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Objective(s): To address the alarming problem of methicillin-resistant Staphylococcus aureus (MRSA), herein, a marine Streptomyces capable of producing an anti-MRSA compound has been studied. Materials and Methods: Strain MN41 was morphologically and physiologically characterized and then, molecularly identified using 16SrRNA analysis. To produce the bioactive compound in large scale, a kind of submerged liquid fermentation was adopted. The antibacterial agent was purified using a silica gel column followed by a semi-preparative HPLC and the isolated metabolite was identified using mass spectrometry, Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR). Finally, the production process was subjected to a two steps optimization using Plackett-Burman design (PBD) and Response Surface Method (RSM), respectively. In addition, the antitumor activity of the active agent was studied. Results: The purified compound with a molecular weight of 421.2 was identified as a natural pyrrole-derivative. The optimization revealed a significant effect for starch, pH, calcium carbonate and peptone on the production of this anti-MRSA compound and resulted in a 218% increase in the production yield. Conclusion: The isolated pyrrole-derivative showed a remarkable activity against MRSA and also showed some promising anti-tumor activity. [ABSTRACT FROM AUTHOR]

Background and purpose: Actinomycetes were always considered as a source of essential new antibiotic producers and secondary metabolite in pharmaceutical industries. This study aimed to isolate antibiotic producing actinomycetes from sediments of the Caspian Sea and investigate their potential as antifungal metabolites production. Materials and methods: Sediments of the Caspian Sea were collected from 5 and 10 meters depth. Samples were diluted and cultured in Starch Casein Agar (SCA) selective media. The strains were isolated and purified using morphological and microscopy methods. The primary screening was performed by the cross streak method in order to find the active strains. The produced metabolites were extracted from active strains and antifungal activities were evaluated against pathogen fungus by the disc diffusion method. Results: Of the sediments, 20 strains were isolated and identified. All of the seven strains were determined as active actinomycetes in the primary screening. Results in the secondary screening showed that the active isolates had a good antifungal effect on Candida sp. and Aspergillus sp. The results revealed that the strains MN1, MN2 and MN3 were shown more antifungal activities than the others. Conclusion: Results of this study declared that sediments of the Caspian Sea are rich in actinomycetes, active in the case of new antifungal compounds production, that need to be identified and purified. [ABSTRACT FROM AUTHOR]

Considering antimicrobial resistance problem, marine microorganisms with the bioactivity against multi-drug resistant (MDR) pathogens have attracted many scientific interests. To address this issue, a total of 21 marine actinomycetes isolated from the Caspian Sea have been screened out. Primary screening via cross-streak method revealed that 3 strains: MN2, MN39, and MN40 produce antimicrobial agents with wide spectrum activity. In the second step, the potent strains were characterized morphologically, and then identified genetically using 16S rRNA analysis. After that, the bioactivity of the ethyl acetate extracts of liquid culture against some MDR bacteria has been studied using disc diffusion method. Finally, the exoenzymatic activity of the strains, and the anti-vibrio activity of the extracts have been evaluated. The nucleotide sequence of the 16S rRNA gene (1.5 kb) showed that the potent strains belong to the genus Streptomyces . The results of disk diffusion method indicated that among the 3 potent isolates, MN39 and MN2 produce biomolecules with antibacterial activity against MDR bacteria specially methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). In addition, potent strains showed remarkable anti-vibrio activity as well as extracellular enzyme production including amylase and protease. The results of this study revealed that the marine actinomycetes isolated from the sediments of Caspian Sea produce biomolecules effective against MDR bacteria, and suggested that these strains deserve to be studied as potential probiotics due to their anti-vibrio activity besides exoenzyme production., Competing Interests: The authors declare that they have no conflict of interests.

Actinomycetes are interesting as a main producer of secondary metabolites and industrial antibiotics from marine environments. A total of 44 strains of actinomycetes were isolated from Caspian Sea sediments at a depth of 5-10 m. Preliminary screening was done using cross-streak method against 2 gram-positive and 4 gram-negative pathogen bacteria. The most potent strains MN2, MN3, MN38, MN39, MN40, MN41, and MN44 were used to extract the antibacterial substances. The antibacterial activities were performed using Kirby-Bauer disk diffusion method. Potent actinomycetes were screened for hydrolytic exoenzymatic activities (amylase and protease). All of the 24 isolates were active against at least to one of the test organisms. The MN38 strain showed activity against Staphylococcus aureus (20.0±0.5mm), Bacillus subtilis (27.0±0.2 mm), and Escherichia coli (20.0±0.3 mm). The MN39 strain was also active against E. coli (23.0±0.4mm), B. subtilis (23.0±0.2mm), Klebsiella pneumonia (24±0.1mm), whereas, the MN3 strain showed activity against Pseudomonas aeruginosa (20.0±0.2mm). The results of this investigation revealed that the marine actinomycetes of Caspian Sea sediments were potent source of novel antibiotics and bioactive compounds.