In vitro anti-methicillin-resistant Staphylococcus aureus activity of 2,4-diacetylphloroglucinol produced by Pseudomonas sp. AMSN isolated from a marine alga

2,4-Diacetylphloroglucinol (DAPG) derivatives rapidly eradicate methicillin-resistant staphylococcus aureus without resistance development by disrupting membrane

Methicillin-resistant Staphylococcus aureus (MRSA) causes severe public health challenges throughout the world, and the multi-drug resistance (MDR) of MRSA to antibiotics necessitates the development of more effective antibiotics. Natural 2,4-diacetylphloroglucinol (DAPG), produced by Pseudomonas, displays moderate inhibitory activity against MRSA. A series of DAPG derivatives was synthesized and evaluated for their antibacterial activities, and some showed excellent activities (MRSA MIC = 0.5-2 μg/mL). Among these derivatives, 7g demonstrated strong antibacterial activity without resistance development over two months. Mechanistic studies suggest that 7g asserted its activity by targeting bacterial cell membranes. In addition, 7g exhibited significant synergistic antibacterial effects with oxacillin both in vitro and in vivo, with a tendency to eradicate MRSA biofilms. 7g is a promising lead for the treatment of MRSA.

Genomic and phenotypic characterization of Pseudomonas sp. GOM7, a novel marine bacterial species with antimicrobial activity against multidrug-resistant Staphylococcus aureus

Antimicrobial resistance (AMR) represents a serious threat to global health. The development of new drugs to combat infections caused by bacteria resistant to multiple or even all available antibiotics is urgent. Most antibiotics used up to date have been identified from soil microorganisms. The marine environment represents an alternative source with great potential for the identification of microorganisms that produce bioactive molecules, including antibiotics. In this study, we analyzed the antibacterial activity of a collection of 82 bacterial strains isolated from marine water and sediment samples collected from the Southwestern Gulf of Mexico. Eight of the marine isolates inhibited the growth of different pathogenic bacteria, seven of which were identified as presumptive Pseudomonas aeruginosa. Interestingly, genome sequencing and phylogenetic analysis revealed that the remaining marine isolate showing antibacterial activity is a novel Pseudomonas species that we denominated Pseudomonas sp. GOM7, which was not pathogenic in the Galleria mellonella infection model in the conditions tested. Notably, Pseudomonas sp. GOM7 inhibited the growth of multidrug and methicillin-resistant strains of the priority pathogen Staphylococcus aureus. Our results show that the anti-S. aureus compound(s) produced by Pseudomonas sp. GOM7 can be extracted from the culture supernatant of this bacterium with the organic solvent ethyl acetate. Annotation of the Pseudomonas sp. GOM7 genome revealed the presence of several biosynthetic gene clusters predicted to code for possible antimicrobial compounds. Our results further highlight the potential of bacteria from the Gulf of Mexico as a source of novel antimicrobials.

Pharmacological potential of seaweed-associated heterotrophic Firmicutes

Seaweed-associated bacterial symbionts are sources of potential pharmacological properties. The present study resulted in the culture-dependent isolation of bioactive heterotrophs belonging to the bacterial phylum Firmicutes, which were dominated more than 30% of the 127 cultivable isolates, among which 23 of them showed potential antimicrobial activities against a wide range of pathogens. The symbionts isolated from the seaweed Sargassum wightii showed significant bioactivity. Those were characterised as Bacillus safensis MTCC13040, B. valismortis MTCC13041, B. velezensis MTCC13044, B. methylotrophicus MTCC13042, Oceanobacillus profundus MTCC13045, B. tequilensis MTCC13043, and B. altitudinis MTCC13046. The organic extracts of the studied isolates showed potential antimicrobial properties against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci (minimum inhibitory concentration 6.25-12.5 μg ml^-1 ). The organic extract of B. altitudinis MTCC13046 displayed significantly greater radical quenching ability (IC₉₀ 133 μg ml^-1 , p < 0.05) other than attenuating hydroxymethyl glutaryl coenzyme A reductase (IC₉₀ 10.21 μg ml^-1 , p < 0.05) and angiotensin converting enzyme-1 (IC₉₀ 498 μg ml^-1 , p < 0.05) relative to other studied heterotrophs. The organic extract of B. tequilensis MTCC13043 displayed significantly greater attenuation potential against pro-inflammatory 5-lipooxygenase (IC₉₀ 5.94 μg ml^-1 , p < 0.05) and dipeptidyl peptidase-4 (IC₉₀ 271 μg ml^-1 , p < 0.05). The seaweed-associated B. altitudinis MTCC13046 and B. tequilensis MTCC13043 could be used to develop promising pharmacological leads.

Phloroglucinol and Its Derivatives: Antimicrobial Properties toward Microbial Pathogens

Phloroglucinol (PG) is a natural product isolated from plants, algae, and microorganisms. Aside from that, the number of PG derivatives has expanded due to the discovery of their potential biological roles. Aside from its diverse biological activities, PG and its derivatives have been widely utilized to treat microbial infections caused by bacteria, fungus, and viruses. The rapid emergence of antimicrobial-resistant microbial infections necessitates the chemical synthesis of numerous PG derivatives in order to meet the growing demand for drugs. This review focuses on the use of PG and its derivatives to control microbial infection and the underlying mechanism of action. Furthermore, as future perspectives, some of the various alternative strategies, such as the use of PG and its derivatives in conjugation, nanoformulation, antibiotic combination, and encapsulation, have been thoroughly discussed. This review will enable the researcher to investigate the possible antibacterial properties of PG and its derivatives, either free or in the form of various formulations.

Marine Bacterial Secondary Metabolites: A Treasure House for Structurally Unique and Effective Antimicrobial Compounds

The prevalence of antimicrobial resistance reduces the effectiveness of antimicrobial drugs in preventing and treating infectious diseases caused by pathogenic organisms, such as bacteria, fungi, and viruses. Because of the burgeoning growth of microbes with antimicrobial-resistant traits, there is a dire need to identify and develop novel and effective antimicrobial agents to treat infections from antimicrobial-resistant strains. The marine environment is rich in ecological biodiversity and can be regarded as an untapped resource for prospecting novel bioactive compounds. Therefore, exploring the marine environment for antimicrobial agents plays a significant role in drug development and biomedical research. Several earlier scientific investigations have proven that bacterial diversity in the marine environment represents an emerging source of structurally unique and novel antimicrobial agents. There are several reports on marine bacterial secondary metabolites, and many are pharmacologically significant and have enormous promise for developing effective antimicrobial drugs to combat microbial infections in drug-resistant pathogens. In this review, we attempt to summarize published articles from the last twenty-five years (1996–2020) on antimicrobial secondary metabolites from marine bacteria evolved in marine environments, such as marine sediment, water, fauna, and flora.

Bacterial-Derived Plant Protection Metabolite 2,4-Diacetylphloroglucinol: Effects on Bacterial Cells at Inhibitory and Subinhibitory Concentrations

2,4-Diacetylphloroglucinol (2,4-DAPG) is a well-known bacterial secondary metabolite, however, its mechanism of inhibitory and subinhibitory action on bacterial cells is still poorly understood. The mechanism of 2,4-DAPG action on model bacterial strains was investigated using fluorescent spectroscopy and the action of the antibiotic was found to involve a rapid increase in membrane permeability that was accompanied by a reduction in its viability in nutrient-poor medium. At the same time, antibacterial action in nutrient-rich medium developed for several hours. Atomic force microscopy demonstrated time-dependent disturbances in the outer membrane of Escherichia coli when exposed to 2,4-DAPG, while Staphylococcusaureus cells have been visualized with signs of intracellular leakage. In addition, 2,4-DAPG inhibited the metabolic activity of S. aureus and E. coli bacterial cells in mature biofilms. Observed differences in the antibiofilm activity were dependent upon antibiotic concentration. The intracellular targets of the action of 2,4-DAPG were assessed using bacterial biosensors with inducible bioluminescence corresponding to DNA and protein damage. It was unable to register any positive response from either sensor. As a result, the bactericidal action of 2,4-DAPG is believed to be associated with the destruction of the bacterial barrier structures. The subinhibitory effect of 2,4-diacetylphloroglucinol was tested on quorum-sensing mediated processes in Pectobacterium carotovorum. Subinhibitory concentrations of 2,4-DAPG were found to lower the biosynthesis of acyl-homoserine lactones in P. carotovorum in a dose-dependent manner. Further investigation elucidated that 2,4-DAPG inhibits the metabolic activity of bacteria without affecting their viability.

Antibacterial pyrrolidinyl and piperidinyl substituted 2,4-diacetylphloroglucinols from Pseudomonas protegens UP46

In the search for new antibiotic compounds, fractionation of Pseudomonas protegens UP46 culture extracts afforded several known Pseudomonas compounds, including 2,4-diacetylphloroglucinol (DAPG), as well as two new antibacterial alkaloids, 6-(pyrrolidin-2-yl)DAPG (1) and 6-(piperidin-2-yl)DAPG (2). The structures of 1 and 2 were determined by nuclear magnetic resonance spectroscopy and mass spectrometry. Compounds 1 and 2 were found to have antibacterial activity against the Gram-positive bacteria Staphylococcus aureus and Bacillus cereus, with minimal inhibitory concentration (MIC) 2 and 4 μg ml^-1, respectively, for 1, and 2 μg ml^-1 for both pathogens for 2. The MICs for 1 and 2, against all tested Gram-negative bacteria, were >32 μg ml^-1. The half maximal inhibitory concentrations against HepG2 cells for compounds 1 and 2 were 11 and 18 μg ml^-1, respectively, which suggested 1 and 2 be too toxic for further evaluation as possible new antibacterial drugs. Stable isotope labelling experiments showed the pyrrolidinyl group of 1 to originate from ornithine and the piperidinyl group of 2 to originate from lysine. The P. protegens acetyl transferase (PpATase) is involved in the biosynthesis of monoacetylphloroglucinol and DAPG. No optical rotation was detected for 1 or 2, and a possible reason for this was investigated by studying if the PpATase may catalyse a stereo-non-specific introduction of the pyrrolidinyl/piperidinyl group in 1 and 2, but unless the PpATase can be subjected to major conformational changes, the enzyme cannot be involved in this reaction. The PpATase is, however, likely to catalyse the formation of 2,4,6-triacetylphloroglucinol from DAPG.

Targeting antimicrobial drug resistance with marine natural products

The rise and spread of antimicrobial resistance represents one of the most pressing health issues of today. Antimicrobial resistance in micro-organisms can arise due to a multiplicity of factors, including permeability changes in the cell membrane, increase of drug efflux pumps, enzymatic modification or inactivation of the antibiotic, target site modification, alternative metabolic pathways and biofilm formation. The marine environment is a valuable source of diverse natural products with a huge variety of biological activities. Among them, antimicrobial compounds show promising biological activities against numerous drug-resistant bacteria and fungi, making marine natural products a very promising resource in the search for novel antimicrobial agents. This review summarises the state-of-art of marine natural products with antibacterial and antifungal properties against drug-resistant micro-organisms. These natural products were categorised based on their chemical structure, and their respective sources and activities are highlighted. The chemical diversity associated with these marine-derived molecules is enormous, including peptides, polyketides, alkaloids, sterols, terpenoids, lactones, halogenated compounds, nucleosides, etc., some of which have rare substructures. Some of the marine compounds mentioned do not have intrinsic antimicrobial activity but potentiate the antimicrobial effect of other antimicrobials via inhibition of efflux pumps. Although these agents are still in preclinical studies, evidence of their in vivo efficacy suggest research of new drugs from the ocean to overcome antimicrobial resistance in order to fulfil an unmet medical need.

Potential of marine natural products against drug-resistant bacterial infections

Natural products have been a rich source of compounds with structural and chemical diversity for drug discovery. However, antibiotic resistance in bacteria has been reported for nearly every antibiotic once it is used in clinical practice. In the past decade, pharmaceutical companies have reduced their natural product discovery projects because of challenges, such as high costs, low return rates, and high rediscovery rates. The largely unexplored marine environment harbours substantial diversity and is a large resource to discover novel compounds with novel modes of action, which is essential for the treatment of drug-resistant bacterial infections. In this Review, we report compounds derived from marine sources that have shown in-vivo and in-vitro efficacy against drug-resistant bacteria. Analysis of the physicochemical properties of these marine natural products with activity against drug-resistant bacteria showed that 60% of the compounds have oral bioavailability potential. Their overall distribution pattern of drug characteristics agrees with the observation that marketed antibacterial drugs have a polar distribution, with a lower median calculated logP. The aim of this Review is to summarise the diversity of these marine natural products, with a special focus on analysis of drug bioavailability. Such biologically active compounds, with high degrees of bioavailability, have the potential to be developed as effective drugs against infectious diseases.

Isolation, purification, structural elucidation and antimicrobial activities of kocumarin, a novel antibiotic isolated from actinobacterium Kocuria marina CMG S2 associated with the brown seaweed Pelvetia canaliculata

AIMS

Screening of seaweed-associated bacteria capable of producing antimicrobials.

METHODS AND RESULTS

Fifteen microbial strains, associated to the brown seaweed Pelvetia canaliculata (Linnaeus) attached to the rocks of Sonmiani Beach (Karachi, Pakistan), were screened. Crude extract filtrates of CMG S2 strain grew on Zobell marine agar (ZMA) had the most remarkable antimicrobial activity. Based on its phenotypic aspects (e.g. Gram-positive, microccoid form), biochemical characteristics (e.g. halotolerance) and genetic analyses, CMG S2 is identified as a putatively new Kocuria marina type strain belonging to the actinobacteria's class and micrococcaceae family. Thereby, the nucleotide sequence analysis of its full-length 16S ribosomal ribonucleic acid (rRNA) gene (GenBank accession number EU073966.1) displayed highest identity (i.e. 99%) and score (2630) with K. marina KMM 3905. Phylogenic trees analysis using the neighbor-joining method showed closest evolutionary distance of CMG S2 with KMM 3905 strain and K. carniphila (DC2201) specie. Interestingly, a unique ultraviolet (UV)-bioactive compound was purified from CMG S2 crude extracts by flash silica gel column and thin-layer chromatography (TLC) techniques. Its chemical structure was unraveled as 4-[(Z)-2 phenyl ethenyl] benzoic acid (PEBA, later named kocumarin) by nuclear magnetic resonance (NMR) spectroscopy techniques. Importantly, kocumarin demonstrated prominent and rapid growth inhibition against all tested fungi and pathogenic bacteria including methicillin-resistant Staphylococcus aureus (MRSA), with a minimal fungal inhibitory concentration (MFC) of 15-25μg/mL and a minimal (bacterial) inhibitory concentration (MIC) of 10-15μg/mL.

SIGNIFICANCE AND IMPACT OF THE STUDY

Kocumarin represents a new promising natural antibiotic for in vivo and environmental applications.

Antimicrobial compounds from seaweeds-associated bacteria and fungi

In recent decade, seaweeds-associated microbial communities have been significantly evaluated for functional and chemical analyses. Such analyses let to conclude that seaweeds-associated microbial communities are highly diverse and rich sources of bioactive compounds of exceptional molecular structure. Extracting bioactive compounds from seaweed-associated microbial communities have been recently increased due to their broad-spectrum antimicrobial activities including antibacterial, antifungal, antiviral, anti-settlement, antiprotozoan, antiparasitic, and antitumor. These allelochemicals not only provide protection to host from other surrounding pelagic microorganisms, but also ensure their association with the host. Antimicrobial compounds from marine sources are promising and priority targets of biotechnological and pharmaceutical applications. This review describes the bioactive metabolites reported from seaweed-associated bacterial and fungal communities and illustrates their bioactivities. Biotechnological application of metagenomic approach for identifying novel bioactive metabolites is also dealt, in view of their future development as a strong tool to discover novel drug targets from seaweed-associated microbial communities.

Whole animal automated platform for drug discovery against multi-drug resistant Staphylococcus aureus

Staphylococcus aureus, the leading cause of hospital-acquired infections in the United States, is also pathogenic to the model nematode Caenorhabditis elegans. The C. elegans-S. aureus infection model was previously carried out on solid agar plates where the bacteriovorous C. elegans feeds on a lawn of S. aureus. However, agar-based assays are not amenable to large scale screens for antibacterial compounds. We have developed a high throughput liquid screening assay that uses robotic instrumentation to dispense a precise amount of methicillin resistant S. aureus (MRSA) and worms in 384-well assay plates, followed by automated microscopy and image analysis. In validation of the liquid assay, an MRSA cell wall defective mutant, MW2ΔtarO, which is attenuated for killing in the agar-based assay, was found to be less virulent in the liquid assay. This robust assay with a Z'-factor consistently greater than 0.5 was utilized to screen the Biomol 4 compound library consisting of 640 small molecules with well characterized bioactivities. As proof of principle, 27 of the 30 clinically used antibiotics present in the library conferred increased C. elegans survival and were identified as hits in the screen. Surprisingly, the antihelminthic drug closantel was also identified as a hit in the screen. In further studies, we confirmed the anti-staphylococcal activity of closantel against vancomycin-resistant S. aureus isolates and other Gram-positive bacteria. The liquid C. elegans-S. aureus assay described here allows screening for anti-staphylococcal compounds that are not toxic to the host.

Methicillin-resistant Staphylococcus aureus, Vancomycin-resistant Enterococcus faecalis and Enterococcus faecium active Dimeric Isobutyrylphloroglucinol from Ivesia gordonii

Bioassay-guided fractionation of the chloroform soluble fraction of stem, leaf, and flower extracts of the American plant Ivesia gordonii led to the isolation of a new dimeric acylphloroglucinol, 3,3′-diisobutyryl-2,6′-dimethoxy-4,6,2′,4′-tetrahydroxy-5,5′dimethyldiphenyl methane (1), to which we have assigned the trivial name of ivesinol (1), together with a known monomeric acylphloroglucinol, 1,5-dihydroxy-2-(2′-methylpropionyl)-3-methoxy-6-methylbenzene (2). The structures of the isolated compounds were characterized using 1D- and 2D- NMR spectroscopy, including COSY, HMQC, HMBC, and ROESY experiments, as well as mass spectrometry. Ivesinol (1) showed potent activity against Staphylococcus aureus (SA) and methicillin-resistant S. aureus (MRSA) with IC50/MIC/MBC values of 0.10/1.25/>20 μg/mL and 0.05/0.31/>20 μg/mL, respectively (vs. IC50/MIC/MBC 0.13/0.5/1.0 μg/mL and 0.13/0.5/1.0 μg/mL of ciprofloxacin), while the corresponding monomer 2 was found to be less active. Compound 1 also demonstrated strong activity against vancomycin-resistant Enteococcus faecium ( VRE) with IC50/MIC/MBC values of 0.22/1.25/>20 μg/mL, whereas the reference standard ciprofloxacin was found to be inactive against this strain. In addition, compound 2 showed moderate activity against two species of Candida and Cryptococcus neoformans, while 1 was inactive against these fungi. In order to evaluate the influence of the acyl group(s) in phloroglucinol (3) as a ligand, the mono- (4) and diacetylphloroglucinol (5) were prepared from 3, and evaluated for their in vitro SA, MRSA, and VRE activities; 2,4-diacetylphloroglucinol (5) showed potent activity, like 1, against SA, MRSA, and VRE (ATCC 700221) with IC50/ MIC values of 0.3/2.5, 0.23/2.5, and 0.86/2.5 μg/mL, respectively, while 4 was inactive.

Marine bacteria: potential sources for compounds to overcome antibiotic resistance

Methicillin-resistant Staphylococcus aureus (MRSA) is the most problematic Gram-positive bacterium in the context of public health due to its resistance against almost all available antibiotics except vancomycin and teicoplanin. Moreover, glycopeptide-resistant S. aureus have been emerging with the increasing use of glycopeptides. Recently, resistant strains against linezolid and daptomycin, which are alternative drugs to treat MRSA infection, have also been reported. Thus, the development of new drugs or alternative therapies is clearly a matter of urgency. In response to the antibiotic resistance, many researchers have studied for alternative antibiotics and therapies. In this review, anti-MRSA substances isolated from marine bacteria, with their potential antibacterial effect against MRSA as potential anti-MRSA agents, are discussed and several strategies for overcoming the antibiotic resistance are also introduced. Our objective was to highlight marine bacteria that have potential to lead in developing novel antibiotics or clinically useful alternative therapeutic treatments.

Pharmacologically prospective antibiotic agents and their sources: a marine microbial perspective

Marine microbes have been a storehouse of bioactive metabolites with tremendous potential as drug candidates. Marine microorganism derived secondary metabolites (chemical compounds/peptides) are considered to be a burning area of research since recent past. Many of such compounds have been proven to be anti-bacterial, anti-fungal, anti-algal, anti-HIV, anti-helminthic, anti-protozoan, anti-tumor and anti-allergic agents. Marine bacteria and fungi have been reported to be the producers of such compounds owing to their defense mechanisms and metabolic by products. Although the number of natural products isolated from these classes of marine microbial flora is large, a limited number of such compounds reach the clinical trial and even less number of them get approved as a drug. Here we discuss the recent studies on the isolation, characterization and the pharmacological significances of anti-bacterial, anti-fungal and anti-infective agents of marine microbial origin. Further, the clinical status of such compounds has also been discussed in comparison with those derived from their terrestrial counterparts.

Novel bioactive metabolites producing endophytic fungus Colletotrichum gloeosporioides against multidrug-resistant Staphylococcus aureus

The emergence of antibiotic-resistant bacteria such as Staphylococcus aureus calls for inventive research and development strategies. Inhibition of this bacterial pathogenesis may be a promising therapeutic approach. The screening of antimicrobial compounds from endophytes is a promising way to meet the increasing threat of drug-resistant strains of human and plant pathogens. In the present study, a novel endophytic fungus, Colletotrichum gloeosporioides, was isolated from the medicinal plant Vitex negundo L. Extracts of C. gloeosporioides were obtained using hexane, ethyl acetate and methanol solvents. The fungal extracts exhibited an effective antimicrobial activity against bacterial and fungal strains. The extracts were also analysed for antibacterial activity against methicillin-, penicillin- and vancomycin-resistant S. aureus strains (1-10). The methanol extract showed an effective antibacterial activity against S. aureus strain 9, with a minimal inhibitory concentration of 31.25 μg mL(-1) . The synergistic action of endophytic fungal extract with antibiotics such as methicillin, penicillin and vancomycin was observed against S. aureus strain 6. The fractional inhibitory concentration index of methanol extract with methicillin, penicillin and vancomycin was 1.0, 0.5 and 0.375, respectively. These results clearly indicate that the metabolite of endophytic fungus C. gloeosporioides is a potential source of new antibiotics.

Novel anti-infective compounds from marine bacteria

As a result of the continuous evolution of microbial pathogens towards antibiotic-resistance, there have been demands for the development of new and effective antimicrobial compounds. Since the 1960s, the scientific literature has accumulated many publications about novel pharmaceutical compounds produced by a diverse range of marine bacteria. Indeed, marine micro-organisms continue to be a productive and successful focus for natural products research, with many newly isolated compounds possessing potentially valuable pharmacological activities. In this regard, the marine environment will undoubtedly prove to be an increasingly important source of novel antimicrobial metabolites, and selective or targeted approaches are already enabling the recovery of a significant number of antibiotic-producing micro-organisms. The aim of this review is to consider advances made in the discovery of new secondary metabolites derived from marine bacteria, and in particular those effective against the so called "superbugs", including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (VRE), which are largely responsible for the increase in numbers of hospital acquired, i.e., nosocomial, infections.

Bioactive substances produced by marine isolates of Pseudomonas

Pseudomonas is a genus of non-fermentative gram-negative Gammaproteobacteria found both on land and in the water. Many terrestrial isolates of this genus have been studied extensively. While many produce bioactive substances, enzymes, and biosurfactants, other Pseudomonas isolates are used for biological control of plant diseases and bioremediation. In contrast, only a few marine isolates of this genus have been described that produce novel bioactive substances. The chemical structures of the bioactive substances from marine Pseudomonas are diverse, including pyroles, pseudopeptide pyrrolidinedione, phloroglucinol, phenazine, benzaldehyde, quinoline, quinolone, phenanthren, phthalate, andrimid, moiramides, zafrin and bushrin. Some of these bioactive compounds are antimicrobial agents, and dibutyl phthalate and di-(2-ethylhexyl) phthalate have been reported to be cathepsin B inhibitors. In addition to being heterogeneous in terms of their structures, the antibacterial substances produced by Pseudomonas also have diverse mechanisms of action: some affect the bacterial cell membrane, causing bacterial cell lysis, whereas others act as acetyl-CoA carboxylase and nitrous oxide synthesis inhibitors. Marine Pseudomonas spp. have been isolated from a wide range of marine environments and are a potential untapped source for medically relevant bioactive substances.

A new antibacterial compound produced by an indigenous marine bacteria--fermentation, isolation, and biological activity

The use of microorganisms for biological purpose has become an effective alternative to control pathogens. A marine bacterium Pseudomonas aeruginosa was isolated from Eal fish of Baluchistan coast of Pakistan. This strain produced a bactericidal antibiotic against environmental and clinical isolates. In this study, we purified bactericidal antibiotic from the ethyl acetate extract of the cells of P. aeruginosa and analyzed its chemical structure. Based on spectrometric analysis, this compound 1 is proposed to be 1-methyl-1,4 dihydroquinoline and is active against methicillin-resistant Staphylococcus aureus (MRSA), methicillin-sensitive S. aureus (MSSA), Salmonella typhi, Shigella flexneri, Escherichia coli, Proteus mirabilis, Vibrio aliginolyticus, Micrococcus luteus, Enterococcus faecalis, Enterobacter faecium but it is not active against G streptococci, Candida albicans, Aspergillus niger. Minimal inhibitory concentration for Gram-positive bacteria was between 50 and 75 microg mL(-1) and for Gram-negative bacteria 75-100 microg mL(-1).

A Large Scale Synthesis of a Natural Antibiotic, 2,4-Diacetylophloroglucinol (DAPG)

A natural antibiotic, 2,4-diacetylophloroglucinol (DAPG), has been prepared by the acetylation of phloroglucinol (PhL) with acetic anhydride in the presence of boron trifluoride etherate complex. The crude DAPG is efficiently purified using chromatographic filtration with boiling eluent.

Inhibitory action of marine algae extracts on the Trypanosoma cruzi dihydroorotate dehydrogenase activity and on the protozoan growth in mammalian cells

Trypanosoma cruzi, the causative agent of Chagas' disease, replicates in mammalian cells and relies on the de novo pyrimidine biosynthetic pathway that supplies essential precursors for nucleic acid synthesis. The protozoan dihydroorotate dehydrogenase (DHOD), the fourth enzyme of the pathway catalyzing production of orotate from dihydroorotate, markedly differs from the human enzyme. This study was thus aimed to search for potent inhibitors against T. cruzi DHOD activity, and a number of methanol extracts prepared from green, brown, and red algae were assayed. The extracts from two brown algae, Fucus evanescens and Pelvetia babingtonii, yielded 59 and 58% decrease in the recombinant DHOD activity, respectively, at the concentration of 50 microg/ml. Inhibition by these extracts was noncompetitive with respect to dihydroorotate, with apparent Ki values of 35.3+/-5.9 and 10.3+/-4.4 microg/ml, respectively. Further, in an in vitro T. cruzi-HeLa cell infection system, ethanol-reconstituted F. evanescens and P. babingtonii extracts at the concentration of 1 microg/ml, respectively, decreased significantly the infection rate of host cells and the average parasite number per infected cell. These results imply that F. evanescens and P. babingtonii contain inhibitor(s) against the T. cruzi DHOD activity and against the protozoan infection and proliferation in mammalian cells. Identification of inhibitor(s) in these two brown algae and further screening of other marine algae may facilitate the discovery of new, anti-trypanosomal lead compounds.

Pseudoalteromonas phenolica sp. nov., a novel marine bacterium that produces phenolic anti-methicillin-resistant Staphylococcus aureus substances

Four strains of aerobic, Gram-negative rods, motile by means of a single polar flagellum, that produced phenolic anti-methicillin-resistant Staphylococcus aureus (MRSA) substances and brown-pigmented colonies, were isolated from sea water. The G + C content of the DNA ranged from 39.9 to 40.6 mol%. The isolates grew at 18-37 degrees C and pH 6.5-9.5 (optimal pH 7.5-9) and in medium containing 1-5% (w/v) NaCl (optimal NaCl concentration 2-3.5%). The isolates grew optimally in medium dissolved in 40-100% artificial sea water. Based on 16S rDNA similarities, the novel strains were closely related to Pseudoalteromonas luteoviolacea and Pseudoalteromonas piscicida, with 96.3 and 95.7% sequence similarity, respectively. However, the strains could be differentiated from P. lutioviolacea by seven traits and from P. piscicida by 10 traits. Analysis of DNA-DNA relatedness to these related species revealed low levels of DNA hybridization (19.6% to P. luteoviolacea and 22.4% to P. piscicida). However, the type strain, O-BC30T, and the other three bacterial isolates showed high DNA relatedness to each other, ranging from 84.8 to 93.7%. Based on the results of phenotypic characterization, phylogenetic analysis based on 16S rDNA sequences and DNA-DNA hybridization, it is concluded that these isolates represent a novel species in the genus Pseudoalteromonas. Because the type strain, O-BC30T (=IAM 14989T =KCTC 12086T), produces phenolic anti-MRSA substances, the name proposed for this novel species is Pseudoalteromonas phenolica sp. nov.

Lysis of methicillin-resistant Staphylococcus aureus by 2,4-diacetylphloroglucinol produced by Pseudomonas sp. AMSN isolated from a marine alga

Previously 2,4-diacetylphloroglucinol (DAPG) produced by Pseudomonas sp. AMSN isolated from a marine alga, had demonstrated a high level of anti-methicillin-resistant Staphylococcus aureus (MRSA) comparable with that of vancomycin. In this study, this substance had bacteriolytic activity against MRSA at 1 microg/ml as well as similar activity against Vibrio parahaemolyticus at 24 microg/ml that suggests a novel antibacterial mode of action by this substance. Heat and pH stability tests showed it to be stable at temperatures ranging from 35 to 70 degrees C and at pHs ranging from 2-7. It was not acutely toxic to mice at levels up to 100 mg/kg.