A novel compound from the marine bacterium Bacillus pumilus S6-15 inhibits biofilm formation in gram-positive and gram-negative species

Anti-Biofilm Extracts and Molecules from the Marine Environment

Pathogenic bacteria and their biofilms are involved in many diseases and represent a major public health problem, including the development of antibiotic resistance. These biofilms are known to cause chronic infections for which conventional antibiotic treatments are often ineffective. The search for new molecules and innovative solutions to combat these pathogens and their biofilms has therefore become an urgent need. The use of molecules with anti-biofilm activity would be a potential solution to these problems. The marine world is rich in micro- and macro-organisms capable of producing secondary metabolites with original skeletons. An interest in the chemical strategies used by some of these organisms to regulate and/or protect themselves against pathogenic bacteria and their biofilms could lead to the development of bioinspired, eco-responsible solutions. Through this original review, we listed and sorted the various molecules and extracts from marine organisms that have been described in the literature as having strictly anti-biofilm activity, without bactericidal activity.

Two promising Bacillus-derived antifungal lipopeptide leads AF4 and AF5 and their combined effect with fluconazole on the in vitro Candida glabrata biofilms

Introduction: Candida species are endowed with the ability to produce biofilms, which is one of the causes of pathogenicity, as biofilms protect yeasts from antifungal drugs. Candida glabrata (Nakaseomyces glabrata) is one of the most prevalent pathogenic yeasts in humans and a biofilm producer. Methods: The study was aimed at evaluating the combined effects of two highly promising antifungal biomolecules (AF4 and AF5) lipopeptide in nature, chromatographically purified to homogeneity from Bacillus subtilis (B. subtilis) and the standard antifungal fluconazole (at different concentrations) to demonstrate C. glabrata biofilm formation inhibition. Biofilm production and inhibition were evaluated by quantification of the biofilm biomass and metabolic activity using crystal violet (CV) staining and XTT reduction assays, respectively. Microscopic techniques such as confocal scanning laser microscopy (CSLM) and scanning electron microscopy (SEM) were employed to visualize biofilm formation and inhibition. Results and Discussion: Compared to untreated and fluconazole-treated biofilms, an enhanced in vitro anti-biofilm effect of the antifungal lipopeptides AF4/AF5 alone and their combinations with fluconazole was established. The lipopeptides AF4/AF5 alone at 8 and 16 μg/mL exhibited significant biomass and metabolic activity reductions. SEM and CSLM images provided evidence that the lipopeptide exposure results in architectural alterations and a significant reduction of C. glabrata biofilms, whereas (2', 7'-dichlorofluorescin diacetate (DCFDA) and propidium iodide (PI) analyses showed reactive oxygen species (ROS) generation along with membrane permeabilization. The estimation of exopolysaccharides (EPS) in AF4/AF5-treated biofilms indicated EPS reduction. The combinations of fluconazole (64/128 μg/mL) and AF4/AF5 lipopeptide (16 μg/mL) were found to significantly disrupt the mature (24 h) biofilms as revealed by CSLM and SEM studies. The CSLM images of biofilms were validated using COMSTAT. The FTIR-analyses indicate the antibiofilm effects of both lipopeptides on 24 h biofilms to support CSLM and SEM observations. The combinations of fluconazole (64/128 μg/mL) and AF4/AF5 lipopeptide were found to disrupt the mature biofilms; the study also showed that the lipopeptides alone have the potentials to combat C. glabrata biofilms. Taken together, it may be suggested that these lipopeptide leads can be optimized to potentially apply on various surfaces to either reduce or nearly eradicate yeast biofilms.

Evaluation of novel compounds as anti-bacterial or anti-virulence agents

Antimicrobial resistance is a global threat, leading to an alarming increase in the prevalence of bacterial infections that can no longer be treated with available antibiotics. The World Health Organization estimates that by 2050 up to 10 million deaths per year could be associated with antimicrobial resistance, which would equal the annual number of cancer deaths worldwide. To overcome this emerging crisis, novel anti-bacterial compounds are urgently needed. There are two possible approaches in the fight against bacterial infections: a) targeting structures within bacterial cells, similar to existing antibiotics; and/or b) targeting virulence factors rather than bacterial growth. Here, for the first time, we provide a comprehensive overview of the key steps in the evaluation of potential new anti-bacterial and/or anti-virulence compounds. The methods described in this review include: a) in silico methods for the evaluation of novel compounds; b) anti-bacterial assays (MIC, MBC, Time-kill); b) anti-virulence assays (anti-biofilm, anti-quorum sensing, anti-adhesion); and c) evaluation of safety aspects (cytotoxicity assay and Ames test). Overall, we provide a detailed description of the methods that are an essential tool for chemists, computational chemists, microbiologists, and toxicologists in the evaluation of potential novel antimicrobial compounds. These methods are cost-effective and have high predictive value. They are widely used in preclinical studies to identify new molecular candidates, for further investigation in animal and human trials.

The antibiofilm potential of a heteropolysaccharide produced and characterized from the isolated marine bacterium Glutamicibacter nicotianae BPM30

Biofilms are the significant causes of 80% of chronic infections in the oral cavity, urinary tract, biliary tube, lungs, gastrointestinal tract, and so on to the general public. Treatment of pathogenic biofilm using bacterial exopolysaccharides (EPS) is an effective and promising strategy. In the present work, a marine bacterium was isolated, studied for exopolysaccharide production, and tested for its antibiofilm activity. Approximately 1.31 ± 0.07 g/L of a purified extracellular polysaccharide was produced and characterized from the isolated marine bacterium Glutamicibacter nicotianae BPM30. The hydrolyzed EPS contains multiple monosaccharides such as rhamnose, fructose, glucose, and galactose. The EPS demonstrated potential antibiofilm activity on four tested pathogens in a concentration-dependent mode. The antibiofilm activity of the purified EPS was studied by crystal violet assay and fluorescence staining method. Comparative inhibition results obtained for the tested strains are 93.25% ± 5.25 and 88.56% ± 2.25 for K. pneumoniae; 92.65% ± 7.6 and 98.33% ± 0.85 for P. aeruginosa; 90.36% ± 6.3 and 52.08% ± 7.74 for S. typhi; 84.62% ± 5.6 and 77.90% ± 5.90 for S. dysenteriae. The results of the present work demonstrated the antibiofilm potential of EPS, which could be helpful in the invention of novel curative approaches in battling bacterial biofilm-related medical complications.

Exopolysaccharides produced by Bacillus spp. inhibit biofilm formation by Staphylococcus aureus strains associated with bovine mastitis

Bovine mastitis is a costly disease in the dairy sector worldwide. Here the objective was to identify and characterize anti-biofilm compounds produced by Bacillus spp. against S. aureus associated with bovine mastitis. Results showed that cell-free supernatants of three Bacillus strains (out of 33 analysed) reduced S. aureus biofilm formation by approximately 40 % without affecting bacterial growth. The anti-biofilm activity was associated with exopolysaccharides (EPS) secreted by Bacillus spp. The EPS decreased S. aureus biofilm formation in a dose-dependent manner, inhibiting biofilm formation by 83 % at 1 mg/mL. The EPS also showed some biofilm disruption activity (up to 36.4 %), which may be partially mediated by increased expression of the aur gene. The characterization of EPS produced by Bacillus velezensis 87 and B. velezensis TR47II revealed macromolecules with molecular weights of 31.2 and 33.7 kDa, respectively. These macromolecules were composed mainly of glucose (mean = 218.5 μg/mg) and mannose (mean = 241.5 μg/mg) and had similar functional groups (pyranose ring, beta-type glycosidic linkage, and alkynes) as revealed by FT-IR. In conclusion, this study shows the potential applications of EPS produced by B. velezensis as an anti-biofilm compound that could contribute to the treatment of bovine mastitis caused by S. aureus.

Antimicrobial Resistance, Phenotypic Characteristics, and Biofilm Production in Citrobacter freundii Isolates Obtained from Urinary Tract Infections

Objective

To evaluate the link between phenotypic traits, antimicrobial resistance, and biofilm-producing capacity of urinary isolates of Citrobacter freundii ( C. freundii).

Methods

Both pan-antibiotic-susceptible and -resistant C. freundii isolates ( n = 120) obtained from laboratory-confirmed urinary tract infections were analyzed for their link between antimicrobial resistance, phenotypic characteristics, and biofilm production.

Results

Of the total C. freundii isolates ( n = 120), 30% (37/120) of them formed large colonies. Among the total large colonies produced ( n = 37), they were present in 21.62%, 10.81%, 13.5%, 16.2%, 21.62%, and 16.21% in the control group, CIP-group, FOS-group, COT-group, Gent-group, and ESBL groups, respectively. Compared to the pan-susceptible isolates, the occurrence of large-sized-colony-forming strains was relatively reduced in most of the drug-resistant groups. The overall distribution of mucoid colonies produced ( n = 54) includes 9.25%, 18.51%, 16.66%, 18.51%, 20.3%, and 16.66% in the control group, CIP-group, FOS-group, COT-group, Gent-group, and ESBL groups, respectively. Of the total isolates that produced biofilm ( n = 51), 11.76% of isolates showed biofilm formation in the control group. Alternatively, the rate was found to be 15.68%, 11.76%, 25.49%, 19.6%, and 15.68% in the CIP-group, FOS-group, SXT-group, Gen-group, and ESBL-groups, respectively.

Conclusion

This study correlates the association between phenotypic characteristics, antimicrobial resistance, and biofilm production, the three main characteristics of C. freundii.

Extracytoplasmic sigma factor AlgU contributes to fitness of Pseudomonas aeruginosa PGPR2 during corn root colonization

In bacteria, sigma factors are crucial in determining the plasticity of core RNA polymerase (RNAP) while promoter recognition during transcription initiation. This process is modulated through an intricate regulatory network in response to environmental cues. Previously, an extracytoplasmic function (ECF) sigma factor, AlgU, was identified to positively influence the fitness of Pseudomonas aeruginosa PGPR2 during corn root colonization. In this study, we report that the inactivation of the algU gene encoded by PGPR2_23995 hampers the root colonization ability of PGPR2. An insertion mutant in the algU gene was constructed by allele exchange mutagenesis. The mutant strains displayed threefold decreased root colonization efficiency compared with the wild-type strain when inoculated individually and in the competition assay. The mutant strain was more sensitive to osmotic and antibiotic stresses and showed higher resistance to oxidative stress. On the other hand, the mutant strain showed increased biofilm formation on the abiotic surface, and the expression of the pelB and pslA genes involved in the biofilm matrix formation were up-regulated. In contrast, the expression of algD, responsible for alginate production, was significantly down-regulated in the mutant strain, which is directly regulated by the AlgU sigma factor. The mutant strain also displayed altered motility. The expression of RNA binding protein RsmA was also impeded in the mutant strain. Further, the transcript levels of genes associated with the type III secretion system (T3SS) were analyzed, which revealed a significant down-regulation in the mutant strain. These results collectively provide evidence for the regulatory role of the AlgU sigma factor in modulating gene expression during root colonization.

Tetracycline-loaded magnesium oxide nanoparticles with a potential bactericidal action against multidrug-resistant bacteria: In vitro and in vivo evidence

Worldwide, the emergence of diarrhoea-causing multi-drug resistant (MDR) bacteria has become a crucial problem in everyday life. Tetracycline (TC) is a bacteriostatic agent that has a wide spectrum of antibacterial activity. One potential strategy to enhance the penetration and antibacterial activity of antibiotics is the use of nanotechnology. In this context, this study dealt with the synthesis of TC loading in biocompatible magnesium oxide nanoparticles (MgONPs), its characterization, and the potency of killing against diarrhoea-causing MDR bacteria E. coli and S. flexneri. TC loaded- MgONPs (MgONPs-TC) were characterized by DLS, SEM-EDS, UV-vis spectroscopy, and FTIR techniques with adequate physical properties. Antibacterial and antibiofilm studies indicate that this nanoparticle successfully eradicated both planktonic and sessile forms of those bacteria. It also significantly reduced the production of bacterial EPS, different levels of antioxidant enzymes, and induced reactive oxygen species (ROS) in the bacterial cell as a mode of antibacterial action. In particular, MgONPs-TC were efficient in reducing the colonization of MDR E. coli and S. flexneri in the C. elegans model. Therefore, all these data suggest that MgONPs-TC are a highly promising approach to combating diseases associated with diarrhoea-causing MDR bacteria in the medical field with limited health care budgets.

Anti-Larval and Anti-Algal Natural Products from Marine Microorganisms as Sources of Anti-Biofilm Agents

Bacteria growing inside biofilms are more resistant to hostile environments, conventional antibiotics, and mechanical stresses than their planktonic counterparts. It is estimated that more than 80% of microbial infections in human patients are biofilm-based, and biofouling induced by the biofilms of some bacteria causes serious ecological and economic problems throughout the world. Therefore, exploring highly effective anti-biofilm compounds has become an urgent demand for the medical and marine industries. Marine microorganisms, a well-documented and prolific source of natural products, provide an array of structurally distinct secondary metabolites with diverse biological activities. However, up to date, only a handful of anti-biofilm natural products derived from marine microorganisms have been reported. Meanwhile, it is worth noting that some promising antifouling (AF) compounds from marine microbes, particularly those that inhibit settlement of fouling invertebrate larvae and algal spores, can be considered as potential anti-biofilm agents owing to the well-known knowledge of the correlations between biofilm formation and the biofouling process of fouling organisms. In this review, a total of 112 anti-biofilm, anti-larval, and anti-algal natural products from marine microbes and 26 of their synthetic analogues are highlighted from 2000 to 2021. These compounds are introduced based on their microbial origins, and then categorized into the following different structural groups: fatty acids, butenolides, terpenoids, steroids, phenols, phenyl ethers, polyketides, alkaloids, flavonoids, amines, nucleosides, and peptides. The preliminary structure-activity relationships (SAR) of some important compounds are also briefly discussed. Finally, current challenges and future research perspectives are proposed based on opinions from many previous reviews.

Inactivation of CbrAB two-component system hampers root colonization in rhizospheric strain of Pseudomonas aeruginosa PGPR2

Two-component systems (TCS) are one of the signal transduction mechanisms, which sense physiological/biological restraints and respond to changing environmental conditions by regulating the gene expression. Previously, by employing a forward genetic screen (INSeq), we identified that cbrA gene is essential for the fitness of Pseudomonas aeruginosa PGPR2 during root colonization. Here, we report the functional characterization of cbrAB TCS in PGPR2 during root colonization. We constructed insertion mutants in cbrA and its cognate response regulator cbrB. Genetic characterization revealed drastic down-regultion of sRNA crcZ gene in both mutant strains which play a critical role in carbon catabolite repression (CCR). The mutant strains displayed 10-fold decreased root colonization efficiency when compared to the wild-type strain. On the other hand, mutant strains formed higher biofilm on the abiotic surface, and the expression of pelB and pslA genes involved in biofilm matrix formation was up-regulated. In contrast, the expression of algD, responsible for alginate production, and its associated sigma factor algU was significantly down-regulated in mutant strains. We further analyzed the transcript levels of rsmA, controlled by the algU sigma factor, and found that the expression of rsmA was hampered in both mutants. The ability of mutant strains to swim and swarm was significantly hindered. Also, the expression of genes associated with type III secretion system (T3SS) was dysregulated in mutant strains. Taken together, regulation of gene expression by CbrAB TCS is intricate, and we confirm its role beyond carbon and nitrogen assimilation.

Anthraquinones as Potential Antibiofilm Agents Against Methicillin-Resistant Staphylococcus aureus

Biofilms formed by methicillin-resistant Staphylococcus aureus (MRSA) are one of the contributing factors to recurrent nosocomial infection in humans. There is currently no specific treatment targeting on biofilms in clinical trials approved by FDA, and antibiotics remain the primary therapeutic strategy. In this study, two anthraquinone compounds isolated from a rare actinobacterial strain Kitasatospora albolonga R62, 3,8-dihydroxy-l-methylanthraquinon-2-carboxylic acid (1) and 3,6,8-trihydroxy-1-methylanthraquinone-2-carboxylic acid (2), together with their 10 commercial analogs 3-12 were evaluated for antibacterial and antibiofilm activities against MRSA, which led to the discovery of two potential antibiofilm anthraquinone compounds anthraquinone-2-carboxlic acid (6) and rhein (12). The structure-activity relationship analysis of these anthraquinones indicated that the hydroxyl group at the C-2 position of the anthraquinone skeleton played an important role in inhibiting biofilm formation at high concentrations, while the carboxyl group at the same C-2 position had a great influence on the antibacterial activity and biofilm eradication activity. The results of crystal violet and methyl thiazolyl tetrazolium staining assays, as well as scanning electron microscope and confocal scanning laser microscopy imaging of compounds 6 and 12 treatment groups showed that both compounds could disrupt preformed MRSA biofilms possibly by killing or dispersing biofilm cells. RNA-Seq was subsequently used for the preliminary elucidation of the mechanism of biofilm eradication, and the results showed upregulation of phosphate transport-related genes in the overlapping differentially expressed genes of both compound treatment groups. Herein, we propose that anthraquinone compounds 6 and 12 could be considered promising candidates for the development of antibiofilm agents.

Exploring the Antivirulence Activity of Pulverulentone A, a Phloroglucinol-Derivative from Callistemon citrinus Leaf Extract, against Multi-Drug Resistant Pseudomonas aeruginosa

(1) Background: Bacterial resistance to antibiotics is a global life-threatening issue. Antivirulence therapy is a promising approach to combat bacterial infections as it disarms the bacteria from their virulence factors with reduced selective pressure and a lower chance of resistance. (2) Methods: Callistemon citrinus leaf extract and its major constituent, Pulverulentone A, were tested for their ability to inhibit biofilm, exopolysaccharides, pyocyanin and proteases produced by MDR P. aeruginosa. In addition, a Galleria mellonella larvae model was employed to evaluate the in vivo cytotoxicity of Pulverulentone A and its ability to combat Pseudomonas infection. Docking study was further performed to investigate Pulverulentone A druggability against main quorum sensing (QS) targets expressed by P. aeruginosa; (3) Results: Both C. citrinus extract and the isolated compound could inhibit biofilm formation, extracellular polymeric substances (EPS) and pigment production by the tested isolates. Unexpectedly, no significant inhibition was observed on proteases production. The in silico docking analysis revealed good interactions of Pulverulentone A with all QS targets examined (LasR, MyfR/PqsR, QscR). Pulverulentone A was safe up to 400 µg·mL⁻¹ in Galleria caterpillars. Moreover, pre-treatment of P. aeruginosa with Pulverulentone A slightly enhanced the survival of the infected larvae. (4) Conclusions: The present study proves Pulverulentone A safety with significant in vitro and in silico antivirulence potential against P. aeruginosa.

Biosurfactant synergized with marine bacterial DNase disrupts polymicrobial biofilms

Globally, the occurrence of biofilm associated infection has become an alarming menace to the medical fraternity because the thick exopolysaccharide layer encasing the biofilms makes the biofilm producing pathogens inherently resistant to antibiotics. Candida albicans, the most common pathogen among Candida spp. is the causative agent for superficial and invasive candidiasis. The morphological phase switching from yeast to hyphal form is one of the virulent traits of C. albicans critical for its pathogenicity. Owing to the emergence of antifungal resistance among this opportunistic fungus, there is a dire need for improvised alternative antifungal agents. In the present study, we have evaluated a biosurfactant from a marine bacterium for its biofilm disruption ability against C. albicans. This biosurfactant had the potential to disrupt biofilms as well as to inhibit the morphological transition from yeast to hyphae. In addition, this biosurfactant showed enhance disruption of mixed species biofilms of C. albicans and Staphylococcus epidermidis when combined with DNase isolated from marine bacteria. From the results obtained, it is evident that the biosurfactant could act as a potential antibiofilm agent against drug resistant C. albicans strains.

Challenges of antibiotic resistance biofilms and potential combating strategies: a review

In this modern era, medicine is facing many alarming challenges. Among different challenges, antibiotics are gaining importance. Recent years have seen unprecedented increase in knowledge and understanding of various factors that are root cause of the spread and development of resistance in microbes against antibiotics. The infection results in the formation of microbial colonies which are termed as biofilms. However, it has been found that a multiple factors contribute in the formation of antimicrobial resistance. Due to higher dose of Minimum Bactericidal Concentration (MBC) as well as of Minimum Inhibitory Concentration (MIC), a large batch of antibiotics available today are of no use as they are ineffective against infections. Therefore, to control infections, there is dire need to adopt alternative treatment for biofilm infection other than antibiotics. This review highlights the latest techniques that are being used to cure the menace of biofilm infections. A wide range of mechanisms has been examined with particular attention towards avenues which can be proved fruitful in the treatment of biofilms. Besides, newer strategies, i.e., matrix centered are also discussed as alternative therapeutic techniques including modulating microbial metabolism, matrix degrading enzyme, photodynamic therapy, natural compounds quorum sensing and nanotechnology which are being used to disrupt extra polymeric substances (EPS) matrix of desired bacterial biofilms.

Solvothermal-assisted green synthesis of hybrid Chi-Fe3O4 nanocomposites: a potential antibacterial and antibiofilm material

In this present study, a hybrid Chi-Fe₃O₄ was prepared, characterised and evaluated for its antibacterial and antibiofilm potential against Staphylococcus aureus and Staphylococcus marcescens bacterial pathogens. Intense peak around 260 nm in the ultraviolet-visible spectrum specify the formation of magnetite nanoparticles. Spherical-shaped particles with less agglomeration and particle size distribution of 3.78-46.40 nm were observed using transmission electron microscopy analysis and strong interaction of chitosan with the surface of magnetite nanoparticles was studied using field emission scanning microscopy (FESEM). X-ray diffraction analysis exhibited the polycrystalline and spinel structure configuration of the nanocomposite. Presence of Fe and O, C and Cl elements were confirmed using energy dispersive X-ray microanalysis. Fourier transform infrared spectroscopic analysis showed the reduction and formation of Chi-Fe₃O₄ nanocomposite. The antibacterial activity by deformation of the bacterial cell walls on treatment with Chi-Fe₃O₄ nanocomposite and its interaction was visualised using FESEM and the antibiofilm activity was determined using antibiofilm assay. In conclusion, this present study shows the green synthesis of Chi-Fe₃O₄ nanocomposite and evaluation of its antibacterial and antibiofilm potential, proving its significance in medical and biological applications.

Optimization of Fungal Dextranase Production and Its Antibiofilm Activity, Encapsulation and Stability in Toothpaste

Dextranase catalyzes the degradation of the substrate dextran, which is a component of plaque biofilm. This enzyme is involved in antiplaque accumulation, which can prevent dental caries. The activity of crude dextranase from Penicillium roquefortii TISTR 3511 was assessed, and the maximum value (7.61 unit/g) was obtained at 37 °C and pH 6. The Plackett–Burman design was used to obtain significant factors for enhancing fungal dextranase production, and three influencing factors were found: Dextran, yeast extract concentration and inoculum age. Subsequently, the significant factors were optimized with the Box–Behnken design, and the most suitable condition for dextranase activity at 30.24 unit/g was achieved with 80 g/L dextran, 30 g/L yeast extract and five day- old inoculum. The use of 0.85% alginate beads for encapsulation exhibited maximum dextranase activity at 25.18 unit/g beads, and this activity was stable in toothpaste for three months of testing. This study explored the potential production of fungal dextranase under optimal conditions and its encapsulation using alginate for the possibility of applying encapsulated dextranase as an additive in toothpaste products for preventing dental caries.

Allelochemical catechol comprehensively impedes bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) induces bacterial leaf blight (BLB), is known to be the most devastating disease of rice. The present investigation for the first time explains the antibacterial, anti-biofilm, and antivirulence potential of the simplest allelochemical catechol. Bacterial viability and growth are significantly reducing in catechol treatment. Further study also reveals that catechol also inhibits primary attachment and preformed biofilm of Xoo even at half MIC concentration. The half MIC concentration of catechol also induce a significant decrease in virulence factors like swimming, swarming, exopolysaccharide, and xanthomonadin production. Next, we investigate the possible antibacterial mode of action of catechol against Xoo. Results show that, the catechol caused oxidative stress and targets cell membrane for its antibacterial activity. Whereas, in silico study reveals that, catechol binds with the catalytic domain of XanA protein and this may be consider as a reason for antibiofilm activity of catechol. Moreover, in virulence assay on rice plants, we observe significant decrement in lesion length in catechol and Xoo co-treated rice leaves as compared with only Xoo treated leaves. All the results clearly show, allelochemical catechol to be a potential compound for the antibacterial, anti-biofilm, and antivirulence agent against Xoo and consequently mitigating the BLB disease advancement in rice.

Photodynamic antimicrobial chemotherapy (PACT) using riboflavin inhibits the mono and dual species biofilm produced by antibiotic resistant Staphylococcus aureus and Escherichia coli

PURPOSE

Multispecies biofilms play a significant role in persistent infections. Furthermore, by interspecies transfer of antibiotic resistance genes, multispecies biofilms spread antibiotic resistance. The purpose of this study was to investigate the effect of Photodynamic Antimicrobial Chemotherapy (PACT) using riboflavin on mono and multi species biofilms.

METHODS

For this we used two clinically relevant opportunistic pathogens species E. coli and S. aureus as mono-species and multispecies biofilms. We did broth dilution assay for antibacterial, crystal violet assay for biofilms and fluorometric study for reactive oxygen species (ROS) and extracellular polymeric substance (EPS) production by phenol-HCl method.

RESULTS

Antibacterial study revealed that photo-illuminated riboflavin shows bactericidal effect against each bacteria and their mix culture. E. coli was found to be little more resistant than S. aureus. Crystal violet assay revealed photo-illuminated riboflavin shows anti-biofilms activity against both mono and mix species biofilms. But mix species biofilms were more resistant to PACT than mono species biofilms. Further study revealed this may be due to the interaction between different EPS production, hence in mix species biofilms EPS production is less affected after PACT than mono species biofilms. We found photo-illuminated riboflavin increased the intracellular ROS production.

CONCLUSION

Photo-illuminated riboflavin shows bactericidal and anti-biofilms effect against each bacteria and their mix culture. Photo-illuminated increased intracellular ROS production, which may induce the oxidative stress and destroy the respiratory system of bacteria.

Molecular and taxonomic characterization of arsenic (As) transforming Bacillus sp. strain IIIJ3-1 isolated from As-contaminated groundwater of Brahmaputra river basin, India

Background

Microbe-mediated redox transformation of arsenic (As) leading to its mobilization has become a serious environmental concern in various subsurface ecosystems especially within the alluvial aquifers. However, detailed taxonomic and eco-physiological attributes of indigenous bacteria from As impacted aquifer of Brahmaputra river basin has remained under-studied.

Results

A newly isolated As-resistant and -transforming facultative anaerobic bacterium IIIJ3–1 from As-contaminated groundwater of Jorhat, Assam was characterized. Near complete 16S rRNA gene sequence affiliated the strain IIIJ3–1 to the genus Bacillus and phylogenetically placed within members of B. cereus sensu lato group with B. cereus ATCC 14579(T) as its closest relative with a low DNA-DNA relatedness (49.9%). Presence of iC17:0, iC15:0 fatty acids and menaquinone 7 corroborated its affiliation with B. cereus group, but differential hydroxy-fatty acids, C18:2 and menaquinones 5 & 6 marked its distinctiveness. High As resistance [Maximum Tolerable Concentration = 10 mM As³⁺, 350 mM As⁵⁺], aerobic As³⁺ (5 mM) oxidation, and near complete dissimilatory reduction of As ⁵⁺ (1 mM) within 15 h of growth designated its physiological novelty. Besides O₂, cells were found to reduce As⁵⁺, Fe³⁺, SO₄²⁻, NO₃⁻, and Se⁶⁺ as alternate terminal electron acceptors (TEAs), sustaining its anaerobic growth. Lactate was the preferred carbon source for anaerobic growth of the bacterium with As⁵⁺ as TEA. Genes encoding As⁵⁺ respiratory reductase (arr A), As³⁺ oxidase (aioB), and As³⁺ efflux systems (ars B, acr3) were detected. All these As homeostasis genes showed their close phylogenetic lineages to Bacillus spp. Reduction in cell size following As exposure exhibited the strain’s morphological response to toxic As, while the formation of As-rich electron opaque dots as evident from SEM-EDX possibly indicated a sequestration based As resistance strategy of strain IIIJ3–1.

Conclusion

This is the first report on molecular, taxonomic, and ecophysiological characterization of a highly As resistant, As³⁺ oxidizing, and dissimilatory As⁵⁺ reducing Bacillus sp. IIIJ3–1 from As contaminated sites of Brahmaputra river basin. The strain’s ability to resist and transform As along with its capability to sequester As within the cells demonstrate its potential in designing bioremediation strategies for As contaminated groundwater and other ecosystems.

Gallic Acid an Agricultural Byproduct Modulates the Biofilm Matrix Exopolysaccharides of the Phytopathogen Ralstonia solanacearum

Ralstonia solanacearum is a soil-borne plant pathogen which causes wilt disease in economically important crops of the Solanaceae family in tropical and temperate regions. As biofilm formation is the major virulence factor in R. solanacearum, research inputs are necessary to identify natural biofilm inhibitors to mitigate virulence of this bacterium. Hence in the present work, the anti-biofilm potential of phytochemical compound gallic acid (GA) isolated from an agricultural byproduct (cashewnut shell) was investigated. Initially the Minimum inhibitory concentration (MIC) of crude extracts of cashewnut shell and coconut shell against R. solanacearum were investigated. The MIC of both the extracts were 400 µg/ml and their sub-MIC (200 µg/ml) inhibited biofilms in the range of 62-70% and 49-57%, respectively. As the cashewnut shell extract have higher biofilm inhibitory effect compared to coconut shell extract, we proceeded our further study by isolating the major compound GA from cashewnut shell by acid hydrolysate method. The sub-MIC of crude cashewnut shell extract inhibited 85% of young biofilms. The MIC of GA were observed at 3 mg/ml and sub-MIC (1.5 mg/ml) was found to eradicate 85% of mature biofilms which was confirmed by standard crystal violet assay and the biofilm reduction was further visualized under light microscopy and scanning electron microscopic images. Toxicity of GA was evaluated against R. solanacearum through XTT cell viability assay and found no antibacterial effect at sub-MIC. Additionally, it is confirmed with growth curve and time kill assays. Swimming and twitching motility were considered as an important virulence factors to invade plants and to block the xylem vessels. Therefore, sub-MIC of GA was found to inhibit both swimming and twitching motility of about 93% and 63% respectively. Anti-biofilm efficacy of GA was also worked well with tomato plant model where remarkable biofilm inhibition was found on treatment with GA before and after 24 h of infection with R. solanacearum. Hence GA will be an alternative, cheap source which is eco-friendly as well as novel source for the treatment of R. solanacearum biofilms and to prevent wilt disease in important crops.

Antibacterial, anti-biofilm activity and mechanism of action of pancreatin doped zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus

Staphylococcus aureus are known to cause diseases from normal skin wound to life intimidating infections. Among the drug resistant strain, management of methicillin resistant Staphylococcus aureus (MRSA) is very difficult by using conventional antibiotic treatment. Both Zinc oxide nanoparticles (ZnONPs) and pancreatin (PK) are known to have antibacterial activity. Our main objective is to dope PK on ZnONPs to reduced zinc-oxide toxicity but increased anti-bacterial and anti-biofilms activity. In present study, we showed that, functions of zinc oxide nanoparticles with pancreatin enzyme (ZnONPs-PK) have anti-bacterial, anti-biofilms, anti-motility and anti-virulence properties against MRSA. Moreover, ZnONPs-PK were more potent to eradicate MRSA than only ZnONPs and PK. Application of the produced nano-composites as treatment on infected swine dermis predominantly reflects the potential treatment property of it. The vancomycin sensitivity of MRSA was significantly increased on application with ZnONPs-PK. Further study revealed cell membrane was the target of the ZnONPs-PK and that leads to oxidative damage of the cells. The produced nanoparticles were found completely non-toxic to human's keratinocytes and lung epithelial cell lines at its bactericidal concentration. Overall, this study emphasizes the potential mechanisms underlying the selective bactericidal properties of ZnONPs-PK against MRSA. This novel nanoparticle strategy may provide the ideal solution for comprehensive management of MRSA and its associated diseases with minimising the use of antibiotics.

Chumacin-1 and Chumacin-2 from Pseudomonas aeruginosa strain CGK-KS-1 as novel quorum sensing signaling inhibitors for biocontrol of bacterial blight of rice

The in vitro inhibition of quorum sensing signal, xanthan gum secretion, biofilm formation in different Xanthomonas pathovars and biological control of bacterial blight of rice by the two bioactive extrolites produced by Pseudomonas aeruginosa strain CGK-KS-1 were explored. These extrolites were extracted from Diaion HP-20 resin with methanol and purified by preparative-thin layer chromatography. Further, spectroscopic structural elucidation revealed the tentative identity of these extrolites to be (R,3E,5E,9Z,11E)-13-((3S,5R)-5-acetyl-2,6-dimethylheptan-3-yl)-10-hydroxy-4-methyl-1,8-diazabicyclo[9.3.1]pentadeca-3,5,9,11(15),13-pentaen-2-one and (R,3E,5E,8E,11E)-13-((3S,5R)-5-acetyl-2,6-dimethylheptan-3-yl)-4-methyl-1,8-diazabicyclo[9.3.1]pentadeca-3,5,8,11(15),13-pentaene-2,10-dione, named as Chumacin-1 and Chumacin-2, respectively. Antimicrobial assay showed Chumacin-1 and Chumacin-2 exhibited a strong in vitro growth inhibition against various Xanthomonas pathovars. Quorum sensing overlay assay using a reporter strain Chromobacterium violaceum strain CV026 showed that Chumacin-1 and Chumacin-2 inhibited quorum sensing signaling. The mechanistic studies revealed that these extrolites inhibited the production of quorum sensing signaling factor, cis-11-methyl-2-dodecenoic acid; suppressed the xanthan gum secretion and also inhibited the biofilms formed by various Xanthomonas pathovars. Both Chumacin-1 and Chumacin-2 showed ROS generation in the test Xanthomonas strains, resulting in in vitro cell membrane damage was revealed through CSLM and FE-SEM micrographs. Further, greenhouse experiments using Samba Mashuri (BPT-5204) revealed that seed treatment with Chumacin-1 and Chumacin-2 along with foliar spray groups showed up to ˜80% reduction in bacterial blight disease in rice. To the best of our knowledge, this is the first report on new quorum sensing inhibitors, Chumacin-1 and Chumacin-2 produced by Pseudomonas aeruginosa strain CGK-KS-1 exhibiting DSF inhibition activity in Xanthomonas oryzae pv. oryzae.

Antibiotics versus biofilm: an emerging battleground in microbial communities

Biofilm is a complex structure of microbiome having different bacterial colonies or single type of cells in a group; adhere to the surface. These cells are embedded in extracellular polymeric substances, a matrix which is generally composed of eDNA, proteins and polysaccharides, showed high resistance to antibiotics. It is one of the major causes of infection persistence especially in nosocomial settings through indwelling devices. Quorum sensing plays an important role in regulating the biofilm formation. There are many approaches being used to control infections by suppressing its formation but CRISPR-CAS (gene editing technique) and photo dynamic therapy (PDT) are proposed to be used as therapeutic approaches to subside bacterial biofim infections, especially caused by deadly drug resistant bad bugs.

Inhibition of biofilm formation, quorum sensing activity and molecular docking study of isolated 3, 5, 7-Trihydroxyflavone from Alstonia scholaris leaf against P.aeruginosa

The current study is to evaluate the inhibition of biofilm formation and quorum sensing activity of isolated 3, 5, 7-Trihydroxyflavone (TF) from A.scholaris leaf extract against Pseudomonas aeruginosa. The effects of isolated TF on quorum sensing-regulated virulence factors production such as swimming motility, pyocyanin production, proteolytic, EPS, metabolic assay and inhibition of biofilm formation against P.aeruginosa was evaluated by standard protocols. In addition, the interaction between the isolated TF and active sites of QS- gene (LasI/rhlI, LasR/rhlR, and AHLase) in P.aeruginosa was evaluated by molecular docking studies using AutoDock Tools version 1.5.6. Based on the structural elucidation of the isolated compound was identified as 3, 5, 7-Trihydroxyflavone. Consequently, the isolated TF shows a significant reduction of biofilm formation through the inhibition of QS-dependent phenotypes such as pyocyanin production, proteolytic, swimming motility, EPS activities against P.aeruginosa in a dose-dependent manner. Molecular docking analysis of isolated TF can interfere the signaling [N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL)] molecules in P.aeruginosa by QS genes (LasI, LasR, rhlI, and AHLase) regulation. The isolated TF compound from A.scholaris reveals a greater potential to inhibit biofilm and QS dependent virulence factor production in P.aeruginosa. Docking interaction studies of TF-LasR complex express higher binding affinity than the other QS gene in P.aeruginosa.

Halotolerant bacteria belonging to operational group Bacillus amyloliquefaciens in biocontrol of the rice brown stripe pathogen Acidovorax oryzae

AIMS

The aim of this study was to evaluate the antagonistic activity of halotolerant bacteria against rice brown stripe pathogen Acidovorax oryzae.

METHODS AND RESULTS

Fifteen of 136 isolates of halotolerant bacteria exhibited strong in vitro and in vivo antagonistic activity against both strains of A. oryzae. The 15 antagonistic isolates were identified as 'operational group Bacillus amyloliquefaciens' based on physiological and biochemical features, fatty acid profiles as well as sequence analysis of 16S rRNA, gyrA and rpoB genes. Furthermore, this result indicated that the most effective antagonistic isolates K5-3 and PPB6 could produce siderophore in iron-limiting medium, and four kinds of secondary metabolites based on MALDI-TOF analysis. In addition, the culture filtrates of isolates K5-3 and PPB6 caused the damage of cell membrane evidenced by the TEM images, and resulted in 73-80% reduction in cell numbers, 55-65% reduction in biofilm formation, and 42-50% reduction in swimming ability of both strains of A. oryzae.

CONCLUSIONS

These isolates in particular K5-3 and PPB6 of halotolerant bacteria markedly inhibited the growth of A. oryzae.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first report on biological control of halotolerant bacteria against bacterial brown stripe of rice.

Essential oils from unexplored aromatic plants quench biofilm formation and virulence of Methicillin resistant Staphylococcus aureus

In the current study we have evaluated the antibiofilm and antivirulent properties of unexplored essential oils (EOs) obtained from Pogostemon heyneanus and Cinnamomum tamala against Methicillin Resistant Staphylococcus aureus (MRSA) strains. The EOs from both the aromatic plants was screened for their ability to prevent biofilm formation and to disrupt preformed biofilms. The efficacy of both the EOs to disrupt the preformed biofilms of various MRSA strains was determined by Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM).The EOs were further able to reduce the Extracellular polymeric substance (EPS) and slime synthesis the two factors of the biofilm assemblage. The EOs was also found to be effective in reducing virulence factors like staphyloxanthin and hemolysin. In silico docking studies were performed for the major components of essential oils and dehydroxysqualene synthase of MRSA which is responsible for the synthesis of staphyloxanthin. The results suggest that (E)-nerolidol showed better binding affinity towards the enzyme. Other compounds have similar binding strengths with the enzyme. Furthermore, the synergistic effect EOs along with the commercially available DNaseI and Marine Bacterial DNase (MBD) showed that the synergistic effect had enhanced biofilm disruption ability. The results show that EOs from P. heyneanus and C. tamala has potential antivirulent and biofilm inhibitory properties against clinical and drug resistant S. aureus strains. The present study highlights the importance of bioprospecting plant based natural products as an alternative for antibiotics owing to the emergence of multi-drug resistant strains.

Cytotoxicity and antimicrobial action of selected phytochemicals against planktonic and sessile Streptococcus mutans

Background

Dental caries remains the most prevalent and costly oral infectious disease worldwide, encouraging the search for new and more effective antimicrobials. Therefore, the aim of this work was to study the antimicrobial action of selected phytochemicals (eugenol, citronellol, sabinene hydrate, trans-cinnamaldehyde, terpineol and cinnamic acid) against Streptococcus mutans in planktonic and biofilm states as well as the cytotoxicity of these compounds.

Methods

The antibacterial activity of the selected compounds was evaluated by the determination of the minimal bactericidal concentration. The resazurin assay was used to assess the metabolic activity of sessile S. mutans. The cytotoxicity was determined using a fibroblast cell line.

Results

Among the tested phytochemicals, citronellol, cinnamic acid and trans-cinnamaldehyde were the most effective against both planktonic and sessile S. mutans, an effect apparently related to their hydrophobic character. Additionally, these three compounds did not compromise fibroblasts cell viability.

Discussion

Citronellol, cinnamic acid and trans-cinnamaldehyde demonstrated significant antimicrobial activity and low cytotoxicity proposing their potential as a novel group of therapeutic compounds to control oral infectious diseases. Moreover, their effects are particularly relevant when benchmarked against eugenol, a phytochemical commonly used for prosthodontic applications in dentistry.

Competitive inter-species interactions underlie the increased antimicrobial tolerance in multispecies brewery biofilms

Genetic diversity often enhances the tolerance of microbial communities against antimicrobial treatment. However the sociobiology underlying this antimicrobial tolerance remains largely unexplored. Here we analyze how inter-species interactions can increase antimicrobial tolerance. We apply our approach to 17 industrially relevant multispecies biofilm models, based on species isolated from 58 contaminating biofilms in three breweries. Sulfathiazole was used as antimicrobial agent because it showed the highest activity out of 22 biofilm inhibitors tested. Our analysis reveals that competitive interactions dominate among species within brewery biofilms. We show that antimicrobial treatment can reduce the level of competition and therefore cause a subset of species to bloom. The result is a 1.2-42.7-fold lower percentage inhibition of these species and increased overall tolerance. In addition, we show that the presence of Raoultella can also directly enhance the inherent tolerance of Pseudomonas to antimicrobial treatment, either because the species protect each other or because they induce specific tolerance phenotypes as a response to competitors. Overall, our study emphasizes that the dominance of competitive interactions is central to the enhanced antimicrobial tolerance of the multispecies biofilms, and that the activity of antimicrobials against multispecies biofilms cannot be predicted based on their effect against monocultures.

An in vitro and in silico identification of antibiofilm small molecules from seawater metaclone SWMC166 against Vibrio cholerae O1

This study aimed to determine the antibiofilm activity of seawater microbes against Vibrio cholerae (VCO1) through functional metagenomics approach. A metagenomic library was constructed from Palk Bay seawater and the library was screened to identify the biofilm inhibitory metaclone. Metaclone SWMC166 (harbouring ∼30 kb metagenomic insert) was found to exhibit antibiofilm activity against VCO1. The biofilm inhibitory potential of partially purified ethyl acetate extract of SWMC166 (EA166) was further evaluated through microscopic studies and biochemical assays. Further, EA166 treated VCO1 divulged up-regulation of genes involved in high cell density-mediated quorum sensing (QS) pathway which was analysed by real-time PCR. In order to identify the genes of interest (within ∼30 kb insert), subcloning was performed through shotgun approach. Small molecules from positive subclones SC5 and SC8 were identified through HRLC-MS analysis. Resulted small molecules were docked against QS receptors of V. cholerae to identify the bioactive metabolites. Docking studies revealed that totally seven metabolites were able to interact with QS receptors that can possibly trigger the QS cascade and sequentially inhibit the biofilm formation and virulence factors of VCO1.

Efficacy of cell free supernatant from Bacillus licheniformis in protecting Artemia salina against Vibrio alginolyticus and Pseudomonas gessardii

Bacterial diseases are widespread in aquaculture farms and causative agents often adapt to biofilm mode of growth. These biofilms are detrimental to aquaculture species as they resist antibiotics and other agents that are used to control them. Two bacterial pathogens isolated from infected prawn samples were identified as Vibrio alginolyticus and Pseudomonas gessardii on the basis of morphological features, biochemical characteristics, 16S r RNA gene sequencing and phylogenetic analysis. Their pathogenic nature was confirmed by performing in vivo challenge experiments using Artemia salina as a model system. Seven days post infection, the mortality observed with V. alginolyticus and P. gessardii was 97 ± 4.08% and 77.5 ± 5.24%, respectively. The isolates formed extensive biofilms on polystyrene and glass surfaces. These infections could be controlled in an effective manner by using the cell free supernatant (CFS) of a tropical marine epizoic strain of Bacillus licheniformis D1 that is earlier reported to contain an antimicrobial protein (BLDZ1). The CFS inhibited biofilms in an efficient manner (82.35 ± 1.69 and 82.52 ± 1.11% for V. alginolyticus and P. gessardii, respectively) on co-incubation. In addition, pre-formed biofilms of V. alginolyticus and P. gessardii were also removed (84.53 ± 1.26 and 67.08 ± 1.43%, respectively). Fluorescence and scanning electron microscopic studies confirmed the antibiofilm potential of this protein on glass surfaces. The antibiofilm nature was due to the anti-adhesion and antimicrobial properties exhibited by the CFS. Treatment of A. salina with CFS (6 h prior to infections) was effective in protecting larvae against infections by field isolates. This study highlights the significance of marine natural products in providing alternative biofilm controlling agents to tackle infections and decreasing the usage of antibiotics in aquaculture settings.

Vanillic acid from Actinidia deliciosa impedes virulence in Serratia marcescens by affecting S-layer, flagellin and fatty acid biosynthesis proteins

Serratia marcescens is one of the important nosocomial pathogens which rely on quorum sensing (QS) to regulate the production of biofilm and several virulence factors. Hence, blocking of QS has become a promising approach to quench the virulence of S. marcescens. For the first time, QS inhibitory (QSI) and antibiofilm potential of Actinidia deliciosa have been explored against S. marcescens clinical isolate (CI). A. deliciosa pulp extract significantly inhibited the virulence and biofilm production without any deleterious effect on the growth. Vanillic acid was identified as an active lead responsible for the QSI activity. Addition of vanillic acid to the growth medium significantly affected the QS regulated production of biofilm and virulence factors in a concentration dependent mode in S. marcescens CI, ATCC 14756 and MG1. Furthermore vanillic acid increased the survival of Caenorhabditis elegans upon S. marcescens infection. Proteomic analysis and mass spectrometric identification of differentially expressed proteins revealed the ability of vanillic acid to modulate the expression of proteins involved in S-layers, histidine, flagellin and fatty acid production. QSI potential of the vanillic acid observed in the current study paves the way for exploring it as a potential therapeutic candidate to treat S. marcescens infections.

Mini-Review: Antifouling Natural Products from Marine Microorganisms and Their Synthetic Analogs

Biofouling causes huge economic loss and generates serious ecological issues worldwide. Marine coatings incorporated with antifouling (AF) compounds are the most common practices to prevent biofouling. With a ban of organotins and an increase in the restrictions regarding the use of other AF alternatives, exploring effective and environmentally friendly AF compounds has become an urgent demand for marine coating industries. Marine microorganisms, which have the largest biodiversity, represent a rich and important source of bioactive compounds and have many medical and industrial applications. This review summarizes 89 natural products from marine microorganisms and 13 of their synthetic analogs with AF EC50 values ≤ 25 μg/mL from 1995 (the first report about marine microorganism-derived AF compounds) to April 2017. Some compounds with the EC50 values < 5 μg/mL and LC50/EC50 ratios > 50 are highlighted as potential AF compounds, and the preliminary analysis of structure-relationship (SAR) of these compounds is also discussed briefly. In the last part, current challenges and future research perspectives are proposed based on opinions from many previous reviews. To provide clear guidance for the readers, the AF compounds from microorganisms and their synthetic analogs in this review are categorized into ten types, including fatty acids, lactones, terpenes, steroids, benzenoids, phenyl ethers, polyketides, alkaloids, nucleosides and peptides. In addition to the major AF compounds which targets macro-foulers, this review also includes compounds with antibiofilm activity since micro-foulers also contribute significantly to the biofouling communities.

Antivirulent Properties of Underexplored Cinnamomum tamala Essential Oil and Its Synergistic Effects with DNase against Pseudomonas aeruginosa Biofilms - An In Vitro Study

Pseudomonas aeruginosa is a nosocomial pathogen colonizing patients with chronic infectious diseases and has gained resistance to all the known broad spectrum antibiotics available today. The present study showcases the antibiofilm potential of an essential oil (EO) from an underexplored Cinnamomum species namely, C. tamala, against P. aeruginosa biofilms. Furthermore, the synergistic effects of the EO along with a commercially available DNase (DNaseI) and a DNase (MBD) isolated from a marine bacterium were explored for its antibiofilm activity. The results showed that the synergized action has maximum efficacy in inhibiting young and preformed biofilms. The synergized effect of EO and DNaseI showed 70% inhibition against matured biofilms of P. aeruginosa. The EO from C. tamala also showed quorum sensing inhibitory potential as it could inhibit the swarming motility behavior of P. aeruginosa. The synergistic action of EO and DNases offers a novel alternate therapeutic strategy for combating P. aeruginosa biofilm associated infections.

Streptomyces sp. AT37 isolated from a Saharan soil produces a furanone derivative active against multidrug-resistant Staphylococcus aureus

A novel actinobacterium strain, named AT37, showed a strong activity against some multidrug-resistant Staphylococcus aureus, including methicillin-resistant S. aureus MRSA ATCC 43300, other clinical isolates of MRSA and vancomycin resistant S. aureus VRSA S1. The strain AT37 was isolated from a Saharan soil by a dilution agar plating method using chitin-vitamin agar medium supplemented with rifampicin. The morphological and chemical studies indicated that this strain belonged to the genus Streptomyces. Its 16S rRNA gene sequence was determined and a database search indicated that it was closely associated with the type strain of Streptomyces novaecaesareae NBRC 13368^T with 99.6% of similarity. However, the comparison of the morphological and the physiological characteristics of the strain with those of the nearest species showed significant differences. The strain AT37 secreted the antibiotic optimally during mid-stationary phase of growth. One active compound (AT37-1) was extracted from the culture broth with dichloromethane, separated on silica gel plates and purified by HPLC. Based on spectroscopic analysis of UV-Visible, infrared, and ¹H and ¹³C NMR spectra and spectrometric analysis, the chemical structure of the compound AT37-1 was identified as 5-[(5E,7E,11E)-2,10-dihydroxy-9,11-dimethyl-5,7,11-tridecatrien-1-yl]-2-hydroxy-2-(1-hydroxyethyl)-4-methyl-3(2H)-furanone. Minimum inhibitory concentrations and minimum biofilm inhibitory concentration (MBIC₅₀) of this compound showed significant activity against multidrug-resistant S. aureus with 15-30 and 10-15 μg/mL, respectively.

Marine Sponge-Derived Streptomyces sp. SBT343 Extract Inhibits Staphylococcal Biofilm Formation

Staphylococcus epidermidis and Staphylococcus aureus are opportunistic pathogens that cause nosocomial and chronic biofilm-associated infections. Indwelling medical devices and contact lenses are ideal ecological niches for formation of staphylococcal biofilms. Bacteria within biofilms are known to display reduced susceptibilities to antimicrobials and are protected from the host immune system. High rates of acquired antibiotic resistances in staphylococci and other biofilm-forming bacteria further hamper treatment options and highlight the need for new anti-biofilm strategies. Here, we aimed to evaluate the potential of marine sponge-derived actinomycetes in inhibiting biofilm formation of several strains of S. epidermidis, S. aureus, and Pseudomonas aeruginosa. Results from in vitro biofilm-formation assays, as well as scanning electron and confocal microscopy, revealed that an organic extract derived from the marine sponge-associated bacterium Streptomyces sp. SBT343 significantly inhibited staphylococcal biofilm formation on polystyrene, glass and contact lens surfaces, without affecting bacterial growth. The extract also displayed similar antagonistic effects towards the biofilm formation of other S. epidermidis and S. aureus strains tested but had no inhibitory effects towards Pseudomonas biofilms. Interestingly the extract, at lower effective concentrations, did not exhibit cytotoxic effects on mouse fibroblast, macrophage and human corneal epithelial cell lines. Chemical analysis by High Resolution Fourier Transform Mass Spectrometry (HRMS) of the Streptomyces sp. SBT343 extract proportion revealed its chemical richness and complexity. Preliminary physico-chemical characterization of the extract highlighted the heat-stable and non-proteinaceous nature of the active component(s). The combined data suggest that the Streptomyces sp. SBT343 extract selectively inhibits staphylococcal biofilm formation without interfering with bacterial cell viability. Due to absence of cell toxicity, the extract might represent a good starting material to develop a future remedy to block staphylococcal biofilm formation on contact lenses and thereby to prevent intractable contact lens-mediated ocular infections.

Diversity and antagonistic potential of marine microbes collected from south-west coast of India

The diversity of some of the culturable microorganisms associated with marine flora and fauna collected off Vizhinjam and Mulloor coast of South India was evaluated and their bioactive production potential determined. From a total of 24 bacteria, 4 actinomycetes and 8 fungi isolated from diverse marine sources, five bacterial species-BLM3, BSP2, BCS1, BCS4 and BMA6 showed inhibitory activity against at least one of the tested pathogens viz., Klebsiella pneumonia KU1, Pseudomonas aeruginosa VL3, Salmonella enterica typhimurium MTCC 98, Escherichia coli MTCC 40, Micrococcus luteus MTCC 105, Staphylococcus simulans MTCC 3610, Proteus vulgaris MTCC 426, Vibrio fluvialis, Vibrio sp. P3a and Vibrio sp. P3b. The isolated actinomycetes and fungi did not produce significant inhibition zones against the tested pathogens; however, the macroalgal isolated actinomycetes strain AMA1 produced reddish pigment in Starch Casein medium which remained stable till the stationary phase of growth. The marine sediment isolate BCS4, identified as Bacillus sp. showed wide spectrum of activity against the tested Gram positive bacteria, S. simulans MTCC 3610 and Gram negative bacteria, Proteus vulgaris with zone of inhibitions of 25 and 11 mm respectively. Better extraction of the bioactive compound was obtained with ethyl acetate when compared with methanol, benzene and hexane and TLC analysis revealed the presence of an active compound. The 16SrRNA sequencing confirmed the potent strain belong to Bacillus sp. and hence designated Bacillus sp. BCS4.

Using Molecular Networking for Microbial Secondary Metabolite Bioprospecting

The oceans represent an understudied resource for the isolation of bacteria with the potential to produce novel secondary metabolites. In particular, actinomyces are well known to produce chemically diverse metabolites with a wide range of biological activities. This study characterised spore-forming bacteria from both Scottish and Antarctic sediments to assess the influence of isolation location on secondary metabolite production. Due to the selective isolation method used, all 85 isolates belonged to the phyla Firmicutes and Actinobacteria, with the majority of isolates belonging to the genera Bacillus and Streptomyces. Based on morphology, thirty-eight isolates were chosen for chemical investigation. Molecular networking based on chemical profiles (HR-MS/MS) of fermentation extracts was used to compare complex metabolite extracts. The results revealed 40% and 42% of parent ions were produced by Antarctic and Scottish isolated bacteria, respectively, and only 8% of networked metabolites were shared between these locations, implying a high degree of biogeographic influence upon secondary metabolite production. The resulting molecular network contained over 3500 parent ions with a mass range of m/z 149–2558 illustrating the wealth of metabolites produced. Furthermore, seven fermentation extracts showed bioactivity against epithelial colon adenocarcinoma cells, demonstrating the potential for the discovery of novel bioactive compounds from these understudied locations.

An in silico, in vitro and in vivo investigation of indole-3-carboxaldehyde identified from the seawater bacterium Marinomonas sp. as an anti-biofilm agent against Vibrio cholerae O1

Biofilm formation is a major contributing factor in the pathogenesis of Vibrio cholerae O1 (VCO1) and therefore preventing biofilm formation could be an effective alternative strategy for controlling cholera. The present study was designed to explore seawater bacteria as a source of anti-biofilm agents against VCO1. Indole-3-carboxaldehyde (I3C) was identified as an active principle component in Marinomonas sp., which efficiently inhibited biofilm formation by VCO1 without any selection pressure. Furthermore, I3C applications also resulted in considerable collapsing of preformed pellicles. Real-time PCR studies revealed the down-regulation of virulence gene expression by modulation of the quorum-sensing pathway and enhancement of protease production, which was further confirmed by phenotypic assays. Furthermore, I3C increased the survival rate of Caenorhabditis elegans when infected with VCO1 by significantly reducing in vivo biofilm formation, which was corroborated by a survivability assay. Thus, this study revealed, for the first time, the potential of I3C as an anti-biofilm agent against VCO1.

Quorum quenching: role in nature and applied developments

Quorum sensing (QS) refers to the capacity of bacteria to monitor their population density and regulate gene expression accordingly: the QS-regulated processes deal with multicellular behaviors (e.g. growth and development of biofilm), horizontal gene transfer and host-microbe (symbiosis and pathogenesis) and microbe-microbe interactions. QS signaling requires the synthesis, exchange and perception of bacterial compounds, called autoinducers or QS signals (e.g. N-acylhomoserine lactones). The disruption of QS signaling, also termed quorum quenching (QQ), encompasses very diverse phenomena and mechanisms which are presented and discussed in this review. First, we surveyed the QS-signal diversity and QS-associated responses for a better understanding of the targets of the QQ phenomena that organisms have naturally evolved and are currently actively investigated in applied perspectives. Next the mechanisms, targets and molecular actors associated with QS interference are presented, with a special emphasis on the description of natural QQ enzymes and chemicals acting as QS inhibitors. Selected QQ paradigms are detailed to exemplify the mechanisms and biological roles of QS inhibition in microbe-microbe and host-microbe interactions. Finally, some QQ strategies are presented as promising tools in different fields such as medicine, aquaculture, crop production and anti-biofouling area.

Effect of the synthetic cannabinoid HU-210 on quorum sensing and on the production of quorum sensing-mediated virulence factors by Vibrio harveyi

Background

Bacterial populations communicate through the cell density-dependent mechanism of quorum sensing (QS). Vibrio harveyi, one of the best studied model organisms for QS, was used to explore effects of the synthetic cannabinoid HU-210 on QS and different QS-regulated physiological processes in bacteria.

Results

Analysis of QS-regulated bioluminescence in wild-type and mutant strains of V. harveyi revealed that HU-210 affects the autoinducer-2 (AI-2) pathway, one of three known QS cascades of V. harveyi. Furthermore, QS-mediated biofilm formation and swimming motility in the mutant strain BB152 (AI-1⁻, AI-2⁺) were significantly reduced in the presence of HU-210. HU-210 inhibited QS-mediated virulence factor production without any inhibitory effect on bacterial growth. It also alters the expression of several genes, which are regulated by QS, specifically downregulating the genes of the AI-2 QS cascade.

Conclusion

First evidence is being provided for interference of bacterial signal-transduction systems by a synthetic cannabinoid. The effect of HU-210 was specific to the AI-2 cascade in V. harveyi. AI-2 is known as a "universal autoinducer" and interference with its activity opens a broad spectrum of applications for synthetic cannabinoids in future research as a potential anti-QS agent.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0499-0) contains supplementary material, which is available to authorized users.

Usnic acid inhibits biofilm formation and virulent morphological traits of Candida albicans

Biofilm formation and the yeast to hyphal switch are considered to be important virulence factors of Candida albicans. The present study reports about the potential of usnic acid, a lichen secondary metabolite inhibiting these virulent factors. Usnic acid, at its biofilm inhibitory concentration (BIC) largely reduced the viability of the metabolically active cells in matured C. albicans biofilms, exhibited significant biofilm inhibition (65%) and prevented the property of adhesion. Light microscopic images revealed that usnic acid effectively inhibited the yeast to hyphal switch and confocal microscopy showed that usnic acid greatly reduced the thickness of matured biofilms. Furthermore, usnic acid was able to reduce various sugars present in the exopolysaccharide layer (EPS) which was also confirmed by FT-IR analysis. Taken together, the present study showcases usnic acid as a potent anti-virulent compound against C. albicans and opens up a new avenue for bioprospecting lichen secondary metabolites as anti-virulent compounds.

Bacillus amyloliquefaciens-secreted cyclic dipeptide – cyclo(l-leucyl-l-prolyl) inhibits biofilm and virulence production in methicillin-resistant Staphylococcus aureus

The current study explores the inhibitory efficacy of cyclo(l-leucyl-l-prolyl) (CLP), a cyclic dipeptide fromBacillus amyloliquefacienson the biofilm and virulence production of methicillin-resistantStaphylococcus aureus(MRSA).

Synthesis and characterization of biocompatibility of tenorite nanoparticles and potential property against biofilm formation

Aim is to assess the anti-biofilm property of tenorite nanoparticles and to study their suitability as a possible coating material for medical implants. Tenorite (CuO) nanoparticles were synthesized by the optimized thermal decomposition method and characterized using TEM, XRD, FTIR and UV-Vis analysis. Their influence on biofilm formation of microbes was studied by growing multi drug resistant bacterial strains in the presence or absence of these nanoparticles at various concentrations. The cytotoxicity of nanoparticles on mammalian cells was studied at the corresponding concentrations. The nanoparticles were found to be uniformly dispersed, spherical shaped and <50 nm in size. They showed various degrees of anti-biofilm property against clinically isolated, biofilm forming multi drug resistant microorganisms such as Staphylococcus aureus, Pseudomonas fluorescens, Burkholderia mallei, Klebsiella pneumoniae, and Escherichia coli. Furthermore, Hep-2 cells showed excellent viability at tenorite nanoparticles concentration toxic to microbial growth. These results indicate that tenorite nanoparticles may be ideal candidates for being utilized as coating on medical implants in general and dental implants in particular.