Swarming Motility Research Articles

Salpianthus macrodontus Extracts, a Novel Source of Phenolic Compounds with Antibacterial Activity against Potentially Pathogenic Bacteria Isolated from White Shrimp.

This study aimed to evaluate the antibacterial activity in vitro of Salpianthus macrodontus and Azadirachta indica extracts against potentially pathogenic bacteria for Pacific white shrimp. Furthermore, the extracts with higher inhibitory activity were analyzed to identify compounds responsible for bacterial inhibition and evaluate their effect on motility and biofilm formation. S. macrodontus and A. indica extracts were prepared using methanol, acetone, and hexane by ultrasound. The minimum inhibitory concentration (MIC) of the extracts was determined against Vibrio parahaemolyticus, V. harveyi, Photobacterium damselae and P. leiognathi. The polyphenol profile of those extracts showing the highest bacterial inhibition were determined. Besides, the bacterial swimming and swarming motility and biofilm formation were determined. The highest inhibitory activity against the four pathogens was found with the acetonic extract of S. macrodontus leaf (MIC of 50 mg/mL for Vibrio spp. and 25 mg/mL for Photobacterium spp.) and the methanol extract of S. macrodontus flower (MIC of 50 mg/mL for all pathogens tested). Both extracts affected the swarming and swimming motility and the biofilm formation of the tested bacteria. The main phenolic compounds related to Vibrio bacteria inhibition were naringin, vanillic acid, and rosmarinic acid, whilst hesperidin, kaempferol pentosyl-rutinoside, and rhamnetin were related to Photobacterium bacteria inhibition.

Antibiofilm and Antimicrobial Activities of Chloroindoles Against Uropathogenic Escherichia coli.

Uropathogenic Escherichia coli (UPEC) is a nosocomial pathogen associated with urinary tract infections and expresses several virulence factors that cause recurring infections and cystitis of the bladder, which can lead to pyelonephritis. UPEC uses different types of extracellular appendages like fimbriae and pili that aid colonization and adherence to bladder epithelium and can form persistent biofilm-like bacterial communities that aid its survival after the deployment of host immune responses. We investigated the antibiofilm, antimicrobial, and antivirulence properties of three indole derivatives namely, 4-chloroindole, 5-chloroindole, and 5-chloro 2-methyl indole. All the three chloroindoles had MICs of 75 μg/ml and inhibited biofilm formation by an average of 67% at 20 μg/ml. In addition, they inhibited swarming and swimming motilities, which are essential for dissemination from bacterial communities and colonization, reduced cell surface hydrophobicity, and inhibited indole production and curli formation. Gene expression analysis showed all three chloroindoles significantly downregulated the expressions of virulence genes associated with adhesion, stress regulation, and toxin production. A 3D-QSAR analysis revealed substitutions at the fourth and fifth positions of the indole moiety favored antimicrobial activity. Furthermore, these chloroindoles potently inhibited biofilm formation in other nosocomial pathogens and polymicrobial consortia.

Phytochemical Analysis, Antioxidant, Antimicrobial, and Anti-Swarming Properties of Hibiscus sabdariffa L. Calyx Extracts: In Vitro and In Silico Modelling Approaches.

The aim of this study was to investigate the phytochemical composition of dried Roselle calyx (Hibiscus sabdariffa L.) using both ethanolic and aqueous extracts. We report the antimicrobial activities against a wide range of bacteria, yeast, and fungi. The antioxidant activities were tested using 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, and 2–2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) radical scavenging assays. We report also for the first time the effect of the swarming motility in Pseudomonas aeruginosa PAO1. Our results showed that the tested two extracts were a rich source of phenols, flavonoids, and tannins with different degrees. Additionally, eleven phytoconstituents were identified by LC/MS technique (Hibiscus acid: 3-caffeoylquinic acid, 5-caffeoylquinic acid, 5-feruloylquinic acid, cyanidin 3-o-glucoside, myricetin, quercetin 7-o-rutinoside, quercetin 3-o-glucoside, delphinidin 3-o-sambubioside, and kaempferol 3-o-p-coumaroyl-glucoside). Also, it was shown that the calyx extract can scavenge 86% of the DPPH radical, while the rate of 53% and 23% of inhibition of the DPPH was obtained only at the concentration of 125 and 50 µg/mL, and a small inhibition was made at a concentration of 5 μg/mL. Roselle extracts inhibited the growth of the selected microorganisms at low concentrations, while higher concentrations are needed to completely kill them. However, no activity against CVB-3 was recorded for both extracts. In addition, the obtained extracts reduced the swarming motility of P. aeruginosa at 2.5 mg/ml. The docking simulation showed acceptable binding affinities (up to −9.6 kcal/mol) and interaction with key residues of 1JIJ, 2QZW, and 2UVO. The obtained results highlighted the potential use of Roselle extract as a source of phytoconstituents with promising antimicrobial, antioxidant, and anti-quorum sensing activities.

Aromatherapeutic essential oils and their pharmaceutical combinations: Tools for inhibition of quorum sensing activity and biofilm formation of human pathogens

Background and Aims: Aromatherapy, as one of the complementary therapies, uses essential oils as the main therapeutic agents to treat several diseases. In the present study, it was aimed to investigate inhibition of quorum sensing (QS) and biofilm formation of aromatherapeutic essential oils (AEOs) and their pharmaceutical combinations (PC-I and PC-II). Methods: The anti-QS potential of AEOs were determined using the biosensor strains Chromobacterium violaceum ATCC 12472 and Pseudomonas aeruginosa PAO1. Anti-QS activity was detected by agar-well diffusion and violacein pigment inhibition assays. Blocking of PAO1 swim and swarm motilities and biofilm formation was also performed. Results: Most of the AEOs demonstrated highly active (>95%) violacein pigment inhibition. Additionally, they inhibited swarming (40.34%-72.80%) and swimming (20.06%-50.08%) motilities of PAO1. Moreover, the majority of AEOs also decreased the biofilm formation, particularly on P. aeruginosa and S. aureus. Conclusion: Consequently, aromatherapeutic formulations might be a complementary or prophylactic cure for infectious disease by their anti-QS and antibiofilm activities rather than just antimicrobial effects.

The Bacillary Postbiotics, Including 2-Undecanone, Suppress the Virulence of Pathogenic Microorganisms

Secreted molecules from probiotic Bacilli have often been considered potential pharmaceuticals to fight infections caused by bacterial or yeast pathogens. In the present study, we investigated the antagonistic potential of secreted probiotic filtrates (hereafter, postbiotics) derived from Lactobacillus plantarum cells against pathogenic microorganisms, such as Escherichia coli, Staphylococcus aureus, and Candida albicans. We found that the postbiotics mitigate the biofilms of the tested pathogens with no notable effect on their planktonic growth. In addition, the postbiotics suppressed some virulence traits, for instance, the dendrite swarming motility of E. coli and yeast-to-hyphal switch in C. albicans. Further assays with an active constituent produced by the L. plantarum cells–2-undecanone revealed two significant findings: (i) 2-undecanone inhibits C. albicans biofilms and hyphae in vitro and in a Caenorhabditis elegans model, and (ii) it interacts specifically with Gln 58 amino acid residue of hyphal wall protein-1 (Hwp-1) in molecular docking analysis. The results suggest the targeted mode of antagonistic action of 2-undecanone against C. albicans biofilm. In total, the findings of the study depict an appealing strategy to use postbiotics, including specific ketone molecules, produced by L. plantarum for developing novel antibiofilm and anti-hyphal pharmaceuticals.

Chemical control over Asialo-GM1: A dual ligand for pili and Lectin A that activates swarming motility and facilitates adherence of Pseudomonas aeruginosa

Glycolipid, ganglio-N-tetraosylceramide (asialo-GM1), on the mammalian cells are known to be recognized by type IV pili of Pseudomonas aeruginosa. In this work, we show that asialo-GM1 can also be recognized by Lectin A (LecA), another adhesin protein of the P. aeruginosa, by a fluorescent polarization assay, a label-free bacterial motility enabled binding assay, and bacterial mutant studies. On hydrated semi-solid gel surfaces, asialo-GM1 enables swarming and twitching motilities, while on solid surfaces facilitates the bacterial adherence of P. aeruginosa. These results indicate that asialo-GM1 can modulate bioactivities, adherence, and motilities, that are controlled by opposite signaling pathways. We demonstrate that when a solution of pilin monomers or LecA proteins are spread on hydrated gel surfaces, the asialo-GM1 mediated swarming motility is inhibited. Treatment of artificial liposomes containing asialo-GM1 as a component of lipid bilayer with pilin monomers or LecA proteins caused transient leakage of encapsulated dye from liposomes. These results suggest that pili and LecA proteins not only bind to asialo-GM1 but can also cause asialo-GM1 mediated leakage. We also show that both pili and LecA mutants of P. aeruginosa adhere to asialo-GM1 coated solid surfaces, and that a class of synthetic ligands for pili and LecA inhibits both pili and LecA-mediated adherence of P. aeruginosa on asialo-GM1-coated surfaces.

Characterization of GefA, a GGEEF Domain-Containing Protein That Modulates Vibrio parahaemolyticus Motility, Biofilm Formation, and Virulence.

Vibrio parahaemolyticus is a significant foodborne pathogen that causes economic and public health problems worldwide and has a high capacity to adapt to diverse environments and hosts. The second messenger cyclic diguanylate monophosphate (c-di-GMP) allows bacteria to shift from a planktonic form to a communal multicellular lifestyle and plays an important role in bacterial survival and transmission. Here, we characterized single-domain c-di-GMP synthetases in V. parahaemolyticus and identified a novel GGEEF domain-containing protein designated GefA that modulates bacterial swarming motility, biofilm formation, and virulence. GefA inhibits swarming motility by regulating the expression of lateral flagella, while it enhances biofilm formation by controlling exopolysaccharide biosynthesis. Under high-c-di-GMP conditions caused by scrABC knockout, we found that GefA is bifunctional, as it has no effect on swarming motility, but retains the ability to regulate biofilm formation. Subsequent studies suggested that GefA regulates the expression of type III secretion system 1 (T3SS1), which is an important virulence factor in V. parahaemolyticus. Here, we also revealed that the flagella participate in the infection of V. parahaemolyticus. We found that both the T3SS1 and flagella contribute to the GefA-mediated virulence of V. parahaemolyticus in the zebrafish model. Our results expand the knowledge of the V. parahaemolyticus c-di-GMP synthetases and their roles in social behaviors and pathogenicity. IMPORTANCE The c-di-GMP metabolic enzymes constitute one of the largest clusters of potential orthologues in Vibrio parahaemolyticus. However, the specific roles that these individual c-di-GMP metabolic enzymes play are largely unknown. Here, we identified a GGEEF domain-containing protein designated GefA that regulates bacterial behaviors and virulence. We also demonstrated that flagella participate in the infection of this bacterium, through which GefA regulates bacterial virulence. To our knowledge, the roles that c-di-GMP and flagella play in V. parahaemolyticus virulence have never been revealed. Our findings contribute to a better understanding of the function of c-di-GMP and its synthetases in V. parahaemolyticus.

Quantifying Bacterial Surface Swarming Motility on Inducer Gradient Plates.

Bacterial swarming motility is a common microbiological phenotype that bacterial communities use to migrate over semisolid surfaces. In investigations of induced swarming motility, specific concentrationof an inducer may not be able to report events occurring within the optimal concentration range to elicit the desired responses from a species. Semisolid plates containing multiple concentrations are commonly used to investigate the response within an inducer concentration range. However, separate semisolid plates increase variations in medium viscosity and moisture content within each plate due to nonuniform solidification time. This paper describes a one-step method to simultaneously test surface swarming motility on a single gradient plate, where the isometrically arranged test wells allow the simultaneous acquisition of multiconcentration responses. In the present work, the surface swarming of Escherichia coli K12 and Pseudomonas aeruginosa PAO1 were evaluated in response to a concentration gradient of inducers such as resveratrol and arabinose. Periodically, the swarm morphologies were imaged using an imaging system to capture the entire surface swarming process. The quantitative measurement of the swarm morphologies was acquired using ImageJ software, providing analyzable information of the swarm area. This paper presents a simple gradient swarm plate method that provides qualitative and quantitative information about the inducers' effects on surface swarming, which can be extended to study the effects of other inducers on a broader range of motile bacterial species.

Retarded Swarming Motility in Bacillus Subtilis NRS-762 and Pseudomonas Aeruginosa PRD-10

Coping with nutritional stress is essential for cell survival, of which many strategies at the cellular level lend support for ensuring the survival of the population at a particular habitat. One postulated mechanism is swarming motility in bacterial cells, where, upon depletion of nutrients at a locale, cells would coordinate their movement, synthesize more flagella, and secrete lubricants for moving rapidly across surfaces in search for food. Known to engage in swarming motility, Bacillus subtilis and Pseudomonas aeruginosa are two common bacterial species with versatile metabolism that use the motility mode to colonize new habitats with more favourable environmental and nutritional conditions. However, experimental observations of bacteria growth on a variety of agar media revealed that B. subtilis NRS-762 (ATCC 8473) and P. aeruginosa PRD-10 (ATCC 15442) exhibited retarded swarming motility upon entry into stationary phase on solid media. Specifically, B. subtilis NRS-762 colonies exhibited round, wrinkled morphologies compared to complex filamented swarming patterns common in strains able to engage in swarming motility. On the other hand, P. aeruginosa PRD-10 colonies were round, mucoid, and expanded outwards from the colony centre without extending filaments from the centre; thereby, indicating retarded swarming motility. Thus, impaired cellular machinery for swarming motility or mutated and deleted genes likely account for observed retarded swarming motility in B. subtilis NRS-762 and P. aeruginosa PRD-10. More importantly, observations of small filaments extending radially from an expanded colony of P. aeruginosa PRD-10 grown on minimal salts medium supplemented with yeast extract highlighted possible loss of function of effector molecules that transmit cellular decision at swarming motility into movement, while sensory mechanisms feeding into the motility mechanism remained intact. More broadly, observations of impaired swarming motility in B. subtilis NRS-762 and P. aeruginosa PRD10 in two species otherwise endowed with the motility mode highlighted the presence of additional triggers for swarming motility are likely present, and the motility mode may have been evolutionary selected for other functions in addition to foraging for food in times of nutritional stress Graphical Abstract.

The QseEF Two-Component System-GlmY Small RNA Regulatory Pathway Controls Swarming in Uropathogenic Proteus mirabilis.

Bacterial sensing of environmental signals through the two-component system (TCS) plays a key role in modulating virulence. In the search for the host hormone-sensing TCS, we identified a conserved qseEGF locus following glmY, a small RNA (sRNA) gene in uropathogenic Proteus mirabilis. Genes of glmY-qseE-qseG-qseF constitute an operon, and QseF binding sites were found in the glmY promoter region. Deletion of glmY or qseF resulted in reduced swarming motility and swarming-related phenotypes relative to the wild-type and the respective complemented strains. The qseF mutant had decreased glmYqseEGF promoter activity. Both glmY and qseF mutants exhibited decreased flhDC promoter activity and mRNA level, while increased rcsB mRNA level was observed in both mutants. Prediction by TargetRNA2 revealed cheA as the target of GlmY. Then, construction of the translational fusions containing various lengths of cheA 5′UTR for reporter assay and site-directed mutagenesis were performed to investigate the cheA-GlmY interaction in cheA activation. Notably, loss of glmY reduced the cheA mRNA level, and urea could inhibit swarming in a QseF-dependent manner. Altogether, this is the first report elucidating the underlying mechanisms for modulation of swarming motility by a QseEF-regulated sRNA GlmY, involving expression of cheA, rcsB and flhDC in uropathogenic P. mirabilis.

Biosynthesis of Silver Chloride Nanoparticles by Rhizospheric Bacteria and Their Antibacterial Activity against Phytopathogenic Bacterium Ralstonia solanacearum.

Ralstonia solanacearum is the most destructive pathogen, causing bacterial wilt disease of eggplant. The present study aimed to develop green synthesis and characterization of silver chloride nanoparticles (AgCl-NPs) by using a native bacterial strain and subsequent evaluation of their antibacterial activity against R. solanacearum. Here, a total of 10 bacterial strains were selected for the biosynthesis of AgCl-NPs. Among them, the highest yield occurred in the synthesis of AgCl-NPs using a cell-free aqueous filtrate of strain IMA13. Ultrastructural observation revealed that the AgCl-NPs were spherical and oval with smooth surfaces and 5–35 nm sizes. XRD analysis studies revealed that these particles contained face-centered cubic crystallites of metallic Ag and AgCl. Moreover, FTIR analysis showed the presence of capping proteins, carbohydrates, lipids, and lipopeptide compounds and crystalline structure of AgCl-NPs. On the basis of phylogenetic analysis using a combination of six gene sequences (16S, gyrA, rpoB, purH, polC, and groEL), we identified strain IMA13 as Bacillus mojavensis. Three kinds of lipopeptide compounds, namely, bacillomycin D, iturin, and fengycin, forming cell-free supernatant produced by strain IAM13, were identified by MALDI-TOF mass spectrometry. Biogenic AgCl-NPs showed substantial antibacterial activity against R. solanacearum at a concentration of 20 µg/mL−1. Motility assays showed that the AgCl-NPs significantly inhibited the swarming and swimming motility (61.4 and 55.8%) against R. solanacearum. Moreover, SEM and TEM analysis showed that direct interaction of AgCl-NPs with bacterial cells caused rupture of cell wall and cytoplasmic membranes, as well as leakage of nucleic acid materials, which ultimately resulted in the death of R. solanacearum. Overall, these findings will help in developing a promising nanopesticide against phytopathogen plant disease management.

Correlation between phenotypic virulence traits and antibiotic resistance in Pseudomonas aeruginosa clinical isolates

Pseudomonas aeruginosa is a ubiquitous pathogen capable of infecting virtually all tissues and its one of the standout amongst the most hazardous microorganisms of high morbidity and mortality rates especially in debilitated patients with few successful antibiotic choices available. This pathogen regulating most virulence traits by that so-called quorum sensing (QS), a cell to cell communication system. the present study was intended to phenotypically evaluate the activity of specific virulence traits (including swarming and swimming motility, protease, pyocyanin, and biofilm production) in Pseudomonas aeruginosa clinical isolates and assess the statistical correlation between these traits and antibiotic resistance. One hundred and thirteen bacterial isolates were obtained from different clinical samples and identified as P. aeruginosa, among them, 73.4% have the ability to forming biofilm with different degrees; 59.2% were able to produce pyocyanin pigment while all isolates having the ability to make swarming and swimming motility and able to produce protease enzyme with different degrees. The isolates that produce the higher levels of the virulence traits were identified by both biochemical using Vitek2 automated system and genetically via 16s rRNA gene analysis. The statistical analysis results indicate that a positive significant correlation was found between biofilm formation and other studied virulence traits except for protease (r = 0.584: 0.324, P < 0.05) while a non-significant correlation was found between biofilm formation and protease activity (r = 0.105, P ˃ 0.05). Swimming and swarming motility have a positive significant correlation with other studied virulence traits (r = 0.613: 0.297, P < 0.05) except for protease. Pyocyanin pigment production have a positive significant correlation with other studied virulence traits (r = 0.33: 0.297, P < 0.05) except for protease. on the other hand, negative significant correlations were found between biofilm formation, swimming; and swarming motility, Pyocyanin pigment production, and the susceptibility of antibiotics (r = −0.512: −0.281, P < 0.05). Detection of such correlations in P. aeruginosa is useful for study the behavior of this pathogen and may be provide a new target for the treatment of MDR infections.

Anti-Virulence Properties of Coridothymus capitatus Essential Oil against Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients.

Pseudomonas aeruginosa is an opportunistic pathogen responsible for nosocomial infections, and is often involved in airway infections of cystic fibrosis (CF) patients. P. aeruginosa virulence is related to its ability to form biofilm, trigger different types of motilities, and produce toxins (for example, bacterial pigments). In this scenario, essential oils (EOs) have gained notoriety for their role in phenotype modulation, including virulence modulation. Among different EOs previously analyzed, herein we investigated the activity of Coridothymus capitatus EO (CCEO) against specific virulence factors produced by P. aeruginosa isolated from CF patients. CCEO showed inhibition of new biofilm formation and reduction in mature biofilm in about half of the tested strains. On selected strains, SEM analysis provided interesting information regarding CCEO action in a pre-adhesion assay. CCEO treatment showed a dramatic modification of the extracellular matrix (ECM) structure. Our results clearly showed a drastic reduction in pyocyanin production (between 84% and 100%) for all tested strains in the presence of CCEO. Finally, CCEO was also able to strongly affect P. aeruginosa swarming and swimming motility for almost all tested strains. In consideration of the novel results obtained on clinical strains isolated from CF patients, CCEO may be a potential candidate to limit P. aeruginosa virulence.

Fis Connects Two Sensory Pathways, Quorum Sensing and Surface Sensing, to Control Motility in Vibrio parahaemolyticus.

Factor for inversion stimulation (Fis) is a global regulator that is highly expressed during exponential phase growth and undetectable in stationary phase growth. Quorum sensing (QS) is a global regulatory mechanism that controls gene expression in response to changes in cell density and growth phase. In Vibrio parahaemolyticus, a marine species and a significant human pathogen, the QS regulatory sRNAs, Qrr1 to Qrr5, are expressed during exponential growth and negatively regulate the high cell density QS master regulator OpaR. OpaR is a positive regulator of capsule polysaccharide (CPS) formation, which is required for biofilm formation, and is a repressor of lateral flagella required for swarming motility. In V. parahaemolyticus, we show that Fis is a positive regulator of the qrr sRNAs expression. In an in-frame fis deletion mutant, qrr expression was repressed and opaR expression was induced. The Δfis mutant produced CPS and biofilm, but swarming motility was abolished. Also, the fis deletion mutant was more sensitive to polymyxin B. Swarming motility requires expression of both the surface sensing scrABC operon and lateral flagella laf operon. Our data showed that in the Δfis mutant both laf and scrABC genes were repressed. Fis controlled swarming motility indirectly through the QS pathway and directly through the surface sensing pathway. To determine the effects of Fis on cellular metabolism, we performed in vitro growth competition assays, and found that Δfis was outcompeted by wild type in minimal media supplemented with intestinal mucus as a sole nutrient source. The data showed that Fis positively modulated mucus components L-arabinose, D-gluconate and N-acetyl-D-glucosamine catabolism gene expression. In an in vivo colonization competition assay, Δfis was outcompeted by wild type, indicating Fis is required for fitness. Overall, these data demonstrate a global regulatory role for Fis in V. parahaemolyticus that includes QS, motility, and metabolism.

Inhibition of Quorum Sensing and Biofilm Formation of Esculetin on Aeromonas Hydrophila.

Quorum sensing (QS) and biofilm formation inhibition activity of esculetin on Aeromonas hydrophila SHAe 115 were evaluated. Exposure to esculetin at 25, 50, and 100μg/ml significantly inhibited the production of protease and hemolysin, the formation of biofilms and attenuated the swarming motility of A. hydrophila SHAe 115. Biofilm forming inhibition was also observed through confocal laser scanning microscopy and scanning electron microscope. Quantitative real-time PCR analysis indicated that genes positively related to QS and biofilm formation were downregulated to varying degrees, while gene (litR) negatively related to biofilm formation was significantly upregulated. The phenotypic results were in good agreement with gene expression levels. These results indicated that esculetin would be a potential QS inhibitor for A. hydrophila.

Exploring Phenolic Compounds as Quorum Sensing Inhibitors in Foodborne Bacteria.

The emergence of multidrug-resistant bacteria stimulates the search for new substitutes to traditional antimicrobial agents, especially molecules with antivirulence properties, such as those that interfere with quorum sensing (QS). This study aimed to evaluate the potential of phenolic compounds for QS inhibition in a QS biosensor strain (Chromobacterium violaceum) and three foodborne bacterial species (Aeromonas hydrophila, Salmonella enterica serovar Montevideo, and Serratia marcescens). Initially, an in silico molecular docking study was performed to select the compounds with the greatest potential for QS inhibition, using structural variants of the CviR QS regulator of C. violaceum as target. Curcumin, capsaicin, resveratrol, gallic acid, and phloridizin presented good affinity to at least four CviR structural variants. These phenolic compounds were tested for antimicrobial activity, inhibition of biofilm formation, and anti-QS activity. The antimicrobial activity when combined with kanamycin was also assessed. Curcumin, capsaicin, and resveratrol inhibited up to 50% of violacein production by C. violaceum. Biofilm formation was inhibited by resveratrol up to 80% in A. hydrophila, by capsaicin and curcumin up to 40% in S. Montevideo and by resveratrol and capsaicin up to 60% in S. marcescens. Curcumin completely inhibited swarming motility in S. marcescens. Additionally, curcumin and resveratrol increased the sensitivity of the tested bacteria to kanamycin. These results indicate that curcumin and resveratrol at concentrations as low as 6μM are potential quorum sensing inhibitors besides having antimicrobial properties at higher concentrations, encouraging applications in the food and pharmaceutical industries.

Anti-Virulence Activity of the Cell-Free Supernatant of the Antarctic Bacterium Psychrobacter sp. TAE2020 against Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients.

Pseudomonas aeruginosa is an opportunistic pathogen often involved in airway infections of cystic fibrosis (CF) patients. Its pathogenicity is related to several virulence factors, such as biofilm formation, motility and production of toxins and proteases. The expression of these virulence factors is controlled by quorum sensing (QS). Thus, QS inhibition is considered a novel strategy for the development of antipathogenic compounds acting on specific bacterial virulence programs without affecting bacterial vitality. In this context, cold-adapted marine bacteria living in polar regions represent an untapped reservoir of biodiversity endowed with an interesting chemical repertoire. In this paper, we investigated the biological activity of a supernatant derived from a novel Antarctic bacterium (SN_TAE2020) against specific virulence factors produced by P. aeruginosa strains isolated from FC patients. Our results clearly show a reduction in pyocyanin and protease production in the presence of SN_TAE2020. Finally, SN_TAE2020 was also able to strongly affect swarming and swimming motility for almost all tested strains. Furthermore, the effect of SN_TAE2020 was investigated on biofilm growth and texture, captured by SEM analysis. In consideration of the novel results obtained on clinical strains, polar bacteria might represent potential candidates for the discovery of new compounds limiting P. aeruginosa virulence in CF patients.

IMPACT OF TEA TREE OIL ON BIOFILM FORMATION AND SWARMING MOTILITY BY MDR PROTEUS MIRABILIS

Emergence of multi-drug resistant isolates of P. mirabilis and development of new resistant microbial phenotypes are growing and the outlook for the use of antimicrobial drugs in the future is still uncertain. Therefore, there is an increased demand for developing alternative strategies to conventional antibiotic therapy and to continue studies to develop new drugs, either synthetic or natural. In this study, 25 isolates of P. mirabilis were isolated from different clinical samples collected from different departments of Tanta University hospitals. All isolates were resistant to amoxicillin, azithromycin and tetracycline. A high incidence of resistance was also recorded for cefprozil (96%) and cefotaxime (80%). P. mirabilis isolates were moderately resistant to imipenem (64%), lomefloxacin (64%), ampicillin (60%), cefepime (60%) and ciprofloxacin (52%). However, the lowest incidence of resistance was recorded for amikacin (8%). All isolates showed MAR indices &gt;0.2 and exhibited MDR profile. The antimicrobial activity of tea tree oil was evaluated using agar dilution method recording MIC50 value of 12.8 mg/ml. The effect of tea tree oil on the strong biofilm producer isolates with relatively wide swarming zone diameters was evaluated. Results obtained showed that tea tree oil (1/4 and 1/2 MIC) presented significant and dose-dependent inhibition in the biofilm production by the tested isolates of P. mirabilis by ≥50%. In addition, tea tree oil inhibited the swarming motility of P. mirabilis isolates in a dose-dependent manner. Therefore, tea tree oil could act as a potential source of alternative antimicrobials or as antipathogenic compound against MDR P.mirabilis.

Toxicity and bacterial anti-motility activities of the hydroethanolic extract of Acacia senegal (L.) Willd (Fabaceae) leaves

BackgroundAcacia senegal is a plant traditionally used for its various properties, including the treatment of infectious diseases. Recently, our team has demonstrated the ability of the hydroethanolic extract of the leaves to increase the activity of phenicol antibiotics against multi-resistant bacteria. The aim of this work is to determine the toxicological effects of the extract and its capacity to inhibit the bacterial mobility of Gram-negative bacteria, in order to evaluate the level of safety use of this plant.MethodsThe cytotoxicity test was performed using the neutral red absorption method. Acute and sub-acute oral toxicity were conducted on NMRI mice and Wistar rats. The behaviour and adverse effects were recorded during the 14 days of the acute study. For the subacute test, biochemical parameters, food and water consumption, and morphological parameters were determined. The anti-motility activities were evaluated on Pseudomonas aeruginosa PA01 and Escherichia coli AG100, using specific concentrations of Agar as required by the method.ResultsHEASG induced inhibition of keratinocytes cell growth with an IC50 of 1302 ± 60 μg/mL. For the acute toxicity study in mice, the single dose of extract of 2000 mg/kg body weight caused no deaths and no behavioural changes were observed; therefore, the median lethal dose (LD50) of HEASG was calculated to 5000 mg/kg body weight. In Wistar rats, no mortality was observed at 250, 500 and 1000 mg/kg/day during the 28-day subacute oral toxicity study. The weights of both females and males increased globally over time, regardless of the batch. No statistically significant differences were registered for organ weights and biochemical parameters, except for chloride for biochemical parameters. Water and food consumption did not change significantly. Furthermore, no macroscopic changes in organ appearance were observed. Regarding anti-motility activity, the extract has reduced the swarming motility of PA01 and AG100 significantly at the concentration of 32 μg/mL (P < 0.001). The extract has reduced the swimming motility (P < 0.01) of PA01 but not AG100.ConclusionsThe results suggest that hydroethanolic extract of A. senegal leaves has significant activity against bacterial motility and relatively low toxicity.

In Silico and In Vitro Screening of Antipathogenic Properties of Melianthus comosus (Vahl) against Pseudomonas aeruginosa.

Bacterial quorum sensing (QS) system regulates pathogenesis, virulence, and biofilm formation, and together they contribute to nosocomial infections. Opportunistic pathogens, such as Pseudomonas aeruginosa, rely on QS for regulating virulence factors. Therefore, blocking the QS system may aid management of various infectious diseases caused by human pathogens. Plant secondary metabolites can thwart bacterial colonization and virulence. As such, this study was undertaken to evaluate three extracts from the medicinal plant, Melianthus comosus, from which phytochemical compounds were identified with potential to inhibit QS-dependent virulence factors in P. aeruginosa. Chemical profiling of the three extracts identified 1,2-benzene dicarboxylic acid, diethyl ester, neophytadiene and hexadecanoic acid as the common compounds. Validation of antibacterial activity confirmed the same MIC values of 0.78 mg/mL for aqueous, methanol and dichloromethane extracts while selected guanosine showed MIC 0.031 mg/mL. Molecular docking analysis showed anti-quorum sensing (AQS) potential of guanosine binding to CviR’ and 2UV0 proteins with varying docking scores of −5.969 and −8.376 kcal/mol, respectively. Guanosine inhibited biofilm cell attachment and biofilm development at 78.88% and 34.85%, respectively. Significant swimming and swarming motility restriction of P. aeruginosa were observed at the highest concentration of plant extracts and guanosine. Overall, guanosine revealed the best swarming motility restrictions. M. comosus extracts and guanosine have shown clear antibacterial effects and subsequent reduction of QS-dependent virulence activities against P. aeruginosa. Therefore, they could be ideal candidates in the search for antipathogenic drugs to combat P. aeruginosa infections.