Exploring rose absolute and phenylethyl alcohol as novel quorum sensing inhibitors in Pseudomonas aeruginosa and Chromobacterium violaceum.

Inter-cellular signaling, referred to as quorum sensing (QS), regulates the production of virulence factors in numerous gram-negative bacteria, such as the human pathogens Pseudomonas aeruginosa and Chromobacterium violaceum. QS inhibition may provide an opportunity for the treatment of bacterial infections. This represents the initial study to examine the antibiofilm and antivirulence capabilities of rose absolute and its primary component, phenylethyl alcohol. QS inhibition was assessed by examining extracellular exopolysaccharide synthesis, biofilm development, and swarming motility in P. aeruginosa PAO1, along with violacein production in C. violaceum ATCC 12472. Molecular docking analysis was conducted to explore the mechanism by which PEA inhibits QS. Our results indicate that rose absolute and PEA caused decrease in EPS production (60.5-33.5%), swarming motility (94.7-64.5%), and biofilm formation (98.53-55.5%) in the human pathogen P. aeruginosa PAO1. Violacein production decreased by 98.1% and 62.5% with an absolute (0.5 v/v %) and PEA (2 mM). Moreover, the molecular docking analysis revealed a promising competitive interaction between PEA and AHLs. Consequently, this study offers valuable insights into the potential of rose absolute and PEA as inhibitors of QS in P. aeruginosa and C. violaceum.

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.

In Situ Spatiotemporal SERS Profiling of Bacterial Quorum Sensing by Hierarchical Hydrophobic Plasmonic Arrays in Agar Medium.

A feedback inhibition effect of high autoinducer levels on metabolite secretion in Chromobacterium subtsugae (C. subtsugae) was evidenced by in situ spatiotemporal surface-enhanced Raman spectroscopy (SERS) profiling. The hierarchical hydrophobic plasmonic array in agar medium is structured by oil/water/oil (OL/W/OH) triphasic interfacial self-assembly. The hydrophobic layer acts as a "door curtain" to selectively permit adsorption of a quorum sensing (QS)-regulated fat-soluble metabolite, i.e., violacein (Vio), and significantly blocks nonspecific adsorption of water-soluble proteins, etc. The SERS profiling clearly evidences that the diffusion of N-hexanoyl-l-homoserine lactone (C6-HSL) in agar medium quickly triggers the initial synthesis of Vio in C. subtsugae CV026 but surprisingly inhibits the intrinsic synthesis of Vio in C. subtsugae ATCC31532. The latter negative response might be related to the VioS repressor of ATCC31532, which negatively controls violacein production without influencing the expression of the CviI/R QS system. Moreover, two sender-receiver systems are constructed by separately coculturing CV026 or ATCC31532 with Hafnia alvei H4 that secretes large amounts of C6-HSL. Expectedly, the cocultivation similarly triggers the initial synthesis of Vio in CV026 but seems to have a quite weak negative effect on the intrinsic synthesis in ATCC31532. In fact, the negative regulation in ATCC31532 might be affected by a diffusion-dependent concentration effect. The H4 growth and its secretion of C6-HSL are a slow and continuous process, thereby avoiding the gathering of local high concentrations. Overall, our study put forward an in situ SERS strategy as an alternative to traditional bioluminescent tools for highly sensitively analyzing the spatiotemporal communication and cooperation in live microbial colonies.

The Zinc Transporter ZnuABC Is Critical for the Virulence of Chromobacterium violaceum and Contributes to Diverse Zinc-Dependent Physiological Processes.

Chromobacterium violaceum is a ubiquitous environmental bacterium that causes sporadic life-threatening infections in humans. How C. violaceum acquires zinc to colonize environmental and host niches is unknown. In this work, we demonstrated that C. violaceum employs the zinc uptake system ZnuABC to overcome zinc limitation in the host, ensuring the zinc supply for several physiological demands. Our data indicated that the C. violaceum ZnuABC transporter is encoded in a zur-CV_RS15045-CV_RS15040-znuCBA operon. This operon was repressed by the zinc uptake regulator Zur and derepressed in the presence of the host protein calprotectin (CP) and the synthetic metal chelator EDTA. A ΔznuCBA mutant strain showed impaired growth under these zinc-chelated conditions. Moreover, the deletion of znuCBA provoked reductions in violacein production, swimming motility, biofilm formation, and bacterial competition. Remarkably, the ΔznuCBA mutant strain was highly attenuated for virulence in an in vivo mouse infection model and showed low capacities to colonize the liver, grow in the presence of CP, and resist neutrophil killing. Overall, our findings demonstrate that ZnuABC is essential for C. violaceum virulence, contributing to subversion of zinc-based host nutritional immunity.

4-methoxybenzalacetone, the cinnamic acid analog as a potential quorum sensing inhibitor against Chromobacterium violaceum and Pseudomonas aeruginosa.

The continuous increase in the incidence of infectious diseases and the rapid unchecked rise in multidrug-resistance to conventional antibiotics have led to the search for alternative strategies for treatment and clinical management of microbial infections. Since quorum sensing (QS) regulates numerous virulence determinants and pathogenicity in bacteria, inhibition of QS promises to be an attractive target for development of novel therapeutics. In this study, a series of cinnamic acid analogs and benzalacetone analogs were designed and synthesized, and their QS-inhibitory activities explored. We found that, among the test compounds, 4-methoxybenzalacetone (8) exhibited potent anti-quorum sensing property, as evidenced by inhibition of QS-controlled violacein production of Chromobacterium violaceum ATCC12472. The inhibitory activity of such a compound, which was the methyl keto analog of the corresponding cinnamic acid, was not only stronger than the parent cinnamic acid (1), but also superior to that of furanone, the reference drug. Based on our observations, its mechanism of quorum sensing inhibition is likely to be mediated by interference with N-acyl-homoserine lactones (AHL) synthesis. Moreover, 4-methoxybenzalacetone (8) also suppressed the production of pyocyanin, rhamnolipids and swarming motility of Pseudomonas aeruginosa, suggesting a broad spectrum of anti-QS activities of this compound. In terms of structure-activity relationship, the possible chemical substitutions on the scaffold of cinnamic acid required for QS inhibitory activity are also discussed. Since 4-methoxybenzalacetone (8) showed no toxicity to both bacteria and mammalian cells, our findings therefore indicate the anti-QS potential of this compound as a novel effective QS inhibitor.

Micro and nanoemulsions of Carissa spinarum fruit polyphenols, enhances anthocyanin stability and anti-quorum sensing activity: Comparison of degradation kinetics.

The low stability of anthocyanins is a constraint in the food industry. The present work has been carried out to overcome this low stability by encapsulating fruit concentrate of underutilized plant Carissa spinarum (CS) with polyphenols in microemulsions (CSME) and nanoemulsions (CSNE). Increasing the amount of CS reduced the particle size from 1154 to 70-300 nm whereas addition of Tween 80 reduced it optimally to 5-25 nm. Degradation of anthocyanins in control and ME/NE proceeded with zero- and first-order reaction rates, respectively, at 28 °C (half-life 6, 25 and 40 days, respectively). The degradation kinetics of phenolics-flavonoids were also studied. CSNE exhibited higher anti-quorum sensing (QS) activity than CSME against Chromobacterium violaceum (73.7%); it inhibited biofilm formation by 70.1 and 64.4% in Pseudomonas aeruginosa, and Yersinia enterocolitica, respectively. This is the first report of using the more stable ME/NE to study anti-QS activity, an alternative to conventional antibiotics.

Microbial exopolysaccharide production of Streptococcus thermophilus and its antiquorum sensing activity.

Interest in the production of exopolysaccharides by microorganisms has increased in the recent years. Using low-cost product is the main step of microbial production to reduce cost and compete with chemical production. In this work, EPS production of Streptococcus thermophilus isolates from yogurt (S2), kefir (S3), and S. thermophilus ATCC 19258 (S1) isolate which was used as control strains were investigated by using different fruit pulps. S. thermophilus isolates were identified by morphological and 16S sequence analysis. The amount of EPS obtained was measured spectrophotometrically using glucose as standard with phenol sulfuric acid method. All three isolates produced higher amounts of EPS on M17 medium than Nutrient medium. When the fruit pulp was added to the medium, EPS production increased in all three isolates. When different nitrogen sources were added together with fruit pulp juice, EPS production increased. The highest amount of EPS produced by ATCC 19258 strain (21.570 mg/L) and S3 isolate (29.131 mg/L) is the medium where mixed fruit pulp juice and nitrogen source is tryptophan. It has been shown that EPS production is increased by adding fruit pulps to the prepared media. It is thought that apricot pulp can be a good alternative in EPS production especially in the evaluation of wastes. Also, antiquorum sensing activity of the highest amount EPS was determined by using Chromobacterium violaceum CV026 strain and found effective on violacein pigment inhibition and C6-AHL production of biosensor strain.

Disrupting quorum sensing alters social interactions in Chromobacterium violaceum.

Quorum sensing (QS) is a communication system used by bacteria to coordinate a wide panel of biological functions in a cell density-dependent manner. The Gram-negative Chromobacterium violaceum has previously been shown to use an acyl-homoserine lactone (AHL)-based QS to regulate various behaviors, including the production of proteases, hydrogen cyanide, or antimicrobial compounds such as violacein. By using combined metabolomic and proteomic approaches, we demonstrated that QS modulates the production of antimicrobial and toxic compounds in C. violaceum ATCC 12472. We provided the first evidence of anisomycin antibiotic production by this strain as well as evidence of its regulation by QS and identified new AHLs produced by C. violaceum ATCC 12472. Furthermore, we demonstrated that targeting AHLs with lactonase leads to major QS disruption yielding significant molecular and phenotypic changes. These modifications resulted in drastic changes in social interactions between C. violaceum and a Gram-positive bacterium (Bacillus cereus), a yeast (Saccharomyces cerevisiae), immune cells (murine macrophages), and an animal model (planarian Schmidtea mediterranea). These results underscored that AHL-based QS plays a key role in the capacity of C. violaceum to interact with micro- and macroorganisms and that quorum quenching can affect microbial population dynamics beyond AHL-producing bacteria and Gram-negative bacteria.

Screening and quantification of anti-quorum sensing and antibiofilm activity of Actinomycetes isolates against food spoilage biofilm-forming bacteria.

BACKGROUND: Biofilms can form in many industries, one of them is the food industry. The formation of biofilms in this industry could cause immense economic losses and endanger public health. Biofilms formation is mainly triggered by quorum sensing. Therefore, inhibition of quorum sensing could be an innovative approach to inhibit the formation of biofilms. One way to inhibit quorum sensing is by using anti-quorum sensing compounds. Actinomycetes are a group of bacteria that is acknowledged to produce these compounds. RESULTS: There were eight crude extracts of Actinomycetes isolates that showed promising anti-quorum sensing activity against Chromobacterium violaceum. The concentration of the crude extracts was 20 mg/mL. All the crude extracts showed no antibacterial activity against food spoilage bacteria, except for crude extracts of isolate 18 PM that showed antibacterial activity against Bacillus subtilis. They also showed various antibiofilm activity, both inhibition and destruction. The highest inhibition and destruction activity sequentially was done by crude extracts of isolate 12 AC with 89.60% against Bacillus cereus and crude extracts of isolate SW03 with 93.06% against Shewanella putrefaciens. CONCLUSIONS: Actinomycetes isolates that isolated from different regions in Indonesia can be used as potential candidates to overcome biofilms formed by food spoilage bacteria using their ability to produce anti-quorum sensing compounds.

Citral and its derivatives inhibit quorum sensing and biofilm formation in Chromobacterium violaceum.

With an upsurge in multidrug resistant bacteria backed by biofilm defence armours, there is a desperate need of new antibiotics with a non-traditional mechanism of action. Targeting bacteria by misguiding them or halting their communication is a new approach that could offer a new way to combat the multidrug resistance problem. Quorum sensing is considered to be the achilles heel of bacteria that has a lot to offer. Since, both quorum sensing and biofilm formation have been related to drug resistance and pathogenicity, in this study we synthesised new derivatives of citral with antiquorum sensing and biofilm disrupting properties. We previously reported antimicrobial and antiquorum sensing activity of citral and herein we report the synthesis and evaluation of citral and its derivatives (CD1-CD3) for antibacterial, antibiofilm and antiquorum sensing potential against Chromobacterium violaceum using standard methods. Preliminary results revealed that CD1 is the most active of all the derivatives. Qualitative and quantitative evaluation of antiquorum sensing activity at sub-inhibitory concentrations of these compounds also revealed high activity for CD1 followed by CD2, CD3 and citral. These compounds also inhibit biofilm formation at subinhibitory concentrations without causing any bacterial growth inhibition. These results were replicated by RT-qPCR with down regulation of the quorum sensing genes when C. violaceum was treated with these test compounds. Overall, the results are quite encouraging, revealing that biofilm and quorum sensing are interrelated processes and also indicating the potential of these derivatives to impede bacterial communication and biofilm formation.

Screening of antibiofilm and anti-quorum sensing activty of Actinomycetes isolates extracts against aquaculture pathogenic bacteria.

BACKGROUND: Indonesia is the third largest producer of fish and other aquaculture products in the world, making this industry a major contributor in the economy of Indonesia. However, this industry continually overcome challenges, one of them are bacterial outbreaks. In addition, the emergence of these bacterial outbreaks were worsen due to the biofilm produced by many significant pathogenic bacteria and the impact of increased antibiotic resistance. These issues have become a global concern, because antibiotics are currently one of the main treatments available to overcome this problems. Therefore, studies aimed at finding and characterizing bioactive compounds to combat these issues. In this study actinomycetes isolates were screened and characterized for their bioactive compounds produced which have inhibitory and destructive activity and also QS inhibitors against biofilm structure of aquatic pathogenic bacteria, such as Vibrio harveyi, A. hydrophila, and S. agalactiae. RESULT: Extracts (20 mg/mL) produced by sixteen Actinomycetes isolates showed anti-quorum sensing activity towards reporter stain Chromobacterium violaceum wild-type. Most of these extracts showed better inhibitory activity on all of the pathogenic bacteria biofilm structure tested than the destructive activity on the preformed of those biofilm structure. Subsequently, we also performed characterization of bioactive compound and found that in this study, polysaccharide is the most common antibiofilm agents, which were responsible to their antibiofilm activity. Finally, we found that the value of LC50 of all extracts tested were more than 1 mg/mL, thereby all of extracts tested did not show cyto-toxic effect against Artemia salina. CONCLUSION: All of the extracts of Actinomycetes isolates showed promising inhibitory activity towards biofilm structure of pathogenic bacteria tested. So far, all of the extracts are potential to be QS inhibitors and antibiofilm agents of all pathogenic bacteria tested.

Infection of highly insecticide-resistant malaria vector Anopheles coluzzii with entomopathogenic bacteria Chromobacterium violaceum reduces its survival, blood feeding propensity and fecundity.

BACKGROUND: This is now a concern that malaria eradication will not be achieved without the introduction of novel control tools. Microbiological control might be able to make a greater contribution to vector control in the future. The interactions between bacteria and mosquito make mosquito microbiota really promising from a disease control perspective. Here, the impact of Chromobacterium violaceum infections, isolated from both larvae and adult of wild-caught Anopheles gambiae sensu lato mosquitoes in Burkina Faso, was evaluated on mosquito survival, blood feeding and fecundity. METHODS: To assess entomopathogenic effects of C. violaceum infection on mosquitoes, three different types of bioassays were performed in laboratory. These bioassays aimed to evaluate the impact of C. violaceum infection on mosquito survival, blood feeding and fecundity, respectively. During bioassays mosquitoes were infected through the well-established system of cotton ball soaked with 6% glucose containing C. violaceum. RESULTS: Chromobacterium violaceum kills pyrethroid resistant Anopheles coluzzii (LT80 of 8.78 days ± 0.18 at 108 bacteria cell/ml of sugar meal). Interestingly, this bacterium had other negative effects on mosquito lifespan by significantly reducing (~ 59%, P < 0.001) the mosquito feeding willingness from day 4-post infection (~ 81% would seek a host to blood feed) to 9- day post infection (22 ± 4.62% would seek a host to blood feed). Moreover, C. violaceum considerably jeopardized the egg laying (~ 16 eggs laid/mosquito with C. violaceum infected mosquitoes vs ~ 129 eggs laid/mosquito with control mosquitoes) and hatching of mosquitoes (a reduction of ~ 22% of hatching rate with C. violaceum infected mosquitoes). Compared to the bacterial uninfected mosquitoes, mosquitoes infected with C. violaceum showed significantly higher retention rates of immature eggs and follicles. CONCLUSION: These data showed important properties of Burkina Faso C. violaceum strains, which are highly virulent against insecticide-resistant An. coluzzii, and reduce both mosquito blood feeding and fecundity propensities. However, additional studies as the sequencing of C. violaceum genome and the potential toxins secreted will provide useful information render it a potential candidate for the biological control strategies of malaria and other disease vectors.

Phenotypic detection of quorum sensing inhibition in Pseudomonas aeruginosa pyoverdine and swarming by volatile organic products.

Aim: To determine phenotypically the anti quorum-sensing (QS) activity of 30 volatile organic products (VOPs) through the inhibition of swarming motility and pyoverdine production in Pseudomonas aeruginosa. Materials & methods: Twenty-four essential oils and six small volatile organic compounds randomly selected were screened for their anti-QS activity by violacein inhibition on Chromobacterium violaceum. The VOPs with positive results were subsequently evaluated for swarming motility and pyoverdine production on P. aeruginosa determining the colony diameter and fluorescence under UV light, respectively. Results: Fifty percent of VOPs tested showed strong violacein inhibition, 40% presented anti-swarming activity and 33% inhibited pyoverdine production. Conclusion: Our data demonstrate that VOPs have a great potential to inhibit virulence factors mediated by QS in P. aeruginosa.

Ferric Uptake Regulator Fur Coordinates Siderophore Production and Defense against Iron Toxicity and Oxidative Stress and Contributes to Virulence in Chromobacterium violaceum.

Iron is a highly reactive metal that participates in several processes in prokaryotic and eukaryotic cells. Hosts and pathogens compete for iron in the context of infection. Chromobacterium violaceum, an environmental Gram-negative bacterial pathogen, relies on siderophores to overcome iron limitation in the host. In this work, we studied the role of the ferric uptake regulator Fur in the physiology and virulence of C. violaceum A Δfur mutant strain showed decreased growth and fitness under regular in vitro growth conditions and presented high sensitivity to iron and oxidative stresses. Furthermore, the absence of fur caused derepression of siderophore production and reduction in swimming motility and biofilm formation. Consistent with these results, the C. violaceum Δfur mutant was highly attenuated for virulence and liver colonization in mice. In contrast, a manganese-selected spontaneous fur mutant showed only siderophore overproduction and sensitivity to oxidative stress, indicating that Fur remained partially functional in this strain. We found that mutations in genes related to siderophore biosynthesis and a putative CRISPR-Cas locus rescued the Δfur mutant growth defects, indicating that multiple Fur-regulated processes contribute to maintaining bacterial cell fitness. Overall, our data indicated that Fur is conditionally essential in C. violaceum mainly by protecting cells from iron overload and oxidative damage. The requirement of Fur for virulence highlights the importance of iron in the pathogenesis of C. violaceumIMPORTANCE Maintenance of iron homeostasis, i.e., avoiding both deficiency and toxicity of this metal, is vital to bacteria and their hosts. Iron sequestration by host proteins is a crucial strategy to combat bacterial infections. In bacteria, the ferric uptake regulator Fur coordinates the expression of several iron-related genes. Sometimes, Fur can also regulate several other processes. In this work, we performed an in-depth phenotypic characterization of fur mutants in the human opportunistic pathogen Chromobacterium violaceum We determined that fur is a conditionally essential gene necessary for proper growth under regular conditions and is fully required for survival under iron and oxidative stresses. Fur also controlled several virulence-associated traits, such as swimming motility, biofilm formation, and siderophore production. Consistent with these results, a C. violaceumfur null mutant showed attenuation of virulence. Therefore, our data established Fur as a major player required for C. violaceum to manage iron, including during infection in the host.

Bacteria associated with marine macroorganisms as potential source of quorum-sensing antagonists.

Samples were collected from different undisturbed areas along the coast of Gujarat like Okha, Diu, Veraval, and Somnath. A total of 68 marine isolates were obtained out of which 53 were associated with various marine macroorganisms like sponges, gastropods, and algae, whereas 15 were free living. Quorum-quenching ability of all the isolates was tested against Chromobacterium violaceum MK by co-culture technique as a way to simultaneously detect signal-degrading as well as nondegrading quorum-sensing inhibitors. Nineteen macroorganism-associated bacteria and eight free-living bacteria were found to possess quorum-sensing inhibitory activity against C. violaceum MK without affecting its growth. Isolate OA22 from grape alga and OA10 from purple sponge (Haliclona sp.) were found to possess the highest C6-HSL degradation activity and extracellular non-N-acyl-homoserine lactone degrading QSI activity, respectively. OA22 was also found to degrade 3-oxo-C12 homoserine lactone. Acid recovery of both the C6- and C12-HSL after degradation by OA22 indicated the presence of lactonase enzyme in the isolate. Cell-free supernatant of OA10 was extracted with ethyl acetate to obtain the quorum-quenching compound. Pigment inhibition in C. violaceum MK treated with OA10 extract was demonstrated in various ways and was indicative of QSI activity of the extract without degradation of the quorum-sensing signaling molecule. The isolates OA22 and OA10 were identified as Desemzia incerta and Bacillus sp., respectively, by 16S ribosomal DNA sequence analysis.

Calpurnia aurea (Aiton) Benth Extracts Reduce Quorum Sensing Controlled Virulence Factors in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is the causative agent of several life-threatening human infections. Like many other pathogens, P. aeruginosa exhibits quorum sensing (QS) controlled virulence factors such as biofilm during disease progression, complicating treatment with conventional antibiotics. Thus, impeding the pathogen's QS circuit appears as a promising alternative strategy to overcome pseudomonas infections. In the present study, Calpurnia aurea were evaluated for their antibacterial (minimum inhibitory concentrations (MIC)), anti-quorum sensing/antivirulence (AQS), and antibiofilm potential against P. aeruginosa. AQS and antivirulence (biofilm formation, swimming, and swarming motility) activities of plant extracts were evaluated against Chromobacterium violaceum and P. aeruginosa, respectively. The in vitro AQS potential of the individual compounds were validated using in silico molecular docking. Acetone and ethanolic extracts of C. aurea showed MIC at 1.56 mg/mL. The quantitative violacein inhibition (AQS) assay showed ethyl acetate extracts as the most potent at a concentration of 1 mg/mL. GCMS analysis of C. aurea revealed 17 compounds; four (pentadecanol, dimethyl terephthalate, terephthalic acid, and methyl mannose) showed potential AQS through molecular docking against the CviR protein of C. violaceum. Biofilm of P. aeruginosa was significantly inhibited by ≥60% using 1-mg/mL extract of C. aurea. Confocal laser scanning microscopy correlated the findings of crystal violet assay with the extracts significantly altering the swimming motility. C. aurea extracts reduced the virulence of pseudomonas, albeit in a strain- and extract-specific manner, showing their suitability for the identification of lead compounds with QS inhibitory potential for the control of P. aeruginosa infections.

Marine bacteria associated with shallow hydrothermal systems in the Gulf of California with the capacity to produce biofilm inhibiting compounds.

Shallow hydrothermal systems are extreme environments. The sediments and fluids emitted from the vents present unusual physical and chemical conditions compared to other marine areas, which promotes unique biodiversity that has been of great interest for biotechnology for some years. In this work, a bioprospective study was carried out to evaluate the capacity of bacteria associated with shallow hydrothermal vents to produce biofilm-inhibiting compounds. Degradation assays of N-acyl homoserine lactone (AHL) autoinducers (C6HSL) involved in the quorum sensing process were carried out on 161 strains of bacteria isolated from three shallow hydrothermal systems located in Baja California Sur (BCS), Mexico. The biosensor Chromobacterium violaceum CV026 was used. Twenty-three strains showed activity, and organic extracts were obtained with ethyl acetate. The potential of the extracts to inhibit the formation of biofilms was tested against two human pathogenic strains (Pseudomonas aeruginosa PAO1 and Aeromonas caviae ScH3), a shrimp pathogen (Vibrio parahaemolyticus M8), and two marine strains identified as producing biofilms on submerged surfaces (Virgibacillus sp C29 and Vibrio alginolyticus C96). The results showed that Vibrio alginolyticus and Brevibacillus thermoruber, as well as some thermotolerant strains (mostly Bacillus), produce compounds that inhibit bacterial biofilms (B. licheniformis, B. paralicheniformis, B. firmus, B. oceanizedimenis, B. aerius and B. sonorensis).

The Anti-infective Potential of Hydroalcoholic Extract of Phyllanthus emblica Seeds Against Selected Human-pathogenic Bacteria.

INTRODUCTION: In the context of the global threat of antimicrobial resistance (AMR) among bacterial pathogens against conventional bactericidal antibiotics, investigation on complementary/ alternative approaches to manage bacterial infections is warranted. The present study aimed at investigating the anti-pathogenic potential of Phyllanthus emblica seed extract (PESE) against four different pathogenic bacteria. METHODS: Hydroalcoholic extract of P. emblica seeds was tested for its possible in vitro quorummodulatory potential against Chromobacterium violaceum, Serratia marcescens, Pseudomonas aeruginosa, and Staphylococcus aureus through broth dilution assay. In vivo efficacy of PESE was assayed employing Caenorhabditis elegans as the model host for these four pathogens. RESULTS: PESE was found to exert in vitro quorum-modulatory effect on C. violaceum, S. marcescens, P. aeruginosa, and S. aureus at ≥50 µg/mL. This extract could curb the haemolytic activity of all the four test bacteria by 23-65%, inhibit biofilm formation, and was also able to modulate their antibiotic susceptibility (AS) and catalase activity. Susceptibility of P. aeruginosa and S. aureus to lysis by human serum was enhanced under the influence of this extract by 23% and 49%, respectively. Repeated exposure of both these notorious pathogens to PESE did not induce resistance in them. In vivo assay confirmed the anti-virulence effect of this extract in the C. elegans host, wherein the nematode host challenged with the PESE-treated pathogenic bacteria scored better survival. PESE also displayed notable prebiotic potential by promoting the growth of three probiotic strains. CONCLUSION: To the best of our awareness, this is the first report on the quorum-modulatory potential of P. emblica seed extract, validating its anti-infective potential and prebiotic property.

Communication within East Antarctic Soil Bacteria.

Antarctica, being the coldest, driest, and windiest continent on Earth, represents the most extreme environment in which a living organism can survive. Under constant exposure to harsh environmental threats, terrestrial Antarctica remains home to a great diversity of microorganisms, indicating that the soil bacteria must have adapted a range of survival strategies that require cell-to-cell communication. Survival strategies include secondary metabolite production, biofilm formation, bioluminescence, symbiosis, conjugation, sporulation, and motility, all of which are often regulated by quorum sensing (QS), a type of bacterial communication. Until now, such mechanisms have not been explored in terrestrial Antarctica. In this study, LuxI/LuxR-based quorum sensing (QS) activity was delineated in soil bacterial isolates recovered from Adams Flat, in the Vestfold Hills region of East Antarctica. Interestingly, we identified the production of potential homoserine lactones (HSLs) with chain lengths ranging from medium to long in 19 bacterial species using three biosensors, namely, Agrobacterium tumefaciens NTL4, Chromobacterium violaceum CV026, and Escherichia coli MT102, in conjunction with thin-layer chromatography (TLC). The majority of detectable HSLs were from Gram-positive species not previously known to produce HSLs. This discovery further expands our understanding of the microbial community capable of this type of communication, as well as provides insights into physiological adaptations of microorganisms that allow them to survive in the harsh Antarctic environment.IMPORTANCE Quorum sensing, a type of bacterial communication, is widely known to regulate many processes, including those that confer a survival advantage. However, little is known about communication by bacteria residing within Antarctic soils. Employing a combination of bacterial biosensors, analytical techniques, and genome mining, we found a variety of Antarctic soil bacteria speaking a common language, via LuxI/LuxR-based quorum sensing, thus potentially supporting survival in a mixed microbial community. This study reports potential quorum sensing activity in Antarctic soils and has provided a platform for studying physiological adaptations of microorganisms that allow them to survive in the harsh Antarctic environment.

A Quorum-Sensing Inhibitor Strain of Vibrio alginolyticus Blocks Qs-Controlled Phenotypes in Chromobacterium violaceum and Pseudomonas aeruginosa.

The cell density-dependent mechanism, quorum sensing (QS), regulates the expression of virulence factors. Its inhibition has been proposed as a promising new strategy to prevent bacterial pathogenicity. In this study, 827 strains from the microbiota of sea anemones and holothurians were screened for their ability to produce quorum-sensing inhibitor (QSI) compounds. The strain M3-10, identified as Vibrio alginolyticus by 16S rRNA gene sequencing, as well as ANIb and dDDH analyses, was selected for its high QSI activity. Bioassay-guided fractionation of the cell pellet extract from a fermentation broth of strain M3-10, followed by LC-MS and NMR analyses, revealed tyramine and N-acetyltyramine as the active compounds. The QS inhibitory activity of these molecules, which was confirmed using pure commercially available standards, was found to significantly inhibit Chromobacterium violaceum ATCC 12472 violacein production and virulence factors, such as pyoverdine production, as well as swarming and twitching motilities, produced by Pseudomonas aeruginosa PAO1. This constitutes the first study to screen QSI-producing strains in the microbiota of anemones and holothurians and provides an insight into the use of naturally produced QSI as a possible strategy to combat bacterial infections.