Two novel quinomycin derivatives, RK-1355A (1) and B (2), and one known quinomycin derivative, UK-63,598 (3), were isolated from a microbial metabolites fraction library of Streptomyces sp. RK88-1355 based on Natural Products Plot screening. The structural elucidation of 1 and 2 was established through two-dimensional NMR and mass spectrometric measurements. They belong to a class of quinomycin antibiotics family having 3-hydroxyquinaldic acid and a sulfoxide moiety. They are the first examples for natural products as a quinoline type quinomycin having a sulfoxide on the intramolecular cross-linkage. They showed potent antiproliferative activities against various cancer cell lines and they were also found to exhibit moderate antibacterial activity.
Langkocyclines A1-A3 and B1 and B2, five new angucycline antibiotics produced by Streptomyces sp. Acta 3034, were detected in the course of our HPLC-diode array screening. The producing strain was isolated from the rhizospheric soil of a Clitorea sp. collected from Burau Bay, Langkawi, Malaysia, and was characterized by morphological, physiological and chemotaxonomic features in addition to 16S ribosomal RNA gene sequence information. Strain Acta 3034 is closely related to Streptomyces psammoticus NBRC 13971(T) and Streptomyces lanatus NBRC 12787(T). Langkocyclines consist of an angular tetracyclic benz[a]anthracene skeleton and hydrolyzable O-glycosidic sugar moieties. The yellow-colored A-type langkocyclines differ in their aglycon from the blue-lilac-colored B-type langkocyclines. The A-type langkocycline aglycon is identical to that of aquayamycin and urdamycin A. The chemical structures of the langkocyclines were elucidated by HR-MS, 1D and 2D NMR experiments. They are biologically active against Gram-positive bacteria and exhibit a moderate antiproliferative activity against various human tumor cell lines.
In this study, potential probiotic strains were isolated from fermented pickles based on antagonistic activity against two shrimp pathogens (Vibrio harveyi and Vibrio parahaemolyticus). Two strains L10 and G1 were identified by biochemical tests, followed by16S ribosomal RNA gene sequence analysis as Bacillus subtilis, and characterized by PCR amplification of repetitive bacterial DNA elements (Rep-PCR). Subsequently, B. subtilis L10 and G1 strains were tested for antibacterial activity under different physical conditions, including culture medium, salinity, pH and temperature using the agar well diffusion assay. Among the different culture media, LB broth was the most suitable medium for antibacterial production. Both strains showed the highest level of antibacterial activity against two pathogens at 30 °C and 1.0% NaCl. Under the pH conditions, strain G1 showed the greatest activity against V. harveyi at pH 7.3-8.0 and against V. parahaemolyticus at pH 6.0-8.0, whereas strain L10 showed the greatest activity against two pathogens at pH 7.3. The cell-free supernatants of both strains were treated with four different enzymes in order to characterize the antibacterial substances against V. harveyi. The result showed considerable reduction of antibacterial activity for both strains, indicating the proteinaceous nature of the antibacterial substances. A wide range of tolerance to NaCl, pH and temperature was also recorded for both strains. In addition, both strains showed no virulence effect in juvenile shrimp Litopenaeus vannamei. On the basis of these results and safety of strains to L. vannamei, they may be considered for future challenge experiments in shrimp as a very promising alternative to the use of antibiotics.
Antimicrobial resistance (AMR) threatens the effective prevention and treatment of a wide range of infections. Governments around the world are beginning to devote effort for innovative treatment development to treat these resistant bacteria. Systems biology methods have been applied extensively to provide valuable insights into metabolic processes at system level. Genome-scale metabolic models serve as platforms for constraint-based computational techniques which aid in novel drug discovery. Tools for automated reconstruction of metabolic models have been developed to support system level metabolic analysis. We discuss features of such software platforms for potential users to best fit their purpose of research. In this work, we focus to review the development of genome-scale metabolic models of Gram-negative pathogens and also metabolic network approach for identification of antimicrobial drugs targets.
The emergence of drug resistance in bacterial pathogens is a growing clinical problem that poses difficult challenges in patient management. To exacerbate this problem, there is currently a serious lack of antibacterial agents that are designed to target extremely drug-resistant bacterial strains. Here we describe the design, synthesis and antibacterial testing of a series of 40 novel indole core derivatives, which are predicated by molecular modeling to be potential glycosyltransferase inhibitors. Twenty of these derivatives were found to show in vitro inhibition of Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. Four of these strains showed additional activity against Gram-negative bacteria, including extended-spectrum beta-lactamase producing Enterobacteriaceae, imipenem-resistant Klebsiella pneumoniae and multidrug-resistant Acinetobacter baumanii, and against Mycobacterium tuberculosis H37Ra. These four compounds are candidates for developing into broad-spectrum anti-infective agents.
The novel antifungal agent ASP2397 (Vical's compound ID VL-2397) is produced by the fungal strain MF-347833 that was isolated from Malaysian leaf litter and is identified here as an Acremonium species based on its morphology, physiological properties and 28S ribosomal DNA sequence. Because of its potential importance for producing novel antifungal agents, we determined the taxonomic and biologic properties of MF-347833. We show here that ASP2397 is a cyclic hexapeptide that chelates aluminum ion and is therefore similar to ferrichrome, a hydroxamate siderophore. However, ASP2397 differs structurally from licensed antifungal agents such as amphotericin B, triazoles and echinocandins. To understand the relationship between chemical structure and biological function, we isolated certain ASP2397 derivatives from the culture broth, and we further chemically converted the metal-free form to other derivatives.
Six new 11-mer peptaibols designed as zealpeptaibolins, A - F were isolated from the soil fungus, Trichoderma sp. RK10-F026, based on the principal component analysis of the MS data from five different culture compositions. Previously, 20-mer peptaibols from the same fungal strain were identified; 11-mer peptaibols in contrast were discovered from a different culture condition, signifying peptaibol production was culture condition-dependent. These peptaibols contained three Aib-Pro motifs in the sequence. The structures were established by NMR and HR-MS experiments including detailed MS/MS fragmentations. The absolute configurations were determined by Marfey's analysis. Zealpeptaibolin F exhibited the strongest cytotoxicity toward K562 leukemia cells with an IC50 value of 0.91 µM.
Polymyxin B and colistin were examined for their ability to inhibit the type II NADH-quinone oxidoreductases (NDH-2) of three species of Gram-negative bacteria. Polymyxin B and colistin inhibited the NDH-2 activity in preparations from all of the isolates in a concentration-dependent manner. The mechanism of NDH-2 inhibition by polymyxin B was investigated in detail with Escherichia coli inner membrane preparations and conformed to a mixed inhibition model with respect to ubiquinone-1 and a non-competitive inhibition model with respect to NADH. These suggest that the inhibition of vital respiratory enzymes in the bacterial inner membrane represents one of the secondary modes of action for polymyxins.
Polymyxins are last-line antibiotics against multidrug-resistant Klebsiella pneumoniae but using polymyxins alone may not be effective due to emerging resistance. A previous study found that combining polymyxin B with chloramphenicol effectively kills MDR K. pneumoniae, although the bone marrow toxicity of chloramphenicol is concerning. The aim of this study is to assess the antibacterial efficacy and cytotoxicity of polymyxin B when combined with chloramphenicol and its derivatives, namely thiamphenicol and florfenicol (reported to have lesser toxicity compared to chloramphenicol). The antibacterial activity was evaluated with antimicrobial susceptibility testing using broth microdilution and time-kill assays, while the cytotoxic effect on normal bone marrow cell line, HS-5 was evaluated using the MTT assay. All bacterial isolates tested were found to be susceptible to polymyxin B, but resistant to chloramphenicol, thiamphenicol, and florfenicol when used alone. The use of polymyxin B alone showed bacterial regrowth for all isolates at 24 h. The combination of polymyxin B and florfenicol demonstrated additive and synergistic effects against all isolates (≥ 2 log10 cfu ml-1 reduction) at 4 and 24 h, respectively, while the combination of polymyxin B and thiamphenicol resulted in synergistic killing at 24 h against ATCC BAA-2146. Furthermore, the combination of polymyxin B with florfenicol had the lowest cytotoxic effect on the HS-5 cells compared to polymyxin B combination with chloramphenicol and thiamphenicol. Overall, the combination of polymyxin B with florfenicol enhanced bacterial killing against MDR K. pneumoniae and exerted minimal cytotoxic effect on HS-5 cell line.