الفهرس 
Actinomycetes
Formation of antibiotic in nature:Only 14 pages are availabe for public view
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Abstract
This study was concerned with extraction and purification of bioactive compounds from actinomycetes. Also, natural polymers were prepared and modified to overcome the problem of multiple drug resistance and the inability to control certain infectious diseases. Seventy-one actinomycetes were isolated from Egyptian soils. The isolated actinomycetes were then screened with regard to their potential to generate bioactive compounds. Nine isolates (12.67%) showed antibacterial activity against at least two test-bacteria among two Gram-positive and three Gram-negative multidrug-resistant bacterial isolates. Two actinomycetes; Sohag18 & Hurghada55 were highly active with mean values of inhibition zone ranged from 20.3 to 28.3 mm. The most potent producing isolates (Sohag 18 & Hurghada 55) were subjected to conventional morphological, cultural, physiological and biochemical analysis, in addition to molecular identification by 16s rRNA gene sequencing. The characters and 16s rRNA gene sequencing data confirmed that the actinomycete isolates Sohag18 & Hurghada55 could be identified as Streptomyces rochei NRRL B-1559 and Streptomyces albogrisulous NBRC 3413, respectively. The extraction of the fermentation broth of these strains resulted in the isolation of one major compound, which was active in-vitro against both Gram-positive and Gram-negative tested bacteria. The chemical structure of these bioactive compounds was elucidated based on the spectroscopic data obtained from the application of IR, UV, 1H NMR, GC-MS, and elemental analysis techniques. Via comparison to the reference data in the relevant literature and in the database search, this antibacterial agent extracted from S. rochei, had a molecular formula of C25H42N4O4 and a molecular weight of 462 and identified as 2-Nonadecanone 2, 4 di-nitro-phenyl hydrazine, and the antibiotic extracted from S. albogrisulous, had a molecular formula of C23H45N5O14 and a molecular weight of 615 and identified as paromomycin. On the other hands, crab shells were collected from locally fish restaurant in the city of Tanta, Egypt. Chitosan has been extracted from crab shell waste by chemical method then modified chemically by introducing carboxymethyl group into its back bone. The antibacterial activity of chitosan and Ocarboxymethyl chitosan was tested against multidrug-resistant bacteria by cut-plug method. It was found that the antibacterial activity of modified chitosan was better than the native one. The minimum inhibitory concentration (MICs) of the purified bioactive agents and biopolymers were also determined. The cytotoxicity and antiviral activity of the purified antibacterial agents and biopolymers were screened. They have cytotoxic effect on liver carcinoma cell line and their toxicities on normal human fibroblasts were negligible. On the other hands, the antiviral activity of bioactive agents and biopolymers were tested by cytopathic effect inhibition assay. The biopolymers showed good inhibitory effect against HAV-10 virus, while bioactive agents showed weak inhibitory activity. Finally, antibacterial activities of bioactive agents and biopolymers were evaluated in-vivo; the results showed that they were highly active and safe in the treatment of the artificial wound infection.