Mercedes de la Cruz

A New Approach to Drug Discovery High-Throughput Screening of Microbial Natural Extracts against Aspergillus fumigatus Using Resazurin

Natural products are an inexhaustible source for drug discovery. However, the validation and selection of primary screening assays are vital to guarantee a selection of extracts or molecules with relevant pharmacological action and worthy of following up. The assay must be rapid, simple, easy to implement, and produce quick results and preferably at a low cost. In this work, we developed and validated a colorimetric microtiter assay using the resazurin viability dye. The parameters of the resazurin method for high-throughput screening (HTS) using natural extracts against Aspergillus fumigatus were optimized and set up. The extracts plus RPMI-1640 modified medium containing the spores and 0.002% resazurin were added per well. The fluorescence was read after 24 to 30 h of incubation. The resazurin proved to be as suitable as Alamar Blue for determining the minimal inhibitory concentration of different antifungals against A. fumigatus and effective to analyze fungicidal and fungistatic compounds. An HTS of 12 000 microbial extracts was carried out against two A. fumigatus strains, and 2.7% of the extracts displayed antifungal activity. Our group has been the first to use this methodology for screening a collection of natural extracts to identify compounds with antifungal activity against the medically important human pathogen A. fumigatus.

Antimicrobial activity of heterotrophic bacterial communities from the marine sponge Erylus discophorus (Astrophorida, Geodiidae).

Heterotrophic bacteria associated with two specimens of the marine sponge Erylus discophorus were screened for their capacity to produce bioactive compounds against a panel of human pathogens (Staphylococcus aureus wild type and methicillin-resistant S. aureus (MRSA), Bacillus subtilis, Pseudomonas aeruginosa, Acinetobacter baumanii, Candida albicans and Aspergillus fumigatus), fish pathogen (Aliivibrio fischeri) and environmentally relevant bacteria (Vibrio harveyi). The sponges were collected in Berlengas Islands, Portugal. Of the 212 isolated heterotrophic bacteria belonging to Alpha- and Gammaproteobacteria, Actinobacteria and Firmicutes, 31% produced antimicrobial metabolites. Bioactivity was found against both Gram positive and Gram negative and clinically and environmentally relevant target microorganisms. Bioactivity was found mainly against B. subtilis and some bioactivity against S. aureus MRSA, V. harveyi and A. fisheri. No antifungal activity was detected. The three most bioactive genera were Pseudovibrio (47.0%), Vibrio (22.7%) and Bacillus (7.6%). Other less bioactive genera were Labrenzia, Acinetobacter, Microbulbifer, Pseudomonas, Gordonia, Microbacterium, Micrococcus and Mycobacterium, Paenibacillus and Staphylococcus. The search of polyketide I synthases (PKS-I) and nonribosomal peptide synthetases (NRPSs) genes in 59 of the bioactive bacteria suggested the presence of PKS-I in 12 strains, NRPS in 3 strains and both genes in 3 strains. Our results show the potential of the bacterial community associated with Erylus discophorus sponges as producers of bioactive compounds.

Antisense-Guided Isolation and Structure Elucidation of Pannomycin, a Substituted cis-Decalin from Geomyces pannorum

Antisense-based screening strategies can be used to sensitize a microorganism and selectively detect inhibitors against a particular cellular target of interest. A strain of Staphylococcus aureus that generates an antisense RNA against SecA,a central member of the protein secretion machinery, has been used to screen for novel antibacterials. Possible inhibitors of the SecA ATP-ase were selected with a high-throughput, two-plate agar-based whole cell differential sensitivity screen. After screening a library of over 115 000 natural products extracts with the SecA antisense strain, an extract of Geomyces pannorum was identified as providing increased activity against the sensitized strain as compared with the wild-type control. Bioassay-guided isolation of the active component from this fungal extract provided a new cis-decalin secondary metabolite, which we have named pannomycin.

Sponge-Derived Kocuria and Micrococcus spp. as Sources of the New Thiazolyl Peptide Antibiotic Kocurin

Forty four marine actinomycetes of the family Microccocaceae isolated from sponges collected primarily in Florida Keys (USA) were selected from our strain collection to be studied as new sources for the production of bioactive natural products. A 16S rRNA gene based phylogenetic analysis showed that the strains are members of the genera Kocuria and Micrococcus. To assess their biosynthetic potential, the strains were PCR screened for the presence of secondary metabolite genes encoding nonribosomal synthetase (NRPS) and polyketide synthases (PKS). A small extract collection of 528 crude extracts generated from nutritional microfermentation arrays was tested for the production of bioactive secondary metabolites against clinically relevant strains (Bacillus subtilis, methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii and Candida albicans). Three independent isolates were shown to produce a new anti-MRSA bioactive compound that was identified as kocurin, a new member of the thiazolyl peptide family of antibiotics emphasizing the role of this family as a prolific resource for novel drugs.

Isolation, structure elucidation, and biological activity of virgineone from Lachnum virgineum using the genome-wide Candida albicans fitness test

A glycosylated tetramic acid, virgineone (1), was isolated from saprotrophic Lachnum virgineum. The antifungal activity of the fermentation extract of L. virgineum was characterized in the Candida albicans fitness test as distinguishable from other natural products tested. Bioassay-guided fractionation yielded 1, a tyrosine-derived tetramic acid with a C-22 oxygenated chain and a beta-mannose. It displayed broad-spectrum antifungal activity against Candida spp. and Aspergillus fumigatus with a MIC of 4 and 16 microg/mL, respectively. Virgineone was also identified in a number of Lachnum strains collected from diverse geographies and habitats.

Kocurin, the True Structure of PM181104, an Anti-Methicillin-Resistant Staphylococcus aureus (MRSA) Thiazolyl Peptide from the Marine-Derived Bacterium Kocuria palustris

A new thiazolyl peptide, kocurin (1), was isolated from culture broths of a marine-derived Kocuria palustris. Its structural elucidation was accomplished using a combination of spectroscopic and chemical methods, including HRMS, extensive 1D and 2D NMR analysis, MS/MS fragmentation, and chemical degradation and Marfey’s analysis of the resulting amino acid residues. The structure herein reported corrects that previously assigned to PM181104 (3). Kocurin displayed activity against methicillin-resistant Staphylococcus aureus (MRSA), with MIC values in the submicromolar range.

Anti-fungal and anti-bacterial activities of ethanol extracts of selected traditional Chinese medicinal herbs.

OBJECTIVE To evaluate in vitro antimicrobial activities of selected 58 ethno-medicinal plant extracts with a view to assess their therapeutic potential. METHODS A total of 58 traditional Chinese medicinal plants were carefully selected based on the literature review and their traditional use. The antimicrobial activities of ethanol extracts of these medicinal plants were tested against fungi (Aspergillus fumigatus), yeast (Candida albicans), gram-negative (Acinetobacter baumannii and Pseudomonas aeruginosa) and gram-positive bacteria (Staphylococcus aureus). The activities were tested at three different concentrations of 1.00, 0.10 and 0.01 mg/mL. The data was analysed using Gene data Screener program. RESULTS The measured antimicrobial activities indicated that out of the 58 plant extracts, 15 extracts showed anti-fungal activity and 23 extracts exhibited anti-bacterial activity. Eight plant extracts have exhibited both anti-bacterial and anti-fungal activities. For instance, Eucommia ulmoides, Polygonum cuspidatum, Poria cocos and Uncaria rhyncophylla showed activity against both bacterial and fungal strains, indicating their broad spectrum of activity. CONCLUSIONS The results revealed that the ethanol extracts of 30 plants out of the selected 58 possess significant antimicrobial activities. It is interesting to note that the findings from the current study are consistent with the traditional use. A clear correlation has also been found between the antimicrobial activity and the flavonoid content of the plant extracts which is in agreement with the literature. Hence, the results presented here can be used to guide the selection of potential plant species for the isolation and structure elucidation of novel antimicrobial compounds in order to establish the structure-activity relationship. This in turn is expected to lead the way to the discovery of novel antimicrobial agents for therapeutic use.

Chemical and Physical Modulation of Antibiotic Activity in Emericella Species

The addition of epigenetic modifying agents and ion‐exchange resins to culture media and solid‐state fermentations have been promoted as ways to stimulate expression of latent biosynthetic gene clusters and to modulate secondary metabolite biosynthesis. We asked how combination of these treatments would affect a population of screening isolates and their patterns of antibiosis relative to fermentation controls. A set of 43 Emericella strains, representing 25 species and varieties, were grown on a nutrient‐rich medium comprising glucose, casein hydrolysate, urea, and mineral salts. Each strain was grown in untreated agitated liquid medium, a medium treated with suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, 5‐azacytidine, a DNA methylation inhibitor, an Amberlite non‐ionic polyacrylate resin, and the same medium incorporated into an inert static vermiculite matrix. Species‐inherent metabolic differences more strongly influenced patterns of antibiosis than medium treatments. The antibacterial siderophore, desferritriacetylfusigen (1), was detected in most species in liquid media, but not in the vermiculite medium. The predominant antifungal component detected was echinocandin B. Some species produced this antifungal regardless of treatment, although higher quantities were often produced in vermiculite. Several species are reported for the first time to produce echinocandin B (3). A new echinocandin analog, echinocandin E (2), was identified from E. quadrilineata.

New Ikarugamycin Derivatives with Antifungal and Antibacterial Properties from Streptomyces zhaozhouensis

A bioassay guided fractionation of the ethyl acetate extract from culture broths of the strain Streptomyces zhaozhouensis CA-185989 led to the isolation of three new polycyclic tetramic acid macrolactams (1–3) and four known compounds. All the new compounds were structurally related to the known Streptomyces metabolite ikarugamycin (4). Their structural elucidation was accomplished using a combination of electrospray-time of flight mass spectrometry (ESI-TOF MS) and 1D and 2D NMR analyses. Compounds 1–3 showed antifungal activity against Aspergillus fumigatus, Candida albicans and antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).

Balibalosides, an original family of glucosylated sesterterpenes produced by the Mediterranean sponge Oscarella balibaloi.

The chemical investigation of the recently described Mediterranean Homoscleromorpha sponge Oscarella balibaloi revealed an original family of five closely related glucosylated sesterterpenes 1–4, named balibalosides. Their structure elucidation was mainly inferred from NMR and HRMS data analyses. Balibalosides differ by the pattern of acetyl substitutions on the three sugar residues linked to the same aglycone sesterterpenoid core. From a biosynthetic perspective, these compounds may represent intermediates in the pathways leading to more complex sesterterpenes frequently found in Dictyoceratida, a sponge Order belonging to Demospongiae, a clade which is phylogenetically distinct from the Homoscleromorpha. While steroid and triterpenoid saponins were already well known from marine sponges, balibalosides are the first examples of glycosilated sesterterpenes.