial activity of linalool, a bioactive monoterpene commonly present in many essential oils having anti-inflammatory and antimicrobial activities to target different opportunistic pathogens commonly found in the chronic wound. We included some of the common pathogens such as Acinetobacter baumannii, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus, to study the broad range antimicrobial efficacy of linalool. The in vitro effect of linalool on biofilm was quantified in pre-treatment, post-treatment, repetitive treatment, and polymicrobial biofilm scenarios. Time-kill and XTT (2,3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2 H-tetrazolium-5-carboxanilide) assays were performed to confirm the efficacy of linalool against wound infections, and these results were further validated using simulated wound exudates medium (WEM) which mimics the wound environment. The mechanism of bactericidal action was determined using assays for membrane integrity and oxidative stress. The results indicated the broad range antimicrobial activity of linalool with minimum inhibitory concentration (MIC) ranging from 2.5 to 5 µL/mL against E. coli, A. baumannii, E. faecalis, S. aureus, and K. pneumoniae, while for P. aeruginosa the MIC was 20 µL/mL. Linalool was most effective against E. coli, E. faecalis, K. pneumoniae, A. baumannii, and S. aureus, and could inhibit the growth and biofilm by more than 90% and 80%, respectively, at 5 µL/mL. The XTT assay confirmed the MIC results, showing a significant reduction in the metabolic activity of the pathogens (p < 0.001). In the simulated WEM similar response of the bacteria to linalool treatment was observed. At 5 to 20 µL/mL concentrations, linalool significantly inhibited the polymicrobial biofilm consisting of P. aeruginosa, A. baumannii, and S. aureus in two species combinations. The mechanism of bactericidal action was associated with the increased reactive oxygen species production and disruption in the membrane integrity leading to release of cellular content. The anti-inflammatory activity of linalool, assessed using the albumin denaturation method showed significant activity at the tested concentrations. In conclusion, the findings suggest the therapeutic potential of linalool in treating biofilm associated chronic wound infections due to its versatile broad spectrum activity.

Advancing Anti-Biofilm Strategies: Innovations to Combat Biofilm-Related Challenges and Enhance Efficacy

Biofilms are complex communities of microorganisms that can cause significant challenges in various settings, including industrial processes, environmental systems, and human health. The protective nature of biofilms makes them resistant to traditional anti-biofilm strategies, such as chemical agents, mechanical interventions, and surface modifications. To address the limitations of conventional anti-biofilm methods, researchers have explored emerging strategies that encompass the use of natural compounds, nanotechnology-based methods, quorum-sensing inhibition, enzymatic degradation, and antimicrobial photodynamic/sonodynamic therapy. There is an increasing focus on combining multiple anti-biofilm strategies to combat resistance and enhance effectiveness. Researchers are continuously investigating the mechanisms of biofilm formation and developing innovative approaches to overcome the limitations of conventional anti-biofilm methods. These efforts aim to improve the management of biofilms and prevent infections while preserving the environment. This study provides a comprehensive overview of the latest advancements in anti-biofilm strategies. Given the dynamic nature of this field, exploring new approaches is essential to stimulate further research and development initiatives. The effective management of biofilms is crucial for maintaining the health of industrial processes, environmental systems, and human populations.

Staphylococcus aureus major cell division protein FtsZ assembly is inhibited by silibinin, a natural flavonolignan that also blocked bacterial growth and biofilm formation

The bacterial cell division protein FtsZ has been considered a potential therapeutic target due to its rapid treadmilling that induces cellular wall construction in bacteria. The current study discovered a novel antimicrobial compound, silibinin, a natural flavonolignan and its impact on the recombinant S. aureus FtsZ (SaFtsZ). Silibinin inhibited S. aureus Newman growth in a dose-dependent manner. The IC50 and MIC values for silibinin were 75 μM and 200 μM, respectively. It had no cytotoxicity against HEK293 cells in vitro. Silibinin also enlarged the bacterial cell morphology by ∼40 folds and showed antibiofilm property. It perturbed the S. aureus membrane potential both at IC50 conc. and at MIC conc. Further, it inhibited both the polymerization and GTPase activity of SaFtsZ. It did not inhibit tubulin assembly, a eukaryotic FtsZ homolog. A fluorescence quenching study yielded the Kd value for SaFtsZ-Silibinin interaction and binding stoichiometry 0.857 ± 0.188 μM and 1:1, respectively. Both in silico study and competition assay indicated that silibinin binds at the GTP binding site on SaFtsZ. The Ki value for the silibinin-mediated inhibition of SaFtsZ was 8.8 μM. Therefore, these findings have comprehensively shown the antimicrobial behavior of silibinin on S. aureus Newman cells targeting SaFtsZ.

Comparative Study of Quercetin and Hyperoside: Antimicrobial Potential towards Food Spoilage Bacteria, Mode of Action and Molecular Docking

The antibacterial activities of quercetin and hyperoside were evaluated towards two major spoilage bacteria in fish, Pseudomonas aeruginosa (PA) and Shewanella putrefaciens (SP). Hyperoside showed a lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) towards both spoilage bacteria, PA and SP, than quercetin. Cell membrane morphology was affected when treated with hyperoside and quercetin. The release of content from the treated cells occurred, as ascertained by the release of potassium and magnesium ions and the increase in conductivity of the culture media. The morphology of cells was significantly changed, in which shrinkage and pores were obtained, when observed using SEM. Both compounds negatively affected the motility, both swimming and swarming, and the formation of extracellular polymeric substance (EPS), thus confirming antibiofilm activities. Agarose gel analysis revealed that both compounds could bind to or degrade the genomic DNA of both bacteria, thereby causing bacterial death. Molecular docking indicated that the compounds interacted with the minor groove of the DNA, favoring the adenine-thymine-rich regions. Thus, both quercetin and hyperoside could serve as potential antimicrobial agents to retard the spoilage of fish or perishable products.

Surface adherence and vacuolar internalization of bacterial pathogens to the Candida spp. cells: Mechanism of persistence and propagation

BACKGROUND

The co-existence of Candida albicans with the bacteria in the host tissues and organs displays interactions at competitive, antagonistic, and synergistic levels. Several pathogenic bacteria take advantage of such types of interaction for their survival and proliferation. The chemical interaction involves the signaling molecules produced by the bacteria or Candida spp., whereas the physical attachment occurs by involving the surface proteins of the bacteria and Candida. In addition, bacterial pathogens have emerged to internalize inside the C. albicans vacuole, which is one of the inherent properties of the endosymbiotic relationship between the bacteria and the eukaryotic host.

AIM OF REVIEW

The interaction occurring by the involvement of surface protein from diverse bacterial species with Candida species has been discussed in detail in this paper. An in silico molecular docking study was performed between the surface proteins of different bacterial species and Als3P of C. albicans to explain the molecular mechanism involved in the Als3P-dependent interaction. Furthermore, in order to understand the specificity of C. albicans interaction with Als3P, the evolutionary relatedness of several bacterial surface proteins has been investigated. Furthermore, the environmental factors that influence bacterial pathogen internalization into the Candida vacuole have been addressed. Moreover, the review presented future perspectives for disrupting the cross-kingdom interaction and eradicating the endosymbiotic bacterial pathogens.

KEY SCIENTIFIC CONCEPTS OF REVIEW

With the involvement of cross-kingdom interactions and endosymbiotic relationships, the bacterial pathogens escape from the environmental stresses and the antimicrobial activity of the host immune system. Thus, the study of interactions between Candida and bacterial pathogens is of high clinical significance.

Curcumin affects function of Hsp90 and drug efflux pump of Candida albicans

Candida albicans is a pathogenic yeast that causes candidiasis in immunocompromised patients. The overuse of antifungal drugs has led to the development of resistance to such drugs by this fungus, which is a major challenge in antifungal chemotherapy. One approach to this problem involves the utilization of new natural products as an alternative source of antifungals. Curcumin, one such natural product, has been widely studied as a drug candidate and is reported to exhibit antifungal activity against C. albicans. Although studies of the mechanism of curcumin against human cancer cells have shown that it inhibits heat shock protein 90 (Hsp90), little is known about its function against C. albicans. In this paper, using a doxycycline-mediated HSP90 strain and an HSP90-overexpressing strain of C. albicans, we demonstrated that the curcumin triggered a decrease in Hsp90 by affecting it at the post-transcriptional level. This also led to the downregulation of HOG1 and CDR1, resulting in a reduction of the stress response and efflux pump activity of C. albicans. However, the inhibition of HSP90 by curcumin was not due to the inhibition of transcription factors HSF1 or AHR1. We also found that curcumin can not only decrease the transcriptional expression of CDR1, but also inhibit the efflux pump activity of Cdr1. Hence, we conclude that disruption of HSP90 by curcumin could impair cell growth, stress responses and efflux pump activity of C. albicans.

Proteomic alterations in Paracoccidioides brasiliensis caused by exposure to curcumin

Paracoccidioides spp. are the etiological agent of paracoccidioidomycosis, a disease that causes skin lesions and affect the lungs and other organs. The current management of the disease is long and has several side effects that often lead the patient to give up the treatment, sequelae and even death. The search for new forms of treatment that minimize these drawbacks is very important. Thus, natural compounds are targets of great interest. Curcumin is one of the main components of the tubers of Curcuma longa, presenting medicinal effects well described in the literature, including the antifungal effect on Paracocidioides brasiliensis. Nevertheless, the mechanisms related to the antifungal effect of such compound are still unknown, so the objective of the present research is to understand what changes occur in the metabolism of P. brasiliensis after exposure to curcumin and to identify the main targets of the compound. Proteomic analysis as based on nanoUPLC-MS analysis and the functional classification of the identified proteins. The main metabolic processes that were being regulated were biologically validated through assays such as fluorescence microscopy, EPR and phagocytosis. Proteomic analysis revealed that curcumin regulates several metabolic processes of the fungus, including important pathways for energy production, such as the glycolytic pathway, beta oxidation and the glyoxylate cycle. Protein synthesis was down-regulated in fungi exposed to curcumin. The electron transport chain and the tricarboxylic acid cycle were also down-regulated, indicating that both the mitochondrial membrane and the mitochondrial activity were compromised. Plasma membrane and cell wall structure were altered following exposure to the compound. The fungus' ability to survive the phagocytosis process by alveolar macrophages was reduced. Thus, curcumin interferes with several metabolic pathways in the fungus that causes paracoccidioidomycosis. BIOLOGICAL SIGNIFICANCE: The challenges presented by the current treatment of paracoccidioidomycosis often contributing to patients' withdrawal from treatment, leading to sequelae or even death. Thus, the search for new treatment options against this disease is growing. The discovery that curcumin is active against Paracoccidioides was previously reported by our study group. Here, we clarify how the compound acts on the fungus causing its growth inhibition and decreased viability. Understanding the mechanisms of action of curcumin on P. brasiliensis elucidates how we can seek new alternatives and which metabolic pathways and molecular targets we should focus on in this incessant search to bring the patient a treatment with fewer adverse effects.