Chromobacterium Violaceum Research Articles

Roles of transcriptional factor PsrA in the regulation of quorum sensing in Pseudomonas aeruginosa PAO1.

The transcription factor PsrA regulates fatty acid metabolism, the type III secretion system, and quinolone signaling quorum sensing system in Pseudomonas aeruginosa. To explore additional roles of PsrA in P. aeruginosa, this study engineered a P. aeruginosa PAO1 strain to carry a recombinant plasmid with the psrA gene (pMMBpsrA) and examined the impact of elevated psrA expression to the bacterium. Transcriptomic analysis revealed that PsrA significantly downregulated genes encoding the master quorum-sensing regulators, RhlR and LasR, and influenced many quorum-sensing-associated genes. The role of PsrA in quorum sensing was further corroborated by testing autoinducer synthesis in PAO1 [pMMBpsrA] using two reporter bacteria strains Chromobacterium violaceum CV026 and Escherichia coli [pSB1075], which respond to short- and long-chain acyl homoserine lactones, respectively. Phenotypic comparisons of isogenic ΔpsrA, ΔlasR, and ΔpsrAΔlasR mutants revealed that the reduced elastase, caseinase, and swarming activity in PAO1 [pMMBpsrA] were likely mediated through LasR. Additionally, electrophoretic mobility shift assays demonstrated that recombinant PsrA could bind to the lasR promoter at a 5'-AAACGTTTGCTT-3' sequence, which displays moderate similarity to the previously reported consensus PsrA binding motif. Furthermore, the PsrA effector molecule oleic acid inhibited PsrA binding to the lasR promoter and restored several quorum sensing-related phenotypes to wild-type levels. These findings suggest that PsrA regulates certain quorum-sensing phenotypes by negatively regulating lasR expression, with oleic acid acting as a crucial signaling molecule.

Ocimum sanctum as a Source of Quorum Sensing Inhibitors to Combat Antibiotic Resistance of Human and Aquaculture Pathogens.

Biofilms play a decisive role in the infectious process and the development of antibiotic resistance. The establishment of bacterial biofilms is regulated by a signal-mediated cell-cell communication process called "quorum sensing" (QS). The identification of quorum sensing inhibitors (QSI) to mitigate the QS process may facilitate the development of novel treatment strategies for biofilm-based infections. In this study, the traditional medicinal plant Ocimum sanctum was screened for QS inhibitory potential. Sub-MICs of the extract significantly affected the secretion of EPS in Gram-negative human pathogens such as Escherichia coli, Pseudomonas aeruginosa PAO1, Proteus mirabilis, and Serratia marcescens, as well as aquaculture pathogens Vibrio harveyi, V. parahaemolyticus, and V. vulnificus, which render the bacteria more sensitive, leading to a loss of bacterial biomass from the substratum. The observed inhibitory activity of the O. sanctum extract might be attributed to the presence of eugenol, as evidenced through ultraviolet (UV)-visible, gas chromatography-mass spectroscopy (GC-MS), Fourier transformer infrared (FTIR) spectroscopy analyses, and computational studies. Additionally, the QSI potential of eugenol was corroborated through in vitro studies using the marker strain Chromobacterium violaceum.

Ice nucleation active bacteria metabolites as antibiofilm agent to control Aeromonas hydrophila and Streptococcus agalactiae infections in Aquaculture

ObjectivesThe aim of this study was to quantify and identify metabolites of Ice Nucleation Active (INA) bacteria as an anti-biofilm agent against biofilms of fish pathogens such as Aeromonas hydrophila and Streptococcus agalactiae.ResultsIce nucleation active bacteria, which have the ability to catalyze ice nucleation, isolated from rainwater in previous studies, were used. All INA isolates were tested in several assays, including the antimicrobial test, which uses streptomycin as the positive control and none of the isolates were found positive in the antimicrobial test. As for the quorum quenching assay, it was found that four out of ten isolates were able to disturb the communication system in Chromobacterium violaceum wild type, which was used as the indicator bacteria. On the next assay, all ten isolates were tested for Biofilm Inhibition and Destruction and showed anti-biofilm activity with the highest percentage inhibition of 33.49% by isolate A40 against A. hydrophila and 77.26% by isolate A19 against S. agalactiae. C1 performed the highest destruction against A. hydrophila and S. agalactiae, with percentages of 32.11% and 51.88%, respectively. As for the GC-MS analysis, supernatants of INA bacteria contain bioactive compounds such as sarcosine and fatty acids, which are known to have antibiofilm activity against several biofilm-forming bacteria. Through 16s rRNA sequencing, identified bacteria are from the Pantoea, Enterobacter, and Acinetobacter genera. As for the conclusion, ice nucleation active bacteria metabolites tested showed positive results against pathogenic bacteria Aeromonas hydrophila and Streptococcus agalactiae in destructing and inhibiting biofilm growth.

Clinical Presentation and Outcomes Following Infection With Vibrio spp, Aeromonas spp, Chromobacterium violaceum, and Shewanella spp Water-Associated Organisms in Tropical Australia, 2015-2022.

Water-associated bacterial infections cause a wide spectrum of disease. Although many of these infections are typically due to human host commensal Staphylococcal or Streptococcal spp, water exposure can result in infections with environmental gram negatives such as Vibrio spp, Aeromonas spp, Chromobacterium violaceum, and Shewanella spp (collectively VACS). We performed a retrospective analysis of the epidemiology, clinical presentation, and outcomes of deep and superficial infections associated with VACS organisms in our health service between 1 January 2015 and 31 December 2023. We identified 317 patient episodes of infection with VACS organisms over this period. Of these, Aeromonas spp (63%) was the most common, followed by Vibrio spp (19%), Shewanella spp (13%), and C violaceum (5%). The majority were isolated from males (74.4%) and involved the lower limb (67.5%). Mild infections were more common than severe presentations, with only 15 (4.7%) admissions to the intensive care unit and 8 (2.5%) deaths. Colonization occurred in 6.9% of patients, in contrast to the perceived severity of some of these bacteria. Copathogens were common and included Staphylococcus aureus (48%) and enteric bacteria (57%). The majority of patients (60%) had no documented water exposure. Initial empiric antimicrobial therapy presumptively covered the susceptibilities of the isolated organisms in 47.3% of patients; however, a lack of VACS-covering empirical therapy was not associated with readmission. The isolation of a VACS organism in our setting was often not associated with documented water exposure, which has implications for empiric antimicrobial therapy. Severe disease and death were uncommon.

Multifunctional chitosan-cross linked- curcumin-tannic acid biocomposites disrupt quorum sensing and biofilm formation in pathogenic bacteria

Natural products have a long history of success in treating bacterial infections, making them a promising source for novel antibacterial medications. Curcumin, an essential component of turmeric, has shown potential in treating bacterial infections and in this study, we covalently immobilized curcumin (Cur) onto chitosan (CS) using glutaraldehyde and tannic acid (TA), resulting in the fabrication of novel biocomposites with varying CS/Cur/TA ratios. Comprehensive characterization of these ternary biocomposites was conducted using FTIR, SEM, XPS, and XRD to assess their morphology, functional groups, and chemical structures. The inhibitory efficacy of these novel biocomposites (n = 4) against the growth and viability of Pseudomonas aeruginosa (ATCC27853) and Chromobacterium violaceum (ATCC12472) was evaluated and the most promising composite (C3) was investigated for its impact on quorum sensing (QS) and biofilm formation in these bacteria. Remarkably, this biocomposite significantly disrupted QS circuits and effectively curtailed biofilm formation in the tested pathogens without inducing appreciable toxicity. These findings underscore its potential for future in vivo studies, positioning it as a promising candidate for the development of biofilm disrupting antibacterial agents.

Computational exploration of Picrasma quassioides compounds as CviR-mediated quorum sensing inhibitors against Chromobacterium violaceum.

Chromobacterium violaceum an opportunistic human pathogenic bacterium, exhibits resistance to conventional antibiotics by exploiting its quorum sensing mechanism to regulate virulence factor expression. In light of this, disrupting the quorum sensing mechanism presents a promising avenue for treating infections caused by this pathogen. The study focused on using the cytoplasmic quorum sensing receptor CviR from C. violaceum as a model target to identify novel quorum sensing inhibitors from P. quassioides through in silico computational approaches. Molecular docking analyses unveiled that several phytochemicals derived from Picrasma quassioides exhibit the potential to inhibit quorum sensing by binding to CviR protein. Notably, the compounds such as Quassidine I (- 8.8kcal/mol), Quassidine J (- 8.8kcal/mol), Kumudine B (- 9.1kcal/mol) and Picrasamide A (- 8.9kcal/mol) exhibited high docking scores, indicating strong binding affinity to the CviR protein. The native ligand C6-HSL (N-hexanoyl-L-homoserine lactone) as a positive control/co-crystal inhibitor also demonstrated a significant binding energy of-7.7kcal/mol. The molecular dynamics simulation for 200 ns showed the thermodynamic stability and binding affinity refinement of the top-ranked CviR inhibitor (Kumudine B) with its stable binding and minor fluctuations compared to positive control (C6-HSL). Pharmacokinetic predictions indicated that Kumudine B possesses favourable drug-like properties, which suggest its potential as a drug candidate. The study highlight Kumudine B as a potential agent for inhibiting the CviR protein in C. violaceum. The comprehensive evaluation of Kumudine B provides valuable insights into its pharmacological profiles, facilitating its assessment for diverse therapeutic applications and guiding future research activities, particularly as antibacterial agents for clinical drug development.

Bacillus Strains as Effective Biocontrol Agents Against Phytopathogenic Bacteria and Promoters of Plant Growth.

Modern crop production relies on the application of chemical pesticides and fertilizers causing environmental and economic challenges. In response, less environmentally impactful alternatives have emerged such as the use of beneficial microorganisms. These microorganisms, particularly plant growth-promoting bacteria (PGPB), have demonstrated their ability to enhance plant growth, protect against various stresses, and reduce the need for chemical inputs. Among the PGPB, Bacillus species have garnered attention due to their adaptability and commercial potential. Recent reports have highlighted Bacillus strains as biocontrol agents against phytopathogenic bacteria while concurrently promoting plant growth. We also examined Bacillus plant growth-promoting abilities in Arabidopsis thaliana seedlings. In this study, we assessed the potential of various Bacillus strains to control diverse phytopathogenic bacteria and inhibit quorum sensing using Chromobacterium violaceum as a model system. In conclusion, our results suggest that bacteria of the genus Bacillus hold significant potential for biotechnological applications. This includes developments aimed at reducing agrochemical use, promoting sustainable agriculture, and enhancing crop yield and protection.

Quorum quenching mediated biofilm impediment in Chromobacterium violaceum and Staphylococcus aureus by leaf extracts of Delonixelata

Biofilms are complex communities of microorganisms that cause systemic infections, resistance development and delay in healing wounds. Biofilms can form in various parts of the human body, such as the teeth, lungs, urinary tract, and wounds. Biofilm complicates the effects of antibiotics in treating infections. In search of a cure, a plant-based phyto component was selected for this investigation as an anti-quorum-mediated biofilm restricting agent in Gram-negative Chromobacterium violaceum and Gram-positive Staphylococcus aureus. The bioactive components in Delonix elata (DE) ethyl acetate extract were identified using Gas chromatography and mass spectrometry. The extract was examined for toxicity using 3T3 cell lines and brine shrimp and ascertained to be non-toxic. Violacein was inhibited up to 68.81 % in C. violaceum at 0.6 mg/ml concentration. Hemolysin synthesis impediments in C. violaceum and S. aureus were 80 % and 51.35 %, respectively, at 0.6 mg/ml of DE extract. At 0.6 mg/ml, EPS was abated by up to 49 % in C. violaceum and 35.26 % in S. aureus. DE extract prevented biofilm formation in C. violaceum and S. aureus up to 76.45 % and 58.15 %, respectively, while associated eDNA was suppressed up to 67.50 % and 53.47 % at the respective sub-MIC concentrations. Expression of genes such as cviI, cviR, vioA, vioB, and vioE were dramatically reduced in C. violaceum, while genes such as agrA, sarA, fnbA, and fnbB were significantly reduced in S. aureus. Docking demonstrates that two or more DE molecules bind efficiently to the QS receptors of C. violaceum and S. aureus. Thus, DE extract can be investigated for therapeutic purposes against pathogenic microorganisms by rendering them less virulent through quorum quenching mediated action.

Biological activities of Elaeagnus umbellata methanol extract

Elaeagnus umbellata, known as Autumn olive and growing widely in Asia and Southern Europe, is a shrub tree used in the traditional treatment of many diseases, including cancer. In this study, it was aimed to investigate the several biological effects of methanol extract of E. umbellate. The activity of the extract on 11 microorganisms was determined by the agar well diffusion technique. The anti-quorum sensing activity of the extract was tested using Chromobacterium violaceum ATCC 12472. The anti-biofilm and anti-swarming activities were tested using Pseudomonas aeruginosa PAO1. Cytotoxic effect of the extract against pancreatic tumoral cell line (AR42J), breast cancer cell line (MDA-MB-231), lung adenocarcinoma cell line (A549), and normal epithelial cell line (Vero), and antiviral effect of the extract against herpes simplex virus type 1 was analyzed using the MTT method. It was determined that the extract was moderately effective against 6/11 microorganisms and showed anti-quorum sensing activity. While the extract did not have a cytotoxic effect on cancer cell lines, it was found to have a cytotoxic effect on Vero cells at concentrations of 100 µg/mL and above. However, no anti-biofilm, anti-swarming, and antiviral activity of the extract was observed. The study shows that E. umbellata fruit has limited biological activity.

Linalool Reduces Virulence and Tolerance to Adverse Conditions of Listeria monocytogenes.

Listeria monocytogenes, a foodborne pathogen causing listeriosis, poses substantial societal, economic, and public health challenges due to its resistance, persistence, and biofilm formation in the food industry. Exploring subinhibitory concentrations of compounds to target virulence inhibition and increase susceptibility to adverse conditions presents a promising strategy to mitigate its impact of L. monocytogenes and unveils new potential applications. Thus, this study aims to explore the effect of linalool on virulence factors of L. monocytogenes and potential use in the reduction in its tolerance to stressful conditions. This action was analysed considering the use of two sub-inhibitory concentrations of linalool, 0.312 and 0.625 mg/mL. We found that even with the lowest tested concentrations, a 65% inhibition of violacein production by Chromobacterium violaceum, 55% inhibition in biofilm formation by L. monocytogenes and 62% reduction on haemolysis caused by this bacterium were observed. In addition to its impact on virulence factors, linalool diminished the tolerance to osmotic stress (up to 4.3 log reduction after 24 h with 12% NaCl), as well as to high (up to 3.8 log reduction after 15 min at 55 °C) and low temperatures (up to 4.6 log reduction after 84 days with 12% NaCl at 4 °C). Thus, this study paves the way to further investigation into the potential utilization of linalool to mitigate the threat posed by L. monocytogenes in the field of food safety and public health.

Clinical presentation and treatment of 2 patients with infection caused by Chromobacterium violaceum in Vietnam

Chromobacterium violaceum is a rare but severe and often fatal cause of disease in humans. We present 2 clinical cases of sepsis and skin abscesses / cellulitis caused by C. violaceum seen in a referral hospital for infectious diseases in Vietnam. Both patients survived, but appropriate antibiotic treatment was only installed after culture of the organism. We reviewed and summarised the characteristics of C. violaceum infection and treatment.

Aerobic Vaginal Microflora in Gestational and Non-Gestational Bitches (Canis lupus familiaris).

The vaginal tract comprises commensal microorganisms, which play an essential role in the health of the reproductive tract. Any dysbiosis in the vaginal microenvironment may lead to severe urinary tract infections or even infertility. This study aimed to evaluate the aerobic bacterial flora isolated from vaginal samples from 100 lactating bitches in the antepartum period (n = 3), postpartum period (n = 80), and with Lactatio sine graviditate (n = 17). Before vaginal swabs, all the bitches went through a gynecology consult, along with milk and blood sampling. Standard microbiological techniques were used for bacterial isolation. Among the 100 vaginal samples analyzed, 82% had a positive microbiological outcome, while 18% were negative. The microbiologic profile listed 17 different genera. The main isolated bacterial families were Micrococcaceae, Staphylococcaceae, Morganellaceae, Bacillaceae, and Rhizobiaceae. At the same time, strains like Agrobacterium radiobacter, Ochrobactrum anthropi, Chromobacterium violaceum, Burkholderia mallei, Bacillus pumllus, or Staphylococcus xylosus were isolated for the first time from the vaginal secretion of lactating bitches. The microbiological data demonstrates that lactating bitches' vaginal discharge is heterogeneous and may be affected by coitus, sampling season, age, and reproductive status.

Isolation and characterization of thymoquinone from Nigella sativa essential oil: antioxidant and antibacterial activities, molecular modeling studies, and cytotoxic effects on lung cancer A549 cells

Thymoquinone (TQ), a bioactive compound found in Nigella sativa seeds, has gained considerable attention due to its potential therapeutic properties. This study aimed to isolate and characterize TQ from Nigella sativa essential oil and evaluate its antioxidant capacity, antibacterial activity, and cytotoxic effects on lung cancer A549 cells. Moreover, The binding potential of TQ to Keap1 (Kelch-like ECH associated protein 1) was investigated through molecular docking. The stability of the resulting complex was evaluated through molecular dynamics (MD) simulation. The CUPRAC assay revealed significant antioxidant capacity of TQ, as indicated by its high molar absorptivity coefficient. TQ also demonstrated notable free radical scavenging activity, with efficacy increasing with concentration. In terms of antiquorum sensing activity, TQ displayed effectiveness against all tested virulence factors in P. aeruginosa PAO1 and Chromobacterium violaceum in different range. Additionally, TQ induced cytotoxicity in non-small lung cancer cells, inhibiting cell viability. In conclusion, this study successfully isolated and characterized TQ from Nigella sativa seeds and demonstrated its remarkable antioxidant capacity, antibacterial activity, and cytotoxic effects on lung cancer cells. These findings suggest the potential of TQ for various applications in the food and pharmaceutical industries. The wet-lab study demonstrated that TQ had an antioxidant effect. The TQ was found to have high binding potential to Keap1 as it formed four conventional hydrogen bonds with the protein. The resulting Keap1-TQ complex was also found to be stable. Further research is warranted to explore the therapeutic potential of TQ and develop novel treatments based on its properties.

Biogenic synthesis of Psidium guajava‐mediated silver nanoparticles: A comprehensive antibiofilm and antivirulence study

AbstractIn this study, at sub‐MIC, the efficacy of green synthesized Psidium guajava‐mediated silver nanoparticles (Pg@AgNPs) in inhibiting quorum sensing facilitated virulence factors and suppressing biofilm formation was evaluated against clinical multidrug resistant (MDR) isolates, specifically Chromobacterium violaceum MCC‐2290 and Pseudomonas aeruginosa PAO1. The AgNPs were synthesized by adding the leaf extract to a solution of silver nitrate, and the reduction of Ag+ ions to Ag0 was confirmed by the appearance of brown color. The Pg@AgNPs were characterized using Fourier transform infrared (FTIR), UV/Vis spectroscopy, TEM, and XRD. The UV/Vis spectrum showed the characteristic absorption peak of Pg@AgNPs in the range of 350–480 nm. FTIR analysis substantiated the existence of functional groups implicated in the synthesis and stabilization of AgNPs. The XRD analysis elucidated the crystalline characteristics of the nanoparticles. The TEM images further confirmed the spherical shape and size of the nanoparticles, which ranged between 5 and 25 nm. The AgNPs demonstrated notable antibacterial efficacy against C. violaceum and P. aeruginosa. Moreover, the Pg@AgNPs effectively suppressed both biofilm formation and the production of quorum sensing‐mediated virulence factors such as pyoverdin (77.2%), pyocyanin (78.12%), and violacein (83.4%). Additionally, the Pg@AgNPs demonstrated broad‐spectrum activity against biofilm formation, showing the biofilm inhibition in C. violaceum and P. aeruginosa by 81.86% and 87.89%, respectively. Under light microscopy, it is also observed that Pg@AgNPs reduce the formation of biofilm in both tested bacteria. The present finding highlights the potential of green‐synthesized AgNPs using P. guajava leaf extract as antimicrobial agents with potential applications in combating bacterial infections and biofilm‐related diseases.

Anti-Biofilm and Anti-Quorum-Sensing Activity of Inula Extracts: A Strategy for Modulating Chromobacterium violaceum Virulence Factors.

The formation of microbial biofilm is a self-organizing process among bacterial cells, regulated by quorum-sensing (QS) mechanisms, contributing to development of infections. These processes, either separately or in combination, significantly contribute to bacterial resistance to antibiotics and disinfectants. A novel approach to addressing the challenge of treating infections due to antibacterial resistance involves the use of plant metabolites. In recent years, there has been increasing recognition of different phytochemicals as potential modulators. In our study, we evaluated the synergistic effect of chloroform and methanol extracts from Inula species against key virulence factors, including biofilm formation, violacein production, and swarming motility. Each of the 11 examined plant extracts demonstrated the ability to reduce biofilms and pigment synthesis in C. violaceum. Two of the extracts from I. britannica exhibited significant anti-biofilm and anti-quorum-sensing effects with over 80% inhibition. Their inhibitory effect on violacein synthesis indicates their potential as anti-QS agents, likely attributed to their high concentration of terpenoids (triterpenoids, sesquiterpene lactones, and diterpenoids). Scanning electron microscopy revealed a notable reduction in biofilm biomass, along with changes in biofilm architecture and cell morphology. Additionally, fluorescence microscopy revealed the presence of metabolically inactive cells, indicating the potent activity of the extracts during treatment. These new findings underscore the effectiveness of the plant extracts from the genus Inula as potential anti-virulent agents against C. violaceum. They also propose a promising strategy for preventing or treating its biofilm formation.

An In-Depth Study on the Inhibition of Quorum Sensing by Bacillus velezensis D-18: Its Significant Impact on Vibrio Biofilm Formation in Aquaculture.

Amid growing concerns about antibiotic resistance, innovative strategies are imperative in addressing bacterial infections in aquaculture. Quorum quenching (QQ), the enzymatic inhibition of quorum sensing (QS), has emerged as a promising solution. This study delves into the QQ capabilities of the probiotic strain Bacillus velezensis D-18 and its products, particularly in Vibrio anguillarum 507 communication and biofilm formation. Chromobacterium violaceum MK was used as a biomarker in this study, and the results confirmed that B. velezensis D-18 effectively inhibits QS. Further exploration into the QQ mechanism revealed the presence of lactonase activity by B. velezensis D-18 that degraded both long- and short-chain acyl homoserine lactones (AHLs). PCR analysis demonstrated the presence of a homologous lactonase-producing gene, ytnP, in the genome of B. velezensis D-18. The study evaluated the impact of B. velezensis D-18 on V. anguillarum 507 growth and biofilm formation. The probiotic not only controls the biofilm formation of V. anguillarum but also significantly restrains pathogen growth. Therefore, B. velezensis D-18 demonstrates substantial potential for preventing V. anguillarum diseases in aquaculture through its QQ capacity. The ability to disrupt bacterial communication and control biofilm formation positions B. velezensis D-18 as a promising eco-friendly alternative to conventional antibiotics in managing bacterial diseases in aquaculture.

Exploring the effects of honey's anti-quorum sensing activity on bacterial cell membrane

In recent years, honey is being assayed in the food industry to inhibit communication between pathogenic microorganisms. One strategy to attack antibiotic resistant strain is by the development of new ways that reduced the virulence expression. Here, we evaluated the anti-Quorum Sensing (QS) activity of multi-floral honeys using Chromobacterium violaceum. The disruption of the cell membrane was confirmed through FT-IR spectroscopy, hydrophobicity, and Scanning Electron Microscopy (SEM). Shifts in the frequency of the main peaks (cm−1), showed that bioactive compounds from honey affected the structure of the C. violaceum membrane. The most significant changes were observed at the membrane proteins and lipids level. The polarity of the cell membrane affects the diffusion of the inducing molecules. Supporting the changes in hydrophobicity, SEM revealed alterations in the appearance of the cell surface. Consequently, honey contributes to avoid bacterial injury by the disruption of membrane, and hence, cell communication and virulence.

Effect of a phthalate derivative purified from Bacillus zhangzhouensis SK4 on quorum sensing regulated virulence factors of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes life-threatening diseases and is resistant to almost all conventional antibiotics. The quorum sensing (QS) system of P. aeruginosa contributes to many pathogenic factors some of which are pigment production, motility, and biofilm. The disruption of quorum sensing system may be an impactful strategy to deal with infections. The present study investigates the anti-quorum sensing property of a bioactive molecule extracted from marine epibiotic bacteria present on the surface of seaweeds. Among all the isolates tested against monitor strain Chromobacterium violaceum (MTCC 2656), the one with the highest activity was identified as Bacillus zhangzhouensis SK4. The culture supernatant was extracted with chloroform which was then partially purified by TLC and column chromatography. The probable anti-QS compound was identified as 1,2-benzenedicarboxylic acid, bis (2-methylpropyl ester) by GC-MS and NMR analysis. The treatment of P. aeruginosa MCC 3457 with the lead compound resulted in the reduced production of pyocyanin, rhamnolipids, exopolysaccharide, biofilm, and motility. The observations of light and scanning electron microscopy also supported the biofilm inhibition. The lead compound showed synergism with the meropenem antibiotic and significantly reduced MIC. The molecular docking and pharmacokinetics study predicted 1, 2-benzenedicarboxylic acid, bis (2-methylpropyl ester), a phthalate derivative as a good drug candidate. The molecular dynamics study was also performed to check the stability of the lead compound and LasR complex. Further, lead compounds did not exhibit any cytotoxicity when tested on human embryonic kidney cells. As per our knowledge, this is the first report on the anti-QS activity of B. zhangzhouensis SK4, indicating that epibiotic bacteria can be a possible source of novel compounds to deal with the multidrug resistance phenomenon.

CHEMICAL COMPOSITION AND BIOACTIVITIES OF ESSENTIAL OIL FROM AN ENDEMIC SALVIA ABSCONDITIFLORA GREUTER & BURDET

Objective: The study aimed to determine the chemical composition and antibacterial, antibiofilm, and anti-quorum sensing activities of the essential oil of Salvia absconditiflora Greuter & Burdet (an endemic species) growing wildly in Türkiye. Material and Method: The essential oil from the aerial parts of the plant was obtained by hydro-distillation (0.4%) and analyzed by GC-FID and GC-MS. In addition, the broth microdilution method was used to determine antibacterial activity. The crystal violet assay was performed for antibiofilm activity, and the reporter bacteria Chromobacterium violaceum ATCC 12472 was used in the anti-quorum sensing activity test. Result and Discussion: The major components of the essential oil were identified as 1,8-cineole (32.2%), camphor (13.6%), α-pinene (7.6%), camphene (5.5%), and viridiflorol (5.1%). The essential oil showed the best antibacterial activity against Gram-positive test bacteria, with a minimum inhibitory concentration (MIC) of 0.0078 (v/v) against Staphylococcus aureus strains. The percentage biofilm inhibition value of the essential oil was determined as 84.4%. The inhibition of violacein production by the essential oil in Chromobacterium violaceum ATCC 12472 indicated the possibility of anti-quorum sensing activity. The results of this study show that the essential oil of S. absconditiflora could be a promising alternative in fighting bacterial infections.

2,3-Dimethoxycinnamic Acid from a Marine Actinomycete, a Promising Quorum Sensing Inhibitor in Chromobacterium violaceum.

An ethyl acetate extract of a marine actinomycete strain, Nocardiopsis mentallicus SCSIO 53858, isolated from a deep-sea sediment sample in the South China Sea, exhibited anti-quorum-sensing (QS) activity against Chromobacterium violaceum CV026. Guided by the anti-QS activity, a novel active compound was isolated and purified from the extract and was identified as 2,3-dimethoxycinnamic acid (2,3-DCA) through spectral data analysis. At a concentration of 150 μg/mL, 2,3-DCA exhibited robust inhibitory effects on three QS-regulated traits of C. violaceum CV026: violacein production, swarming motility, and biofilm formation, with inhibition rates of 73.9%, 65.9%, and 37.8%, respectively. The quantitative reverse transcription polymerase chain reaction results indicated that 2,3-DCA can disrupt the QS system in C. violaceum CV026 by effectively suppressing the expression of QS-related genes, including cviR, vioA, vioB, and vioE. Molecular docking analysis revealed that 2,3-DCA hinders the QS system by competitively binding to the same binding pocket on the CviR receptor as the natural signal molecule N-hexanoyl-L-homoserine lactone. Collectively, these findings suggest that 2,3-DCA exhibits promising potential as an inhibitor of QS systems, providing a potential solution to the emerging problem of bacterial resistance.